Numerical feasibility study of using ultrasonic surface vibration as a new technique for thermal management of the electronic devices

https://doi.org/10.1016/j.enconman.2022.116481Get rights and content

Highlights

  • Numerical study of using ultrasonic wave for thermal management of CPUs.

  • Totally 31 scenarios are examined by altering location and number of transducers.

  • Impact of Reynolds number and transducer frequency on the outcomes are assessed.

  • Case with transducers at ceiling and lateral walls (case#27) has the highest PEC.

  • The maximum PEC belongs to the case#27 and occurs at Re = 1000 for F = 30 kHz.

Abstract

The suitable thermal management of electrical devices leads to their reliable operation and durability. The present study investigates the application of ultrasonic surface vibration in a pin–fin heatsink to improve hydrothermal performance. To this end, a totally 31 scenarios were examined by altering the location of the vibrating transducers at four lateral walls and the top plate of the heatsink. The numerical calculations were performed within Reynolds number (Re) ranges of 500–2000 and frequency magnitude (F) of 15–30 kHz. Our results showed that the heatsink with three transducers at the top plate and two lateral adjacent walls (near and the opposite side of the inlet), namely case#27, exhibits the highest heat transfer coefficient and performance evaluation criteria (PEC) of 1.38 over the base case without transducers (WOT) at Re = 2000 and F = 30 among the studied cases. In addition, case#27 has its highest heat transfer coefficient and pressure drop (ΔP) at Re = 2000, while its maximum PEC is obtained as 1.78 at Re = 1000 for F = 30 kHz over the base case without vibration. Moreover, the maximum heat transfer coefficient and the lowest ΔP for case#27 at Re = 2000 were obtained at = 25 kHz. In such a case, the PEC was obtained as 1.06 over the base case.

Introduction

The fast pace of electronic cooling technology progress implies different methods are examined and tested for the thermal management of electronic devices. Mainly two active and passive techniques are used to improve the heat transfer in a heat dissipation system. In the active technique, an external source of energy is used to move or make rotational flow on the coolant fluid using inserts [1], [2], applying the magnetic field [3], [4] or vibration [5], [6] at the surface or in the fluid flow to improve the heat transfer performance. However, the passive technique doesn’t benefit an external source of energy and relies on the changing in the system geometry such as the increasing of the heat transfer surfaces by using the fins [7], [8], [9], splitters [10], [11], and applying the textured or curvy surfaces [12], [13]. The combination of both techniques leads to improving heat transfer performance more than is possible by using any of them acting alone. For instance, applying the textured finned tubes with twisted tape inserts [14] in the heat exchangers or using fins and subjecting the fluid to the vibrations [15]. The vibration can destabilize the fluid flow in a heat exchange device, thereby leading to an increase in the boundary layer growth leading to improve the heat exchange rate. In other words, by applying ultrasonic vibrations into a medium, sound waves which are known as mechanical waves are propagated into the domain. Acoustic streaming is the most remarkable phenomenon which is generated by the propagation of ultrasonic waves into a fluid medium [16]. In addition, acoustic streaming is known as a steady flow and the friction between the solid wall and vibrating fluid near the wall as well as the attention of wave energy propagated into the medium are the main reasons to generate acoustic streaming. This steady flow causes better fluid mixing and destabilizes the thermal boundary layer, and consequently is responsible for significant heat transfer enhancement [17]. The heatsinks are used for the thermal management of electronic devices due to their small sizes and low costs. Several research studies have been performed on the heat transfer improvement of the heatsinks by either changing the heatsink geometry or using different Nano fluids (NFs) due to their higher thermal conductivity of them over pure water. The following literature studies the previous research works conducted on the heat transfer under the vibration effect and the scientific efforts performed to improve the heat transfer performances of different heatsinks.

