Phase Change Temperature Of Phase Change Material Research Articles

Effect of steam flow parameters on the partial load behaviour of a PCM storage

To estimate the achievable thermal power in passive latent heat thermal energy storage (LH-TES) systems and the corresponding charging/discharging times for customised storage design and operation, relevant influencing parameters and their impact must be sufficiently known and understood. These parameters include not only the well-researched parameters on the phase change material (PCM) side, but also the parameters on the heat transfer fluid (HTF) side, such as the inlet temperature, the mass flow rate and the resulting heat transfer coefficient (HTC) between the HTF flow and the tube wall. For heat exchangers, these influences have been studied well, however for highly transient LH-TES studies are scarce. This article presents the influence of relevant parameters focusing on the ones related to the HTF side, using analytical and numerical parameter studies in Matlab®. The effect of different HTCs for varying flow conditions of the HTF in different zones of the tube is utilised to introduce the dominant heat transfer surface between the storage and the HTF (DHTS) as an indirect operating parameter. It corresponds to the area where the HTF phase change occurs and where most of the total energy is transferred. The numerical study indicates that the size of the dominant heat transfer area and thus the DHTS can be adapted by the HTF mass flow rate and the temperature difference between the HTF inlet temperature and the PCM phase change temperature. Based on this knowledge, new conjugate design and operating strategies for a test rig with a nominal thermal power of 1 kW using the commercial PCM PLUSICE A133 as storage material are proposed. They lead to a peak shaving behaviour of the storage with defined charging and discharging times.

Techno-Economic Assessment of Residential Heat Pump Integrated with Thermal Energy Storage

Phase change material (PCM)-based thermal energy storage (TES) can provide energy and cost savings and peak demand reduction benefits for grid-interactive residential buildings. Researchers established that these benefits vary greatly depending on the PCM phase change temperature (PCT), total TES storage capacity, system configuration and location and climate of the building. In this study, preliminary techno-economic performance is reported for a novel heat pump (HP)-integrated TES system using an idealized approach. A simplified HP-TES was modeled for 1 year of space heating and cooling loads for a residential building in three different climates in the United States. The vapor compression system of the HP was modified to integrate with TES, and all heat transfer to and from the TES was mediated by the HP. A single PCM was used for heating and cooling, and the PCT and TES capacity were varied to observe their effects on the building’s energy consumption, peak load shifting and cost savings. The maximum reduction in electric consumption, utility cost and peak electric demand were achieved at a PCT of 30 °C for New York City and 20 °C for Houston and Birmingham. Peak energy consumption in Houston, New York City, and Birmingham was reduced by 47%, 53%, and 70%, respectively, by shifting peak load using a time-of-use utility schedule. TES with 170 MJ storage capacity allowed for maximum demand shift from on-peak to off-peak hours, with diminishing returns once the TES capacity equaled the daily building thermal loads experienced during the most extreme ambient conditions.

Phase change material based ventilation module - Numerical study and experimental validation of serial design

There is an increasing demand for innovative, efficient, and environmentally friendly cooling technologies as alternatives to the conventional vapor compression-based technologies. In this study, a theoretical and experimental investigation of a Phase Change Material (PCM)-based module for a ventilation system is presented. An in-situ application employing the considered PCM module is investigated. A one-dimensional numerical model is developed to predict the dynamic performance of the PCM-driven ventilation system. In addition, the model is validated with data collected from the experimental application and the PCM hysteresis behavior is calibrated. The developed model predicts the system well, with an average deviation of less than 6% and less than 4% for the PCM and air temperatures, respectively. Parametric analysis is conducted to assess the impact of design and operational parameters on the performance. This includes, volume flow rate, PCM mass and PCM phase change temperature interval. Larger PCM mass is found to decrease efficiency of the PCM module but increase the peak heat transfer. An optimal PCM melting temperature of 20 °C is found to increase the cooling provided per kg of PCM and peak cooling capacity as compared to the reference melting temperature of 22.32 °C by 38.4% and 71.1%, respectively.

