Heat transfer and fluid flow characteristics of combined microchannel with cone-shaped micro pin fins
Introduction
The rapid development of the industry had brought new challenges and opportunities for development of other disciplines, such as the rapid evolution in integrated circuits, the growing emergence of advanced energy and power, further improvement of the laser technology and so on. Common technical characteristics embodied in these fields from the point of view of heat transfer are high speed and frequency, high heat flux and micro/nano-scale. Thermal management has already become a key issue to limit the rapid development and reliable operation of electronic components. Thus, this led to a rising demand for more effective cooling method to ensure the reliable and efficient operation of microelectronic device.
Microchannel heat sink (MCHS) has been believed to be the most effective way to solve the cooling problem of electronic chip featured by high heat flux and small scale. Improving the heat removal rate of MCHS further has become a key issue in future development of high performance integrated circuits. Rectangular channel which is one of the most fundamental and effective structures of MCHS has been widely researched and applied in industry. Many investigators applied the analytical [1], [2], numerical [3], [4] and experimental methods [5], [6] to explore the performance of this fundamental MCHS. Qu and Mudawar [7] carried out the experimental and numerical analysis to obtain the heat transfer characteristics and pressure drop of a single-phase MCHS. They demonstrated that the conventional mass and momentum equations, energy equations provided satisfactory simulations of the fluid flow and thermal performance of MCHS. Lee et al. [8] proposed the generalized correlations of local and average Nusselt number through the rectangular microchannel. The results showed that the prediction correlations matched well with the experimental and numerical results. Ryu et al. [9] conducted a three-dimensional analysis procedure to optimize the channel shape with the limitation of thermal resistance minimization. The results suggested that the channel width had a significant influence on performance of MCHS. Steinke and Kandlikar [10] extracted 5000 experimental date points to validate the appropriateness of traditional friction factor theory for microchannel with the range of Re and hydraulic diameter.
In recent years, as miniaturized and intensified processes of electronic components, traditional smooth and straight MCHSs cannot meet the demand of electronic chips' heat dissipation. Accordingly, various novel structural designs based on different heat transfer mechanism have been put forward, such as the extended surfaces, roughness surfaces which are able to increase the heat transfer area, disrupt the thermal boundary layer or induce secondary flow. Many researchers arranged micro-structures on the side-walls of smooth rectangular microchannel to ameliorate heat transfer performance. Chai et al. [11], [12], [13] numerically investigated the thermal and hydraulic performance of microchannel fabricated aligned or offset fan-shaped ribs on the side-walls. They also designed five different rib shapes on side-walls to compare the thermo-hydraulic performance of MCHS [14]. The shapes of rib included: rectangular, forward triangular, backward triangular, isosceles triangular, and semi-circular. The results revealed that the overall performance of microchannel with ribs is higher than smooth microchannel. The microchannel with forward triangular and semi-circular ribs exhibited the highest performance with Re < 350 and Re > 400, respectively. The heat transfer performance was enhanced in these microchannels due to the interruption and redevelopment of hydraulic/thermal boundary layer. Meanwhile, the ribs on the side-walls shifted the region of maximum velocity resulting in the local heat transfer improvement. However, the fluid velocity near the walls is still very low and the pressure drop penalty is very high. So, it requires an optimization procedure to the ribs construction in order to maintain lower pressure drop.
Introducing micro structures on bottom wall of channels is also widely used to enhance heat transfer due to the effect of shunt and acceleration of flow which increase the mixing between fluid layers near the wall and central core. Li et al. [15] inserted vertical Y-shaped bifurcations into microchannel and Xie et al. [16], [17] designed multistage bifurcations at the entrance or exit region of the smooth microchannel. The results demonstrated that the thermal performance of microchannel combined bifurcations was better than smooth microchannel due to the generation of bifurcation flow. It might enhance the cooling performance resulting from the restarting of the boundary of layer. Micro pin fins surface is one of the most efficient means to improve the heat transfer of MCHS and the shape of pin fins, such as circular [18], cone-shaped, rectangular [19], hydrofoil [20], or square shape [21] have been studied adequately. What's more, some researchers inserted one or several micro pin fins aligned into the microchannel as the extended surface or vortex promoters to enhance the thermal performance. Shafeie et al. [22] used numerical method to compare the heat removal fluxes in pin-fined MCHSs and pin fin heat sinks. The results showed that the MCHSs with oblique pin-fins had better heat transfer performance and the higher depth of the microchannel in the studied case, the higher heat removal of the MCHSs. Adewumi et al. [23] made the minimum peak temperature and maximum thermal conductance as the objectives to optimize the geometric configuration of the microchannel inserted micro pin fins. The results indicated that microchannel inserted micro pin fins had less peak temperature and larger thermal conductance than microchannel without fins. Yadav [24] integrated the rectangular microchannel with cylindrical microfins as extended faces to enhance the thermal performance of the channel. The geometrical parameters were optimized by the univariate search method. Li et al. [25] and Ghani et al. [26] combined cavities arranged on sidewalls with ribs located at the channel center. They concluded that ribs at channel center were beneficial to promote the mainstream separation, increase the flow rate at cavities and enhance the impact effect of the fluid on the channel sidewalls.
