Heat transfer and flow characteristics of sinusoidal wavy plate fin heat sink with and without crosscut flow control

https://doi.org/10.1016/j.ijheatmasstransfer.2019.03.114Get rights and content

Highlights

  • Sinusoidal wavy plate fins with phase shift of 0°, 90° and 180° are investigated.

  • Thermal performance of SW-PFHS and CCSW-PFHS are compared.

  • The phase shift has significant effect on the thermal performance.

  • The proper working conditions of sinusoidal wavy fins heat sinks are reported.

Abstract

This article presents new experimental data on the influence of phase shift, air velocity, heat sink base surface temperature on heat transfer coefficient, and pressure drop of airflow through sinusoidal wavy plate fin heat sinks (SW-PFHS) and crosscut sinusoidal wavy plate fin heat sinks (CCSW-PFHS). Sinusoidal wavy plate fins with a wave length of 18.68 mm, amplitude of 2.0 mm, and phase shift of 0°, 90°, and 180° are used. For CCSW-PFHS, the sinusoidal wavy plate fin is cut transversely at crests and troughs with a 2 mm length. The test runs are performed at an air velocity ranging between 1 and 5 m/s and a heat sink base surface temperature of 70 °C, 90 °C, and 110 °C. The results show that the higher phase shift and air velocity lead to the enhancement of the heat transfer coefficient and pressure drop. Conversely, the heat sink base surface temperature has a slight effect on the heat transfer coefficient and pressure drop. The heat transfer coefficient of SW-PFHS is enhanced when increasing the phase shift compared with a phase shift of 0°. Under the same phase shift, the Nusselt number of CCSW-PFHS is higher than that of SW-PFHS by about 5.9–19.1%. The CCSW-PFHS with a phase shift of 180° yields the highest TPF.

Introduction

Owing to the small size and high powerful electronic devices such as central processing units, power transistors, graphics processors, light emitting diodes (LEDs), and lasers that have been continuously developed, it led to the rapid increase of heat rejection and a decrease in the reliability and lifetime of these devices. Although, the plate fin heat sinks are popularly used in this application, they may not work properly under high heat flux conditions. Therefore, the development of the plate fin heat sink performance which is suited for high heat flux conditions is the motivation of the present work. During the past decade, the heat transfer enhancement using plate fin heat sink have been studied especially, the sinusoidal wavy channel. The sinusoidal wavy plate fin heat sink (SW-PFHS) is developed to generate the turbulence of fluid flow in the flow channel. However, a clear understanding about the effect of working conditions and channel configurations on heat transfer and flow characteristics is needed to obtain optimum thermal performance. Recent studies associated with the thermal performance of sinusoidal wavy plate fins have been carried out by the following researchers. Nilpueng and Wongwises [1] studied the flow behavior of single-phase flow and air–water flow in sinusoidal wavy channels. Three different phase shifts of 0°, 90°, and 180° were used. The experimental results showed that recirculation flows appeared at the troughs and it led to the turbulence of flow in the channel. Kim and Kim [2] experimentally investigated the effects of crosscuts including length, position, and the number of crosscuts on thermal resistance of parallel flow of air through the heat sinks. The plate fin heat sinks with a crosscut ranging between 0.5 and 10 mm were tested. They stated that crosscut length had the most important effect on the crosscut heat sinks performance compared with other relevant parameters. Nilpueng and Wongwises [3] studied the air–water flow behavior in a plate heat exchanger. The commercial plates had the corrugated sinusoidal shape of unsymmetrical chevron angles of 55° and 10°. The visual observation showed that the bubbles were spun between the troughs. The heat transfer and flow characteristics of Al2O3-water nanofluid inside the sinusoidal-corrugated channel were numerically investigated by Khoshvaght-Aliabadi [4]. The effects of phase shift, wave length, wave amplitude, channel length, and channel height were presented. The experiment was performed at Reynolds numbers ranging from 6000 to 22,000 and nanoparticle volume fractions ranging from 0 to 4%. Thermal hydraulic performance of printed circuit heat exchanger (PCHE) was numerically studied by Khan et al. [5]. The numerical simulations were done at bend angle ranging between 0° and 15° and Reynolds number ranging between 350 and 2100. Thermal hydraulic performance of the wavy channel was higher than that of the plane channel. Chiam et al. [6] numerically and experimentally investigated the fluid flow and heat transfer in novel sinusoidal wavy micro-channels with alternating secondary branches. Two secondary branches with different amplitudes of waviness were studied at a Reynolds number ranging from 50 to 200. They reported that the heat transfer performance of wavy micro-channels with secondary branches was enhanced when compared to the referenced conventional wavy channel. Khoshvaght-Aliabadi et al. [7] studied the performance of a square cross-section sinusoidal wavy minichannel heat sink. The effects of channel configurations, i.e., wave length and wave amplitude, were tested. They reported that the heat transfer coefficient was enhanced about 200% in the sinusoidal wavy minichannel heat sink with l = 20 mm and a = 2.0 mm. The heat transfer enhancement in wavy fin heat exchangers by using crosscut flow control was numerically studied by Kim et al. [8]. Five wavy fins with a corrugation angle of 20° were simulated, and crosscut was applied at the third wave perpendicular to the flow direction. The numerical results showed that the optimum heat transfer performance of a crosscut wavy fin was enhanced 23.81% and that the pressure drop increased by 7.04% compared with a typical wavy fin. Chingulpitak et al. [9] experimentally and numerically investigated the flow characteristics of crosscut heat sinks. They reported that, under the same pumping power, a thermal resistance of a crosscut heat sink with a length of 1.5 mm and a crosscut number of 6 were lower than that of a conventional plate fin heat sink by 16.2%. Zhang et al. [10] experimentally and numerically studied the thermal hydraulic characteristics of a heat exchanger with humped wavy fins. Wavy fins with humped radii ranging between 0.3 and 0.9 mm and Reynolds numbers ranging between 500 and 5000 were used. They reported that the overall thermal hydraulic characteristics of humped wavy fin were better than that of a triangular wavy fin. Khoshvaght-Aliabadi et al. [11] studied the thermal performance enhancement of nanofluids inside straight and wavy miniature heat sinks (MHSs) using pin-fin interruptions. Three pin-fin interruptions were tested at a Reynolds number ranging from 100 to 900. They concluded that the hydrothermal performance of straight and wavy MHSs with pin-fin interruptions was higher than that from straight and wavy MHSs. Yu et al. [12] analytically studied the friction factor and the Nusselt number of two sinusoidal wavy plate fins under the low-Reynolds number. A 2-D flow of fluid between two wavy plate fins was assumed, and the simulations were made using FLUENT. The results showed that the fRe was monotonically increased when the dimensionless waviness (a/L) had increased. It was also found that the decrease of H/L resulted in the increase of the Nusselt number to the peak value before it was decreased. Nilpueng et al. [13] presented the experimental data of water flow in a plate heat exchanger with surface roughness. The stainless steel corrugated plates with a sinusoidal shape and a symmetrical chevron angle of 30° and 60° were used. The heat transfer rate and pumping power of water through a sinusoidal wavy channel increased when decreasing the chevron angle. Aneesh et al. [14] numerically investigated the effects of wavy channel configurations on the thermal hydraulic characteristics of Printed Circuit Heat Exchanger (PCHE). Three wavy channel configurations such as triangular, sinusoidal, and trapezoidal were simulated, and the thermal performances of these models were compared with the straight channel. The sinusoidal, trapezoidal, and triangular wavy-channel PCHE gave the heat transfer enhancement about 33%, 41%, and 28%, respectively. The flow and heat transfer characteristics inside a wavy channel were numerically investigated by Harikrishnan and Tiwari [15]. Effects of wave amplitude, skewness angle, and Reynolds number (Re), which was computed using ANSYS Fluent 16.1, were presented. They reported that the skewness resulted in the stronger secondary flow in the wavy channel.

