Phase Change Material Plates Research Articles

Experimental Study of the Performance of Phase Change Material Air Cooling Rig

The power supply challenges faced by South Africa over the last two years, coupled with the escalating electricity tariffs, demands improvement in demand side energy management. Given the significant proportion of energy consumed in buildings and building cooling in particular, heating, ventilation and air conditioning (HAVC) systems offer opportunities to reduce building energy consumption. This paper reports on experimental testing of a phase change material (PCM) cold storage rig with potential to reduce electricity consumption in HVAC systems. The rig captures night time cold for use during the day to cool ventilation air. The aim of the study was to assess the performance of the PCM rig with the ultimate goal of developing PCM design selection tools for air cooling applications. The rig was built from PCM encapsulated in aluminum plates. The PCM had a melting point of 22-26oC. The plates (15 plates) were in turn assembled in a Plexiglas box to minimize heat loss. The separation distance between plates was set at 10mm. Air flow over the plates was supplied by an axial fan through insulated galvanized ducting. Ambient temperatures and air temperatures along the air flow path were monitored using thermocouples for varying air flow rates over a 24 hour period (day and night). Air mass flow rates of 0.027, 0.061 and 0.075kg/sec were used. As expected, the air temperature decrease was affected by air flow rate. The lower the mass flow rate, the more effective the cooling effect. The recorded average temperature changes were 2.9oC, 2.4oC and 1.4oC for mass flow rates of 0.027, 0.061 and 0.075kg/sec respectively. These also corresponded to energy transfers of 2.3kJ, 1.1kJ and 0.9kJ respectively. Thus for effective use of such systems in air cooling, a balance must be struck between the ASHARE recommended air exchanges and the number of PCM plates required.

Air–PCM heat exchanger for peak load management: Experimental and simulation

Peak power consumption is becoming an increasing problem worldwide and particularly in France during the late afternoon winter periods. This paper describes the experimental and numerical studies carried out to investigate the potential of a PCM (phase change material) – Air heat exchanger, conceived for load shifting purposes. The objective is to possess the necessary tools for the development of advanced control strategies taking into account various factors: peak power reduction, thermal comfort and indoor air quality. The experimental approach involved the construction of a heat exchanger coupled to an experimental cell. The heat storage system is composed of a set of PCM (paraffin) plates, embedded in the exchanger and integrated in a ventilation system. In parallel, a numerical model was developed using the apparent heat capacity approach and the finite differences method. Furthermore, a series of characterization tests was conducted and the experimental data were used for model calibration and validation. The model was then coupled with a building simulation program, presenting good agreement between the integrated model prediction and the experimental data.Finally, a preliminary control strategy of the test cell is presented along with results demonstrating the capabilities of such system for peak load management.

A correlation of the convective heat transfer coefficient between an air flow and a phase change material plate

This paper provides a new correlation to determine the heat transfer coefficient between an air flow and a plate made of phase change material (PCM). This correlation was built for the simulation of heat storage units containing PCM plates subjected to an inlet temperature step. The presented correlation has the following form: Nux,tPCM=NuPSM·fPCM. The first term NuPSM is for a plate made of traditional material. The term fPCM is a perturbation due to the phase change in the plate. Each term depends on 5 non-dimensional parameters. One of them represents the advance in the total heating or cooling process, in order to take into account the transient evolution of the convective coefficient. The correlations are built using the Least Squares Method, from series of CDF simulation data. The shape of the perturbation fPCM reveals a complex evolution of the temperature repartition in the PCM plate. Finally, a nodal model of the plate has been developed in order to test the provided new correlation and other correlations available in the literature. The results obtained with the present correlation show better agreements with the CFD results, which make this correlation suitable for the simulation of PCM heat storage systems.

Numerical analysis of effect of shape-stabilized phase change material plates in a building combined with night ventilation

Effect of shape-stabilized phase change material (SSPCM) plates combined with night ventilation in summer is investigated numerically. A building in Beijing without active air-conditioning is considered for analysis, which includes SSPCM plates as inner linings of walls and the ceiling. Unsteady simulation is performed using a verified enthalpy model, with time period covering the summer season. Effects of the following factors on room air temperature are investigated: the thermophysical properties of the SSPCM, the thickness of SSPCM plate and air change per hour (ACH) at both nighttime and daytime. The results show that the SSPCM plates could decrease the daily maximum temperature by up to 2 °C due to the cool storage at night. The appropriate values for melting temperature, heat of fusion, thermal conductivity and thickness of SSPCM plates need to be considered and calculated according to the climate conditions and building structure. The ACH at night needs to be as high as possible but the ACH at daytime should be controlled.

