Phase change materials for thermal energy storage in industrial applications

Abstract

This study reports the results of the screening process done to identify viable phase change materials (PCMs) to be integrated in applications in two different temperature ranges: 60–80 °C for mid-temperature applications and 150–250 °C for high-temperature applications. The comprehensive review involved an extensive analysis of scientific literature and commercial material datasheets. A total of 65 PCMs for mid-temperature applications and 36 PCMs for high-temperature applications were identified through this extensive search. Moreover, an extensive experimental characterization of 14 preselected PCMs is included. Experimental techniques including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and hot disk were used. The values obtained were compared to the ones found in the available literature and technical datasheets to see potential differences in the thermal behavior.

Highlights

• •Screening process done to identify viable phase change materials (PCMs).
• •Applications in industry.
• •Complete characterization of PCMs.
• •Highlight of differences with available data.

1. Introduction

According to the International Energy Agency [1], in 2022 industry was directly responsible for emitting 9.0 Gt of CO₂ (including process emissions but not including indirect emissions from electricity used for industrial processes.), which was around 25 % of the global energy system CO₂ emissions. The industry sector showed modest improvements in energy efficiency and in renewable energy implementation, but this is still considered to be too slow to reach the stablished targets.

Due to the wide type of processes and products that are part of the industry sector, its decarbonisation is a real challenge [2]. Moreover, this wide range of processes and products leads to the thought that decarbonisation options are process specific, have long investment times with low profit margins, and can imply high energy use [3]. Thermal energy storage (TES) with phase change materials (PCM) was applied as useful engineering solution to reduce the gap between energy supply and energy demand in cooling or heating applications by storing extra energy generated during peak collection hours and dispatching it during off-peak hours [4]. Different industrial thermal processes can be improved by implementing this technology, such as sterilization process in canned food industry (110–120 °C) [5,6]; In pasteurization and sterilization processes of dairy products industry (60–145 °C) [5,7]; In drying processes of dairy products industry (120–180 °C) [5,7], of agriculture products (80–200 °C) [5,8], of textile products (100–130 °C) [5,8], of plastics (180–200 °C) [5,8], and non-ferrous metals (60–200 °C) [5,9]; In bleaching process of paper manufacturing (130–150 °C) [5,6]; In evaporating waste water process (130–150 °C) [5,9]; In synthetic rubber production (150–200 °C) [5,9]; In soaps production (200–260 °C) [5,9], and in frying and baking process of food industry (up to 250 °C) [6].

Within the decarbonisation options heat pumps are a good option for many industries, such as food and drink [10]. High-temperature heat pumps are often coupled to energy storage systems [11]. The addition of a thermal energy storage system in both sides of the heat pump gives better efficiency due to better performance in the heat pump. Therefore, the use of thermal energy storage (TES) with phase change materials (PCMs) is a very good option to achieve such objective. For industrial applications, two temperature levels are identified of interest, a mid-temperature range between 60 °C and 80 °C, and a high-temperature range from 150 °C to 250 °C.

Although the literature gives a large option of PCMs to be used in TES applications [[12], [13], [14], [15]], the selection of the right PCM is still difficult due to the lack of a good compilation of data for these temperature ranges. Therefore, this paper aims at filling this literature gap by providing such data for use in further studies and commercial applications.

2. Materials and methods

2.1. Methodology

A collection of the available materials was collected consulting scientific literature (Scopus database) and datasheets of commercial materials (from the companies Rubitherm, PCMproducts, PLUSS, and CRODA). To support the final selection of the PCM, the following parameters were considered.

• •Melting temperature - T_melting (ºC): it is the main parameter to select a PCM and it depends on the final application.
• •Melting enthalpy - ΔH_melting (J/g) – it is one of the most important properties of the PCM which defines the energy stored during the phase change.
• •Specific heat (solid and liquid) - C (J/g·ºC) – this property affects the heat energy absorbed by the PCM when it is in solid or liquid phase.
• •Density (solid and liquid) - ρ (kg/m³) – this property expresses the ratio between the weight and the volume of the PCM.
• •Thermal conductivity - k (W/m·ºC) – this property is fundamental to estimate the power of charging and discharging of the TES.
• •Degradation temperature - T_degradation (°C) – this property is fundamental to understand the working temperature limit of the material.
• •NFPA 704 hazardous material standard – this indicates the hazard potential of the materials for its handling, processing, or transport.

2.2. Materials

Seven chemicals were obtained from different suppliers: magnesium nitrate hexahydrate Mg(NO₃)₂·6H₂O (98 %, Merk, Germany), magnesium chloride hexahydrate MgCl₂·6H₂O (99 %, Merk, Germany), palmitic acid (98 %, Merk, Germany), stearic acid (98 %, Merk, Germany), lithium nitrate LiNO₃ (98 %, Pan reac, Spain), sodium nitrate NaNO₃ (99 %, VWR, Spain), and potassium nitrate KNO₃ (99 %, VWR, Spain). Moreover, four commercial PCMs were purchased, three organic PCMs: RT 54 HC, RT 55, and RT 64 H from Rubitherm (Germany) and one inorganic PCM E 58 from PCM products (United Kingdom).

2.3. Analytical methods

The phase change temperature, enthalpy, and thermal behaviour analysis of the selected PCMs were determined by differential scanning calorimetry (DSC). The equipment used to carry out this experimentation is the STARe SYSTEM DSC 3+ from METTLER TOLEDO. A small amount of sample (around 15 mg) was placed in sealed aluminium crucibles (40 μL) and the tests were carried out in an inert N₂ atmosphere. The accuracy of the equipment is ±0.1 °C for temperature results and ±3 J/g for enthalpy results. The samples preparation is shown in Fig. 1. The measurements were carried out within the temperature range from about 50 °C below the melting temperature found in the literature to about 50 °C above it, with a heating/cooling rate of 1 K/min, and 3 cycles were performed for each sample.

Fig. 1.

Sample preparation for DSC and TGA measurements.

The decomposition temperature, enthalpy and melting temperature, and thermal behaviour of the selected PCMs were studied by thermogravimetric analysis (TGA). The equipment used to carry out this experimentation is the STARe SYSTEM TGA/DSC 3+ from METTLER TOLEDO. A small amount of sample (around 15 mg) was placed in sapphire crucibles (70 μL) without lids (opened crucibles), and the tests were carried out in an inert N₂ atmosphere. This equipment has a balance with a precision of ±0.00001 g which allows to quantify the loss of mass associated with the decomposition process. The accuracy of the equipment is ±0.1 °C for temperature results and ±3 J/g for enthalpy results. The samples preparation, which was the same as in the DSC samples, is shown in Fig. 1. The measurements were carried out with a heating rate of 1 K/min for all samples. The temperature range considered was from 25 °C to 250 °C for the mid-temperature PCMs, and from 25 °C to 400 °C for the high-temperature PCMs.

The thermal conductivity of the selected PCMs was evaluated by Hot Disk TPS 2500 S. The measurements were carried out at room temperature using the sensor Kapton 5506 F2. To perform these measurements, it was necessary to prepare compact and flat solid samples with the selected PCMs, with a radius and thickness enough to represent an infinite plane. The preparation of the samples is shown in Fig. 2. Moreover, the thermal conductivity values obtained by hot disk came from iteration obtained by the adjustment of two parameters, measurement time (s) and heating power (mW) until get an error of error of $1\times {10}^{-4}$ (mean deviation). In consequence, once the reliable value was obtained with the correct parameters and mean deviation of $1\times {10}^{-4}$, three more measurements were performed using the same parameters for each sample. The values reported in our results correspond to the average of these three measurements.

Fig. 2.

Sample preparation for thermal conductivity measurements.

3. Results

3.1. Potential PCMs identified for the given application

A total of 45 PCM and 20 PCM for mid-temperature application were retrieved in the literature and commercial datasheets, respectively (Fig. 3). The PCM available with their thermal characteristics are reported in Table 1; as shown, it was not possible to find all the characteristics and properties of the PCMs identified in the literature assessed. In the case of high-temperature application, 30 PCM and 6 were retrieved in the literature and commercial datasheets, respectively (Fig. 3). The PCM available with their thermal characteristics are reported in Table 2.

Fig. 3.

First selection of suitable PCMs.

Table 1.

PCM suitable to be used in a range of 60–80 °C.

