In recent years, the systematic application of phase change materials (PCM) is continuously developing. In this paper, an innovative PCM ceiling coupled with earth-air heat exchanger (EAHE) cooling system was proposed for building cooling. The system aimed to combine the cooling capacity of soil and the energy storage capacity of PCM, thus improving the indoor thermal environment. Performance of the system was tested by experimental method while data analysis focused on the indoor side. To research the effect of cold storage time on the performance of the system, two different operation strategies were adopted for comparison: 8-h cold storage strategy and 12-h cold storage strategy. Moreover, a control group was set up to observe the performance of the system on indoor temperature under the same weather conditions. The result showed that the experimental room in which we installed this system could reduce peak temperature by 2.1 °C under 8-h timed cold storage strategy and 2.7 °C under 12-h timed cold storage strategy. What is more, under the two operation strategies, temperature and heat flux of the PCM ceiling had similar distribution characteristics. Different strategies mainly affected the sustainability of the system and phase transition efficiency of the PCM ceiling.
To study how the geometry of the plenum chamber in the bleed system of an axial compressor influences the losses therein and to establish a theoretical loss model for this system, a 1.5-stage axial compressor with a bleed system is studied numerically by means of computational fluid dynamics (CFD). The results show that losses in the bleed system occur mainly in the axisymmetric bleed slot and plenum chamber, accounting for ca. 85% of the total loss. For a bleed system with a vertical axisymmetric slot, the loss is more sensitive to the radial height than to the axial width of the plenum chamber. A loss model for each part of the bleed system is established via theoretical analysis, and then, a model of the overall bleed system is established by combining these submodels. The predictions of the theoretical loss model agree well with the CFD results: the maximum prediction error for the coefficient of the stagnation pressure loss in the bleed system is −1.38%, and the average prediction error is −0.8%. This loss model can be used when designing the geometry of a bleed system.
To improve the prediction accuracy of profile loss at low Reynolds number, a typical low-pressure turbine cascade T106D-EIZ was selected to numerically investigate the effect of Reynolds number on turbine cascade flow. A detailed analysis of profile loss was performed and a profile loss model considering the low-Re effect was developed. Results showed that the incidence angle has a great effect on the inlet and outlet Mach number at low Reynolds number, and the variation of inlet and outlet Mach number further affects the blade profile loss. A correction factor was introduced to consider the effect of incidence angle and Mach number on the profile loss. The profile loss coefficient and stalling incidence angle were both extended to lower Reynolds number based on the numerical results. A Smart Through Flow Analysis Program (STFAP) was developed using the finite volume method to solve the circumferentially averaged Euler equations of S2 surface. Aerodynamic performance of E3 5-stage low-pressure turbine was predicted by STFAP coupled with low-Re profile loss model. Compared with K-O model, the prediction accuracy of efficiency of low-pressure turbine last stage is improved by nearly 1.1 percentage points when the 5-stage low-pressure turbine is in a low Reynolds number state.
The electrostatic jet flow has been widely employed to crop-dusting, painting, fuel spray and combustion, electrostatic painting, dust particles and flue gas removal. In order to investigate the convolution flow structure near the nozzle, discuss the effects of electrostatic voltages on convolution flow form, development and the aggrandizement of droplets mass transfer. PIV (Particle Image Velocimetry) was employed to measure and analyze the convolution flow near the nozzle under different voltages, and the velocity vectors and streamlines were gained. Experiment and analysis indicate that convolution flow structure has been existed in electrostatic jet flow brim and the main jet flow section change is inconspicuous with voltages adding; Electrical filed intensity has been enhanced and the droplets convolution flow was picked up with the electrostatic voltages adding. The convolution flow structure could quicken the gas mix into the main jet flow, and enhanced the droplets absorbency.
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