Optimized output electricity of thermoelectric generators by matching phase change material and thermoelectric material for intermittent heat sources

Thermoelectric generators (TEGs) are usually working in intermittent heat source environments, and thus the phase change material (PCM) has been widely adopted in to maintain relatively stable temperature difference. The property matching between the PCM and the TEGs is one of the crucial problems to influence the performance of the PCM-TEG system. In this work, the influence of the phase change temperature of the PCM on the output power and generated electricity of PCM-TEG system is studied. Classic Enthalpy model and three-dimensional coupled thermo-electric equations are applied to study the heat transfer and energy conversion mechanisms. Our results show that the output electric energy of a PCM-TEG system can be optimized by tuning the phase change temperature of PCM. The total generated electricity can be enhanced as large as 15.6% by matching the PCM with the thermoelectric properties of the thermoelement. Moreover, by comparing three cases with different thermoelectric materials, we give relationship between the optimal phase change temperature of PCM and the temperature for maximum figure of merit (ZT) of the thermoelement, which provides a selection criterion of PCM for TEG module. Our work could be helpful to realize further high efficiency thermoelectric generators for intermittent heat sources.

Experimental and numerical study on performance enhancement of photovoltaic panel by controlling temperature with phase change material

In order to enhance the electricity generation performance of photovoltaic (PV) panel, experimental and numerical studies were carried out to control the temperature by using phase change material (PCM). The PV combined with PCM (PV-PCM) device and PV-PCM with foam copper were designed, and their temperature, voltage, and output power were measured and compared with those of PV panel. The mathematical model of heat transfer for PV-PCM was established and verified by experiment. And the influences of PV-PCM tilt angle, PCM properties and thickness, and ambient temperature on the temperature control effect were studied numerically. The results illuminate that the PV panel's temperature decreases significantly with the using of PCM, which correspondingly enlarges its open circuit voltage and output power. And the PCM with foam copper has a better effect. The temperature control effect of the PV-PCM system is better with the increase of the tilt angle, the PCM thermal conductivity and thickness, and the decrease of PCM phase change temperature. But there are limited conditions for them. The higher the ambient temperature, the worse the temperature control effect. The present study has important reference value for PV performance enhancement.

Experimental investigation on thermal behavior of paraffin in a vertical shell and spiral fin tube latent heat thermal energy storage unit

Aided by the phase change material (PCM) with high thermal storage density, latent heat thermal energy storage (LHTES) technology may provide a solution to the energy supply-demand dilemma, e.g. LHTES in solar energy utilization and waste heat recovery. This paper presents an experimental investigation on the thermal performance of a LHTES unit equipped with vertical multitube shell and spiral-finned tube. Using paraffin as PCM and water as heat transfer fluid (HTF), the thermal charging and discharging characteristics of the LHTES unit can be evaluated. The thermophysical properties of latent heat and phase change temperature of PCM were characterized by the differential scanning calorimeter (DSC). Tests were conducted under different inlet temperatures and flow rates of HTF, during which the temperature variation of PCM, heat stored/released, mean charging/discharging power, total charging/discharging time and instantaneous effectiveness were acquired. Experimental results indicate that the natural convection of melted paraffin impacts substantially on the phase-change rate of paraffin. Once melt completes, the natural convection intensity surges temporarily. Moreover, the increase of inlet HTF temperature and flow rate during charging can dramatically improve the heat transfer between HTF and PCM, which in turn shortens the total charging time. The HTF flow rate was found to play little role on the heat transfer during discharging since the thermal resistance of the solidified PCM increases considerably.

