Heat Transfer (HT)

Q:   A plane slab of thickness L and thermal conductivity k is heated with a fluid on one side (P), and the other side (Q) is maintained at a constant temperature, TQ of 25∘C, as shown in the figure. The fluid is at 45∘C and the surface heat transfer coefficient, h, is 10 W/m² K . The steady state temperature, Tp, (in∘C) of the sid e which is exposed to the fluid is _______ (correct to two decimal places).

Q:   The peak wavelength of radiation emitted by a black body at a temperature of 2000 K is 1.45 µm. If the peak wavelength of emitted radiation changes to 2.90 µm, then the temperature (in K) of the black body is

• A:  500
• B:  1000
• C:  4000
• D:  8000

Q:   An engine operates on the reversible cycle as shown in the figure. The work output from the engine (in kJ/cycle) is ______ (correct to two decimal places).

Q:   Saturated steam at 100∘C condenses on the outside of a tube. Cold fluid enters the tube at 20∘C and exits at 50∘C. The value of the Log Mean Temperature Difference (LMTD) is _____________°C.

Q:   Two black surfaces, AB and BC, of lengths 5 m and 6 m, respectively, are oriented as shown. Both surfaces extend infinitely into the third dimension. Given that view factor F₁₂=0.5, T₁ = 800K, T₂ = 600K, T_surrounding=300K and Stefan Boltzmann constant, σ=5.67×10^-8W/(m²K⁴), the heat transfer rate from surace 2 to the surrounding environment is _____________kW

Q:   Heat is genrated uniformly in a long solid cylindrical rod (diameter = 10 mm) at the rate of 4×10³W/m³. The thermal conductivity of the rod material is 25 W/m.K. Under steady state conditions, the temperature diffrence between the centre and the surface of the rod is _____________ºC

Q:   The heat loss from a fin is 6 W. The effectiveness and efficiency of the fin are 3 and 0.75, respectively. The heat loss (in W) from the fin, keeping the entire fin surface at base temperature, is__________

Q:   The emissive power of a blackbody is P. If its absolute temperature is doubled, the emissive power becomes

• A:  2 P
• B:  4 P
• C:  8 P
• D:  16 P

Q:   In a counter-flow heat exchanger, water is heated at the rate of 1.5kg/s from 40 ºC to 80 ºC by an oil entering at 120 ºC and leaving at 60 ºC. The specific heats of water and oil are 4.2 kj/kg⋅K and are 2 kj/kg⋅K, respectively. The overall heat transfer coefficient is 400 W/m²k. The required heat transfer surface area (in m2) is

• A:  0.104
• B:  0.022
• C:  10.4
• D:  21.84

Q:   A plastic sleeve of outer radius r0=1mm covers a wire (radius r = 0.5 mm) carrying electric current. Thermal conductivity of the plastic is 0.15 W/m-K. The heat transfer coefficient on the outer surface of the sleeve exposed to air is 25W/m²−K. Due to the addition of the plastic cover, the heat transfer from the wire to the ambient will

• A:  increase
• B:  remain the same
• C:  decrease
• D:  be zero