Noisy film boiling, which is characterized by a loud noise andsevere mechanical vibration, is a particular phenomenon of superfluid helium II (He II). Experiments have been conducted under various thermal conditions b...Noisy film boiling, which is characterized by a loud noise andsevere mechanical vibration, is a particular phenomenon of superfluid helium II (He II). Experiments have been conducted under various thermal conditions by varying the heating time th and the heat flux q, and the temperature oscillation during noisy film boiling is measured by the superconductor temperature sensors in order to understand the physical mechanism of noisy film boiling.展开更多
Challenges of electronic cooling are becoming increasingly urgent due to the exponential rise in power densities and the non-uniform distribution of heat sources.Vapor chambers utilizing liquid-vapor phase change heat...Challenges of electronic cooling are becoming increasingly urgent due to the exponential rise in power densities and the non-uniform distribution of heat sources.Vapor chambers utilizing liquid-vapor phase change heat transfer are appealing due to their high performance and potentially low cost.However,heat dissipation performance,depending on the thin film evaporation,is limited by the capillary dry-out of wicking structures.Here,we demonstrate a large-scale vapor chamber enabled by high-performance liquid film boiling mode on the hierarchical mesh-wicking structures for high-power electronics cooling.The composite columns integrating with copper foam and copper powder are patterned in a zoned configuration to promote vapor diffusion and two-phase flow.The effects of the filling rate and cooling water temperature on the vapor flow and liquid film distribution are investigated.The results show that the X-shaped distribution of composite columns in the heat source region promotes the vapor diffusion throughout the vapor chamber,resulting in a thermal resistance of 0.04℃/W at the heat flux of 100 W/cm^(2)from an area of 775 mm^(2).The findings provide theoretical guidance for the structure design of high-performance large vapor chambers.展开更多
The regime of horizontal subcooled film boiling is characterized by the formation of a thin layer of vapor coveringthe surface of a flat horizontal heater. Based on the equations of motion of a viscous incompressible ...The regime of horizontal subcooled film boiling is characterized by the formation of a thin layer of vapor coveringthe surface of a flat horizontal heater. Based on the equations of motion of a viscous incompressible fluid and theequation of heat transfer, the stability of such a vapor film is investigated. The influence of the modulation of thegravity field caused by vertical vibrations of the heater of finite frequency, as well as a constant electric fieldapplied normal to the surface of the heater, is taken into account. It is shown that in the case of a thick vaporfilm, the phase transition has a little effect on the thresholds for the occurrence of parametric instability in thesystem and its transformation into the most dangerous one. At the same time, the electric field contributes toan increase in these thresholds. It was found that the effect of vibrations on the stabilization of non-parametricinstability in the system is possible only in a narrow region of the parameter space where long-wave damped disturbances exist and consists of reducing the critical heat flux of stabilization. A vapor film stabilized in this waycan be destroyed due to the development of parametric instability. In contrast to the case of a thick vapor layer,the threshold for the onset of parametric instability for thin films largely depends on the value of subcooling in thesystem. In addition, this threshold decreases with increasing electric field strength. For a vapor film ten micronsthick, the instability threshold can be reduced by a factor of three or more by applying an electric field of aboutthree million volts per meter.展开更多
Managing high-flux waste heat with controllable device working temperature is becoming challenging and critical for the artificial intelligence,communications,electric vehicles,defense and aerospace sectors.Spray cool...Managing high-flux waste heat with controllable device working temperature is becoming challenging and critical for the artificial intelligence,communications,electric vehicles,defense and aerospace sectors.Spray cooling,which combines forced convection with phase-change latent heat of working fluids,is promising for high flux heat dissipation.Most of the previous studies on spray cooling enhancement adopted high spray flow rates to strengthen forced convection for high critical heat flux(CHF),leading to a low heat transfer coefficient(HTC).Micro/nanostructured surfaces can enhance boiling,but bubbles inside the structures tend to form a vapor blanket,which can deteriorate heat transfer.This work demonstrates simultaneous enhancement of CHF and HTC in spray cooling by improving both evaporation and liquid film boiling on three-dimensional(3D)ordered hierarchical micro/nano-structured surface.The hierarchical micro/nano-structured surface is designed to coordinate the transport of spray droplets,capillary liquid films,and boiling bubbles to enhance spray cooling performance.Boiling inversion where superheat decreases with increasing heat flux is observed,leading to an ultra-high HTC due to the simultaneous promotion of bubble nucleation and evaporation.Unprecedented CHF is obtained by overcoming the liquid–vapor counterflow,i.e.,synergistically facilitating bubble escape and liquid permeation.A record-breaking heat transfer performance of spray cooling is achieved with a maximum heat flux of1273 W/cm^(2)and an HTC of 443.7 kW/(m^(2)K)over a 1 cm^(2)heating area.展开更多
Experimental investigations of boiling heat transfer from porous suffaces at atmospheric pressure were performed. The porous surfaces are plain tubes covered with metal screens, V-shaped groove tubes covered with sc...Experimental investigations of boiling heat transfer from porous suffaces at atmospheric pressure were performed. The porous surfaces are plain tubes covered with metal screens, V-shaped groove tubes covered with screens, plain tubes sintered with screens, and V-shaped groove tubes sintered with screens.The experimental results show that siatering metal screens around spiral V-shaped groove tubes can greatly improve the boiling heat transfer. The boiling hysteresis was observed in the experiment. This paper discusses the mechanism of the boiling heat transfer horn those kinds of porous surfaces stated above.展开更多
基金This work was supported by the National Nature Science Foundation of China, Science and Technology Foundation of Shanghai Jiaotong University, Ministry of Education of China.
