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Optimizing cooling electronic chips at high altitude with consideration of solar radiation
Abstract
Maintaining a proper working environment for electronic chips is challenging for airships, as the ambient parameters at high altitude are largely different from those on the ground, which can influence the performance of cooling. This work aims to optimize the finned sink to minimize the weight with the consideration of the impact of solar radiation. By using a validated 3D model, it was found that the ignorance of the solar radiation can lead to a temperature deviation of 4.1 °C for electronic chips at 20 km when the solar radiation intensity was 1400 W/m² and the wind speed was 10 m/s. Meanwhile, compared to the solar radiation intensity and the emissivity, the direction of solar radiation showed more impacts. In addition, even though the solar radiation doesn't influence the optimal fin height, fin number, and fin thickness, it would clearly affect the optimal heat transfer area ratio. As a result, it can clearly change the optimized weight, which was 5.7% higher if the solar radiation was not considered.
... While in the polar regions, the direct angle of the sun is small, so the amount of solar radiation is relatively low. With the increase of altitudes, the solar radiation becomes stronger 31 . www.nature.com/scientificreports/ ...
Few scholars study light efficiency of solar-cell arrays in theory, while it is difficult to experimentally determine the maximum capacity of a photovoltaic panel to collect solar radiation. This paper proposes a solar energy comparison model (SECM), considering the sunshine duration changes every day to optimize the solar radiation collection model in an ideal state for a whole year, which is easy to use, and can quickly obtain the optimal tilt angle of photovoltaic panels and the solar radiation collecting efficiency enhancement of intelligent light tracking photovoltaic panels. The results show that the sunshine duration is an important factor affecting the solar radiation received by photovoltaic panels. In regions from 66°34′N to 66°34′S, intelligent light tracking photovoltaic panels can increase the collected solar radiation by at least 63.55%, up to 122.51% compared to stationary photovoltaic panels during the effective light time, which is much higher than what most people generally thought. And the advantage of intelligent light tracking photovoltaic panels is more obvious in high latitudes, with a longer and more variable sunshine duration. These findings provide a theoretical basis for the solar radiation collection and photovoltaic panels.
... Therefore, this research studies the functionality of a mobile solar charging system incorporated into an electric vehicle with a low cost system, but especially considering that the established study area is the city of Cuenca, located in the Andes Mountains at 2500 to 2700 m above sea level, with a radiation index of 1517.02 kWh/m 2 [27,28] and the higher the altitude, the lower the thickness of the atmosphere and, therefore, the lower the absorption and reflection of shortwave solar energy [29,30]. ...
This research focuses on the measurement of the solar generation potential on the roads of the Andean city of Cuenca, Ecuador, and its application in electric vehicles. The tests were conducted in real environments, whereby natural and artificial structures obstruct direct radiation to the panel during the trajectory. An initial study is presented with daily operating conditions, using an urban bus route as a case study. The methodology used consists of taking measurements on different days and weather conditions to evaluate the photovoltaic generation and its contribution to the energy autonomy of the electric vehicle. Additionally, the energy autonomy between the electric vehicle with its factory configuration versus the one equipped with the solar panel is compared. For this purpose, a photovoltaic panel is installed on the roof of the vehicle, connected to a control system that monitors the radiation and current data, regulating the charging and discharging of the batteries. The aim is to demonstrate that the installation of solar panels on electric vehicles can significantly increase their energy autonomy. The contribution of this research could serve as an initial guide for governments and private companies to make decisions on the deployment of electric buses, electric vehicles and other vehicles integrated with solar photovoltaic energy, taking into account their routes. The findings of the study reveal that the implementation of the mobile charging system improves the range of the electric vehicle used in this study. In detail, an average increase of 40% in range was achieved in favorable environmental conditions and an increase of 14% in unfavorable environmental conditions. It is important to highlight that Cuenca has favorable conditions for solar systems due to its geographical location: altitude, hours of radiation and angle of incidence.
Recently, the thermal management of power electronic converters has gained significant attention due to the continuous trend of developing very compact power electronic converters with high power density. With the evolution of power semiconductor devices, high operating temperatures and large thermal cycles have become possible, necessitating a significant improvement in thermal system designs. Researchers have made significant efforts to develop effective thermal management systems for improving the reliability and lifetime of power electronic converters. This article intends to present a thorough review of thermal management systems employed in power electronics cooling. The applied thermal management techniques have been reviewed from the perspective of electrical parameter regulation and heat dissipation control. Regulation of electrical parameters involves active thermal control, which is a method for controlling junction temperature and thermal cycling of power semiconductor devices. The active thermal control implementation processes reviewed in this article consist of increasing overload capacity, manipulating switching and conduction losses, employing modified modulation process, balancing thermal stress at the converter level, and controlling thermal stress at the system level. Control of heat dissipation can be achieved through direct and indirect cooling of power electronic converters with air or liquid as the coolant. The effectiveness and implementation methods of these cooling techniques, such as channel cooling, phase change material-based cooling, immersion cooling, jet impingement and spray cooling, are reviewed in this paper. Moreover, performance-enhancing ideas and challenges for these techniques are discussed. The primary objective of this review paper is to bridge the existing gap in the literature by offering a comprehensive comparison of commonly employed thermal management techniques.
