Which refrigeration system is driven by low-grade energy?
Steam jet refrigeration system is driven by low-grade energy.
Steam jet refrigeration
The boiling point of a liquid changes with a change in external pressure. In normal conditions, the pressure exerted on the surface of any liquid is the atmospheric pressure. If this atmospheric pressure is reduced on the surface of a liquid, by some means, then the liquid will start boiling at a lower temperature, because of reduced pressure. This basic principle of boiling liquid at a lower temperature by reducing the pressure on its surface is used in the steam jet refrigeration system.
This system is also driven by low-grade energy, that is, by process steam in chemical plants or a boiler. This is not an economical process, and hence it has been replaced by steam-driven LiBr systems in most places.
This system consists of two loops i.e. the power loop and the refrigeration loop
In the power loop, low-grade heat, Qb, is used in a boiler or generator to evaporate high-pressure liquid refrigerant (process 1-2)
The high-pressure vapour generated, known as the primary fluid, flows through the ejector where it accelerates through the nozzle.
The reduction in pressure that occurs induces vapour from the evaporator, known as the secondary fluid, at point 3. The two fluids mix in the mixing chamber before entering the diffuser section where the flow decelerates and pressure recovery occurs.
The mixed fluid then flows to the condenser where it is condensed rejecting heat to the environment, Qc.
A portion of the liquid exiting the condenser at point 5 is then pumped to the boiler for the completion of the power cycle.
The remainder of the liquid is expanded through an expansion device and enters the evaporator of the refrigeration loop at point 6 as a mixture of liquid and vapour. The refrigerant evaporates in the evaporator producing a refrigeration effect, Qe, and the resulting vapour is then drawn into the ejector at point 3.