Heat Sink Capacity Research Articles

Experimental investigation of a PCM-HP heat sink on its thermal performance and anti-thermal-shock capacity for high-power LEDs

High-power LEDs demonstrate a number of benefits compared with conventional incandescent lamps and fluorescent lamps, including a longer lifetime, higher brightness and lower power consumption. However, owing to their severe high heat flux, it is difficult to develop effective thermal management of high-power LEDs, especially under cyclic working modes, which cause serious periodic thermal stress and limit further development. Focusing on the above problem, this paper designed a phase-change material (PCM) base heat pipe heat sink (PCM-HP heat sink) that consists of a PCM base, adapter plate, heat pipe and finned radiator. Different parameters, such as three types of interior materials to fill the heat sink, three LED power inputs and eight LED cyclic working modes, were separately studied to investigate the thermal performance and anti-thermal-shock capacity of the PCM-HP heat sink. The results show that the PCM-HP heat sink possesses remarkable thermal performance owing to the reduction of the LED heating rate and peak temperature. More importantly, an excellent anti-thermal-shock capacity of the PCM-HP heat sink is also demonstrated when applied in LED cyclic working modes, and this capacity demonstrates the best range.

Numerical study and optimizing on micro square pin-fin heat sink for electronic cooling

Micro pin-fin heat sink, characterized by low thermal resistance, compact structure and uniform temperature distribution along the flow direction, is effective and valuable for thermal management of electronic devices. To enhance the cooling performance of the micro square pin-fin heat sink, a geometry optimizing method changing pin-fin porosity and pin-fin located angle is proposed in this paper. The flow and heat transfer characteristics were studied numerically and the geometry of the micro square pin-fin heat sink was optimized. To reveal the characteristics and advantages of the micro square pin-fin heat sink, the comparison between the square pin-fin and the column pin-fin was made. Numerical results indicate that both the pin-fin porosity and located angle are important for the cooling capacity and thermal performance of the micro square pin-fin heat sink; the optimal porosity and located angle for thermal performance are 0.75 and 30° respectively. Furthermore, micro heat sinks with the optimized square pin-fin present better thermal performance than micro column pin-fin heat sinks, which implies that there is great potential to employ micro square pin-fin heat sinks for thermal management on electronic devices with high energy density.

Evaluation of heat sink capability and deposition propensity of supercritical endothermic fuels in a minichannel

Abstract The aim of this study was to develop approaches for the evaluation of heat sink capabilities and deposition propensities of different endothermic fuels in a minichannel. It should be noted that compared with our previous paper [23] which proposed the hydraulic resistance method (HRM) and validated it using one fuel pyrolyzed at different fluid temperatures, the significant one of the innovative points of this paper is that the HRM was corrected and applied to evaluate five different hydrocarbons, which are three pure hydrocarbons (cyclohexane, n-hexane and toluene), one petroleum-derived fuel and one synthetic fuel that were modeled as endothermic fuels. All of these fuels were tested in a minichannel with an internal diameter of 2.0 mm. The qualities of high volumetric heat sink capacity and good anti-coking capability were proven to be two contrary features in endothermic fuels. All of the five hydrocarbons tested had a mass heat sink of approximately 3.4 MJ/kg at a temperature of 750 °C and pressure of 5 MPa. However, the volumetric heat sinks (per unit volume hydrocarbon at the standard condition) were considerably different due to the hydrocarbons’ varying densities. Overall, cyclohexane showed better performance than the other four hydrocarbons, as it had a relatively high volumetric heat sink and good anti-coking characteristics. The coking runs were designed for a steady state at a bulk fluid temperature of 750 °C for 20 min, which allowed measureable coke deposition layers to accumulate on the channel’s inside surface. Another innovative point is that except the HRM, methods used to assess the deposition propensity included pressure drop changes during the coking run process, measurements of coke deposition in the filter, observations of the color features of liquid products and the weighing method, all of those methods are aided for the HRM to better differentiate the deposition propensity for different fuels. These different methods yielded a common conclusion that the coke deposit rates of the tested hydrocarbons could be ranked as follows: endothermic fuel > cyclohexane > n-hexane > toluene. It was found, however, that the deposit thickness was only one of the factors affecting heat transfer performance for different hydrocarbons, and the thickness was far from sufficient to reduce the heat transfer that led to the increased wall temperatures.

