Enhanced thermal performance of phase change material-integrated fin-type heat sinks for high power electronics cooling

https://doi.org/10.1016/j.ijheatmasstransfer.2021.122257Get rights and content

Highlights

Abstract

We report the enhanced cooling performance of the phase change material (PCM)-integrated fin-type heat sink compared to conventional fin-type heat sink in high power electronics with two localized hot spots. The PCM-integrated fin-type heat sink is fabricated by embedding the phase change composite to the base plate of the heat sink. As an effort to effectively utilize thermal capacitive effects of PCM, the phase change composites with paraffin infiltrated to copper foams are deployed within circular hole arrays in the base plate, which is subsequently covered by a graphite sheet, to achieve excellent heat spreading characteristics. Considering the cooling environments of commercial high power electronics (insulated-gate bipolar transistor (IGBT)), thermal performance of the PCM-integrated and the conventional fin-type heat sinks is experimentally and numerically investigated upon the heating powers of 400∼800 W. While the PCM-integrated fin-type heat sinks have similar heat sink thermal resistance with the conventional fin-type heat sinks, the PCM-integrated fin-type heat sinks exhibit an effective time delay up to ∼27.3% of the hot-spot temperature rise until 80 ℃ of the heat sinks in reduced cooling conditions, showing the potential as an effective thermal managing platform of the PCM-integrated heat sinks in convection-limited cooling environments.

Introduction

High power electronic devices necessitate effective thermal management by using cooling systems for their stable operation [1]. Passive cooling strategies of electronic devices have been widely used for thermal control of electronic devices due to the advantages including non-power consumption and low noise generation [2,3]. However, high power electronics like insulated-gate bipolar transistors (IGBT) or intensive heat-dissipating electronics like light-emitting diodes (LED) are often operated in the confined spaces with the limited cooling resources [4,5]. To fulfill the requirements of effective cooling on those devices, enhancing cooling capacity of heat sinks has been extensively investigated in terms of modifying heat sink designs [6] and developing new cooling materials [7].

Integrating phase change materials (PCMs) to conventional heat sinks has been highlighted in that they can employ a high degree of heat of fusion of PCMs to realize thermal capacitive cooling effects which are beneficial under the circumstances of low cooling rates with high heating rates [8]. As one strategy of PCM integration to heat sinks, filling PCMs to the spaces of fin arrays in conventional heat sinks was proposed by investigating their cooling effects. Placing (C25H52, melting temperatures of 53–57 °C) to the spaces among the fin arrays of fin-type aluminum heat sinks decreased the maximum temperature of the heat sinks by 5 °C in natural convection when 4 W heating loads were applied until solid paraffin was fully converted to liquid state, due to the incorporation of thermal capacitive effects to cooling [9]. Likewise, the maximum temperature rises of circular pin-fin aluminum heat sinks decreased by 7 °C in natural convection under 8 W heating loads for 90 min, when paraffin was added to the spaces of pin-fin geometries [10]. Applying the synthesized phase change composites, in which paraffin (C26H54, melting temperatures of 58–60 °C) was mixed with 0.2 wt% graphene, over fin-type aluminum heat sinks enabled the 3 °C lower maximum temperature of the fin-type heat sinks than the control heat sinks coated with phase change materials only under natural convection with 10 W heat loads for 83 min, due to the higher thermal conductivity of phase change composites [11]. Placing inorganic salt-hydrate PCM (Mn(NO3)2, a melting temperature of 37 °C) into the fin arrays of fin-type aluminum heat sinks reduced the maximum temperature of the heat sink by 9 °C under forced convection with a heating load of 22.5 W for 120 min [12]. When paraffin (C21H44, melting temperature of 40–46 °C) was infiltrated into the fin arrays of fin-type aluminum heat sinks, the maximum temperature rise decreased by ∼3 °C, compared to bare fin-type heat sinks, under forced convection with a heating load of 30.2 W for 60 min [13]. Full exploitation of thermal capacitive effects of PCMs necessitates their sufficient thermal conductance [14]. Hence, such PCM-fin integration strategies can compensate low thermal conductivities of PCMs by increasing the contact surface areas between PCM and fins, thereby enhancing the utilization of thermal capacitive effects of PCMs. However, as PCM is integrated over the fin arrays, the surface areas of heat sinks decrease to lower their convective heat transfer characteristics.

