Heat flux increases with temperature drop beyond the Leiden frost point in the plot of heat flux vs. temperature drop for a boiling liquid, because___________________?

Related Mcqs:

1. 1000 Kg of liquid at 30°C in a well stirred vessel has to be heated to 120°C, using immersed coils carrying condensing steam at 150°C. The area of the steam coils is 1.2 m2 and the overall heat transfer co-efficient to the liquid is 1500 W/m2.°C. Assuming negligible heat loss to the surrounding and specific heat capacity of the liquid to be 4 kJ/kg.°C, the time taken for the liquid to reach desired temperature will be__________________?

   A. 15 min
   B. 22 min
   C. 44 min
   D. 51 min

2. The radiation heat flux from a heating element at a temperature of 800°C, in a furnace maintained at 300°C is 8 kW/m2. The flux, when the element temperature is increased to 1000°C for the same furnace temperature is_____________________?

   A. 11.2 kW/m2
   B. 12.0 kW/m2
   C. 14.6 kW/m2
   D. 16.5 kW/m2

3. In case of _______________ boiling, the liquid temperature is below the saturation temperature and the boiling takes place in the vicinity of the heated surface?

   A. Nucleate
   B. Local
   C. Pool
   D. Saturated

4. As the difference between the wall temperature and bulk temperature increases, the boiling heat transfer co-efficient ?

   A. Continues to increase
   B. Continues to decrease
   C. Goes through a minimum
   D. Goes through a maximum

5. The heat flux in the nucleate boiling regimes is proportional to (where, ΔT = excess temperature) ?

   A. (ΔT)2
   B. (ΔT)4
   C. (ΔT)3
   D. √(ΔT)

6. A hot liquid is kept in a big room. The logarithm of the numerical value of the temperature difference between the liquid and the room is plotted against time. The plot will be very nearly a/an___________________?

   A. Ellipse
   B. Straight line
   C. Parabola
   D. Circular arc

7. 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

8. 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

9. In the free convection regime of pool boiling, the heat flux is proportional to__________________?

   A. Δt1/2
   B. Δt2
   C. Δt5/4
   D. Δt

10. In a boiling curve, the peak heat flux is called the _____________ point?

    A. Nusselt
    B. Leidenfrost
    C. Boiling
    D. Burnout