Lab 1 - Refrigerator Condensation.docx

ABSTRACT/ SUMMARY

INTRODUCTIONRefrigeration cycle is a sequence of thermodynamic process whereby heat is withdrawn from a cold body and move to hot body. It is a reverse heat engine cycle. In general word, refrigeration is a process of removing the heat from the enclosed space, or from substances to lowering its temperature. The primary device that can do the process is called the refrigerator and the working fluid used in the cycle process is called refrigerant. A refrigerator uses the evaporation of liquid to absorb heat. The liquid that is the refrigerant used the refrigerator evaporates at low temperature creating cooling or freezing temperature inside the refrigerator. Evaporators and condenser of the system is used for the absorption and rejection of heat respectively involve the field of heat transmission. Steady state are involve in the determination process cooling load requirement. The job of the refrigeration cycle is to remove unwanted heat from one place and discharge it into another. To accomplish this, the refrigerant is pumped through a closed refrigeration system. If the system was not closed, it would be using up the refrigerant by dissipating it into the surrounding media; because it is closed, the same refrigerant is used over and over again, as it passes through the cycle removing some heat and discharging it. The closed cycle serves other purposes as well; it keeps the refrigerant from becoming contaminated and controls its flow, for it is a liquid in some parts of the cycle and a gas or vapor in other phases.During the simple refrigeration cycle, and major components of which it is made: two different pressures exist in the cycle. The evaporating or low pressure in the low side and the condensing, or high pressure, in the high side. These pressure areas are separated by two dividing points; one is the metering device where the refrigerant flow is controlled, and the other is at the compressor, where vapor is compressed. The metering device is a point where we will start the trip through the cycle. This may be a thermal expansion valve, a capillary tube, or any other device to control the flow of refrigerant into the evaporator, or cooling coil, as a low-pressure, low-temperature refrigerant. The expanding refrigerant evaporates as it goes through the evaporator, where it removes the heat from the substance or space in which the evaporator is located. Heat will travel from the warmer substance to the evaporator cooled by the evaporation of the refrigerant within the system, causing the refrigerant to boil and evaporate, changing it to a vapor. This is similar to the change that occurs when a pail of water is boiled on the stove and the water changes to steam, except that the refrigerant boils at a much lower temperature. Now this low-pressure, low-temperature vapor is drawn to the compressor where it is compressed into a high-temperature, high-pressure vapor. The compressor discharges it to the condenser, so that it can give up the heat that it picked up in the evaporator. The refrigerant vapor is at a higher temperature than the air passing across the condenser or water passing through the condenser therefore that is transferred from the warmer refrigerant vapor to the cooler air or water. In this process, as heat is removed from the vapor, a change of state takes place and the vapor is condensed back into a liquid, at a high-pressure and high-temperature. The liquid refrigerant travels now to the metering device where it passes through a small opening or orifice where a drop in pressure and temperature occurs, and then it enters into the evaporator or cooling coil. As the refrigerant makes its way into the large opening of the evaporator tubing or coil, it vaporizes, ready to start another cycle through the system. The refrigeration system requires some means of connecting the basic major components - evaporator, compressor, condenser, and metering device - just as roads connect communities. Tubing or lines make the system complete so that the refrigerant will not leak out into the atmosphere. The suction line connects the evaporator or cooling coil to the compressor, the hot gas or discharge line connects the compressor to the condenser, and the liquid line is the connecting tubing between the condenser and the metering device that is the thermal valve. Some systems will have a receiver immediately after the condenser and before the metering device, where the refrigerant is stored until it is needed for heat removal in the evaporator.

OBJECTIVES

Experiment 1: Determination of power input, heat output and coefficient of performance

To determine the power input, heat output and coefficient of performance of a vapour compression heat pump system.

Experiment 2: Production of heat pump performance curves over a range of source and delivery temperatures To produce the performance of heat pump over a range of source and delivery temperatures.

Experiment 3: Production of vapour compression cycle on p-h diagram and energy balance study To plot the vapour compression cycle on the p-h diagram and compare with the ideal cycle. To perform energy balances for the condenser and compressor.

Experiment 4: Production of heat pump performance curves over a range of evaporating and condensation temperatures

To plot the performance of heat pump over a range of evaporating and condensation temperatures which are the saturation temperature at condensing pressure.

