Elsevier

Energy Conversion and Management

Volume 174, 15 October 2018, Pages 439-452
Energy Conversion and Management

Experimental investigation on thermal and hydraulic performance of microchannels with interlaced configuration

https://doi.org/10.1016/j.enconman.2018.08.054Get rights and content

Highlights

  • A novel microchannel with interlaced configuration is fabricated.

  • Side walls of channel as the main heat transfer surfaces is realized.

  • Experimental investigation on the thermal and hydraulic performance is performed.

  • A better heat transfer performance of interlaced microchannel is obtained.

Abstract

In this study, a novel interlaced microchannel with a “cold water-hot water-cold water” counterflow arrangement was designed. The influences of microchannel configurations on the thermal and hydraulic performance were studied by comparing the proposed microchannel configuration with parallel and traditional spiral configurations. The results showed that the effective heat transfer area of the interlaced microchannel was 6.4 and 8.4 times that of the parallel and spiral configurations, respectively. For interlaced microchannels, the maximum temperature difference between the cross sections was 0.07 °C, and the temperature rise along the flow direction was only 6 °C. When the Reynolds number was 492, the Nusselt number of the interlaced microchannels was 2 and 10 times that of the parallel and spiral microchannels, respectively. The heat transfer performance of interlaced microchannels was improved by 83.46% compared with that in the literature. The influence of microchannel configurations on the pressure drop and the entrance length were negligible. The interlaced microchannel exhibited its lowest thermal resistance of 0.015 °C/W and lowest entropy production of 22.6 W/ °C at a Reynolds number of 492. The heat transfer enhancement coefficient of the interlaced microchannel and parallel microchannel were 5 and 2.8 times that of the traditional spiral microchannel, respectively. The maximum heat load of loop heat pipe was enhanced by 4 times with the integration of interlaced microchannel as the condenser.

Introduction

The demand for heat dissipation in high heat flux microelectronics such as processors and high-power Light Emitting Diodes (LEDs) has become a bottleneck in the development and reliable operation of electronics with the rapid development of micro-nano technology [1]. Microchannels have been widely used in the fields of microelectronics, aerospace, and the chemical industry because of their advantages of small volume, high heat transfer performance, and low manufacturing cost. However, the temperature rise along the flow direction produces local hot spots on the chip surface, which severely shortens the service life. Therefore, extensive research has been carried out to improve the thermal performance of microchannels, such as optimizing the microchannel geometric design and improving the thermophysical properties of the working fluid.

Optimizing the microchannel cross-sectional structure is the most effective method. The heat transfer area is increased to strengthen the heat transfer and reduce the flow resistance with a trapezoidal microchannel [2]. The application of a Ω-shaped microchannel effectively increases the heat transfer and hydraulic performance [3]. Some special microchannel configurations such as sinusoidal microchannels [4], convergent microchannels [5], fractal microchannels [6], and Y-shaped microchannels [7] have been proposed to redevelop the thermal boundary layer and enhance the heat transfer performance.

By adding pin fins to the microchannel, the disturbance is enhanced and the heat transfer performance is improved [8]. A microchannel with zigzag [1] or semicircular [9] side walls breaks the thermal boundary layer and increases the heat transfer area. In addition, the heat transfer area and disturbance of the liquid are increased by filling the porous material into the microchannel [10]. Although the addition of microfin pins, special side wall structures, and porous material strengthen the heat transfer performance, the pressure drop increases. Therefore, the concept of a double-layered microchannel has been proposed [11], which not only maintains high heat transfer performance but also reduces the pressure drop along the flow direction [12]. In order to further decrease the pressure drop, methods such as optimizing the entrance to the microchannel using a genetic algorithm [13], changing the inlet number, and decreasing the flow length of the working fluid [14], [15] have been proposed by homogenizing the distribution of the fluid.

The optimization of the thermophysical properties of working fluids has attracted significant interest. Owing to the excellent electrical properties of dielectric fluid, the thickness of liquid film is reduced and the two-phase heat transfer performance is strengthened [16]. Liquid metal with a low boiling point and high thermal conductivity is a promising working fluid for the cooling of electronic chips [17]. The thermal conductivity of the fluid is effectively improved by adding nanoparticles such as CuO [18], Al2O3 [19], [20], and TiO2 [21], and the thermal boundary layer was broken to enhance heat transfer between the fluid and the wall. However, the deposition of nanoparticles limits the application of nanofluids [22]; therefore, it became of great interest to study the influence of nanoparticle concentration on heat transfer performance [23], [24].

Although the microchannel has been widely investigated, studies on the interlaced arrangement of channels have rarely been reported. In this study, a novel interlaced microchannel (IM) with hot- and cold-fluid channels located on the same side of the microchannel substrate was designed. For comparison, a parallel microchannel (PM) and traditional spiral microchannel (SM) were manufactured. The effects of the microchannel configurations on the thermal and hydraulic performance were studied.

Section snippets

Microchannel design

In this study, three kinds of microchannels with IM, PM, and SM configurations were manufactured, as shown in Fig. 1. The IM and PM configurations were rectangular microchannels. The depth-width ratio of the IM was 3:1, and hot and cold water were counterflowed on the same side of the microchannel substrate in a “C-H-C” arrangement. The hot and cold water flow direction and heat transfer direction are shown in the left view of Fig. 1(a). The heat transfer mainly occurred on the two side walls

Hydraulic performance

The Reynolds number (Re) is defined as [26]Re=ρfVchDhμfwhere ρf is the fluid density, Vch is the velocity inside the channel, Dh is the hydraulic diameter of the microchannel, and μf is the dynamic viscosity.

The pressure drop measured by the differential pressure transmitter includes the following parts [27]:

  • (1)

    Friction loss inside the microchannel.

  • (2)

    Pressure loss caused by the abrupt contraction and expansion of channels at the inlet/outlet manifolds.

  • (3)

    Local pressure loss caused by the passage

Temperature distribution

Fig. 4 shows the variation in the average wall temperature with the Re for different microchannel configurations. The average wall temperature of the IM was the lowest among the three configurations. Owing to the unique design of the IM, the heat transfer direction was perpendicular to the side wall of the channel, as shown in Fig. 1(a), and the two side walls of the channel served as the main heat transfer surface. Because of a larger heat transfer area, the heat from the hot-fluid channel was

Conclusions

In this study, a novel interlaced microchannel with a “C-H-C” counterflow arrangement was designed and compared with conventional parallel and spiral microchannels. The thermal and hydraulic performances of the microchannels were studied and analyzed by changing the cold-water flow rate. The main conclusions were as follows:

  • (1)

    Two side walls of the channel served as the main heat transfer surface for the IM. The total heat transfer area of the IM was 6.4 and 8.4 times those of the PM and SM,

Acknowledgements

This work was supported by the Natural Science Foundation of Fujian Province of China (No. 2017J06015), National Natural Science Foundation of China (Project No 51475397). In addition, the supports from the Fundamental Research Funds for Central Universities, Xiamen University, China (Nos. 20720160079 and 2072062009).

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