Heat Transfer During Heating and Cooling of a Packed Bed Comprised of Encapsulated Phase Change Material

2017 ◽  
Author(s):  
Glen O. West ◽  
Kent S. Udell
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Internal Heat ◽  
Packed Bed ◽  
High Energy ◽  
Air Injection ◽  
Cold Air ◽  
Phase Change Temperature ◽  
Hot Air ◽  
Change Temperature

Phase change materials (PCMs) are attractive components of thermal energy storage systems due to their high energy densities and the relatively small temperature differences needed for effective charging and discharging. In this study, experimental data were examined in order to better understand energy exchange in packed beds and porous media comprised of solid/liquid phase change capsules. Air was used as the heat transfer fluid; hot air was injected in order to drive the melting process, while cold air was injected to accomplish freezing or solidification of the PCM. Theory was developed to describe the temperature variations throughout the bed. Temperatures in the bed were found to vary exponentially near the phase change fronts. For cold air injection into a bed initially above the phase change temperature, a second wave was observed ahead of the phase change front that can be described as a broadening traveling thermal wave due to diffusion/dispersion. For hot air injection into a packed bed of solidified PCM capsules initially at a temperature below the phase change temperature, the thermal waves in the cold region showed isotherm velocity retardation due to incomplete thawing. A shrinking core model of the melting or solidification of the PCM in the capsules was developed to document the internal heat transfer constraints within the capsules. The results of that study support the conclusion that slower wave velocities occur due to partial melting.

Numerical Simulation on Phase-Change Heat Transfer Within Microencapsulated Phase Change Material

2003 ◽  
Author(s):  
Yu Rao ◽  
Guiping Lin
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Control Volume ◽  
Computation Model ◽  
Carrier Fluid ◽  
Phase Change Temperature ◽  
Microencapsulated Phase Change Material ◽  
Change Temperature ◽  
Phase Change Heat Transfer ◽  
Change Material

A source item-based computation model is developed for analysing phase-change heat transfer within Microencapsulated PCM suspending in a flowing carrier fluid to enhance convective heat transfer, with the consideration of phase-change temperature range and varying thermal properties. Solution is obtained by developing a control volume-based finite difference code, in which TDMA method combined with under-relaxation is used to solve a strong nonlinear equation. The code developed for this study can be used for evaluating Microencapsulated PCM suspension and instructing the preparation of Microencapsulated PCM.

Heat Transfer Characteristics of Microencapsulated Phase Change Material Slurry Flows Under a Constant Heat Flux Boundary

2011 ◽  
Author(s):  
James A. Howard ◽  
Patrick A. Walsh
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Phase Change ◽  
Phase Change Material ◽  
Heat Transfer Characteristics ◽  
Phase Change Temperature ◽  
Transfer Characteristics ◽  
Microencapsulated Phase Change Material ◽  
Change Temperature ◽  
Change Material

This paper investigates laminar heat transfer characteristic of two-phase microencapsulated phase change material (MPCM) suspension flows within mini-channels under a constant wall heat flux boundary. Capsules containing paraffin wax with phase change temperature between 35.1°C and 44°C are examined and found to be well suited for electronics cooling applications using liquid cold plate technologies. In particular, it is shown that the large thermal capacity of MPCM slurries around the phase change temperature can lead towards greater isothermality of isoflux systems, a characteristic of significant interest to telecommunication, laser and biomedical applications. The principal focus of the study is to examine heat transfer characteristics within standard tube flow geometries, quantify the heat transfer augmentation/degradation observed and finally, elucidate the mechanisms from which these result. Through the study volume concentrations of the MPCM slurry were varied between 30.2% and 5.03%. High resolution local heat transfer measurements were obtained using infrared thermography and results presented in terms of local Nusselt number versus inverse Graetz parameter. These spanned both the thermal entrance and the fully developed flow regions with inverse Graetz number ranging from 10−3 to 100. Results show that significant heat transfer enhancements are attainable via the use of MPCM slurries over conventional single phase coolants. Overall, the study highlights mechanisms that lead to significant heat transfer enhancements in heat exchange devices employing micro-encapsulated phase change material slurries.

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

Energies ◽  
2020 ◽  
Vol 13 (23) ◽  
pp. 6455
Author(s):  
Yue Hu ◽  
Rui Guo ◽  
Per Kvols Heiselberg ◽  
Hicham Johra
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Phase Change ◽  
Building Energy ◽  
Heat Transfer Process ◽  
Strong Impact ◽  
Phase Change Temperature ◽  
Change Temperature ◽  
Modelling Methods

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.

A Study on the Cooling Characteristics of TMA Clathrate Compound with Additives

2006 ◽  
Vol 326-328 ◽  
pp. 1275-1278 ◽  
Author(s):  
Chang Oh Kim ◽  
Jin Heung Kim ◽  
Nak Kyu Chung
Keyword(s):  
Heat Source ◽  
Phase Change ◽  
Specific Heat ◽  
Freezing Point ◽  
Phase Change Temperature ◽  
Source Temperature ◽  
Heat Source Temperature ◽  
Clathrate Compound ◽  
Supercooling Degree ◽  
Change Temperature

This study aims to find out cooling characteristics of TMA 25wt%-water clathrate compound with ethanol such as supercooling, phase change temperature and specific heat. For this purpose, ethanol is added as per weight concentration and cooling experiment is performed at -6, -7 and -8, cooling heat source temperature, and it leads the following result. (1) Phase change temperature is decreased due to freezing point depression phenomenon. Especially, it is minimized as 5.1 and 5.0, 3.8 according to cooling source temperature in case that 0.5wt% of ethanol is added. (2) If 0.5wt% of ethanol is added, average supercooling degree is 0.9 and minimum supercooling is 0.8, 0.7 according to cooling heat source temperature. The restraint effect of supercooling is shown. (3) Specific heat shows tendency to decrease if ethanol is added. It is 3.013~3.048 kJ/kgK according to cooling heat source temperature if 0.5wt% of ethanol is added. Phase change temperature higher than that of water and inhibitory effect against supercooling can be confirmed through experimental study on cooling characteristics of TMA 25wt%-water clathrate compound by adding additive, ethanol.

scholarly journals Experimental Study on Flow Characters of Salt Hydrate Slurry in Phase Change Temperature Range

2017 ◽  
Vol 21 (5) ◽  
pp. 15-23
Author(s):  
Muhammad Irsyad ◽  
Yuli S. Indartono ◽  
Ari D. Pasek ◽  
Willy Adriansyah
Keyword(s):  
Experimental Study ◽  
Phase Change ◽  
Salt Hydrate ◽  
Phase Change Temperature ◽  
Temperature Range ◽  
Change Temperature
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