Numerical study on pressure drop and heat transfer characteristics of gas-liquid Taylor flow in a microchannel based on FFR method
Introduction
With the rising demand for high performance and integration in an electronic system, heat dissipation has become a critical problem limiting both the safe and reliable operation of microelectronic equipment and the rapid development of this filed. To disperse high heat flux in the electronic system, some technologies including heat pipes [1,2], jet impingement [3], and spray cooling [4,5] have been proposed and applied by numerous researchers, and a good cooling effect has been achieved. However, these techniques are not available for chip cooling applications [6]. The microchannel device as a high-performance cooling technique offers a larger contact area and shorter transport path than the macroscale and thus achieving the chip cooling. Meanwhile, the use of numerous parallel microchannels offers a potential approach to disperse large heat flux over small areas. However, flow in microchannels is usually laminar with low Reynolds numbers [7], which limits the thermal diffusion process of the fluid in the microchannel.
A few studies on improving the heat transfer capacity in the microchannels have been reported by researchers. They focus mainly on three approaches, namely the employing of high thermal conductivity fluid (e.g., nanofluids), the enhancing of turbulence in the channel and utilizing simultaneously. Many studies have shown that the thermal conductivities of nanofluids are relatively higher than those of conventional fluids [8,9], even nanoparticles with low volume fractions [10]. For example, Zirakzadeh et al. [11] experimentally studied the effects of Al2O3 water nanofluids on cooling heat sinks. The results showed that the heat transfer coefficient was 20% higher than the conventional heat sink. To determine the effects of nanofluids, Sohel et al. [12] compared the thermal performance of three nanofluids in a circular- shaped heat sink. Compared to pure water, 4% CuO-water nanofluid has the highest improvement (13.15%) in heat flux. Another option to promote heat exchange efficiency is to increase turbulence in the channel, which can be achieved by changing curvatures of the microchannel [13,14] or built-in barriers in the flow paths [15,16]. In addition, the above two methods also can be combined. For example, Zhou et al. [17] experimentally studied silver nanofluids through the micro-pin fin heat sink, and Mohammed et al. [18] investigated the comprehensive properties of nanofluid flow and heat transfer in micro-ribbed channels. However, much pumping power is consumed whether using nanofluids (higher viscosity than that of their base fluids) or setting vortex promoter in the flow paths (flow resistance increase), and the increase in heat transfer coefficient is limited.
Two-phase Taylor flow is a simple and effective method to produce vortices by introducing gas or immiscible liquid and has received more and more attention in recent years. This flow regime is characterized by the occurrence of regular bubbles/droplets in a continuous stream of liquid [19]. The presence of bubbles/plugs modifies the flow field in the continuous phase, and then internal circulation is formed. These internal circulations promote the radial mixing of the fluid, which provides a new mechanism for enhancing heat transfers. In recent years, some works have been devoted to study heat transfer characteristics of Taylor flow in the microchannel using experimental or simulation methods. Many investigations have shown that the Taylor flow increases the heat transfer efficiency 2–4 times for that of pure water flow [20,21]. Various parameters affect the Taylor flow heat transfer efficiency, including slug length, channel size, void fraction and flow patterns. An experimental study of Taylor flow heat transfer was first carried out in a 6.4 mm tube by Oliver and Wright [20], the results indicated that the strengthening effect of the short slug is more significant, and the overall heat transfer coefficient is up to 2.5 times than that for water-only flow. Similarly, Leung et al. [21] experimentally studied the flow and heat behaviors of Taylor flow in a vertical channel with a diameter of 2 mm. The effects of bubble length and homogeneous void fraction on Nusselt number were investigated, and the enhancement had been raised 3.2 times as against liquid-only flow. There is a relatively small body of literature that concerned with rectangular channels. Majumder et al. [22] studied the effects of air-water isolated single Taylor bubble and a train of Taylor bubble on heat transfer enhancement in a square channel. They reported that the injection of the Taylor bubble could effectively increase the average heat transfer coefficient by 1.2–1.6 times compared with pure water flow. Mehta and Khandekar [23] also confirmed the high heat transfer efficiency of this flow regime in a square cross-section channel by employing high-resolution InfraRed Thermography, and the enhancement is between 1.2 and 2 times.
Numerical simulation methods offer an effective complementary way to observe many local details difficult to capture in experiments with less expense. According to the simulation of Ua-arayaporn et al. [24], a higher Nusselt number exists in the liquid film region. They argued this could be for the small temperature difference between the local wall and bulk fluid. This finding is consistent with that of Mehdizadeh et al. [25] who showed that the heat transfer in the liquid film region accounts for about one-fourth of the overall heat transfer. More recently, Zhang et al. [26] carried out several investigations into the flow and thermal characteristics of two-phase Taylor flow in vertical channels. They found that as the Capillary number increased, the circulation volume decreased, and the dimensionless circulation time increased. These are all important parameters that affect heat exchange efficiency. Che et al. [27] studied the droplet heat transfer in rectangular microchannels by three-dimensional numerical simulation. The effects of droplets length and the aspect ratio of the channel cross-section on heat transfer process are discussed.