#	Material	Tmelting (ºC)	ΔHmelting (J/g)	Cpsolid (J/g·ºC)	Cpliquid (J/g·ºC)	ρsolid (kg/m3)	ρliquid (kg/m3)	ksolid (W/m·ºC)	kliquid (W/m·ºC)	Tdegradation (°C)	NPFA	Ref.
1	CRODATHERM60	60.0 [16]	217.0 [16]	2.3 [16]	1.4 [16]	922 [16]	824 [16]	0.29 [16]	0.17 [16]	–	–	[16]
2	Mg(NO3)2·6H2O-MgCl2·6H2O (80-20 wt%)	60.0 [17,18]	150.0 [17,18]	–	–	–	–	–	–	–	3 [19]	[[17], [18], [19]]
3	Mg(NO3)2·6H2O-MgCl2·6H2O (60-40 wt%)	60.0 [20]	132.3 [20]	2.3 [20]	2.8 [20]	1517 [20]	1512 [20]	–	–	130.0 [20]	3 [19]	[19,20]
4	Fe(NO3)2·6H2O	60.0 [17,21,22]	–	–	–	–	–	–	–	–	3 [19]	[17,19,21,22]
5	PureTemp 60	60.0 [23]	220.0 [23]	2.0 [23]	2.4 [23]	960 [23]	870 [23]	0.25 [23]	0.15 [23]		–	[23]
6	RT 60	60,0 [24]	160.0 [24]	2.0 [24]	2.0 [24]	880 [24]	770 [24]	0.20 [24]	0.20 [24]	80.0 [24]	–	[24]
7	Heptaudecanoic acid	60.6 [25,26,26]	189.0 [25,26]	–	–	–	–	–	–	–	3 [19]	[19,25,26]
8	n-octacosane	61.0 [27,28]	254.0 [27,28]	1.9 [27,28]	2.4 [27,28]	803 [27,28]	–	–	–	–	3 [19]	[19,27,28]
9	Mg(NO3)2·6H2O-Al(NO3)2⋅9H2O (53-47 wt%)	61.0 [21,29]	148.0 [21,29]	–	–	–	–	–	–	–	3 [19]	[19,21,29]
10	Palmitic acid	55.0 [26]	163.0 [26] 189.6 [30] 203.4 [17,18,21,31,32] 212.0 [33] 187.0 [17,18,21,31] 185.4 202.5 [21] 222 [17,18,21,31,32]	2.1 [17] 2.2 [32]	2.3 [17] 2.5 [32]	850 [17]	989 [17]	0.17 [17]	0.15 [17] 0.16 [21,29] 0.17 [17]	–	2 [19]	[[17], [18], [19],21,26,31,32]
		59.0 [30]
		61.0 [17,18,21,31,32]
		62.9 [33]
		63.0 [17,18,21,31]
		64.0 [17,18,21,31]
		69.0 [21]
11	NaAl(SO4)2·10H2O	61.0 [25,26]	181.0 [25,26]	–	–	–	–	–	–		2 [19]	[19,25,26]
12	a-chloroacetic acid	61.2 [25,26]	130.0 [25,26]	–	–	–	–	–	–	–	3 [19]	[19,25,26]
13	Bee wax	61.8 [25,26]	177.0 [25,26]	–	–	–	–	–	–	–	1 [19]	[19,26]
14	RT 62 HC	62.0 [24]	230.0 [24]	2.0 [24]	2.0 [24]	850 [24]	840 [24]	0.20 [24]	0.20 [24]	90.0 [24]	–	[24]
15	A 62	62.0 [34]	205.0 [34]	2.2 [34]	–	910 [34]	–	0.22 [34]	0.22 [34]	250.0 [34]	–	[34]
16	n-nonacosane	63.0 [17,28]	239.0 [17,28]	1.9 [17,28]	2.5 [17,28]	805 [17,28]	–	–	–	–	2 [19]	[17,19,28]
17	Glyolic acid	63.0 [26,35]	109.0 [26,35]	–	–	–	–	–	–	–	3 [19]	[19,26,35]
18	Pure Temp 63	63.0 [23]	206.0 [23]	1.9 [23]	2.2 [23]	920 [23]	840 [23]	0.25 [23]	0.15 [23]	–	–	[23]
19	p-bromophenol	63.5 [25,26]	86.0 [25,26]	–	–	–	–	–	–	–	3 [19]	[19,25,26]
20	NaOH⸱H2O	58.0 [21,36]	272.0 [37] 273.0 [26]	–	–	–	–	–	–	–	3 [19]	[19,21,26,36,37]
		64.0 [37]
		64.3 [26]
21	RT 64 HC	64.0 [24]	250.0 [24]	2.0 [24]	2.0 [24]	880 [24]	780 [24]	0.20 [24]	0.20 [24]	95.0 [24]	–	[24]
22	Acetamide + stearic acid (50-50 wt%)	65.0 [26]	218.0 [26]	–	–	–	–	–	–	–	3 [19]	[19,26]
23	Na3PO4⸱12H2O	65.0 [26]	190.0 [26] 178.0 [38]	–	–	–	–	–	–		3 [19]	[19,21,26,36,38]
		64.9 [38]
		69.0 [21,36]
24	RT 65	65.0 [24]	150.0 [24]	2.0 [24]	2.0 [24]	880 [24]	780 [24]	0.20 [24]	0.20 [24]	85.0 [24]	–	[24]
25	Mg(NO3)2·6H2O-MgBr2·6H2O (59-41 wt%)	66.0 [26]	168.0 [26]	–	–	–	–	–	–	–	3 [19]	[19,26]
26	n-triacontane	66.0 [17]	252.0 [17]	1.9 [17]	2.5 [17]	806 [17]	–	0.23 [39]	–	–	2 [19]	[17,19,39]
		65.4 [39]	251.0 [39]	2.1 [39]	–	810 [39]
27	Didodecyl terephthalate (DDDT)	66.0 [40]	179.2 [40]	–	–	–	–	–	–	–	2 [19]	[19,40]
28	Napthalene + benzoic acid (67-33 wt%)	67.0 [26,41]	123.4 [26,41]	–	–	–	–	0.28 [41]	0.14 [41]	–	3 [19]	[19,26,41]
29	Azobenzene	67.1 [26]	121.0 [26]	–	–	–	–	–	–	–	2 [19]	[19,26]
30	Stearic acid	67.8 [17,26,41]	198.9 [17,26,41] 202.5 [21,41] 186.5 199.0 [26] 203.0 [17,18,21,29] 201.8 [42] 222 [33]	1.6 [17] 2.8 [43]	2.2 [17] 2.4 [43]	848 [17] 1080 [43]	965 [17] 1015 [43]	–	0.17 [17] 0.18 [43]	–	2 [19]	[[17], [18], [19],21,26,29,42,43]
		69.0 [21,41]
		60.0–61.0
		69.4 [26]
		70.0 [17,18,21,29]
		69.6 [33]
		69.1 [42]
31	n-hentriacontane	68.0 [27,28]	242.0 [27,28]	1.9 [27,28]	2.5 [27,28]	808 [27,28]	–	–	–	–	3 [19]	[19,27,28]
32	Diaminopentaerythritol	68.0 [17]	184.0 [17]	–	–	–	–	–	–	–	2 [19]	[17,19]
33	Acrylic acid	68.0 [26]	115.0 [26]	–	–	–	–	–	–	–	2 [19]	[19,26]
34	PureTemp 68	68.0 [23]	213.0 [23]	1.9 [23]	1.9 [23]	960 [23]	870 [23]	0.25 [23]	0.15 [23]	–	–	[23]
35	RT 69	69.0 [24]	230.0 [24]	2.0 [24]	2.0 [24]	940 [24]	840 [24]	0.20 [24]	0.20 [24]	100.0 [24]	–	[24]
36	n-dotricontane	70.0 [27,28]	266.0 [27,28]	1.9 [27,28]	2.4 [27,28]	809 [27,28]	–	–	0.21 [27,28]	–	2 [19]	[19,27,28]
37	LiCH3COO⸱2H2O	70.0 [26]	150.0 [26]	–	–		–	–			2 [19]	[19,26]
38	RT 70	70.0 [24]	260.0 [24]	2.0 [24]	2.0 [24]	880 [24]	770 [24]	0.20 [24]	0.20 [24]	100.0 [24]	–	[24]
39	SP 70	70.0 [24]	150.0 [24]	2.0 [24]	2.0 [24]	1500 [24]	1300 [24]	0.60 [24]	0.60 [24]	90.0 [24]	–	[24]
40	S 70	70.0 [24]	100.0 [24]	2.1 [24]	–	1680 [24]	–	0.56 [24]	0.56 [24]	120.0 [24]	–	[24]
41	A 70	70.0 [34]	225.0 [34]	2.2 [34]	–	890 [34]	–	0.23 [34]	0.23 [34]	250.0 [34]	–	[34]
42	n-tritricontane	72.0 [27,28]	256.0 [27,28]	1.9 [27,28]	2.4 [27,28]	810 [27,28]	–	–	–	–	2 [19]	[19,27,28]
43	Al(NO3)2⸱9H2O	72.0 [17,26]	155.0 [17,26,44,45]	–	–	1555 [44,45]	–	–	–	–	3 [19]	[17,19,26,44,45]
		70.0 [44,45]
44	S 72	72.0 [34]	155.0 [34]	2.1 [34]	–	1666 [34]	–	0.58 [34]	0.58 [34]	120.0 [34]	–	[34]
45	H 72	72.0 [46]	162.0 [46]	2.3 [46]	2.9 [46]	1504 [46]	1494 [46]	0.32 [46]	0.30 [46]	90.0 [46]	–	[46]
46	n-tetratriacontane	71.0 [27,28]	268.0 [27,28]	1.6 [27,28]	2.4 [27,28]	811 [27,28]	–	–	–	–	3 [19]	[19,27,28]
47	A 73	73.0 [34]	225.0 [34]	2.2 [34]	–	890 [34]	–	0.23 [34]	0.23 [34]	250.0 [34]	–	[34]
48	Ditetradecyl terephthalate (DTDT)	73.0 [40]	183.6 [40]	–	–	–	–	–	–	–	2 [19]	[19,40]
49	CRODATHERM74	74.0 [16]	226.0 [16]	–	–	–	858 [16]	–	–	–	–	[16]
50	n-pentatriacontane	75.0 [27,28]	257.0 [17,27,28]	1.9 [27,28]	2.5 [27,28]	812 [27,28]	–	–	–	–	2 [19]	[19,27,28]
51	n-hexatriacontane	76.0 [27,28]	269.0 [27,28]	1.9 [27,28]	2.4 [27,28]	814 [27,28]	–	–	–	–	2 [19]	[19,27,28] [17,19]
52	Urea + NH4Br (66.6–33.4 wt%)	76.0 [17,21,26,41]	151.0 [17,21,26,41]	–	–	–	–	0.65 [41]	0.33 [41]	–	2 [19]	[17,19,21,26,41]
53	Phenylacetic acid	76.7 [26,35]	102.0 [26,35]	–	–	–	–	–	–	–	2 [19]	[19,26,35]
54	Thiosinamine	77.0 [26,35]	140.0 [26,35]	–	–	–	–	–	–	–	2 [19]	[19,26,35]
55	Bromcamphor	77.0 [26,35]	174.0 [26,26,35]	–	–	–	–	–	–	–	2 [19]	[19,26,35]
56	Ba(OH)2⸱8H2O	78.0 [17,21,36,37,41,45]	301.0 [35]	1.2 [35,37,45] 1.3 [17,27,35,45]	2.4 [17,27,35,45]	2180 [17,27,35,45]	1937 [17,27,35,45]	1.23 [17,27,35,45]	0.65 [17,27,35,45] 0.68	–	3 [19]	[17,19,21,27,35,36,41,45]
			266.0 [17,21,36,37,41,45]
			298.0
			265.7 [17,21,36,37,41,45]
			267.0 [17,21,36,37,41,45]
			280.0 [17,27,35,45]
57	n-heptatriacontane	78.0 [27,28,45]	259.0 [27,28,45]	1.8 [27,28,45]	2.5 [27,28,45]	815 [27,28,45]	–	–	–	–	2 [19]	[19,27,28,45]
58	A 78	78.0 [34]	225.0 [34]	2.2 [34]	–	890 [34]	–	0.23 [34]	0.23 [34]	250.0 [34]	–	[34]
59	Benzylamine	78.0 [26,45]	174.0 [26,45]	–	–	–	–	–	–	–	2 [19]	[19,26,45]
60	Ammediol (AMPD)	78.0–80.0 [27,35,45]	223.9–264.0 [27,35,45]	1.7 [27,35,45]	–	–	–	–	–	–	3 [19]	[19,27,35,45]
61	AlK(SO4)2⋅12H2O	78.0 [35]	184.0 [35]	–	–	–	–	–	–	–	2 [19]	[19,26,35]
		80.0 [21]
62	n-octatriacontane	79.0 [27,28,45]	271.0 [27,28,45]	1.8 [27,28,45]	2.4 [27,28,45]	815 [27,28,45]	–	–	–	–	3 [19]	[19,27,28,45]
63	Nitroisobutylglycol (NMPD)	79.0–80.0 [27,35,45]	190.0–201.0 [27,35,45]	–	–	–	–	–	–	–	2 [19]	[19,27,35,45]
64	n-nonatriacontane	80.0 [27,28,45]	271.0 [27,28,45]	1.3 [27,28,45]	2.5 [27,28,45]	816 [27,28,45]	–	–	–	–	2 [19]	[19,27,28,45]
65	RT 80	80.0 [24]	220.0 [24]	2.0 [24]	2.0 [24]	900 [24]	800 [24]	0.2 [24]	0.2 [24]	110.0 [24]	–	[24]

