A Computer Model To Simulate Heat Transfer InHeat Sinks

One of the major concerns in the operability of power generation systems is their susceptibility to combustion instabilities. In this work, we aim to examine the effective use of heat exchangers, an integral component in any power generation system, to passively control combustion instability. The combustor is modelled as a quarter-wave resonator (1-D, open at one end, closed at the other) with a compact heat source within, which follows time lag law for heat release. The heat exchanger (hex) is modelled as an array of tubes with bias flow and is placed near the closed end of the resonator, causing it to behave like a cavity-backed slit plate: an effective acoustic absorber. For simplicity and ease of analysis, we treat the physical processes of heat transfer and acoustic scattering occurring at the hex as two individual processes separated by an infinitesimal distance. The aeroacoustic response of the tube array is modelled using a quasi-steady approach and the heat transfer across the hex is modelled by assuming it to be a heat sink. Unsteady numerical simulations were carried out to obtain the heat exchanger transfer function (HTF), which is the response of the heat transfer at hex to upstream velocity perturbations. Combining the aeroacoustic response and the HTF, in the limit of the infinitesimal distance between these processes tending to zero, gives the net influence of the hex. Other parameters of interest are the heat source location and the cavity length (the distance between the tube array and the closed end). We then construct stability maps for the first resonant mode of the aforementioned combustor configuration, for various parameter combinations. Preliminary observations show that stability can be achieved for a wide range of parameters.

Reliable and efficient cooling solutions for portable electronic devices are now at the forefront of research due to consumer demand for manufacturers to downscale existing technologies. To achieve this, the power consumed has to be dissipated over smaller areas resulting in elevated heat fluxes. With regard to cooling such devices, the most popular choice is to integrate a fan driven heat sink, which for portable electronic devices must have a low profile. This paper presents an experimental investigation into such low profile cooling solutions, which incorporate one of the smallest commercially available fans in series with two different heat sink designs. The first of these is the conventionally used finned heat sink design, which was specifically optimized and custom manufactured in the current study to complement the driving fan. While the second design proposed is a novel “finless” type heat sink suitable for use in low profile applications. Together the driving fan and heat sinks combined were constrained to have a total footprint area of 465 mm2 and a profile height of only 5 mm, making them ideal for use in portable electronics. The objective was to evaluate the performance of the proposed finless heat sink design against a conventional finned heat sink, and this was achieved by means of thermal resistance and overall heat transfer coefficient measurements. It was found that the proposed finless design proved to be the superior cooling solution when operating at low fan speeds, while at the maximum fan speed tested of 8000 rpm both provided similar performance. Particle image velocimetry measurements were used to detail the flow structures within each heat sink and highlighted methods, which could further optimize their performance. Also, these measurements along with corresponding global volume flow rate measurements were used to elucidate the enhanced heat transfer characteristics observed for the finless design. Overall, it is shown that the proposed finless type heat sink can provide superior performance compared with conventional finned designs when used in low profile applications. In addition a number of secondary benefits associated with such a design are highlighted including lower cost, lower mass, lower acoustics, and reduced fouling issues.

Cooling of electronic circuits is a necessity to ensure their reliability and optimum working conditions. In this work different types of pin fin based bio-inspired flow fields are analyzed. The flow fields are of differently shaped pin fin arrays, with leaf-type branching secondary channels, having a porosity range of 0.520.78. The number of inlet and outlet pairs for the models analyzed varies from one to four, to cater to the increased heat flux inputs. The simulation of the heat sink models is done using COMSOL. The coupling between heat transfer and laminar fluid flow is done using conjugate heat transfer analysis. The heat sinks are subjected to a constant heat flux input and tested for the laminar Re range of 10002300. The square pin fin model is validated at a porosity of 0.52 and aspect ratio-8.6, for test conditions specified in reference work. Validation of simulation results is done by comparing the mixing cup temperature with that obtained by applying the heat balance equation. The results prove that, the thermal and hydraulic resistance of bio-inspired pin fin models studied in this investigation is lower than that of traditional pin fin array models, leading to a higher Nu for similar pressure drops. The four-inlet heat sink models show a thermal resistance of 0.130.15 C/W at an inlet Re of 2300 with a calculated pumping power of 0.081-0.132 W for the flow field. The reduced porosity square pin fin model has a thermal resistance of 0.0673 C/W at pumping power of 3.44 W.

