PCM Temperature Research Articles

Heat transfer efficiency and electrical performance evaluation of photovoltaic unit under influence of NEPCM

In present study, a design of PVT unit involving PCM has been analyzed. The influence of several types of nanofluids and NEPCMs at different concentrations on the system efficaciousness is assessed. The SiC, ZnO, MCNT (multi-walled carbon nanotube), Al2O3, Cu, and Ag nanoparticles are utilized within water and phase change material at concentrations of 0, 0.02, 0.04. The impact of different flow rates and various solar radiation intensities are also evaluated. In addition, the influence of using multilayer of PCMs (including OM35, RT35HC, and eicosane) with different combinations inside the PCM receptacle on the productivity of component is assessed. At last, a comparison study between PVT, PVT/PCM, PVT-TE (thermoelectric module), and PVT-TE/PCM collector is conducted to assess the impact of TE module integration with the PVT systems from the electrical and thermal perspectives. To simulate the procedure of the charging of paraffin, the enthalpy-porosity approach is used. In addition, a transient solver and pressure-based finite volume approach are selected to perform the simulation. Based on the acquired results, enhancing the flow rate of coolant from 3.77 to 7.54 ml/s leads to 7.21% reduction in liquid fraction. It also de-elevates the average PV temperature, average outlet temperature, and the PCM temperature by 7.06%, 35.13%, and 3.62%, respectively. Enhancement of the NEPCM concentration from 0 to 4% improves the escalating charging rate, however, it de-elevates the temperature of PV unit and the Tout of coolant slightly.

Enhancing the Productivity of Tubular Solar Still by Using the Phase Change Material

In this article, a theoretical simulation of a modified tubular solar still (TSS) integrated with a rectangular basin painted black color was investigated. The simulation was conducted out using a 2-dimensional computational fluid dynamics by COMSOL metaphysics software. The two different types of phase change materials- PCMs have been used as a heat storage medium; paraffin wax and stearic acid. Influence of several parameters PCM mass, solar radiation, wind speed and temperature environment (ambient temperature) was studied. Therefore, a set of numerical simulations were displayed out to study the effect of heat transfer within the TSS. A series of this analysis in various real weather conditions (Najaf, latitude = 32° 1′ 38.55″ N, longitude = 44° 19′ 59.22″ E) on the TSS with seven PCM layers having a different thickness (tPCM = 5, 10, 20, 30, 40, 50 and 60 mm) were performed. The simulation results indicate that within the daytime, a more applicably performance of TSS was achieved with 40 mm PCM (2.664 kg of paraffin wax or 3.143 kg of stearic acid) compared to TSS without PCM. They are shown that the proposed solar system with PCM is significantly better due to thermal loss reduction. In general, the system including paraffin wax is most effective with or without stearic acid. The results of the analytical simulation were validated with experimental field results. It was found a good agreement between the numerical data obtained, and the experimental data have been obtained (rMBE = 0.022).

Performance prediction and optimization of a photovoltaic thermal system integrated with phase change material using response surface method

Abstract In this study, a predictive model is developed based on the response surface method (RSM), to show the relationship between the operating factors (independent parameters) and some important response factors (dependent parameters) of a photovoltaic thermal system integrated with phase change material (PVT/PCM). The considered phase change material is the Rubitherm (RT) series of organic phase change materials. Moreover, both single and multi-objective optimization are conducted using RSM for different optimization objectives to recommend the optimal values of control factors for different operating conditions. The selected operating factors include PCM layer thickness, solar radiation, melting temperature of PCM and ambient temperature. Five response factors, including electrical power, thermal power, electrical exergy, thermal exergy and entropy generation are considered. To evaluate the model statistical adequacy, diagnostic analysis is performed for each response to indicate that the predictive model has a reasonable accuracy. The analysis of variance (ANOVA) test and perturbation analysis are also applied to evaluate the suitability and statistical importance of the recommended model and they show that the sensitivity of solar radiation on energy and exergy outputs is higher than that of other operating factors. According to the results, to maximize the electrical power, thermal power, electrical exergy, thermal exergy, and to minimize the entropy generation, simultaneously, it is recommended to select the PCM layer thickness of 1.5 cm, solar radiation of 901 W/m2, melting temperature of 25 °C, and the ambient temperature of 40 °C, based on the proposed method in this study.

