Refrigeration Laboratory - Lab Report Example

REFRIGERATION LABORATORY By + Introduction Refrigeration is the mean of removing energy through heat transfer from a body at a temperature T1 and rejecting the energy at certain higher temperature T2. In bid to accomplish external energy input ( Work) is demanded. As a temperature difference exist amidst the cold store and the surroundings, heat will be continuously transferred to the corresponding cold store from those surrounding and this ought to be continuously removed in order to maintain the temperature T1. Numerous techniques of refrigeration are in use, and all practical systems operate in a cyclic manner since it requires continuous energy removal. A refrigeration cycle is a cycle that aids in the transfer heat from the low-temperature sink to a relatively high temperature through application of energy from the third source (Dincer & Kanoglu, 2013, pp.123-167). It differs from the heat pump since it has desired output, which is the heat transfer from the underlying cold sink at the expense of the heat transfer from the corresponding hot sink. Mechanical compression cycle is the common type of the refrigeration cycle as the Rankine cycle running backwards (Pauken, 2011, pp.234-278). Refrigeration effect is computed as Q4-1= m (h1-h4) Where m= mass flow rate of the refrigerant h=specific enthalpy Coefficient of Performance (COP) For a Refrigerator, COPR=Q4-1/W1-2=h1-h4/h2-h1 Heat Pump COPR= Q2-3/W1-2/h2-h3/h2-h1 Objective The primary purpose of the refrigeration laboratory report is to undertake an energy balance on a vapour compression refrigerator and to determine the coefficient of performance. Apparatus The Cussons vapour compression refrigerator functions with the R12 as its refrigerant. The underlying evaporator consists of the heat exchanger in which one fluid is the brine, and its temperature is typically maintained at 0o C through electrical heating process. The condenser consists of the heat exchanger, which contain water as one of the fluid. Process 1-2: The refrigerant enters the prevailing compressor, which is superheated. The refrigerant is subsequently compressed to a relatively higher pressure Process 2-3: The fluid condenses at a relatively higher pressure then leaves the condenser within a sub-cooled state Process 3-4: The refrigerant expands via a throttle valve to a relatively lower pressure Process 4-1: The refrigerant enters the evaporator at a relatively lower pressure and temperature. The heat essential for evaporation emanates from the corresponding cold source. Experimental procedure The refrigeration plant ought to be operational under stable conditions, and the readings were recorded as depicted in the results table. Barometric Head 100762 N/m2 Dynamometer Torque 2.75 N-m Dynamometer Speed 10.5 rev/s Water Flow rate 60 g/s Refrigerant Flow rate 3g/s Compressor Delivery Pressure 4 bar Compressor Suction Pressure 0.5 bar Expansion Pressure 0.5 bar Heater Current 4.2A Heater Resistance 38.6Ω Temperature T1( compressor inlet temperature) 3oC T2( compressor outlet temperature/ condenser inlet) 43OC T3( compressor outlet temperature) 11 oC T4 -14 oC T5( Evaporator outlet) 1 oC T6(the temperature in the evaporator) 0 oC T7(water temperature inlet) 11 oC T8( water temperature outlet 15 oC For plotting the chart Compressor suction= 100762+50,000= 150,762=0.15MPa Compressor delivery= 100762+ 4*105=500,762= 0.5MPa Expansion Pressure= 100762+ 0.5*105=150762= 0.15MPa Results a.) Plot the cycle on the refrigeration chart b. Calculation of mechanical power input, P Given: Dynamometer Speed = (2π)(10.5) rad/s Dynamometer Torque = 2.75 Nm Mechanical power input, P = (2π)(10.5) rad/s* 2.75Nm =181.4270 Watts The Work input from the compressor is Wcompressor=m ( h2-h1) = 0.003 kg/s (440-405) = 105 Watts c.) Computation of the rate of the heat input within the evaporator, Qev Qevap= = 0.003 kg/s (405-214) = 573 Watts d.) Computation of the rate output from the condenser Qcondenser= m (h3-h2) = 0.003 kg/s (214-440) = -678 Watts. m= 0.003 kg/s Since there is water going into the condenser; mrefrigerant((h2-h3) = mwater((h8-h7) Using steam table to compute the values of enthalpy of h8 and h7 At T8 = 15oC, h8= 62.9kJ/kg At T7= 11oC, h7=42.6kJ/kg Thus, mwater((h8-h7)= 0.006(62.9-42.6) =20.3*0.06 =1.218 e.) Computation of the refrigeration effect of the plant Q4-1= m (h1-h4) m= 0.003 kg/s h=specific enthalpy Thus, Q4-1= m (h1-h4) = 0.003(405-214) =0.573 g.) Computation of coefficient of performance of the plant For a Refrigerator, COPR=Q4-1/W1-2=h1-h4/h2-h1 h1=405, h2=440, h3=h4= 214 COPR=Q4-1/W1-2=h1-h4/h2-h1 = 405-214/(440-405) = 191/35 =5.4571 h.) Complete an energy balance on the plant Input Energy = Output Energy Qout= Win + Qin = 105 watts + 573 watts = 678 watts Discussion The analysis of the data attained within the lab is made easier with the postulation of the states on the schematic diagram of the refrigerator R-134a. Moreover, evaluation of the R-134a refrigerant, which is the working fluid flowing via the system, demands the temperature and pressure of particular locations (Dincer & Kanoglu, 2013, pp.123-167). In collaboration with the R-134a properties, tables, the corresponding enthalpy of the fluid was determined through interpolation. There was a big difference of 76.427 amidst power computed by the formula and the corresponding power calculated from the mechanical data. The difference is due to the losses in the power transfer such as friction losses. The rate of heat output from the condenser was theoretically computed and found to be 678 watts while the calculated value was found to be 1218 watts. Under normally operation of the system 678 would be the amount of heat energy dissipation for efficient system function. Nevertheless, due