Thermal and Performance Analysis of R600a in Vapour Compression Cycle

Thermal and Performance Analysis of R600a in Vapour Compression Cycle

Shailesh Golabhanvi

Assistant Professor, Mechanical department Alvas Institute of Engineering and Technology

Moodbidri-574225, Manglore, DK, Karnataka, India

Abstract The aim of this project is to comparatively analyze of COP using R134a & R600a Refrigerant in Domestic refrigerator at steady state condition. Two different refrigerant are R600a (Isobutene) and R134a (tetrafluoroethae). R134a is zero ozone depletion layer and high global warning and R600a is zero ozone depletion layer and negligible global warning. In domestic refrigerator was selected by the obtained result from R134a and an experiment using 170 g of R600a which indicate the similar result as R134a. Based on outcomes R600a charge amount, condenser evaporator and compressor coefficient of performance were selected for design. The analysis of variance result is indicated that R600a charge amount was the most effective parameter. At optimum condition the amount of charge is required for R600a was 170 g, 66% lower than R134a one, which not only being economic advantages, but also significantly reduces the of flammability of the hydrocarbon refrigerant. Thus in the present work comparatively analyze of COP using R134a & R600a Refrigerant in Domestic refrigerator at steady state condition. All the result were compared. Comparison of performance domestic refrigerator at steady state condition of the system was also studied. The result is indicate that R600a COP is more than R134a.CFD Analysis of condenser & evaporator also shows system effectiveness with respect to the R134a & R600a.

1. INTRODUCTION

   Refrigeration may be defined as the process of achieving and maintaining a temperature below that of the surroundings, the aim being to cool some product or space to the required temperature. One of the most important applications of refrigeration has been the preservation of perishable food products by storing them at low temperatures. Refrigeration systems are also used extensively for providing thermal comfort to human beings by means of air conditioning. Air Conditioning refers to the treatment of air so as to simultaneously control its temperature, moisture content, cleanliness, odour and circulation, as required by occupants, a process, or products in the space. The subject of refrigeration and air conditioning has evolved out of human need for food and comfort, and its history dates back to centuries. The history of refrigeration is very interesting since every aspect of it, the availability of refrigerants, the prime movers and the developments in compressors and the methods of refrigeration all are a part of it. The French scientist Roger ThÝvenot has written an excellent book on the history of refrigeration throughout the world.

   Vivekanand Navadagi

   Assistant Professor, Mechanical department JSPMs Imperial College of Engineering and Research

   Wagholi, Pune-412107, Maharashtra, India

2. METHODOLGY

   1. Properties of R600a

      Its numerical designation is R600a or Isobutane. Its chemical formula (CH3) 3 CH.

      Normal boiling point = 260-264 °K at atm pressure Critical Temperature = 135°C

      Critical pressure = 3.65 MPa

      Vapour pressure = 204.8 KPa at 21°C

      Specific heat of liquid = 2.38 KJ/Kg°C at 25°C Molar mass = 58.12 g mol1

      Density = 2.51 kg/m3, gas (15 °C, 1atm) 593.4 kg/m3, liquid

      Melting point = -159.6 °C, 114 K, -255 °F

      Boiling point = -11.7 °C, 261 K, 11 °F Solubility in water = Insoluble

      Ozone depletion potential (ODP) = 0 Global warming potential (GWP) = 3 Flash point = -83 °C, 117 °F; 190 K

      Latent heat of evaporation = 362.6 KJ/Kg at atm pressure Specific Heat Ratio Cp/Cv = 1.091(atm,25.C)

      Assigned colour code = Colourless gas

   2. Vapour compression cycle

      Fig 1. VCC Cycle

   3. Component list

   4. System description

      TABLE I

      LIST OF COMPONENTS

      diameter reduce the pressure from condensing pressure to evaporator pressure. Overall Dimension is (Bore x Length) = 0.50 x 5 x 1

      Drier: The primary function of the drier is to separate gas and liquid. The secondary

      purpose is to remove moisture and filter out dirt.

      Pt 100-sensors (Pencil Type & Bulb Type): The temperatures at different points in the system are measured by using RTD (PT 100) sensors. These are Resistance Temperature Detectors operating on principle of change in Resistance with change in temperature.

      Evaporator: This is made up of S.S material having inbuilt coil and heater. It is used as an evaporator in the system.

