Question

A flat-plate solar collector is used to heat atmospheric air flowing through a rectangular channel. The bottom surface of the channel is well insulated, while the top surface is subjected to a uniform heat flux 96,which is due to the net effect of solar radiation absorption and heat exchange between the absorber and cover plates. W Transparent cover plate Absorber plate Rectangular channel Air Tmi, m Beginning with an appropriate differential control volume, obtain an equation that could be used to determine the mean air temperature Tm(x) as a function of distance along the channel. Solve this equation to obtain an expression for the mean temperature of the air leaving the collector. With air inlet conditions of m=0.1 kg/s and Tm.i = 40°C, what is the air outlet temperature, in °C, if L = 2.4 m, w = 1 m, and 9% = 700 W/m2? The specific heat of air is cp = 1008 J/kg.K. Tm,0 = i

Answer 1

Sol. Given Dală • A feat atmospheric plate S heat s to used be flat plate Solar Collector is used to heat a air flowing through a rectangular channel. top surface is subjected to a veuform heat flux ato • Begining with an appropriate astrol volume. differential Control vol and obtaining an equation that could be used Determines the mean air temperature TMC). with air inlet Conditions of n =ool kg Isec & This = 40 we have to Rind the air out het temperature in if 2.2.4 Walm and no = 700 w/n". The speu fic heat of air is cpa is cp=w08, lkg.k heat of air Absorber Rectangular Channel Transparent Cover plate) Considering the Expression for differential Control Volume platt Ein = out mcptm t quo (w. a) = mcp (Tm td Tm) de inte avslu Tonym From the expression, separating and integrating between the limits of x=0&x Imix) TM, i + avo" (w.) ince Tm, o = Tm,it wo (W.L) ② Now what are the values are given in the above be we are substituting in the top of @ Tmio = 4ó + 700 (2.4x1) x 40+ 16.666 0.181008 Tm, o = 56-6660 The required outlet temperature is getting Imio = 56.66 €