Water (Cp = 4.18 kJ/kg.K) at 80°C enters a counter flow heat exchanger with a mass flow rate of 0.5 kg/s. Air (Cp = 1 kJ/kg.K) enters at 30°C with a mass flow rate of 2.09 kg/s. If the effectiveness of the heat exchanger is 0.8, the LMTD (in °C) is
10
Both heat-capacity rates equal 2.09 kW/K. Effectiveness 0.8 gives a 40°C temperature change for each stream: hot outlet 40°C and cold outlet 70°C. Both counterflow end differences are 10°C, so LMTD=10°C.
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
