• Energy Research

An experimental investigation is presented in this paper on the vapor compression refrigeration cycle used in an ice-making machine with a multi-channel evaporator. To study the operation performan...

Heat and mass transfer occurs among different species during the pressurization process with helium gas in cryogenic storage tanks, for which detailed investigations are necessary. In this article,...

Abstract A three-evaporator and dual-ejector refrigeration system was presented in this paper. By combining two single ejectors as a whole, the authors attempted to discuss the effects of key geometric dimensions of each stage on both stage performances with two-dimensional CFD simulation method. First, the CFD models were validated by experimental data. Then, the primary nozzle diameters of both stages were determined by the cooling load demands of the refrigerating and air-conditioning chambers. Next, the detailed effects of key geometric parameters such as the length of constant-pressure mixing section, the length of constant-area mixing section and area ratio of each stage on two-stage performances were identified with simulations. Finally, the optimum values of the key geometric parameters were obtained, and the results showed that the area ratio had the most significant influences on the entrainment ratio of both stages as compared to other parameters.

Abstract A calculation model is developed to investigate the pressurization performance and thermal stratification in a liquid hydrogen (LH2) tank. Viscous flow is considered in the stratification model to ensure the continuity of fluid flow and heat exchange. The tank pressure rise, energy distribution and thermal stratification are studied respectively. Compared to the results without considering the phase change, the tank pressure, the stratified layer temperature and the ullage temperature calculated with phase change considered, have increased about 69.98%, 70.90% and 15.53%. Moreover, influences of the gravity level, initial wall temperature and initial liquid height on the development of thermal stratification are analyzed. It turns out that the larger the gravity level is, the faster the liquid thermal stratification develops. The effect of the initial wall temperature on the growth of thermal stratification is the same. Both the ullage pressure and the stratified temperature increase with time. While the gravity level is larger than a certain value and the initial wall temperature is less than a certain value, the ullage pressure and the stratified temperature decrease firstly, and then increase. Meanwhile, it costs much more time for fluid thermal stratification development fully for a larger initial liquid height.

An oscillating heat pipe (OHP) is an effective heat transfer device for the thermal management of electronic devices. However, the heat transfer mechanism of the OHP was not fully understood due to its complicated operation characteristics. In this paper, the thermal performance of an OHP was experimentally studied. The condensation and evaporation temperature variations were monitored under different heat inputs and were then used to evaluate the OHP system operating characteristics. Thermal resistance was used as a key parameter to evaluate the thermal performance of the OHP system. The results indicated that as the heat input increased from 25 to 100 W, the average thermal resistance decreased while the stable evaporating and condensing temperatures increased. The equivalent heat transfer coefficient was derived theoretically. It showed that the reciprocal of the radial heat transfer coefficient increased with increasing liquid film thickness. Based on this result, an empirical correlation was proposed to evaluate the thermal resistance of an OHP system. This correlation was validated using both the experimental data provided in this study and the data collected from the open literature. The comparison results indicated that the proposed empirical correlation could reasonably predict the thermal resistance under different filling ratios and heat inputs.

Abstract Thermodynamic vent system (TVS) is of significance to long term on-orbit storage of cryogenic fuel. In the present study, one ground experiment is established to investigate the pressure control performance of TVS with the working fluid of HCFC123. The tank pressure variation and fluid temperature change are respectively studied in self-pressurization, injection mixing and active refrigeration phases. The refrigeration capacity supplied by TVS and fluid thermal stratification during different phases, are specially illustrated. The effectiveness of the pressure control performance by means of TVS has been proven in the present experiment. The total venting gas loss is about 17.3 kg for 16 throttling cycles. The corresponding refrigeration capacity of TVS is 1216–1415 W, with circulation volume flow of 95 L/h and throttling ratio of 16.8–18.9%. Moreover, it costs approximately 6 h for the liquid thermal stratification developing fully. While in active refrigeration phase, the vapor has the maximum temperature reduction of 9.2 °C, and the variation of the liquid temperature is limited in 2.0 °C. When compared to direct venting method, TVS has recovered more than 23.22% venting loss for 4.75 h' operation. On the whole, the effective pressure control and heat load elimination of TVS are greatly confirmed.