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. 2024 Sep 23;26(9):809. doi: 10.3390/e26090809

The Application of Pinch Technology to a Novel Closed-Loop Spray Drying System with a Condenser and Reheater

Zexin Lei 1,*, Thomas O’Neill 1, Timothy Langrish 1
Editors: Marco Aurélio Dos Santos Bernardes1, Xinping Zhou1
PMCID: PMC11431052  PMID: 39330142

Abstract

Spray drying is an energy-intensive process in industrial use, making energy recovery a critical focus for improving overall efficiency. This study investigates the potential of integrating heat-recovery systems, including an innovative air reheater, into a closed-loop spray-drying unit to maximise energy savings. Through detailed pinch analysis, the system achieved a very low approach temperature, averaging 3.48 K, which is significantly lower than that of conventional open-loop systems. The study quantifies the energy-recovery potential by demonstrating that the integration of heat-recovery components can reduce the external heating demand by up to 30%. This not only enhances heat-transfer efficiency but also lowers operational costs and reduces the system’s environmental impact. The results suggest that closed-loop systems with air reheaters offer a scalable solution for improving energy efficiency across different industrial applications. The research highlights a new paradigm: focusing on latent energy within the system rather than adjusting individual operational variables.

Keywords: pinch analysis, closed-loop spray-drying system, air reheater, heat recovery, approach temperatures

1. Introduction

A drying system separates liquid or moisture from a substance through controlled heat, mass, and momentum transfer [1]. Drying preserves the dried materials and reduces product volume and weight, facilitating storage and handling. It is a traditional preservation method, extending back thousands of years [2], now utilized across various industries, such as industries producing timber, polymers, ceramics, minerals, and pharmaceuticals [3]. Spray dryers are examples of dryers that are used to produce powders from solutions or slurries. A basic open-loop spray-drying system involves discharging the drying gas into the wider environment at the end of the dryer. However, this drying gas contains a large amount of thermal energy which is removed from the system when the gas is discharged, decreasing the overall energy utilisation of the equipment. Energy conservation and process optimisation are important in industries where large-scale drying processes, such as spray drying, dominate operations [4]. Traditionally, the focus has been on open-loop systems, where significant energy losses occur due to the exhaust of hot drying gases. This study improves on open-loop approaches by focusing on closed-loop systems, a design that inherently recycles energy, making it an ideal candidate for advanced heat- recovery technologies. Closed-loop spray-drying systems present a unique opportunity to significantly improve thermal efficiency by capturing and reusing waste heat through a carefully designed heat-recovery network [5].

Closed loops have been used within superheated steam-drying systems for some time and there is considerable research into them [6]. This is because condensation of the outlet steam is relatively straightforward and recovers the latent heat of vaporisation for water. Superheated steam is also faster during the falling-rate drying period above the inversion temperature [7], where the drying rate decreases as water activity within the material decreases. The higher thermal conductivity and heat capacity of superheated steam leads to higher drying rates for surface moisture above the inversion temperature [8]. To analyse energy consumption more comprehensively in different drying scenarios, the concepts of pinch analysis were developed [9].

Pinch analysis involves identifying the location and magnitude of energy losses in the process, and then using this information to develop a strategy to reduce these losses [10]. It is based on the concept of a “pinch point”, the location in the process where the temperature difference between hot and cold streams is at a minimum. Once this pinch point is calculated, the process conditions are then adjusted to minimise energy losses and to minimise the total hot and cold utilities [11]. It is a key part of process integration, where interactions between unit operations are considered, rather than analysing each unit separately.

Pinch analysis is often used in situations where the hot and cold streams have a large temperature difference, and where heating and cooling are both required in the operation. It has been commonplace in distillation columns due to this feature, but it is suitable for any operation which contains both a heating element and a cooling element [12]. In the case of a closed-loop dryer, the heating element is the hot feed gas, and the cooling element is the condenser loop. By connecting the hot outlet stream to the cold inlet stream with a heat exchanger, overall energy use can be significantly lowered. The hot air leaving the spray dryer can be reused. The recycled heat can also be used to heat the liquid solution before atomisation, reducing the energy requirement for evaporation. Pinch analysis can also help identify opportunities for process optimisation and design changes to be implemented to reduce energy consumption in spray drying [13]. The spray dryer’s design can be altered to improve heat-transfer efficiency between the liquid solution and hot air. For example, it can be used to determine the optimal location and heat of the atomisation nozzle, which can improve the efficiency of the drying process and reduce energy consumption.

