Carnot cycle

Question 1

How do you calculate the work done by a (Carnot) heat engine from the energy out and in

Answer 1

Work done = energy out - energy in.

Question 2

How do you calculate maximum carnot efficiency of a heat engine for a given delta T.

Answer 2

Tc/Th. The temperature of the cold reservoir divided by temperate of the hot reservoir. Note these temps must be in kelvin.

Question 3

How do you calculate the quantity of energy entering and leaving the system.

Answer 3

TC/TH = QC/QH

Question 4

How do you calculate the efficiency of a real heat pump in proportion of its carnot efficiency.

Answer 4

Real efficiency/carnot efficiency.

Question 5

How do you calculate how much compression will heat up a gas

Question 6

What are the causes of inefficiencies in a heat pump?

Answer 6

Evaporating temperature not falling to abient temperature. Friction on the motor, heat losses from the condenser. Leakage to suction line on the compression stroke. Leakage to delivery line on the suction stroke. Leakage between the piston and the seal.

Question 7

What is specific work of the compressor?

Answer 7

It is the work input of the compressor per KG of refrigerant gas

Question 8

What is the symbol indicating the refrigerant flow rate

Answer 8

Mr (dot over the M)

Question 9

What is the symbol of heat transfered by the condenser?

Answer 9

Qc (dot over the Q)

Question 10

How do you calculate the efficiency of a compressor

Answer 10

Ideal H1-H2/Actual H1-H2

Question 11

What are typical efficiencies of a compressor

Answer 11

60-80. Scroll compressors are more efficient at compression ratios below 3.5. Piston compressors are more effective above that range.

Question 14

What is the selection criteria for refrigerants

Answer 14

Boiling point should be low, liquid specific heat capacity should be low, latent heat of vapourisation should be high, cost should be low, global warming potential low, ozone depletion potential low, toxicity, flammability, low viscosity.

Question 15

What is the isentropic index of compression

Answer 15

It is the amount that temperature will increase when a gas is compressed

Question 16

What is the room temperature differential and what design considerations are there when designing it.

Answer 16

It is the difference between the room air temperature and the supply air temperature in summer. The idea is that cold drafts must be avoided. This depends upon the height of the diffuser and the quality of the diffusers. If the diffuser is higher and/or better able to disperse the air then the supply air can be colder without