Analysis of The Performance of A PV/PCM System in Variable Solar Radiation Conditions

This paper studies the performance of a PV/PCM system operating at variable solar radiation conditions. The system has been tested for six different solar radiation levels, from 250 W/m2 to 950 W/m2 determining the steady-state temperature for every case. An algorithm has been developed to predict the steady-state temperature. This prediction has produced values within 97% accuracy of experimental data. A reduction of temperature up to 18.9ºC has been achieved. An algorithm has been developed to correlate reduction in temperature with solar radiation levels. This algorithm can be combined with the classical expression for the PV panel efficiency resulting in a good method for determining the increase of the efficiency. Additionally, the system has been tested for continuous solar radiation evolution, analyzing the system response under the transient state. The procedure has been conducted for the former six solar radiation levels considering the solar radiation evolves linearly from one value to another during a time interval. The simulation has been tested against outdoor solar radiation with an accuracy higher than 98%. The predicted value of the PCM Temperature at the end of the day as shown matches the melting point of the PCM used in the experiment (55ºC), which has been verified experimentally. Besides, the transient state analysis has given the temperature evolution of the PCM at every interval, resulting in a very good match with experimental tests. The analysis of the transient state that the system reaches the melting point at 1/3 of the solar day length, maintaining the phase change state for the rest of the day. This is in good agreement with the experimental observation.

Thermal performance augmentation in latent heat storage unit using spiral fin: An experimental analysis

Abstract A comprehensive experimental analysis is reported to evaluate the heat transfer augmentation in vertical shell and tube Latent Heat Storage Unit (LHSU) with installation of spiral fins. Influence of spiral fins on charging and discharging rate is evaluated. PCM and HTF used in the existing experimental test setup is stearic acid and water respectively. To obtain accurate PCM temperature in radial, angular and axial direction, total 45 temperature sensors are installed in the annulus of the shell. Simulations have been also performed to track the interface of solid-liquid during charging and discharging. Experimental findings infer that installation of the spiral fins improve melting and solidification time due to the transport of thermal energy in the middle and lower axial planes, which expedites the energy storage/retrieval process. Installation of spiral fins lead to a reduction in the charging and discharging time by 41.48% and 22.16% respectively. The total cycle (charging + discharging) rate is reduced by 31.82% due to installation of spiral fins. Simulation results also depict significant reduction in charging and discharging time.

Replacement model of phase change building materials for heat load calculation

AbstractPhase change materials (PCMs) may contribute to room temperature stability and heat load reduction. This research proposes a method to calculate heat load using a PCM replacement model for a thermal storage wall. Regarding the replacement of PCM with internal thermal mathematical models, the replaced PCM temperature and room temperature are related. The method to replace PCM in adjoining rooms is based on the heat transfer coefficient, heat transmission coefficient, solar absorptance on the surface of a wall, ceiling, or floor, etc. We compare the results of the proposed replacement model of room temperature and heat load to a detailed heat load calculation.

Thermal behavior of a sodium acetate trihydrate-based PCM: T-history and full-scale tests

Latent heat thermal energy storage (LHTES) has been receiving increasing attention from researchers and engineers. A practical LHTES installation requires a deep understanding of phase change material’s (PCM’s) thermal behavior under thermal property testing and realistic operating conditions. To enrich this understanding, an experimental study on a commercial sodium acetate trihydrate-based PCM (Climsel C58) is presented in this article. C58 was characterized with two test methods: T-history tests and full-scale LHTES tests. The results are presented and discussed to exhibit the thermal behavior of C58 with these two test methods and the variations between them. With T-history tests, the thermal properties of C58 such as melting/solidification temperature range (57–61 °C/55–50 °C) and latent heat of fusion (216 kJ/kg) were determined. In full-scale LHTES tests, a parametric study was conducted to investigate the effects of heat transfer fluid flowrate and operating temperature range on the thermal performance of a 0.38 m3 storage prototype containing cylindrically macro-encapsulated C58. Moreover, longitudinal and radial PCM temperature distributions in full-scale tests were analyzed, suggesting the presence of phase separation. In general, C58 behaved differently between the two test methods regarding phase separation (negligible in T-history tests), supercooling effects (within 3 K in full-scale but up to 10 K in T-history tests), and thermal energy storage capacity (10% lower in full-scale tests). When using C58 or other salt hydrate-based PCMs for large-scale heat storage, these thermal behavior differences between the property-measurement and the application-oriented environments should be properly addressed in the design stage to ensure performance.