Although some numerical simulation research has been carried out on Taylor flow and heat transfer characteristics, the research to date has tended to focus on the moving frame of reference (MFR) rather than the fixed frame of reference (FFR) systems. Previous studies of Taylor flow heat transfer have not dealt with its complete development process, whereas the often overlooked FFR method is particularly useful in studying this issue. Hence, this paper has been divided into four sections and attempts to show the special feasibility of the FFR method in numerical simulation of Taylor flow and heat transfer. The specific numerical methods are described in section 2, and the characteristics of pressure drop and heat transfer are analyzed in section 3. This will be of practical significance to the application of Taylor flow in microchannels in the heat dissipation of electronic devices.
Section snippets
Computation domain and boundary conditions
There are two basic numerical approaches currently being adopted in research into Taylor flow and heat transfer. One is the fixed frame of reference method (FFR), and the other is the moving frame of reference method (MFR) [28]. The MFR method focuses on a specific part of the flow, such as an individual droplet [29] or a two-phase unit cell [30]. This method is a more practical way for steady-state analysis of Taylor bubbles and reduces the numerical time effectively. In contrast to the MFR
Pressure drop along the channel length
The total pressure gradient in a microchannel for both two-phase flow and single-phase liquid flow can be compared in Fig. 3 (solid black and red line). Obviously, the injection of gas-phase increases the overall pressure drop in the channel.
For laminar single-phase liquid flow, the pressure drop changes smoothly along channel length, only large fluctuations occur in the junction area. This is mainly because the two inlet fluids are mixed at this position and the velocity increases rapidly,
Conclusions
In the present study, the two-dimensional FFR simulations for Taylor flow pressure drop and thermodynamic characteristics were carried out with constant temperature boundary condition in a width of 1 mm microchannel. The possibility of the Taylor flow heat transfer enhancement in practical applications is verified, and the following conclusions can be drawn.
- 1.
The injection of gas-phase can cause an internal circulation flow inside the liquid slug, leading to an increase in pressure gradient and
Credit author statement
Changliang Wang: Conceptualization, Methodology, Writing - Original Draft.
Maocheng Tian: Supervision, Resources.
Jingzhi Zhang: Software.
Guanmin Zhang: Formal analysis.
Yi Zhang: Investigation.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This work was supported by the National Natural Science Foundation of China (No. 51676114), the Shandong Provincial Natural Science Foundation (No. ZR2016EEM26).
References (54)
- et al.
Parametric analysis of loop heat pipe operation: a literature review
Int. J. Therm. Sci.
(2007) Heat pipes in modern heat exchangers
Appl. Therm. Eng.
(2005)- et al.
A review of heat transfer data for single circular jet impingement
Int. J. Heat Fluid Flow
(1992) Spray cooling heat transfer: the state of the art
Int. J. Heat Fluid Flow
(2007)- et al.
Heat transfer characteristics of spray cooling in a closed loop
Int. J. Heat Mass Transf.
(2003) - et al.
Heat transfer performance and transport properties of ZnO–ethylene glycol and ZnO–ethylene glycol–water nanofluid coolants
Appl. Energy
(2014) - et al.
Effective viscosities and thermal conductivities of aqueous nanofluids containing low volume concentrations of Al2O3 nanoparticles
Int. J. Heat Mass Transf.
(2008) - et al.
Investigating the heat transfer performance and thermophysical properties of nanofluids in a circular micro-channel
Int. Commun. Heat Mass Transf.
(2013) - et al.
Analysis on multiplicity and stability of convective heat transfer in tightly curved rectangular ducts
Int. J. Heat Mass Transf.
(2009) - et al.
Heat transfer enhancement in micro-channels caused by vortex promoters
Int. J. Heat Mass Transf.
(2010)
Heat transfer enhancement using rectangular vortex promoters in confined quasi-two-dimensional magnetohydrodynamic flows
Int. J. Heat Mass Transf.
Thermal and hydraulic characteristics of turbulent nanofluids flow in a rib–groove channel
Int. Commun. Heat Mass Transf.
Formation characteristics of Taylor bubbles in power-law liquids flowing through a microfluidic co-flow device
J. Ind. Eng. Chem.
Heat transfer in well-characterised Taylor flow
Chem. Eng. Sci.
Local Nusselt number enhancement during gas–liquid Taylor bubble flow in a square mini-channel: an experimental study
Int. J. Therm. Sci.
Measurement of local heat transfer coefficient during gas–liquid Taylor bubble train flow by infra-red thermography
Int. J. Heat Fluid Flow
Numerical simulation of thermofluid characteristics of two-phase slug flow in microchannels
Int. J. Heat Mass Transf.
Heat transfer and pressure drop characteristics of gas–liquid Taylor flow in mini ducts of square and rectangular cross-sections
Int. J. Heat Mass Transf.
Three dimensional features of convective heat transfer in droplet-based microchannel heat sinks
Int. J. Heat Mass Transf.
Numerical simulation of the pressure drop and heat transfer of two phase slug flows in microtubes using moving frame of reference technique
Int. J. Heat Mass Transf.
Slug flow heat transfer in square microchannels
Int. J. Heat Mass Transf.
Numerical study on gas and liquid slugs for Taylor flow in a T-junction microchannel
Chem. Eng. Sci.
Computational modelling of slug flow in a capillary microreactor
J. Comput. Appl. Math.
On the CFD modelling of Taylor flow in microchannels
Chem. Eng. Sci.
Numerical simulation of Taylor bubble formation in a microchannel with a converging shape mixing junction
Chem. Eng. J.
A continuum method for modeling surface tension
J. Comput. Phys.
Gas-liquid two-phase flow in microchannels: part II: void fraction and pressure drop
Int. J. Multiph. Flow.
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