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GATE ME: Heat Transfer Champion Quiz 4
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Question 1
NTU method is used to calculate:
Question 2
A solid sphere of radius r1 = 20 mm is placed concentrically inside a hollow sphere of radius r2 = 30 mm as shown in the figure.
The view factor F21 for radiation heat transfer is
The view factor F21 for radiation heat transfer is
Question 3
For infinite parallel planes with emissivities 
and 
, the interchange factor for radiation from surface 1 to surface 2 is given by
and , the interchange factor for radiation from surface 1 to surface 2 is given by Question 4
In a heat exchanger, it is observed that ΔT1=ΔT2, where ΔT1 is the temperature difference between the two single phase fluid streams at one end and ΔT2 is the temperature difference at the other end. This heat exchanger is
Question 5
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 6
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 7
Air enters a counter-flow heat exchanger at 70 °C and leaves at 40 °C. Water enters at 30 °C and eaves at 50 °C. The LMTD in deg. C is
Question 8
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
The exit temperature (in °C) for the cold fluid is
Question 9
A thin metal plate is exposed to solar radiation. The air and the surroundings are at 30 °C. The heat transfer coefficient by free convection from the upper surface of the plate is 17.4 W/m2K. The plate has an absorptivity of 0.9 at solar wavelength and an emissivity of 0.1 at the long wavelength. Neglecting any heat loss from the lower surface, determine the incident solar radiation intensity in kW/m2, if the measured equilibrium temperature of the plate is 50 °C. Stefan Boltzmann constant is 5.67×10-8 W/m2K4.
Question 10
Hot oil is cooled from 80 to 50 °C in an oil cooler which uses air as the coolant. The air temperature rises from 30 to 40 °C. the designer uses a LMTD value of 26 °C. the type of heat exchanger is
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Jul 16ESE & GATE ME
