Design and Thermal Analysis of a Microscale Solar Collector
Date Issued
2015
Date
2015
Author(s)
Li, Yu-Lin
Abstract
This study focuses on the design of the microscale solar collector for a medium-temperature Rankine Cycle. The influences of the material of the absorption layer, the working fluid, and the microchannel design on the efficiency of the microscale solar collector are discussed. Three different working fluids are tested: water, ethanol, sulfated castor oil/water emulsion with a mass fraction of 0.3 and sulfated castor oil/water emulsion with a mass fraction of 0.001. Experimental results show that the absorption layer of microscale solar collector needs to be a high emissivity metal material, the higher the emissivity, the more heat from the radiation can be absorbed by the microscale solar collector. We measure the temperature difference between inlet and outlet to calculate the enthalpy increase per unit volume, which serves as a reference to evaluate the thermal performance of the collector. From the results, we find that water and sulfated castor oil/water emulsion with a mass fraction of 0.001 lead to the highest efficiency. On the other hand, increasing the mass fraction to 0.3 brings moderate performance, and ethanol results in the poorest efficiency. Among the four microchannel designs, serpentine and double serpentine channel have the best outcome. This is because serpentine and double serpentine channel have higher overall heat transfer coefficient than oblique-rib and rod-bundle channel. In contrast, there exists dead zones in the diagonal corner of the oblique-rib channel design, where working fluid is stagnant and convection is poor, so the performance of oblique-rib channel is the worst. The temperature difference and the enthalpy difference per unit volume both decreases with the increase of the volumetric flow rate and the efficiency of the microscale solar collector is actually enhance by increasing volumetric flow rate. The results of this study help to elaborate the heat transfer mechanisms and the leverage between different important parameters in the solar collector design, which will serve as the foundation to employ emulsions in a medium-temperature Rankine-cycle system in the future.
Subjects
solar
Rankine cycle
emulsion
microchannel design
thermal analysis
Type
thesis
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