Modeling PCM Phase Change Temperature and Hysteresis in Ventilation Cooling and Heating Applications

Applying phase change material (PCM) for latent heat storage in sustainable building systems has gained increasing attention. However, the nonlinear thermal properties of the material and the hysteresis between the two-phase change processes make the modelling of PCM challenging. Moreover, the influences of the PCM phase transition and hysteresis on the building thermal and energy performance have not been fully understood. This paper reviews the most commonly used modelling methods for PCM from the literature and discusses their advantages and disadvantages. A case study is carried out to examine the accuracy of those models in building simulation tools, including four methods to model the melting and freezing process of a PCM heat exchanger. These results are compared to experimental data of the heat transfer process in a PCM heat exchanger. That showed that the four modelling methods are all accurate for representing the thermal behavior of the PCM heat exchanger. The model with the DSC Cp method with hysteresis performs the best at predicting the heat transfer process in PCM in this case. The impacts of PCM phase change temperature and hysteresis on the building energy-saving potential and thermal comfort are analyzed in another case study, based on one modelling method from the first case study. The building in question is a three-room apartment with PCM-enhanced ventilated windows in Denmark. The study showed that the PCM hysteresis has a larger influence on the building energy consumption than the phase change temperature for both summer night cooling applications and for winter energy storage. However, it does not have a strong impact on the yearly total energy usage. For both summer and winter transition seasons, the PCM hysteresis has a larger influence on the predicted percentage of dissatisfied (PPD) than the phase change temperature, but not a strong impact on the transition season average PPD. It is therefore advised to choose the PCM hysteresis according to whether it is for a summer night cooling or a winter solar energy storage application, as this has a significant impact on the system’s overall efficiency.

Numerical study of a Phase Change Material (PCM) embedded solar thermal energy operated cool store: A feasibility study

Solar energy has proved to be an ideal alternative for fossil fuels, however, due to its intermittency in availability, systems operated by solar energy face serious limitations. In this study, a simplified dynamic model is developed to investigate the behavior of a PCM-embedded cool store. The main application of this type of cool store is to be operated with a solar thermal refrigeration system to compensate for the intermittency in energy availability. 8640 kg of crops (potatoes) is considered to be stored inside the cool store along with PCM cold thermal energy storage units. 9 h of active and 15 h of inactive period are considered for 24 h operation of the refrigeration system based on the solar energy availability data. During the active period, PCM units charge, and during the inactive period, they discharge and regulate the temperature inside the cool store. It was revealed that by choosing the right properties, PCM can keep the temperature of the crops in the desired range during the inactive period of the refrigeration system. Also, it was observed that the amount of PCM used and the phase change temperature of the PCM has a significant impact on the performance of the system. The lowest temperature obtained for the crops during the inactive period of the refrigeration system is for the case with PCM to crops amount ratio of 0.026 with PCM phase change temperature of 9 °C in which the discharge process finishes around the end of the inactive period of the refrigeration.

Research on applications of phase change materials in solar cell thermal control

In order to grasp the characteristics of phase change material (PCM) in solar cell thermal control, a two-dimensional thermal control structure model of PV/PCM solar cell thermal control system was established, and study was conducted on influence of PCM phase change temperature, thermal conductivity, latent heat value, etc. on the temperature control characteristics of solar cells. The results show that PCM phase change temperature, thermal conductivity, latent heat value will affect solar cell temperature control characteristics in varying degrees. At the same time, thermal control characteristics of PCM are greatly affected by environmental meteorological conditions (solar irradiance, ambient temperature). The research results provide a reference for optimization design of PV/PCM solar cell thermal control system.

