The doctoral thesis at hand analyzes the characteristics and the potential of an exhaust gas heat driven jet-ejector cooling process working with R134a as refrigerant which is used for charge air cooling consecutive to the conventional charge air cooler of gasoline combustion engines in vehicles. The analysis focuses on the exhaust gas heat exchanger and the jet-ejector as core components of the cooling process which have been investigated separately by means of experiments and simulation. The heat flows transferable from the exhaust gases to the refrigerant are gene-rally sufficient to operate the jet-ejector cooling process almost in the entire operating range of the combustion engine. The necessary refrigerant-side conditions have been achieved in a simple heat exchanger prototype and the process may easily be controlled by the high side pressure of the refrigerant. The heat exchange at super-critical refrigerant pressures can be simulated with the developed model employing the adequate corrections of the well-established Nusselt relations with an arithmetic aver-age deviation of only 4.7% from the experimental results. The results of the model developed for the heat exchange at subcritical refrigerant pressures reproduce the experimental results satisfactorily for scope of the thesis. The down-scaling of the jet-ejector cooling process to the cooling capacity range of 1.5kW to 6kW for the automotive application has been experimentally demonstrated. A sufficient temperature lift and absolute evaporation temperatures of down to -15°C for the continued charge air cooling have been achieved. The entrainment ratio of the jet-ejection can be calculated for a given ejector geometry dependent on the three stagnation conditions with an arithmetic aver- age deviation of 7.8% using a simulation model which accounts for real gas effects and allows a fit of the calculated to the experimental results by means of a loss coefficient with a clear physical meaning. The potential charge air temperatures of 12°C to -3°C are adequate for improving the efficiency of gasoline engines. The additional energy consumption due to the refrigerant pump and the heat rejection demand, rather than the elevated back pressure or the additional fuel consumption due to the device's weight, may at low thermal coefficients of performance overcompensate the system's advantage. The high sensitivity of the thermal coefficient of performance to an increase of the ambient temperature is another essential disadvantage of the jet-ejection cooling process. The power densities are the substantial system advantage.
|School:||Technische Universitaet Berlin (Germany)|
|Source:||DAI-C 81/1(E), Dissertation Abstracts International|
|Subjects:||Mechanical engineering, Thermodynamics|
|Keywords:||Jet ejector cooling|
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