Dataset on thermal conductivity of composted olive cake (COC)

Abstract

Thermal properties play a critical role in the compost used as a soil amendment for different agricultural applications especially for green roof buildings. Despite this importance, there remains insufficient information on thermal conductivity of composted olive cake (COC), K, and how it is influenced by bulk its density and water content. This shows how thermal conductivity (K) is affected by these two parameters and the potential use of COC as cheap padding in geothermal heat storage and green roof building applications. Thermal conductivities of 30 samples of (COC) were measured experimentally at different moisture contents and bulk densities using a hot wire technique. The results revealed that thermal conductivity exhibits a linear increase as both bulk density and water content increased. It increased from 0.10 to 0.60 W/(m K) at saturation levels ranging from dry to 90 %. The highest thermal conductivity of 0.60 W/m K was revealed at a water content of 90 %. Therefore, (COC) might be used as an inexpensive padding in geothermal heat storage applications and as an eco-friendly insulation pad in green- roof buildings, leading to passive energy savings. Overall, the study provides important insights into the thermal properties of COC and its potential as a sustainable insulation material.

Specifications Table

Subject	Agricultural Sciences.
Specific subject area	Agricultural Engineering; composting, insulation.
Type of data	Figure, Raw, Analyzed.
Data collection	Moisture contents were achieved by mixing oven dried 0.25 cm sieve composted olive oil (COC) with certain water contents. Next day, a certain amount of compost was packed into a 30 cm long marked cylinder with diameter of 15 cm to get the desired bulk density. The temperature rise with time was measured by a thermocouple inserted in the compost near the hot wire and was saved by a data logger. The thermal conductivity was evaluated by the equation K = 0.0796 I2R/S; where, K is the thermal conductivity (W/m.K), I is the current (A), R is the wire resistance (Ω/m), and S is the slope of the line (i.e., S = ∆T/∆ln(t)).
Data source location	Latitude and longitude: 32.4950° N, 35.9912° E.
Data accessibility	Please note: All raw data referred to in this article must be made publicly available in a data repository prior to publication. Please indicate here where your data are hosted (the URL must be working at the time of submission and editors and reviewers must have anonymous access to the repository): Repository name: Mendely Data identification number: DOI: 10.17632/ypxkk6khk6.2 Direct URL to data: Thermal conductivity raw data.xlsx - Mendeley Data Instructions for accessing these data: Ctrl + Click to follow the link
Related research article	Adnan I. Khdair, Ghaida Abu-Rumman & Sawasn I. Khdair (2020): Thermal Conductivity of Olive Cake Compost (OCC) as Affected by Moisture and Density: An Experimental and Mathematical Modelling, Compost Science & Utilization, DOI:10.1080/1065657X.2020.1755386 To link to this article: https://doi.org/10.1080/1065657X.2020.1755386.

1. Value of the Data

• •(COC) has low thermal conductivity (Max: 0.60 W/m K) at maximum moisture content and bulk density. Therefore, COC can be used as an inexpensive insulator in geothermal heat storage applications.
• •It provides important insights into the thermal properties of (COC) and its potential use as a sustainable insulation material.
• •It can be used as an eco-friendly insulation layer in green roof buildings, leading to passive energy savings.
• •Proposed model provides a robust representation of the association between thermal conductivity of (COC) and a single dimensionless parameter, i.e., the degree of saturation, Φ, by the relation (K = 0 0.046 + 0728Φ).

2. Background

Thermal properties play an important role in the compost used as a soil amendment for different agricultural applications Despite this importance, no information is available on thermal conductivity of composted olive cake (COC), K, and how it is influenced by water content and bulk density. Investigation compost and agriculture soil compaction is important because it might affect seedling root growth because of increasing soil strength due to the increase in bulk density, therefore decreasing water and oxygen availability as porosity decreased [1,2]. Compaction is a consequence of human activities effect during soil management and settling over time. Compaction is postulated to affect the thermal properties of the farming land, yet there are no studies related to (COC) growing medium Khdair et al. [1,3].

3. Data Description

3.1. Effects of compost compaction on dry thermal conductivity

To better understand how compost compaction may influence thermal conductivity in field applications. Samples of compost were oven dried at 105 °C for 24 h. Thermal conductivities of the dry samples were measured at seven compaction levels ranging from 320 to 770 kg/m³. A linear correlation was developed between dry (COC) thermal conductivity and compost bulk density as shown in Fig 1. The best model fit (r² = 0.95) was represented by:

$${\mathrm{K}}_{\text{dry}}=0.68\rho -0.023$$ (1)

where ρ is the dry bulk density of the compost in g/cm³. It is also noticed that compaction of compost can raise thermal conductivity by 30–40 % relative to loose compost (Fig. 1).

Fig. 1.

Dry compost thermal conductivity vs. compaction level.

3.2. Effect of moisture contents and bulk densities on compost thermal conductivities

Rigor's laboratory tests were performed for thermal conductivity measurements (K) of (COC). Thirty samples at different volume fractions of water content (V_w), solids (V_s) and air (V_a). The moisture levels covered the range of 0.10–0.90 at various compaction levels (400–900 g/cm³). Fig. 2 shows that thermal conductivities increase as bulk densities and moisture content increased.

Fig. 2.

(COC) thermal conductivity at different bulk densities (400–900 g/cm³) and moisture levels (10–90 %).

It showed that water content is a key determinant of thermal conductivity [1,2]; a result that agrees with the results stated by other researchers [[4], [5], [6]] for green roof soil, and leaf compost, because the conduction through soil is mainly electrolytic [1]. The results also indicate the significant effect of compost porosity on thermal conductivity at all moisture content levels, it increased linearly as compaction level increased. Dry compost at low bulk density showed small thermal conductivity because of the existence of high air shares in the pour; and can be considered as inefficient conductor.

