Experiment: Determination of the COP and analysis of the cycle of a heat pump

Topics covered:

- Heat cycles of a refrigeration machine

- Changes of state

- Compressor efficiency

- Determination of the coefficient of performance

- Cycle analysis in a Mollier diagram

Principles and objectives:

The heat pump D is used to illustrate the operation of a refrigerator or an electric compression heat pump. The compressor, condenser, expansion valve, and evaporator components are mounted on a base plate and are connected by a closed system of copper tubes and can, thanks to their transparent arrangement,

be directly related to the succession of state changes in the thermal pump cycle.

Consisting of copper coils, the evaporator and condenser are immersed in a water tank serving as a thermal reservoir to determine the heat absorbed or released. Two digital thermometers,

allow to determine the respective temperature of the two reservoirs.

Compressor efficiency:

The compressor efficiency co is the result of the ratio between the amount of heat Q2 supplied to the hot water tank per unit of time t and the driving power P of the compressor. The greater the temperature difference between the condenser and the evaporator, the lower it becomes.

Representation in the Mollier diagram:

Thanks to the gauges and thermometers of the model, it is

possible to trace the cycle followed by the refrigerant fluid and then determine the amount of heat generated or consumed

by a temperature change or at the time of a change of state (liquid/vapor).

Theoretical coefficient of performance:

The theoretical coefficient of performance of the ideal cycle can be calculated from the specific enthalpies recorded in the Mollier diagram h1, h2 and h3.

- 120 W compressor, condenser, and evaporator - R134A refrigerant - Thermal tanks, 2000 ml each - Low and high-pressure gauges - Thermometer -20°C, -110°C - Didactic thermal camera (ref 277001) - Modimontage stand (ref 701293)