Large Heat Sink Research Articles

Enhanced flow boiling by manipulating two-phase flow in Tesla channel heat sink using HFE-7100

Flow boiling of dielectric fluids in copper microchannel heat sinks is highly desirable for cooling large-sized insulated gate bipolar transistor (IGBT) power electronic modules. However, dielectric fluids present challenges in flow boiling because of their unfavorable thermophysical properties. These factors make it difficult to enhance critical heat flux (CHF) without precooling. To address this, we developed a large copper heat sink (10 cm × 5 cm) with Tesla microchannels designed to suppress vapor backflow and promote intense fluid mixing. The microchannels have a high length to hydrodynamic diameter ratio of approximately 220, significantly higher than those in previous studies. Flow boiling experiments using HFE-7100 were conducted for both Tesla and plain-wall microchannels. Tesla channels demonstrated a 26.2 % increase in CHF and a 120 % improvement in heat transfer coefficient (HTC). These enhancements are attributed to the vapor backflow suppression and improved fluid mixing. Moreover, the standard deviation of wall temperature in plain-wall microchannels was 10 times higher than in Tesla channels, highlighting the effectiveness of the periodic Tesla valves in reducing two-phase flow instabilities. Flow pattern visualization was conducted to further understand the mechanism behind vapor regulation, clarifying the role of Tesla valves in controlling vapor backflow. This study demonstrates the potential of dielectric fluids in Tesla microchannels for flow boiling applications, offering a promising solution for cooling large electronics.

An experimental investigation on passive cooling of a triple-junction solar cell at high concentrations using various straight-finned heat sink configurations

The current study evaluates the energy, exergy, and environmental performance of concentrated triple junction photovoltaic (CPV TJ) cells at various concentration ratios with solar incident irradiance (CRs) ranging from 56 to 550 suns in Saudi Arabia during hot weather. Therefore, the integrated solar cells employed four distinct heat sinks: two with dimensions of 40 × 40 mm2, one with full straight fins (HS-A) and the other with chopped fins (HS-B), and the remaining two with dimensions of 150 × 70 mm2, one with full straight fins (HS-D) and the other with chopped fins (HS-C). The large heat sink (type-D) is 40.48% more efficient than the smaller one (type-B), which is only 39.7% efficient at a CR of 550. Regarding weight, the lighter heat sink (type-B) generates a higher relative power of roughly 1.22 W/g.cm2 than the heaviest one (type-D), which produces 0.22 W/g.cm2. According to exergy, the heat sink raised the solar cell improvement potential (IP) to 6.3, with exergy cost up to 0.085 $/cm2 higher than the uncooled cell. Based on an environmental study, combining the TJ cell with heat sinks reduces yearly carbon emissions by 311.9–327 tons/m2 compared to 43 tons/m2 for the uncooled cell.

The thermodynamic potential of high-temperature transcritical heat pump cycles for industrial processes with large temperature glides

Industrial heat pumps up to 200 °C are an emerging technology with the potential to reshape the industrial heating supply. For large heat sink temperature glides, transcritical cycles are able to increase the power-to-heat efficiency. Its potential is however yet to be unlocked. To examine this potential, a thermodynamic optimization model is proposed. The model includes robust cycle optimization, is able to screen a large set of working fluids, and includes proper post-processing. This model is applied to three highly relevant industrial cases, namely thermal oil heating, superheated steam drying and spray drying. The heat sink temperature glides for the respective case studies are 60 K, 81 K and 105 K. The results show that a temperature glide larger than 60 K is desired to achieve a better coefficient of performance (COP) with transcritical cycles compared to the classical subcritical cycles. Moreover, potential working fluids were identified for these high operational temperatures. For the case study with a heat sink temperature glide of 81 K, transcritical cycles allowed for a COP increase of 4.6%, whereas this increased to 7.3% for a heat sink temperature glide of 105 K. Furthermore, transcritical cycles introduce a much larger volumetric heating capacity, a lower compressor discharge temperature and a substantially lower pressure ratio. In addition, the best performing working fluids for subcritical cycles are highly flammable, which is only the case for some transcritical working fluids. Therefore, these cycles can be beneficial for temperature glides below 60 K. The compressor for transcritical cycles should however be able to cope with pressures up to 60 bar. If these compressors are available, transcritical cycles are shown to be superior compared to classical subcritical cycles.

