52) The counter-current flow heat exchanger can transfer __________ heat than parallel flow heat exchanger.

53) The freon group of refrigerants are

54) For evaporators and condensers, for the given conditions, the logarithmic mean temperature difference (tm) for parallel flow is __________ that for counter flow.

55) A vapour absorption refrigerator uses __________ as a refrigerant.

56) Thermal conductivity of air increases with rise in temperature.