Haizhen Xian

Instability of interfaces of gas bubbles in liquids under acoustic excitation with dual frequency

Instability of interfaces of gas bubbles in liquids under acoustic excitation with dual frequency is theoretically investigated. The critical bubble radii dividing stable and unstable regions of bubbles under dual-frequency acoustic excitation are strongly affected by the amplitudes of dual-frequency acoustic excitation rather than the frequencies of dual-frequency excitation. The limitation of the proposed model is also discussed with demonstrating examples.

Heat Transfer Characteristics of Oscillating Heat Pipe With Water and Ethanol as Working Fluids

In this paper, experiments were conducted to achieve a better understanding of the oscillating heat pipe (OHP) operating behavior with water and ethanol as working fluid. The experimental results showed that there existed a necessary temperature difference between the evaporator and the condenser section to keep the heat pipe working. The maximum effective conductivity of the water OHP reached up to 259 kW/m K, while that of the ethanol OHP is of 111 kW/m K. Not all the OHPs are operated in the horizontal operation mode. The heat transfer performance of the ethanol OHP was obviously affected by the filling ratio and the inclination angle but the influence law is irregular The effect of the filling ratio and the inclination angle of the water OHP were smaller than that of the ethanol one. The heat transfer performance of the OHP was improved with increase of operating temperature. The startup characteristics of the OHP depended on the establishment of the integral oscillating process, which was determined by the operating factors. The startup temperature of the ethanol OHP varied from 40 degrees C to 50 degrees C and that of the water, OHP varied from 40 degrees C to 60 degrees C without considering the horizontal operating mode. The water OHP showed a better performance and more stable heat transfer characteristics than the ethanol OHP, which had no obvious advantages of the startup capability as well. [DOI: 10.1115/1.4002366]

Investigation on the Feasibility of Oscillating-Flow Heat Pipe Applied in the Solar Collector

Oscillating-flow heat pipe (OFHP) is a new type of heat-transfer device with many novel properties, having an attractive prospect for application in solar thermal utilization. Experiments on the heat-transfer performance of the OFHP with common size and the OFHP components designed for solar collectors were carried out. The results showed that the heat-transfer performance of OFHP of common dimensions varied slightly when the filling ratio varied from 40% to 60% and confirmed that the OFHP with an appropriate filling ratio has an excellent heat-transfer performance at most of inclination angles. The experiments also confirmed the feasibility for the OFHP application in solar collectors.

Study on Heat Transfer Enhancement of Oscillating-Flow Heat Pipe for Drying

The application of oscillating-flow heat pipe (OFHP) in drying is of great potential. In this article, two methods are proposed to enhance the heat transfer of OFHP: (1) pulse heating is adopted instead of conventional continuous heating; and (2) a tube with a nonuniform cross section is introduced. Experiments on the effects of these two methods have been studied in comparison with ordinary OFHP. Experimental results indicate that using the pulse heating and the nonuniform cross section channel can improve the oscillating process and the heat transport performance in the OFHP. The heat transfer rate of pulse heating OFHP is higher than that of the continuous by 15–38%, and the effective thermal conductivity is higher by 12–63% at the same heating power. The effective thermal conductivity and the heat transfer rate of the nonuniform cross section heat pipe are also higher than that of the uniform cross section heat pipe when the heating power is more than 100 W.

Experimental Study on the Heat Transfer Enhancement of Oscillating-Flow Heat Pipe by Acoustic Cavitation

Experimental investigations on the heat transfer characteristics of an oscillating-flow heat pipe with acoustic cavitation in comparison with the ordinary oscillating-flow heat pipe are given in this article. The experimental results showed that the heat transfer rate of an oscillating-flow heat pipe with an acoustic cavitation field imposed on the evaporator section was higher than that without a cavitation field by 8–24.5%. It has been proved that acoustic cavitation can enhance the heat transfer performance of an oscillating-flow heat pipe. However, for the case of acoustic cavitation applied on the condenser section, not all ultrasonic fields applied were effective, and the heat transfer rate increased from −39 to 77%. Further discussion on the experimental results is provided.

Enhancement of heat and mass transfer by cavitation

In this paper, a brief summary of effects of cavitation on the heat and mass transfer are given. The fundamental studies of cavitation bubbles, including its nonlinearity, rectified heat and mass diffusion, are initially introduced. Then selected topics of cavitation enhanced heat and mass transfer were discussed in details including whales stranding caused by active sonar activity, pool boiling heat transfer, oscillating heat pipe and high intensity focused ultrasound treatment.

Experiments on Enhanced Heat Transfer of Self-Exciting Mode Oscillating-Flow Heat Pipe with Non-Uniform Structure

Experiments were performed on a closed loop self-exciting mode oscillating flow heat pipe (SEMOS HP) with uniform and non-uniform structures under the same tested conditions. The heat transfer characteristics are analyzed by comparing the temperature of wall of the heat pipe and output power when the heat input of the electric heating board and heating position are changed. The result shows that the heat transfer rate could be improved by using a non-uniform structure under low or middle heat input, and it gives the highest heat transfer performance when the non-uniform diameter section is at the bottom of the heat pipe and the heating source located below the non-uniform section.

Heat Transfer Characteristics of Oscillating Heat Pipe With Ethanol as Working Fluid

In this paper, experimental investigations on the heat transfer characteristics of OHP with ethanol as working fluid were conducted. The experimental results show that there exists a necessary temperature difference between evaporator and condenser section to keep the heat pipe working. The minimum temperature differences for the optimal operating conditions varied from 1.5 to 2.0°C. The maximum effective conductivity achieved could reach up to 111kW/m•°C. The heat pipe was obviously affected by the filling ratio in some cases but the influence law is irregular and related to inclination angles and heating temperatures. Not all OHPs operated well in the limiting case of a zero inclination angle. In most cases, the optimal value of the inclination angle went up when the heating temperature increased. An appropriate high heating temperature is helpful for the OHP to achieved excellent performances. The startup temperature varied from 40°C to 50°C without considering the horizontal heating mode.Copyright

Quantitative analysis of backflow of reversible pump-turbine in generating mode

Significant vibration and pressure fluctuations are usually observed when pump- turbine is operated during the off-design conditions, especially turbine brake and runaway. The root cause of these instability phenomena is the abnormal unsteady flow (especially the backflow) inside the pump-turbine. In the present paper, numerical simulation method is adopted to investigate the characteristics of the flow inside the whole passage of pump-turbine with two guide vane openings (6° and 21° respectively) and three kinds of operating conditions (turbine, runaway and turbine braking respectively). A quantitative analysis of backflow is performed in both the axial and radial directions and the generation and development of backflow in the pump turbine are revealed with great details.

Theoretical Analysis on the Thermal Characteristics of Oscillating Heat Pipe

Theoretical analysis on the thermal characteristics of the looped oscillating heat pipe was given to predict oscillation characteristics affected by filling ratio, inclination angle and heating power. The numerical results show that the alternative expansion and compression of vapors make the working fluid keep an oscillating flow in the heat pipe. This oscillating flow is affected by the inclination angle, filling ratio and heating power.Copyright