Flow visualization and heat transfer characteristics of gas–liquid two-phase flow in microtube under constant heat flux at wall

Convective heat transfer in droplet-based microchannel heat sinks can be enhanced by the recirculating vortices due to the presence of interfaces. In rectangular microchannels, the three dimensional structures of the vortices and the 'gutters' (i.e., the space between the curved droplet interface and the corner of the microchannel) can significantly affect the heat transfer process. Numerical simulations of the heat transfer process are performed to study the three dimensional features in droplet-based microchannel heat sinks. The finite volume method and the level set method are employed to simulate the flow dynamics, the evolution of the interface, and the heat transfer. The results show that the 'gutters' can hinder the heat transfer process because of its parallel flow, whereas the recirculating flow in droplets and in slug regions between successive droplets can enhance the heat transfer by advecting hot fluid towards the center of the droplets/slugs and advecting fresh fluid towards the wall of the channel. The effects of the length of droplets, the aspect ratio of the channel cross sections, and the Peclet number are analyzed.

Section: Introductionmentioning

confidence: 99%

Three dimensional features of convective heat transfer in droplet-based microchannel heat sinks

Che

Wong

Nguyen

et al. 2015

“…Although a number of experimental and numerical works have been undertaken examining the heat transfer enhancements associated with Taylor flows - [16,21,22,25] -few have proposed correlations to model the thermal behaviour. Of the works that have, the majority have proposed correlations for liquid-gas flows subject to an isoflux boundary condition [38,41,42].…”

Section: Heat Transfer Correlationmentioning

confidence: 99%

“…Analysing the problem analytically, Muzychka et al [23] came to similar conclusions, that the improved thermal performance is attributable to the modified velocity profile in the liquid slug and the internal circulation. A number of studies have examined the problem experimentally, [15,24,25], and have reported Nusselt number enhancements up to 600% over conventional Poiseuille flows, [26]. In the majority of these studies, the flow regime consisted of gaseous bubbles dispersed in a continuous liquid medium.…”

Section: Introductionmentioning

confidence: 99%

Local Nusselt number enhancements in liquid–liquid Taylor flows

Eain

Egan

Punch

2015

a b s t r a c tThermal management has emerged as a critical requirement to ensure the performance and reliability of electronic devices and systems. System level heat fluxes are approaching the limits of conventional forced air cooling, and there is a need to develop alternative cooling techniques for devices such as processors, power amplifiers and laser arrays. This paper examines the potential heat transfer enhancements of a two phase liquid-liquid Taylor flow regime. The primary focus of the work was to examine the influence of slug length and carrier phase variations on the local Nusselt numbers. An experimental facility was designed and commissioned to subject the flow to a constant heat flux boundary condition, a boundary condition commonly encountered in thermal management applications. Local temperature measurements were acquired using a high resolution infrared thermography system. Experiments were carried out over slug length, Capillary and Prandtl numbers that spanned several orders of magnitude in a minichannel geometry. Reductions in carrier slug length and increases in dispersed slug length were found to augment the heat transfer rates, with the greatest enhancements observed in flows with carrier slug lengths approaching the channel diameter. The thickness of the liquid film separating the dispersed slugs from the heated capillary walls was found to play a significant role in the removal of heat, with increases in film thickness resulting in a reduction in the heat transfer rates. Based on the characteristics identified, a novel correlation is proposed to model the flow in the thermally developing and fully-developed regions.

“…The temperature was measured using several thermal couples along the tube. Lim et al [21] used borosilicate circular glass tubes with inner diameters of 300 and 500 µm, and a thin layer of Indium Tin Oxide (ITO) coating on the tubes as the heat source.…”

Section: Introductionmentioning

confidence: 99%

Asymmetric heat transfer in liquid–liquid segmented flow in microchannels

Che¹,

Wong²,

Nguyen³

et al. 2014

Heat transfer in segmented flow in microchannels can be significantly enhanced by recirculating vortices, due to the presence of interfaces. The processes of heat transfer in segmented flow subjecting to asymmetric boundary conditions are studied. Two types of boundary conditions are considered, asymmetric constant surface temperature and asymmetric constant surface heat flux. The paths of heat flow and the effects of the thermal conductivity, the plug length, and the Peclet number are studied.The results show different features from those at symmetric boundary conditions. The heat transfer process at asymmetric boundary conditions is controlled by both thermal advection and diffusion at the mid-plane of the channel. The coupling effects between the adjacent plugs complicate the process by the heat transfer across plug-plug interfaces.