3.3. Data correlations and prediction equations

Relationships between thermal conductivity, bulk densities and moisture levels of the samples are illustrated in Fig. 3. These findings show that when compost moisture content increased from dry to saturation, the thermal conductivity increased by five folds from 0.10 to 0.50 W/m.K (Fig. 3).

Fig. 3.

Compost thermal conductivity (K) versus volume fractions of air and water.

Thermal conductivity of (COC) varies with water, air, and solid materials content in the compost. These elements have their own thermal properties values, but these parameters might not be independent of each other. In this data, the combined effect of these three parameters on (COC) thermal conductivity was investigated using the concept degree of saturation (Φ). The degree of saturation is the ratio of water volume (V_w) to the overall voids volume (V_v). The void volume represents the summation of the volumes of water and air [1].

Fig. 3. shows a linear fit with r² of 88.96 % between thermal conductivity and water contents (V_w). By contrast, (Fig. 3) shows an inverse correlation between thermal conductivity and air-filled porosity (V_a). Fig. 3 also suggests that thermal conductivity (K) depends on the degree of saturation (Φ).

Based on these findings, regression was used to represent K as a function of V_w, V_a, V_w and Φ. The strongest association was obtained when K was correlated by Φ and V_a and is presented by:

$$\mathrm{K}=0.036+0.72\Phi +0.039{\mathrm{V}}_{\mathrm{a}}$$ (2)

The linear regression model shown in (Eq. (2)) gives r² of 0.90. The parameters, Φ, and V_a in (Eq. (2)) sufficiently represent the volume fractions of water, air and solid.

The model showed that water content has a higher effect on (COC) thermal conductivity, indicating that water adsorbed tightly to compost medium because of the adsorptive forces. Compost is also a good organic fertilizer that might boost plant growth and increase the soil holding a capacity of water [7], can maintain a suitable soil structure, increasing pore space suitable for water retention, [8,9].

Furthermore, Eq. (2) showed that the parameter degree of saturation (Φ) has a 20 times greater effect on thermal conductivity compared to V_a. Therefore, regression analysis was repeated by removing V_a from (Eq. (2)) and the resulted model can be simplified by:

$$\mathrm{K}=0.046+0.728\Phi$$ (3)

The r² in (Eq. (3)) is also 0.90; a value like in (Eq. (2)). Fig. 4 shows all the experimental data can be represented by (Eq. (3)), and the linear relation between K and Φ (dimensionless parameter), has been proved for (COC).

Fig. 4.

Thermal conductivity (K) versus degree of saturation, (Φ).

Compost has low thermal conductivity due to its low bulk density relative to natural soils, in addition to the lower thermal conductivity of minerals making up the compost material. Also, the low thermal conductivity may be because of the greater air-filled porosity (a poor conductor) due to the reduction in particle size that resulted in increased thermal resistance between compost aggregate [1,10].

This implies that compost will counter less surface temperature changes relative to other soils under similar heat quantity. This may provide an advantage to compost to serve as a good insulator, in addition to nutritional values on soil surfaces in cold or hot seasons. The compost can be used also in many other engineering applications that require available low-priced environmentally friendly good natural insulator with minor changes in thermal conductivity as water content increases [1].

This has relevance to the biofilter industry in humid regions like the Arabian Gulf region. Real evaluation of biofilters performance requires information on the thermal properties of the medium that relies heavily on moisture content. Also, compost pads on a green roof house adjust the surface energy balance and therefore affect the heat transfer to the atmosphere.

4. Experimental Design, Materials and Methods

Thermal conductivity of composted olive cake (COC) was studied in the laboratory at different bulk densities (400–900 g/cm³) and different moisture contents (400–900 g/cm³). (COC) was obtained from the National Center for Agricultural Technology (NCART). It consisted of dried olive pomace composted with dead chicken, the proximate analysis of the compost was 48 % fixed carbon, 20 % organic matter, 30 % moisture, and 2 % ash. The compost is used as a fertilizer in olive grove and in green roof soils given its lightweight properties [1,5,11].

4.1. Sample preparation

Compost samples were air-dried and stored in tightly sealed containers. The desired moisture levels were obtained by mixing a certain ratio of oven dried (COC) with specific amount of water. The moist samples were mixed thoroughly in nylon bags and kept overnight to allow thermal equilibrium. Next day, compost of given weight was filled into a marked cylinder (30 cm long and a diameter of 15 cm) to specific marked volumes on the tube to get the desired density.

A single thermal probe was used to measure compost temperature with time [10]. After packing the compost in the cylinder, the wire was heated for a short time by 10-volt DC power supply until thermal equilibrium was reached. Temperature rise with time was sensed by a thermocouple embedded in the compost close to the hot wire and was connected to a data logger (Fig. 5). A plot of temperature rise of the probe versus the heating time natural logarithm produces a linear relationship. The thermal conductivity was estimated as the slope of the fitted straight segment. The current was also recorded to be used in (Eq. (1)). The thermal conductivity might be easily calculated by the formula presented by [10] as:

$$\mathrm{K}=0.0796{\mathrm{I}}^2\mathrm{R}/\mathrm{S}$$ (4)

Fig. 5.

Experiment setup.

Limitations

Not applicable.

Ethics Statement

N.A.

CRediT authorship contribution statement

Adnan Khdair: Conceptualization, Methodology, Software, Data curation, Writing – original draft, Visualization, Investigation, Supervision, Validation, Writing – review & editing.

Data Availability

• Raw Data of thermal conductivity of OOC (Original data) (Mendeley Data).