In this article, the confined jet impingement cooling of a semi-cylindrical concave plate is analyzed numerically. The investigation is done for different jet Reynolds numbers (Rej)ranging from 100 to 1000, as the Richardson number (Ri) corresponding to this interval ranges between 0.1 and 10. For any Richardson number, the modified Grashof number (Gr*) is fixed at 105. When analyzing the impact of inter-surface radiation between the target plate and confined surfaces on the overall cooling performance, three emissivity values (ε0.05, 0.5 and 0.9) are taken into consideration. Additionally, simulations are done for the pure convective heat transfer, ignoring inter-surface radiation (ε=0.0). The influence of surface emissivity and the Richardson number on velocity, temperature and pressure distribution in the flow region, local dimensionless temperature (θ) alterations on the target plate and confined walls, alterations in convective (Nuc), radiative (Nur), overall Nusselt numbers (Nuover), pressure coefficient (Cp) and ratio of radiative Nusselt number to overall Nusselt number (Nur/Nuover) on the target plate are highlighted. The findings demonstrate that surface emissivity has significant influence on thermal and hydrodynamic boundary layer formation, buoyancy induced flow and heat transfer, and the proportion of inter-surface radiation in overall heat transfer rises as the Richardson number and surface emissivity increase. At low Richardson numbers, the pressure in the stagnation region is greater than the atmospheric pressure. However, as the buoyancy effect increases, the pressure in the stagnation region falls below the atmospheric pressure and rises towards the exit.
For increasing the solar energy harvesting performance, any solar tracking system must track the sun at the right angle during periods of daytime. We proposed an enhanced solar tracking instrument to solve the issues of low sunlight incident angles and manual orientation/elevation calibrations. This novel tracker used two Global Positioning System (GPS) receivers with Real-Time Clock (RTC) forming a satellite compass and combined with an inclinometer to follow the sun trajectory correctly without manual aligning the heading of system to orientation of North-South. Such a dual-axis instrument was controlled by a microcontroller unit (MCU) integrated with servo-motors, satellite compass and inclinometer. The embedded Solar Position Algorithm (SPA) can determine the angles of the sun vector at the given date, time and geographical information from the satellite compass. The power generated by the proposed tracking instrument, compared with a fixed-tilted photovoltaic (PV) tracker, was proven in scenarios of fixing, rotating and moving. The proposed solar tracker with satellite compass after field measurement extracted more energy than the fixed-tilted solar tracker under fixed location with mostly clear day 35.91%, in different locations with clear day 38.72% and 38.40%; in heading variation and moving conditions were 60.00% and 113.70%. Therefore, this solar tracker is not only suitable for PV grid but also well suitable for mobile vehicles with keeping the panel aligned with the sun automatically, whether geographical position in northern or southern Hemisphere independently and without solar panel tilted orientation adjustment to achieve the robust, convenient and reliable requirements.
The heat transfer enhancement of air-cooled heat sink using multiple synthetic jets is investigated experimentally. A heat sink is located inside synthetic jet actuator cavity in order to reduce space occupied by the cooling device. It has been observed that heat sink located inside the synthetic jet actuator cavity dissipates heat in a manner similar to the heat sink cooled by impinging synthetic jet. The thermal resistance of the heat sink depends on the synthetic jet Reynolds number and dimensionless stroke length. The paper presents experimental results of synthetic jet Reynolds number, dimensionless stroke length as well as the heat sink thermal resistance and coefficient of performance. The value of the heat sink thermal resistance of 0.22 K/W was measured during operation of synthetic jest cooling while the thermal resistance of the heat sink without loudspeaker was found to be 1.4 K/W. A correlation of thermal resistance as a function of Reynolds number and dimensionless stroke length based on the experimental results is presented and discussed.
