CONCLUSION

 

            As the conclusion, we can say that, refrigerator consists with two compartments - one for frozen items and the other for items requiring refrigeration but not freezing. It can throw all the heat from the loads inside the compartments and make it cooled and long lasting life. It suitable for application in food and medical industry.

            We can also said that the objective of this experiment have been completely achieved as required and at the same time, all the parameters required to be solved have been calculated and solved accordingly. In addition, all of the experiments have eventually being done according to the procedures given systematically and appropriately. 

DiSCUSSION 5

1)      Outline at least 3 measures to increase the COP_ref of a refrigeration system.

           

            To increase the COP_ref of a refrigeration system, some consideration must be taken. Such as:

                                       

                     i.            The Work input, W_net,in for the whole refrigerator.

                   ii.            Temperature difference between actual and before the process started.

                  iii.            Secondary working fluid. Such as ammonia.

                 iv.            The fluctuating of pressure that affect the refrigeration systems.

 

 

DiSCUSSION 4

1)      Give examples with appropriate diagrams and explanations of actual loads in refrigeration practice in a factory.

 

 

 

 

Figure 1: Batch continuous air blast freezer with counter flow air circulation

 

 

 

Figure 2: Batch continuous air blast freezer with cross flow air circulation

Figure 3: Batch continuous air blast freezer with cross flow air circulation

(Also constructed with counter current series flow air circulation

           

            As we know, the refrigerator is use to keep all the things cold by lowering their original temperatures; instead, an evaporating gas called a refrigerant draws heat away, leaving the surrounding area much colder. Refrigerators work on the principle of cooling through evaporation.

            A refrigerator consists of two storage compartments - one for frozen items and the other for items requiring refrigeration but not freezing. These compartments are surrounded by a series of heat-exchanging pipes. Near the bottom of the refrigerator unit is a heavy metal device called a compressor. The compressor is powered by an electric motor. More heat-exchanging pipes are coiled behind the refrigerator. Running through the entire system is pure ammonia, which evaporates at -27 degrees Fahrenheit (-32 Celsius). This system is closed, which means nothing is lost or added while it is operating. Because liquid ammonia is a powerful chemical, a leaking refrigerator should be repaired or replaced immediately.

            The same goes with the refrigeration practice (with actual loads) in a factory. As the example we can see from Figure 1, 2, 3 that the refrigerator fills with fish. The refrigeration process begins with the compressor. The process start when Ammonia gas is compressed until it becomes very hot from the increased pressure. This heated gas flows through the coils behind the refrigerator, which allow excess heat to be released into the surrounding air. This is why users sometimes feel warm air circulating around the fridge. Eventually the ammonia cools down to the point where it becomes a liquid. This liquid form of ammonia is then forced through a device called an expansion valve. Essentially, the expansion valve has such a small opening that the liquid ammonia is turned into a very cold, fast-moving mist, evaporating as it travels through the coils in the freezer. Since this evaporation occurs at -27 degrees F (-32 degrees Celsius), the ammonia draws heat from the surrounding area. This is the Second Law of Thermodynamics in effect. Cold material, such as the evaporating ammonia gas, tends to take heat from warmer materials, such as the water in the ice cube tray.

            As the evaporating ammonia gas absorbs more heat, its temperature rises. Coils surrounding the lower refrigerator compartment are not as compact. The cool ammonia still draws heat from the warmer objects in the fridge, but not as much as the freezer section. The ammonia gas is drawn back into the compressor, where the entire cycle of pressurization, cooling and evaporation begins anew. 

DiSCUSSION 3

1)      Explain the tem of COPref and its effect in rating refrigeration systems against economic considerations  

 

The energy efficiency or Coefficient of Performance (COP) of a refrigerating system can be defined as the ratio between the refrigerating capacity of the plant, which is given by Q (cooling/freezing capacity, kW) as well as the power or electricity consumption, P (kW) of the compressors and pumps. In terms of the COP, it is basically and primarily depending on the working cycle and the levels of temperature at evaporating or condensing temperature and the same goes with the properties of the refrigerant and system design as well as the size factor. In a way or another. The efficiency of a refrigerator is expressed in terms of the coefficient of performance (COP) and it denoted by the COP_ref as equation below:

For the refrigerator, the important thing is the quantity of the heat supply to the system from the surrounding. The power input is important because from its quantity, we can know how much must be paid for and constitutes the main item of the running cost. In a way or another, if the usage of electricity is high, certainly it may result to a higher cost and be very costly. Whereas, at lower electricity power consumption, it will certainly be more economical and lower down the cost factor.

DISCUSSION 2

1)      Fill in the parameters from a set of experimental data into the refrigeration system diagrams

           

 

DISCUSSION 1

 

1)      Plot the graph of COPref against evaporator load at constant condenser saturation     temperature. From the graph, discuss the effect on the COPref as the evaporation load is increased at a constant condenser temperature.

 

 

3

2

QC = 15.05

 

 

 

 

 

 

 

 

 

 

 

 

                                                    

	Qe = 13.7

 

 

From the experiment that we have done, it can be said that the maximum value of COP_ref obtained is given by the value of 10.94 which the load used is given by the value of 60N. While, the minimum value of COP_ref obtained is 8.00 which where the load is at 20N value. As for the graph obtained, it can be noted that, the graph tends to decrease at the value of load from 0N until 40N. Whereas, at the value between 40N to 60N, the graph line starts to increase and it actually reaches its maximum point (highest peak) at the value of 60N. However, the graph begins to decrease after it reaches its highest peak until to the value of 80N (final load).

 

Sample calculation

 

Load = 0

 

Evaporator

 

Q_4-1 = m_r (h1- h₄)

  m_r = 0.07441,                         h₁= 317.4,       h₄ = 132.6

Q_{4-1 =} 0.07441(317.4 – 132.6)

        = 13.7

 

Condenser

 

Q_2-3 = m_r (h₂- h₃)

    m_r = 0.07441,                       h₂ = 334.8,      h₃ = 132.6

Q_2-3 = 0.07441 (334.8 – 132.6)

       = 15.05  

 

Compressor

 

W_1-2 = P =    m_r (h₁- h₂₎            

         m_r = 0.07441,                  h₁= 317.4,    h₃ = 132.6      

W_1-2 = P =  0.07441(317.4- 132.6)        

              = 1.29             

 

COP_ref  =  

            =   317.4-132.6

                  334.8-317.4   

            =    10.62