The inverter controller produces large heat flux during the high-frequency operation of inverter air conditioners and the heat flux should be dissipated in time. The objective of this study is to propose a novel cooling method based on the heat pipe heat sink (HPHS) for the inverter controller. The heat flux of the chips in the controller is transferred to heat pipes by conduction and then dissipated to the ambience by the efficient heat convection between the dense fins and the air. Two types of HPHSs (i.e. vertical U-type and L-type) are designed, and their cooling performance are investigated and compared with the conventional plate-fin heat sink based on simulation. The application of HPHS cooling method in a real inverter air conditioner shows that, L-type HPHS and U-type HPHS can reduce the average temperatures of chips by 7.9 oC and 5.2 oC compared to the conventional plate-fin heat sink, respectively.

The present study utilized piezoelectric ceramics (PC) as actuators to design five new piezoelectric heatsinks and preliminarily investigated the different design types and their operating conditions, such as the frequency, placement distance, thickness between piezoelectric sheets, piezoelectric sheet size, and noise produced. The results showed that when the micro heatsink bearingless piezo jet was placed too close to the heat source, the high temperature sucked back the surrounding fluids, causing the fluid chamber temperature to rise and the cooling effect to be reduced. Therefore, the heatsink should be placed between 10 and 20 mm from the heat source. With the proper distance, the heat convection coefficient was 200% greater than that of a traditional rotary fan. The cooling effect of the five heatsinks was calculated using the thermal analysis method, and the results indicated that the convection thermal resistance of the best heatsink could be reduced by about 36%, and the frequency, flow velocity, and noise were all positively correlated. When the supplied piezoelectric frequency was 300 Hz, the noise level was similar to that of a commercial rotary fan. The tested heatsinks had one of two volumes depending on the size of the piezoelectric sheet, including 3150 mm3 or 4050 mm3, respectively. An array of 25 to 32 micro heatsinks of the same size were connected in series. The power consumption of any single heatsink was 10% of that for a rotary fan. Among the five types of heatsinks, the best type had a piezoelectric sheet diameter of 41 mm, a piezoelectric thickness of 2 mm, and an opening length of 4 mm. Furthermore, the best operating conditions were found at a frequency of 300 Hz and a placement distance of 20 mm.

This report presents a system thermal-hydraulic analysis code ATHLET-MF --- a new version of ATHLET. This code has been developed on the basis of ATHLET for the thermal-hydraulic analysis of multi-fluid systems, includingthe liquid LBE-cooled systems. A fluid index was introduced in ATHLET-MF so that the user can easily adapt the code for various fluids. The current version of ATHLET-MF has the fluid options of water, liquid LBE and Diphyl THT. Empirical equations of physical properties of liquid LBE and of Diphyl THT, and the heat transfer correlation of liquid LBE were implemented in ATHLET-MF for its application to the LBE-cooled ADS systems. The physical properties and heat transfer correlation of liquid LBE were used based on the comprehensive review and assessment of the thermophysical properties of liquid LBE and of the heat transfer correlations for heat transfer in heavy liquid metals in the open literature. The ATHLET-MF code was applied to the analyses of the target cooling systems of XADS, MEGAPIE and MITS under various transient conditions. The code was assessed against two home-made system analysis codes HERETA and HETRAF by performing the simulation of the dynamic behavior of the target cooling system of XADS under beam power switch-on conditions. Results from the three different codes show a good agreement, indicating the applicability of the ATHLET-MF code to LBE cooled systems. Simulation of the beam power interruption of XADS shows that transient with longer beam interrupt time undergoes a deeper drop of the fluid temperature and of the mass flow rate. However, the drop of fluid temperature is limited by the heat transferred from the reactor pool and the reactor core after the switch-off of the beam power. It is shown that the beam interrupts with duration shorter than 0.1 s are less critical than those with duration longer than 0.1 s. In the case of loss of heat sink, the proton beam should be switched off in 200 s after the occurrence of the transient in order to avoid the failure of the window. For the beam trips of MEGAPIE and MITS, a proper regulation of the 3-way valve in the intermediate cooling loop can effectively limit the LBE temperature fluctuation at the exit of the target heat exchanger. The peaks of LBE temperatures at the inlet and exit of the target heat exchanger after the beam power recovery can be reduced or even eliminated by opening the 3-way valve in the intermediate cooling loop at an early time. Comparison shows that the drop of fluid temperature under the transient of beam trip of MITS is much smaller than that of the MEGAPIE. The steady state natural circulation of LBE is established after the loss of pump power supply for both MEGAPIE and MITS. The natural circulation flow rate is about 46% of its initial value for MEGAPIE and about 37% of its initial value for MITS, which is about 24% less than that calculated based on the proposed scaling principles of a scaled experiment.