Passive aircraft cooling systems for variable thermal conditions

A novel design for a heat exchanger system [1], for which a patent application has been filed, was experimentally evaluated in the laboratory under variable thermal conditions characteristic of an aircraft in operation. The passive heat exchanger prototype consists of a loop-thermosyphon with two condensers and a common evaporator. Water was applied as the working fluid. Natural convection, forced convection and a combination of forced and natural convection at each condenser were replicated. The fuselage condenser performance was tested at temperatures ranging from −30 to 50 °C with heat transfer coefficients ranging from natural convection to values of around 200 W/(m2 K). Air supply to the air conditioning condenser was kept at 20 °C with coefficients ranging from natural convection to around 50 W/(m2 K). Input power up to 900 W was provided to the evaporator section by an embedded electrical resistance. Cooling system malfunction is not observed when the water within the fuselage heat sink is frozen, for input power below 300 W. Under cruise flight conditions, the cooling system is able to dissipate 900 W maintaining vapor temperatures at around 41 °C. The evaporator temperature increases by approximately 0.014 °C/W when start-up occurs. Refrigeration on the ground requires air duct speeds of around 6.1 m/s to keep the vapor temperatures below 100 °C for an input power of ca. 1 kW. When forced convection acts in both condensers, the heat removal capacity of the fuselage heat sink is dominant (around 90%).

Numerical Analysis and Optimization on Flow Distribution and Heat Transfer of a U-Type Parallel Channel Heat Sink

The issue of uniform flow distribution has recently received growing attention for heat sinks design. In order to improve the flow uniformity and heat transfer capacity of a U-type heat sink, a multiobjective optimization design is presented based on the orthogonal experiment design method. Therefore, a computational fluid dynamics model is established, and then the flow fields and temperature fields are investigated. The results show that the distribution of the fluid into each parallel channel not only is a function of the flow conditions in the header but also is affected by the geometric size of the header and the parallel channels and that the optimum U-type heat sink based on orthogonal experiment design method can give uniform flow distribution.

고속 비행체 연료공급 및 냉각계통 예비 열설계

고속 비행체에 연료를 공급하고, 내/외부의 열부하를 처리하기 위한 연료공급 및 냉각계통의 예비 열설계를 수행하였다. 이를 위해 임의의 임무형상에 대한 해석모델을 구성하고 성능해석을 진행하였다. 산출된 연료소모율과 내부의 유동 상태량을 이용하여 시스템의 각부 경계조건에 대한 열부하량을 계산하고 검증하였다. 이를 연료의 흡열반응을 이용한 시스템의 냉각성능과 비교하여 설계 요구조건을 충족시키는 것을 확인하였다. In this study, preliminary thermal sizing was performed with the aim of developing a fuel supply and cooling system design to solve the heating problems in high-speed vehicles. First, an analysis model was used to satisfy an optional mission profile. The heat loads were computed under boundary conditions. The results were verified using the precedent design case. Then, fuel consumption rates were estimated for the analysis trajectory. Accordingly, the cooling capacity in the system was calculated using the heat sink capacity of the endothermic fuel. Lastly, the fulfillment of the design requirements was confirmed in comparison to the cooling needs.

Cooling-Performance Estimation of the Composite-Graphite Heat Sink with Annular Conductive Base for LED Lamp

This work experimentally investigated the material effect of heat sinks of LED lamps on the heat transfer and illumination characteristics under the free-convection condition. The experimental results indicated that the heat-transfer capacity of the pure aluminum-alloy heat sink was better than those of the composite-graphite heat sinks. However, the cost and weight of the composite-graphite heat sinks were reduced much more by comparing with those of the pure aluminum-alloy heat sink. Besides, the illuminations of these test heat sinks were similar after 2000-hour lighting continuously. Therefore, the composite-graphite heat sink is useful for the cooling of the LED lamp and the electric equipment. It has large potential in the relevant markets.