This paper presents the heat spreading of the cold plate heat sink with different fin shapes (rectangular, circular, conical) using the jet impingement technique impinging on the heating surface. The parametric monitoring mainly focused on the liquid mass flow rate, inlet coolant temperature, and fin shapes are investigated. The results showed that the fin shapes of the heat sink influencing its total thermal resistance but small decrement in heat spreading resistance. By fixing other parameters and a jet-plate spacing to jet diameter ratios H/D = 0.8 is considered, it is shown that the circular fin has a higher thermal performance by lowering thermal resistance of the heatsink for 12%, and 25% compared with the rectangular and the conical fin, respectively. More importantly, the lower coolant temperature is reduced heat spreading, results in total thermal resistance are developed. The numerical was carried out, and the clear temperature distribution phenomena with different fin shapes are obtained, which contribute to the heat spreading, spreading resistance, and thermal resistance to the cold plate heat sink for cooling in electronic applications.
Unmanned Aerial Vehicle (UAV) is developing towards the direction of High Altitude Long Endurance (HALE). This will have an important influence on the stability of its airborne electronic equipment using passive thermal management. In this paper, a multi-node transient thermal model for airborne electronic equipment is set up based on the thermal network method to predict their dynamic temperature responses under high altitude and long flight time conditions. Some relevant factors are considered into this temperature prediction model including flight environment, radiation, convection, heat conduction, etc. An experimental chamber simulating a high altitude flight environment was set up to survey the dynamic thermal responses of airborne electronic equipment in a UAV. According to the experimental measurement results, the multi-node transient thermal model is verified without consideration of the effects of flight speed. Then, a modified way about outside flight speed is added into the model to improve the temperature prediction performance. Finally, the corresponding simulation code is developed based on the proposed model. It can realize the dynamic temperature prediction of airborne electronic equipment under HALE conditions.
The design and operation of a high altitude scientific balloon requires adequate knowledge of the thermal characteristics of the balloon to make it safe and reliable. The thermal models and dynamic models of altitude scientific balloons are established in this paper. Based on the models, a simulation program is developed. The thermal performances of a super pressure balloon are simulated. The influence of film radiation property and clouds on balloon thermal behaviors is discussed in detail. The results are helpful for the design and operate of safe and reliable high altitude scientific balloons.
Solar array is essential for converting sunlight energy to electricity and ensure normal operation of propellers, payloads and avionics of stratospheric airship. Apart from electrical energy, excess solar irradiation is transformed to heat load on the airship, seriously affecting the pressure balance and structural integrity. However, the investigation of insulation layers between solar cells and airship film are rare. This paper aims to maximize the output energy of solar array through optimizing the configuration of insulation layers. The energy model and heat transfer model are established. Based on the theoretical model, the influence of insulation parameters on the output energy of solar array and differential pressure are studied. The energy acquirement and differential pressure have negligible change when increasing the thermal conductivity and thickness of insulation substrate in the same proportion. The thermal impedance as the ratio of thickness to thermal conductivity is firstly adopted to describe the configuration of insulation structure. The optimal thermal impedance can be obtained based on flight missions considering airspeeds, latitudes and dates. The output energy can be maximized while keeping the differential pressure within limited range with the optimal thermal impedance. The result provides a conducive reference for the preparation of solar powered airship.
Current conventional finned PCM heat sinks employ fins that are surrounded by PCM body while being attached to a hot base that receives heat from the source that requires cooling. The fins in this case enhance heat dissipation thus charging and discharging rates from the sink. In the present work, counter intuitively, we propose using a new fins concept wherein the bottom ends of the fins are lifted (i.e. detached) from the hot sink base, instead of being attached to the base. Thereby, the thermal management characteristics of a heat sink filled with solid gallium as a phase change material and integrating vertical plate fins within the gallium with different levels of fin detachment from the base of the sink that receives heat from the hot source are numerically investigated. The rationale behind considering the proposed lifted fins approach is twin-pronged: Firstly, lifting the fin while keeping its total height fixed, gives an additional room for greater PCM quantity to be stored in the sink thereby giving the sink larger capability to absorb latent heat from the hot source. Secondly, it would also imply that the extent of fin protruding out of the sink (given that total fin height is kept constant) would increase. Thus, fins outer surface area would also increase resulting in faster heat dissipation into the ambient. This study aims at shedding light on the benefits of fin lifting over the case of direct fin attachment to the base and the extent to which fin lifting could be beneficial for discharging heat from the sink during operation under high heat flux conditions. The impact of the extent of fin lifting on the buoyancy-driven internal motions within the molten gallium and thus the overall performance of the sink is investigated.
The straight microchannel heat sink is relatively low in heat transfer efficiency due to the influence of the thermal boundary layer, and the thermal requirements of which may fail to be met under high heat flux conditions. In this paper, the fins were introduced to form a secondary channel to optimize the heat dissipation effect of the microchannel heat sink. Combined with CFD method, the structure parameters (the angle, lateral spacing and vertical spacing) and arrangement ways (the aligned, staggered) of internal fins in microchannel were analyzed. At the same time, CFD method is verified by experiments, and the relative errors are within 2%. Under the mass flow rate of 3.5 gs⁻¹, compared with the straight microchannel heat sink, the maximum temperature and average temperature of optimized model are reduced by 3.04 K (6.67%), 2.86 K (6.75%), respectively. And the uniformity of temperature also is increased by 0.005 (8.47%). The pressure drop is reduced by 226.5 Pa (13.33%). At same time, the value of the performance evaluation can reach 1.285. In actual design and application, appropriate mass flow rate can be selected by the heating power to ensure the cooling effect of the microchannel heat sink and the power loss of the pump.