Offline UPS for Regenerative Loads

Abstract: This paper presents describes about a unique DC Discharge System for Offline UPS. Whenever an offline mode UPS is connected to a motor load, as the motor decelerates either through the change of torque or due to the Dynamic braking there will be a regenerative energy produced. If this regenerative energy flows back into the UPS, then over-voltage condition takes place and causes damage to the UPS. This regenerative energy can bypass through the battery in online mode. But online mode operation of UPS needs high cost as large heat sinks are required. So, offline mode of operation is preferred in most of the cases. The proposed system dissipates the regenerative energy through the connected resistors and the remaining energy is used for the gating of semiconductor switches inside the UPS. The detailed principle of the proposed method is discussed in this project. The entire Discharge System and Gate pulse generating System are simulated in Proteus Software and the results are provided.

Offline UPS for Regenerative Loads

This paper presents describes about a unique DC Discharge System for Offline UPS. Whenever an offline mode UPS is connected to a motor load, as the motor decelerates either through the change of torque or due to the Dynamic braking there will be a regenerative energy produced. If this regenerative energy flows back into the UPS, then over-voltage condition takes place and causes damage to the UPS. This regenerative energy can bypass through the battery in online mode. But online mode operation of UPS needs high cost as large heat sinks are required. So, offline mode of operation is preferred in most of the cases. The proposed system dissipates the regenerative energy through the connected resistors and the remaining energy is used for the gating of semiconductor switches inside the UPS. The detailed principle of the proposed method is discussed in this project. The entire Discharge System and Gate pulse generating System are simulated in Proteus Software and the results are provided.

Novel TIM Evaluation Method With in Situ Electrical Monitoring

Thermal interface materials (TIMs) transfer heat between two surfaces in electronic assemblies. Specifically, a TIM 2 is a TIM used to transfer heat from a component’s lid to a heat sink. During use, TIM 2s experience thermal aging and mechanical stress (caused by board/component/heat sink expansion mismatches and warpage during heating/cooling). Understanding the response of TIMs to these stresses is critical for understanding TIM and product reliability. However, the responses of TIMs are complex and difficult to predict or model. TIMs are often polymeric materials heavily loaded with thermally conductive fillers and have time, temperature, and rate-dependent properties. Therefore, experimental studies are needed to address TIM reliability. However, monitoring TIM stability or performance while in situ is difficult. Electrical capacitance has been used to monitor the stability of dielectric TIM in situ, allowing for monitoring TIM stability and, indirectly, the TIM thermal performance, but electrically conductive TIMs cannot be used with capacitance measurements, so a new technique is needed. Monitoring a conductive TIM’s electrical resistance could give insight into a TIM’s stability, as both thermal and electrical resistances are affected by a TIM’s contact with surfaces, thickness, and area. This study examines four electrically conductive graphite pad TIMs on a test board, representing a large printed circuit board with a large shared heat sink, in an accelerated thermal cycle from 0 °C to 100 °C. The electrical resistance of the TIMs was monitored in situ, and after testing, postmortem failure analysis of the TIMs was done. The efficacy of electrical resistance monitoring for evaluating TIM stability was examined, and correlations with failure analysis results were made. Electrical resistance monitoring provided insight into the TIMs’ stability, failure time, and extent of failure.

Passive cooling of highly-concentrator triple-junction solar cell using a straight-finned heat sink: An experimental investigation

Herein, an experimental setup in Saudi Arabia's hot weather conditions is used to assess the electrical and thermal performance of concentrator photovoltaic triple junction (CPV TJ) cells fed through various Fresnel lenses with concentration ratios (CRs) ranging from 30.5 to 109 suns. The thermal characteristics of triple junction solar cells are investigated in passive cooling utilizing two straight-finned heat sinks with dimensions 40 × 40 mm (HS-A) and 40× 100 mm (HS–B). Results show that the temperature and power production of the cells increases with the solar concentration ratio, whereas its efficiency decreases. It is found that using a heat sink, reduces the cell's temperature and improves heat uniformity. The larger heat sink (HS–B) performs better since it maintains the cell operating temperature at 44.7, 46.8, and 52.5 °C for the CRs of 68, 80, and 109 suns, respectively, compared to 46.5, 55.4, and 66.4 °C for the smaller one (HS-A) under the same operating conditions. Furthermore, at a CR of 68 suns, the TJ cell with the aluminium finned heat sink generates an electric output of 2.32 W/cm2 using HS-B and 2.29 W/cm2 using (HS-A), compared to 2.22 W/cm2 produced by the uncooled cell without heat sink under the same conditions.