Thermal Analysis of Heat Sink Employed on Tunnel Lighting Lamps

As a new type of solid-state light source, LED has many advantages. Its lifetime and lighting effect are related to its thermal performance. In this study the effect of heat sink cooling capacity from factors were researched, and the factors were such as material of heat sink, height of heat sink and the number of fins. It was observed that the cooling capacity of heat sink increases with increasing of thermal conductivity. Copper and silver are not fit for heat sink materials though they have excellent cooling capacity because of their high density and price, while aluminum and its alloy are the better choices. And it was revealed that the cooling capacity of heat sink increases with increasing of the height of fins, but this trend has slowed down when the average height reached 40mm.It was also observed that the cooling capacity of heat sink increases with increasing of the number of fins when fins are less, while the heat sink was higher, the cooling capacity maybe decrease with the increasing of the number of fins.

Experimental and CFD Study on Natural Circulation Phenomenon in Lead Bismuth Eutectic Loop

A test loop, HANS (Heavy metal Alloy Natural circulation Study loop) is installed in BARC (Bhabha Atomic Research Centre) for thermal hydraulic, instrumentation development and material compatibility related studies in Lead Bismuth Eutectic (LBE) coolant. Steady state natural circulation characteristics in the LBE loop were investigated at different power levels. Significant natural convection flow was observed in the experiments. It was found that the natural circulation was easily established and stabilized. It took only a few minutes to have a stable natural circulation at a constant power level. The natural circulation flow rate depends on the loop resistance and the temperature difference between the hot leg and the cold leg, as determined by the power level and the heat sink capacity. The heater power is varied from 1200W to 2700W and the temperature difference found across the heater is 80°C to 165oC. The natural circulation in the loop is simulated in a CFD code PHOENICS. The predictions of PHOENICS code are found to be in good agreement with the experimental data.

Computation of melting with natural convection inside a rectangular enclosure heated by discrete protruding heat sources

This paper presents the results of a numerical investigation of the heat transfer by natural convection during the melting of a phase change material (PCM, n-eicosane with melting point of 36°C) contained in a rectangular enclosure. This latest is heated by three discrete protruding heat sources (simulating electronic components) placed on one of its vertical walls. The power generated by heat sources is dissipated in PCM. The advantage of using this cooling scheme is that the PCMs are able to absorb high amount of heat generated by the heat sources, without acting the fan during the charging process (melting of the PCM). The thermal behavior and thermal performance of the proposed PCM based-heat sink are numerically investigated by developing a mathematical model based on the mass, momentum and energy conservation equations. The obtained numerical results show the impact of various key parameters on the cooling capacity of the PCM-based heat sink. Correlations encompassing a wide range of parameters were developed in terms of the dimensionless secured operating time (time required by one of the electronic components before reaching its critical temperature, Tcr∼75°C) and the corresponding liquid fraction, using the asymptotic computational fluid dynamics (ACFD) technique.

Thermal Performance Analysis Based on Micro-Channel Structure of Heat Sink

Thermal performance determines the normal operation of electronic circuits and power devices. The required cooling capacity is always increasing with the abroad application of electronic system. Especially in high frequency and large power fields, the defection of fan-cooled radiator comes out. By comparison, liquid cooling system possesses better heat stability and conductivity, which not only improves the stability of system, but also reduces the working costs greatly. Cooling capacity of heat sink is mainly determined by the inner mechanical structure, it is necessary to study the different influences of related structure, so as to guide the structural design of heat sink effectively. Based on thermal analysis by changing a single structure parameter, the structural influences on thermal performance are discussed, and the acquired conclusions are of great importance in thermal design practice of heat sink.

Thermal Cracking and Heat Sink Capacity of Aviation Kerosene Under Supercritical Conditions

pressurerangeof3–4.5MPa,andaresidencetimerangeof0.6–3s.Thechemicalheatsinkwasdeterminedthrougha control volume analysis of the fuel flow. Compositions of the cracked gaseous and liquid products were analyzed via gas chromatography. Based on the results of fuel conversion, the temperature range for the active cracking was observedtobeapproximately800–1000K,beyondwhichthecrackingapproachescompletion.Itwasalsofoundthat the variation of the chemical heat sink with temperature can be nonmonotonic and a maximum endothermicity was seen to occur in the temperature range of 900–960 K, depending on the residence time. For the current operation conditions, the maximum chemical heat sink reached 0:5 MJ=kgat a fuel conversion of 45%. Composition analysis ofthegaseousproductindicatedthatthesaturatedhydrocarbonssuchasmethanebecamedominantastemperature