文摘Noisy film boiling, which is characterized by a loud noise andsevere mechanical vibration, is a particular phenomenon of superfluid helium II (He II). Experiments have been conducted under various thermal conditions by varying the heating time th and the heat flux q, and the temperature oscillation during noisy film boiling is measured by the superconductor temperature sensors in order to understand the physical mechanism of noisy film boiling.
基金supported by the National Key Research and Development Program(Grant No.2022YFB3806504)the National Natural Science Foundation of China(Grant No.52376047)+1 种基金the Xingliao Talent Program of Liaoning Province(Grant No.XLYC2203193)the Fundamental Research Funds for the Central Universities(Grant No.DUT24ZD201,DUT22LAB610,DUT23BK017,and DUT23BK046)。
文摘Challenges of electronic cooling are becoming increasingly urgent due to the exponential rise in power densities and the non-uniform distribution of heat sources.Vapor chambers utilizing liquid-vapor phase change heat transfer are appealing due to their high performance and potentially low cost.However,heat dissipation performance,depending on the thin film evaporation,is limited by the capillary dry-out of wicking structures.Here,we demonstrate a large-scale vapor chamber enabled by high-performance liquid film boiling mode on the hierarchical mesh-wicking structures for high-power electronics cooling.The composite columns integrating with copper foam and copper powder are patterned in a zoned configuration to promote vapor diffusion and two-phase flow.The effects of the filling rate and cooling water temperature on the vapor flow and liquid film distribution are investigated.The results show that the X-shaped distribution of composite columns in the heat source region promotes the vapor diffusion throughout the vapor chamber,resulting in a thermal resistance of 0.04℃/W at the heat flux of 100 W/cm^(2)from an area of 775 mm^(2).The findings provide theoretical guidance for the structure design of high-performance large vapor chambers.
基金supported by the Ministry of Science and High Education of Russia(Theme No.121031700169-1).
文摘The regime of horizontal subcooled film boiling is characterized by the formation of a thin layer of vapor coveringthe surface of a flat horizontal heater. Based on the equations of motion of a viscous incompressible fluid and theequation of heat transfer, the stability of such a vapor film is investigated. The influence of the modulation of thegravity field caused by vertical vibrations of the heater of finite frequency, as well as a constant electric fieldapplied normal to the surface of the heater, is taken into account. It is shown that in the case of a thick vaporfilm, the phase transition has a little effect on the thresholds for the occurrence of parametric instability in thesystem and its transformation into the most dangerous one. At the same time, the electric field contributes toan increase in these thresholds. It was found that the effect of vibrations on the stabilization of non-parametricinstability in the system is possible only in a narrow region of the parameter space where long-wave damped disturbances exist and consists of reducing the critical heat flux of stabilization. A vapor film stabilized in this waycan be destroyed due to the development of parametric instability. In contrast to the case of a thick vapor layer,the threshold for the onset of parametric instability for thin films largely depends on the value of subcooling in thesystem. In addition, this threshold decreases with increasing electric field strength. For a vapor film ten micronsthick, the instability threshold can be reduced by a factor of three or more by applying an electric field of aboutthree million volts per meter.
基金National Natural Science Foundation of China(52036002)。
文摘Managing high-flux waste heat with controllable device working temperature is becoming challenging and critical for the artificial intelligence,communications,electric vehicles,defense and aerospace sectors.Spray cooling,which combines forced convection with phase-change latent heat of working fluids,is promising for high flux heat dissipation.Most of the previous studies on spray cooling enhancement adopted high spray flow rates to strengthen forced convection for high critical heat flux(CHF),leading to a low heat transfer coefficient(HTC).Micro/nanostructured surfaces can enhance boiling,but bubbles inside the structures tend to form a vapor blanket,which can deteriorate heat transfer.This work demonstrates simultaneous enhancement of CHF and HTC in spray cooling by improving both evaporation and liquid film boiling on three-dimensional(3D)ordered hierarchical micro/nano-structured surface.The hierarchical micro/nano-structured surface is designed to coordinate the transport of spray droplets,capillary liquid films,and boiling bubbles to enhance spray cooling performance.Boiling inversion where superheat decreases with increasing heat flux is observed,leading to an ultra-high HTC due to the simultaneous promotion of bubble nucleation and evaporation.Unprecedented CHF is obtained by overcoming the liquid–vapor counterflow,i.e.,synergistically facilitating bubble escape and liquid permeation.A record-breaking heat transfer performance of spray cooling is achieved with a maximum heat flux of1273 W/cm^(2)and an HTC of 443.7 kW/(m^(2)K)over a 1 cm^(2)heating area.
文摘Experimental investigations of boiling heat transfer from porous suffaces at atmospheric pressure were performed. The porous surfaces are plain tubes covered with metal screens, V-shaped groove tubes covered with screens, plain tubes sintered with screens, and V-shaped groove tubes sintered with screens.The experimental results show that siatering metal screens around spiral V-shaped groove tubes can greatly improve the boiling heat transfer. The boiling hysteresis was observed in the experiment. This paper discusses the mechanism of the boiling heat transfer horn those kinds of porous surfaces stated above.