Table 2.

PCM suitable to be used in a range of 150–250 °C.

#	Material	Tmelting (ºC)	ΔHmelting (J/g)	Cpsolid (J/g·ºC)	Cpliquid (J/g·ºC)	ρsolid (kg/m3)	ρliquid (kg/m3)	ksolid (W/m·ºC)	kliquid (W/m·ºC)	Tdegradation (°C)	NPFA	Ref.
1	LiNO3-NaNO3-KNO3 (20-28-52 wt%)	150.0 [47,48]	–	1.1 [47,48]	–	–	–	–	–	550.0	2 [19]	[19,48,49]
2	PureTemp 151	151.0 [23]	217.0 [23]	2.1 [23]	2.2 [23]	1490 [23]	1360 [23]	0.25 [23]	0.15 [23]	–	–	[23]
3	Adipic acid	151.0–155.0 [50,51]	260.0 [50,51]	–	–	1360 [45]	–	–	–	–	2 [19]	[19,45,[50], [51], [52]]
		153.0 [52]
4	Phenyldrazone benzaldehyde	155.0 [53,54]	134.9 [53,54]	–	–	–	–	–	–	–	2 [19]	[19,50,53]
5	Salicylic acid	159.0 [25,45,50,53,55]	199.0 [25,45,50,53,55]	–	–	1443 [25,45]	–	–	–	–	2 [19]	[19,25,45,50,53,55]
		159.1 [53,55]	161.5 [55]
6	LiNO3-NaNO3-KCl (55.4–4.5-40.1 wt%)	160.0 [56] [50,56,57]	266.0 [50,56,57]	–	–	–	–	–	–	–	2 [19]	[19,50,56,57]
7	H 160	160.0 [34]	105.0 [34]	1.5 [34]	–	1910 [34]	–	0.51 [34]	0.51 [34]	200.0 [34]	–	[34]
8	Mannitol	165 [58,59]	341.0 [58,59]	–	–	–	–	–	–	280.0 [59]	2 [19]	[19,25,45,58,59]
		165.0–168.0 [25,45]	294.0–341.0 [25,45]
9	LiNO3-KCl (58.1–40.9 wt%)	166.0 [45,50,56,57]	272.0 [45,50,56,57] [56]	–	–	–	–	–	–	–	3 [19]	[19,45,50,56,57]
10	Benzanilide	161.0 [25,45,50,53,55]	162.0 [25,45,50,53,55]	–	–	–	–	–	–	–	2 [19]	[25,45,50,53,55]
11	D-mannitol	167.0 [53,55]	316.0 [53,55]	–	–	1489 [25,45]	1520 [25,45]	–		–	2 [19]	[19,25,45,50,55,60]
		166.8 [55]	260.8 [55]
		165.0–168.0 [25,45]	294-341 [25,45]
		166.0 [50,60]	279.0 [50,60]
12	NaOH-KOH (50-50mol%)	169.0–171.0 [45,50,56,61]	202.0–213.0 [45,50,56,61]	–	–	–	–	–	–	–	3 [19]	[19,45,50,56,61]
13	Hydroquinone	172.4 [25,45,50,53,55]	258.0 [25,45,50,53,55]	–	–	1358 [55]	–	–	–	–	3 [19]	[25,45,50,53,55] [19,25,45,50,53,55]
		172.5 [55]	235.2 [55]
14	Potassium thiocyanate	173.0 [25,45,50,53,55]	280.0 [25,45,50,53,55]	–	–		–	–	–	–	2 [19]	[19,25,45,50,53,55]
		176.6 [55]	114.4 [55]
15	Galactitol	178.9 [50,62]	246.4 [50,62]	–	–	1470 [50,62]	–	–	–	–	3 [19]	[19,45,50,62]
		188.0–189.0 [45]	351.0 [45]
16	LiNO3-LiCl-NaNO3 (47.9–1.4-50.7 wt%)	180.0 [45,50,56,57]	265.0 [45,50,56,57]	–	–		–	–	–	–	2 [19]	[19,45,50,56,57]
17	p-aminobenzoic	187.0 [25,45,50,53]	153.0 [25,45,50,53]	–	–	–	–	–	–	–	2 [19]	[19,25,45,50,53]
18	H 190	190.0 [34]	170.0 [34]	1.5 [34]	–	2300 [34]	–	0.51 [34]	0.51 [34]	500.0 [34]	–	[34]
19	AlCl3	192.0 [58,59]	280.0 [58,58,59]	–	–	–	–	–	–	–	3 [19]	[19,45,58,60,63]
		192.4 [45,63]	272.0–280.0 [45,63]
20	LiNO3-NaNO3 (57-43 wt%)	193.0 [45,50,56,57]	248.0 [45,50,56,57]	–	–	–	–	–	–	–	2 [19]	[19,45,50,56,57]
21	LiNO3-NaNO3 (49-51 wt%)	194.0 [50,56,61,64]	265.0 [50,56,61,64]	–	–	–	–	–	–	–	2 [19]	[19,50,56,61,64]
22	LiNO3-NaNO3 -Sr(NO3)2 (45-47-8 wt%)	200.0 [45,50,56,57]	199.0 [45,50,56,57] [56]	–	–	–	–	–	–	–	2 [19]	[19,45,50,56,57]
23	NaOH-LiOH (70-30mol%)	210.0–216.0 [45,50,56,57]	278.0–329.0 [56] [45,50,56,57]	–	–	–	–	–	–	–	3 [19]	[19,45,50,56,57]
24	NaNO3– KNO3 (50–50 wt%)	220.0 [58,61]	100.7 [58,61]	2.3 [45,61]	1.4 [45,61]	1920 [58]	–	–	0.56 [45,58,61]	–	2 [19]	[19,45,58,61]
		220.0–222.0 [45,61]	100.0–100.7 [45,58,61]
25	H 220	220.0 [34]	100.0 [34]	1.5 [34]	–	2000 [34]	–	0.52 [34]	0.52 [34]	390.0 [34]	–	[34]
26	Myo-inositol	224-227 [62,65,66]	266.0 [66]	–	–	–	–	–	–	–	2 [19]	[19,62,[65], [66], [67]]
		223.9–225.0 [62,67]	260.0 [62,67]
		235.0 [66]	223.0 [66]
27	NaNO3–KNO3 (60–40 wt%)	227.0 [4]	109.0	–	1.42 [68] 1.28 [69]	–	–	–	0.24 [4]	624.0 [4] 588.5 [68,70]	2 [19]	[4,19,50,56,64,66,[68], [69], [70]]
		222.0 [50,56,64,66]
		221.1 [68]
		224.7 [69]
28	Ca(NO3)2-NaNO3 (45-55 wt%)	230.0 [66,71]	110.0 [54,71]	–	–	–	–	–	–	–	2 [19]	[19,66,71]
29	NaOH-NaNO2 (20–80mol%)	230.0–232.0 [45,50,56,66,72] [54]	206.0–252.0 [45,50,56,66,72]	–	–	–	–	–	–	–	3 [19]	[19,45,50,56,66,72]
30	H 230	230.0 [34]	105.0 [34]	1.5 [34]	–	1553 [34]	–	0.52 [34]	0.52 [34]	300.0 [34]	–	[34]
31	NaOH-NaNO2 (73-27mol%)	237.0 [45,50,56,66,72]	249.0–295.0 [45,50,56,66,72]	–	–	–	–	–	–	–	3 [19]	[19,45,50,56,66,72]
32	NaOH-NaCl-NaNO3 (78.1–3.6–18.3mol%)	242.0 [45,50,56,73]	242.0 [45,50,56,73]	–	–	–	–	–	–	–	3 [19]	[19,45,50,56,73]
33	NaOH-NaNO3 (28–72mol%)	246.0 [45,50,56,73]	182.0–257.0 [54]	–	–	–	–	–	–	–	3 [19]	[19,45,50,56,73]
34	NaOH-NaCl-NaNO3 (55.6–4.2–40.2mol%)	247.0 [45,50,56,73]	213.0 [54]	–	–	–	–	–	–	–	3 [19]	[19,45,50,56,73]
35	NaOH-NaNO3 (30-70 wt%)	247.0 [45,50,56,73]	158.0 [45,50,56,73]	–	–	–	–	–	–	–	3 [19]	[19,45,50,56,73]
36	LiNO3	250.0 [45,56,58,59,63]	370.0 [45,56,58,59,63]	1.8 [71,75]	–	2380 [71,75]	–	1.7 [76] 0.58 [71,75]	–	470.0 [76]	2 [19]	[19,45,56,58,59,61,63,71,[74], [75], [76]]
		250.0–254.0 [25,26,45,56,61,63]	360.0–363.0 [25,26,45,56,61,63]
		252.0 [74]	370.0 [74]
		253.0 [71,75]	360.0 [71,75]
		249.7 [76]	300.0 [76]
37	H 250	250.0 [34]	280.0 [34]	1.5 [34]	–	2380 [34]	–	0.52 [34]	0.52 [34]	600.0 [34]	–	[34]

