The Coefficient of Performance for a Refrigeration System - Lab Report Example

Laboratory Report: Refrigeration ME209 Experimental Methods University: Student Name: Student Reg. No.: Group: Lecturer: Submission Date: Summary In this experiment a four state-stage points were used to help in determining the coefficient of performance for a refrigeration system. It was easy to determine the power drawn by the COP by the use of this system. In addition, in this experimental report there is a report on the comparison between calculated results and recorded results. Assumptions were made while working on this experiment to determine the source of errors that might be present in the results that are tabulated and recorded. To get the difference in real and ideal refrigeration cycle was used to crosscheck the requirements for the experiment. While measuring and recording, the results a number of errors were recorded and they were assumed to the causes on data redundancy. The COP of the refrigeration system can be determined if the compressor can properly draw the power and the state properties. However, using the compressor input work, it is easier to determine the COP, or allow the working fluid be subjected to work. When comparing the ideal vapour compression refrigeration cycle (VCRC), the actual results, which are tabulated, are got and calculated from the laboratory, and they are dissented from results from the ideal cycle. Introduction To gain proper way to comprehend on vapour compression refrigeration cycle, this experimental lab experiment was conducted for comparing the real cycle with ideal cycle. Therefore, dichlorofluoroethane was the refrigerant that was used in the lab experiment while the water entering the evaporator had its mass flow rate varied, which was the case for the condenser. Objectives The objectives of this laboratory are to: Acquire knowledge on the operation of a refrigeration system. Calculate the Coefficient of Performance, COP, based on the electrical input, motor input and indicted power. Determine the various energy transfers in the system. Study the effects of varying the refrigeration load on the cycle parameters. Determine the compressor efficiencies. Compare the results manually with those obtained by the computer. Theory In this experiment, main equipment used to measure pressure was the use of bourdon gauge and a thermometer for temperature. While the current and voltage was measured using analogue ammeter and voltmeter. Experimental Procedure Safety COSSH requires students to adhere to safety regulations on chemical usage for every student to have protective clothing. Apparatus In this experiment, rig used is the Hilton Computer-Linked Refrigeration Laboratory Unit RC712. All the instruments are connected to the desktop computer see figure 2. In order to display properly, a set of programs are used: A schematic diagram and system parameters at 60 s intervals; Transient data; and The refrigeration cycle diagram and update it at 60 s intervals. Refrigerant R134a Compressor Twin cylinder, Belt-driven from an electric motor Bore = 40 mm; Stroke = 30 mm. Belt pulley ratio, Pr = 3.17 Total swept volume, Vswept = 75.5x10-6 m3 per rev. Torque arm radius, r = 0.165 m Condenser Shell and coil type. Heat transfer area = 0.075 m2. Evaporator Compact once-through concentric tube with refrigeration load supplied by two concentric heating elements Refrigerant flow meter calibration factor 13.3 Water flow meter calibration factor 4.78 Compressor friction force 5 N Table 1: Refrigerator specification Figure 1: RC712 Computer Linked Refrigeration Laboratory Unit. Procedure The procedure was conducted as per the laboratory instruction given in experiment instructions; Sources of error Main sources of error in this experiment may be because of the error from the assumptions on the equipment and measurement equipment. Results Test 1 Evaporator load Variable Results Evaporator pressure 1.46 bar Condenser pressure 6.16 bar Brake Force (Fg) 120N Refrigerator mass flow rate 4.2g/s Water mass flow rate 30g/s Motor speed 450 rpm T 1 15.50C T 2 26.5 0C T3 19.4 0C T4 17 0C T5 15.8 0C T6 19.5 0C Test 2 Load Motor load Variable Results Evaporator pressure 1.15 bar Condenser pressure 5.5 bar Brake Force (Fg) 140N Refrigerator mass flow rate 1.8g/s Water mass flow rate 30g/s Motor speed 455 rpm T 1 -20.20C super heat T 2 28.2 0C T3 18.3 0C sub cooling T4 -20.8 0C T5 15.1 0C T6 18.60C Test 3 Load on evaporator Compressor load Variable Results Evaporator pressure 1.2 bar Condenser pressure 5.8 bar Brake Force (Fg) 144N Refrigerator mass flow rate 1.2g/s Water mass flow rate 30g/s Motor speed 455 rpm T 1 3.50C super heat T 2 38.60C after compressor T3 18.60C sub cooling T4 17.10C T5 14.90C T6 19.40C Test 4 Evaporator load Compressor load Variable Results Evaporator pressure 1.8 bar Condenser pressure 6.3 bar Brake Force (Fg) 164N Refrigerator mass flow rate 3.5g/s Water mass flow rate 30g/s Motor speed 451 rpm T 1 3.20C super heat T 2 450C after compressor T3 210C sub cooling T4 -9.90C T5 14.80C T6 21.10C Test 5 Evaporator load Compressor load Variable Results Evaporator pressure 2.5bar Condenser pressure 7.2 bar Brake Force (Fg) 184N Refrigerator mass flow rate 5 g/s Water mass flow rate 30g/s Motor speed 447 rpm T 1 110C super heat T 2 50.50C after compressor T3 24.50C sub cooling T4 -2.30C T5 14.80C T6 23.30C Analysis Figure 2: refrigeration cycle for ideal cycle Assumptions made to make the calculations easier included The operation was based on steady state conditions; There are negligible changes on potential and kinetic energy; The system does not have any frictional pressure drops; The flow of the refrigerant is constant in both the condenser and the evaporator; The flow is adiabatic in both the pipes and the extension valves; When the refrigerant enters the compressor in state 1 it is a saturated vapour, and into the condenser as superheated vapour in state 2; When leaving the condenser the refrigerant is in saturated liquid, state 3; and When leaving the evaporator the refrigerant is saturated vapour. All the calculations in this experiment are based on ideal-compression cycle and it used a number of considerations of Newton’s law of cooling: For the condenser For the evaporator, Direction of heat flow for the evaporator is dictated by the temperature difference between the evaporator and the air around it. Coefficient of performance, The amount of power is given as: To calculate the energy balance in the condenser, this is the important equation used: Where, – Enthalpy state 2 and state 3, respectively This way the energy balance gives Where, Discussion Although a lot of care was taken during data collection process, actual refrigerator has values that are not equal to those of the ideal refrigerator.  Therefore, it is easier to associate the differences with the possibility to measure accurate results, methods used to measure the results; as a result, these would create an impact on the value of the calculated COP (Whitman, 2012, 47). For the data recorded in the results the graphs for the tests 1 to 5 are shown in appendix figures 3 to 7. Conclusion Calculations were done based on the vapour compression with four state points from the laboratory report on refrigeration for the enthalpy, pressure and temperature. The COP of the refrigeration system can be determined if the compressor can properly draw the power and the state properties. However, using the compressor input work, it is easier to determine the COP, or allow the working fluid be subjected to work. References Whitman, (2012). Refrigeration and Air Conditioning Technology. New York: Cengage Learning. Pp 44-50 Wang, S., (2000). Handbook of Air Conditioning and Refrigeration. New York: McGraw-Hill Education. P.67 Appendix Figure 3: Test 1 Figure 4: Test 2 Figure 5: Test 3 Figure 6: Test 4 Figure 7: Test 5 Read More