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Heat Transfer Test - 7
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Heat Transfer Test - 7
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  • Question 1/10
    4 / -1

    Which of the following is having the lowest value of overall heat transfer coefficient?

    Solutions

    Overall heat transfer coefficient for air condensers is 780 W/m2 K while that of steam condensers, air to low viscosity liquids and feed water heaters are 5000 W/m2 K, 600 W/m2 K and 8500 W/m2 K.

     

  • Question 2/10
    4 / -1

    A cross-flow type air heater has an area of 50 cm2. The overall heat transfer coefficient is 100 W/m2 K and the heat capacity of both hot and cold streams is 1000 W/m K. The value of NTU is

    Solutions

    NTU = A U/C MIN = 5.

     

  • Question 3/10
    4 / -1

    An oil cooler in a high-performance engine has an outside surface area 0.12 m2 and a surface temperature of 65 degree Celsius. At any intermediate time air moves over the surface of the cooler at a temperature of 30 degree Celsius and gives rise to a surface coefficient equal to 45.4 W/ m 2 K. Find out the heat transfer rate?

    Solutions

    Q = (T2 – T1) A h = 0.12 (65-30) 45.4 = 190.68 W.

     

  • Question 4/10
    4 / -1

    Which of the following statement is incorrect according to heat transfer?

    Solutions

    Heat flows from higher to lower temperature.

     

  • Question 5/10
    4 / -1

    Consider a convective heat flow to water at 75 degree Celsius from a cylindrical nuclear reactor fuel rod of 50 mm diameter. The rate of heat generatioN is 50000000 W/m3 and convective heat transfer coefficient is I kW/m2 K. The outer surface temperature of the fuel element would be

    Solutions

    t w = t a + q g R/ 2h.

     

  • Question 6/10
    4 / -1

    For a cylindrical rod with uniformly distributed heat sources, the thermal gradient at half the radius location will be

    Solutions

    t = t w + q g (R2 – r2)/4k. (d t /d r) r = R/2 = 1/2(d t/d r) r = R.

     

  • Question 7/10
    4 / -1

    Water (specific heat = 4 k J/kg K) enters a cross flow exchanger (both fluids unmixed) at 15 degree Celsius and flows at the rate of 7.5 kg/s. It cools air (C P = 1 k J/kg K) flowing at the rate of 10 kg/s from an inlet temperature of 120 degree Celsius. For an overall heat transfer coefficient of 780 k J/m2 hr degree and the surface area is 240 m2, determine the NTU

    Solutions

    NTU = U A/C MIN = 5.2.

     

  • Question 8/10
    4 / -1

    A heat exchanger to preheat oil for a furnace was designed without considering the possibility of scale formation, and the overall heat transfer coefficient based on the fuel oil side was 3200 k J/m2 hr degree. What would be the corrected coefficient of heat transfer if a fouling factor of 0.00025 m2 hr degree/k J for the fuel oil is taken into account?

    Solutions

    U = 1/ (R + 1/h S).

     

  • Question 9/10
    4 / -1

    Which of the following is the value of fouling factor for engine exhaust?

    Solutions

    Its unit is m2 hr K/kcal and it represents the reciprocal of the scale coefficient i.e. heat transfer.

     

  • Question 10/10
    4 / -1

    The value of fouling factor for industrial liquids is ______

    Solutions

    Its unit is m2 hr K/kcal and it represents the reciprocal of the scale coefficient i.e. heat transfer.

     

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