Performance of a hybrid heating system with thermal storage using shape-stabilized phase-change material plates

Performance of a hybrid heating-system, combined with thermal storage using shape-stabilized phase-change material (SSPCM) plates, is investigated numerically. A direct gain passive solar house in Beijing is considered, which includes SSPCM plates as the inner linings of walls and the ceiling. Unsteady simulation is performed using a verified enthalpy model, with a time period covering the winter heating-season. Additional heat supply is employed during load hours at late night and early morning (23:00–07:00 in Beijing) or during the whole day necessary to keep the minimum indoor air temperature above 18 °C. The results indicate the thermal storage effect of SSPCM plates, which improves the indoor thermal comfort level and saves about 47% of normal-and-peak-hour energy use and 12% of total energy consumption in winter in Beijing.

An assessment of mixed type PCM-gypsum and shape-stabilized PCM plates in a building for passive solar heating

Thermal performance of two phase change material (PCM) composites, mixed type PCM-gypsum and shape-stabilized PCM plates, has been numerically evaluated in a passive solar building in Beijing with an enthalpy model. Effects of the melting temperature and phase transition zone of the PCM are analyzed and a comparison between the two types of PCM composites is performed. The results show that: (1) for the present conditions, the optimal melting temperature is about 21 °C; (2) PCM composites with a narrow phase transition zone provide better thermal performance; (3) both mixed type PCM-gypsum and shape-stabilized PCM plates effectively shave the indoor temperature swing by 46% and 56%, respectively; (4) the shape-stabilized phase change material (SSPCM) plates respond more rapidly than the mixed type PCM-gypsum and prove to be thermally more effective in terms of utilizing the latent heat.

Experimental study of under-floor electric heating system with shape-stabilized PCM plates

This paper put forward a new kind of under-floor electric heating system with shape-stabilized phase change material (PCM) plates. Different from conventional PCM, shape-stabilized PCM can keep the shape unchanged during phase change process. Therefore, the PCM leakage danger can be avoided. This system can charge heat by using cheap nighttime electricity and discharge the heat stored at daytime. In the present work, the thermal physical properties of shape-stabilized PCM developed by us were measured. A prototype room with this system was set up in Beijing to testify its thermal performance and feasibility of this heating mode. The results show that temperature of the PCM plates upper surface can be kept near the phase transition temperature in whole day and a lot of off-peak period electricity can be used for space heating in stead of using peak period electricity, which obviously lowers the electricity tariff.

Modeling and simulation of under-floor electric heating system with shape-stabilized PCM plates

A model is developed to analyze the thermal performance of a room applying a new kind of under-floor electric heating system with shape-stabilized phase change material (PCM) plates, which is verified by our experimental data. This system can charge heat by using cheap nighttime electricity and discharge the heat stored at daytime. The thermal performance of the heating system and the effects of various factors on it are analyzed through simulation. The results show that the heating system can be used in various climates if its structure is properly designed. The model and the discussion are helpful to design such kind of under-floor electric heating systems.

Study of the thermal behavior of a latent heat cold storage unit operating under frosting conditions

A study is performed of the thermal behavior of a latent heat cold storage unit operating under frosting conditions. This unit is employed to maintain the temperature inside the refrigerated compartment of a truck below 265 K. The system consists of parallel plates filled with a phase change material (PCM) that absorbs heat from the flow of warm moist air. A mathematical model for the system is first presented and, next, validated with numerical and experimental data. It is then exploited to assess the effects of design parameters and operating conditions on the performance of the system. The recommended thickness and distance separating the PCM plates are found to be 50×10 −3 and 30×10 −3 m, respectively. The results indicate that the performance of the unit is enhanced by turbulent air flow in spite of the increased pressure loss and accentuated frost growth. The unit also performs well even when the surrounding relative humidity is 100%.