A Hybrid Modulation Featuring Two-Phase Clamped Discontinuous PWM and Zero Voltage Switching for 99% Efficient DC-Type EV Charger

Two-stage AC-DC converters are considered as a prominent solution for DC-type electric vehicle (EV) chargers. However, this kind of architecture suffers from high switching losses with large heatsink and DC-link capacitor volume. To relieve this issue, this paper presents a new hybrid modulation for DC-type EV chargers, where a two-phase clamped discontinuous pulse-width-modulation (DPWM) in the front-end circuit is cooperated with the variable frequency triangular-current-mode (TCM) zero voltage switching (ZVS) or its simplified implementation, i.e., boundary-ZVS (B-ZVS) strategy, in the back-end circuit. The former can stop the switching actions in the front-end stage during two-thirds of the grid period, while the AC currents are at their highest values, which can yield to the best switching loss reduction and deliver high power factor operation. Besides, TCM-ZVS or B-ZVS modulations can achieve ZVS turn-on action for all semiconductors during all operating range in the DC-DC stage to further reduce the power losses on the semiconductors. With such characteristics, the proposed strategies can reduce the switching losses of the system to the best extent, and thus allow an enhancement of the system power density by improving the power conversion efficiency. The proposed strategy is described, analyzed, validated, and benchmarked in a 5 kW SMD SiC MOSFET-based two-stage AC-DC converter. A 99% power efficiency can be achieved with the solution implementing the TCM-ZVS strategy at an output voltage of 400 V and rated power.

CANDU-Like Features in Emerging Small Modular Reactor Designs

Abstract Several small modular reactor (SMR) designs are emerging, but only the CANDU® SMR and a couple of Indian designs incorporate the familiar features of the larger CANDU reactors. This paper shows that while the CANDU-reactor concept did not seem to receive wider attention among SMR designers, it has influenced a few. The paper discusses how the CANDU-reactor operating experience can aid in the construction and operation of some SMRs. For example, the concept of passive reactor shutdown by draining the moderator, which was utilized in the early Pickering A units, is adopted in the Copenhagen Atomics Waste Burner; a molten slat (LiF-ThF 4) heavy-water moderated reactor. The heavy-water and lithium in this salt produce tritium and can benefit from the CANDU-reactor experience in handling tritium. The online refueling of CANDU reactors, their large heat sinks, and seamless configuration are also reflected in SMR designs.

Miniaturisation of Electronic Components and the Problem of Device Overheating

With the ever-increasing rate of data generation and communication, as well as the constant push to reduce the size and costs of industrial converter systems, the power density of electronics has risen. Consequently, cooling, with its enormous energy and water consumption, has an increasingly large environmental impact, and new technologies are needed to extract the heat in a more sustainable way-that is, requiring less water and energy. Embedding liquid cooling directly inside the chip is a promising approach for more efficient thermal management. However, the electronics and cooling are treated separately, leaving the full energy-saving potential of embedded cooling untapped. By removing the need for large external heat sinks, this approach should enable the realization of very compact power converters integrated on a single chip.

