PCM Temperature Research Articles

Development and experimental validation of a 3D numerical model to investigate performance of phase change based cooling vest in hot environments

To ensure health and safety of outdoor workers exposed to harsh environment, particularly during summer, they must be protected against heat-related injuries. Personal cooling device like cooling vest are viable solution in such situations considering their cooling capabilities and ergonomic aspects. In the present study, a 3D numerical model is developed for analyzing performance of PCM vest and it is validated with experimental results obtained from a torso thermal manikin facility fabricated in-house. Thermal performance of the PCM vest is analyzed in terms of temperature, liquid fraction and energy storage of PCM and skin temperature for different thermophysical properties of PCM, ambient conditions and mode of operations. Based on the study, PCM with higher latent heat and melting temperature is recommended for the longer working duration of the vest. Increasing ambient temperature from 40 °C to 45 °C reduces the effectiveness time by 20 % while decreasing ambient temperature from 40 °C to 35 °C increases effectiveness time of the PCM vest by 32 %. Fraction of energy stored by the PCM from the body and environment remains unaffected by the change in the latent heat of PCM. Further, it is noticed that increasing the air flow rate or using the PCM vest in hybrid mode of operation is not recommended from the point of view of its effective useable duration. Overall, the study presents a comprehensive approach to estimate performance of the PCM vest realistically and provides guidelines for the design of effective cooling vest for various practical applications.

Simulation and design of a solar chimney integrated with phase change material layer for building ventilation

The development of modern life requires new energy sources, and one of this energy is renewable solar energy uses in solar chimney for natural ventilation, but at the present time it is not greatly invested, taking into account the weather conditions of the region and the physical characteristics of solar radiation and air in the area in which the study will be conducted. The current study was carried out in Basrah city- Iraq, at longitude 47.749° and latitude 30.568°, where the solar chimney was facing south. The investigation was conducted using both theoretical and experimental studied. In the theoretical study, the solar chimney with the room in the presence and absence of PCM was simulated numerically using the finite volume method using the soft package ANSYS-Fluent/2021/R2. The effect of different tilt angles (α = 30°, 45°, and 60°), solar chimney air gap (gab = 10 cm, 15 cm, and 20 cm), and PCM basin thickness (tPCM = 3 cm, 4 cm, and 5 cm) were investigated. The results were presented in the form of contours of the distribution of streamlines, velocity, temperature, and liquid fraction of the solar chimney with the room, rate of temperature of the absorber plate with time and the rate of temperature of the PCM (TPCM) with time, rate of air change per hour (ACH). As for the experimental side, the device was built, and the intensity of solar radiation was studied for several days on 30 Sep. and 15 Oct. 2023, the temperature distribution rate of the absorbent plate over time, the PCM temperature rate, and the air change per hour (ACH). The theoretical results were compared with the experimental results, where there was good agreement, and the theoretical comparison was also made with several researchers. Significant results showed that the optimal ratio of the air gap width of the solar chimney is 15 cm, the inclination angle of the solar chimney α = 30°, and the thickness of the PCM basin (tPCM = 4 cm) to obtain the maximum ventilation rate. The thickness of the PCM basin = 4 cm gives the largest liquid fraction along time and maximum average temperature of the absorber plate. On the experimental, it was found that PCM convert into the liquid phase after its melting point, which is 340 K, after 12 noon, and the highest value of ACH reached 37 on September 30/2023 at midday.

Silicon porous disc featured parabolic trough collector functioned with paraffin: Thermal performance study

The advancement of renewable solar energy has potential for industrial heat exchanger applications, and its performance is enhanced by using nanofluid. Besides, the losses of heat during the energy transfer from solar to heat exchanger limit thermal performance and lead to reduced thermal efficiency. The conventional solar system functioning with nanofluid needs to be upgraded with an advanced thermal management system to limit energy loss and enrich the thermal performance of the overall system. The investigation aims to enrich the thermal performance of a parabolic trough solar collector (PTC), which features silicon porous discs and phase change material (PCM-paraffin). During the investigation, the flow of fluid ranged from 100 to 200 LPH with an interval of 50 LPH. Influences of silicon porous disc and phase change material melting phase on fluid temperature, temperature, energy stored, and thermal efficiency of the present system are experimentally investigated, and its values are related to conventional absorber performance without porous material and phase change material. The output results prove the significance of silicon porous and phase change material related to conventional absorber systems. The parabolic solar collector functioned with silicon porous material with phase change material phase on 200LPH spotted superior thermal performance including fluid temperature, PCM temperature, energy stored by phase change material, and average thermal & exergy efficiency of 84.2 °C, 98.5 °C 599.7 kJ, and 73.8 % & 15.1 %. These findings underscore the promising potential of porous medium absorbers in significantly elevating the efficiency of parabolic trough collector systems.

