Abstract
Due to an increased awareness of climate change and other environmental issues, methods to reduce the energy consumption of buildings has become of great importance. One way to improve the efficiency of a building is to use thermal storage material. A recent thermal storage strategy is to use phase change material (PCM) which allows for the storage and release of thermal energy. One of the main advantages of using PCM over traditional thermal storage (like concrete) is that PCM can achieve the same level of thermal storage as concrete while using less material. Using PCM can also reduce and delay peak load, improve the thermal comfort, and reduce the overall energy consumption of a building. One of the main parameters that affect the performance and effectiveness of PCM in buildings is the convective heat transfer between a PCM wall and room air. Current convective heat transfer coefficients used in whole building simulation and in building codes (such as ASHRAE) may not be adequate for PCM applications. The present study investigates thermal performance of a vertical PCM panel. The investigation includes experiments using laser MachZehnder Interferometry (MZI) and a comparative numerical study using computational fluid dynamics (CFD). The study focuses on a vertical flat plate filled with PCM (soy wax) undergoing transient convective heat transfer by natural convection while the PCM solidifies. A novel method was developed to make interferometric surface temperature measurements using partial fringes as a reference temperature. The experimental results show a deviation from predicted heat transfer coefficients from established correlation and significant subcooling was observed as a temperature jump. The subcooling effect was reproduced using CFD by implementing the speed of crystallization within the PCM cavity.
Highlights
Due to an increased awareness of climate change and other environmental issues, methods to reduce the energy consumption of buildings has become of great importance
The present study investigates thermal performance of a vertical phase change material (PCM) panel
A recent thermal storage strategy is to use phase change material (PCM) which allows for the storage and release of thermal energy
Summary
The results from the Mach-Zehnder Interferometer (MZI) have a degree of uncertainty from a variety of sources. The current uncertainty analysis was performed on the results from the finite fringe interferogram image #470 which corresponds to 40 minutes into the experiment. This case was chosen because it represents typical experimental parameters and offers a range of variables to investigate the errors of the measurements. Where appropriate the average of the 17 scans was used to determine the uncertainty in derived parameters such as convective heat transfer, Rayleigh number etc. The finite fringe interferograms were set at a spacing of d = 1 mm while the model was unheated. It was determined that the maximum the fringe alignment could be off by is approximately φ = 1° With all of these parameters known, the fringe shift error was calculated to be ±0.014. Letting wR be the uncertainty of R and w1, w2, w3,...,wn be the uncertainty of the independent variables, the uncertainty of R can be expressed as follows:
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