For the pinch analysis of the open-loop system, the external temperature often has a significant impact on the pinch analysis of the entire system [14]. In the closed-loop system, any unused thermal energy is returned to the dryer [15]. The closed-loop system is more complex than an open-loop system, so it provides more parameters for adjustment, increasing the optimisation opportunities of the system. For the closed-loop spray-drying system used in this study, cooling the dryer walls by heating recirculating water for the air reheater is beneficial for reducing the deposition of particles on the walls.

The objective of this work was to use pinch analysis to analyse and assess the energy efficiency of a novel closed-loop spray-drying system containing a condenser and reheater. The novelty of the pinch analysis is that it was applied to the analysis of this closed-loop spray-drying system. This system has the advanced aspect of having two interconnected countercurrent loops, one of which is the drying air stream, with the other being the water stream which carries energy back to an air reheater. The air reheater is a new aspect of this closed-loop system that has not been previously reported. Technically, this work assesses the performance of a novel closed-loop spray-drying system containing a condenser and reheater using pinch analysis, providing an accessible and easily used analytical approach to a novel drying system, which is a technically useful advance.

2. Materials and Methods

2.1. Modelling of Spray Dryer

Following the finer-scale parallel flow/plug flow approach outlined in Langrish (2009) [15], the modelling approach divides the spray dryer into a sequence of control volumes, over which mass and energy balances are performed, and also over which calculations are carried out to estimate heat and mass-transfer rates between the particles or droplets and the gas. The calculation of heat-transfer rates includes estimates of heat losses from the dryer, and the concept of a Characteristic Drying Curve has been used to model the drying kinetics, which are an important part of the mass-transfer calculations.

2.2. Experimental Setup

The closed-loop spray-drying system with condenser and air reheater is shown in Figure 1. The air pipes are specially marked, and the remaining connections are condensate pipes. The equipment used is a Buchi B-290 Mini Spray Dryer (Büchi, Switzerland), connected to a condenser and reheater loop. A photograph of the condenser setup is shown in Figure 2A. The solution being sprayed enters at the spray nozzle of the dryer, where it is then sprayed through the spray chamber into the cyclone and separated into its liquid and solid components. The warm, humid air enters the condenser, where the water is condensed and cooled down by a cooling water stream. The condensate liquid is removed after the condenser stage. The cool, drier gas is then sent to an air heater and heated up to the required dryer fluid temperature and used to dry more solution.

Figure 1.

Figure 1

Schematic diagram of multi-section condenser closed-loop drying system. (The temperature values in blue are from Run 13, Table A1, with the gas and cooling water temperatures marked in black and blue, respectively.)

Figure 2.

Figure 2

(A) Condenser setup of spray dryer; (B) Water-fed heat-recycling system [16].

Temperature probes were placed at points around the spray dryer, where it was then used until it was found to be at steady state. This was repeated multiple times with different flow rates and system configurations. This was covered in insulation in some later tests. Water was also pumped in vinyl tubing around the dryer and cyclone to recycle heat lost to the environment. This arrangement is displayed photographically in Figure 2B.

2.3. Operating Conditions and Parameters

Different flow rates of water were tested by altering the speed of the feed pump located within the bucket water reservoir. Similarly, by adjusting the aspirator and pump rate, the flow of sprayed solution was changed [17]. To determine the ability of the system to run with other solutions, reconstituted powdered milk was also examined. Each set of experiments first pumped water for 30 min to allow the equipment to reach steady state. Parameters which were tested are listed in Table A1.

2.4. Preliminary Pinch Analysis Information

The gathered data was further analysed using heat integration and pinch analysis. MATLAB (R2023b) was used to aid in computation, combined with Microsoft Excel, which was also used for the initial data management and temporary graphing. The setup at the time of experimentation is demonstrated diagrammatically in Figure 3, along with the heat flows and hot and cold streams. As can be seen, three streams were located for pinch analysis: two hot and one cold.

Figure 3.

Figure 3

Spray dryer diagram with heat flows demonstrating location of pinch analysis.

3. Results

3.1. Sample Data and Typical Pinch Analysis

Air and water temperatures were recorded as functions of time with thermocouples placed systematically around the spray-dryer setup. After 30 min of continuous running, the system was found to be at steady state, and the temperatures at designated points were collected. Once enough data were gathered, the system was gradually allowed to relax to ambient temperature. The temperatures during the steady-state period were then averaged to give values for further calculations. An example experiment (Run 1, Table A1) was used to demonstrate the calculation process.