Characterizations and Energy Analysis of Hydroxyl Group Functionalized Graphene (Nanomaterial) Mixed with Paraffin Wax (Polymer Pcm) as Thermal Energy Storage Materials And Applications

This work comprised of Paraffin wax as phase change material mixed/doped with functionalized graphene (hydroxyl group) for countering the poor thermal conductivity of the pristine phase change material. Firstly, Experiments were conducted on Thermal energy storage system during charging (melting) of the doped PCM. The main outcomes of these experiments were that as the volume concentrations of doped PCM and flow rate of the heat transfer fluid (HTF) were increased the charging time decreases along with increments in PCM temperature and accumulated energies. In case of OH functionalized graphene mixed with paraffin wax the charging time decreases by 38.4% to 84.61% for the HTF flow rate 25 ml/s over pure paraffin wax. Secondly, the advanced functional materials i.e., Paraffin wax mixed with functionalized hydroxyl group graphene was characterized by FTIR, XRD, TGA, DSC and FESEM, . The latent heat of melting obtained was 179.36 J/g for 1% graphene doping by DSC.

A numerical study on the influence of fin numbers and material embedded with heat pipe for thermal charging in a trapezoidal container

This study delves into the thermal charging of a PCM accommodating thermal energy storage system within a trapezoidal enclosure, incorporating variable-length fins and heat pipes, through numerical analysis. The investigation employs multiple variable-length fins, and Steel, Aluminum (Al), and Copper (Cu) are considered potential fin materials. The study utilizes six key benchmarks—completes melting duration, enhancement ratio, total accumulated energy, average PCM temperature, mean power, and cost per mean power to comprehensively assess the impact of varying fin numbers and materials. The findings reveal that while an increased number of Al fins results in a higher enhancement ratio, this effect diminishes with a further increase in the number of fins. The scenario featuring 12-Steel-fins demonstrates the most uniform temperature distribution. Furthermore, an augmentation in the number of fins and their thermal conductivity corresponds to an improvement in mean power. Notably, the cases of 12-Cu-fins and 12-Al-fins exhibit equal and the lowest cost per mean power among all scenarios.

Numerical investigation of phase change material integration in structured thermocline systems for concentrated solar power

The integration of encapsulated PCM in a structured thermal energy storage system is studied. The fluid and filler material are discretized using a one-dimensional approach, while the PCM is discretized two-dimensionally. The accumulated energy for the height percentage of PCM and cutoff temperature differences are obtained for three PCMs, NaNO3, KOH and H380, to obtain the best options to enhance the accumulated energy using encapsulated PCM.

On the performance of a latent heat thermal storage unit integrated with a helically coiled copper tube and organic phase change materials: A lab-scale experimental study

In this study, the performance of a latent heat thermal storage (LHTS) unit integrated with a helically coiled copper tube and organic phase change materials is investigated using a lab-scale experimental setup. The effects of various operating conditions such as the coil thickness, testing fluid temperature/flow rate, PCM type, turbulator, and stirrer rotational speed on phase change behavior are investigated. The evaluation is based on PCM temperature variations, total heat transfer coefficient, and thermal effectiveness. The effects of testing fluid temperature, PCM type, turbulator, and stirring speed on phase change behavior are found to be more pronounced compared to those of the coil thickness and the fluid volume flow rate. Considering the melting process, it is found that the average temperature of the PCM in the LHTS unit with a turbulator is higher than that of the case without turbulator by nearly 10 °C which indicates an improvement in the heat transfer between water-PCM. The average PCM temperature is found to increase by 2 °C and 3.5 °C when a stirrer with a rotational speed of 200 and 400 rpm is employed, respectively. The total heat transfer coefficient for the LHTS unit at a stirring speed of 400 rpm (200 rpm) shows a significant increase of 39.6% (27%) compared to the scenario without a stirrer.