Heat transfer and pressure drop characteristics of R134a flow boiling in the parallel/tandem microchannel heat sinks

Heat sources in proton exchange membrane (PEM) fuel cells

This study describes a thermal design method of forced convection cooling in high-density packaging electronic equipment for upstream design processes by flow and thermal resistance network analysis. Forced convection cooling by combining fans and heat sinks is the most standard strategy for dissipating heat from electronic equipment. In recent years, the thermal design of electronic equipment becomes more critical, and fast thermal design is required due to the rapid development of final products. We have been developing the flow and thermal resistance network analysis as the quick thermal design method for electronic equipment. However, an accurate prediction of forced convection cooling performance by finned heat sinks mounted in high-density packaging electronic equipment is generally tricky. Some bypasses, which are clearances between the heat sinks and enclosure walls or other components, exist around the heat sinks. Therefore, a flow rate distribution between the heat sink fins and the bypasses should be predicted. Many researchers have investigated hydrodynamic characteristics and heat transfer characteristics of finned heat sinks. However, many previous studies have been conducted on the finned heat sink performance when there are no bypasses. In order to achieve an optimum design of the finned heat sinks in the upstream configuration regardless of the heat sink dimensions, a systematic database of hydrodynamic characteristics and heat transfer characteristics of the finned heat sinks with bypasses should be investigated. This paper discusses the development of function models of pressure drop, flow rate distribution, and heat transfer of the finned heat sinks with the bypasses for the resistance network analysis through experiments and CFD analysis. Several types of finned heat sinks with 40 mm in width and 80 mm in length were prepared, and these were mounted in a rectangular enclosure with 45 mm in width and height. First, the pressure drop characteristic around the heat sink was investigated. In addition, the flow rate distribution between the heat sink and the bypass was evaluated separately. A flow branching coefficient was developed to predict the flow rate distribution around the heat sink combined with the pressure drop coefficient. Using the developed flow branching coefficient, the flow and thermal resistance network model around the finned heat sink was developed. The results from the proposed resistance network model showed good agreement with those from the experiment.

Optimum design of a radial heat sink under natural convection

The findings of the experimental study into optimizing the heat transfer rate of a PCM-based heat sink for high-power LEDs are presented in this work. The study investigated five heat sink types, with and without PCM. The LED case and junction temperatures, LED module temperatures, heat storage and release rate analyses, analyses of three types of cyclic operation modes, luminous flux, and heat sink thermal resistance were all examined independently. The results indicated that the PCM-based LED heat sink had improved thermal performance. The LED junction temperature of the PCM-equipped E-20 heat sink is nine degrees Celsius lower at 10 W than that of the heat sink without PCM. Furthermore, the E-20 heat sink with PCM extends the LED module’s critical lifespan. As a bonus, the E-20 with PCM had a 38.19 percent lower thermal resistance at 10 W than the E-20 without PCM. According to these results, the heat sink E-20 emits 715 lm at 10 W when operated without a phase-change material (PCM). With the same input power, the luminous flux of an E-20 equipped with a heat sink and a phase-change material (PCM) is 750 lm, a gain of 4.7%. Finally, clearly recommend the heat E-20 sink with PCM suitable for high-power LED thermal management system.

