A Theoretical Analysis of Air Cooling System Using Thermal Ejector Adapted to Operation Conditions for Control Strategy

The thermal ejector is a passive component used for thermal compression, activated by heat

(waste or solar), applied mainly for cooling and refrigerating. Nowadays, it is of interest to

many researchers and engineers worldwide. The present study introduces a theoretical analysis

of the cooling system which uses a gas ejector thermal compression. In such work, the ejector

performance is adapted according to the operation conditions of the cooling system in order to

attain a control strategy to satisfy the required cooling load with acceptable performance.

Theoretical models are developed and applied for the design and simulation of the ejector.

Besides the conservation equations of mass, energy and momentum, the gas dynamic equations,

state equations, isentropic relations as well as some appropriate assumptions are applied to simulate

the flow and mixing in the ejector. These models coupled with the equations of the other components

(condenser, evaporator, pump, and generator) are used to analyze the performance of the cooling system.

Two FORTRAN programs are developed to carry out the investigation; one for the ejector design and the

other is for the simulation purpose. Properties of refrigerant R134a are calculated using real gas equations.

Among many parameters, it is thought that the generator pressure is the cornerstone in the cycle. So, it is considered as the

key parameter in this investigation to evaluate the cycle performance. The effectiveness of the model is verified by

comparing the calculated results with experimental data available in the literature. Then, the simulation results have

been used to propose a control strategy to select the appropriate ejector for a given operating condition,

where multiple parallel ejectors are used in the system. From the study results, it was found that; for generator pressures

lower than the design pressure, the ejector is working very well, where the cycle performance parameters equal to or lower

than the required values by the system design. At high generator pressures, strong shock waves inside the ejector are occurred,

which leads to significant condensing pressure at the ejector exit (condenser inlet). At such high pressure, the designed system

has the ability to deliver cooling capacity for high condensing pressure during hot seasons.

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