MELTING CHARACTERISTICS OF CAPSULATED PHASE CHANGE MATERIALS

An experimental and computational investigation studied phase change material melting in a cylindrical capsule with PCM. The capsule is placed horizontally in a rectangular test section, where it is insulated from all sides’ wall except the front one. The PCM capsule is heated by passing hot water from downward to upward with different inlet mean water temperatures (327.9, 333.7, 338 and 343) K, different velocities, varied thermal conductivities of capsule material wall (copper, iron, pyrex-glass, and polyethylene), and PCM. Experiment during melting inside a pyrex-glass capsule was performed and compared with prediction analysis by using CFD ANSYS 2019 R2. Image processing of melting photographs along with melted time were used in comparison. The comparison between the liquid fraction and energy stored with time for lauric acid and paraffin wax was analyzed. PCM liquid fraction, temperature and energy stored measurements for lauric acid were assessed numerically. The results reveal for lauric acid that the total melting time was enhanced 43% for 4.6% increase in water mean inlet temperature, 18% for 500% increase in inlet water mean velocity, and 7% when used copper capsule wall. The results proved that the lauric acid charged with energy stored were 47% more than paraffin wax during the total melting time of it, and the effect of different water mean inlet temperatures was the main factor for the charging process to improve the PCM melting time.

Experimental study of charging a compact PCM energy storage device for transport application with dynamic exergy analysis

Thermal energy storage is essential whenever there is a mismatch between the supply and consumption of energy. When the air conditioning system is applied in transport, a great challenge occurred due to frequent fluctuations of cooling load which causes comfort degradation and even healthy concern. In this study, we evaluate charging performance including charging time, transient charging rate, overall energetic and exegetic efficiency of the designed device under different operating conditions. Evolutions of PCM temperature with processing time both in the axial and radial directions are also investigated. What’s more, the dynamic exergy efficiency is studied for the first time to assess the optimal charging depth and charging time. The experimental results show that the charging time can be reduced by 49% and 28% by dropping the charging temperature from 15 to 11 °C and increasing the inlet air velocity from 0.70 to 1.20 m/s. The designed energy storage device has flexible charging rates with the maximum value of 1.3 kJ/s, high thermal efficiencies at 87% and overall exergy efficiencies up to 70%. Both the drop of the inlet air temperature and the rise of the inlet air velocity contribute to the energy efficiency. The analysis of dynamic exergy efficiency shows that the maximum exergy efficiency can reach around 90% with the optimal charging time varying from 10 to 52 min. The corresponding optimal charging depth varies between 46% and 58% under the studied conditions. These findings could provide guidelines for the design and optimization of PCM energy storage device specifically when it is used in the transport field.

An experimental and numerical study on the effect of inclination angle of phase change materials thermal energy storage system

Abstract The main purpose of the present study is to investigate the melting characteristics of a PCM cylindrical thermal storage system using experimental and numerical approaches. Three inclination positions are considered from vertical to horizontal. Paraffin wax has been used as the phase change material with a melting temperature ranged between 35 and 37 oC. The melting behaviour of the PCM inside the storage is characterised using different parameters of temperature distribution, imaging of PCM melting profiles, rate of stored heat, and liquid PCM flow within the storage. The results show that the PCM storage inclination angle has a significant effect on the PCM temperature distribution, PCM melting time and profile. It is noted that PCM in the storage in the 45° inclination angle from the horizontal location has the fastest melting rate is the fastest in melting compared to the 0° and 90° inclination angles. The simulation models enable understanding the internal flow of liquid PCM where it has been found that the direction of buoyant force resulting from the melted liquid PCM has a major role in both melting rate and melting direction within the PCM storage. In addition, it has been observed that the charging rate has no effect on the PCM melting profile.

