Profit and performance boost of straight, wavy, and combined minichannel heat sinks by counter-current pattern

Highlights

• Co- and counter-current patterns are investigated for straight and wavy MCHSs.

• 3D numerical simulation with experimental validation is carried out.

• Replacing co-current with counter-current can significantly reduce ∆T_max and r_t.

• Maximum performance index of 2.22 is found for a counter-current wavy MCHS.

Abstract

A 3D numerical simulation is carried out to investigate thermal and hydraulic characteristics of the straight, wavy, and combined minichannel heat sinks (MCHSs) with both co- and counter-current patterns. An aspect ratio with a hydraulic diameter of 1 mm is adopted for all models. The coolant is water under laminar flow regime (Re = 100 – 900), and the input heat flux is 100 kW/m². First, the employed procedure and obtained results are verified by using the current experimental results and previous data reported by literature. Then, a detailed analysis is performed to find the profit and performance boost of the counter-current pattern compared to the co-current pattern. The results show that replacing the co-current pattern with the counter-current pattern can significantly reduce the maximum temperature difference at the base of MCHSs, leading to more uniform temperature. This reduction can reach up to about 18.5 K at Re = 100. The important point is that the effect of changing the flow pattern in the straight MCHS is greater than the other ones. However, all enhanced MCHSs (wavy and combined) illustrate better overall performances compared to the straight one. A continuous enhancement is observed in the overall performance index with increasing Reynolds number, and the maximum value of 2.22 is found at Re = 900 for the wavy MCHS with counter-current pattern. Finally, a comparative study is carried out, and it found that a change in the flow pattern can work better than many structural modifications in wavy MCHSs.

Introduction

Along with an unbroken trend in miniaturizing electronic devices, the main challenge coming up is to prevent excessive heat load that can cause detrimental effects on the electronic components [1]. Consequently, effective improvement in cooling system design to maintain the temperature of the devices at a reasonable operating level is essential [2,3]. In the recent years, one of most favorable and promising systems utilized to tailor this issue is the heat sinks. To date, several studies in the open literature have been addressed to optimize the heat removal process of heat sinks both experimentally and numerically.

Heat sinks with simple structure seem not to be helpful under high heat flux conditions, but the performance of them can be improved through altering flow path pattern to non-straight structure. For instance, the wavy channel structure have advantages over straight passages in that they achieve much better performance than the straight ones, which origins from the generation of secondary flow and fluid mixing [4]. Employing wavy design instead of straight geometry was first proposed by Sui et al. [5]. They also examined the effects of geometrical parameters, including wave amplitude, wavelength, at Reynolds numbers of 300–800 on the forced convection flow inside a wavy microchannel heat sink [6]. Their experimental results indicated that by increasing the wave amplitude and/or decreasing the wave-length, the thermal performance possessed higher values. Since then, many researchers have devoted themselves to evaluating the thermal performance of wavy heat sinks [7], [8], [9], [10], [11], [12], having reported the similar results. Lin et al. [13] introduced a modified design of wavy heat sink with altering the wavelength or amplitude along the flow direction. It was found that the thermal resistance decreases with an increment in amplitude or with decrement in wavelength relative to the conventional wavy design. Zhu et al. [14] performed a numerical simulation that focused on the thermal performance of the left-right and up-down wavy heat sinks. The outcomes of study revealed the superiority of the up-down wavy design in terms of thermal performance.

The flow behavior and heat transfer of a microchannel heat sink were discussed by Mohammed et al. [15] through performing three-dimensional simulation in which the influence of wave shape, including zigzag, curvy, and step, was analyzed. The results revealed that zigzag configuration had the best thermal performance among other wall shapes. Khoshvaght-Aliabadi et al. [16,17] compared three corrugated heat sinks both numerically and experimentally, and reported that the heat transfer performance was improved effectively in a non-straight shapes, owing to the formation of swirl flows, and chaotic advection of boundary layer, as compared to conventional cases. Moreover, the sinusoidal geometry achieved the highest overall performance, and the triangular and trapezoidal heat sinks were in the next. Chiam et al. [18] introduced a new wavy micro-channel with secondary branches being employed to the peaks and the troughs. They pointed out that there was a notable improvement in the heat transfer performance, in spite of being accompanied with pressure drop penalties. Following this work, a novel structure of zigzag heat sink had been considered by Khoshvaght-Aliabadi et al. [19] in which the effect of three kinds of non-flat nooks in both negative and positive directions were examined. The considered designs exhibited better temperature uniformity compared to flat zigzag MHS. In addition, when the negatively directed nooks were adopted, the recirculation strength and size were considerable.

According to the literature survey, most of previous researches have been done on the influence of the geometrical variables of wavy heat sinks on the hydrothermal performance, and it can be found that none of them focused on the combination of wavy and straight patterns to generate a modified heat sink. Also, to the authors' best knowledge, the comparison between co- and counter-current patterns in the wavy heat sinks are rather scare. Only Shen et al. [20] evaluated both co- and counter-current patterns arrangements of the wavy double-layer heat sink. Accordingly, there is still room for further investigations. The novelty of present study is as follows. Firstly, four arrangements of sinusoidal wavy and straight structure of minichannels according Fig. 1 has been designed. Furthermore, the hydrodynamic and thermal transport characteristics of the considered designs are investigated under both co- and counter-current conditions.