Techno-Economic Assessment of Waste Heat Recovery Technologies for the Food Processing Industry

The food manufacturing sector is one of the most dominant consumers of energy across the globe. Food processing methods such as drying, baking, frying, malting, roasting, etc. rely heavily on the heat released from burning fossil fuels, mainly natural gas or propane. Less than half of this heat contributes to the actual processing of the product and the remaining is released to the surroundings as waste heat, primarily through exhaust gases at 150 to 250 °C. Recovering this waste heat can deliver significant fuel, cost and CO2 savings. However, selecting an appropriate sink for this waste heat is challenging due to the relatively low source temperature. This study investigates a novel application of gas-to-air low temperature waste heat recovery technology for a confectionary manufacturing process, through a range of experiments. The recovered heat is used to preheat a baking oven’s combustion air at inlet before it enters the fuel-air mixture. The investigated technology is compared with other waste heat recovery schemes involving Regenerative Organic Rankine Cycles (RORC), Vapour Absorption Refrigeration (VAR) and hot water production. The findings indicate that utilising an oven’s exhaust gases to preheat combustion air can deliver up to 33% fuel savings, provided a sufficiently large heat sink in the form of oven combustion air is available. Due to a lower investment cost, the technology also offers a payback period of only 1.57 years, which makes it financially attractive when compared to others. The studied waste heat recovery technologies can deliver a CO2 savings of 28–356 tonnes per year from a single manufacturing site. The modelling and comparison methodology, observations and outcomes of this study can be extended to a variety of low temperature food manufacturing processes.

KARAKTERISTIK AMPLIFIER CLASS D MENGGUNAKAN FIELD EFFECT TRANSISTOR (FET) TYPE IRF9530 DAN IRF630

In the development of power amplifiers, MOSFETs are widely used in the composition of the manufacture. As is known, MOSFETs have a longer on-off time loss compared to IGBT. The loss on the on-off time has an impact on the heat generated by the MOSFET. Class D Audio Amplifier is basically a Switching-Amplifier or Pulse Width Modulation-Amplifier. High efficiency means that it will produce low power dissipation, thus the power wasted is relatively lower when compared to class A, B or AB amplifiers. Because the class D audio amplifier can be said to be more economical because it does not require a large heatsink and a large power supply. The manufacture of the Class D power amplifier system uses a voltage of 28.5 volts DC on the final transistor IRF9530 AND IRF630 measuring the input transistors of 3.3 volts DC, 28.5 volts DC. In the test using an oscilloscope type LS 8050, 50 MHz frequency, the position of the audio input off of the amplifier has sound defects. Testing of the power amplifier is carried out when the treble on the input tone control is full db in the defective amplifier wave.

Co-designing electronics with microfluidics for more sustainable cooling

Thermal management is one of the main challenges for the future of electronics1-5. With the ever-increasing rate of data generation and communication, as well as the constant push to reduce the size and costs of industrial converter systems, the power density of electronics has risen6. Consequently, cooling, with its enormous energy and water consumption, has an increasingly large environmental impact7,8, and new technologies are needed to extract the heat in a more sustainable way-that is, requiring less water and energy9. Embedding liquid cooling directly inside the chip is a promising approach for more efficient thermal management5,10,11. However, even in state-of-the-art approaches, the electronics and cooling are treated separately, leaving the full energy-saving potential of embedded cooling untapped. Here we show that by co-designing microfluidics and electronics within the same semiconductor substrate we can produce a monolithically integrated manifold microchannel cooling structure with efficiency beyond what is currently available. Our results show that heat fluxes exceeding 1.7 kilowatts per square centimetre can be extracted using only 0.57watts per square centimetre of pumping power. We observed an unprecedented coefficient of performance (exceeding 10,000) for single-phase water-cooling of heat fluxes exceeding 1 kilowatt per square centimetre, corresponding to a 50-fold increase compared to straight microchannels, as well as a very high average Nusselt number of 16. The proposed cooling technology should enable further miniaturization of electronics, potentially extending Moore's law and greatly reducing the energy consumption in cooling of electronics. Furthermore, by removing the need for large external heat sinks, this approach should enable the realization of verycompact power converters integrated on a single chip.