Go [18] experimentally and numerically investigated the heat transfer performance of a micro-fin heatsink under the vibration effect for the air flow coolant. A nearly 5.5–11% increase in the heat transfer rate was reported by using the micro-fins as compared to the plain wall heatsink. In addition, the micro-fin vibrating displacement increases as air velocity increases. Fu et al. [6] inspected the heat transfer and fluid flow in a rectangular duct heat exchanger under the vibration effect. They concluded that the vibration amplitude has a higher effect on the hydrothermal performance than the vibration frequency. Besides, the vibration causes to enhance the velocity gradient which synergizes with the temperature gradient and thereby improves the heat transfer performance. The effect of vibration on the heat transfer and frictional losses inside an air heat exchanger was investigated by Mohammed et al. [19] considering Re numbers of 10000–55000. Based on the results, the vibration escalated ΔP and enhances the heat transfer rate by 95% and 110%, respectively. Also, it was observed that the frequency is the most effective parameter on the heat transfer performance as compared to the vibration amplitude. Zhang et al. [20] explored the hydrothermal behavior of fluid turbulent flow (Re = 5971–13933) in a tube under the periodical vibration effect considering the vibration amplitude and frequency ranges of 1–5 mm and 1–10 Hz, respectively. They concluded that the heat transfer rate and ΔP under the vibration effect increased to 2.83 times and 83%, respectively, over the static tube. Hosseinian et al. [21] performed the experimental analysis of MWCNT/water flow and heat transfer inside a double pipe heat exchanger under the vibration effect. The results of that study showed that the vibration decreases the nanoparticle deposition and enhances the heat transfer rate. In addition, the vibration effect decreases as fluid flow increases. The highest enhancement coefficient of the vibration was obtained as 2% at nanoparticle concentration (φ) of 0.04% and will be decreased to 1.75 atφ = 0.25%. The experimental analysis of the vibration effect on the heat transfer performance of a double pipe heat exchanger was performed by Setareh et al. [22] considering the vibration frequency of 26.7 kHz. The results demonstrated that the ultrasonic vibration enhances the heat transfer rate by 60% at cold and hot fluid flow rates of 0.5 L/min. This percentage increase reduces to 20% when cold and hot stream flow rates escalate to 1 L/min and 1.5 L/min, respectively. The main important result of that study is that the vibration ultrasonic waves propagate and cause a cross-stream flow into the fluid leading to enhance heat transfer performance. A numerical analysis of the effect of mechanical vibration in a battery thermal management system including the phase change material was performed by Zhang et al. [23] for vibration amplitude and frequency range of 2–4 mm and 10–30 Hz, respectively. The results indicated that too low or high vibration frequency has no significant effect on the heat transfer performance. Also, the vibration causes to accelerate the collision and dispersion of the particles with high thermal conductivity leading to improve heat dissipation rate.

The following literature reviews the most recent studies on the hydrothermal aspects of different heatsinks with and without NF coolants. The performance of microchannel heatsinks could be improved by applying wavy channels, serpentine channels, plane fins, perforated fins, textured fins and etc. [8]. For instance, the numerical analysis of a pin–fin heatsink with NF coolant was performed by Khetib et al. [24] considering the square, hexagonal, triangular, and circular shaped pin-fins and brick, blade, plate, and cylinder-shaped nanoparticles. The results showed that the highest heat transfer performer and lowest ΔP are associated with the circular-shaped pin-fins and brick-shaped nanoparticles. In addition, the increase in NF velocity was shown to improve the heat transfer performance of the system. Shahsavar et al. [25] explored the force convection laminar flow of water flow ins a pin–fin heatsink using various numbers and arrangements of the inlet/outlet for the heatsink. Based on the results, the application of two inlets and two outlets leads to a low ΔP and heat transfer rate. However, the configuration with one inlet and two outlets on the opposite sides of the heatsink exhibited the highest heat transfer performance and moderate pumping power. Besides, this configuration has a performance evaluation criteria (PEC) of 19.77% higher than that for the other configuration with two inlets and two outlets. In another research, Shahsavar et al. [26] performed a numerical analysis to evaluate the influence of using tip clearance on the hydrothermal behavior of a pin–fin heatsink considering different pin–fin heights (1.5 mm-2.5 mm). The results demonstrated that the highest heat transfer rate, the minimum CPU temperature, and the minimum entropy generation rate are associated with the pin–fin heights of 2.25 mm, 2.5 mm, and 1.5 mm respectively. However, the maximum PEC of 1.28 was obtained for the pin–fin height of 2.25 mm. Radwan and Ahmed [27] studied the application of different configurations of a microchannel heatsink for cooling the Concentrative Photovoltaic Thermal (CPVT) solar collector performing the numerical and experimental analyzes. Three configurations of microchannels namely a) wide rectangular, b) single-layer parallel (or counter) flow and c) double-layer(or counter) flow were investigated. Based on the findings, the single-layer parallel-flow and single-layer counter-flow microchannel exhibited the minimum and maximum cell temperatures, respectively. In addition, the highest electrical efficiency and net power also are associated with the single-layer parallel-flow microchannel. The application of metal foam under the jet impingement inside a heatsink was numerically and experimentally investigated by Wang et al. [28] considering two configurations with 8 and 22 fins. The effects of fin height, metal foam density, and Re (2053–12737) on the hydrothermal performance of the heatsink were investigated. The results indicated that the application of metal foam significantly enhances the heat transfer rate under an extra pressure drop penalty. Han et al. [29] investigated three configurations (serpentine channel, counter-flow channel, and double U-shaped counter-flow channel) of liquid-cooled heatsinks for cooling a 30 kW motor inverter through numerical and experimental analyzes. The results showed that the serpentine channel heatsink provides the best cooling performance as compared to the two other configurations. Besides, the intensification in the fin thickness entails a decrease in ΔP and increase in heat source temperature. The optimization outcomes portrayed that the best performance belongs to the serpentine heatsink with a fin thickness of 1.2 mm and the inlet coolant flow rate of 3 L/min. Chen et al. [30] explored the performance of a serpentine reentrant microchannel heatsink for cooling a CPVT solar collector. Their results proved that the studied heatsink provides better thermal performance, and thereby lower cell temperature (25 °C-31 °C) and more suitable cell temperature uniformity as compared to the finned heatsink with cell temperature of 45–63 °C. Consequently, the output power and electrical efficiency of the CPVT with serpentine reentrant microchannel heatsink enhance by 115% and 15–20% over the finned heatsink.