Preparation and properties of phase change temperature-tuned composite phase change material based on sodium acetate trihydrate–urea/fumed silica for radiant floor heating system

In this work, a novel phase change temperature-tuned composite phase change material (PCM) for the PCM floor was developed by using sodium acetate trihydrate-urea non-eutectic mixture as PCM and fumed silica (SiO2) as both supporting material and temperature regulator. The thermoregulation mechanism of SiO2 and the properties of the resulting composite PCM were studied. The results showed that the addition of SiO2 could adjust melting temperature of the non-eutectic mixture from 34.36 to 48.45 °C, reduce supercooling degree and prevent leakage. With SiO2 mass fraction of 30%, the composite PCM had a suitable melting temperature (35.75 °C), high latent heat (151.6 kJ·kg−1) and low supercooling degree (1.14 °C). Meanwhile, the composite PCM possessed a good form stability and excellent thermal reliability and favorable thermal conductivity. Considering the above, the novel composite PCM has a great potential for the PCM floor. It is also expected that the present work can provide a new insight into tailoring phase change temperature of PCMs.

Numerical model of applying PCM boards for energy saving in lightweight buildings in Shanghai

The lightweight building industry develops fast, but it has competitively worse thermal comfort than traditional buildings because of less thermal mass. The use of phase change material (PCM) can help to solve the problem and boost the energy efficiency. In this paper, the effect of applying PCM-boards in air-conditioned lightweight buildings in Shanghai has been evaluated. A parametric study is performed considering different PCM-boards configurations, using an EnergyPlus single-zone model. The daily and annual situation have been simulated in this study, and the predictions show that the energy saving depends on the phase change temperature of PCM and seasonal temperature. The application of PCM can save up to 20.88% of energy for air conditioning system in buildings. The daily assessment reveals that the passive PCM technology inside the wall saves more energy under heating conditions than the cooling condition because of the overheating.

Optimization of phase change materials to improve energy performance within thermal comfort range in the South Korean climate

Worldwide growth and the pursuit of comfort in buildings have led to significant increase in energy consumption, which is considered a current issue. Phase change material (PCM), a thermal energy storage (TES) material, is considered an effective and promising material to reduce energy consumption. In recent years, research on the application of PCM to provide higher comfort for occupants has been growing rapidly. Studies show that it is necessary to consider the optimized phase change temperature of PCMs within the comfort temperature and specific climate conditions. Thus, the objective of this study is to investigate the best optimized PCM under thermal comfort range in the climate conditions of South Korea, and analyze the energy savings of PCMs, using DesignBuilder. The prepared PCMs were n-octadecane (OT), n-heptadecane (HT), and n-hexadecane (HX), which phase change temperatures were close to the thermal comfort range. The results of the circulation water bath test showed that the phase change temperature of the mixed PCMs by OT and HT was (22–23) °C, within the thermal comfort range. According to the various mixing ratios of OT to HT, the phase change temperatures of PCMs for OH91, OH73, OH55, OH37, and OH19 appeared at ((24–26), (23–24), (22–23), (21–23), and (20–22)) °C, respectively. For energy simulation, gypsum boards with OT, OHs, and HT were prepared, and analyzed by replacing conventional gypsum board of the standard residential construction house model in South Korea. As a result, the maximum energy savings were shown by OH73 in cooling, and OH19 in heating. Consequently, the maximum total energy savings were achieved for OH73, which means that the best optimized PCM for South Korea demonstrated a phase change temperature of (23–24) °C.

Influence of PCM thermal conductivity and HTF velocity during solidification of PCM through the free cooling concept – A parametric study