An efficient method for modelling thermal energy storage in packed beds of spherically encapsulated phase change material

An approach for modelling melting (and solidification) in packed beds of encapsulated spherical PCM is presented. The approach includes a calibration step based on comparisons of simulations with experimental results of PCM melting in a cylindrical geometry, followed by detailed simulations of melting in an isolated encapsulated PCM sphere and a PCM sphere in a representative elemental volume of packed PCM spheres to study the impact of external flow conditions on PCM heating and melting. The detailed simulations show that the enthalpy-porosity model provides a reasonable estimate of the overall melting time and a good approximation of the evolution of the liquid/solid melt front during the melting process. The simulations also confirm the dominance of convection during most of the melting process. The temporal integral results of overall heat transfer coefficient and overall energy fraction from the detailed simulations are combined to yield a relationship between overall heat transfer coefficient and overall energy fraction such that the process can be modelled in terms of the condition inside the encapsulated PCM sphere, wherein the condition can also be obtained from the fraction of heat absorbed compared to the energy capacity of the PCM sphere. This relationship is then used as an input to a finite-volume model for packed beds which can be used to predict the charging time of entire packed beds of encapsulated spherical PCM. Results from the simple model show correct trends for the temporal evolution of liquid fraction and PCM temperature, and for overall charging times for the cases considered. This simple approach can substantially reduce the simulation time required to model beds of different shaped encapsulated PCMs and different dimensions.

Transient solidification and melting numerical simulation of lauric acid PCM filled stepped solar still basin used in water desalination process

It is crucial to produce potable water from salt water in arid places using a stepped solar still desalination process. This work presents the temperature distribution and phase transformation of lauric acid PCM in inclined stepped solar still desalination system. A second-order finite volume method is employed for discretizing the two-dimensional geometry, while energy, continuity, and momentum equations are solved and then coupled using the second-order PRESTO algorithm. The solidification and melting CFD models have been used to capture the melting stages of lauric acid PCM. Four steps with an inclination of 30° to ground and two different cases with saline water levels of 10 mm and 40 mm have been reported. The results reveal that the temperature and mass fraction of lauric acid PCM strongly depends on the saline water level at each step, the number of steps, the angle of inclination, and the location of the solar still step. The maximum percentage increase in PCM melting fraction is 50%, and a PCM temperature rise of 4 °C is observed in the case of SWL-max compared to SWL-min. The total enthalpy of lauric acid PCM is increased by 30% for the SWL-max water level compared to the SWL-min water level.

Heat transfer characteristics of PCM inside a modified design of shell and tube latent heat thermal energy storage unit

Shell and tube latent heat thermal energy storage systems are compact and effective among other types of energy storage systems. The present numerical study deals with geometry optimization of a modified design of shell and tube latent heat thermal energy storage system over melting and solidification cycles. The modified design was produced by splitting the single inner tube into three smaller inner tubes arranged in a line array with different orientations. The numerical model covered four different line array orientations: 0°, 30°, 60°, and 90°, along with a storage model consisting of a single inner tube. The surface temperature, perimeter of inner tubes, and mass of PCM in all numerical cases were assumed to be identical. The numerical model has been validated by comparing the melting fraction contours and the PCM temperature with the experimental published data. It has been found that the line array of 0° orientation has the minimum full cyclic duration with an improvement of 44.4% compared to the base case. Conversely, the line array of 90° orientation has the maximum full cyclic time; 15.83% longer compared to the base case of a single inner tube. Lastly, the orientation of the line array is more significant for melting compared to the solidification.

Determination of thermal efficiency of air ETSC-PCM using artificial neural network technique

