Which of the following is the most controlling factor for the rate of bubble detachment from the hot solid surface ?

Related Mcqs:

1. 200 kg of solids (on dry basis) is subjected to a drying process for a period of 5000 seconds. The drying occurs in the constant rate period with the drying rate as, Nc = 0.5 × 10-3 kg/m2.s. The initial moisture content of the solid is 0.2 kg moisture/kg dry solid. The interfacial area available for drying is 4 m2/1000 kg of dry solid. The moisture content at the end of the drying period is (in kg moisture/kg dry solid)?

   A. 0.5
   B. 0.05
   C. 0.1
   D. 0.15

2. For a given ambient air temperature with increase in the thickness of insulation of a hot cylindrical pipe, the rate of heat loss from the surface would ?

   A. Decrease
   B. Increase
   C. First decrease and then increase
   D. First increase and then decrease

3. 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

4. The interchange factor for radiation heat transfer from surface ‘x’ to surface ‘y’ in case of an infinite parallel planes with emissivities εx & εy is given by_______________?

   A. εx + εy
   B. εx . εy
   C. 1/εx + 1/εy
   D. (εx + εy)/( εx + εy – εx . εy)

5. In a laboratory test run, the rate of drying was found to be 0.5 x 10-3 kg/m2.s, when the moisture content reduced from 0.4 to 0.1 on dry basis. The critical moisture content of the material is 0.08 on a dry basis. A tray dryer is used to dry 100 kg (dry basis) of the same material under identical conditions. The surface area of the material is 0.04 m2/kg of dry solid. The time required (in seconds) to reduce the moisture content of the solids from 0.3 to 0.2 (dry basis) is______________________?

   A. 2000
   B. 4000
   C. 5000
   D. 6000

6. In case of _____________ boiling, the bubbles formed on a submerged hot surface get absorbed in the mass of the liquid?

   A. Nucleate
   B. Pool
   C. Low pressure
   D. None of these

7. A hot body will radiate heat most rapidly, if its surface is___________________?

   A. White & rough
   B. Black & rough
   C. White & polished
   D. Black & polished

8. Bulk of the convective heat transfer resistance from a hot tube surface to the fluid flowing in it, is __________________?

   A. In the central core of the fluid
   B. Uniformly distributed throughout the fluid
   C. Mainly confined to a thin film of fluid near the surface
   D. None of these

9. 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

10. 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