What happens when latent heat is removed from a substance?

It causes a change in phase but not in temperature.

It causes a change in temperature but not in phase.

The substance becomes subcooled.

The substance becomes superheated.

What is a common description of a vacuum?

B. Any pressure well below normal atmospheric pressure.

A. A pressure between plus 1.0 bar to minus 1.0 bar.

When no pressure is being exerted

What must be present for the pressure temperature relationship to be correct?

Subcooled vapour and superheated liquid.

What effect does subcooled liquid have on system performance?

Increased discharge temperature.

Decreased discharge temperature.

What is a function of the compressor?

To increase the pressure in the evaporator.

To maintain the pressure in the evaporator.

To reduce the pressure in the liquid line.

To increase the pressure in the suction line.

What is the source of the total heat rejected by the condenser?

The compressor work done, suction line superheat and liquid line sub-cooling.

Only the heat absorbed in the evaporator.

The refrigerant mass flow rate only.

What happens to the system refrigerant during compression?

The temperature and enthalpy increase, the entropy remains constant.

The pressure, temperature and entropy increase.

The enthalpy and temperature increase, the entropy decreases.

The enthalpy and pressure decrease, and the entropy remains constant.

What is the benefit of having superheated vapour at the compressor inlet?

It ensures that no liquid enters the compressor.

It ensures the compressor oil is free flowing.

It prevents frost formation on the compressor body.

It evaporates condensate around the compressor.

What is the most likely reason for the PH plot of a cooling system, shown as ABCD on the chart, to change to AEFG?

Increase in crankcase temperature.

What would cause the cycle shown as ABCD on the PH chart to change to cycle EFGH?

Worn suction and discharge reed valves.

What would cause the cycle shown as ABCD on the PH chart to change to the cycle shown as EFGH?

Excessive suction line superheat.

What happens to moist air when it passes through the indoor unit of an air conditioning system?

The air is cooled and some of the moisture vapour condenses.

As air is cooled, moisture vapour stays at the same temperature.

As the air temperature falls, the moisture content stays the same.

The combined air and moisture vapour begin to condense.

When measuring an air sample using wet and dry bulb thermometers, what indicates that the air is at maximum humidity?

The wet and dry bulb temperatures are the same.

The wet and dry bulb temperatures are slightly different.

The dry bulb temperature is much lower than the wet bulb temperature.

The wet bulb temperature is much lower than the dry bulb temperature.

How is a wet bulb thermometer kept moist?

By a wick tube connected to a reservoir.

By gravity feed of water from a reservoir.

By immersion in a water reservoir.

What feature is available from a standard wall mounted split AC system?

Re-humidification of supply air.

Simultaneous heating and cooling.

What is the effect of reducing the evaporator saturation temperature?

Increased air moisture content.

Air moisture content unchanged.

Increase in air moisture density.

What describes the term 'temperature difference' for a ground source heat pump?

It is the difference between the ground and collector coil temperatures.

It is the difference between the evaporator and collector coil temperatures.

It is the difference between the condenser and evaporator temperatures.

What is the difference between the heat outputs of a gas boiler, with an efficiency of 80%, compared to a heat pump with an EER of 4.0?

The heat pump gives off 4.0 times as much heat/kW input.

The heat pump gives off 1.6 times as much heat/kW input.

The heat pump gives off twice as much heat/kW input.

The heat pump gives off 5.0 times as much heat/kW input.

What is the result of high pressure drop in the liquid line of an RAC system?

Condensing pressure will reduce.

What is the impact of installing undersized pipework?

A decrease in cooling capacity.

A decrease in flash gas formation.

An increase in refrigeration effect.

What ensures oil returns to the compressor under full load conditions?

Pipes are sized for correct velocity.

Use of mineral oil in the compressor.

Pipes are sized to give minimum pressure drop.

A miscible oil is used in the compressor.

Refrigeration and Thermodynamics sample

Authored by Jermaine Taffe

Science

University

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55 questions

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MULTIPLE CHOICE QUESTION

30 sec • 1 pt

What is the SI base unit for temperature?

Fahrenheit.

Celsius.

Kelvin.

Rankine.

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

What is the derived SI unit of the measurement of the rate of energy flow?

Watt.

Joule.

Kelvin.

Newton.

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

What is the same when two bodies are in thermal equilibrium?

Their energy content.

Their temperature.

Their thermal conductivity.

Their mass.

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

Which is an absolute temperature scale?

Fahrenheit.

Celsius.

Centigrade.

Kelvin.

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

What happens to molecules at absolute zero?

They vibrate very fast.

They vibrate very slowly.

They are motionless.

They change state.

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

What is 62°C converted to Kelvin?

228 K.

258 K.

288 K.

335 K.

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

Which thermodynamic law states that energy cannot be created or destroyed, but only converted?

Boyle's law.

Charles' law.

First law.

Second law.

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Refrigeration and Thermodynamics sample

What is the SI base unit for temperature?

What is the derived SI unit of the measurement of the rate of energy flow?

What is the same when two bodies are in thermal equilibrium?

Which is an absolute temperature scale?

What happens to molecules at absolute zero?

What is 62°C converted to Kelvin?

Which thermodynamic law states that energy cannot be created or destroyed, but only converted?

Which thermodynamic law describes ice melting in a glass of warm water?

The heat from the sun travels to Earth by which process or processes?

What is the SI unit for energy?

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