Experiment 5: Estimation of the effect of compressor pressure ratio on volumetric efficiency To determine the compression ratio and volumetric efficiency

THEORYWhen enough heat is released from a glass of water, the water will freeze to ice. When that heat is absorbed by the ice, the ice will melt. Heat has its own laws, called the laws of thermodynamics. One of those laws is that heat will move from a place that has a lot of heat to a place that has less heat, or another way to put it is that heat will move from a place of higher intensity to a place of lower intensity. From refrigeration theory, air conditioning and refrigeration equipment is designed to create a cold area that acts as a "heat sponge" that will soak up heat from air or food. The heat is then moved to a place where it can be released safely and efficiently. The second point is to understand about refrigeration theory has to do with why we use evaporators and condensers. When a liquid like water or refrigerant absorbs enough heat to start boiling, what's happening is that the added heat energy causes the vibration of the liquid's molecules to speed up to the point where they move far apart from each other. When the molecules of liquid reach a certain distance from each other, the liquid changes into a vapor. This is called boiling, evaporating, or vaporizing. A liquid absorbs some levels of heat as it changes state to a vapor and air conditioning and refrigeration equipment is designed to use this point of refrigeration theory by keeping a constant flow of refrigerant vaporizing and absorbing heat in the evaporator. The evaporator is the "heat sponge" area, and the refrigerant vaporizing inside of it is absorbing the heat. When vapor cools and releases enough heat energy, it's molecules will slow down and move closer together to the point where the vapor changes into a liquid. This is called condensation, and it's also a change of state. To condense, a vapor must release the same level of heat that it absorbed when it vaporized. Air conditioning and refrigeration uses this point of refrigeration theory by causing refrigerant to cool and condense in the condensing unit. The refrigerant repeats this cycle continuously, absorbing heat in the evaporator and releasing it in the condenser.

APPARATUS 1. R-134-A Compressor2. Evaporator3. Water inlet and water outlet4. Filter dryer5. Power supply6. Water7. Valve

PROCEDURESGeneral Start-up Procedures1. Both of the water source and the drain were checked before being connected, then water supply is opened and the flow rate of cooling water was set to be at 1.0 LPM.2. Checked that the drain hose at the condensate collector is connected.3. The power supply is connected and switched on the main power follows by main switch at the control panel.4. Then switched on the refrigerant compressor until the pressure and temperature were in stabilizing condition.

General Shut-down Procedures1. Turned off the compressor, followed by main switch and power supply.2. Closed the water supply and make sure that there is no water left running.

Experiment 1: Determination of power input, heat output and coefficient of performance1. Set up the apparatus.2. The flow rate of cooling water was adjusted to 40%.3. The system was run for 15 minutes.4. Recorded all the data into the experimental data sheet.Experiment 2: Production of heat pump performance curves over a range of source and delivery temperatures1. By continuing the steps in experiment 1, we adjusted the cooling water flow rate to 60%.2. The data was recorded.3. The experiment was repeated with reducing water flowrate so that the cooling.water outlet temperature increases by about 3C.4. Repeated similar steps until the compressor delivery pressure reaches around 14.0 bars.5. All the steps were repeated by different ambient temperature.

Experiment 3: Production of vapour compression cycle on p-h diagram and energy balance study1. Followed the general start-up steps.2. The flow rate of cooling water is adjusted to 40% and let the system run for 15 minutes.3. Recorded all data in the experiment.

Experiment 4: Production of heat pump performance curves over a range of evaporating and condensation temperatures1. The general start-up procedures are handled.2. Adjusted the cooling water flow rate to 60% and allowed the experiment for 15 minutes.3. All data are recorded. 4. The experiment was repeated with increasing the compressor delivery pressure about 0.6 bars with reducing the water flow rate. Maintained the evaporating temperature (TT4) by covering part of the evaporator.5. Similar steps were repeated with a different water flow rate that must be more than 20%. Make sure that the compressor delivery pressure does not exceed 14.0 bars.6. The experiment is repeated with another constant evaporating temperature (TT4).Experiment 5: Estimation of the effect of compressor pressure ratio on volumetric efficiency1. Followed the general start-up steps.2. Adjusted the cooling water flow rate to 40% and let the system run for 15 minutes.3. All the data is recorded.4. Repeated the experiments by using different compressor delivery pressure.