The heat capacity rates were calculated from the mass flow rates of the streams and the known heat capacities of water and of air. This is demonstrated in Equation (1) [18] .

Heat Capacity Rate = specific heat capacity × mass flow rate (1)
CP = cp × m (2)

To determine the total heat duty for each unit operation in a stream, the heat capacity rate was multiplied by the temperature change in the stream. This is explained mathematically in Equation (3) below.

Q = CP × (Tsource − Ttarget) (3)

The inlet and outlet, or source and target temperatures of previously designated hot and cold streams, are also shown below in Table 1, along with the heat capacity rates.

Table 1.

Thermodynamic information of designated streams.

Stream Source Temperature (°C) Target Temperature (°C) Heat Capacity Rate (W/K)
H1 75.17 62.72 10
H2 63.70 47.50 69.77
C1 46.34 63.70 69.77

To determine the pinch point, the streams were graphed on a temperature–enthalpy diagram or by using the problem table method [19]. In this instance, the graphical method was used first to visualise the minimum approach temperature, or ΔTmin, clearly.

By graphing the known heat loads and temperatures of the hot streams, a hot T/H graph was made. Since there are two streams, a composite curve was created. The initial chart of both hot streams is shown in Figure 4A. The composite curve graph of heat flow can be divided into three parts, and the “dashed lines” are used to mark where the temperature of two heat flows overlaps. The heat load between 75.17 °C and 63.70 °C is represented solely by H1, whilst the heat load between 63.70 °C and 62.72 °C is a combination of both H1 and H2, and the heat load between 62.72 °C and 47.50 °C is solely represented by H2. The heat load was calculated by summing the heat-capacity rates of all streams within the temperature section and is tabulated in Table 2. The heat loads of each section were then determined by multiplying the temperature difference by the total heat capacity rate by again using Equation (3). These values have been added to Table 2. Please refer to the attached Figure-A1 for the temperature–enthalpy graph of all experimental data.

Figure 4.

Figure 4

(A) Temperature–enthalpy graph for the hot streams. (B) Temperature–enthalpy graph of hot and cold streams on a composite curve.

Table 2.

Heat capacity rates and heat loads of hot-stream sections.

Interval (°C) Temperature Difference Total Heat Cap Rate (W/K) Heat Load (W)
75.17–63.70 11.48 10 114.76
63.70–62.72 0.9748 79.77 77.75
62.72–47.50 15.23 69.77 1062.34

The pinch point and corresponding approach temperature were determined using Figure 4B. The closest approach between the hot and cold stream, the pinch temperature, occurred when the hot stream was at a temperature of 63.7 °C. By calculating the vertical distance from this point and the cold stream, the minimum approach temperature was calculated. In this instance, the ΔTmin was determined to be 1.0075 °C. As can be seen, the minimum approach temperature was very low, which indicates efficient heat exchange between the hot and cold streams. In this situation, there was no need for additional heat exchangers, as the system was already very efficient. The heat exchangers, which are already present in the form of the condenser and the reheater, could be decreased in size if required for cost savings, but this is not necessary.

As previously mentioned, the minimum approach temperature works as a good metric for the efficiency of heat transfer between the hot and cold streams and therefore the effectivity of the heat-exchange networks within the system. By calculating and comparing the values of ΔTmin for many runs, assessments to find the most sensitive parameters can be performed. A series of experiments testing the values noted in Table 2 were completed and the data collated. These data were analysed with the same methods as the sample calculation previously, and the results are shown in the figures below. The range of calculated ΔTmin values is shown graphically in Figure 5. There are a few values of ΔTmin that are negative, indicating a ‘cold’ stream with a higher temperature than that of the corresponding ‘hot’ stream (Run 9, 29, 33 in Table A1).

Figure 5.

Figure 5

ΔTmin values for all experiments.

The only commonality between these runs is that the cooling water flow rate was at the lowest tested value. A possible reason is that, when the humid air in the system undergoes phase change (condensation or evaporation), additional energy is released, raising the temperature of the “cold” stream above that of the “hot” stream, particularly when the approach temperatures are low [20]. An average approach temperature, ΔTmin, of 3.48 K, was calculated. This is very low, indicating a heat-transfer rate which is near the maximum physical limit.

