Hot water (0.01 m3 /min) enters the tube side of a counter current shell and tube heat exchanger at 80°C and leaves at 50°C. Cold oil (0.05 m3/min) of density 800 kg/m3 and specific heat of 2 kJ/kg.K enters at 20°C. The log mean temperature difference in °C is approximately ?

Related Mcqs:

1. In a parallel flow heat exchanger, if the outlet temperature of hot and cold fluids are the same, then the log mean temperature difference (LMTD) is_________________?

   A. Minimum
   B. Maximum
   C. Zero
   D. Infinity

2. It is desired to concentrate a 20% salt solution (20 kg of salt in 100 kg of solution) to a 30% salt solution in an evaporator. Consider a feed of 300 kg/min at 30°C. The boiling point of the solution is 110°C, the latent heat of vaporisation is 2100 kJ/kg and the specific heat of the solution is 4 kJ/kg.K. The rate at which the heat has to be supplied in (kJ/min) to the evaporator is____________________?

   A. 3.06 × 105
   B. 6.12 × 105
   C. 7.24 × 105
   D. 9.08 × 105

3. Air is to be heated by condensing steam. Two heat exchangers are available (i) a shell and tube heat exchanger and (ii) a finned tube heat exchanger. Tube side heat transfer area are equal in both the cases. The recommended arrangement is________________?

   A. Finned tube heat exchanger with air inside and steam outside
   B. Finned tube heat exchanger with air outside and steam inside
   C. Shell and tube heat exchanger with air inside tubes and steam on shell side
   D. Shell and tube heat exchanger with air on shell side and steam inside tubes

4. For the same heat load and mass flow rate in the tube side of a shell and tube heat exchanger, one may use multipass on the tube side, because it__________________?

   A. Decreases the pressure drop
   B. Decreases the outlet temperature of cooling medium
   C. Increases the overall heat transfer coefficient
   D. None of these

5. The inside heat transfer co-efficient in case of turbulent flow of liquid in the tube side in a 1-2 shell and tube heat exchanger is increased by ______________ times, when the number of tube passes is increased to 8?

   A. 20.8
   B. 40.8
   C. 40.4
   D. 20.4

6. In a shell and tube heat exchanger, the tube side heat transfer co-efficient just at the entrance of the tube is_________________?

   A. Infinity
   B. Zero
   C. Same as average heat transfer co-efficient for tube side
   D. None of these

7. Log mean temperature difference (LMTD) cannot be used, if ___________________?

   A. Heat transfer co-efficient over the entire heat exchanger is not constant
   B. There exists an unsteady state
   C. The heat capacity is not constant and there is a phase change
   D. None of these

8. A metal ball of radius 0.1 m at a uniform temperature of 90°C is left in air at 30°C. The density and the specific heat of the metal are 3000 kg/m3 and 0.4 kJ/kg.K respectively. The heat transfer co-efficient is 50 W/m2.K Neglecting the temperature gradients inside the ball, the time taken (in hours) for the ball to cool to 60°C is_________________?

   A. 555
   B. 55.5
   C. 0.55
   D. 0.15

9. In case of parallel flow heat exchanger, the lowest temperature theoretically attainable by the hot fluid is _____________ the outlet temperature of the cold fluid?

   A. Equal to
   B. More than
   C. Less than
   D. Either more or less than (depending upon the fluid)

10. Steam is to be condensed in a shell and tube heat exchanger, 5 m long with a shell diameter of 1 m. Cooling water is to be used for removing the heat. Heat transfer co-efficient for the cooling water, whether on shell side or tube side is the same. The best arrangement is_____________?

    A. Vertical heat exchanger with steam on tube side
    B. Vertical heat exchanger with steam on shell side
    C. Horizontal heat exchanger with steam on tube side
    D. Horizontal heat exchanger with steam on shell side