As another strategy of PCM integration to heat sinks, embedding PCMs to the base plate of heat sinks has been suggested. Specifically, in fin-type copper heat sinks, inserting phase change composites (a thermal conductivity of 11.3 W/m•K) of paraffin and copper foams to the copper base plate could retard the initial temperature rise under natural convection, showing the potentials of the PCM integration to the base-plates of heat sinks [15]. When the phase change composites of 15 wt% graphite nanoplates in paraffin was integrated to the base plates of fin-type aluminum heat sinks, the maximum temperature rise decreased by ∼3.9 °C, compared to bare fin-type heat sinks, under natural convection with 20 W heating loads for 20 min [16]. Although the enhancement of cooling performance in heat sinks has been successfully achieved by incorporation of PCMs, most studies focused on the initial thermal performance of newly developed heat sinks integrated with PCMs until the phase change of PCMs occurred to highlight their thermal capacitive effects in temporally high heating load conditions. However, the PCM-integrated heat sinks typically suffered from higher temperatures in steady states than the control heat sinks due to the increased thermal resistances by incorporation of PCMs [16,17].

For ubiquitous applications of PCM-integrated heat sinks, further optimizations must be carried out to consider both transient and steady-states of their operations. Herein, we demonstrate fabrication and thermal characterization of aluminum fin-type heat sinks with PCM-integrated base plates where high thermal conductive phase change composites are embedded. Specifically, to minimize the increase of the thermal resistance of a base plate by embedding PCMs, the circular hole arrays are fabricated in an aluminum base plate, and phase change composites with paraffin in copper foams are installed within the circular holes, followed by the plate covering with a graphite sheet. The resulting effective thermal conductivity of the PCM-integrated base plate is numerically estimated as 123.7 W/m•K, while that of aluminum base plates is 237.0 W/m•K. Mimicking the cooling environments of commercial IGBT modules, thermal performance of our proposed heat sinks is experimentally investigated with a home-built laboratory apparatus. Consequently, under heating loads of 400 W and normal cooling conditions, the PCM-integrated fin-type heat sinks exhibit similar steady-state temperatures within a difference of 3.9 °C with the conventional fin-type heat sink. More importantly, considering the stable operating temperature of the IGBT modules [18], our PCM-integrated fin-type heat sinks delay the time to reach the target temperature of 80 °C by 22∼27% in heating loads of 400∼800 W and reduced cooling conditions, compared to the conventional fin-type heat sink, showing the effective thermal capacitance and the corresponding thermal damping behaviors.

Section snippets

Thermal characterization of heat sinks

Thermal performance of conventional and PCM-integrated fin-type heat sinks were experimentally investigated by using a home-built laboratory experimental setup to mimic the cooling system of high power electronics (Fig. 1). Specifically, the model cooling system was adopted from the static inverter (SIV) system, consisting of three SIVs, in railway vehicles to convert direct currents (DC) of 1500 V to three-phase alternating currents (AC) of 380 V [19]. Each SIV, which was installed vertically,

Validation for experimental and numerical models

Field testing results of the conventional fin-type heat sink was compared with the laboratory experimental results and numerical calculations as shown in Fig. 4a. Specifically, in the field test, one SIV for the W phase of a SIV stack was operated with an apparent power of 180 kVA (each IGBT was operated with an apparent power of 90 kVA), and the heat loss was estimated as ∼400 W per one SIV inverter consisting of two IGBTs in the operating condition [20]. Accordingly, for the comparison with

Conclusions

Thermal performance of the PCM-integrated fin-type heat sinks for managing heat emission from high power electronics consisting of two IGBTs with two localized hot spots (400 W) is experimentally and numerically investigated. The conventional fin-type heat sinks are modified to have a thick base plate for integration of PCMs, and thermal performance, such as heat sink thermal resistance and hot-spot temperatures, are numerically characterized in terms of the thermal conductivity of the embedded

CRediT authorship contribution statement

Su Ho Kim: Conceptualization, Methodology, Software, Writing – original draft. Chang Sung Heu: Conceptualization, Methodology, Investigation, Writing – original draft. Jin Yong Mok: Methodology, Investigation. Seok-Won Kang: Conceptualization, Methodology, Supervision. Dong Rip Kim: Conceptualization, Methodology, Writing – review & editing, Supervision.

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.

Acknowledgment

This research was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (No. 20208901010010).

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These authors contributed equally to this work.

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