This paper presents an experimental and numerical investigation on the thermofluidic performance of 0.5–2.0 % of the volumetric concentration of Al2O3-water nanofluids through oblique fin heat sink microchannel (OFHS MC) in the Reynolds number range 100–300. In comparison, experiments were also performed using a straight channel heat sink microchannel (SCHS MC) of the same hydraulic diameter as the oblique fin channel. The fluid flow is simulated using the RNG k-ε model in both periodic and full domain numerical analysis. The phenomenological behaviour of the nanofluid flow is further studied using numerical results. The oblique fin microchannel encouraged the secondary flow, thus enhanced the macroscopic mixing. Boundary layer disruption and vortices generation in the secondary channel is the critical phenomena of improved heat transfer. A substantial improvement of heat transfer coefficient is achieved for nanofluid and oblique fin heat sink combinations compared to the straight channel heat sink. The heat transfer coefficient is increased at increasing nanofluid concentrations for any given Reynolds number and channel configuration. The enhancement of about 55 % in the heat transfer coefficient with a 2 % volumetric concentration of nanofluid is achieved at Re = 300 in an oblique fin heat sink. The heat transfer enhancement is always significant than the pressure penalty. The oblique fin heat sink improves the average junction temperature considerably compared to the straight channel heat sink. The inclusion of nanofluid can reduce the experimental junction temperature by up to 6 °C. Therefore, the combined advantage of the oblique fin heat sink with nanofluid is anticipated as one of the potential alternatives for electronics cooling.
The double-layer microchannel heat sink (DL-MCHS) is commonly applied for thermal management of high heat flux surfaces, including electronic chips and concentrator photovoltaic (CPV). However, most of the recent studies neglected the header effect in the simulation of the DL-MCHS. The current study compressively investigated the impact of considering the inlet and outlet headers on the CPV systems' performance. A three-dimensional conjugate heat transfer model of the fluid flow in the DL-MCHS coupled with the CPV layers' thermal model was employed. The thermal performances of DL-MCHS with and without considering the headers were evaluated. Parallel flow (PF) and counter flow (CF) conditions at a solar concentration ratio (CR) of 20 suns were studied. The results showed that the header section should be considered in the numerical model for obtaining a more realistic average and local silicon layer temperature profile, especially in the CF operation. For instance, the difference in solar cell temperature between including and ignoring the header section is about 13.86 K for CF operation at CR of 20 and 200 mL/hr coolant flowrate. The predicted pumping power and net gained electric power were also significantly affected by neglecting the headers in the numerical modelling. The electrical efficiency deviation reached about 23.5% at CF, while PF reported almost 4.0%.
The compact equipment, area restriction for air-cooled devices, and thermal management of microchips have attracted the attention of researchers concerned with superior liquid cooling systems. During the present study, the impact of using nanofluids for cooling a chip was carried out experimentally and numerically. The experiments were conducted to validate the CFD model. Then the CFD model was applied for examining the impact of nanofluid concentration, and coolant flow rate on the thermal-hydraulic characteristics of the heat sink. CuO-water nanofluid was used with five different nanoparticle volume fractions of 0.5, 0.86, 1.5, 2.25, 3.5 and 5 vol.%. The developed CFD model was validated with the obtained experimental results and with results of different researchers, which showed good agreement. The results showed that for the investigated electronic chip with an area of 5 cm by 5 cm and dissipated power of 130 W, an enhancement of 8.1% in thermal conductance was noticed when using nanofluids as compared to water for the studied operating range. The overall thermal hydraulic performance of using nanofluid is found to accomplish higher value of 1.47 at nanoparticle volume fraction of 5% of CuO and Reynolds number of 800.