In this study, the thermal efficiency of an air-type vacuum tube combined phase-change material solar collector (air ETSC-PCM) was tested to establish a theoretical mathematical model of thermal efficiency through linear approximation. Various artificial neural network (ANN) models were used to predict the thermal efficiency of the collector and the results were compared with actual experimental data to improve the thermal efficiency of the collector. The ANN model used six parameters (irradiation intensity, inlet temperature, outlet temperature, ambient temperature, air temperature in vacuum tube, and PCM temperature) and two parameters (thermal efficiency of fluid and thermal efficiency of PCM) for the input layer and the output layer, respectively. A statistical error analysis demonstrated that the prediction result of the LM6-3-2 algorithm had a higher R2 value, the prediction errors of BR6-5-2 and RBF-2 algorithms were similar, and the accuracy of the SCG6-5-2 algorithm was the lowest. In addition, linear approximation proved to be suitable for predicting the thermal efficiency of the fluid. However, an opposite was observed while predicting the thermal efficiency of the PCM, and a maximum error of 2.13 was obtained. Additionally, the sensitivity of input variables was investigated and it was demonstrated that solar radiation had the greatest impact on thermal efficiency. Furthermore, it was observed that the thermal efficiency can be improved by reducing the thermal resistance between the vacuum tube and the air to enhance the rate of heat transfer in the aluminum shell of PCM-rod.

Parametric effects of ring-shaped phase change module on the temperature regulation of ultra-low carbon shallow geothermal ventilation system

As one of the most representative geothermal systems, shallow geothermal ventilation (SGV) system has been widely used with the advantages of simple configuration and low operation cost. However, this system is characterized by relatively large temperature fluctuations at the outlet in many application scenarios, which will reduce the thermal comfortable of the delivery outlet air temperature. The existing model development of horizontal buried-pipe SGV system tends to ignore the vertical buried-pipe part of the air inlet and outlet, and only considers the heat transfer model of horizontal buried-pipe, which may affect the accuracy of the developed model to a certain extent. Based on these, this study proposes a SGV system integrating the ring-shaped phase change material (RSPCM) module, and develops the dynamic heat transfer model considering the vertical part of the air inlet and outlet of the system. In this study, firstly, a relevant field experimental testbed is built and the developed dynamic model is verified with good agreement based on the experimental data, which has a maximum relative error of 4.83 %. In addition, the effects of RSPCM and its different parameters on the thermal performance of SGV system are investigated based on the developed model. The results show that RSPCM arranged at the air outlet can regulate the outlet temperature fluctuation of the SGV system and improve the comfort of the air supply temperature to a certain extent. When the inlet air velocity is 1 m/s, the temperature fluctuation at the outlet is 1.73 °C for the system comprising RSPCM, while the corresponding temperature fluctuation at the outlet is 2.10 °C for the system without RSPCM. The effect of thermal conductivity on the PCM's temperature regulation ability is not obvious enough for the proposed system application. Therefore, in practice, by increasing the thermal conductivity of RSPCM is not an optimal and feasible way when considering the economic cost. The RSPCM thickness is increased to a certain level and then this measure will not have much effect to improve the system's thermal performance. For this system structure and operating conditions, a more suitable RSPCM thickness should be about 20 mm, and the RSPCM with a phase-change temperature of 24 °C has a relatively good temperature regulation capability. The RSPCM has a better temperature regulation capability for the system outlet temperature when it is located at the outlet position. This study provides a novel research possibility for the application of SGV in buildings, and can also provide theoretical guidelines for designers and constructors in practice to apply SGV systems.

Exergoeconomic and enviroeconomic evaluations of conventional solar still using PCM and electric heater powered by solar energy: an experimental study

Solar stills are used in distant and arid areas to convert brackish or salty water into potable water fit for human use in a simple, affordable, and effective manner. Even when PCM materials are used, typical solar systems still have minimal production per day. In this study, experimental tests were carried out in order to increase the performance of a single-slope solar still combined with PCM material (paraffin wax) and a solar-powered electric heater. Two identical single-slope solar stills were designed, fabricated, and tested under the same climatic conditions during the summer and spring seasons of 2021 in Al-Arish, Egypt. The first is a conventional solar still (CVSS), and the other is also a conventional still but with PCM and an electric heater (CVSSWPCM). Several parameters were measured during the experiments, including sun intensity, meteorological aspects, cumulative freshwater production, average glass, and water temperatures and PCM temperature. The improved solar still was evaluated at different operating temperatures and was compared to the conventional traditional one. There were four cases studied: one case without a heater (paraffin wax only) and three other cases with a heater operating at 58 °C, 60 °C, and 65 °C, respectively. The experimental results revealed that activating the heater inside the paraffin wax increased daily production (i) in the spring by 2.38, 2.66, and 3.1 times and (ii) and in the summer by 2.2, 2.39, and 2.67 times at the three above-mentioned temperatures respectively (when compared to the traditional still). In addition, the maximum rate of daily freshwater production was achieved at paraffin wax temperature of 65 °C in both spring and summer (Case 5). Finally, the economic evaluation of the modified solar still was carried out according to cost per litre. The modified solar still with a heater operating at 65 °C has a higher exergoeconomic value than the traditional one. The maximum CO2 mitigation in cases 1 and 5 was approximately 28 tons and 160 tons, respectively.

