For a heat exchanger, define ΔTmax = Th,in − Tc,in, the hot-inlet minus cold-inlet temperature. ΔTmin denotes the minimum local temperature difference; LMTD is the log mean temperature difference. Cmin and Cmax are the minimum and maximum heat capacity rates. The theoretical maximum possible heat transfer Qmax is
Cmin ΔTmax
The smaller heat-capacity stream limits heat transfer. Thus \(Q_{max}=C_{min}(T_{h,in}-T_{c,in})=C_{min}\Delta T_{max}\).
Important Questions from Heat Exchanger Analysis
The logarithmic mean temperature difference for parallel flow heat exchangers is
The fin effectiveness can be enhanced by selecting _____ value of heat transfer co-efficient.
A cold liquid enters a counter flow heat exchanger at 15 deg at a rate of 8 kg/s. A hot stream of the same liquid enters the heat exchanger at 75 deg at 2 kg/s. Assuming the specific heat of the fluid as 4 kJ/kg.°C, determine the maximum heat transfer rate.
For the same inlet and exit temperatures of the hot and cold fluids, the Log mean temperature difference (LMTD) is
In a heat exchanger, the hot liquid enters with a temperature of 180°C and leaves at 160°C. The cooling fluid enters at 30°C and leaves at 110°C. The capacity ratio of the heat exchanger is