Experimental and numerical investigation of the effect of number of parallel microchannels on flow boiling heat transfer

A combined numerical and experimental investigation to elucidate the two-phase flow behaviour and heat transfer during subcooled boiling of water in 1 × 1 cm2 footprint area heat sinks with six, ten, and fourteen parallel microchannels is performed. A three-dimensional, laminar, multi-phase, transient numerical model is developed to simulate flow boiling in microchannels. This study is one of the first studies which reports a three-dimensional numerical simulation of flow boiling in a large area multiple parallel microchannels heat sink including the effect of inlet and outlet plenums. We show an excellent agreement in heat transfer and pressure drop data with experimental results on a heat sink with fourteen parallel microchannels over a wide range of applied heat flux spanning various boiling regimes. The results show that the vapour blocking in the channel near the outlet is primarily responsible for instabilities and oscillations in the pressure drop, the surface temperature, and the mass flux. Intensified confinement due to the decrease in the number of the channels for a constant fin width results in increased surface temperatures. Similarly, increase in the number of the channels from six to fourteen improved heat transfer significantly wherein a significant drop of 45.5 °C in surface temperature with little increase of 37% in pressure drop is observed for a mass flux of 500 kg/m2s and a heat flux of 220 W/cm2. Microchannel heat sink with fourteen channels demonstrates on an average nearly 240% higher heat transfer coefficient in comparison to the heat sink with six channels. The numerical modelling framework used in this study can be used to provide design guidelines for microchannel heat sinks.

Highly Ordered and Dense Thermally Conductive Graphitic Films from a Graphene Oxide/Reduced Graphene Oxide Mixture

Summary We report a new approach to making highly dense, oriented, and crystalline graphite films from heat-treated and pressed graphene oxide (G-O). By introducing small-diameter reduced graphene oxide (rG-O) flakes into the graphene oxide starting material, we found that after heat treatment at 3,000°C, the sample density and atomic order substantially improved over a film composed, at the outset, only of pure G-O flakes. A subsequent mechanical press increased the density but reduced the atomic order. A second 3,000°C heat treatment restored the graphitic structure with graphitization metrics exceeding even those of the first heat treatment. The optimized graphitic film with an original concentration of 15 wt % reduced G-O in G-O gave well-oriented graphitic films with a density of 2.1 g cm−3, cross-plane thermal conductivity of 5.65 W m−1 K−1, and in-plane thermal conductivity of 2,025 ± 25 W m−1 K−1.

Design Considerations for Hybrid, Energy-Efficient, and Fast Industrial Power Amplifiers With Supply Modulation

In industrial applications, such as modern piezoelectric inkjet printers or automated device testers, arbitrary voltage waveforms need to be reproduced onto a different type of loads, providing four-quadrant operation with excellent linearity, preserving high signal-to-noise ratio with acceptable stability margin and high EMI immunity. These stringent requirements can be easily addressed if linear power amplifiers (LPAs) are employed. Nevertheless, their power density is limited by the large heat-sinks due to dissipative behavior of the Class A/AB/B output stage. In order to improve the performance of LPAs, hybrid PAs (HPA) are utilized, which involve highly efficient switched-mode power converters, called tracking power supplies (TPSs). In this article, the concept of HPAs based on only one TPS which modulates both supply rails is elaborated and exploited in two design examples, for different requirements regarding the output voltage dynamics. The first design is applicable in cases with a very fast output voltage dynamics (slew-rates up to $45~\textrm {V}/\mu \textrm {s}$ ) and capacitive loads (piezoelectric nozzles), while the second design provides an optimized, very compact GaN-based solution in case when alleviated requirements regarding the output voltage dynamics (slew-rates up to $1~\textrm {V}/\mu \textrm {s}$ ) have to be met for all types of passive loads (four-quadrant operation).

Experimental investigation into the thermal augmentation of pigmented asphalt

Asphalt binder is a temperature dependent material and is more susceptible to damage at higher temperatures. During summers, low thermal conduction and high specific heat of conventional asphalt results in extreme pavement surface temperatures and increased vulnerability. The situation demands for use of additives/modifiers that could help reduce pavement surface temperature. Thermal conduction of pigment modified/non-black asphalt mixtures is investigated in this research. Study focuses both on heating and cooling phase w.r.t time. Asphalt mixtures were evaluated for thermal conduction using larger heat sink with internal dimensions of 100×100×50 mm3. However, bituminous mixtures were examined in smaller heat sink with internal dimensions of 60×60×25 mm3. Both heat sinks were subjected to 800, 1000, and 1200 W/m2 heat flux and measurements were recorded accordingly. DC power supply was used as a heating source and silicon heater as a heating surface. Sinks were connected with data logger via calibrated K-type thermocouples. Iron oxide red and Titanium dioxide white pigments are used to decolour the black mixes. 4% by weight of total mix of each pigment is used to colour the black binder. Results have shown that at the end of 3 h of heating phase, pigment modified samples remain 8–10 °C cooler in case of bitumen binder and 4–5 °C cooler in case of asphalt mixtures. At the end of 2 h of cooling phase, a difference of 3–4 °C was noted between pigmented and conventional asphalt. Results also show that pigmented mixtures not only conduct more heat but also cool faster. Quantitatively, pigmented mixtures conduct 10%–15% more heat in comparison to the unmodified/black asphalt mixtures. The reduction in temperature susceptibility of pigmented mixtures may also help improve their high temperature performance.