Heat sink performances of GaN/InGaN flip-chip light-emitting diodes fabricated on silicon and AlN submounts

Fabricating flip-chip light emitting diodes (FCLEDs) with two good thermal conductivity materials of silicon and aluminum nitride (AlN) as submount are investigated on its output power and heat sink capacity. It is known that many advantages exist in FCLED structures. In addition to the upward emitting light, the downward propagating light is reflected up by a high reflectance contact, increasing the light extraction. The heat generated in the LED flows directly through the interconnect metal of the submount, improving thermal conduction. Except blue shift at the low current injection region (0–0.3A), the heat induced bang gap narrowing (red shift) at high current injection region (0.3–0.7A) is observed with a red shift of 8.92nm for conventional LED, 4.62nm for silicon submount FCLED, and only 2.87nm for AlN submount FCLED. The light intensity of FCLEDs with silicon and AlN submounts exhibits 1.6 and 7 times at an injection current of 0.35 and 0.7A, respectively, larger than that of conventional LED.

Effect of Pore Diameter Distribution on Heat Transfer Capacity of Lotus-Type Porous Copper Heat Sink for Air Cooling

Lotus-type porous metal with many straight pores is attractive as a heat sink because larger heat transfer capacity is obtained due to the small diameter of the pores. The heat transfer capacity of the lotus-type porous copper heat sink was calculated using the model with the pores of uniform diameters. However, actual lotus-type porous metals have a distribution of pore diameter. In the present work, we investigated the lotus-type porous copper fin model by considering size distribution of the lotus-type porous copper fin. Prediction of the heat transfer characteristics for the lotus-type porous copper heat sink shows a good agreement with the experimental data.

Optimization of Piezoelectric Oscillating Fan-Cooled Heat Sinks for Electronics Cooling

Piezoelectric fans have been investigated for electronics cooling over the last decade. The primary usage or method has been to place the vibrating fan near the surface to be cooled. The piezofan used in the current study is composed of a piezo actuator attached to a flexible metal beam. It is operated at up to 120-VAC and at 60 Hz. While most of the research in the literature focused on cooling bare surfaces, larger heat transfer rates are of interest in the present study. A system of piezoelectric fans and a heat sink is presented as a more efficient method of system cooling with these fans. In this paper, a heat sink and piezoelectric fan system demonstrated a cooling capability of 1 C/W over an area of about 75 cm2 where electronic assemblies can be mounted. The heat sink not only provides surface area, but also flow shaping for the unusual 3-D flow field of the fans. A volumetric coefficient of performance (COPv) is proposed, which allows a piezofan and heat sink system volume to be compared against the heat dissipating capacity of a similar heat sink of the same volume for natural convection. A piezofan system is shown to have a COPv of five times that of a typical natural-convection solution. The paper will further discuss the effect of nozzles in flow shaping obtained via experimental and computational studies. A 3-D flow field of the proposed cooling scheme with a piezofan is obtained via a flow visualization method. Velocities at the heat sink in the order of 1.5 m/s were achieved through this critical shaping. Finally, the overall system characterization to different heat loads and fan amplitudes will be discussed.

Heat Transfer Capacity of Lotus-type Porous Copper Heat Sink for Air Cooling

Lotus-type porous metal with many straight pores is attractive as a heat sink because larger heat transfer capacity is obtained due to the small diameter of the pores. The heat transfer capacity of the lotus-type porous copper heat sink was calculated using the model with the pores of uniform diameters. However, actual lotus-type porous metals have a distribution of pore diameter. In the present work, we investigated the lotus-type porous copper fin model (non-uniform pore model) by considering size distribution of measured on the actual measurement of the pore diameters on a cross-section of the lotus-type porous copper fin. Prediction of the heat transfer characteristics for the lotus-type porous copper heat sink shows a good agreement with the experimental data. In addition, the predicted heat transfer coefficient of non-uniform pore model also shows a good agreement with the uniform pore models. Thus, it is clarified that the heat transfer characteristic of the lotus-type porous copper heat sink can be predicted by the uniform pore model.

