In this practice set, we use what we've learned about energy flows, temperature changes, and phase changes to make sense of how heat pumps work. A heat pump contains a fluid called a refrigerant. The refrigerant repeatedly flows through a 4 step cycle. In the diagram below, the refrigerant flows in the direction indicated by the arrows. Step 1. (Expansion) The refrigerant enters the expansion valve as a hot, high-pressure liquid. After it passes through the expansion valve, it is a mixture of very cold liquid and vapor just at the boiling temperature of the refrigerant (which is a very low temperature at this pressure). For simplicity, we assume the refrigerant is still completely in its liquid phase upon exiting the expansion valve. Step 2. (Evaporation) The very cold, liquid refrigerant passes through the evaporator. Heat flows from the environment outside the heat pump into the refrigerant, and its phase changes to vapor without a change in temperature. Step 3. (Compression) The very cold, vaporized refrigerant enters a compressor. The compressor consumes work and considerably increases the vapor's temperature and pressure, but no phase change occurs. Step 4. (Condensation) The very hot, vaporized refrigerant enters the condenser where two things happen. First, heat flows to the environment outside the heat pump, causing the refrigerant to change phase from vapor to liquid. Second, more heat flows to the environment decreasing the liquid refrigerant's temperature. The refrigerant emerges from the condenser as a hot liquid. Consider a heat pump containing 4 kilograms of a refrigerant called R-100], all of which goes through the 4-step process described above during every cycle. When the refrigerant passes through the evaporator, its latent heat of vaporization is about 500k]/kg. When it passes through the condenser, its latent heat of vaporization is about 200k]J /kg, and it's specific heat in the liquid phase is about 100k]/(kg - K). During the part of the condensation step after the refrigerant has changed phase to a liquid, it cools down from about 140F to about 127F. Notice that the refrigerant's latent heat of vaporization is different during the evaporation and condensation steps. This makes sense because the latent heat of vaporization typically depends on pressure, and the pressures are different during those steps of the process. 5. Compute both COP_,, and COPy,; for this heat pump (i.e. the coefficients of performance of the heat pump if it were operating as a cooler and as a heater respectively)