3.2. Pinch Analysis for All Data and Approach Temperatures

The initial analysis, based on a visual inspection of the 3D scatter plots (Figure 6), suggested that there may be interactions between variables such as pump rate, cooling water flow rate, and the inlet temperature on ΔTmin. For example, the pump rate and cooling-water flow rate significantly influence ΔTmin. As the pump rate increases, ΔTmin shows a general increasing trend. The inlet temperature (°C), represented by the colour gradient, also plays an important role in influencing ΔTmin. Higher inlet temperatures tend to correlate with higher ΔTmin values, suggesting that the inlet temperature strongly affects the heat-transfer efficiency within the system. At different aspirator values, which are the main air flow rates through the dryer, the interactions between these variables differ. At the higher aspirator rate of 6.6 m/s, the effects of pump rate and cooling water flow on ΔTmin become more complex, indicating that the increased airflow may introduce non-linear effects on the overall heat-transfer processes.

Figure 6.

Figure 6

Impact of pump rate, cooling water flow, and inlet temperature on ΔTmin across different aspirators (3.7, 5.6, 6.6 m/s) and its ANOVA results.

However, after conducting the ANOVA analysis, there was no statistically significant effect of any individual variable on ΔTmin, which aligns with the subjective review of the approach temperatures. It should also be noted that all approach temperatures are very low, with all values below 10 K, indicating very good heat recovery [21]. The standard error for the temperature data is also shown to be approximately 2.7 K, which further reinforces the suggestion that the approach temperatures are near zero, as many values are smaller than the calculated standard error. In these cases, the approach temperatures are likely to be very close to zero, indicating that the heat-transfer efficiencies were close to the physical limits for heat recovery. This situation may also partially explain the negative approach temperature values seen in some of the runs, as their actual approach temperature might just have been very low, and the uncertainty in the temperature measurements might have resulted in an apparently negative approach temperature. Heat transfer could be increased further but only with the input of additional mechanical energy, such as vapour recompression [22], although research into the feasibility of such a system is outside of the scope of this analysis.

These results again indicate that the improvement potential of the heat-recovery system created around the spray-dryer system is very small, as the heat recovery is near or at the limit, as shown by the low approach temperatures. As mentioned previously, it may be possible to decrease the number of stages within the condenser and reheater while keeping a similar rate of heat recovery. This is due to the ratio between the surface area, the temperature differences, and the heat-transfer rates within a heat exchanger not being linear, especially when close to the maximum transfer rates [5]. Further research into the economic feasibility will be required, as the removal of stages will result in a lower capital cost and a decrease in the required space for the equipment. This is a future extension of this research.

It can also be seen that as the p-values for all results are much higher than 0.05, the null hypothesis of no significant effects of operating conditions on the approach temperatures should be accepted statistically. The 3D plots served as an initial exploration tool, offering visual insight into potential trends, but the statistical evidence from ANOVA confirms that these interactions were not significant. This suggests that the system’s performance is not significantly reliant on the variations in drying parameters, and that the heat-recovery system is operating near its physical limit, requiring additional mechanical energy (such as vapour recompression) to achieve further improvements. As a result, the lack of a significant relationship between input parameters and ΔTmin points to a broader applicability of the heat-recovery network, which could function across different systems and scales without being sensitive to specific operating conditions.

4. Discussion

4.1. Approach Temperature and Heat-Transfer Performance

The minimum approach temperature found here of 3.48 K (under 4 K) may be compared with the literature on pinch analysis as applied to other drying systems. Kemp [20] suggests using a minimum approach temperature difference of 20 K for the pinch analysis of drying systems in general. Studying an alcohol distillery with pulp drying, Ficarella and Laforgia [23] used a minimum approach temperature difference of 10 K. Our values of under 4 K for the minimum approach temperature are comparable with those of Harkin et al. [24], who studied a power plant involving the pre-drying of coal. They suggested a minimum approach temperature difference of 20 K, and they stated that a difference of 3 K was optimistic. The closest analysis in the literature to this study is that by Patel and Bade [5], who studied a spray dryer and heat-recovery system with a minimum approach temperature of 10 K. Kaviani et al. [25] studied a dairy factory involving milk powder production and a spray dryer, using a minimum approach temperature of 50 K. The minimum approach temperature found in this study is therefore low by the standards of the literature.