Numerical Study on Melting Heat Transfer in Dendritic Heat Exchangers

The dendritic fin was introduced to improve the solid-liquid phase change in heat exchangers. A theoretical model of melting phase change in dendritic heat exchangers was developed and numerically simulated. The solid-liquid phase interface, liquid phase rate and dynamic temperature change in dendritic heat exchanger during melting process are investigated and compared with radial-fin heat exchanger. The results indicate that the dendritic fin is able to enhance the solid-liquid phase change in heat exchanger for latent thermal storage. The presence of dendritic fin leads to the formation of multiple independent PCM zones, so the heat can be quickly diffused from one point to across the surface along the metal fins, thereby making the PCM far away from heat sources melt earlier and faster. In addition, the dendritic structure makes the PCM temperature distribution more uniform over the entire zone inside heat exchangers due to high-efficient heat flow distribution of dendritic fins. As a result, the time required for the complete melting of the PCM in dendritic heat exchanger is shorter than that of the radial-fin heat exchanger.

Experimental analysis of the effective thermal conductivity enhancement of PCM using finned tubes in high temperature bulk tanks

Solar cooling is a promising solution to overcome the high energy demand of buildings. Nevertheless, the time dependent nature of the solar source leads to the need of storage systems in order to better match the energy demand and supply. For this purpose, thermal energy storage was considered during last decades as the optimal solution at commercial scale. Latent thermal energy storage offers higher energy densities together with more constant outlet temperature than sensible heat storage, but the low thermal conductivities of PCMs represents the main drawback which limits its applicability. Several studies based on heat transfer enhancement techniques applied in latent thermal energy storage have already been performed. Specifically, the technique of adding fins in storage tanks, which is the most known and studied. However, there are few experimental studies at pilot plant scale focused on this technique and less on the analysis of the heat transfer enhancement through the parameter effective thermal conductivity. This paper presents an experimental study where this parameter is determined and compared using of two identical latent storage tanks, one with 196 transversal squared fins and another one without fins. In this case, hydroquinone was selected as PCM. A set of six experiments was performed at pilot plant of the University of Lleida (Spain), combining three different HTF flow rates and two temperature gradients between HTF inlet temperature and initial PCM temperature. Experimental results showed that the addition of fins can increase the effective thermal conductivity between 4.11% and 25.83% comparing the experiment with highest and lowest thermal power supplied to the PCM, respectively.

Thermal characteristic and analysis of closed loop oscillation heat pipe/phase change material (CLOHP/PCM) coupling module with different working media

Aimed to understand the thermal characteristic of closed loop oscillation heat pipe/phase change material (CLOHP/PCM) coupling module filled with different working media for thermal energy storage and thermal management application, experimental investigation on the heat charge and discharge process of the coupling module under different conditions was carried out. The main result shows that the CLOHP filled with self-rewetting fluid (SRWF) and not placed horizontally has better thermal transfer performance relative to the water case as the heat load is low. But, the CLOHP filled with water has better thermal transfer performance than the SRWF case in horizontal condition especially under low heat load. The rise speed of temperature in the heating section increases when the phase transition completes. The highest temperature of the PCM locates in the middle region. Standard deviation (STD) of PCM temperature keeps relative stable for a long time and then increases rapidly and the rise speed has a positive correlation with the heat load. The uniformity of PCM temperature has been greatly improved for those three cases compared to that without working medium. During the discharge process, the fluctuation occurs only when the temperature of evaporation exceeds about 60 °C.

습식 및 온수 바닥 복사 난방 시스템에서 PCM 적용을 위한 상변화온도 영향 분석

This study aims to design the PCM radiant floor heating system and to calculate optimal temperature of the PCM. The results of this study is as following. A existing radiant floor heating system have some problems to use a lot of hot water and energy owing to low heat storage performance of autoclaved lightweight concrete and mortar. for this problem, this study suggested the design of PCM radiant floor heating system applied to PCM, which is a heat storage material. The PCM radiant floor system consists of 210 mm concrete slab, 20 mm cushioning material, 15 mm mortar, 10 mm PCM aluminum case, 55 mm mortar, and a finishing material. It was analyzed that the PCM temperature (Melting point) scope for the PCM radiant floor heating system is 32-39℃ through the heat transfer model if a finishing material of 5 mm thickness is used.

Charging properties of a compact energy storage device for transport air conditioning applications

Air conditioning system in transport applications is a great challenge due to the frequently fluctuated load which causes comfort degradation and even healthy concern. In our previous study, a compact energy storage device filled with PCM was designed and experimentally tested which showed great potential for thermal comfort improvement and efficiency improvement. In this study, charging properties of the energy storage device for train air conditioning systems are experimentally investigated. Time evolutions of PCM temperature during the charging process are presented. The charging performances including charging time, transient charging rate, thermal efficiency and exergy efficiency are revealed. The results show that the designed device has excellent heat transfer behaviors with exergy efficiency up to 78%. The designed device is feasible to be used in transport air conditioning systems due to the quick charging.