THERMAL VALIDATIONS OF ADDITIVE MANUFACTURED NON-METALLIC HEAT SPREADING DEVICE FOR HOT SPOT MITIGATION IN POWER MODULES

Abstract As energy demands and power electronics density scale concurrently, reliability of such devices is being challenged. Inadequate thermal management can cause system-wide failures due to thermal run-away, thermal expansion induced stresses, interconnect fractures and many more. Conventional techniques used to cool devices consist of heavy, metallic systems such as cold plates and large heat sinks, which can significantly reduce the overall system power density. Moreover, the manufacturing of such components is expensive and often requires custom-made cold plates for improved integration with the electronic system. Although used as a standard practice, these metallic thermal management systems have the potential to intensify electro-magnetic interference (EMI) when coupling with high frequency switching power electronics, and the material density increases the weight of the system, which is detrimental in mobile applications. Lastly, cold plates and heat sinks can create non-uniform cooling profiles in the electronics due to the insufficient management of hot-spots. To combat these drawbacks, a new heat spreader design has been proposed which reduces weight and EMI effects while eliminating hot-spots through localized fluid impingement. This current study describes the methodology and construction of the experimental test setup to characterize the performance of the heat spreading device compared to an off-the-shelf cold plate. Through infrared imagining, the viability of two heated test sections are evaluated in their ability to replicate power module temperature profiles during operation.

The Silicon Photomultiplier as a modern solid-state replacement of the vacuum photomultiplier tube

A simple, self-contained, thermo-electrically cooled SiPM system is presented which cools a SiPM array to -20̂C. The array views a NaI scintillator through a 75 mm diameter glass window. Waste heat is removed with a large heat sink and AC fans. Above 40 keV in an air-coupled 2′′ × 2′′ NaI scintillator, the SiPM dark count rate was reduced by a factor ∼1000 when cooled. Performance when cooled was very similar to a PMT tested in the same setup and adequate for nuclear spectroscopy above 25 keV. Originally, water cooling was used but it was replaced by air cooling which is more suitable for a self-contained system, giving the advantage of portability without degrading performance. Straightforward improvements would allow cooling the SiPM to -30̂C or below, which would further reduce the dark count rate and extend the spectroscopically useful range to even lower energies. Such a system would be rugged and suitable for field use, for instance for inspection of cargo for gamma ray emissions.

Thermal Performance and Operating Regimes of a Flat Pulsating Heat Pipe for the Temperature Homogenization of Two Symmetric Plates

Abstract A copper–water closed flat pulsating heat pipe (PHP), 3.4 m long and of inner diameter 4 mm, was manufactured and tested. This PHP aims both at homogenizing the temperature of a large aluminum plate, of surface area 150 × 420 mm2, and at lowering its mean temperature by transferring the heat to an adjacent heat sink of same dimensions. The PHP thermal resistance is measured at various heat transfer rates, condenser temperatures, and inclination angles. It decreases when the heat transfer rate increases or when the PHP is progressively tilted from the vertical unfavorable orientation to a favorable one. Resistance values as low as 0.04 K/W are measured. Whatever the conditions, a minimum heat input of 200 W is necessary for the correct start-up of the PHP. A map of the operating regimes—no-flow, oscillating, intermittent, and stable behavior—is proposed. Nonreproducibility effects are highlighted in tilted position, leading to different operating regimes at increasing and decreasing heat loads, but also more broadly depending on the history of the working operating conditions of the PHP. However, the concept proposed in this work is very promising for applications involving large heat source and heat sink.