Several cases of negative approach temperatures were also observed, which might have resulted from the phase changes within the system, such as condensation, where latent heat is released, increasing the temperature of the cold stream beyond that of the hot stream. These anomalies emphasise the complexity of accurately predicting heat-transfer behaviour in highly efficient systems. The data collected consistently highlight the stability of the heat-recovery system in this spray-drying setup. The low approach temperatures achieved suggest that the heat exchangers, including the condenser and reheater, were operating at high efficiency. More importantly, the stability of ΔTmin across various experimental conditions demonstrates that the system can maintain effective heat recovery despite fluctuations in operational parameters. This indicates that the system can be applied across different scales without the need for significant changes to its configuration.

4.2. Comparison with Existing Studies

Pinch technology has already been applied to open-loop drying systems by Kemp [20], but this open-loop system effectively recaptures and reuses energy in a way that is novel and has not been reported before, particularly by using the air reheater to recover energy from the condenser. The approach temperatures used in these open-loop studies are considerably greater (20 K) than those found in this experimental study for the integrated closed-loop system (under 4 K), indicating significantly better thermal integration in this closed-loop system compared with many open-loop systems. Other studies of energy efficiency on open-loop systems (Sarker et al. [26]; Surendhhar et al. [27]) have confirmed their low thermal efficiencies.

This closed-loop drying system has novelty in that it includes an air reheater to recover energy from the condenser. Drying with superheated steam is another way to recover energy from drying systems (for example, Guo et al. [28]), but the need to address the pressurisation requirements of superheated steam drying is a disincentive to use these systems. The system described in this paper is a normal air-water vapour system, with the unique features of including a closed loop with both a condenser and reheater.

Another approach to the analysis of this drying system is a full energy and exergy analysis (for example, Aghbashlo et al. [29]; Amjad et al. [30]; Dincer and Rosen [31]; Erbay and Hepbashli [32]; Johnson and Langrish [33]; Lei and Langrish [16]), which is a more comprehensive, complex, and more difficult analytical technique. This approach has the advantage of including non-thermal components of energy availability, such as pressure. However, the data collection and analysis requirements are more challenging, and pinch analysis, as used in this work, offers potential advantages in ease-of-use for operational engineering purposes.

Another advantage of a closed system is a higher recirculation rate. Golman and Julklang [34] found, in their study of open-loop systems, that increasing the recirculation ratio of exhaust gas can improve the energy efficiency of spray-drying equipment. A closed system can be considered as an infinite loop system. In addition to improving the recirculation ratio, our closed-loop system goes a step further by integrating air reheaters. This approach results in even lower approach temperatures (ΔTmin), suggesting superior heat-recovery performance.

4.3. Future Research Suggestions and Prospects for Practical Applications

However, this study also encountered limitations, such as phase changes and extreme temperature conditions that were not fully accounted for in the experimental design. These factors could introduce complexities that influence heat-transfer behaviour. For the purposes of this analysis, however, the primary focus was on evaluating the overall heat-recovery potential, which remains consistent across various operational configurations. As future research expands to larger-scale systems, these complexities will need to be considered in greater detail, particularly in industrial-scale applications where heat- transfer dynamics may differ.

Some valuable future work could include testing different configurations of condensers and reheaters, as well as exploring the use of steam recompression to enhance heat-transfer rates [35]. Furthermore, the scalability of this system should be explored through larger-scale tests to verify that the energy-recovery performance remains consistent when applied to industrial-scale equipment.

5. Conclusions

It can be seen from the results of ANOVA tests that there is no significant effect of any variable on the approach temperature. The consistently small approach temperatures (all below 10 K, with an average of 3.48 K) suggest excellent heat recovery. In several instances these approach temperatures are very close to zero, demonstrating the attainment of the physical limit for heat transfer and recovery. This is further supported by the standard error of 2.7 K, indicating that the minimum approach temperatures may be lower than are calculated, indicating possibly an even better heat-transfer rate. The presence of negative approach temperature values in some runs is most likely a result of very low approach temperatures combined with unaccounted-for phase transitions in the system.

The results collected unequivocally indicate the value of integrating a heat-recovery system into spray-drying equipment. The low approach temperature denotes a high rate of heat transfer, which stayed relatively constant over different testing parameters. There is clearly more room for experimentation and research in this area, such as testing the sizing of and number of stages of the condenser and reheater and the addition of vapour recompression to further increase the heat-transfer rate. The lack of relationship between any input parameters and result denotes that the heat-recovery network is not dependent on one particular variable and can most likely be transferred to other spray-drying systems at different scales. Scale-up tests on larger pieces of equipment with a greater powder production capability must be performed to confirm these hypotheses.

