Fabrication On Domestic Refrigerator

3.6    CONDENSER
The condenser is designed in allowing the cooling medium to maintain effective temperature difference over all area of the transfer cements. The refrigerant employed the system which generally governs the kind of medium employed for cooling the condenser which in turn limits the selection of condenser type. The condenser surface area required is calculated from the heat transfer formula.
 Q=udt…………………………….(Marsh,R.W.& Olivia C,(1976).
Where Q=heat reject by the conderser
Q=792.7 walts
u=over all the heat coefficient
U=397.6w/m2k
dT=(335-323)C
dT=120C
3.7    EVAPORATION
The direct dry type of evaporator is considered in the project base on the following factor:-
    The cost requirement
    Fabrication procedure
    Material availability
    Size of unit
The surface area of evaporator is derived from the heat transferformular.
3.8    IINSULAT1ON
There are material having extremely low heat conduction capacity,i.e the used in the construction of low temperature chamber such as domestic refrigerator, cabinet and cold covering are selected primarily for their ability to retard the flow of heat through their homogenous and heterogeneous mass. The characteristic of insulation used for structural and economic are as follow.
    It has strength
    It contain fire proof
    Low thermal conductivity
    Performance
    Light weight
    Water replant
3.9    CAPILLARY TUBE
The capillary tube is employed as a throttling device on a small commercial and domestic refrigerator unit only it is a small diameter tube that forms a permanently open artery between the high and side of the system.
Q=F (P2-P1…………………ThrelkeldJ.K,( 1970)
From system analysis base on the available data, the following procedure should be taken in selecting the appropriate tube diameters.
Data:    refrigerant mass flow rate = l8.92xl03
Refrigerant employed = Rl349
Inlet pressure outside the capacity 〖= 874kn/m〗^2
3.10    SUCTION LINE
It  is the usual practice to size the suction line so that the total loss in pressure will be approximately equivalent about 16.7C drop in the saturation temperature for halogenated hydrocarbon refrigerant and not over -172C for ammonia refrigerant. From the thermodynamic table of properties, volume of R134 gas at evaporator cullet of 118C is 0.1088m/kg. The mass flow rate in the system is l8.924xl0-3kg/s. The mass flow refrigerant is uniform throughout the system irrespective of the refrigerantas it flows through the cycle. Therefore the volume flow rate at the outlet of the evaporator (inlet to the suction line) is equal to mass flow ate by specific volume.
3.11    HEAT BALANCE FOR THE SYSTEM
From the first law of thermodynamic, in any thermodynamic process, there is no gain or loss of energy to each process of the cycle.
NOTE:     In applying the steady flow energy equation the kinetic and potential energy term were omitted. This is almost justifiable because the velocity of flow is slow, to avoid undesirable press loses and variation in lengthnothing the system is small for heat balance in the system the heat rejected in the condenser must be equal to form of heat added to the refrigerant one to the work of compressor.
For the value obtained above, heat rejected to the condenser.
3.12     COEFFICIENT OF PERFORMANCE (C.O.P)
The coefficient of performance is the ratio of heat absorb by the refrigerant by the refrigerantwhile passing through the evaporator to the work input required compressing the refrigerant in the compressor It the performance of a refrigerating system.
By definition,C.O.P.   (refrigerating effect )/(network input)[Osare O.A.,(1999)]
Therefore, the cycle.
C.O.P  (h_1-h_2)/(h_2-h_1 )………………………….[Osare O.A,,(1999)]
C.O.P  (17873-6459)/(206.88-178.73)
C.O.P  114.14/(28.-15)=4.05
C.O.P=4.05