A highly efficient solution of off-sunshine solar air heating using two packed beds of latent storage energy

Abstract In order to increase the efficiency of the solar air collector and to improve their thermal efficiency in terms of operating time, hot outlet air temperature and starting operation time, the performance of a compact phase change material solar air heater collector based on latent heat storage energy was investigated. In this solar collector, the two-packed bed absorber unit performs two functions: absorbing the solar energy and storing the thermal heat onto PCM. The solar energy was stored as sensible heat and latent heat in the encapsulated PCM as spherical capsules forms. The experimental apparatus designed and realized in the Research and Technology Center of Energy (CRTEn) in Tunisia. Moreover, the solar air heater with PCM is used only at night on natural convection mode. To assess the performances of the collector, outdoor experiments was carried out to validate the availability of using this solar collector for air heating application. During the experimental test, the inlet and outlet air temperature, the relative humidity, external wind speed, the global solar radiation and the PCM temperature distribution in different bed of the solar collector were recorded. The experimentally obtained measurements are used to analyze the performance of the PCM system, the thermal instantaneous stored, absorbed and useful energy during the charging and discharge process was calculated. The experimental results showed that in the charging process, the stored heat increasing with the absorbed solar radiation. The daily energy efficiency is around 47%.

Numerical simulation on thermal characteristics of supercooled salt hydrate PCM for energy storage: Multiphase model

Multiphase model is set up and applied to perform a 3D transient CFD simulation on the discharging characteristics of supercooled PCM. Three typical processes are identified and analyzed, i.e. stable supercooling, triggering crystallization and regular solidification periods. The simulation is achieved by loading the source term in energy equation and phase transition term in volume fraction equation. PCM temperature, solid fraction (SF) and heat transfer rate (HTR) to the surroundings are monitored and analyzed during the three stages. It is found that there is little difference among the temperature and SF curves of different z-direction planes during the first two periods but they are distinct during the regular solidification period. For the triggering crystallization period, PCM temperature rises much rapidly up to the melting point within 30s and SF increases up to 0.33 correspondingly. The heat loss is small in this short period and could be simplified as adiabatic. Variations of temperature and SF extend from up and side walls to the interior of the PCM unit. HTR curve fluctuates greatly throughout the three processes with highest value of 1420W occurring in regular solidification period. The developed method can be used for parameter analysis of supercooled PCM thermal storage devices.

Reproducibility of solidification and melting processes in a latent heat thermal storage tank

This study analyzes the reproducibility of solidification and melting tests in a tank containing 181 kg of paraffin for cold storage at around 8 °C. Firstly, an experimental campaign of 10 identical tests was carried out. The performance is practically the same in terms of PCM temperatures and thermal power, with a maximum deviation of 2% in the capacity of all tests. In a second campaign, the impact of the initial conditions was studied. The results indicate that fixing a same mean PCM temperature at the beginning of the tests is insufficient to ensure an accurate reproducibility. Depending on the heat transfer rate during the preparation tests, the capacity differed in up to 33%. In tanks with such quantities of PCM, fixing a uniform initial PCM temperature is hardly possible, thus it is important to prepare the tank with same operation conditions.

동절기 이중외피 시스템에 적용 가능한 PCM재료의 온도설정에 따른 실내 열 성능 분석에 관한 연구

동절기 이중외피 시스템에 적용 가능한 PCM재료의 온도설정에 따른 실내 열 성능 분석에 관한 연구

Prediction of Spherical Phase Change Material Temperature Using RBFNN Model

PCM system particularly plays an important candidate at off peak to improve thermal storage system. In this paper, predication of output temperature in integrated solar heat using RBFNN was proposed. First, a brief PCM numerical model including geometrical and operational parameters and discusses the effect this parameter on the output temperature. The working fluid temperature is uniform distributed and equal to collector output temperature. The learning data is theoretical generated by using standard solar collector integrated with 95 PCM modules. The RBFNN model has 3 input nodes representing spherical size, duct length and number of ball and two output node represented by first and last layer PCM temperature. Simulation result shows the predicted PCM temperature at first and last layer closely match with the analytical data from CFD.