MECHANICAL ENGINEERING 449
Test of a Heat Pump
The purpose of this experiment was to determine the performance values of a Hylton Air and Water Heat Pump System. The system uses refrigerant 134a and water as the working fluids. The power input of the system was measured. The rate of heat output and the coefficient of performance are to be determined. A sketch of the vapor-compression cycle on a pressure-enthalpy diagram is also to be presented. In order to perform this analysis the temperatures at the inlet and outlet of the condenser and evaporator were measured for both the refrigerant and the water. The flow rate of the refrigerant through the system was measured and assumed to be constant throughout. The flow rate of the water was measured through the condenser and evaporator as well as the pressure of the refrigerant through the condenser and evaporator. The water was used to cool the compressor before entering the condenser and the inlet and outlet temperatures were measured. In order to accomplish the objectives energy balances were performed on both the evaporator and condenser for the refrigerant and water. After performing an energy balance on the condenser, the energy lost by the refrigerant was found to be 1,571 Watts. The water through the condenser picked up an energy value of 1,669 Watts. The measured power input of the compressor was used to determine the coefficient of performance (COP) of heating and was found to be approximately 3. The water was assumed to have a constant specific heat value of 4.18 KJ/KG°C. Changes in kinetic and potential energies are also assumed to be negligible as the working fluid passed through the successive volumes. The state of the refrigerant was also assumed to stay constant as it leaves one control volume and enters the next. The zero values for the flow of water and refrigerant were also measured and used to increase the accuracy of the results. After performing an energy balance on the evaporator, the refrigerant was found to gain 1,152 Watts from the cold water. The water was found to loose 1,234 Watts. From this, the COP of cooling was found to be approximately 2.2. The efficiency of the compressor was also determined using the change in enthalpy over the compressor and the flow rate of the refrigerant in conjunction with the measured power input. The efficiency of the compressor was found to be 80.7%. The energy sent of the water in the cooling jacket of the compressor was found to be 22 Watts. The total energy lost in the compression cycle was approximately 100 Watts. This loss is mainly in the form of heat, of which 22 Watts of the 100 Watts was sent to the water in the cooling jacket.
In order to determine the most efficient ways to heat and cool rooms and the like, studies such as this one are extremely important. In a real application, air would be substituted for the water in order to perform the desired heating and cooling function. It is important to analyze the transfer of energy at each control volume in order to optimize the efficiency of the system. In order to achieve 100% efficiency, all the work of the compressor would have to be transferred to the refrigerant. The cooling jacket around the compressor improves the efficiency of the cycle by taking some of the lost energy of the compressor and transferring it to the water before entering the condenser. The applications of heat pumps are limited to environments that do not reach extreme cold temperatures. This is because it is hard to pull energy from extremely cold mediums.
The objective of this experiment was to determine the performance values of a Hylton Air and Water Heat Pump System. The rate of heat output and coefficient of performance are to all be determined. A sketch of the...
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