11. For evaporators and condensers, for the given conditions, the logarithmic mean temperature difference ™ for parallel flow is __________ that for counter flow.
A. equal to
B. less than
C. greater than
12. A vapour absorption refrigerator uses __________ as a refrigerant
A. water
B. ammonia
C. freon
D. aqua-ammonia
13. Thermal conductivity of air increases with rise in temperature.
A. Correct
B. Incorrect
14. The material of pipelines for a system using ammonia as a refrigerant should be copper.
A. Yes
B. No
15. The wave length corresponding to the maximum energy is inversely proportional to the absolute temperature. This statement is called Planck’s law.
A. Yes
B. No
16. Which of the following refrigerant has the highest freezing point.
A. Ammonia
B. Carbon dioxide
C. Sulphur dioxide
D. R-12
17. Air conditioning means
A. cooling
B. heating
C. dehumidifying
D. all of these
18. The emissivity for a black body is
A. 0
B. 0.5
C. 0.75
D. 1
19. Which of the following would lead to a reduction in thermal resistance?
A. In conduction, reduction in the thickness of the material and an increase in thermal conductivity.
B. In convection, stirring of the fluid and cleaning the heating surface.
C. In radiation, increasing the temperature and reducing the emissivity.
D. all of the above
20. The ratio of the thickness of the thermal boundary layer to the thickness of hydrodynamic boundary layer is equal to (Prandtl number)n, where n is equal to
A.-1/3
B.-2/3
C.1
D.-1