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Evaluation of the Effectiveness of Base Insulation on the Productivity of a Packed Bed Solar Air Heater


 Effect of bottom surface thermal energy loss for a packed bed solar air heater is investigated using both one dimensional transient as well as steady state models. While the former is solved numerically, closed form solution is obtained for the latter. Effect of variation in base insulation thickness on the system output is studied. For a given bottom insulation thickness, dependence of its effectiveness on various thermo-geometric parameters is also analyzed. It is observed that a collector with an uninsulated base loses about 60 % of the available incident solar energy. In comparison, when the base insulation is as thick as the base wall, i.e., 50 mm here, the base loss fraction drops to nearly 6 %, thus, highlighting the importance of base insulation. Further, it is seen that the efficiency of a particular base insulation thickness lessens with larger length and width of collector, and rises with larger mass flow rate of air flowing through it. This work presents a mathematical tool to calculate appropriate insulation thermal resistance to be applied at the base of packed bed solar air heaters that yields best possible thermal performance alongside minimum insulation cost.