A Study on Design Parameters in Two-Phase Flow Natural Circulation Used in Solar Energy Collectors

• Main Authors: Woan-Lin Chen, 陳琬琳
• Other Authors: Chun-Kuan Shih
• Format: Others
• Language: zh-TW
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/81419037187135754120

碩士 === 國立清華大學 === 工程與系統科學系 === 88 === Major components in solar energy heaters consist of solar energy collector, circulating loop pipes, and water tank. This thesis formulates the basic theoretical models for solar energy collector and analyses the heat transfer between solar panel and water tank of two-phase flow natural circulation-type of solar energy heater designs. There are two different designs of solar energy collector, loop-model and heatpipe-model. First we try to find the average temperature of solar collector fins by fundamental energy balances, then calculates the panel heat loss in the two models. Second we calculate the collected energy of the solar panel and different parameters of working fluid such as mass flow rate, temperature, quality and superheat as it enters into water tank. Finally, we assume a solar flux-time distribution and divide it into many time steps and integrate the amount of energy of working fluid entering into the water tank to obtain the temperature inside the water tank. From the results of the loop model and the heatpipe model, we found that the heat loss from the solar panel is strongly related to its temperature. The higher temperature of the solar panel results in more heat loss. Lower panel temperatures can be obtained by choosing working fluid with lower saturated temperatures, by increasing the numbers of pipes, and by increasing the filling percentage of working fluid. From the energy balance consideration of the water tank heat exchanger model, we noticed that the performance of the heat exchanger depends on the temperature difference of working fluid and water. Larger temperature differences imply higher heat transfer rates and can be achieved by choosing working fluid with higher saturated temperatures and by decreasing the filling percentage of working fluid.