      Rotameter: This is a variable area glass tube liquid flow- measuring device. The glass tube is enclosed in M.S. structure with transparent glass at two sides to read the readings. Calibrated scale is mounted in the enclosure. The float is lifted up as liquid flows through the glass tube and the lift is proportional to the flow rate. Its range is 6.8-68 LPH

      Pressure Gauge (0 to 300 PSI.): It is a Bourdon type pressure gauge. This is used to measure pressures at discharge point of compressor.

      Compound Gauge. (-30 to 150 PSI.): This Bourdon type pressure gauge measures both negative pressure (Vacuum) as well as positive pressure. This is used to measure pressures at suction point of compressor.

      Motor pump: the pump is used as stirrer in the system so as the refrigeration effect should uniformly done.

      Energy meter : its main purpose is to indicate the energy consumed by the compressor

      Thermostat: it acts as a cut off of the system it switch off the

      In refrigeration test rig, working medium is liquid; which involves sensible as well as latent heat. And coefficient of performance of refrigeration test rig is more than that of aircompression system. Most of the modern refrigerators work on refrigeration test rig. Therefore it is necessary for engineering students to Study the performance of refrigeration cycle & its different parameter, performance, calculations is focus of this trainer.

      Base Stand: This is made up of CRCI square tubes & sheets. This is painted specially with Powder coating. All equipments are mounted on Base stand.

      Hermetically Sealed Compressor: This is used to take the refrigerant Vapor at low pressure & low temperature & compress it to a high pressure & high temperature. The capacity of compressor is 0.75 HP

      Condenser: The condenser is the forced air-cooled type for which condenser fan and motor has been provided. The function of condenser is to convert high-pressure refrigerant Vapor into high-pressure refrigerant liquid. The outside diameter of condenser is 3/8. Size of condenser as per standard specification is 11 x 10 x 3 Rows

      Expansion Devices: (Capillary Tube): Capillary tube is the expansion device

      which is used for small units of ½ to 3 tons. The purpose of expansion valve in a refrigeration system is to reduce the high side pressure to the low side pressure so that liquid can evaporate by picking up heat. The length and the small

      compressor as soon as the temperature of the evaporator drops below set point.

      Herter coil: it acts as the load to the refrigeration effect and the heater is placed inside the evaporator.

      Volt and Ammeter meter: the volt meter indicates the voltage across the heater coil while the ammeter indicates the current drawn by the heat.

      Specification:

      TABLE 2. DIMENSIONS OF CONDENSOR PIPE

      TABLE 3. DIMESIONS OF FINS

      TABLE 4. DIMESIONS OF CONDENSOR SHELLS

      Fig. 2 Evaporator

      Fig. 3 Evaorator

      Fig 4. Compressor

      Fig 5. Compressor

      TABLE 5. Evaporator dimension

      Fig 6. Experimental setup

      TABLE 6. Components of experimental setup

   5. Experimental procedure

      • Fill the evaporator tank up to the end level.

      • Ensure that hand valve is in fully closed.

      • Apply 230 V supply by inserting the three pin top in socket provided on the distribution board in your laboratory.

      • Switch on the mains supply and stirrer on/off switch.

      • Switch on electric heater by rotating dimmer in clockwise direction, and if the ambient temp is less Please load the system initially to 35 0 C before starting the compressor.

      • Switch on the compressor on/off switch.

      • Check that compressor energy meter starts & Rotameter float is lifted up indicating that the compressor is working. The pressure gauge reading is increasing and compound gauge reading is decreasing.

      • Observe that Temperature of load tank (T5) decreases showing cooling effect.

      • Note down the readings according to observation table

      • Switch off the compressor on/off & stirrer on/off switch.

      • Switch off the main switch.

      • Repeat the above procedure for other experiments. Installation Procedure:

      • Connect the 230-VA.C. Supply to the unit. Use Proper neutral & Earthing.

      • Fill the water in the evaporator tank.

      • . Switch on the Compressor on/off switch only if the pressure shows on the Gauges are nearly equal.

      • Check that temperature indicator shows ambient temperature for all 12 channels.

      • The Rotameter shows the flow of refrigerant gas, which is indicated by lift of float in the glass tube. Also check that suction pressure P1 drops and discharge pressure P2 increases.

      • Observe with channel 7, the temperature T7 of the Evaporator tank & see that it is reducing. That means the trainer is giving refrigeration effect.