3.2. Selection of candidates

The selection for the potential PCMs was carried out based on the authors best knowledge considering that commercial PCMs should be included, and from the literature both organic and inorganic PCMs would be included. The list of materials is shown in Table 3 for the mid-temperature range and in Table 4 for the high-temperature range.

Table 3.

List of preselected PCMs for mid-temperature.

#	Material	Tmelting (ºC)	ΔHmelting (J/g)	Tdeg (ºC)	ksolid (W/m·ºC)
1	RT 54 HC	54.0 [24]	182.0 [24]	n.a.	0.20 [24]
2	RT 55	55.0 [24]	158.0 [24]	n.a.	0.20 [24]
3	E 58	58.0 [77]	145.0 [77]	120 [77]	0.69 [77]
4	Mg(NO3)2·6H2O-MgCl2·6H2O (80-20 wt%)	60.0 [17,18]	150.0 [17,18]	n.a.	n.a.
5	Mg(NO3)2·6H2O-MgCl2·6H2O (60-40 wt%)	60.0 [20]	132.3 [20]	130.0 [20]	n.a.
6	Palmitic acid	55.0 [26]	163.0 [26] 189.6 [30] 203.4 [17,18,21,31,32] 212.0 [33] 187.0 [17,18,21,31] 185.4 202.5 [21] 222 [17,18,21,31,32]	n.a.	0.15 [17] 0.16 [21,29] 0.17 [17]
		59.0 [30]
		61.0 [17,18,21,31,32]
		62.9 [33]
		63.0 [17,18,21,31]
		64.0 [17,18,21,31]
		69.0 [21]
7	RT 64 HC	64.0 [24,24]	242.0 [24]	n.a.	0.20 [24,24]
8	Stearic acid	67.8 [17,26,41]	198.9 [17,26,41] 202.5 [21,41] 186.5 199.0 [26] 203.0 [17,18,21,29] 201.8 [42] 222 [33]	n.a.	0.17 [17] 0.18 [43]
		69.0 [21,41]
		60.0–61.0
		69.4 [26]
		70.0 [17,18,21,29]
		69.6 [33]
		69.1 [42]

Table 4.

List of preselected PCMs for high-temperature.

#	Material	Tmelting (ºC)	ΔHmelting (J/g)	Tdeg (ºC)	ksolid (W/m·ºC)
9	LiNO3-NaNO3-KNO3 (20-28-52 wt%)	150.0 [47,48]	n.a.	n.a.	n.a.
10	Salicylic acid	159.0 [25,45,50,53,55]	199.0 [25,45,50,53,55]	n.a.	n.a.
		159.1 [53,55]	161.5 [55]
11	LiNO3-NaNO3 (49-51 wt%)	194.0 [50,56,61,64]	265.0 [50,56,61,64]	n.a.	n.a.
12	NaNO3–KNO3 (50–50 wt%)	220.0 [58,61] 220.0–222.0 [45,61]	100.7 [58,61]	n.a.	0.56 [45,61]
			100.0–100.7 [45,61]
13	NaNO3–KNO3 (60–40 wt%)	227.0 [4]	109.0 [69]	624.0 [4] 588.5 [68,70]	0.24 [69]
		222.0 [50,56,64,66]
		221.1 [68]
		224.7 [69]
14	LiNO3	250.0 [45,56,58,59,63]	370.0 [45,56,58,59,63]	470.0 [76]	1.70 [76] 0.58 [71,75]
		250.0–254.0 [25,26,45,56,61,63]	360.0–363.0 [25,26,45,56,61,63]
		252.0 [74]	370.0 [74]
		253.0 [71,75]	360.0 [71,75]
		249.7 [76]	300.0 [76]

3.3. Characterization of the selected candidates

Since not all the required properties of the found PCMs were found in the literature, after defining system requirements, a full characterization was performed to validate the thermal properties of those PCMs with more potential to be used for any suitable application.

3.3.1. PCM #1 – RT 54 HC

This is a commercial material from the company Rubitherm (Germany). Most probably this is an organic PCM, and its thermal characterisation given by the manufacturer is presented in Fig. 4. This PCM has been used in several applications such as for thermal management of PV collectors [79], thermal management of electronics [80], or as materials in storage tanks [81].

Fig. 4.

Thermal characterisation of PCM #1 – RT 54 HC given by the producer [24].

The results of the characterization of RT 54 HC are presented in Table 5. In the characterisation, this PCM showed good thermal behaviour, with stable cycling behaviour (similar behaviour between the DSC cycles), as shown in Fig. 5a. The melting temperature tested both with DSC and TGA are very similar to that reported by the producer (Fig. 4). The melting enthalpy was about 5 % lower when tested with DSC and about 24 % higher when tested with TGA/DSC (Fig. 5b) (it should be highlighted that DSC is considered a more precise instrument for this experimentation). Moreover, the sample started to degrade at 130.3 °C and half of the material degraded when reaching 196.3 °C. The maximum temperature at which this PCM should be used is 130 °C. The tested thermal conductivity was 0.23 W/m·ºC (Fig. 5c), 15 % higher than that reported in the literature.

Table 5.

Characterization of PCM #1 - RT 54 HC.

#	PCM	Data from literature				Experimental results
						DSC			TGA/DSC					Hot Disk
		Tmelting (ºC)	ΔHmelting (J/g)	Tdeg (ºC)	ksolid (W/m·ºC)	Tmelting (ºC)	ΔHmelting (J/g)	Var (%)	Tvar (ºC)	ΔHvar (J/g)	Var (%)	Tonset (ºC)	Tmid (ºC)	ksolid (W/m·ºC)	Var (%)
1	RT 54 HC	54.0 [24]	182.0 [24]	n.a.	0.20 [24]	Cycle 1: 55.1	Cycle 1: 172.9	−5%	54.7	226.1	+24 %	130.3	196.3	0.23	+15 %
						Cycle 2: 55.4	Cycle 2: 172.1	−5%
						Cycle 3: 55.4	Cycle 3: 172.1	−5%

Fig. 5.

PCM #1 – RT 54 HC: (a) DSC analysis, (b) TGA/DSC analysis, (c) Hot disk analysis.

3.3.2. PCM #2 – RT 55

This is a commercial material from the company Rubitherm (Germany). Most probably this is an organic PCM, and its thermal characterisation given by the manufacturer is shown in Fig. 6. This PCM has been used in studies to improve the thermal conductivity of PCMs with nanoparticles [82] or with the use of fins with different shapes [[83], [84], [85], [86]], or metal foams [87,88]. This PCM was used in applications such as the thermal management of PV collectors [89], thermal management of electronics [88], or recovery of exhaust heat from engines [90].

Fig. 6.

Thermal characterisation of PCM #2 – RT 55 given by the producer [24].