The concentrator photovoltaic (CPV) systems commonly endure high cell temperatures, which affect their overall performance. Besides, the high cell temperature could lead to physical damages within the whole system due to the induced thermal stresses. Therefore, an efficient cooling is mandatory to achieve a higher net output power from the CPV and safe operation. The current work's main purpose is to investigate the integration of double-layered microchannel heat sink (DL-MCHS) with CPV cell as thermal management device. A three-dimensional (3D) model is presented to investigate the performance of a CPV cooled by the DL-MCHS to figure out the ability to handle the effective heat dissipation under different terrestrial conditions. The parallel flow (PF) and counter flow (CF) cooling orientations were studied. Ethanol coolant is used to cool the CPV under different concentration ratios (CR) of 5, 10, 15, and 20 suns. The results show that the temperatures remarkably decreases with the inlet flowrate is increased. The counter flow operation (CF) achieved the best temperature uniformity index (Tuni) when the coolant mass flowrate (V̇) ranged between 200 and 1200 ml/hr. Especially at CR 5 suns, the temperature uniformity index, Tuni, enhanced to 99.87% at 1200 ml/hr.
Semiconductor devices and microelectronic devices are widely used in many applications such as central processing units. These devices produce a huge amount of heat that must be dissipated properly because their operation is sensitive to operating temperature. Under high operating temperatures, physical damage is expected because of thermal stresses harming the structure of the components and increasing the failure rate. The thermal management of these devices is mandatory to fulfill the recommended operating conditions. The complexity of applying even the most powerful single-phase liquid cooling arrangement is that the semiconductor component temperature increases linearly with increasing heat dissipation rate. Consequently, the temperature of the device could reach higher than the maximum temperature limit. Unlike the single-phase flow, the two-phase flow boiling–cooling system can provide more robust thermal management,uniform temperature distribution over the surface and high heat dissipation by the latent heat. Hence, the flow boiling in microscale devices is an effective cooling technique for high dense-power electronic components. The current study used ethanol, acetone, and Novec-7000 coolants with high, medium, and low boiling points, respectively to study the flow boiling in a microchannel device. The effects of the volumetric flow rate and heat flux were experimentally investigated. A graphite sheet was used as thermal interface material (TIM) for further enhancing the heat dissipation, and wall temperature uniformity was assessed under boiling conditions. The Novec-7000 coolant showed outstanding cooling capabilities under ultra-high-heat flux conditions. When TIM was used, effective heat flux increased by 0.62% and 1.62% for acetone and Novec-7000, respectively. Moreover, the experimental results showed that the boiling point is a critical parameter in the system performance of flow boiling–cooling.
Electronic cooling has been a rising issue mainly due to the rapid development of high-throughput computing in data centres as well as battery energy storage, which release huge amount of heat through compact surfaces. The electronic cooling process is not only energy-intensive but also difficult to control. This paper proposes an effective cooling method for electronic devices by integrating phase change materials (PCMs) with three-dimensional oscillating heat pipes (3D-OHPs), where PCMs are used to store heat dissipated by the electronic device and 3D-OHPs to fast transport the stored heat from PCMs to the environment. A novel leaf-shaped structure is designed for the 3D-OHPs. Experimental study is carried out on the leaf-shaped 3D-OHPs with various working parameters including cooling air velocity, wind direction and heat input. Further, the leaf-shaped 3D-OHPs are embedded into PCMs to cool down the electronic devices. Temperature variations and thermal resistance are evaluated and compared with the conventional air cooling method. The experimental results indicate that the surface temperature of electronic devices can be well controlled below 100 oC, which is ∼35 oC lower than that with conventional air cooling. The thermal resistance is decreased up to 36.3%. The 3D-OHPs with a filling ratio of 34-44% achieve the best thermal performance. What’s more, the leaf-shaped structure of the 3D-OHPs contributes to a ∼2 oC lower temperature on the electronic device’s surface than the typical used 3D-OHPs. This research will promote the development of effective cooling for electronic devices.
In the present study, the thermal performance of an enhanced air-cooled heat sink system, comprising of a parallel plate-fin heat sink (PPFHS) with a guide plate installed to alter the bypass flow, was analyzed for fan-driven convection conditions at various altitudes from sea level to 12,000 m. Numerical simulations were carried out using ANSYS Fluent 16.0 with the κ-ω SST turbulence model to analyze the airflow and assess the thermal performance. After validation by experimental data in the literature, numerical results of the flow and temperature fields were obtained for different environmental pressures, several fan speeds and PPFHS design parameters. The measured characteristic fan curves at different altitudes show that the fan delivers approximately the same volume flow rate at different altitudes. For high-altitude operation, using the PPFHS only configuration could lead to electronic failure due to the larger temperature increase compared to using the PPFHS/guide plate configuration. For both configurations, the optimum fin number ranges between 20 and 32, which depends on the environmental pressure and fan speed. Improper use of highly dense PPFHS may lead to inadequate electronic cooling and will add extra weight for high-altitude operation. The optimal fin thickness depends on the fan speed, and the minimum thermal resistance occurs with low fin thickness at the lower fan speeds. Weight optimization procedures were conducted to obtain a considerable decrease in the PPFHS/guide plate weight and to achieve optimal thermal resistance at lower fan speeds.