Abstract The thermal performance of a latent heat thermal energy storage (LHTES) system can be enhanced by incorporation of fins, metal matrices, lessing rings in the phase change material (PCM) encapsulation and by dispersion of high conductive nanomaterials in the PCM itself. Similarly, to increase the heat transfer to PCM, the surface convective heat transfer coefficient (‘h’) can be enhanced by increasing the heat transfer fluid (HTF) velocity (‘u’). However, it is important to know how much increase in PCM thermal conductivity (‘k’) and ‘h’ will be beneficial during the charging of PCM under real-time ambient conditions and when will we reach the margin of diminishing returns. Understanding these are the motivation of the present work which includes the parametric study of the impact of ‘k’ & ‘u’ on the charging of PCM (RT28HC) through free cooling concept under different operating conditions (two different HTF inlet temperature). The numerical results are validated using the experimental data and they both show good agreement with each other. The major inferences from the results are, i) increasing the PCM thermal conductivity reduces the charging duration of the LHTES system for both lower and higher HTF velocity (1 m/s and 8 m/s). However, reduction in charging duration while increasing ‘k’ is higher when the HTF inlet temperature is lower, ii) increasing the HTF velocity is beneficial only when the inlet HTF temperature is higher. For the case of lower HTF inlet temperature, the effect of increasing the HTF velocity is suppressed by the higher temperature driving potential between the HTF inlet temperature and the PCM phase change temperature. It is inferred from the parametric study that, among the three parameters considered (PCM thermal conductivity, HTF velocity, and HTF inlet temperature), HTF inlet temperature has the most influence on the charging of the PCM, followed by the PCM thermal conductivity and HTF velocity.

Effects of various parameters of a PCM on thermal performance of a solar chimney

A validated numerical model is established to study the effects of various parameters on thermal performance of a solar chimney integrated with phase change material (PCM) in terms of the melting/freezing time, air flow rate and air temperature difference between inlet and outlet. The numerical results showed that the phase change temperature of PCM greatly affects the thermal performance of solar chimney. The PCM having wider phase change temperature difference reaches the complete melting earlier than that with narrower one. However, it also fluctuates the room air temperature that may cause the thermal discomfort. The specific heat of PCM affects the way that sensible heat contributes to the melting/freezing process. The average mass flow rate and air temperature difference increase from 0.033 to 0.038kg/s and from 1.5 to 2°C, when the thermal conductivity of PCM is enhanced from 0.2 to 0.6W/m·°C. The initial temperature of PCM has very little influence on the melting process after the early period of melting.

地窓を利用した夜間自然換気による潜熱蓄熱材の蓄冷効果に関する研究

1. Introduction In this paper, we focused on introduction of phase change material(PCM) into a house to secure a cold storage with night natural ventilation. We conducted measurement in order to understand indoor thermal characteristics in a room with night natural ventilation for introducing PCM on the floor of a house to maximize cooling effect. Measurement was mainly conducted for on a room of the full-scale house where it has two openings at floor level. We measured vertical air temperature distribution and inflow wind speed to understand indoor thermal characteristics. And heat flow was also measured on the floor and under the floor to reveal cold storage mechanism. 2. Categorization We categorized measurement results according to weather condition on each day as follows. 1) Day of large air temperature difference between indoor and outdoor(ΔT) with high inflow wind speed, 2) Day of large ΔT with low inflow wind speed, and 3) Day of small ΔT with high inflow wind speed. 3. Measurement summary on indoor thermal characteristics Vertical air temperature distribution of indoor was influenced by inflow wind speed and ΔT. In case that inflow wind speed was lower than 0.1m/s, cold air accumulated along the floor was not mixed with the air at upper area of indoor. In case that inflow wind speed was over 0.1m/s and under 0.3m/s, inlet air mixed with indoor air. At this time, mixing height was determined by ΔT and inflow wind speed. In case that inflow wind speed was over 0.3m/s, indoor air was entirely mixed with outdoor air, thus vertical air temperature distribution tended to be disappeared. 4. Measurement summary on cold storage Cold storage tended to be proportional to ΔT. Cold storage accelerated as the condition of large ΔT and low inflow wind speed because cold air accumulated along the floor was not mixed with upper air of indoor. In case that air temperature near the floor was 2°C lower than phase change temperature of PCM for solidification, latent cold storage begun to progress. Cold storage ratio of latent heat was averagely 70%, and total cold storage tended to change approximate 1.5 times depending on outdoor air temperature. 5. Conclusion Indoor thermal characteristics and cold storage rate were changed by ΔT and inflow wind speed. In some cases, latent cold storage efficiency of PCM on the floor with night natural ventilation was confirmed. In the future, considering the daily life activity of residents, we are going to research passive cooling effect of PCM including the day time. Also, in order to develop a numerical simulation tool for designing a passive cooling house with PCM including a calculation model of vertical air temperature distribution, we will determine the parameter of turbulence diffusion coefficient by CFD simulation.

