摘要
Flat plate air collector is a type of heat exchanger which absorbs radiated solar energy and exchanges it to heat.According to low efficiency of this type of collectors,a suitable approach is investigated in this paper so as to increase thermal performance of the system.Thermal efficiency of solar collector for two models C1(without fins)and C2(with fins)both of 1 m^2 surface area with forced convection flow is studied theoretically and experimentally.Rectangular fins are attached over back board in air channel to create turbulence in air flow.In order to measure air temperature,17 thermal sensors(LM35)are exploited,among which 11 were mounted on absorber plate and the remaining 6 on the back board.Physical design of experimental model are performed in Solidwork and programming of theoretical work in Matlab software.In this research,a fan with constant mass flow rate of 0.033 kg/s is utilized for producing air flow.Results indicate that applying fins in air channel not only reduces Nusselt number from 19.67 to 16.23,but also due to decreasing hydraulic diameter and creating air flow turbulence,causes increase of heat transfer coefficient from absorber plate to air flow and consequently reduction of total heat loss and higher outlet air temperatures.Average difference of outlet air temperature between experimental and theoretical results for both collectors(C1 and C2)was recorded respectively as 7.6% and 9.4%.Thermal efficiency was respectively calculated 30% and 51% for experimental types with and without fins and 33% and 55% for those of theoretical work which generally seem reasonable.
