Heat Of Composite Phase Change Materials Research Articles

Measuring the maximum capacity and thermal resistances in phase-change thermal storage devices

Thermal energy storage can increase the efficiency of the electric grid by adding flexibility to thermal systems. The value of thermal storage is a function of its energy and power density, which are driven by the capacity and thermal resistances in the storage device. Measuring these properties in-situ at the device level is an important step to understanding the performance and improving the design of thermal storage systems. In this paper, we present methods to measure the total capacity and thermal resistances in heat exchangers with integrated phase change materials. These methods are demonstrated on two thermal storage devices—a 570-kWh ice-based storage tank and a 0.35-kWh graphite-tetradecane composite device. The results show how thermal resistances evolve with the state of charge and discharge rate in these devices and quantify the impact of applied pressure on the contact resistance in composite phase change material heat exchangers. The proposed method allows for easy comparison between different systems and provides information on the thermal bottlenecks limiting performance. Ultimately, these measurements will allow designers to make robust, high-performance thermal storage devices for next-generation thermal systems.

Experimental Investigation of Composite Phase Change Material Heat Sinks for Enhanced Passive Thermal Management

AbstractPhase change materials (PCMs) are effective at storing thermal energy and are attractive for use in electronics to smooth temperature peaks during periods of high demand; however, the use of PCMs has been somewhat limited due to the poor thermal properties of the materials. Here, we propose a design for a tunable composite PCM heat sink for passive thermal management in electronic systems and develop an improved test platform to directly compare performance between different designs and PCMs. The composite design leverages high conductivity pathways, which are machined into aluminum heat sinks, and back-filled with PCMs. Two package sizes are considered with several internal fin structures. All designs are evaluated using a test platform with realistic power profiles, controlled interfacial loading, and in situ temperature measurement. The composite PCM heat sinks are benchmarked against solid aluminum packages of the same size. This study focuses on three commercially available PCMs. Performance is evaluated based on (1) the time it takes the test heater chip below each composite PCM package to reach the cut-off temperature of 95 °C and (2) the period of a full melt-regeneration cycle. A range of heat fluxes are considered in this study spanning 6.8–14.5 W cm−2. The isokite design with PlusICE S70 extends the time to reach 95 °C by 36.2% when compared to the solid package, while weighing 17.3% less, making it advantageous for mobile devices.

Experimental and numerical investigations on the effect of porosity and PPI gradients of metal foams on the thermal performance of a composite phase change material heat sink

This paper reports the results of an experimental and numerical study on the thermal performance of a metal foam based composite phase change material (PCM) heat sink cylindrical in shape with porosity and PPI (pores per inch) density gradients. Studies are conducted on different configurations of composite PCM made of an open-cell aluminum metal foams with porosities of 0.9, 0.94 and 0.97 and PPI of 8, 14 and 20 encapsulated with n-eicosane as the PCM. Experiments are carried out on the PCM heat sink heated from the bottom for different configurations of metal foams with a uniform porosity and non-uniform porosity created with layer wise arrangement of metal foams from the bottom to the top. Complementary three-dimensional numerical simulations have been conducted using the enthalpy porosity methodology with a non-thermal equilibrium model to understand the melting and solidification dynamics of PCM while melting (charging) and solidification (discharging) respectively. Heat sink configurations with uniform porosity, and porosity gradient created with bi-layer arrangement of metal foams have been simulated numerically. Further, the numerical simulations have been extended to study heat sink configurations containing metal foams with uniform PPI density and PPI density gradient. From the results, it is seen that the case of non-uniform variation in porosity (decreasing from the bottom to the top) with constant PPI density and the case of non-uniform PPI density (increasing from the bottom to the top) with constant porosity show superior performance up to 28 and 45% over the heat sink configurations with uniform porosity and PPI density respectively in the charging cycle in terms of the time to reach a setpoint temperature. From the numerical simulations, it is seen that the melt fraction of PCM significantly changes the convection velocity cells, which affects the melting dynamics of PCM. Additional numerical simulations have been conducted on PCM heat sink with non-uniform porosity (i.e. decreasing porosity from the bottom to the top) and non-uniform PPI density (i.e increasing PPI density from the bottom to the top) gradients created with three layers (tri-layer) of metal foams. The results show that the PCM heat sink with non-uniform porosity and non-uniform PPI density gradients created with tri-layer metal foams have almost the same performance as a bi-layer metal foam with enhancement ratio up to 4 and 4.4 times respectively over the base line case (i.e. PCM heat sink without metal foams). In the discharging cycle, it is seen that the porosity and PPI gradients do not have any effect on the thermal performance of the heat sink.

Paraffin and paraffin/aluminum foam composite phase change material heat storage experimental study based on thermal management of Li-ion battery

The temperature of battery modules in electric vehicles (EVs) must be controlled adequately to keep within a specified range for optimum performance. The paraffin/aluminum foam composite phase change material (PCM) was investigated experimentally. The experimental results indicate that paraffin/aluminum foam composite PCM has an ideal cooling effect in limiting the temperature rise of the Li-ion battery during the discharge process. The heat storage properties of pure paraffin and the composite PCM are also experimentally studied. The inner temperature distribution of the foam and paraffin is monitored during the melting process. The addition of aluminum foam can largely improve the effective thermal conductivity of the PCM, although its existence suppresses the local natural convection. The experimental results indicate that the use of aluminum foam can speed up the melting process and improve the temperature uniformity of the PCM. When the heat fluxes are 7000 W/m2 and 12,000 W/m2, the heat storage time of the composite PCM is 73.6% and 74.4% of that of pure paraffin, respectively.