A computational study of mixed convective heat transfer with surface radiation in a rectangular channel with heat spreader attached to each heat source is performed. The working fluid is air and flow is steady, incompressible and laminar. The parameters like thickness of the substrate and heat spreader, heat source and channel width and the distance between the heat sources are fixed. The governing equations are solved using ANSYS 16.2 with SIMPLE algorithm. The influence of Reynolds number (Re = 100, 250, 500, and 750), emissivity of the heat source (εc = 0.1 to 0.9), heat spreader (εsp = 0.1 to 0.9) and channel wall (εs = 0.1 to 0.9) on the rate of heat transfer is studied. It is revealed that the non-dimensional maximum temperature (θm) decreases 11.53% at reference values with respect to without spreader case due to insertion of heat spreader. It is also observed that emissivity of the heat source is insignificant compared to emissivity of heat spreader and channel wall.
We report experimental investigations carried out on a new minichannel heat sink (nMCHS) comprising four compartments, each equipped with inlet and outlet plenums for coolant and rectangular minichannels with two miter bends in each channel. For comparison, the performance of a conventional minichannel heat sink (cMCHS) comprising minichannels of same hydraulic diameter as that of the channels in new heat sink was also studied. Reynolds number had a stronger influence on Nusselt number in nMCHS than that in conventional. The experimental data (Reynolds number range from 175.02 to 553.40; pumping power range from 4.47E-3 to 1.89E-1 W) reveals that the total thermal resistance was appreciably reduced in the new heat sink, due to higher heat transfer coefficients caused by developing nature of the flow. The coolant distribution in the new minichannel heat sink contributed to a significant reduction (60%) in substrate temperature gradient.
The potential of using a full shield or partial shield with a guide plate to control the bypass cooling air flowing above a heat sink is numerically modeled using two different scenarios of inlet conditions – fixed mass flow rate and specified fan curve. Excellent agreement is observed when the simulation results are compared with available experimental data in the literature. Under the first inlet condition, the Nusselt numbers associated with the full shield installation are significantly higher than those without a shield, but with a significant pressure drop penalty. Friction factor increases with partial shield height till it reaches a maximum value with the full-shield configuration. Using an inclined guide plate with a partial shield alters the flow direction, forcing the air to impinge on the heat sink. This adds an extra cooling effect but without causing a considerable increase in the friction factor. In the case of fixed inlet mass flow rate, most of the partial shield and guide plate cases show the lowest pressure drop when the ratio of the partial shield height to the total bypass height Hs/HBP is between 0.35 and 0.5. The case with an inclination angle of θP = 15° has the highest thermal performance and the highest pressure drop. Correlations for the average Nusselt number and friction factor are developed to include the effect of Reynolds number, shield height, bypass height and guide plate inclination angle. For the second inlet condition, the test cases are repeated using a selected fan characteristic curve as an alternate to the fixed mass flow rate condition. The specified fan curve case shows that a short partial shield with a slightly inclined guide plate has a better thermal performance than the full shield case. Furthermore, using a guide plate only with a small inclination angle has a superior thermal performance. Changing the position of the guide plate is investigated as well and the optimal location is obtained.
High-altitude solar powered scientific balloon can be powered by thin-film solar panel mounted on the balloon. The temperature change of solar panel might have significant influence on the thermal performance of the balloon, which is closely related to the superheat and overpressure of balloon. The thermal model of solar powered scientific balloon was presented to investigate the thermal performance and compare with unpowered balloon. A user define function program in computational fluid dynamic software was developed based on the model. The effects of layout parameter and area of solar panel on the thermal performance of solar powered balloon were also analyzed. The results show that the temperature of envelope and internal helium of solar powered balloon is much higher than that of unpowered balloon during the daylight, and the maximum velocity of internal helium is decreased with the existence of solar panel. Moreover, the increase of the height and area of solar panel would result the raise of temperature and pressure of internal Helium, but the helium velocity and the flow distribution were hardly changed. The present work may be used to guide the design of solar energy system and the thermal control of scientific balloon.
A numerical analysis is performed for heat sinks with varied inlet and outlet layouts. The traditional model (heat sink A), has its inlet and outlet located on opposing sides. For heat sinks B-D, the coolant flows vertically into the heat sink from the center of the top wall. These models have either one, two, or four outlets near the sides of the top wall. The corresponding temperature fields, flow fields, pressure drop, and thermal characteristics are presented based upon a verified computational model. The numerical results indicate that the Nu number of the heat sink with four outlets is lower than that of the heat sink with one outlet. However, the four-outlet model presents a lower flow resistance and a higher comprehensive coefficient. The same thermal performance can be obtained with lower energy consumption when four-outlet heat sink D is used. This paper demonstrates that utilizing the proper layout can improve the comprehensive coefficient of a heat sink.