It can be noted that most of the previous research works focused on the effects of wave length, wave amplitude, channel length, and channel height and working conditions on thermal performance of sinusoidal wavy channel heat sinks. However, the combination of other heat transfer enhancement techniques on a sinusoidal wavy fin channel such as nanofluid, pinfin interruption, and crosscut flow control has been investigated by a few researchers. As a result, there remains room for further studies, especially the crosscut sinusoidal wavy plate fin heat sink (CCSW-PFHS). In this work, the main concern is to investigate the effect of the phase shift between the side walls of the wavy fins, air velocity, and heat sink base surface temperature on the heat transfer coefficient and pressure drop of SW-PFHS and CCSW-PFHS. The comparison of thermal performance between CCSW-PFHS and SW-PFHS is also presented.

Section snippets

Experimental apparatus and procedure

The experimental apparatus for testing the thermal performance of SW-PFHS with and without crosscut flow control is shown schematically in Fig. 1. It consists of a wind tunnel, heat supply set, test section, and data-acquisition system. The rectangular wind tunnel is made of an acrylic plate with a 5 mm thickness and covered with 6.4 mm-thick Aeroflex insulation to reduce the heat loss. The dimensions of the channels are 0.075 m wide, 0.8 m long, and 0.027 m high. To control the air velocity

Heat transfer characteristics

Variation of the heat transfer coefficient with an air velocity for different phase shifts of SW-PFHS and CCSW-PFHS is presented in Fig. 5. Based on this experiment, the average relative uncertainties of the heat transfer coefficient are ±2.98%. The heat transfer coefficient increases with increases in air velocity. It can be explained that the recirculation flow occurs at the trough of the sinusoidal wavy channel, and the recirculation flow rate is higher when increasing the air velocity [1],

Conclusions

In this research work, the heat transfer coefficient and pressure drop of airflow through SW-PFHS and CCSW-PFHS are investigated. The comparisons of thermal performance between SW-PFHS and CCSW-PFHS are also presented. SW-PFHS with a heat sink base with a width of 27 mm, a length of 75 mm, a wave length of 18.68 mm, an amplitude of 2.0 mm, and a phase shift of 0°, 90°, and 180° are used for testing. For CCSW-PFHS, the sinusoidal wavy plate fin is cut transversely at crests and troughs with 2-mm

Conflict of interest

Author declares that there is no conflict of interest.

Acknowledgments

The first author thanks the College of Industrial Technology, King Mongkut’s University of Technology North Bangkok, Thailand for Grant No. Res-CIT0212/2017. The second author would like to thank international co-operation in research provided by the National Research Council of Thailand (NRCT) and the National Research Foundation of Korea (NRF), and visiting professorship provided by KMUTT. The fourth author acknowledges the support provided by the “Research Chair Grant” National Science and

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