The results of the characterization of RT 55 are presented in Table 6. In the characterisation, this PCM showed good thermal behaviour, with stable cycling behaviour (similar behaviour between the DSC cycles), as shown in Fig. 7a. The melting temperature tested with DSC is very similar to that reported by the producer, while the TGA/DSC gives a melting temperature 10 °C higher (Fig. 7b). The melting enthalpy was about 30 % lower when tested with DSC and about 80 % higher when tested with TGA/DSC (Fig. 6), this is probably due to the fact that the melting curve of this PCM is much wider than that of the previous PCM. Moreover, the sample started to degrade at 162.4 °C and half of the material degraded when reaching 225.4 °C. The maximum temperature at which this PCM should be used is 162.4 °C. The tested thermal conductivity was 0.27 W/m·ºC (Fig. 7c), 33.6 % higher than the one reported by the provider.

Table 6.

Characterization of PCM #2 - RT 55.

#	PCM	Data from literature				Experimental results
						DSC			TGA/DSC					Hot Disk
		Tmelting (ºC)	ΔHmelting (J/g)	Tdeg (ºC)	ksolid (W/m·ºC)	Tmelting (ºC)	ΔHmelting (J/g)	Var (%)	Tvar (ºC)	ΔHvar (J/g)	Var (%)	Tonset (ºC)	Tmid (ºC)	ksolid (W/m·ºC)	Var (%)
2	RT 55	55.0 [24]	158.0 [24]	n.a.	0.20 [24]	Cycle 1: 55.1	Cycle 1: 111.2	−29 %	65.3	284.9	+80 %	162.4	225.4	0.27	+34 %
						Cycle 2: 55.1	Cycle 2: 113.9	−28 %
						Cycle 3: 55.3	Cycle 3: 114.9	−27 %

Fig. 7.

PCM #2 – RT 55: (a) DSC analysis, (b) TGA/DSC analysis, and (c) Hot disk analysis.

3.3.3. PCM #3 – E 58

This is a commercial material from the company PCM Products (United Kingdom); according to the manufacturer, this is a eutectic of inorganic salts. The results of the characterization of E 58 are presented in Table 7. In the characterisation, this PCM did not show good thermal behaviour, as shown in Fig. 8a. Only the first melting did show a unique peak, but after that, two peaks appeared both in melting and freezing, showing that the eutectic was broken. The first peak observed in the measurements is very close to the phase change temperature reported by the manufacturer. In contrast, a second peak appears at higher temperatures and is linked to a very low enthalpy. Therefore, the first peak is considered the main peak in the characterisation results. On the other hand, the TGA/DSC analysis did not show a clear melting peak (Fig. 8b). The sample started to lose mass at 45.3 °C, most probably water molecules, and the mass of the material is reduced by half when 90.5 °C is reached. For this PCM, it was not possible to measure the thermal conductivity due to its high hygroscopicity (Fig. 9).

Table 7.

Characterization of PCM #3 - E 58.

#	PCM	Data from literature				Experimental results
						DSC			TGA/DSC					Hot Disk
		Tmelting (ºC)	ΔHmelting (J/g)	Tdeg (ºC)	ksolid (W/m·ºC)	Tmelting (ºC)	ΔHmelting (J/g)	Var (%)	Tvar (ºC)	ΔHvar (J/g)	Var (%)	Tonset (ºC)	Tmid (ºC)	ksolid (W/m·ºC)	Var (%)
3	E 58	58.0 [77]	145.0 [77]	120.0 [77]	0.69 [77]	Cycle 1: 72.3	Cycle 1: 12.9	−91 %	–	–	–	45.3	90.5	–	–
						Cycle 2: 57.9	Cycle 2: 13.7	−91 %
						Cycle 3: 57.6	Cycle 3: 13.8	−91 %

Fig. 8.

PCM #3 – E 58: (a) DSC analysis, (b) TGA/DSC analysis.

Fig. 9.

Samples prepared for hot disk analysis of PCM #3 – E 58.

3.3.4. PCM #4 – Mg(NO₃)₂·6H₂O-MgCl₂·6H₂O (80-20 wt%)

This is a mixture of two salt hydrates that have been reported in the early PCM literature [17,18,20]. The results of the characterization of Mg(NO₃)₂·6H₂O-MgCl₂·6H₂O (80-20 wt%) are presented in Table 8. In the characterisation, this PCM showed good thermal behaviour during the thermal cycling, as shown in Fig. 10a. Nevertheless, the melting temperature measured with DSC was 10 °C higher than that reported in the literature [17], while the freezing temperature was that reported; as seen, the PCM did show subcooling (10 °C difference between melting and freezing). Moreover, the melting enthalpy measured was very low compared to that found in the literature. the TGA/DSC analysis showed two peaks (Fig. 10b), which probably corresponds a dehydration process (not a phase change). The sample started to lose mass at 48.7 °C, most probably water molecules, and the mass of the material is reduced by half when 91.7 °C is reached (Fig. 10b). The tested thermal conductivity was not possible to perform, since it was not possible to prepare the solid blocks for the measurement, when the PCM starts to melt to take the samples of the beaker, it becomes mushy (Fig. 11).

Table 8.

Characterization of PCM #4 - Mg(NO₃)₂·6H₂O + MgCl₂·6H₂O (80-20 wt%).

#	PCM	Data from literature				Experimental results
						DSC			TGA/DSC					Hot Disk
		Tmelting (ºC)	ΔHmelting (J/g)	Tdeg (ºC)	ksolid (W/m·ºC)	Tmelting (ºC)	ΔHmelting (J/g)	Var (%)	Tvar (ºC)	ΔHvar (J/g)	Var (%)	Tonset (ºC)	Tmid (ºC)	ksolid (W/m·ºC)	Var (%)
4	Mg(NO3)2·6H2O-MgCl2·6H2O (80-20 wt%)	60.0 [17,18]	150.0 [17,18]	60.0 [17,18]	150.0 [17,18]	Cycle 1: 70.8	Cycle 1: 2.8	−98 %	Peak 1: 38.1 Peak 2: 43.3	Peak 1: 16.7 Peak 2: 36.2	–	48.7	91.7	–	–

Fig. 10.

PCM #4 - Mg(NO₃)₂·6H₂O-MgCl₂·6H₂O (80-20 wt%): (a) DSC analysis, and (b) TGA/DSC analysis.

Fig. 11.

Samples prepared for hot disk analysis of PCM #4 - Mg(NO₃)₂·6H₂O-MgCl₂·6H₂O (80-20 wt%).

3.3.5. PCM #5 – Mg(NO₃)₂·6H₂O-MgCl₂·6H₂O (60-40 wt%)

This is a mixture of two salt hydrates is the same as the previous one but with different weight composition. This mixture has been also investigated by the group led by Prof. S. Ushak at the University of Antofagasta, since one of its components (MgCl₂·6H₂O) is also the main component of a by-product of the salt mines in the desert of Atacama [20], and the results are presented in Fig. 12.

Fig. 12.

DSC (left) and thermal stability (right) results of the mixture Mg(NO₃)₂·6H₂O-MgCl₂·6H₂O (60-40 wt%) reported in the literature [20].

The results of the characterization of Mg(NO₃)₂·6H₂O + MgCl₂·6H₂O (60-40 wt%) are presented in Table 9. In the characterisation, this PCM did not show good thermal behaviour during the thermal cycling, as shown in Fig. 13a. The DSC analysis showed 2 peaks, the first one at 60 °C, the expected melting temperature, and the second one at around 71–72 °C, higher but not of any of the individual salts (the melting temperature of Mg(NO₃)₂·6H₂O is 89 °C and that of MgCl₂·6H₂O is 118 °C). Moreover, the melting enthalpy is lower than that reported in the literature. TGA/DSC results showed a peak in the DSC signal, which probably corresponds a dehydration process (not a phase change) (Fig. 13b). The sample started to lose mass at 40 °C, most probably water molecules, and the mass of the material is reduced by half when 117.7 °C is reached (Fig. 13b). The tested thermal conductivity not possible to perform since during the preparation of the samples, it was not possible to remove the solid blocks from the beakers (Fig. 14). In addition, when this PCM crystallises, cavities form between the crystals, which does not allow us to have the flat surface necessary for hot disk measurement.

Table 9.

Characterization of PCM #5 - Mg(NO₃)₂·6H₂O + MgCl₂·6H₂O (60-40 wt%).

#	PCM	Data from literature				Experimental results
						DSC			TGA/DSC					Hot Disk
		Tmelting (ºC)	ΔHmelting (J/g)	Tdeg (ºC)	ksolid (W/m·ºC)	Tmelting (ºC)	ΔHmelting (J/g)	Var (%)	Tvar (ºC)	ΔHvar (J/g)	Var (%)	Tonset (ºC)	Tmid (ºC)	ksolid (W/m·ºC)	Var (%)
5	Mg(NO3)2·6H2O-MgCl2·6H2O (60-40 wt%)	60.0 [20]	132.3 [20]	130.0 [20]	n.a.	Cycle 1: 60.1	Cycle 1: 28.0	−78 %	48.7	69.1	−47 %	40.4	117.7	–	–
						Cycle 2: 59.6	Cycle 2: 28.9	−78 %
						Cycle 3: 59.6	Cycle 3: 28.5	−78 %

Fig. 13.

PCM #5 - Mg(NO₃)₂·6H₂O-MgCl₂·6H₂O (60-40 wt%): (a) DSC analysis, and (b) TGA/DSC analysis.

Fig. 14.

Samples prepared for hot disk analysis of PCM #5 - Mg(NO₃)₂·6H₂O-MgCl₂·6H₂O (60-40 wt%).

3.3.6. PCM #6 – Palmitic acid

This is a fatty acid, a commodity with well-known properties [17], and this is a material that has been reported in the early PCM literature [17,18,[91], [92], [93]]. Already in 2002, Sari and Kaygusuz [32] reported the thermophysical properties of palmitic acid (Fig. 15). It has also been used extensively in the recent literature related to PCMs [[94], [95], [96]].