It is obviously from above literature review, many studies have been done to optimize the geometric structure using ribs or micro structures with different geometries such as triangular, trapezoidal, circular and so on. The geometry strongly affects the heat transfer and flow characteristic of microchannel. Therefore, there is a need to explore new designs of micro pin fin that provides higher thermal performance in a lower pressure drop. Cone-shaped micro pin fin is an aerodynamic/hydrodynamic cross section shape connecting the semicircle with the triangle part. Since the friction factor of the streamlined pin fin (hydrofoil or cone-shaped) is lower than the other devices [19], [20], [27], [28], cone-shaped micro pin fins are chosen to combine with smooth microchannel as a novel microchannel. Thus, present study aims to utilize the cone-shaped micro pin fins arranged on the central portion of the channel to enhance the performance of MCHS. The characteristics of fluid flow and heat transfer of combined microchannel and cone-shaped micro pin fin (MCPF) were investigated. In addition, the arrangement of micro pin fins has the significant influence on the overall performance of the microchannel. Therefore, the overall performance of fins located in the upstream (case1), middle (case2), downstream (case3) and the whole of channel uniformly (case4) compares with the smooth microchannel. Finally, the dimensionless geometrical parameters, relative fin diameter, relative space between the fins and relative fin height, are optimized with the evaluation criterion based on the thermal enhancement factor η.
Section snippets
Model description
Fig. 1(a) shows the schematic view of the whole MCHS with 30 longitudinal rectangular microchannels which is the reference channel for present study. The overall dimensions of MCHS are 10 mm in length (L), 10 mm in width (W) and 0.35 mm in height (H), respectively. The MCPF is a structural design which inserts the micro pin fins into the Rec microchannel in in-line arrangement and the geometric parameters are similar to the Rec microchannel. Due to the symmetry of each channel, numerical
Governing equations
Before conducting the numerical simulation, several assumptions and simplifications are made as follows:
- 1.
The fluid and solid in this study are deionized water and silicon, respectively. The physical properties of these two materials are independent on temperature except the dynamic viscosity of water.
- 2.
The flow is considered as steady flow of incompressible, laminar and three-dimensional.
- 3.
Gravity and other body forces are neglected.
- 4.
Radiation and natural convection heat transfer are not taken into
Validation with the classical predictions
Before simulation calculations, it is necessary to validate the effectiveness of the numerical model. By comparing with either theoretical or the previous literature, the reliability and accuracy of the numerical results are confirmed. Lots of authors [28], [33], [34] adopted numerical results of rectangular channel to compare with the available data. Many scholars have studied the heat transfer and pressure drop performance of rectangular microchannel and many classical theoretical
Conclusions
In this paper, a novel structural design which combined microchannel with cone-shaped micro pin fins has been put forward and the fluid flow characteristics and thermal performance are numerically investigated. The effects of located position, diameter of fin, fins space and height on the overall performance have been explored. The detail conclusions can be summarized as follows:
- (1)
Relative to Rec microchannel, the present work has attested numerically the advantages of heat transfer improvement
Nomenclature
- Acon
convection heat transfer area (m2)
- Ab
heating area (m2)
- Ab,pf
bottom area of micro pin fin (m2)
- Ach
area of channel bottom surface (m2)
- AR
aspect ratio
- cp
specific heat capacity (J/(kg·K))
- Dh
hydrodynamic diameter (m)
- Dpf
the diameter of micro pin fin (m)
- e
relative error
- Fs
factor of safety for error estimators
- f
friction factor
- GCI
grid convergence index
- h
heat transfer coefficient (W/(m2·K))
- H
height of the MCHS (m)
- Hch
height of microchannel (m)
- Hpf
height of the micro pin fin (m)
- Hs
height of the substrate (m)
- k
Acknowledgements
Our research program is supported by the National Natural Science Foundation of China (No. 51576005).
References (37)
- et al.
Analysis of microchannel heat sinks for electronics cooling
Int. J. Heat Mass Transf.
(2002) - et al.
Single-phase liquid cooled microchannel heat sink for electronic packages
Appl. Thermal Eng.
(2005) - et al.
Effects of thermal property variations on the liquid flow and heat transfer in microchannel heat sinks
Appl. Thermal Eng.
(2007) - et al.
Experimental investigation of flow friction for liquid flow in microchannels
Int. Comm. Heat Mass Transf.
(2000) - et al.
Investigation of heat transfer in rectangular microchannels
Int. J. Heat Mass Transf.
(2005) - et al.
Experimental and numerical study of pressure drop and heat transfer in a single-phase micro-channel heat sink
Int. J. Heat Mass Transf.
(2002) - et al.
Thermally developing flow and heat transfer in rectangular microchannels of different aspect ratios
Int. J. Heat Mass Transf.
(2006) - et al.
Numerical optimization of the thermal performance of a microchannel heat sink
Int. J. Heat Mass Transf.
(2002) - et al.
Single-phase liquid friction factors in microchannel
Int. J. Thermal Sci.
(2006) - et al.
Parametric study on thermal and hydraulic characteristics of laminar flow in microchannel heat sink with fan-shaped ribs on sidewalls-part 1: heat transfer
Int. J. Heat Mass Transf.
(2016)
Parametric study on thermal and hydraulic characteristics of laminar flow in microchannel heat sink with fan-shaped ribs on sidewalls-part 2: pressure drop
Int. J. Heat Mass Transf.
Parametric study on thermal and hydraulic characteristics of laminar flow in microchannel heat sink with fan-shaped ribs on sidewalls-part 3: performance evaluation
Int. J. Heat Mass Transf.
Numerical study of laminar flow and heat transfer in microchannel heat sink with offset ribs on sidewalls
Appl. Therm. Eng.
Forced convective heat transfer across a pin fin micro heat sink
Int. J. Heat Mass Transf.
Thermo-fluid analysis of micro pin-fin array cooling configurations for high heat fluxes with a hot spot
Int. J. Thermal Sci.
Experimental study on liquid flow and heat transfer in micro square pin fin heat sink
Int. J. Heat Mass Transf.
Numerical study of heat transfer performance of single-phase heat sinks with micro pin-fin structures
Appl. Thermal Eng.
Constructal design of combined microchannel and micro pin fins for electronic cooling
Int. J. Heat Mass Transf.
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