Lower Maximum Temperature Research Articles

Conventional and topologically optimized polymer manifolds for direct cooling of power electronics

Single-phase liquid-cooled heat sinks are a preferred mode of thermal management for many power dense electronic applications. This paper studies the design, optimization, and thermal-hydraulic performance of polymer manifolds directing coolant to the base plate of multi-chip power modules. Direct cooling eliminates the need for thermal interface materials which form a major bottleneck to junction-to-coolant thermal resistance reduction in state-of-the-art metallic cold plates. We use 2D topology optimization (TO) to develop designs using side view (SVTO) and top view (TVTO) sections of the flow domain in contact with the power module base plate. We also use 3D TO design (CTO) which combines SCTO and TVTO. The TO designs are compared against conventional mini-channel designs including rectangular, zig-zag and serpentine channels. Cooling performance of the different designs is computed using computational fluid dynamic (CFD) simulations. Experimental quantification is achieved through measurements of the silicon carbide device junction temperature and inter-device temperature difference along with the pressure drop influencing the pumping power requirement. The CFD simulations were used to identify optimized manifold designs which were fabricated using selective laser sintering of PA12 and validated experimentally using surrogate heaters. Zig-zag designs showed the best performance among the conventional designs (0.93 (cm2·K)/W), at the cost of high pressure drop (> 2.4 kPa). Serpentine channel designs were effective in limiting inter-device temperature difference (< 0.26⁰C) through multiple changes of flow direction. The TO designs improved the performance (1.1 (cm2·K)/W) when compared against conventional channels showing lower maximum temperatures with lower pressure drops (0.8 kPa). Fluid manifolds are shown to greatly influence the coolant flow field, leading to flow maldistribution with low velocity pockets, emphasizing the need for optimizing the complete manifold design.

Advanced polyimide separator via co-precursor method for lithium-ion batteries with low thermal runaway risks

Separator is an important component in lithium-ion batteries, and it plays a critical role in ensuring the overall thermal safety and electrochemical performance of a battery. To date, the development of safe and robust lithium-ion batteries is still hindered by the commercial polyolefin membrane due to its poor thermal stability and inferior electrolyte wettability. Thus, to address this shortcoming, an advanced polyimide aerogel separator was designed by simple one-pot reaction via co-precursor and cross-linking methods in this work. Based on molecular structure designation and gelation time control, the as-prepared polyimide aerogel separator (C-PI separator) possessed high porosity, good flexibility, excellent thermal stability, and superior electrolyte wettability, which are essential attributes of a high-performing separator. LiFePO4|Li metal battery was later assembled with C-PI separator, and the cell demonstrated outstanding long-term cyclic performance (>1000 cycles at 1C with 93.6 % retention). Compared with PE separators, the NCM523-graphite pouch cell assembled with C-PI separators exhibited high thermal stability with a higher thermal runaway temperature (204.9 °C vs. 140.4 °C) and a lower maximum temperature rise (0.06 °C/min vs. 8 °C/min), demonstrating its application potential in scenarios with high requirements for safety. Furtherly, the thermal runaway mechanisms of the full cells were explored and explained in this work.

Investigation into the use of phase change materials in thermal management of a solar panel in the vicinity of tubes with slotted rectangular fins

In this paper, a thermal solar panel is simulated numerically. An enclosure of CaCl2·6H2O phase change material (PCM) is placed at the bottom of the panel in the presence of graphene nanoparticles. A tube is placed in the middle of the enclosure in which alumina-water nanofluid flows at the Reynolds numbers of 200 to 800. A number of fins are installed on the tube. The effect of using three different types of fins in a period of 0 to 5 h and Reynolds number on the panel temperature, PCM volume percentage, output nanofluid temperature, bottom panel thermal resistance, and panel temperature uniformity is examined. The finite element method is employed to solve governing equations. The results demonstrate that the best temperature uniformity on the solar panel occurs at Reynolds number of 800. The Reynolds number of 800 also has the lowest maximum temperature, average panel temperature, and thermal resistance. Using the Reynolds number of 800 instead of 200 reduces the PCM volume percentage from 93.14% to 23.40% and reduces the nanofluid output temperature by 4.3 °C. Using fins case 3 creates the minimum temperature on the panel and minimum amount of thermal resistance. The fins case 3 and case 2 produce the minimum and maximum amounts of molten PCM.

Environmental Factors in Northern Italy and Sickle Cell Disease Acute Complications: A Multicentric Study.

Background: Environmental factors seem to influence clinical manifestations of sickle cell disease (SCD), but few studies have shown consistent findings. We conducted a retrospective multicentric observational study to investigate the influence of environmental parameters on hospitalization for vaso-occlusive crises (VOC) or acute chest syndrome (ACS) in children with SCD. Methods: Hospital admissions were correlated with daily meteorological and air-quality data obtained from Environmental Regional Agencies in the period 2011–2015. The effect of different parameters was assessed on the day preceding the crisis up to ten days before. Statistical analysis was performed using a quasi-likelihood Poisson regression in a generalized linear model. Results: The risk of hospitalization was increased for low maximum temperature, low minimum relative humidity, and low atmospheric pressure and weakly for mean wind speed. The diurnal temperature range and temperature difference between two consecutive days were determined to be important causes of hospitalization. For air quality parameters, we found a correlation only for high levels of ozone and for low values at the tail corresponding to the lowest concentration of this pollutant. Conclusions: Temperature, atmospheric pressure, humidity and ozone levels influence acute complications of SCD. Patients’ education and the knowledge of the modes of actions of these factors could reduce hospitalizations.