Fig. 15.

DSC characterization of palmitic acid found in the literature [32].

The results of the characterization of the palmitic acid (C₁₆H₃₂O₂) are presented in Table 10. In the characterisation, this PCM showed good thermal behaviour during the thermal cycling, as shown in Fig. 16a and b. The melting enthalpy measured with DSC and TGA was 62.9 °C, in the range of that reported in the TES literature, although with variation to the maximum and minimum found in the literature. The melting temperature as also very regular in the thermal cycling with DSC (between 186 and 182 J/g), in the middle of the range reported in the literature, while with TGA/DSC, the melting enthalpy measured (250.8 J/g) was between 13 % and 54 % higher (compare to the lowest and highest values reported in the literature). Moreover, the sample started to degrade at 152.7 °C and half of the material degraded when reaching 212.40 °C (Fig. 16b). The maximum temperature at which this PCM should be used is 152.7 °C. The measurement of the thermal conductivity with hot disk gave 0.26 W/m·ºC (Fig. 16), between 53 % and 73 % higher (compared to the lowest and highest values reported in the literature).

Table 10.

Characterization of PCM #6 – Palmitic acid.

#	PCM	Data from literature				Experimental results
						DSC			TGA/DSC					Hot Disk
		Tmelting (ºC)	ΔHmelting (J/g)	Tdeg (ºC)	ksolid (W/m·ºC)	Tmelting (ºC)	ΔHmelting (J/g)	Var (%)	Tvar (ºC)	ΔHvar (J/g)	Var (%)	Tonset (ºC)	Tmid (ºC)	ksolid (W/m·ºC)	Var (%)
6	Palmitic acid	55.0 [26] 59.0 [30] 61.0 [17,18,21,31,32] 62.9 [33] 63.0 [17,18,21,31] 64.0 [17,18,21,31] 69.0 [21]	163.0 [26] 189.6 [30] 203.4 [17,18,21,31,32] 212.0 [33] 187.0 [17,18,21,31] 185.4 202.5 [21] 222 [17,18,21,31,32]	n.a.	0.15 [17] 0.16 [21,29] 0.17 [17]	Cycle 1: 63.8	Cycle 1: 185.6	−14 to −16 %	62.3	250.8	+54 - +13 %	152.7	212.4	0.26	+73 - +53 %
						Cycle 2: 64.1	Cycle 2: 182.7	−12 to −18 %
						Cycle 3: 64.0	Cycle 3: 182.7	−12 to −18 %

Fig. 16.

PCM #6 – Palmitic acid: (a) DSC analysis, (b) TGA/DSC analysis, and (c) Hot disk analysis.

3.3.7. PCM #7 – RT 64 HC

This is a commercial material from the company Rubitherm (Germany). Most probably this is an organic PCM and its thermal characterisation given by the manufacturers is presented in Fig. 17. This PCM has been used in studies about thermal management of batteries [97] and for thermal management of PV collectors [79].

Fig. 17.

Thermal characterisation of PCM #7 - RT 64 HC given by the producer [24].

The results of the characterization of RT 64 HC are presented in Table 11. In the characterisation, this PCM showed good thermal behaviour, with stable cycling behaviour (similar behaviour between the DSC cycles), as shown in Fig. 18a. Nevertheless, the melting and freezing temperatures are lower than that reported by the manufacturer (54 °C and 52 °C vs. 64 °C) (Fig. 17). Moreover, the sample started to degrade at 158.6 °C and half of the material degraded when reaching 225.4 °C (Fig. 18b). The maximum temperature at which this PCM should be used is 158.6 °C. The tested thermal conductivity was 0.33 W/m·ºC, 63.6 % higher than the reported by the producer (Fig. 18c).

Table 11.

Characterization of PCM #7 - RT 64 HC.

#	PCM	Data from literature				Experimental results
						DSC			TGA/DSC					Hot Disk
		Tmelting (ºC)	ΔHmelting (J/g)	Tdeg (ºC)	ksolid (W/m·ºC)	Tmelting (ºC)	ΔHmelting (J/g)	Var (%)	Tvar (ºC)	ΔHvar (J/g)	Var (%)	Tonset (ºC)	Tmid (ºC)	ksolid (W/m·ºC)	Var (%)
7	RT 64 HC	64.0 [24]	242.0 [24]	n.a.	0.20 [24]	Cycle 1: 55.5	Cycle 1: 169.9	−29 %	65.1	309.4	+28 %	158.6	225.4	0.33	+64 %
						Cycle 2: 55.4	Cycle 2: 166.8	−28 %
						Cycle 3: 55.5	Cycle 3: 166.9	−27 %

Fig. 18.

PCM #7 - RT 64 HC: (a) DSC analysis, (b) TGA analysis, and (c) Hot disk analysis.

3.3.8. PCM #8 – Stearic acid

This is a fatty acid, a commodity with well-known properties [17], and this is a material that has been reported in the early PCM literature [17,18,[91], [92], [93]]. Already in 2001, Sari and Kaygusuz [43] reported the thermophysical properties of stearic acid (Fig. 19). Moreover, this material is also used extensively in today literature on PCMs [[98], [99], [100]].

Fig. 19.

DSC characterization of stearic acid found in the literature [43].

The results of the characterization of the stearic acid (C₁₈H₃₆O₂) are presented in Table 12. In the characterisation, this PCM showed good thermal behaviour during the thermal cycling, as shown in Fig. 20a and b. The melting enthalpy measured with DSC and TGA was 69.7 °C, in the range of that reported in the TES literature [17,18,[91], [92], [93]]. The melting temperature as also very regular in the thermal cycling with DSC (between 194 and 198 J/g), in the middle of the range reported in the literature, while with TGA the melting enthalpy measured (255.8 J/g) was between 15 % and 29 % higher (compare to the lowest and highest values reported in the literature). Moreover, the sample started to degrade at 156.4 °C and half of the material degraded when reaching 222.8 °C (Fig. 20b). The maximum temperature at which this PCM should be used is 156 °C. The measurement of the thermal conductivity with hot disk gave 0.26 W/m·ºC (Fig. 20c), between 53 % and 73 % higher (compared to the lowest and highest values reported in the literature).

Table 12.

Characterization of PCM #8 – Stearic acid.

#	PCM	Data from literature				Experimental results
						DSC			TGA/DSC					Hot Disk
		Tmelting (ºC)	ΔHmelting (J/g)	Tdeg (ºC)	ksolid (W/m·ºC)	Tmelting (ºC)	ΔHmelting (J/g)	Var (%)	Tvar (ºC)	ΔHvar (J/g)	Var (%)	Tonset (ºC)	Tmid (ºC)	ksolid (W/m·ºC)	Var (%)
8	Stearic acid	67.8 [17,26,41] 69.0 [21,41] 60.0–61.0 69.4 [26] 70.0 [17,18,21,29] 69.6 [33] 69.1 [42]	198.9 [17,26,41] 202.5 [21,41] 186.5 199.0 [26] 203.0 [17,18,21,29] 201.8 [42] 222 [33]	n.a.	0.17 [17] 0.18 [43]	Cycle 1: 70.6	Cycle 1: 197.8	−0.5 to −11 %	68.7	255.8	+15 - +29 %	156.4	222.8	0.26	53–54 %
						Cycle 2: 70.4	Cycle 2: 193.9	−3 to −13 %
						Cycle 3: 70.5	Cycle 3: 194.4	−2 to −12 %

Fig. 20.

PCM #8 – Stearic acid: (a) DSC analysis, (b) TGA analysis, and (c) Hot disk analysis.

3.3.9. PCM #9 – LiNO₃-NaNO₃-KNO₃ (20-28-52 wt%)

This is a mixture of three salts reported in the literature [47]. This ternary mixture was first reported as PCM by Olivares and Edwards in 2013 [78]. They developed the phase diagram theoretical using the software FactSage (Fig. 21a) and published its thermal characterisation with DSC (Fig. 21b). The influence of lithium nitrate was also assessed in the literature [101].

Fig. 21.

Phase diagram and DSC analysis of PCM #9 – LiNO₃-NaNO₃-KNO₃ (20-28-52 wt%) found in the literature [78].

The results of the characterization of LiNO₃-NaNO₃-KNO₃ (20-28-52 wt%) are presented in Table 13. In the characterisation, this PCM did not show good thermal behaviour during the thermal cycling, as shown in Fig. 22a. The melting temperature of the characterization was around 25 °C higher than that reported in the literature. TGA/DSC results show that this mixture is stable up to 400 °C (Fig. 22b), losing less than 1 % of its initial mass, which could be a little humidity absorbed by the sample before starting the measurement. The tested thermal conductivity was 0.69 W/m·ºC (Fig. 22c).

Table 13.

Characterization of PCM #9 - LiNO₃-NaNO₃-KNO₃ (20-28-52 wt%).

#	PCM	Data from literature				Experimental results
						DSC			TGA/DSC					Hot Disk
		Tmelting (ºC)	ΔHmelting (J/g)	Tdeg (ºC)	ksolid (W/m·ºC)	Tmelting (ºC)	ΔHmelting (J/g)	Var (%)	Tvar (ºC)	ΔHvar (J/g)	Var (%)	Tonset (ºC)	Tmid (ºC)	ksolid (W/m·ºC)	Var (%)
9	LiNO3-NaNO3-KNO3 (20-28-52 wt%)	150.0 [47,48]	n.a.	n.a.	n.a.	Cycle 1: 178.0	Cycle 1: 109.8	–	187.0	169.1	–	>400.0	>400.0	0.69	–
						Cycle 2: 173.9	Cycle 2: 140.9	–
						Cycle 3: 177.8	Cycle 3: 66.4	–

Fig. 22.

