The methods were studied to improve the cooling performance of the absorption refrigeration system(ARS) driven by low-grade solar energy with ultrasonic wave, while the mechanism of ultrasonic wave strengthening boili...The methods were studied to improve the cooling performance of the absorption refrigeration system(ARS) driven by low-grade solar energy with ultrasonic wave, while the mechanism of ultrasonic wave strengthening boiling mass transfer in LiB r solution was also analyzed with experiment. The experimental results indicate that, under the driving heat source of 60–100 oC and the ultrasonic power of 20–60 W, the mass flux of cryogen water in Li Br solution is higher after the application of ultrasonic wave than auxiliary heating with electric rod of the same power, so the ultrasonic application effectively enhances the heat utilization efficiency. The distance H from ultrasonic transducer to vapor/liquid interface significantly affects mass transfer enhancement, so an optimal Hopt corresponding to certain ultrasonic power is beneficial to reaching the best strengthening effect for ultrasonic mass transfer. When the ultrasonic power increases, the mass transfer obviously speeds up in the cryogen water; however, as the power increases to a certain extent, the flux reaches a plateau without obvious increment. Moreover, the ultrasound-enhanced mass transfer technology can reduce the minimum temperature of driving heat source required by ARS and promote the application of solar energy during absorption refrigeration.展开更多
Numerical simulations have been carried out for two dimensional wavy falling liquid films on a vertical wall. The algorithm of the simulation is based on MAC method and schemes for interfacial boundary conditions are ...Numerical simulations have been carried out for two dimensional wavy falling liquid films on a vertical wall. The algorithm of the simulation is based on MAC method and schemes for interfacial boundary conditions are modified. Small artificial perturbations given at the inflow boundary grow rapidly and then the amplitude of the waves approaches to developed waves. Effects of the disturbance frequency on the wave development behavior and heat transfer characteristics are especially investigated. For low frequency, a disturbance wave develops to a solitary wave consisted of a large amplitude roll wave and small amplitude capillary waves. Increasing the frequency, the wave amplitude decreases and the capillary wave disappears. For further high frequency, the disturbance amplitude reduces along down stream. The heat transfer coefficient is enhanced by the surface wave and has a maximum at a certain frequency. The streamlines and the temperature contours are shown for various frequency waves and the heat transfer enhancement mechanism is clarified.展开更多
基金Project(51275180)supported by the National Natural Science Foundation of ChinaProject(S201304416899)supported by the Natural Science Foundation of Guangdong Province,ChinaProject(sybzzxm201213)supported by Doctorate Dissertation Funds of Guangdong Province,China
文摘The methods were studied to improve the cooling performance of the absorption refrigeration system(ARS) driven by low-grade solar energy with ultrasonic wave, while the mechanism of ultrasonic wave strengthening boiling mass transfer in LiB r solution was also analyzed with experiment. The experimental results indicate that, under the driving heat source of 60–100 oC and the ultrasonic power of 20–60 W, the mass flux of cryogen water in Li Br solution is higher after the application of ultrasonic wave than auxiliary heating with electric rod of the same power, so the ultrasonic application effectively enhances the heat utilization efficiency. The distance H from ultrasonic transducer to vapor/liquid interface significantly affects mass transfer enhancement, so an optimal Hopt corresponding to certain ultrasonic power is beneficial to reaching the best strengthening effect for ultrasonic mass transfer. When the ultrasonic power increases, the mass transfer obviously speeds up in the cryogen water; however, as the power increases to a certain extent, the flux reaches a plateau without obvious increment. Moreover, the ultrasound-enhanced mass transfer technology can reduce the minimum temperature of driving heat source required by ARS and promote the application of solar energy during absorption refrigeration.
文摘Numerical simulations have been carried out for two dimensional wavy falling liquid films on a vertical wall. The algorithm of the simulation is based on MAC method and schemes for interfacial boundary conditions are modified. Small artificial perturbations given at the inflow boundary grow rapidly and then the amplitude of the waves approaches to developed waves. Effects of the disturbance frequency on the wave development behavior and heat transfer characteristics are especially investigated. For low frequency, a disturbance wave develops to a solitary wave consisted of a large amplitude roll wave and small amplitude capillary waves. Increasing the frequency, the wave amplitude decreases and the capillary wave disappears. For further high frequency, the disturbance amplitude reduces along down stream. The heat transfer coefficient is enhanced by the surface wave and has a maximum at a certain frequency. The streamlines and the temperature contours are shown for various frequency waves and the heat transfer enhancement mechanism is clarified.
