The rate of heat transfer through a pipe wall is given by, q = 2π k (Ti – T0)/ln (ri/r0). For cylinder of very thin wall, q can be approximated by__________________?

Related Mcqs:

1. A 10 cm dia steam pipe, carrying steam at 180°C, is covered with an insulation (conductivity = 0.6 W/m.°C). It losses heat to the surroundings at 30°C. Assume a heat transfer co-efficient of 0.8 W/m2.°C for heat transfer from surface to the surroundings. Neglect wall resistance of the pipe and film resistance of steam. If the insulation thickness is 2 cms, the rate of heat loss from this insulated pipe will be__________________?

   A. Greater than that for un-insulated steam pipe
   B. Less than that of the un-insulated steam pipe
   C. Equal to that of the un-insulated steam pipe
   D. Less than the steam pipe with 5 cms insulation

2. Extended heat transfer surface like fins are used to increase the heat transfer rate. Fin efficiency is defined as the ratio of heat transferred across the fin surface to the theoretical heat transfer across an equal area held at the________________?

   A. Surrounding temperature
   B. Average temperature of the fin
   C. Temperature of the fin end
   D. Constant temperature equal to that of the base

3. The inner wall of a furnace is at a temperature of 700°C. The composite wall is made of two substances, 10 and 20 cm thick with thermal conductivities of 0.05 and 0.1 W.m-1.°C- 1 respectively. The ambient air is at 30°C and the heat transfer co-efficient between the outer surface of wall and air is 20 W.m-2.°C-1. The rate of heat loss from the outer surface in W.m-2is__________________?

   A. 165.4
   B. 167.5
   C. 172.5
   D. 175

4. The Sieder-Tate correlation for heat transfer in turbulent flow in pipe gives Nu α Re0.8, where, Nu is the Nusselt number and Re is the Reynolds number for the flow. Assuming that this relation is valid, the heat transfer co-efficient varies with the pipe diameter D. as _________________?

   A. D-1.8
   B. D-0.2
   C. D0.2
   D. D1.8

5. In case of heat transfer by conduction in a hollow cylinder, ______________ mean area is used to calculate the heat transfer rate?

   A. Geometric
   B. Arithmetic
   C. Logarithmic
   D. Either A., B. or C.

6. Fouling factor for a heat exchanger is given by (where, U1 = heat transfer co-efficient of dirty surface U2 = heat transfer co-efficient of clean surface) ?

   A. U1 – U2
   B. 1/U1 – 1/U2
   C. 1/U2 – 1/U1
   D. U2 – U1

7. Which of the following situations can be approximated to a steady state heat transfer system ?

   A. A red hot steel slab (having outside surface temperature as 1300°C) exposed to the
   atmospheric air at 35°C
   B. 10 kg of dry saturated steam at 8 kgf/cm2 flowing through a short length of stainless steel pipe
   exposed to atmospheric air at 35°C
   C. Boiling brine kept in open vessel when the bottom surface temperature of the vessel is
   maintained constant at 180°C
   D. A sub-cooled refrigerant liquid at 8°C flowing at the rate of 6 Kg/minute through a copper
   pipe exposed to atmospheric air at 35°C

8. Heat transfer by conduction results due to the transfer of free electrons, kinetic energy & vibrational energy from one molecule to another. Conduction heat transfer cannot take place____________________?

   A. Between two bodies in physical contact with each other
   B. Between two bodies not in physical contact with each other
   C. From one part of a body to the another part of the same body
   D. Both B & C

9. In pipe flow, heat is transferred from hot wall to the liquid by__________________?

   A. Conduction only
   B. Forced convection only
   C. Forced convection and conduction
   D. Free and forced convection

10. For shell and tube heat exchanger, with increasing heat transfer area, the purchased cost per unit heat transfer area___________________?

    A. Increases
    B. Decreases
    C. Remain constant
    D. Passes through a maxima