The output performance of solar array on near-space airship can be effectively improved by the layout optimization of solar array. This paper studied the effect of layout parameters on output energy of solar array on the airship with and without thermal effect, and particularly the optimization of solar array layout under the thermal effect. Based on the thermal model of solar array and the layout optimization model, a Matlab numerical program is adopted to calculate the output power or energy of solar array and latitudes and the change trend of optimum layout parameters for whole year and different latitude. The theoretical model is clearly verified comparing with the experimental result of temperature distribution of solar array. The effect of layout parameter on the thermal performance of airship was then analyzed by CFD simulation. The results show that the output performance of solar array is significantly improved through optimized layout and the output power or energy is decreased when considering thermal effect. The optimization of layout parameter may increase average temperature of airship and the velocity of internal helium of airship. Therefore, it is valuable to investigate the thermal effect of solar array in practical engineering of solar power system.
For the safe and efficient operation of concentrator photovoltaic cells and electronic chips, low and uniform temperature should be attained. Therefore, the prime focus of this study is to design the optimal headers and to evaluate the performance of a monolithic double-layer microchannel heat sink (MDL-MCHS) operating under forced convective boiling conditions. The designed and fabricated heat sink was proved to attain a uniform temperature distribution over the entire surface of the MCHS heated wall, in a narrow temperature range around the coolant boiling point. The designs of the MCHS inlet and outlet headers were computationally optimized to avoid flow maldistribution over 10 parallel channels in each layer. Subsequently, an MDL-MCHS with an optimized header was fabricated using a metal 3D printer, and its thermal characteristics were experimentally evaluated in counterflow and parallel-flow operations under single-phase liquid flow and forced convective boiling conditions. The supplied heat flux was varied from 1.0 to 9.2 kW/m². Ethanol and acetone with a boiling point of 78.4 °C or 56 °C were identically fed into each layer in a flowrate (V̇) range of 15–400 ml/h. At 9.2 kW/m² (11.5 suns), the counterflow operation of forced convective boiling attained temperature uniformity below 1.6 °C and 1.8 °C in the V̇ range of 25–100 ml/h for ethanol and 50–300 ml/h for acetone, respectively. The resultant wall temperature was nearly identical with the boiling point of operated coolant.
Experimental and theoretical studies are reported on the thermal insulation performance of three types of lightweight substrate for application in solar array on stratospheric airships. A concept, specific temperature difference, is proposed which expresses temperature difference of unit area density and can estimate the overall thermal insulation performance of lightweight substrate. The experimental apparatus and instrumentation have been designed and built to measure temperature difference between the upper and lower surface of the test samples under different solar radiation flux conditions. The experimental data are studied to assess thermal insulation performance of the lightweight substrates. The theoretical models of three types of insulation structures are investigated to predict the temperatures. Then, the models are verified by comparison with the experimental data. On the basis of analyzing theoretical models, the effects of two critical parameters of the heat sink substrate on thermal insulation performance are analyzed which give the most important evidences for optimizing the design of heat sink substrate. The obtained result is a valuable reference for the selection of insulation substrate of solar array on stratospheric airships.
Output performance analyses of the solar array are very critical for solving the energy problem of a long endurance stratospheric airship, and the solar cell efficiency is very sensitive to temperature of the solar cell. But the research about output performance of solar array with thermal effect is rare. This paper outlines a numerical model including the thermal model of airship and solar cells, the incident solar radiation model on the solar array, and the power output model. Based on this numerical model, a MATLAB computer program is developed. In the course of the investigation, the comparisons of the simulation results with and without considering thermal effect are reported. Furthermore, effects of the transmissivity of external encapsulation layer of solar array and wind speed on the thermal performance and output power of solar array are discussed in detail. The results indicate that this method is helpful for planning energy management.
Based on the concept configuration of the high altitude airship, electric motors were used to drive the propellers to generate thrust, however no detailed analysis on the motors was presented in the previous literatures. In this paper, the crucial problems were analyzed when the electric motors are applied for a propeller driving the high altitude airships. The main power generated by the solar array and the fuel cells equipped in the airship is in DC form, in addition, the high efficiency, high power/weight ratio and easy modulating speed-torque characteristics are demanded. Therefore the better choice for driving the propeller of high altitude airship is the rare earth permanent magnet brushless motor rather than the AC motor. In order to drive the propeller in a wide aerodynamic operational range, how to determine the rating parameters of rare earth permanent magnet brushless motors was studied. Further more, the part material selection, the bearings lubricant and the temperature rise were discussed. The experimental results showed that the rare earth permanent magnet brushless motor prototype could meet the requirement of a propeller and reached high efficiency.
