Design And Fabrication Of Domestic Deep Freezer

CHAPTER THREE
ANALYSIS OF REFRIGERATION SYSTEM AND CHOICE OF
PROJECT AS BEST
3.0 THE CYCLE OPERATION OF
•    The cycle operation of vapor compression is as follow
•    The liquid refrigerant (e.g Riz) enter the evaporator
•    As liquid refrigerant and absorbs heat in the evaporator, the vapor is drawn through the suction line to the compressor.
•    From the compression the refrigerant is compressed at supper heated temperature and high pressure to the condenser
•    All the condenser the refrigerant is considered at high pressure and heat is disputed
•    The liquid refrigerant is there pass through device to the evaporator at low temperature as a contribution of vapor and liquid
•    At the evaporator, the refrigerant absorb the latent heat to become complete vapor before being passed to the suction side of the compressor.
3.1 TYPES OF GAS COMPRESSOR
The most common compressor used in chiller are reciprocating, rotary screw centrifugal and scroll compressors, each applitrapping refrigerant vapor and reducing the volume of the refrigerant along the rotors to the discharge point (Myers Richard, (2003).
Centrifugal compressor: Centrifugal compressors are dynamic they compress refrigerant by imparting velocity or dynamic energy, using a rotary impeller and converting it to pressure energy.
Scroll compressor: Scroll compressor are also positive displacement compressors, the refrigerant is compressed when are spiral or bit around a second stationary spiral, creating smaller and smaller pocket and higher pressures by the time the refrigerant is discharged it is fully pressurized.
There are many size of compression packages and services from large scale facilities to smaller, short term projects. Flexible options include worldwide new-build compressor packages, used compression package and non- U.S rental and full services.
Gas compression applications as many types these are gas lift and re-injection, gathering, gas processing gas turbine fuel boosting, transmission and storage, Floating Production, Storage and Offloading (FPSO)
3.2 THERMODYNAMIC ANALYSIS OF TIlE SYSTEM
The thermodynamic of the vapor compression cycle can be analyzed on a temperature versus entropy diagram as depicted in figure. The circulating refrigerant enters the compressor as a saturation vapor which is entropically compressed (i.e compressed at constant entropy) and exists the compressor as a super heated vapor (Painker Mike, (1999).
From point 2 and 3, the super heated vapor travel through the part of the condenser which remove the super heat by cooling the vapor between point 3 and 4. The vapor travel through the remainder of the condenser and is condensed into a saturated liquid. The condensation process occurs at essentially constant pressure.
Between point 4 and 5 the saturated liquid refrigerant passes through the expansion value and under goes on abrupt decreases of pressure. The process result in adiabatic flash evaporation and auto refrigeration of the liquid (typically; less, than half of the liquid flashes), the adiabatic flash evaporation process is Isenthelpic (i.e occurs at a constant enthalpy).
Between 5 and 1, the cold are partially vaporized refrigerant through the coil or tubes in the evaporation where it is totally vaporized by the warm air (form the space being refrigerated) the fan circulate across the coil or tube in evaporator. The evaporator operates at essentially constant pressure the resulting saturated refrigerant vapour return to the compressor in let at point 1 to complete the thermodynamic cycles. It should be noted that the above discussion is based on the ideal vapor compression refrigeration cycle which does not take account in real world items like frictional pressure drop in the system, slight internal irreversibility during the compresion of the refrigerant vapor, or non-ideal gas behavior.