Catalytic Cracking and Heat Sink Capacity of Aviation Kerosene Under Supercritical Conditions

pressurerangeof3–4.5MPa,andaresidencetimerangeof0.6–3s.Thechemicalheatsinkwasdeterminedthrougha control volume analysis of the fuel flow. Compositions of the cracked gaseous and liquid products were analyzed via gas chromatography. Based on the results of fuel conversion, the temperature range for the active cracking was observedtobeapproximately800–1000K,beyondwhichthecrackingapproachescompletion.Itwasalsofoundthat the variation of the chemical heat sink with temperature can be nonmonotonic and a maximum endothermicity was seen to occur in the temperature range of 900–960 K, depending on the residence time. For the current operation conditions, the maximum chemical heat sink reached 0:5 MJ=kgat a fuel conversion of 45%. Composition analysis ofthegaseousproductindicatedthatthesaturatedhydrocarbonssuchasmethanebecamedominantastemperature

Co-generation of biofuels for transportation and heat for district heating systems—an assessment of the national possibilities in the EU

Biomass gasification with subsequent synthesis to liquid or gaseous biofuels generates heat possible to use in district heating (DH) systems. The purpose here is to estimate the heat sink capacity of DH systems in the individual EU nations and assess the possibilities for biomass-gasification-based co-generation of synthetic biofuels for transportation and heat (CBH) for DH systems in the EU countries. The possibilities are assessed (i) assuming different levels of competiveness relative to other heat supply options of CBH corresponding to the EU target for renewable energy for transportation for 2020 and (ii) assuming that the potential expansion of the DH systems by 2020 is met with CBH. In general, the size of the DH heat sinks represented by the existing national aggregated DH systems can accommodate CBH at a scale that is significant compared to the 2020 renewable transportation target. The possibilities for CBH also depend on its cost-competitiveness compared to, e.g., fossil-fuel-based CHP. The possible expansion of the DH systems by 2020 represents an important opportunity for CBH and is also influenced by the potential increase in the use of other heat supply options, such as, industrial waste heat, waste incineration, and CHP.

Catalytic cracking of endothermic fuels in coated tube reactor

Suspensoid of HZSM-5 or HY zeolites mixed with a self-made ceramic-like binder was coated on the inner wall of a tubular reactor by gas-aided fluid displacement technology. The coated zeolites were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The coating thickness is 10–20 μm and the particle size of the zeolites is in the range of 1–5 μm. In the coated reactor, cracking of endothermic fuels including n-dodecane and aviation fuel RP-3 was carried out separately under supercritical conditions at 600°C and 625°C to investigate their heat sinks and conversion of catalytic reactions. For the reaction catalyzed by HY (25% mass fraction) coating, the heat sink capacity of n-dodecane are 815.7 and 901.9 kJ/kg higher than that of the bare tube at 600°C and at 625°C, respectively. Conversion of n-dodecane also increases from 42% to 60% at 600°C and from 66% to 80% at 625°C. The coated zeolite can significantly inhibit the carbon deposition during supercritical cracking reactions.

Additives to Improve Fuel Heat Sink Capacity in Air/Fuel Heat Exchangers

Hypersonic air-breathing vehicles travel at high speeds and generate heat loads that are greater than can be met from sensible heating of the fuel. However, the fuel can provide about 50% more heat sink capacity if it undergoes endothermic thermal cracking reactions before combustion. Unfortunately, thermal cracking reactions require high temperatures, in excess of 100°F, to obtain useful reaction rates. However, a fuel additive has been identified that increases the rate of thermal cracking reactions, allowing the same chemical endotherm to be obtained at lower fuel temperatures. This paper describes work in which we conducted extensive laboratory bench-scale calorimetric tests to directly measure the effectiveness of the cracking initiator compound with several prospective fuels, including JP-7 and normal decane. We then used the data obtained from the laboratory experiments to generate rate models, which we then used in the design of a pilot scale fuel/air heat exchanger. Finally, we tested the pilot scale unit at heat fluxes approaching 100,000 Btu /ft 2 ·h with JP-7 and n-decane with and without the initiator. At each test point, the data clearly indicated that the initiator produced significant increases in the rate of cracking and fuel heat sink capacity.