Appendix A

Table A1.

Full dataset used for pinch analysis.

Run Aspirator m/s Pump Flow mL/min Water Flow L/min Spray Dryer °C Dryer Out °C Condenser in (Dry) °C Condenser In (Wet) °C Condenser Out (Dry) °C Condenser Out (Wet) °C Reheater out (Dry) °C Reheater out (Wet) °C Dryer Return °C Water Condenser in °C Water Condenser Out °C Water Cyclone in °C Water Cyclone Out °C Reheater in °C Reheater Out °C Ambient °C Solid Conc.
1 6.6 2.5 1 200 75.1716 71.5650 69.5969 63.2492 60.7077 62.7212 59.8997 59.7385 46.3419 48.7322 46.8536 63.6960 61.3804 47.4942 23 0
2 6.6 2.5 2 200 73.2676 71.0983 70.0348 65.2042 60.9506 64.1115 56.0566 62.8647 47.9838 51.5853 50.2930 63.0232 62.6006 49.1362 23 0
3 6.6 2.5 3 200 73.0557 70.0414 69.2088 62.4383 58.5395 61.4970 54.7905 55.0064 48.7362 53.3926 51.2943 61.2199 60.8099 50.7123 23 0
4 6.6 2.5 4 200 73.7805 69.5490 68.4137 61.6641 60.1421 60.1850 58.5497 57.1121 49.9603 54.1536 52.8001 60.3432 59.1038 51.7962 23 0
5 6.6 2.5 1 200 74.4379 72.7546 66.2832 61.9347 60.5871 59.5908 53.6764 53.8572 46.3158 52.0430 49.4764 61.3903 61.1379 50.8397 23 0
6 6.6 2.5 2 200 74.0747 72.5767 65.4560 59.8542 58.4660 57.0368 51.3401 45.7998 44.7938 51.1428 49.2957 58.7424 55.5523 51.7058 23 0
7 6.6 2.5 3 200 74.5935 72.9138 66.3253 62.4347 60.9557 59.9065 54.2300 48.2158 47.4468 53.9761 52.8337 62.0548 60.6574 53.2377 23 0
8 6.6 2.5 4 200 72.4710 70.8197 68.3685 53.1593 51.6917 50.4036 45.9238 41.4590 39.8112 45.5723 44.1722 50.9115 51.8605 41.2088 23 0
9 6.6 2.5 1 200 75.6280 72.8485 68.3470 64.5862 56.2058 63.7678 54.1171 62.7215 50.3387 53.9736 51.8090 64.6282 63.3372 49.4757 23 0
10 6.6 2.5 2 200 75.9942 73.2409 68.7054 65.1826 56.7303 64.3810 56.4642 63.3208 48.1746 54.3728 52.4255 65.0997 63.4728 53.6270 23 0
11 6.6 2.5 3 200 74.9366 72.4010 67.3160 62.0967 54.1391 60.4718 52.3614 60.2352 44.3232 53.9788 53.1835 61.9069 61.2913 49.8882 23 0
12 6.6 2.5 4 200 75.5303 72.5411 68.6941 64.4329 57.1152 63.3840 55.7056 62.0126 46.8143 53.0367 51.0812 63.2462 63.5067 52.5463 23 0
13 6.6 2.5 1 150 62.4818 59.8986 58.4787 54.5915 52.7616 53.3468 51.7184 52.3748 43.9004 52.8560 46.7391 56.3396 54.8420 49.6587 23 0
14 6.6 2.5 2 150 63.5980 60.9155 60.1536 57.3471 55.0795 56.9267 51.8611 56.4997 43.5770 52.3766 46.4599 55.7672 54.2420 49.0446 23 0
15 6.6 2.5 3 150 62.3273 59.9560 58.2200 53.7477 50.7739 52.7936 49.9203 52.3815 40.8085 46.3682 44.8120 51.6500 50.2093 44.7691 23 0
16 6.6 2.5 4 150 65.1282 62.5910 62.5837 61.1674 59.9958 59.3121 59.0479 57.2354 43.2633 46.4472 45.3751 51.2969 50.3529 45.7208 23 0
17 6.6 2.5 1 150 64.7488 63.0570 59.0870 56.3066 49.4585 55.0577 47.0135 54.2013 43.5524 46.6839 44.7374 54.8074 55.0495 44.2170 23 0
18 6.6 2.5 2 150 63.7057 62.3226 58.1949 53.7238 47.1978 52.5861 43.0198 50.2714 42.2570 46.3626 45.0676 52.2475 51.6151 44.8941 23 0
