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Heat Transfer Test - 6
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Heat Transfer Test - 6
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  • Question 1/10
    4 / -1

    The condensate film runs down a vertical flat surface where saturated steam is allowed to condense. Condensation’s local coefficient of heat transfer

    Solutions

    It decreases with increasing thickness of condensate film.

     

  • Question 2/10
    4 / -1

    A steam condenser is transferring 250 k W of thermal energy at a condensing temperature of 65 degree Celsius. The cooling water enters the condenser at 20 degree Celsius with a flow rate of 7500 kg/hr. If overall heat transfer coefficient for the condenser surface is 1250 W/m2 K, what surface area is required to handle this load?

    Solutions

    Q = U A α m. So, A = 7.08 m2.

     

  • Question 3/10
    4 / -1

    What is the value of overall heat transfer coefficient ammonia condensers?

    Solutions

    It is an electrical device that stores a vast amount of energy.

     

  • Question 4/10
    4 / -1

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

    Solutions

    Feed water heaters have an overall heat transfer coefficient of 8500 W/m2K, whereas steam, alcohol condensers, and ammonia condensers have heat transfer coefficients of 5000 W/mK, 630 W/mK and 1400 W/mK.

     

  • Question 5/10
    4 / -1

    For laminar film condensation on a vertical plate, the local heat transfer coefficient at the lower edge of the plate is given by

    Solutions

    The rate of condensation heat transfer is higher at the upper end of the plate than at the lower end.

     

  • Question 6/10
    4 / -1

    The outer surface of a vertical tube is 1.25 m long and outer diameter is 50 mm is exposed to saturated steam at atmospheric pressure. If the tube surface is maintained at 80 degree Celsius by the flow of cooling water through it, determine the rate of heat transfer to the coolant

    Solutions

    v = 0.943 [k 3 p 2 g h f g/δ l (t sat – t s)] 0.25 = 5046.8 W/m 2 k and heat flow rate = 19879 W.

     

  • Question 7/10
    4 / -1

    What is the value of the overall heat transfer coefficient for air to heavy tars and liquid?

    Solutions

    It is an incompressible fluid which has constant volume independent of pressure.

     

  • Question 8/10
    4 / -1

    Exhaust gases (c = 1.12 k J/kg K) flowing through a tubular heat exchanger at the rate of 1200 kg/hr are cooled from 400 degree Celsius to 120 degree Celsius. This cooling is affected by water (c = 4.18 k J/kg K) that enters the system at 10 degree Celsius at the rate of 1500 kg/hr. If the overall heat transfer coefficient is 500 k J/m2 hr degree, what heat exchanger area is required to handle the load for counter flow arrangement?

    Solutions

    (t h 1 – t h 2) = m (t c 2 – t c 1).

     

  • Question 9/10
    4 / -1

    What is the value of the overall heat transfer coefficient for air condensers?

    Solutions

    It consists of an air coil which is used to remove heat from fluids.

     

  • Question 10/10
    4 / -1

    Heat transfer coefficients for natural convection across the surface of a vertical pipe and a vertical flat plate at the same height. What could be the cause(s) of this?

    (i) Same height
    (ii) Both vertical
    (iii) Same fluid
    (iv) Same fluid flow pattern

    Select the correct answer

    Solutions

    The fluids must be same so their flow pattern.

     

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