Conventional Refrigeration Systems Using Phase Change Material: A Review

A phase change material (PCM) is a substance that can store or release significant amounts of heat energy by changing its phase from liquid to vapor or vice versa. It has already been proven that incorporation of PCM with refrigeration systems improves the energy efficiency as well as the quality of the frozen food. However, the attachment of PCM system with the refrigeration system is a challenging task. Different aspects such as PCM thickness, quantity of PCM, PCM phase change temperature selection for optimizing energy consumptions of refrigeration systems are the main concerns of today’s researches. However, there is no specific study to concern these aspects of PCM in refrigeration systems. Therefore, in this paper, a comprehensive literature review has been made. The effects of different process parameters such as the thickness of PCM, phase change temperature of PCM and position of PCM have been discussed. This paper also presents a review of the modeling approaches as well as experimental approaches for the application of PCM in a refrigeration system. Moreover, the present status of the refrigeration system with PCM has been presented. Finally, the limitations of incorporation of PCM in a refrigeration system have been also discussed.

Investigation of the thermal performance of phase change material/mini-channel coupled battery thermal management system

In order to extend the cycle life of power battery pack within electric vehicle, a phase change material (PCM)/mini-channel coupled power battery thermal management (BTM) system, as well as the three-dimensional battery thermal model, was designed in this paper. The effect of various influencing factors, especially mass flow rate of water, phase change temperature and thermal conductivity of PCM, were investigated numerically. The results showed that the liquid volume fraction of PCM was greatly influenced by the thermal conductivity and the phase change temperature of PCM. The increasing number of channels results in a decrease of the maximum temperature (TMax) and maximum temperature difference (ΔT) of battery packs. The optimal phase change temperature and thermal conductivity of PCM were 308.15K and 0.6Wm−1K−1 respectively when the number of channel was eight and the mass flow rate was 8×10−4kgs−1. Moreover, a maximum temperature of 320.6K was predicted for the PCM/mini-channel coupled BTM system, while a maximum temperature of 335.4K was predicted for the PCM-based BTM system. Additionally, the PCM/mini-channel coupled BTM system presented more effective thermal performance and the research will be a clear indicator for the design of the PCM/liquid coupled BTM system.

Diurnal thermal analysis of microencapsulated PCM-concrete composite walls

This paper examines the benefits of adding microencapsulated phase change material (PCM) to concrete used in building envelopes to reduce energy consumption and costs. First, it establishes that the time-dependent thermal behavior of microencapsulated PCM-concrete composite walls can be accurately predicted by an equivalent homogeneous wall with appropriate effective thermal properties. The results demonstrate that adding microencapsulated PCM to concrete resulted in a reduction and a time-shift in the maximum heat flux through the composite wall subjected to diurnal sinusoidal outdoor temperature and solar radiation heat flux. The effects of the PCM volume fraction, latent heat of fusion, phase change temperature and temperature window, and outdoor temperature were evaluated. Several design rules were established including (i) increasing the PCM volume fraction and/or enthalpy of phase change increased the energy flux reduction and the time delay, (ii) the energy flux reduction was maximized when the PCM phase change temperature was close to the desired indoor temperature, (iii) the optimum phase change temperature to maximize the time delay increased with increasing average outdoor temperature, (iv) in extremely hot or cold climates, the thermal load could be delayed even though the reduction in daily energy flux was small, and (v) the choice of phase change temperature window had little effect on the energy flux reduction and on the time delay. This analysis can serve as a framework to design PCM composite walls in various climates and seasons and to take advantage of time of use electricity pricing.