19 6.6 2.5 3 150 63.9824 62.7074 53.5206 58.6963 50.8856 54.8860 48.6885 54.1493 43.1828 47.0230 46.2847 53.3903 51.2280 43.4638 23 0
20 6.6 2.5 4 150 60.9944 59.8292 55.6201 43.6803 38.0877 41.9691 35.8439 41.0740 35.5947 38.5845 37.6436 42.3927 42.1432 35.8157 23 0
21 6.6 2.5 1 150 64.3330 62.1136 60.3219 60.1368 52.4636 58.6439 50.8940 58.0908 43.0850 52.0906 49.5797 58.7382 58.7667 50.4560 23 0
22 6.6 2.5 2 150 64.5907 62.0912 60.4948 59.8218 52.0853 58.8620 51.1193 58.0709 42.0560 49.5240 49.4595 59.1631 58.4987 51.3731 23 0
23 6.6 2.5 3 150 64.3372 61.9280 60.3121 59.4930 52.2952 58.5138 51.3354 57.8387 43.0070 49.3454 49.1745 58.8703 57.8698 49.9273 23 0
24 6.6 2.5 4 150 64.8557 62.3371 60.6978 59.9265 53.0794 59.1275 52.2994 58.2776 43.5429 49.8127 49.0696 59.4424 58.5646 50.1417 23 0
25 3.7 4.8 1 150 43.0610 42.0934 40.3255 40.1900 38.1705 40.2316 37.5786 39.0654 33.8959 37.1251 35.1198 40.0699 38.0944 34.7726 23 0
26 3.7 4.8 2 150 42.4005 41.4332 39.6324 39.5595 38.1670 39.2535 37.3231 39.3341 33.2073 34.7687 34.3833 39.1461 37.4963 33.5128 23 0
27 3.7 4.8 3 150 41.2514 40.1174 38.5030 38.2831 37.3100 38.3046 36.0507 37.1052 32.4036 34.2982 33.3714 38.4294 37.0754 34.3952 23 0
28 3.7 4.8 4 150 41.1735 40.0006 38.2505 37.9444 36.0789 37.8402 35.8396 37.2014 32.4063 34.9469 33.7657 37.9237 36.2974 34.1599 23 0
29 5.6 7 1 150 59.2081 57.4708 59.3151 54.4179 53.6905 54.7271 51.8439 53.1262 45.7232 48.2874 47.4704 55.2689 51.1556 45.1504 23 0
30 5.6 7 2 150 59.3290 57.1404 59.5271 55.7261 53.5567 54.6225 51.7653 52.5403 44.4190 48.1995 47.3811 55.1818 50.5180 45.3199 23 0
31 5.6 7 3 150 58.6593 57.3873 58.0530 53.2880 51.1264 52.3019 49.7926 50.3541 43.4999 46.1538 45.4126 52.6616 48.6706 44.6377 23 0
32 5.6 7 4 150 58.0039 56.7561 56.4113 51.0477 48.7600 49.9113 46.8551 48.7583 40.9359 44.2051 43.3998 50.1217 47.0328 42.8005 23 0
33 5.6 7 1 150 60.2479 60.0823 58.6729 55.5879 54.8087 55.9241 52.9660 54.3096 46.0346 48.5657 47.9026 55.6471 52.4247 45.4455 23 0
34 5.6 7 2 150 59.7842 59.1857 58.5144 54.4414 52.2584 53.4521 50.9325 51.5064 43.8380 46.5052 45.7740 53.0387 49.0197 44.9693 23 0
35 5.6 7 3 150 60.4843 60.6462 58.2358 56.8068 54.6468 55.7730 52.9022 53.6931 44.7731 48.5299 47.7378 55.5464 50.8544 45.6664 23 0
36 5.6 7 4 150 59.1500 57.8984 57.5606 52.1893 49.9024 51.0592 48.0026 49.9234 42.0854 45.3556 44.6207 51.2414 48.1909 43.9458 23 0
37 6.6 4.8 4 150 65.5202 63.5964 60.2444 59.4349 52.7282 58.5134 51.9039 57.5938 43.7100 49.3801 49.3509 58.8914 57.5729 49.2975 23 0.3
38 6.6 4.8 4 150 74.1482 70.8732 64.9347 55.3062 51.8788 52.9377 47.3341 52.6062 43.2956 48.5530 45.6755 57.8701 56.6894 48.2075 23 0.5
39 6.6 9 4 120 58.7008 55.3529 54.1977 52.1243 50.9580 52.1098 51.7835 49.2899 39.3090 44.8927 44.6517 52.7253 51.4744 47.5482 23 0
40 6.6 9 3 120 58.9906 56.5364 55.5239 54.1905 52.3673 53.2020 50.6812 52.9003 40.0378 45.9908 45.7216 54.2073 53.0120 48.8041 23 0
