AIM: TO STUDY THE PERFORMANCE OF THE DOMESTIC REFRIGERATION RIG.

Transcription

1 AIM: TO STUDY THE PERFORMANCE OF THE DOMESTIC REFRIGERATION RIG. Page1

2 CONTENT: 1. Product Description 2. Product Specifications 3. Operating Procedure 4. Observation Table 5. Calculations 6. Result Page2

3 1. Product Description A domestic refrigerator is one of the simplest of refrigeration devices widely used all over the world. It uses a fractional HP hermetically sealed compressor, a natural convection condenser, a capillary tube as an expansion device, and direct expansion type roll-bond evaporator. As far as the controls are concerned, an ON-OFF type thermostat controls the average temperature of the refrigerator. The inside heat transfer takes place by natural convection and convective currents set due to density difference of cold and warm air. Construction: The domestic refrigerator is having a vertical cabinet. The inside of which is made-up of PVC material. The outside construction is of CRCA sheet metal duly powder coated or epoxy coated paint. These two portions are separated by polyurethane foam insulation. The compressor (a hermetically sealed one ) is located at the rear end bottom portion. The condenser, which is made up of Dia. 5 mm MS tubes made in zigzag pattern. It is a natural convection type condenser. Small wire-like rods (which are called fins ) are fixed to the tubes in order to enhance the heat transfer rate to the surroundings. At the end of the condenser, there is filter /drier. Inside the cabinet, at the upper portion, there is location of evaporator. The evaporator tubes are made up of aluminum through which cold refrigerant circulates. A suction line accumulator is fixed at the end of evaporator. A lighting bulb operated by door switch is housed inside the cabinet. An adjustable thermostat with a defrosting mechanism is placed to control the temperature inside the refrigerator. Suitable shelves, racks and compartments are provided inside the cabinet for the required items to be stored and preserved. Working: The refrigerator works on vapour compression cycle. The refrigerant vapour is compressed by means of compressor to a pressure at which temperature obtained at the end of compression will be more than the atmospheric so that, at this high temperature, it will reject heat to the atmosphere and will then get condensed. The condensate is then allowed to pass through a capillary so that the pressure and temperature are lowered. Capillary tube acts as a throttling device. The low temperature refrigerant enters the evaporator, where it absorbs heat from the Page3

4 surrounding space and consequently, the refrigerant evaporates. This saturated or superheated vapour is sucked by the compressor and the cycle is repeated. Along with these major components, there will strainer/ drier and accumulator. The strainer/drier will absorb residual moisture if at all present in the refrigerant to avoid freezing in the capillary. The accumulator will not allow the liquid refrigerant to enter into the compressor. Defrosting: Frost is collected on the evaporator coil as the temperature of the coil is lower than the freezing temperature of water. Frost thickness increases due to frequent door opening. As Frost (ice) is poor conductor of heat, the accumulation of frost on the coils adversely affects the heat transfer between the cabinet air and the refrigerant. It increases the running time of refrigerator and hence power consumption. Therefore regular de-frosting must be done when frost thickness increases above 6 mm. In the present case, the manual defrosting is done by pushing the red button, which stops the compressor on pushing it. When the ice is melted, the compressor will restart. Page4

5 2. Product Specifications Refrigerator : WHIRPOOL make Capacity : 142 Lit Power Source : V ; 50HZ; 1 Phase, AC Refrigerator : Storage Shelves Provided (2 Shelves) Shelf-half adjustable/full folding provided Crisper, Shelf for Bottle, Eggs provided Load : Heater provided Compressor consumption : Energy Meter provided Heater consumption : Energy Meter Provided HP/LP Cutout : Provided Pressure Gauges, 2 Nos. : For measuring Suction and discharge gas pressure Temperature : Digital Temperature Indicator with selector to display refrigerant temperatures at salient points. Refrigerant : R-134a; Non CFC & Environment friendly. Page5

6 3. Operating Procedure Keep the unit on level surface. Give Stabilized power supply of 230 VAC, 50 Hz to the unit. Place the unit in a properly ventilated room. Start the unit. Wait for minimum 30 minutes to reach steady state. Record all the readings as per following observation table. Page6

7 4. Observation Table Date Sr. No. Parameter Unit Value INITIAL FINAL 1. Ambient Temperature 2. Temperature of refrigerant after compression T 1 3. Temperature of refrigerant after condensation. T 2 4. Temperature of refrigerant after expansion T 3 5. Temperature of refrigerant after evaporation. T 4 6. Average cabinet temperature T 5 7. Energy meter Reading for Compressor KWHr 8. Energy meter Reading for Heater KWHr 9. Suction Pressure Psig 10. Discharge Pressure Psig Page7

8 5. Calculations The Objectives of experiment are: To study construction and working of domestic refrigerator To evaluate cooling capacity of the refrigerator at the ambient temperature. To evaluate the actual Co-efficient of Performance of the refrigeration system. To evaluate the theoretical Co-efficient of Performance of the refrigeration system. To plot the cycle on P-H & T-S charts. Test Parameter Rating Or Normal Load Test Condition at Rated Voltage High Load or Adverse Load test Condition at Rated Voltage Test Ambient 90 0 F ( 30 0 C ) F (43 0 C) Average of liner (Cabinet) Air Temperature 38 F ( 3 0 C) 45 F (7 0 C) Time Requirement for pulldown is not specified by ISI and is left to declaration by manufacturer. However, it should be preferably maintained within these limits. 2 Hrs + ½ Hr. 3 Hrs + ½ Hr Ice formation test 1) Water Temperature at the time of placing Ice Tray (Trays should be loaded after reaching above pull down temperature) 2) Ultimate Ice Formation Temp F (30 0 C) 32 0 F (0 0 C) Page8

9 3) Ice Formation period (maximum Specified by ISI is 180 Minutes) 4) Capacity of Ice Trays 2Hrs + ½ Hr L Upto 100 L 0.50 L Upto 165 L 0.70 L above 165 To evaluate cooling capacity of the refrigerator at the ambient temperature. The actual cooling capacity of the refrigerator (@ particular avg. cabinet temp) = Heater load = Final energy meter readinginitial energy meter reading = #Note: We neglect infiltration effect, i.e., the heat leaking from outside to inside through the cabinet insulation. To evaluate the actual Co-efficient of Performance of the refrigeration system. Actual refrigeration effect = Heater load = Final energy meter reading- initial energy meter reading Compressor work w = Final energy meter reading- initial energy meter reading Actual Coefficient of Performance = Actual refrigeration effect/ actual compressor work To evaluate the theoretical Co-efficient of Performance of the refrigeration system. Theoretical C.O.P. can be evaluated by plotting the cycle on p-h chart and finding out enthalpies at salient points. Page9

10 From P-H chart, Enthalpy of refrigerant after evaporation: H 1 = Enthalpy of refrigerant after compression: H 2 = Enthalpy of refrigerant after condensation: H 3 = Enthalpy of refrigerant after expansion: H 4 = Refrigeration effect N H4 H1 = = Compressor work W = H2 H1 Theoretical C.O.P. = N/W = 6. Results The cooling capacity of the refrigerator : watts Page10

11 The actual C.O.P. of the system: Page11