An electric motor has a name plate rating of 10 HP and 1746

An electric motor has a name plate rating of 10 HP and 1746 rpm. The shaft speed is measured and found to be 1773 rpm. What is a good estimate to the approximate horsepower being produced by the motor?

3 HP

4 HP

5 HP

none of the above answers

A chiller is rated to produce 1000 tons of cooling by dropping the chill water from 55F to 45 F as it moves through the evaporator with a COP = 5. Under the same inlet condenser water temperature and exit chill water temperature conditions, the chill water comes into the evaporator at 48F and leaves at 45 F. The compressor power at this condition would be

About 600 HP

Around 300 HP

About 1000 HP

none of the above answers

An advantage of using a low pressure refrigerant like R123 as compared to a high pressure refrigerant is

a. Its environmental impact is better than any high pressure refrigerant

b. It gives a better performance for the chiller at low loads because one can use a fixed orifice expansion valve

c. Since it enjoys the highest market share for chillers, it is not likely to be phased out

d. None of the above answers

A best condenser water inlet temperature for a centrifugal chiller using a high pressure refrigerant from the list below when the wet bulb is 72 F and dry bulb is 86 F is

76 F

86 F

72 F

55 F

The load on a piston type compressor is controlled by

Intake valve unloading        

Variable speed drive           

Magnetic resonance

None of these

A screw type compressor is a

Positive displacement device

A reciprocating device

A centrifugal device

None of the above answers

The highest possible COP to cool a space at 40 F and reject heat to a space at 140F is approximately

5

7

10

None of the above answers

A demand charge for electricity is levied on

average kw-hr used in a month

average kw use in a month

maximum average kw use over a short time period in a month

none of the above answers

A cooling tower produces condenser water at 80 F on a day when the ambient conditions are 100 F dry bulb, 75 F wet bulb, and 60 F dew point. The tower has a 80 HP fan that is consuming 60 HP. The pressure rise across the fan is actually .5 psi but the fan is rated to produce 1 psi pressure rise. The effectiveness of the tower is:

.8

.5

.667

None of the above answers

A pump is advertised to move 1000 gpm thru a head of 20 psig using 15 HP motor.

The company that advertised this pump is fraudulent and/or ignorant

The pump efficiency is about 75%

The pump could work as advertised but everything would have to be very close to perfect

None of the above answers

PLEASE HELP!!

Solution

the rating as given above is at full load and as motor is found to be working with increased rpm then load is reduced thus power generated will also be reduced as power= torque * ang.speed and so power will be approx 5 rpm.