Solar energy is the ideal power choice for high-altitude long-endurance airships. Photovoltaic array and its operation is one of the most critical aspects to the stratospheric airship's design and capabilities, but the research on thermal characteristics of photovoltaic array for the airship's design is rare. This paper develops the thermodynamic models of photovoltaic array and airship, based on which the three-dimensional temperature profile and output power of photovoltaic array are presented, the effects of the latitude, time of the year, wind speed, and insulation on the power output of the photovoltaic array are investigated, and the effects of photovoltaic array on thermal characteristics of the airship are explored. The results indicate that the latitude, time of the year, wind speed, and insulation affect the quantity and distribution of output power of photovoltaic array, and that the photovoltaic array can aggravate the superheat or supercool of the airship, so that the airship's hull requires higher intensity, expandability, and ductibility.
A 3-D model of multichip module (MCM) is built with ANSYS and the temperature field distribution is studied. A regression equation describing the relationship of structure parameters and material properties with the maximum chip junction temperature of MCM is made, which integrates the response surface methodology and ANSYS. Quantitative analysis of the effect of four design parameters on the maximum chip junction temperature of MCM is studied. The four design parameters are the thickness of the substrate, thermal conductivity of the substrate, thermal conductivity of the thermal grease, and convection heat transfer coefficient, respectively. The accuracy and validity of the regression equation are validated by simulation with ANSYS. In addition, the maximum error between the calculation value of the regression equation and the simulation value with ANSYS is 0.541. With the regression equation, the thermal optimization design results of the four parameters are , , , and , which lead to the maximum chip junction temperature as the minimum value.
Conventional technology to cool desktop computers and servers is that of the "direct heat removal" heat sink, which consists of a heat sink/fan mounted on the CPU. Although this is a very cost effective solution, it is nearing its end of life. This is because future higher power CPUs will require a lower R-value than can be provided by this technology, within current size and fan limits. This paper discusses new technology that uses "indirect heat removal" technology, which involves use of a single or two-phase working fluid to transfer heat from the hot source to an ambient heat sink. This technology will support greater heat rejection than is possible with the "direct heat removal" method. Further, it will allow use of higher performance air-cooled ambient heat sinks than are possible with the "direct heat removal" heat sink. A concern of the indirect heat removal technology is the possibility that it may be orientation sensitive. This paper identifies preferred options and discusses the degree to which they are (or not) orientation sensitive. It should be possible to attain an R-value of 0.12 K/W at the balance point on the fan curve.
Some known results on density currents in liquids are discussed, and the geometry of the frontal regions and of the upcurrents in the region ahead of them is shown to be similar to that of some thunderstorm outflows and sea-breeze fronts. The detailed structure of the frontal region of laboratory density flows is described. An internal Froude number has about the same value in the model and in the atmosphere.
Air-cooling characteristics of an electronic devices heat sink with various square modules array have been experimentally investigated. Flowing air velocities of 3.24–6.84 m/s were circulated through a channel of 0.1 m width and 0.02 or 0.03 m height. Aluminum block of module array was made and the base temperature of modules array of 40–100 °C were adapted to estimate the average heat transfer coefficient between the flowing air and modules array outer surfaces. Four modules arrays of 9, 16, 25 and 36 square poles in the same surface area were protruded to validate the effect of module to channel height ratio, α. The results indicated that the average heat transfer coefficient little increased with increasing the modules array temperature, but the increase was significantly higher with increasing the flowing air velocities. The increasing of module to channel height ratio seems to increase the average heat transfer coefficient. The experimental data of average Nusselt number were correlated as 0.11 Re0.77Pr0.32 within ±15%, and 0.84 Re0.58Pr0.25α0.47 within ±18%. The obtained correlations were compared with other previous data correlation and the comparison was quite good.
This paper provides an overview of the effects of altitude on
electronics cooling. MIL-STD 210 is reviewed to demonstrate the
relationship of altitude to density as well as to outside air
temperature. Once these relationships are understood the paper discusses
the impact of altitude on the performance of air moving devices using
the widely accepted fan laws. A discussion of both constant speed and
altitude compensating fans addresses performance issues such as power
dissipation, pressure drop, and free delivery of fans under these
conditions. Once the fan performance has been characterized, the system
impedance (or pressure drop) must be determined for the appropriate
altitude. The paper covers how system impedance changes under laminar
and turbulent flow regimes as altitude varies. The impact of altitude on
heat transfer is also discussed along with the effects of operating in
the turbulent and laminar regimes. In order to demonstrate the concepts,
an example problem is worked out
Adjusting temperature for high altitude
- Rhee
Interconnect technologies and the thermal performance of MCM
- Ozmat
Design of 7.5kW SiC inverter for electric vehicles
- Su