HEAT TRANSFER IN CONCENTRATED SOLAR POWER SYSTEMS By Nick Smith
INTRODUCTION Concentrating Solar Power Systems (CSPs) focus a large area of sunlight onto a small area. Unlike photovoltaic systems, the sun's energy is not directly converted to electricity. Instead it is used to heat a fluid to steam, which in turn powers a turbine.
INTRODUCTION (CONT. ) Parabolic Solar Trough Power Plant in Israel
SCHEMATIC DRAWINGS
OBJECTIVE Use a simplified Heat Transfer Approach to find the optimum fluid, and length of the parabolic trough.
ASSUMPTIONS q” is evenly distributed Radiation from the across the tubing sun can be Fluid enters tube at approximated ambient temperature, (normalizing for the earth's surface area) 20°C as 680 W/m 2 Effects of the tubing material are negligible Parabola perfectly reflects energy and To function properly, the can be average fluid approximated as a temperature at exit semi-circle should be 400°C Flow-rate is 0. 2 kg/s
APPROACH The heat flux on the tube is equal to the solar heat flux over a semi-circle of 2. 5 m diameter
CALCULATIONS A simple energy balance equation will now give us the ideal length for each potential fluid: Lengths of various materials, using average Cp: Water: 130 m Oil: 71 m Mercury: 3. 85 m
CONCLUSIONS While Mercury would be the ideal material, it is hazardous and expensive, so oil should be used, as it is almost twice as efficient as water. More precise calculations should be done using different types of oil to find the most ideal material, perhaps a mixture with mercury would provide the best properties.
APPENDIX A more complete of heat transfer in CSP systems is available here: http: //pointfocus. co m/images/pdfs/salt w-troughs. pdf Pictures and drawings are courtesy of Andrew Buck, modified by myself
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