Study on spray cooling characteristics of dry ice particles for IGBT in high-speed trains{fr}Etude des caractéristiques de refroidissement par pulvérisation des particules de glace sèche pour l'igbt dans le train à grande vitesse

In the pursuit of optimizing heat dissipation and improving performance in electronic devices, liquid-cooled heat sinks have garnered significant interest due to their potential to improve heat transfer efficiency. Presented study set out to assess the effectiveness of straight channel heat sinks as a thermal solution for high heat generating electronics components, while also investigating the impact of applying a hydrophobic coating on their performance. A series of tests were conducted at different heating powers (50W-250 W) and flow rates (200–950 ml/min), while also considering different orientations and directions of flow. The investigation focused on analysing critical aspects such as heat transfer performance, wall temperature variations, thermal resistance, and pressure drop characteristics of straight channel heat sinks with conventional and hydrophobic-coated surfaces. The results showed that the Nusselt number increased with higher Reynolds numbers and heating powers, indicating improved heat transfer efficiency. However, the hydrophobic coating on the heat sink surface led to a reduction in the Nusselt number due to the formation and retention of bubbles, hindering heat transfer. The maximum average reduction of 20.85% in Nusselt number was noticed at 100 W for the vertically positioned hydrophobic-coated heat sink with downward flow compared to conventional surface (CS) heat sink. Additionally, the findings revealed that pressure drop is influenced by Reynolds number and the presence of bubbles, with gravity playing a role in reducing pressure drop in certain orientations. A hydrophobic coating shows a small decrease in pressure drop, but bubble formation limits its effectiveness to some extent. Comparisons also indicated that the highest average decrease in pressure drop about 11.92% was observed for the same configuration, vertically positioned hydrophobic heat sink with downward flow, at 50 W. Moreover, the study's findings have broader implications beyond electronics. Heat sinks are widely employed in various industries, including automotive, aerospace, renewable energy systems, and industrial processes.

Heat transfer in engineering applications has shown progress, especially in electronic devices that raise the need for better heat sink designs. In addition, the generation of heat in devices and electronic circuits has also augmented, leading to the problem of heat dissipation. This study investigates the thermal and fluid flow characteristics of different geometrical configurations of pin fin heat sink under natural convection. The heat sink models studied are Hybrid Pin Fin with Connector Heat Sink (HPFWC HS) and Pin Fin with Connector Heat Sink (PFWC HS). All heat sinks models were simulated using CFD Ansys to analyse each heat sink’s thermal performances and flow fields. The results show that adding wings to the HPFWC HS significantly increased heat dissipation. In terms of heat transfer characteristics, the HPFWC HS has about a 5.78% increase in Nusselt number compared with HPFWC HS. The reason is that the heat sink HPFWC HS has wings around it, and these wings help to promote vortex formation around the fins, which leads to a higher heat transfer coefficient. A fin spacing of 15mm is the best spacing for the heat sink compared to other fin spacing.

A heat sink is a device used to dissipate heat generated by electrical and electronic devices; it is classified as an active or passive heat sink according to the cooling process. The present study aims to evaluate the effect of forced vibration on heat sink thermal performance. For this purpose, a heat sink with rectangular longitudinal fins with regular aluminum sections has been selected. The heat sink has nine fins, each measuring 100 × 130 mm and having a thickness of 2 mm. These fins are firmly attached to a 100 × 100 × 10 mm aluminum base that contains a 140 W electric heater. It was installed at the middle height of a 75 × 14× 12 cm vertical duct. It was connected to a system that generated vibrations and the electrical power supply. A test rig contains various measurement devices, including a temperature data logger, an anemometer, and voltage and current meters. The tests were done with three different heat flux amounts: 150, 230, and 360 W/m2. The frequency range of the vibrations was 0–50 Hz, and the amplitude ranged from 0.07 to 6.99 mm using free convection. The analysis showed a linear relationship between the heat transfer coefficient and the modified Rayleigh number. This was at a frequency of 0 Hz and a heat flux ranging from 5 to 12 W/m2. Throughout the free-convective heat transfer range, even though vibration increased the heat transfer coefficient, it was found that the maximum heat transfer coefficient for overall heat fluxes was reached at 50 Hz. Regarding 150, 230, and 360 W/m2, respectively, this coefficient increased by 160, 59.5, and 55.2% compared to 0 Hz. Moreover, vibration has contributed to increased air mass flow at 50 Hz (8.8, 12.7, and 25%) compared to 0 Hz. Also, the results showed that the fin's efficiency decreased due to vibration by 9.8, 9.8, and 11.8% for 150, 230, and 360 W/m2, respectively.