   6. Nomenclature

      TABLE 7. Nomenclature

      Calculation for R134a:

      Suction temp.-28.2oC H1= 428 KJ/Kg

      Discharge temp.-86.2 oC H2=485 KJ/Kg Temp. at condenser outlet-39.9 H3=251 KJ/Kg Temp. at evaporator inlet-0.6 H4=251 KJ/Kg

   7. COP Calculation

   Observation table: (R134a)

   Rotameter reading = 45-47 lph, mass of Fluid = 20 kg Pressure in bar- P1=1.24 bar

   P2=9.13 bar

   Fig 7. Representation of cycle of R134a on ph chart Refrigerating Effect= H1- H4

   Refrigerating Effect= 428-251 Refrigerating Effect= 171 KJ/Kg Compressor Work= H2- H1 Compressor Work= 485-428 Compressor Work= 57 KJ/Kg

   COPtheoretical = Refrigetating effect/ Compressor work

   COPtheoretical = 171/57 COPtheoretical = 3.

   Actual COP:

   Refrigerating effect= 0.3256 KW

   R600a:

   Compressor Work = (10*3600)/(33*3200)

   = 0.3409KW

   COPActual = Refrigerating effect/Compressor work

   =0.3256/0.3409 = 0.9556 = 1

   Tonnage Capacity:

   Tonnage capacity = Refrigerating effect/3.51

   = 0.3256/3.51

   = 0.092 tonn

   Calculation: (R600a)

   Rotameter reading = 35-37 lph : mass of Fluid = 20 kg

   Pressure in bar P1=1.37 bar

   P2=6.2 bar

   Suction temp-9.4oC H1=580 KJ/Kg

   Discharge temp-60.4oC H2=640 KJ/Kg Temp. at condenser outlet-42.8o C H3=360 KJ/Kg Temp. at evaporator inlet-6.9oC H4=360 KJ/Kg

   Fig 8. Representation of cycle of R600a on ph chart

   Refrigerating Effect= H1- H4 Refrigerating Effect= 580-360 Refrigerating Effect= 220 KJ/Kg Compressor Work= H2- H1 Compressor Work= 640-580 Compressor Work= 60 KJ/Kg

   COPtheoretical = Refrigetating effect/Compressor work

   = 220/60 = 3.66

   Actual COP:

   R. E = m*Cp*(T11@3:55-T11@4:25)/Time(sec)

   = 20*4.187*(18.3-10.1)/( 30*60)

   = 0.3814KW

   Compressor Work = (10*3600)/(Time*3200)

   = (10*3600)/(36.5*3200)

   = 0.3082 KW.

   COPActual = Refrigerating effect/Compressor work

   = 0.3814/0.3082 = 1.23

   Tonnage Capacity:

   Tonnage capacity = Refrigerating effect/3.51

   = 0.3814/3.51 = 0.108

3. CONCLUSION

• By Changing the Refrigerant from R134a to R600a the system theoretical COP is increased by 22.2% and actual COP by 29.4%.

• Power Consumption is reduced considerably by 9.5%.

• Compressor works controlled temperature under 63 oC which less as compared to R134a i.e. 82 oC.

• We get better cooling effect in less time in evaporator by using R600a.

• Load on the compressor while running on R600a as refrigerant is less as Compared to the compressor running on R134a as refrigerant.

REFERENCES

1. D.Bulter, life after cfcs and HCFC, CIBSE national conference 2001.

2. S.Devotta, S.gopichand, comparative assessment of HFC 134a and some refrigerant as alternative to CFC12, International general of refrigeration 15(1992) 112-118.

3. C.P.Arora, Third edition of refrigeration and air conditioning, Tata McGraw Hill Education Private limited New Delhi P.G. No (3-4)

4. D.Ravindra, Difference between CFC/HCFC and HFC refrigerant Air Conditioning and refrigeration journal Part-II January-February 2014.

5. Vincenzo La Rocca, Giuseppe Panno Experimental performance evolution of a vapour compression refrigerating plant when replacing R22 with alternative refrigerant.

6. Mihail-Dan & N. Staicovici, International Journal of Heat and Mass Transfer, Are investigates A method of improving the effectiveness of a mechanical vapour compression process and of its applications in refrigeration 3 August 2010.

7. Bilal Ahmed Qureshi, Syed M. Zubair, International Journal of Refrigeration, Performance degradation of a vapour compression refrigeration system under fouled conditions Mechanical Engineering Department, King Fahd University of Petroleum & Minerals, KFUPM Box # 1474, Dhahran 31261, Saudi Arabia.