PCM #9 - LiNO₃-NaNO₃-KNO₃ (20-28-52 wt%): (a) DSC analysis, (b) TGA/DSC analysis, and (c) Hot disk analysis.

3.3.10. PCM #10 – Salicylic acid

This is a fatty acid, a commodity with well-known properties [55], and has been used as PCM in some applications or studies [102,103]. The results of the characterization of the salicylic acid (C₇H₆O₃) are presented in Table 14. In the characterisation, this PCM showed good thermal behaviour during the thermal cycling, as shown in Fig. 23a. The melting temperature found with DSC and TGA/DSC are very similar than the reported one. The sample started to degrade at 110.4 °C and half of the material degraded when reaching 157.1 °C, therefore this material thermally decomposes before melting (Fig. 23b). This is reflected in the DSC results; from second cycle the value of enthalpy reduces 37 %; and also in the different melting enthalpies reported in the literature. The measurement of the thermal conductivity was not possible to perform; during the sample preparation the material did not solidify compactly, it crumbled (Fig. 24).

Table 14.

Characterization of PCM #10 – Salicylic acid.

#	PCM	Data from literature				Experimental results
						DSC			TGA/DSC					Hot Disk
		Tmelting (ºC)	ΔHmelting (J/g)	Tdeg (ºC)	ksolid (W/m·ºC)	Tvar (ºC)	ΔHvar (J/g)	Var (%)	Tvar(ºC)	ΔHvar (J/g)	Var (%)	Tonset (ºC)	Tmid (ºC)	ksolid (W/m·ºC)	Var (%)
10	Salicylic acid	159.0 [25,45,50,53,55] 159.1 [53,55]	199.0 [25,45,50,53,55] 161.5 [55]	n.a.	n.a.	Cycle 1: 159.6	Cycle 1: 179.2	+11 to −10 %	158.8	115.3	−29 to −42 %	110.4	157.1	–	–
						Cycle 2: 156.9	Cycle 2: 113.6	−30 to −43 %
						Cycle 3: 106.5	Cycle 3: 12.5	−92 to −94 %

Fig. 23.

PCM #10 – Salicylic acid: (a) DSC analysis, and (b) TGA/DSC analysis.

Fig. 24.

Samples prepared for hot disk analysis of PCM #10 – Salicylic acid.

3.3.11. PCM #11 – LiNO₃-NaNO₃ (49-51 wt%)

This binary mixture has been reported in the literature [56]. The results of the characterization of LiNO₃-NaNO₃ (49–51 wt%) are presented in Table 15. In the characterisation, this PCM did not show good thermal behaviour during the thermal cycling, as shown in Fig. 25a. The melting temperature found with DSC and TGA/DSC is higher than the reported one. TGA/DSC results show that this mixture is stable up to 400 °C (Fig. 25b). The tested thermal conductivity was 0.57 W/m·ºC (Fig. 25c).

Table 15.

Characterization of PCM #11 - LiNO₃-NaNO₃ (49-51 wt%).

#	PCM	Data from literature				Experimental results
						DSC			TGA/DSC					Hot Disk
		Tmelting (ºC)	ΔHmelting (J/g)	Tdeg (ºC)	ksolid (W/m·ºC)	Tmelting (ºC)	ΔHmelting (J/g)	Var (%)	Tvar (ºC)	ΔHvar (J/g)	Var (%)	Tdeg (ºC)	Tdeg (ºC)	ksolid (W/m·ºC)	Var (%)
11	LiNO3-NaNO3 (49–51 wt%)	194.0 [50,56,61,64]	265.0 [50,56,61,64]	n.a.	n.a.	Cycle 1: 174.4	Cycle 1: 80.7	−69 %	185.7	107.6	−65 %	>400.0	>400.0	0.56	–
						Cycle 2: 175.8	Cycle 2: 71.2	−73 %
						Cycle 3: 175.9	Cycle 3: 62.2	−76 %

Fig. 25.

PCM #11 - LiNO₃-NaNO₃ (49-51 wt%): (a) DSC analysis, (b) TGA/DSC analysis, and (c) Hot disk analysis.

3.3.12. PCM #12 – NaNO₃–KNO₃ (50–50 wt%)

This binary mixture has been reported in the literature [58]. The results of the characterization of NaNO₃–KNO₃ (50–50 wt%) are presented in Table 16. In the characterisation, this PCM showed good thermal behaviour during the thermal cycling, as shown in Fig. 26a. The melting temperature measured was around 7 °C lower than that reported in the literature. TGA/DSC results show that this mixture is stable up to 400 °C (Fig. 26b), losing less than 1 % of its initial mass, which could be a little humidity absorbed by the sample before starting the measurement. The tested thermal conductivity was 0.91 W/m·ºC (Fig. 26c), 62.5 % higher than that reported in the literature [45,61].

Table 16.

Characterization of PCM #12 - NaNO₃–KNO₃ (50–50 wt%).

#	PCM	Data from literature				Experimental results
						DSC			TGA/DSC					Hot Disk
		Tmelting (ºC)	ΔHmelting (J/g)	Tdeg (ºC)	ksolid (W/m·ºC)	Tmelting (ºC)	ΔHmelting (J/g)	Var (%)	Tvar (ºC)	ΔHvar (J/g)	Var (%)	Tonset (ºC)	Tmid (ºC)	ksolid (W/m·ºC)	Var (%)
12	NaNO3–KNO3 (50–50 wt%)	220.0 [58,61] 220.0–222.0 [45,61]	100.7 [58,61] 100.0–100.7 [45,58,61]	220.0 [58,61] 220.0–222.0 [45,61]	0.56 [45,61]	Cycle 1: 212.4	Cycle 1: 68.9	−31 to −32 %	213.9	109.7	+10-+9 %	>400.0	>400.0	0.91	+63 %
						Cycle 2: 212.7	Cycle 2: 65.4	−35 %
						Cycle 3: 212.7	Cycle 3: 65.5	−35 %

Fig. 26.

PCM #12 - NaNO₃–KNO₃ (50–50 wt%): (a) DSC analysis, (b) TGA/DSC analysis, (c) Hot disk analysis.

3.3.13. PCM #13 – NaNO₃–KNO₃ (60–40 wt%)

This eutectic mixture is commonly known as Solar Salt in the CSP industry as heat transfer fluid and as storage media and it is included in this deliverable although it was not identified previously. This mixture has been extensively studied and its properties have been reported by several authors [4,69,70,104]. The main attraction of this material is its good thermal stability and its compatibility with metals, showing low corrosion rates. Recently in 2024, Prieto et al. [4]. analysed by DSC and TGA the behaviour and thermal stability of this mixture under different conditions (Fig. 27). These results are interesting for its application as a PCM.

Fig. 27.

DSC (right) and TGA (left) analysis of PCM #13 - NaNO₃-KNO₃ (60–40 wt%) found in the literature [4].

The results of the characterization of NaNO₃–KNO₃ (60–40 wt%) are presented in Table 17. In the characterisation, this PCM showed good thermal behaviour during the thermal cycling, as shown in Fig. 28a. The melting temperature measured was around 4 °C lower than that reported in the literature [4]. TGA/DSC results show that this mixture is stable up to 400 °C. These results agree with the results found in, where the degradation temperature of the mixture found was 624 °C. (Fig. 28b). The tested thermal conductivity was 0.87 W/m·ºC (Fig. 28c), 266 % higher than that reported in the literature [69].

Table 17.

Characterization of PCM #13 – NaNO₃–KNO₃ (60–40 wt%).

#	PCM	Data from literature				Experimental results
						DSC			TGA/DSC					Hot Disk
		Tmelting (ºC)	ΔHmelting (J/g)	Tdeg (ºC)	ksolid (W/m·ºC)	Tmelting (ºC)	ΔHmelting (J/g)	Var (%)	Tvar (ºC)	ΔHvar (J/g)	Var (%)	Tonset (ºC)	Tmid (ºC)	ksolid (W/m·ºC)	Var (%)
13	NaNO3–KNO3 (60–40 wt%)	227.0 [4] 222.0 [50,56,64,66] 221.1 [68] 224.7 [69]	109.0 [69]	624.0 [4] 588.5 [68,70]	0.24 [69]	Cycle 1: 225.8	Cycle 1: 87.6	−20 %	225.3	125.3	+15 %	>400.0	>400.0	0.88	+266 %
						Cycle 2: 223.3	Cycle 2: 86.7	−21 %
						Cycle 3: 223.2	Cycle 3: 84.9	−22 %

Fig. 28.

PCM #13 – NaNO₃–KNO₃ (60–40 wt%): (a) DSC analysis, (b) TGA/DSC analysis, and (c) Hot disk analysis.

3.3.14. PCM #14 – LiNO₃

This salt has been reported in the literature [105,106], although it is more common to find it in mixtures (binary, ternary, or even quaternary). The results of the characterization of LiNO₃ are presented in Table 18. In the characterisation, this PCM showed good thermal behaviour during the thermal cycling, as shown in Fig. 29a. The melting temperature tested both with DSC and TGA/DSC are similar to that reported in the literature [19,45,56,58,59,61,63,71,[74], [75], [76]]. TGA/DSC results show that the sample lost around 6 % of its initial mass at 330 °C. Most probably this mass loss is associated to the degradation of some impurities present in the LiNO₃ used in this measurement, in this case it could be FeSO₄·7H₂O, whose boiling temperature is 330 °C, which coincides with the temperature at which the sample started to lose mass (Fig. 29b). In addition, this PCM is stable up to 400 °C. The tested thermal conductivity was 0.84 W/m·ºC (Fig. 29c) which is 51 % lower than the reported by Ref. [76], and 45 % higher than the reported by Refs. [71,75].