RESULT :1. Experiment 1 : Determination of power input, heat output and coefficient of perfomance

Cooling water flow rate, FT1%40

Cooling water flow rate, FT1LPM2.0

Cooling water inlet temperature, TT5C29.8

Cooling water outlet temperature, TT6C31.0

Compressor power inletW162

2. Experiment 2 : Production of heat pump perfomance curves over a range of source and delivery temperatures

Test123

Cooling water fow rate, FT1%604020

Cooling water flow rate, FT1LPM3.02.01.0

Cooling water inlet temperature, TT5C30.029.829.6

Cooling water outlet temperature, TT6C31.031.032.2

Compressor power inputW160162160

Heat outputW

COPH

3. Experiment 3 : Production of vapor compression cycle on p-h diagram and energy balance studyRefrigerant flow rate, FT2%40

Refrigerant flow rate, FT2LPM0.5

Refrigerant pressure (low), P1Bar (abs)1.9

Refrigerant pressure (high), P2Bar (abs)7.0

Refgirant temperature, TT1C27.5

Refrigerant temperature, TT2C65.5



Cooling water flow rate, FT1%40.3

Cooling water flow rate, FT1LPM2.0




4. Experiment 4 : Production of heat pump perfomance curve over a range of evaporating and condensation temperatures

Test123

Refrigerant flow rate, FT2%604020

Refrigerant flow rate, FT2LPM0.760.500.25

Refigerant pressure (low), P1Bar (abs)2.002.002.40

Refigerant pressure (high), P2Bar (abs)7.107.007.20

Refrigerant temperature, TT1C28.0027.5028.10




Enthalpy 1 (P1,TT1)kJ/kg276.63276.71277.24



Evaporating temperature (TT4)C23.3023.1022.70

Condensing temperatureC25.023.022.5


Heat delivered in condenser (refrigerant)

W

2377.31

1323.67

889.99

COPH14.868.175.56

5. Experiment 5 : Estimation of the effect of compressor pressure ratio on volumetric efficiency

Refrigerant flow rate, FT2%40

Refrigerant flow rate, FT2LPM0.50

Refrigerant pressure (low), P1Bar (abs)1.90

Refrigerant pressure (high), P2Bar (abs)7.00


CALCULATIONS

1. Cooling water flow rate, Cfr (LPM) = 2. Refrigerant flow rate, Rfr (LPM) =

For experiment 1,Cfr = 2.0 LPMi. Power input = 162 Wii. Heat output = Cfr x specific heat capacity x T = = 167.2 Wiii. Coefficient of performance, COPHCOPH = = = 1.03

For experiment 2i. Heat Output:

1. For 60 %

Heat Output = = 69.67W

2. For 40 %

Heat Output = = 83.8 W

3. For 20 %

Heat Output = = 181.13 W

ii. COPH = 1. For 60 %COPH = = 0.435

2. For 40 %COPH = = 0.517

3. For 20 %COPH = = 1.133

For experiment 3i. Energy balance on the condenser

Heat transfer from the refrigerant.

Heat transfer to the cooling water

ii. Energy balance on the compressorPower input in the experiment = 162 W

Heat transfer to the refrigerant

For experiment 5Compressor pressure ratio = = = 3.68

Refrigerant mass flow rate= x x x = 0.00956

Volumetric flow rate of refrigerant at the compressor suction,V1=Refrigerant mass flow rate x specific volume of refrigerant at compressor suction= 0.00956 x 0.059 =0.000564 Compressor swept volume= 2800 x x =

Volumetric Efficiency = = x 100% = 136.56%

EXPERIMENT 2 :Performance of Heat Pump against Cooling water outlet Temperature

COPHCooling Water Outlet Temperature (C)Power Input & Output ( W )

EXPERIMENT 3:

EXPERIMENT 4 :

