In a well-insulated heat exchanger, the overall heat transfer coefficient is 6.6 kW/m2.°C and the total effective heat transfer area is 1.5 m2. The temperature difference between the inlet and exit of the minimum fluid (the fluid with minimum thermal capacity) is 60 ?C and the corrected LMTD of the heat exchanger is 30 °C. Which one about the thermal capacity of the maximum fluid (the fluid with the maximum thermal capacity) is correct?A.The given information is not enough to answer this questionB. Cmax = 4950 W/°CC .Cmax lt; 4950 W/°CD. Cmax gt; 4950 W/°C
I assume the temperature difference for minimum fluid is for cold or hot stream only. Not the difference between them (the cold and hot). U = 6.6 kW/m^2.°C A = 1.5 m^2 ΔT_min = 60 deg. C LMTD = 30 deg. C Q = U*A*LMTD Q = 6.6*1.5*30 Q = 297 kW Heat transfer from cold/hot fluid. Q = Cp_min*ΔT_min Cp_min = 4950 W/°C With, LMTD = ΔT2 - ΔT1 / ln(ΔT2/ΔT1) 30 = ΔT2 - ΔT1 / ln(ΔT2/ΔT1) We have only one equation, with two unknows, temperatur inlet and outlet for maximum fluid, thus it can't be solved. Cp_,max = Q/ΔT_max Cp_max can't be solved because ΔT_max is unknown. So the answer may be A or D. A. The given information is not enough to answer this question D. Cmax > 4950 W/°C However if one just need for range capacity, then the answer is D.