Influence of the location of the phase-change material on heating and cooling the heat-insulating layer

The experimental investigation of thermal parameters during heating and cooling of PCM sample placed at different locations has revealed that the phase transition was accompanied by a significant decrease in the growth rate of the PCM temperature when heating, and a slowdown when cooling. The completion of the phase transition upon heating the PCM sample was accompanied by a sharp increase in the heat flux density at the outer surface of the PCM regardless of its location. The produced experimental results on the change of thermal parameters of the PCM depending on its location will be used to verify the calculation model.

Novel metallic separator coupled composite phase change material passive thermal design for large format prismatic battery pack

To enhance the lithium-ion battery pack's operating performance while it is continuously used at varying charge rate and higher ambient temperatures, the current research proposes a thermal management system composed of a phase change material with a passive metallic connection. Along with constant charge rate of 1C, 2C and 3C rate, battery pack also investigated at harshest 4C rate condition, to check its thermal performance. In total, three configurations are investigated: configuration 1 has no passive cooling arrangement, configuration 2introduces a passive thermal design with a phase change material submerged cooling technique that includes paraffin wax and extended graphene composite phase change material, and configuration 3is a proposed improved thermal design in which a graphene-enhanced high thermal conductive metallic separator is coupled at the PCM wall to increase PCM temperature delay efficiency. A phenomenon of inefficient thermal performance is observed for typical pure PCM form due to its lower thermal conductivity and heat transfer rate, resulting in a loss of capacity to cause temperature delay effect in battery pack. In proposed improved model of having metallic separator at wall of PCM results shows, none of the case had exceeded effective battery temperature limit of 55°C and liquid fraction rate of PCM and EG CPCM remained below liquidious point which allows it to deliver more temperature delay effect. Comparative performance study between paraffin wax PCM and EG CPCM suggest EG CPCM is able to provide more delay effect due to its thermophysical property advantage of higher thermal conductivity and greater heat transfer performance.

Numerical analysis of PCM integrated year-round thermal energy savings building for composite climatic conditions

Incorporating PCM in building envelopes is a promising energy-saving technique. Because the PCM container maintains a constant temperature when storing and retrieving energy. The PCM is used in building envelopes to diminish solar irradiation, reducing heat penetration and lowering heating and cooling loads. It’s vital to get the right PCM for different climates. Because the ambient air temperature fluctuated a lot throughout the year. PCM temperature effectiveness is highly determined by local ambient weather conditions. It is challenging to design the PCM integrated building for year-round thermal regulation. This research discussing PCM’s thermal energy effectiveness in building walls for decreasing interior temperature variance in composite climatic systems using numerical simulation using EnergyPlus software.

A simplified method to simulate tube-in-tank latent thermal energy storage with fin-enhanced phase change material in data center

Latent thermal energy storage (LTES) using PCM is one of the most effective measures to achieve energy saving and emergency cooling in data centers. Adding metal fins is proposed as an efficient solution for the low conductivity challenge of PCM, which severely hinders the application of LTES in practice. Nevertheless, simulating the thermal performance of fin-incorporated PCM is not straightforward due to the considerable effort of modeling individual fins. In this paper, the fin-enhanced PCM is simplified as a non-uniform composite material with anisotropic equivalent conductivity to simulate tube-in-tank latent thermal energy storage. The mean absolute percentage error between simulation result and experimental data are 3.64 % and 2.08 % for charging and discharging process, respectively. The results shown that for Z-direction thermal conductivity of 0.22, 4.95, and 9.9 W/(m·K), the outlet temperature of HTF is basically unchanged. The influence of inlet conditions on the thermal performance of LTES is analyzed, and the transient temperatures and temperature profiles in the fin-enhanced PCM at critical locations are presented. With the flow rate ranging from 10 L/min to 20 L/min, and the inlet temperature ranging from 277.15 K to 281.15 K during the charging process (and 287.15 K–293.15 K for the discharging process), the solidification time varies in the scope of 20 min–43 min (15 min–40 min for the discharging process). In addition, the simulation results show that the PCM temperature difference in Z direction is very small, and PCM temperature is mainly influenced by the closest tube. This work suggests a simple while effective method for simulating metal-fin-enhanced PCM, and could assist the optimization of latent thermal energy storage used in data center.

