The mcrease in heat dissipation by air blasts is due to increase in______________?

Related Mcqs:

1. The heated parts of an electrical machine dissipate heat into their surroundings by which of the following modes of heat dissipation ?

   A. Conduction
   B. Convection
   C. Radiation
   D. All of the above

2. Hydrogen has a heat transfer co-efficient __________ times that of air?

   A. 1.5
   B. 2.5
   C. 3.5
   D. 4.5

3. D.C. servomotors are used in______________?

   A. purely D.C. control systems
   B. purely AC. control systems
   C. both D.C. and AC. control systems
   D. none of the above

4. With conventional hydrogen cooling it is possible to increase the rating of a single unit to___________?

   A. 50 MW
   B. 100 MW
   C. 200 MW
   D. none of the above

5. In D.C. machines, the ________ in field mmf results in increase in size and cost of machines?

   A. increase
   B. decrease
   C. either of the above
   D. none of the above

6. The heat dissipated by from a surface depends upon its temperature and its characteristics like colour, roughness etc?

   A. conduction
   B. convection
   C. radiation
   D. any of the above

7. On which of the following variables heat convected depends ?

   A. Power density
   B. Temperature difference between heated surface and coolant
   C. Thermal resistivity, density, specific heat
   D. Gravitational constant
   E. All of the above

8. The heat dissipating capability of transformers of ratings higher than 30 kVA in increased by providing which of the following ?

   A. Corrugations
   B. Fins
   C. Tubes
   D. Radiator tanks
   E. All of the above

9. The thermal conductivity of hydrogen is _____________ times that of air?

   A. 2
   B. 3
   C. 5
   D. 7

10. D.C. machines designed with a large value of air gap length have_____________?

    A. worst, ventilation
    B. poor ventilation
    C. better ventilation
    D. none of the above