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GATE 2020: Heat Transfer Quiz 4

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Question 1

For a heat exchange, ΔTmax is the maximum temperature difference and ΔTmin is the minimum temperature difference between the two fluids. LMTD is the log mean temperature difference. Cmin and Cmax are the minimum and the maximum heat capacity rates. The maximum possible heat transfer (Qmax) between the two fluids is

Question 2

Two streams of fluids of unit constant specific heat and unit mass flow rate exchange thermal energy in a heat exchanger. The inlet temperature of hot and coldfluid streams are 300 0C and 30 0C respectively. The effectiveness of the heat exchanger if the outlet temperature of both the fluid are equal

Question 3

In a counter flow heat exchanger, hot fluid enters at 60oC and cold fluid leaves at 30oC. Mass flow rate of the hot fluid is 1 kg/s and that of the cold fluid is 2 kg/s. Specific heat of the hot fluid is 10kJ/kgK and that of the cold fluid is 5 kJ /kgK. The Log Mean Temperature Difference (LMTD) for the heat exchanger in is

Question 4

The logarithmic mean temperature difference (LMTD) of a counter flow heat exchanger is 20 °C. The cold fluid enters at 20 °C and the hot fluid enters at 100 °C. Mass flow rate of the cold fluid is twice that of the hot fluid. Specific heat at constant pressure of the hot fluid is twice that of the cold fluid. The exit temperature of the cold fluid

Question 5

In a parallel flow heat exchanger operating under steady state, the heat capacity rates (product of specific heat at constant pressure and mass flow rate) of the hot and cold fluid are equal. The hot fluid, flowing at 1 kg/s with Cp = 4 kJ/kgK, enters the heat exchanger at 102 °C while the cold fluid has an inlet temperature of 15 °C. The overall heat transfer coefficient for the heat exchanger is estimated to be 1 kW/m2K and the corresponding heat transfer surface area is 5 m2. Neglect heat transfer between the heat exchanger and the ambient. The heat exchanger is characterized by the following relation: 2ε = 1 - exp(-2NTU).
The exit temperature (in °C) for the cold fluid is

Question 6

Water at 80 °C enters a counterflow heat exchanger with a mass flow rate or 0.5 kg/s. Air enters at 30 °Cwith a mass flow rate of 2.09 kg/s. If the effectiveness of the heat exchanger is 0.8, the LMTD (in °C) is
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