DISCUSSIONGenerally, this experiment involved the increasing amount of clearance volume is a way of decreasing the capacity of compressor. Capacity control of the compressor is achieved in reciprocating type compressor by varying speed in engine driven units through fuel flow control. But speed reduction is limited to 40% of the top speed to provide constant torque. Capacity control for screw type compressor is done with variable speed and variable compressor displacement. Then, a slide valve is positioned in the casing that directs a portion of the compressed air to the suction valve when the capacity is reduced. In experiment 1, the purpose of the experiment was the determination of power input, heat output and coefficient of performance (COP). COP for heat pump is the ratio of the energy tranferred for heating to the input electric energy used in the process. Based on the theory, ideal COP should be greater than 1 and higher the COPs equate to lower operating costs. From the data, approved that our COP value is 1.03 which is greater than 1. Absolutely proved that the power input is inversely propotional to the coefficient of performance.For experiment 2, we can know the value of cooling outlet temperature, cooling inlet temperature and compressor power. The data will be taken by the change of flow rate water that is 20%, 40% and 60%. The 80% of flow rate water cannot be applied because of the compressor cannot achieve it.Based on the p-h diagram of the refrigeration of the R-134a in experiment 3, there is a process that undergoes when running the experiment that being called as a vapor compression cycle. In the vapor compression cycle process, the process starts with the vaporization of the refrigerant in the evaporator. The process continues with the compression that is used to raise the pressure of the refrigerant so that it can condense at a higher temperature. When all the vapor has condensed, the pressure is reduced in an expansion device, and the refrigerant returns to its original condition. The expansion is a constant enthalpy process. It is drawn as a vertical line on the P-h diagram. No heat is absorbed or rejected during this expansion, the liquid just passes through a valve because the liquid is saturated at the start of expansion by the end of the process it is partly vapor. On the other hand, the compression process is shown as a curve. It is not a constant enthalpy process. The energy used to compress the vapor turns into heat, and increases its temperature. This tends to raise the temperature of the vapor, making it to move further and further into the superheated part of the diagram as compression progresses. It takes a lot of heat to evaporate liquid. In other words a small amount of liquid circulating in a refrigerator can perform a large amount of cooling. This is one reason why the vapor compression cycle is widely used. The refrigeration system can be small and compact. Also from a practical point of view heat exchange is much better when using change of state - evaporation and condensation. However the expansion of the high pressure liquid, the vapour compression cycle is non- reversible.While for experiment 4, based on the graph the value of COPh for evaporating and condensation were different. For evaporating conditions, COPh is increased directly proportional to evaporation temperature. Furthermore, on condensation state, shows a decrease in cup with a decreasing condensation temperature. Basically, the cap decreases with an increase in temperature difference between condensation and evaporation. Based on theory, the value of COPh line must be lower than power input. However, our result was quietly different from the theory value. It may be the cause of some errors while handling the experiment. In experiment 5, we have to calculate the compressor pressure ratio and the volumetric efficiency. First of all, the refrigerant flow rate was set at 40% and we take the reading of the pressure low, P1 and high, P2. So we can calculate the compressor pressure ratio. The compressor pressure ratio is 3.68. For the volumetric efficiency is 136.56%. The result show bigger number and this may be due to some reading errors that we get during experiment. We can prevent this error by check the reading multiple time or repeat the experiment several times to get the average reading.

Conclusion The cooling water and refrigerant flow rate display is in percentage (%).The formula to convert cooling water and refrigerant flow rate to LPM is :

Cooling water flow rate, Cfr (LPM) =

Refrigerant flow rate, Rfr (LPM) =

The Coefficient of Performance is calculated by using the formula :COPh = while for heat output is calculated by using the formula: Heat output = Cfr x specific heat capacity x TFrom all the experiment, we can conclude that, the higher flow rate of water, the lower the coefficient of performance. For the temperature, the lower the flow rate, the higher the temperature of refrigerator. The power input is constant for all water flow rates that is around 160W to 162W. All objective is achieved.

RECOMMENDATION 1. Repeat the experiment a few times to get more accurate readings2. Before the experiment begin, ensure that the mechanical heat pump should run and warm up early for 15 minutes. It should be notice that, surrounding in the laboratory also affect the result, thus it hard to get an accurate reading.

REFERENCES

APPENDICES

Set up apparatus

Water inlet and outlet Compressor of refrigerant (R-134-A)

Documents

Lab 1 - Refrigerator Condensation.docx