Table 18.

Characterization of PCM #14 – LiNO₃.

#	PCM	Data from literature				Experimental results
						DSC			TGA/DSC					Hot Disk
		Tmelting (ºC)	ΔHmelting (J/g)	Tdeg (ºC)	ksolid (W/m·ºC)	Tmelting (ºC)	ΔHmelting (J/g)	Var (%)	Tvar (ºC)	ΔHvar (J/g)	Var (%)	Tonset (ºC)	Tmid (ºC)	ksolid (W/m·ºC)	Var (%)
14	LiNO3	250.0 [45,56,58,59,63] 250.0–254.0 [25,26,45,56,61,63] 252.0 [74] 253.0 [71,75] 249.7 [76]	370.0 [45,56,58,59,63] 360.0–363.0 [25,26,45,56,61,63] 370.0 [74] 360.0 [71,75] 300.0 [76]	470.0 [76]	1.70 [76] 0.58 [71,75]	Cycle 1: 250.1	Cycle 1: 261.5	−13 % to −29 %	253.8	456.5	+52 - +23 %	>400.0	>400.0	0.84	−51 - +45 %
						Cycle 2: 249.0	Cycle 2: 278.7	−7 to −25 %
						Cycle 3: 250.1	Cycle 3: 275.1	−8 to −26 %

Fig. 29.

PCM #14 - LiNO₃: (a) DSC analysis, (b) TGA/DSC analysis, and (c) Hot disk analysis.

3.4. Summary of results

Table 19 summarizes the PCM characterization results. The values of enthalpy and melting temperature in DSC are an average of the second and third cycle, because during the first cycle the initial sample is a powder and is not distributed in the same way as in the subsequent cycles (recrystallised sample) and therefore its behaviour may be a little different, for this reason, it is common not to consider this first value in the average. Moreover, when the decomposition of the PCM is seen no data is added in this table since it is considered that the material would not be a good PCM for any application.

Table 19.

Summary of characterisation of the selected PCMs.

#	PCM	Data from literature				Experimental results
						DSC			TGA/DSC					Hot Disk
		Tmelting (ºC)	ΔHmelting (J/g)	Tdeg (ºC)	ksolid (W/m·ºC)	Tmelting (ºC)	ΔHmelting (J/g)	Var (%)	Tvar (ºC)	ΔHvar (J/g)	Var (%)	Tonset (ºC)	Tmid (ºC)	ksolid (W/m·ºC)	Var (%)
1	RT 54 HC	54.0 [24]	182.0 [24]	n.a.	0.20 [24]	55.4	172.1	−5%	54.7	226.1	+24 %	130.3	196.3	0.23	+15 %
2	RT 55	55.0 [24]	158.0 [24]	n.a.	0.20 [24]	55.2	114.5	−28 %	64.3	284.9	+80 %	162.4	225.4	0.27	+34 %
3	E 58	58.0 [77]	145.0 [77]	120.0 [77]	0.69 [77]	57.7	13.8	−91 %	–	–	–	-- (b)	-- (b)	–	–
4	Mg(NO3)2·6H2O-MgCl2·6H2O (80–20 wt%)	60.0 [17,18]	150.0 [17,18]	n.a.	n.a.	--(a)	--(a)	–	--(a)	--(a)	–	-- (b)	-- (b)	–	–
5	Mg(NO3)2·6H2O + MgCl2·6H2O (60–40 wt%)	60.0 [20]	132.3 [20]	130.0 [20]	n.a.	59.6	28.9	−78 %	48.7	69.1	−47 %	-- (b)	117.7	–	–
6	Palmitic acid	55.0 [26] 59.0 [30] 61.0 [17,18,21,31,32] 62.9 [33] 63.0 [17,18,21,31] 64.0 [17,18,21,31] 69.0 [21]	163.0 [26]	n.a.	55.0 [26] 59.0 [30] 61.0 [17,18,21,31,32] 62.9 [33] 63.0 [17,18,21,31] 64.0 [17,18,21,31] 69.0 [21]	64.0	182.7	−12 to −18 %	62.3	250.8	+54 - +13 %	152.7	212.4	0.26	+73 - +53 %
			189.6 [30]
			203.4 [17,18,21,31,32]
			212.0 [33]
			187.0 [17,18,21,31]
			185.4
			202.5 [21]
			222 [17,18,21,31,32]
7	RT 64 HC	64.0 [24]	242.0 [24]	n.a.	0.20 [24]	55.5	166.9	−31 %	65.1	309.4	+28 %	158.6	225.4	0.33	+64 %
8	Stearic acid	67.8 [17,26,41]	198.9 [17,26,41] 202.5 [21,41] 186.5 199.0 [26] 203.0 [17,18,21,29] 201.8 [42] 222 [33]	n.a.	0.17 [17] 0.18 [43]	70.4	194.2	−4 to −13 %	68.7	255.8	+15 - +29 %	156.4	222.8	0.26	+53 - +54 %
		69.0 [21,41]
		60.0–61.0
		69.4 [26]
		70.0 [17,18,21,29]
		69.6 [33]
		69.1 [42]
9	LiNO3-NaNO3-KNO3 (20-28-52 wt%)	150.0 [47,48]	n.a.	n.a.	n.a.	175.9	103.7	–	187.0	169.1	–	>400.0	>400.0	0.69	–
10	Salicylic acid	159.0 [25,45,50,53,55]	199.0 [25,45,50,53,55]	n.a.	n.a.	--(c)	--(c)	–	--(c)	--(c)	–	110.4	157.1	–	–
		159.1 [53,55]	161.5 [55]
11	LiNO3-NaNO3 (49–51 wt%)	194.0 [50,56,61,64]	265.0 [50,56,61,64]	n.a.	n.a.	175.9	66.7	−75 %	185.7	107.6	−65 %	>400.0	>400.0	0.56	–
12	NaNO3–KNO3 (50–50 wt%)	220.0 [58,61]	100.7 [58,61]	220.0 [58,61]	100.7 [58,61]	212.7	65.4	−35 %	213.9	109.7	+10 -+9 %	>400.0	>400.0	0.91	+63 %
		220.0–222.0 [45,61]	100.0–100.7 [45,58,61]	220.0–222.0 [45,61]	100.0–100.7 [45,58,61]
13	NaNO3–KNO3 (60–40 wt%)	227.0 [4]	109.0 [69]	624.0 [4] 588.5 [68,70]	0.24 [69]	223.2	85.8	−21 %	225.3	125.3	+15 %	>400	>400.0	0.88	+266 %
		222.0 [50,56,64,66]
		221.1 [68]
		224.7 [69]
14	LiNO3	250.0 [45,56,58,59,63]	370.0 [45,56,58,59,63]	470.0 [76]	1.70 [76] 0.58 [71,75]	249.6	276.9	−8 to −25 %	253.8	456.5	+52 - +23 %	>400.0	>400.0	0.84	−51 - +45 %
		250.0–254.0 [25,26,45,56,61,63]	360.0–363.0 [25,26,45,56,61,63]
		252.0 [74]	370.0 [74]
		253.0 [71,75]	360.0 [71,75]
		249.7 [76]	300.0 [76]

(a) No phase change peak.

(b) Dehydration process.

(c) Decomposes thermally before melting.

4. Conclusions

This paper shows the experimental characterization of the PCMs preselected for the selected temperature ranges. A comprehensive list of suitable PCM is presented and experimental techniques including DSC, TGA/DSC and Hot Disk were used to determine the thermal properties of eight PCMs selected for mid-temperature and six PCMs selected for high-temperature respectively. The main properties measured were the melting enthalpy [J/g], the degradation temperature [ºC], and the thermal conductivity at solid state [W/m·ºC]. These properties are the main parameters which affects the selection of PCM. The values obtained were compared to the ones found in the available literature and technical datasheets to see potential differences in the thermal behavior. Results show that this analysis was necessary, since differences were found with the data available; the most important differences being in the thermal stability of the materials.

The most difficult parameter to find was the degradation temperature which represent an important material property to define both safety and operational boundaries. The next activity to develop the thermal energy storage (TES) concept, will be the definition of the operating temperatures of the mid-temperature and high-temperature of the TES related to the final application. Indeed, this data is fundamental to define the most suitable PCM since the first property to be selected, when choosing a PCM, is the phase change temperature. After the phase change temperature, the most suitable PCMs will be selected based on the melting enthalpy, and the thermal conductivity. The first property will indeed affect the energy density thus determining the compactness of the TES. Thermal conductivity, corrosiveness, market availability, price, or other criteria, on the other hand, will affect the power of charging and discharging of the storage system.

CRediT authorship contribution statement

Franklin R. Martínez: Writing – original draft, Visualization, Investigation. Emiliano Borri: Writing – review & editing, Formal analysis. Saranprabhu Mani Kala: Writing – review & editing, Investigation, Formal analysis. Svetlana Ushak: Writing – review & editing, Supervision, Resources, Project administration, Methodology, Funding acquisition. Luisa F. Cabeza: Writing – original draft, Supervision, Resources, Project administration, Methodology, Funding acquisition, Data curation, Conceptualization.

Data availability statement

Data is available on open access under https://doi.org/10.34810/data1822.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.