CHAPTER 2
LITERATURE REVIEW
This chapter will explain the theoretical part of the component and information on the overall trends that will use in this project. This chapter also contains previous
work related to this project.
2.1 SIMULATION MODEL OF A VAPOR COMPRESSION
REFRIGERATION SYSTEM, BY H. YASUDA, S. TOUBER C.H.M.
MACHIELSEN, 1983
In the expansion valve, the only delay considered is that due to the response of the sensing bulb. The dynamics of this bulb are modeled as a series of four lumps,
namely, the refrigerant within the bulb, the body of the bulb, the pipe wall to which the bulb is attached and the refrigerant surrounding the bulb. The inertial transients inherent
in the motion of the valve are considered negligible in comparison with the system transients. The mass flow rate through the TXV is computed as proportional to the
superheat pressure subject to a static superheat pressure.
2.2 RESEARCHES ON DYNAMIC SIMULATION AND OPTIMIZATION OF
AUTOMOBILE AIR-CONDITIONING SYSTEM BY XUEJUN SUN, WEIHUA
LIU, XIONGCAI QUE ZHIJIU CHEN, 1999
The heat exchangers are modeled using a moving-boundary approach with each zone liquid-phase, two-phase superheated-phase modeled in the lumped parameter
form. Equations of mass and energy conservation are applied to each phase along with the heat exchange equations through the heat exchanger wall to the secondary fluid air.
The equations for the refrigerant side use the void fraction concept for each zone, treating the liquid zone as having a void-fraction of 0 and the superheated zone as
having a void-fraction of 1. The length of each zone is inherent in the mass and energy conservation equations for that zone.
The thermostatic expansion valve is modeled using a thermal-inertia delay for the sensing bulb. The sensed superheat is translated into a pressure signal, which is
applied to the diaphragm force balance to determine the nozzle area. This nozzle area and the pressure difference across the valve are used to determine the mass flow rate.
The orifice tube is modeled by the orifice equation and has no ‘input’ signals from the evaporator.
The system modeled includes both a receiver and an accumulator, since either but not both can exist on any given system. In both these components, the refrigerant is
modeled in its liquid and vapor phases as lumped parameters, in thermal equilibrium, and exchanging mass and energy of the phase-change. In both these components, both
phases also exchange heat with the components body. Heat transfer from the body to the ambient is not included.
In the compressor model, individual strokes are not considered and the complete compressor model consists of a mass balance between suction and discharge and an
energy balance between the polytrophic work of compression, enthalpy rise of the refrigerant, thermal capacitance of the compressor wall lumped and the heat
transferred to the ambient from the compressor wall. In addition to the system components, the passenger compartment is modeled
using a discredited disturbance-response transfer function, with the disturbances being the environment temperature and radiant heat and the responses being the cooling load
and the compartment temperature.
2.3 THERMOSTATIC EXPANSION VALVE
