In a cooling tower, water becomes cool by________________?

Related Mcqs:

1. A cube, sphere & a thin circular plate (all having same mass and made of same material) are all heated to 300°C and allowed to cool in natural air. Which one will cool the slowest ?

   A. Cube
   B. Plate
   C. Sphere
   D. All will cool at the same rate

2. 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

3. A body cools down from 75°C to 70°C in 10 minutes. It will cool down from 70° C to 65° C in ______________ minutes?

   A. 10
   B. > 10
   C. < 10
   D. Either B. or C., depends on the mass of the body

4. 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

5. Overall heat transfer co-efficient for cooling of hydrocarbons by water is about_________________?

   A. 50 -100 Kcal/hr.m2.°C
   B. 50 -100 W/m2.°K
   C. 50 -100 BTU/hr. ft.2°F
   D. 1000 – 1500 BTU/hr. ft.2°F

6. The outlet temperature of cooling water in a heat exchanger is generally not allowed to exceed above 50°C in industrial practice mainly to avoid_________________?

   A. Its evaporation loss
   B. Excessive corrosion
   C. Uneconomic LMTD
   D. Decrease in heat exchanger efficiency

7. Fresh orange juice contains 12% (by weight) solids and the rest water 90% of the fresh juice is sent to an evaporator to remove water and subsequently mixed with the remaining 10% of fresh juice. The resultant product contains 40% solids. The kg of water removed from 1 kg fresh juice is__________________?

   A. 0.4
   B. 0.5
   C. 0.6
   D. 0.7

8. A long iron rod initially at a temperature of 20°C has one end dipped in boiling water (100°C) at time, t = 0. The curved surface of the rod is insulated so that heat conduction is one dimensional in the axial direction. The temperature at a distance 100 mm from the dipped end becomes 40°C at time, t = 200 s. The same temperature is achieved at a distance of 200 mm from the dipped end at time ___________________?

   A. t = 283 s
   B. t = 356 s
   C. t = 400 s
   D. t = 800 s

9. Mode of heat transfer involved in the cooling of air cooled internal combustion engine is_________________?

   A. Conduction
   B. Natural convection
   C. Forced convection
   D. None of these

10. Three solid objects of the same material and of equal mass-a sphere, a cylinder (length = diameter) and a cube are at 500°C initially. These are dropped in a quenching bath containing a large volume of cooling oil each attaining the bath temperature eventually. The time required for 90% change in temperature is the smallest for_________________?

    A. Cube
    B. Cylinder
    C. Sphere
    D. Equal for all the three