How Refrigeration System Works - Lab Report Example

Laboratory Report: Refrigeration ME209 Experimental Methods University: Student Name: Student Reg. No.: Group: Lecturer: Submission Date: Summary In refrigeration system the coefficient of performance is determined using four stage points. Therefore, it determining the amount of power drawn by the COP is easy in the system. In this report, there is comparison of the obtained results from the experiments that were conducted in the laboratory. Further, the report indicates the number of assumptions and errors that were made during the experiment. Refrigeration cycle was used in this experiment to determine and crosschecking the main difference between the real and ideal refrigeration. All the errors, that were recorded during the experiment analysis, were concluded to be the main sources of data redundancy. Therefore, determining the refrigeration system COP was only possible if the compressor was able to draw as well as state properties for the refrigerant. When the compressor is used to input the work required by the system, it will be easier to use the input work generated by the compressor. In the end, the ideal vapour compression refrigeration cycle (VCRC) are compared, and the obtained results are calculated and analysed in the laboratory. These results indicate the ideal cycle for the refrigeration system. Introduction When conducting refrigeration experiment it is important to consider the operating conditions under which the experiment is carried out. Therefore, this experiment was done for the purpose of comparing the ideal and real cycle for the purpose of understanding the vapour compression refrigeration cycle. The main refrigerant hat was used in this experiment was dichlorofluoroethane. On the other hand, water was entering the evaporator, and its mass flow rate was measured and the same was done for the condenser. Objectives The objectives of this laboratory are to: Get sufficient knowledge to learn how refrigeration system works; Determine the several energy shifts in the system. Based on the system electrical input, indicated power and motor input, to determine the amount of the Coefficient of Performance, COP; Determine the compressor efficiencies; Examine the results of altering the refrigeration load on the cycle parameters; and Equate manually obtained results with those obtained by the computer. Theory For the purpose of measuring different quantities in the experiment, voltage was measured using the voltmeter and the flowing current was measured using the ammeter. Temperature changes were measured using a thermometer while pressure was measured using the Bourdon gauge. Experimental Procedure Prior to starting the experiment it is important to have proper knowledge on safety and the necessary equipment that are used in the experiment. Safety It is a requirement by COSSH that when working with chemical in the laboratory, students must protective clothing. Apparatus Unit RC712 rig that was used in this experiment was at the Hilton Computer-Linked Refrigeration Laboratory. During the experiment, all the apparatus were connected to the desktop computer see Figure 1. A set of computer programs were used to ensure that the results were properly displayed with: System parameters at 60 s intervals and schematic diagram; Transient data; and At Intervals of 60 s update for the refrigeration cycle diagram. Refrigerant R134a Compressor Twin cylinder, Belt-driven from the 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. Water flow meter calibration factor 4.78 Evaporator Compact once-through concentric tube with refrigeration load supplied by two concentric heating elements Refrigerant flow meter calibration factor 13.3 Compressor friction force 5 N Table 1: Refrigerator Specification Figure 1: RC712 Computer Linked Refrigeration Laboratory Unit. Procedure Laboratory experiment procedures were given from which the experiment instructions were listed; Sources of error Considering the measuring equipment readings were made using the eyes, the main source of error was from the measuring equipment. Results From the experiment that was conducted in the laboratory, the results were as recorded in the tables 1 to 5. 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 subcooling 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 subcooling 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 subcooling 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 subcooling T4 -2.30C T5 14.80C T6 23.30C Analysis Figure 2: refrigeration cycle for ideal cycle The experimental assumptions that were made include: The experimental procedure and operation was based on steady state conditions; The experimental potential and kinetic energy had negligible changes; No frictional pressure drops in the system; For both the condenser and the evaporator, the refrigerant flow is constant; At state 1 when the refrigerant enters the compressor is saturated and in state two it is superheated vapour that enters the condenser; In state 3, when the refrigerant is leaving the condenser is saturated liquid; and The refrigerant leaves the evaporator as saturated vapour. The experimental calculations are based on ideal compression cycle, and they apply newton’s law of cooling: Condenser equation, Evaporator equation, Heat flow direction in the evaporator is determined by the temperature difference between the surrounding air and the internal section of the evaporator. Coefficient of performance, Power is calculated as: And the equation used to calculate energy balance is given as: Where, – Enthalpies for state 2 and state 3 respectively. From the above equation, the enthalpy at state 2 is given as: Where, Discussion Despite the careful data collection and recording process, the actual recorded refrigeration values vary from the ideal refrigeration values. Therefore, it is better if the final results were associated with the accurate results and the methods used in determining the results. This would, therefore, result to getting more accurate values for the calculated COP (Prasad, 2007, 68). All the data recorded and calculated was analysed and plotted in the graph in Figures 3 to 7in the appendix. Conclusion Based on vapour compression for the four state points computations were done for the lab refrigeration experiment for the pressure, enthalpy and temperature. It was also realised that, it was easy to determine the COP of the refrigeration system if the compressor was in a position to draw power and state properties constantly. However, it was determined from the experiment that, if the compressor were used to produce input work, then it would be easy to determine the COP or to subject the working fluid to work. References Prasad, M., (2007) Refrigeration and Air Conditioning. New Delhi: New Age International. 68 Hundy, G. H., Trott, A. R. and Welch, T. C., (2008) Refrigeration and the Air- Conditioning. New York: Butterworth-Heinemann. 78 Dincer, I. and Mehmet, K. (2011) Refrigeration Systems and Applications. New York: John Wiley & Sons. 124. Appendix Figure 3: Test 1 Figure 4: Test 2 Figure 5: Test 3 Figure 6: Test 4 Figure 7: Test 5 Read More