to the high specific heat capacity of water than refrigerant the computed value rate of energy output in condenser of water was far much higher. The rate of heat input within the evaporator was hypothetically computed through using I2R and the result was found to be 0.680904 kW whilst the computed value was found to be 0.576kW. In case the system was to be operated normally, 680.904 watts would be the amount of the heat energy dissipation thereby making the system more efficient. Nevertheless, due to the heat loss to the environment the computed value reduced to 576 watts, which is 104.904 watts less than the theoretically calculated value. Moreover, the rate of the underlying apparent cooling loss with the evaporator pressure is relatively higher than the corresponding generator temperature. The COP of the system was relatively higher and was computed to be 5.4571 depicting that the system was relatively efficient. The value might have been influenced by multiple variables in the experiment, which grants an abnormality when computing the COP utilizing experimental data. The deviation of the COP value emanates from the outcomes of the measuring equipment, experimental equipment setup and corresponding human errors within the reading of the diverse gauges. The compressor the pressure escalates thereby raising the temperature, which subsequently arguments the specific enthalpy from 405kJ/kg entering to the corresponding 440kJ/kg leaving the compressor (Islam, 2008. Pp.145-178). The primary aim is mainly to raise the temperature entering the condenser as lofty as possible in order to make relatively more heat to be rejected to the heat sink. Escalating the high temperature of the prevailing rejection entirely heightens the efficiency of the heat transfer and the corresponding coefficient of performance. Moreover, it is depicted by the reduction in temperature and enthalpy from existing state three to state four. Specific enthalpy decreases from 440kJ/kg for the prevailing refrigerant entering the underlying condenser to 214kJ/kg leaving the condenser (Whitman, Johnson & Tomczyk, 2005, pp.123-189). The rate of heat of transfer was 78.61308 depicting that higher temperature allows transfer of more heat due to the higher rate of reaction and higher temperature (Morvay & Gvozdenac, 2008, 256-289). R-22 is usually a sole hydrochlorofluorocarbon compound, which has relatively low chlorine content and ozone diminution potential (Pauken, 2011, pp.234-278). It is employed is small heat pump system. R-22 is presently on the superheated region granting the fluid of relatively higher quality thus not damaging to the compressor blades. According to the 1995 international agreement, the underlying production of the R-12 was reduced drastically, and its operation ceased in 1997. R12 refrigerant is no longer manufactured since it rises and corrodes stratospheric ozone, a layer of 20 to 40 miles from the prevailing Earth that mainly safeguard populace from the harmful rays of the sun (Dincer & Kanoglu, 2013, pp. 145-178). Moreover, the chemical CCl2F2, which possess high probable cause of the depletion of the ozone layer within the upper layers of the atmospheres thereby causing the greenhouse effect. The best replacement of the R12 is R-134a. R-134a is an HFC thus possessing zero depletions making it probable and extremely low greenhouse effect (Dincer & Kanoglu, 2013, pp. 145-178). Moreover, it is non-flammable, non-explosive and possesses good chemical constancy. R-12 is also replaced by r-401a and corresponding R-401b. Refrigerant 401a contains R-22,R-15a and R-124 in diverse proportions. Conclusion From the underlying refrigeration experiment, the prevailing pressure, enthalpy and the corresponding temperature were computed at the underlying four positions of the Vapour Compression Refrigeration Cycle (VCRC). Due to the state position properties and the power got from the compressor, the COP can be computed. Nevertheless, the COP is frequently determined from the prevailing work input to the existing compressor. Conversely, COP can be defined as the work applicable to the corresponding working fluid. Comparing with the ideal VCRC, the data attained and computed from the laboratory slightly differ from the existing typical cycle (Whitman, Johnson & Tomczyk, 2005, pp.123-189). The differences are due to the assumptions made when undertaking the ideal cycle operations in the simplification of the computations. Moreover, the assumption of taking the compressors to be isentropic depicts the greatest effect on the fluctuation of the ideal and corresponding real cycle. Primary source of error entails the correctness of measuring equipment coupled with the techniques employed in attaining the restrained values (Islam, 2008. Pp.145-178). The practical cycle would massively estimate the ideal cycle values in case the prevailing assumptions are implemented. The assumptions encompass steady pressure heat transfer across the underlying heat exchangers coupled with the reduction of the heat transfers to the environment because of the insinuated devices. References Dincer, I., & Kanoglu, M. (2013). Refrigeration systems and applications. Hoboken, N.J., Wiley. http://rbdigital.oneclickdigital.com. Pauken, M. (2011). Thermodynamics for dummies. Hoboken, NJ, Willey Publishing, Inc. Islam, R. (2008). Nature science and sustainable technology. New York, Nova Science Publishers. Morvay, Z. K., & Gvozdenac, D. D. (2008). Applied industrial energy and environmental management. Chichester, West Sussex, U.K., Wiley. http://search.ebscohost.com/login.aspx?direct=true&scope=site&db=nlebk&db=nlabk&AN=250689. Whitman, W. C., Johnson, W. M., & Tomczyk, J. A. (2005). Refrigeration & air conditioning technology. Australia, Thomson Delmar Learning. Read More