Engineering :: Renewable Sources of Energy

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71.

Water circulates in a thermosiphon hot-water heating system by

A.	forced circulation using a pump	B.	the fact that hot water is less dense than cold water
C.	the fact that cold water is less dense than hot water	D.	gravity flow from top of the collector to the lower storage tank

72.

An advantage of using copper for the absorber plate is that

A.	it has a higher thermal conductivity than other metals	B.	it weights less than steel or aluminium
C.	it is cheaper than steel or aluminium	D.	it will not corrode easily so that water can be used as heat-exchange fluid.

73.

Evacuated flat-plate collectors are better than non-evacuated ones at high operating temperatures because

A.	convective heat losses from the top cover plate are greatly reduced	B.	convective heat losses from the absorber plate are greatly reduced
C.	conductive heat losses from the absorber plate are greatly reduced	D.	radiative heat losses from the absorber plate are greatly reduced

74.

Wind energy transferred to the large sea surface is stored in waves as

A.	chemical energy	B.	thermal energy
C.	electrical energy	D.	mechanical energy

75.

Air velocity in the pipelines should be limited to about

A.	2.25 m/s	B.	10 m/s
C.	25 m/s	D.	50 m/s

76.

Addition of ethylene glycol into the water causes a depression in

A.	freezing point	B.	pour point
C.	boiling point	D.	none of the above

77.

Freezing point and pour point are equal for

A.	water	B.	crude oil
C.	aviation turbine fuel	D.	kerosene

78.

A good selective surface utilizes materials that strongly

A.	absorb both the far-infrared and visible wavelengths	B.	reflect both the far-infrared and visible wavelengths
C.	reflect far-infrared radiation and absorb visible light	D.	reflect visible light and absorb far-infrared radiation

79.

A difference of temperature between the two junctions of a thermocouple will produce

A.	a flow of holes	B.	a voltage difference between the two junctions
C.	melting of wires	D.	no measureable effect

80.

n-type silicon is formed by adding a minute amounts of elements with

A.	three valence electrons	B.	four valence electrons
C.	five valence electrons	D.	six valence electrons