Based on the literature review and to the best of the authors’ knowledge, the application of ultrasonic surface vibration in the heatsinks has not been investigated in previous studies. The propagation of the vibration waves in a different direction inside the fluid flow leads to an increase in the velocity boundary layer and enhance the cooling performance of the heatsink. The pressure drop is also affected by the vibration which could be increased or decreased depending on the location of the vibration transducers, Re number, and the vibration frequency. The present paper investigated the effect of ultrasonic vibration on the hydrothermal performance of a pin–fin heatsink for the first time. To this end, a parametric optimization analysis was performed by altering the location and numbers of transducers, Re number (500, 1000, 1500, and 2000) as well as the vibration frequency (15 kHz-30 kHz). The numerical results were presented in terms of ΔP, convective heat transfer coefficient, temperature uniformity, thermal resistance factors, CPU mean temperature, and PEC.

Section snippets

The geometry, boundary conditions

Fig. 1 shows the schematics of the studied pin–fin heatsink and the location of transducers at one of the lateral walls. Here can be seen that the heatsink length, width, and height are equal to 63 mm, 30 mm, and 12 mm, respectively. The cylindrical pin-fins have a height and diameter of 7.5 mm and 2 mm, respectively. The heatsink possesses one inlet and one outlet on the same lateral side having a diameter and length of 6 mm and 21 mm, respectively. The diameter of the transducer head is equal

Governing equations

The 3D numerical analysis was performed assuming the laminar, incompressible and steady water flow inside the pin–fin heatsink by solving the mass conservation, momentum and energy conservation equations as follows [11]:

Mass:vxx+vyy+vzz=0

where v is the flow velocity.

Momentum:ρvxvxx+vyvxy+vzvxz=-Px+μ2vxx2+2vxy2+2vxz2+Sxρvxvyx+vyvyy+vzvyz=-Py+μ(2vyx2+2vyy2+2vyz2)+Syρvxvzx+vyvzy+vzvzz=-Pz+μ(2vzx2+2vzy2+2vzz2)+Sz

where ρ, P, μ, and S are the density,

Grid independency

The ANSYS Fluent 19 was used to perform the computational procedures applying the second-order upwind scheme to discretize the governing equations. The SIMPLE algorithm was used for coupling between the velocity and pressure fields at the convergence criterion of 10−6. To improve the convergence speed and numerical results accuracy, we adopted an unstructured mapped mesh (Fig. 2). Four mesh with different grid numbers from 450,512 to 2,592,188 were employed and the maximum CPU temperature and

Results and discussions

In the present study, a parametric optimization was performed by altering the location of the vibrator transducers on the lateral heatsink walls and the top surface. A total of 31 scenarios were examined for the transducer location considering different Re numbers (500–2000) and frequency magnitudes of 15000 Hz to 30000 Hz. This section is divided into three parts; 1) investigation of the effect of vibrator transducer locations at constant Re of 2000 and F = 30000 Hz, 2) study of the effect of

Conclusion

The influence of ultrasonic surface vibration on the hydrothermal behavior of a pin–fin heatsink with water coolant was investigated by performing a three-dimensional numerical analysis. Totally 32 cases were examined by changing the vibrating transducers on four lateral walls and the top surface of the heatsink. The laminar force convection and steady-state flow of water with four Re numbers (500, 1000, 1500, and 2000) were investigated considering four different vibration frequency magnitudes

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.

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