Solar-driven melting dynamics in a shell and tube thermal energy store: A numerical analysis

The numerical modeling of solar-driven melting in a shell-and-tube accumulator using paraffin RT70HC as PCM is presented. The coupling between an array of evacuated-tube solar collectors and the TES system is implemented in ANSYS Fluent, allowing for the proper evaluation of the time-dependent heat transfer fluid inlet temperature. A simplification of the TES geometry to a 2D section is accomplished, and an algorithm for the continuous evaluation of the heat transfer fluid temperature across the tubes in a serpentine-type configuration is developed. Validation with experimental results obtained in an outdoor test rig is carried out in terms of PCM temperature evolution. The model provides simulation results in a realistic configuration to be used in low-temperature applications of thermal energy storage for the residential sector. Energy performance is discussed, and the influence of the physics of melting and buoyancy forces leading to stratification are also analyzed, using temperature and liquid fraction contours during the solar irradiance cycle. The numerical results confirmed that natural convection plays an important role during melting of PCM: the motion of the melting front from the bottom to the top of the accumulator is described. Moreover, the results show that an increase of 50% of the solar surface improves the thermal storage by 28.8%, while doubling the solar surface increases the stored energy by 46.2%.

Study on the thermal performance of thermal energy storage and heating module based on a novel embedded heat pipe

A novel embedded heat pipe (HP) for electric thermal energy storage (TES) utilization was designed, which is conveniently embedded in the TES tank, and the evaporation surface and condensation surface are embedded in it. Besides, it can be used with multistage heat pipes. An electric TES heating module for building heating based on the HP was established. The start-up, the temperature uniformity, and heat transfer performance of the HP and the heat storage/release characteristic of the TES module were both studied experimentally. It is found that the novel embedded HP has good heat transfer performance and temperature uniformity. Under the condition of measured heating power, the minimum thermal resistance is as low as 0.077 °C/W, and the equivalent thermal conductivity is up to 91,273 W/(m·°C). In the heat storage process of the TES module, the paraffin completely melts from the top to the bottom, and the axial temperature of the TES module is uniform. But the radial temperature difference is relatively large. In the heat release process, the overall temperature uniformity of the TES module is good. The maximum temperature difference in the radial direction and the axial direction are less than 5 °C and 12 °C, respectively. Besides, the PCM temperature changes rapidly by adjusting the wind speed, and the thermal response of the TES module is quick. In the application of building heating, this TES module can adapt to the need of simultaneous heat storage and heating.

Combining an active method and a passive method in cooling lithium-ion batteries and using the generated heat in heating a residential unit

In this paper, a gentle air flow is simulated among cylindrical lithium-ion battery (LIIB) cells using COMSOL software. A circular PCM compartment is placed around the battery cells. The hot air from cooling the battery is used to heat the house. By changing the battery position in three modes in PCM in the air speed range of 1 × 10−3 to 5 × 10−3m/s, the volume fraction of solid PCM, the average PCM temperature (TAve−PCM), the maximum battery temperature (Tmax−b) and the exhaust air temperature at different times from 0 to 1000 seconds are analyzed. The percentage of time energy provided by this system of the total energy required for this residential house has also been examined. The results of this study show that over time at high speeds, the Tmax−b of the LIIB first increases and then decreases. The passage of time also reduces the amount of TOutlet. If the LIIB is placed on the air inlet side of the PCM instead of the air outlet side, the Tmax−b is reduced by 1.53 degrees at high speeds. Placing the LIIB on the left side of the PCM causes the output temperature (TOutlet) to be higher and also increases the amount of solid PCM by up to 5% in 1000 seconds compared to placing the LIIB on the right side. Using 50 cells of LIIB and air flow of 0.005 m/s in this system can provide up to 22% of the required energy for heating the building in a winter day.