41 6.6 9 2 120 59.0826 57.0488 56.1272 54.8524 52.9781 53.7834 50.9993 53.0240 40.2975 46.7175 46.3749 54.8557 53.5224 49.4213 23 0
42 6.6 9 1 120 58.8236 57.3330 56.5013 55.2390 53.4838 53.9600 51.2352 52.7683 40.7103 46.7482 45.0560 55.1297 54.2785 49.8648 23 0
43 5.6 7 4 120 52.8293 52.5631 51.9299 50.8960 50.1603 50.5494 49.7287 49.2378 37.5746 44.2184 43.5480 47.2485 47.2162 42.1930 23 0
44 5.6 7 3 120 53.1210 52.6973 52.0626 51.0922 49.8989 50.8235 49.4071 50.3030 37.9161 44.4559 43.8870 47.4720 46.6733 42.4596 23 0
45 5.6 7 2 120 53.1719 52.8854 52.3538 51.3648 50.6249 51.2039 49.7381 50.2266 38.1805 44.2317 43.2023 47.6719 46.8098 42.9117 23 0
46 5.6 7 1 120 53.4273 53.5152 52.9259 52.0160 51.2489 51.9207 50.8454 50.3537 38.7065 45.2893 44.6410 47.9875 47.9033 43.6178 23 0
47 3.7 4.8 4 120 40.2615 39.0251 36.0683 37.7155 34.6997 35.6237 31.2515 35.3360 24.6923 32.6744 30.4618 35.5018 34.1155 29.4740 23 0
48 3.7 4.8 3 120 40.9498 39.6639 38.4730 37.3453 33.5291 37.0186 32.8360 36.7503 25.8874 32.1705 30.0846 37.0857 35.4825 30.9051 23 0
49 3.7 4.8 2 120 40.7862 39.4800 38.3624 37.4973 33.5539 36.3201 32.2930 36.5932 26.5587 32.2572 29.9923 37.6397 36.0107 31.2878 23 0
50 3.7 4.8 1 120 40.0784 38.7690 37.7959 37.3102 33.5756 36.8201 32.1513 36.0919 26.8681 33.4480 31.6668 37.2357 35.5271 30.5587 23 0
51 3.7 4.8 4 120 41.7119 40.4313 38.6167 38.7246 37.2602 38.1673 34.2688 37.0507 33.4071 36.2079 34.4072 38.3118 37.5670 33.7110 23 0
52 3.7 4.8 3 120 41.6239 40.2819 38.8122 38.4959 37.3783 38.4377 36.9453 37.1426 33.4491 36.4336 34.4005 38.2860 37.6939 34.3605 23 0
53 3.7 4.8 2 120 41.4106 39.9888 38.7140 38.3102 37.4186 38.4001 37.1410 36.9191 33.5626 36.4908 34.7835 38.2930 37.6616 34.3045 23 0
54 3.7 4.8 1 120 40.6386 39.2694 38.4597 38.1633 37.1657 37.7989 36.7037 36.4290 33.2502 36.3121 34.3388 38.0856 37.4039 33.8363 23 0

Figure A1.

Figure A1

Figure A1

Figure A1

Figure A1

Experimental pinch analysis graphs.

Author Contributions

Z.L.: Conceptualization; Methodology; Formal analysis; Writing—original draft; Data curation; T.O.: Conceptualization; Methodology; Formal analysis; Writing—original draft; Data curation; T.L.: Conceptualization; Methodology; Funding acquisition; Project administration; Writing—review and editing; Supervision; Resources. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

Not applicable.

Data Availability Statement

The original contributions presented in the study are included in the article. Further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

Funding Statement

This research received no external funding.

Footnotes

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

The original contributions presented in the study are included in the article. Further inquiries can be directed to the corresponding author.


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