This doctoral thesis experimentally examines the novel two-component working fluid n-octane/water in an ejector refrigeration system. Water as a conventional working fluid serves as reference. Randomized measurements of water/n-octane are conducted for a more comprehensive comparison. For the first time, to the author's knowledge, the model of (Pounds et al., 2013), which is used to design binary fluid ejectors, is verified for two-component working fluids. Furthermore, the applicability of the diffusion pump model (DP model) of (Jaeckel, 1947), which is used to calculate the pump performance of diffusion pumps, is verified for the first time, to the author's knowledge, to the ejector refrigeration process. A pilot plant is used to conduct the experimental studies. It is driven indirectly on the mo-tive and suction sides by an electric thermostat with an electric power of approx. 3 kW and approx. 2 kW respectively. The pilot plant is operated in batches, which means that the mo-tive fluid and the suction fluid are introduced into the hot and cold evaporator before the experiment starts. The experiments have shown that mass flow ratios μ (= suction mass flow rate ÷ motive mass flow rate) significantly decrease with n-octane/water compared to the single fluid system water, despite a much higher molar mass of the motive fluid compared to the suc-tion fluid. Conversely, the pairing of the working fluid water/n-octane exhibits significantly higher μ-values than water. However, compared to the other two working fluid systems, n-octane/water exhibits a significantly lower μ-drop with decreasing suction pressures at constant process conditions and a suction mode at larger motive nozzle distances. Despite the lower μ-values, n-octane/water proves to be up to 35.7 % more efficient in terms of cooling power to thermal driving power, which can be attributed to the many times lower specific enthalpy difference for heating and evaporation of n-octane as propellant than that of water. The data obtained for n-octane/water and water/n-octane show that the model of (Pounds et al., 2013) is applicable to the design of binary fluid ejectors. However, the design quality strongly depends on the choice of the mixing chamber efficiency, which, while being sub-ject to the process conditions, is mainly determined by the molar mass ratio of the motive and suction fluids. For all three examined working fluid systems, the pump performance of the investigated ejector can be calculated with the DP model. It takes into account the two-component na-ture in the form of the diffusion coefficient, and, in contrast to the model of (Pounds et al., 2013), additionally factors in the motive stream surface in the mixing area involved in the mass transfer. For n-octane/water, the model is most consistent with the experiments’ re-sults, since this working fluid system is most similar to the diffusion pump application due to the high molar mass ratio. Furthermore, the model-based analyses support the findings of the experimental investigation regarding mass transfer in the examined ejector.
Untersuchung des Stofftransports in einem n-Octan/Wasser-betriebenen Dampfstrahlverdichter zur Anwendung in der Kältetechnik
Investigation of mass transfer in a n-octane/water driven ejector for refrigeration application
2021
Miscellaneous
Electronic Resource
German
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