Influence of secondary flow angle and pin fin on hydro-thermal evaluation of double outlet serpentine mini-channel heat sink

Achieving high processing speed in electronic components combined with large amount of generated heat, this heat removed by heat sink. For extreme heat generated, a mini-channel liquid cooled heat sink is used. The aims of the present study are to enhance the efficiency of the serpentine mini-channel heat sink and to uniformly temperature distribute. To achieve that, several variables were studied, namely the double outlet, the secondary flow channel with different backwards angles (45°, 53°, 61°) and finally the combination of secondary flow with pin fin at different pitch distances (5d, 6d, 7d). Ansys Fluent 2020 R2 software was utilized to extract the numerical results. The two models were fabricated and tested experimentally, namely the Basic model and the optimum model (model F), to validate the numerical results. The results of validation showed a good agreement. The results show that the use of a double outlet serpentine mini channel heat sink leads to an increase in overall performance to 1.47 and a lower maximum base temperature. With an 8.7% increase in overall performance and an even lower base temperature, the secondary flow backward angle of 53° (model C) outperforms the other two angles. However, combining the secondary flow with the pin fin enhances the heat sink both thermally and hydraulically. The model F displays the maximum performance with a 1.79 and a Nusselt number of 9.64% as compared to the Basic model.

Heat transfer performance of the solid microencapsulated fuel in light water reactors

Solid Microencapsulated Fuel (SMF) is a kind of new accident-tolerant fuel (ATF) concept that disperses TRISO coated fuel particles directly into a type of matrix in the form of a solid rod. This paper aims to analyze the heat transfer performance of SMF based on a single pin, compared to the traditional fuel design in the 200 MW Nuclear Heating Reactor (NHR200-II). Two kinds of SMFs have been evaluated - fuel particles dispersed into a silicon carbide matrix and fuel particles dispersed into a zirconium matrix. The centerline temperature of the SMF rod at the beginning of life (BOL) was preliminarily calculated based on the effective thermal conductivity (ETC). The ETC was calculated by Maxwell, Chiew&Glandt, and d-EMT models, compared to the finite element models. The ETC of TRISO particle was also calculated before calculating that of the SMF rod because of its multilayer structure. To get a more realistic temperature distribution of SMF rod, a neutronic analysis was done by OpenMC by acquiring the power distribution of randomly distributed TRISO particles. Finally, a practical temperature distribution of SMF rod was achieved by the finite element model considering the random distribution of TRISO particles. This study showed that SMF has a better thermal transfer capacity than conventional fuel design and even fully ceramic microencapsulated (FCM) fuel because of its integral structure and higher matrix thermal conductivity. The helium gap in conventional fuel and FCM fuel would bring a temperature rise of nearly 150˚C in this case. The centerline temperature of SMF is much lower than the traditional fuel. A more refined temperature distribution of SMF rod based on the finite element model showed a lower maximum temperature than the ETC calculated. It also showed a less uniform temperature distribution because of the heat generation of fuel particles and the possible concentration of randomly distributed fuel particles.

Thermosolutal natural convection cooling process of a thermal source inside a partially porous cavity

This work deals with the numerical study of the thermosolutal natural convection from a heat source immerged in a porous layer, which is placed vertically inside a square cavity. All walls of the cavity are thermally insulated, except the right wall, which is maintained at cold temperature. For the mass boundary conditions, the vertical walls are subjected to a gradient of concentration, whereas the horizontal walls and the part of the left wall that contacts with the heat source are impermeable. The finite volume method and the SIMPLER algorithm are employed to solve the mathematical equations. The effects of several geometrical and physical parameters are analyzed, such as vertical heat source positions (0 ≤ Yp ≤ 0.8), the porous layer thickness (0 ≤ Xp ≤ 1), the thermal conductivity ratio (1 ≤ Kr ≤ 100), Darcy number (10−6 ≤ Da ≤ 10−2), Rayleigh number (104 ≤ Ra ≤ 106), Lewis number (0.1 ≤ Le ≤ 10), and the buoyancy ratio (-5 ≤ N ≤ 5). The results indicate that the best cooling of the heat source is observed when the Yp is located between 0.38 and 0.55. Moreover, the case of coupling heat and mass transfer (N ≠ 0) offers low maximum heat source temperature compared to that of the classical natural convection (N = 0), especially with an increase in the Ra number and N and/or a decrease in the Le number. In addition, an increase in the thermal conductivity ratio and the permeability of the porous layer (Da) enhances the cooling process of the thermal source.

An energy-efficient battery thermal management system incorporating a porous metal-based multiscale flow manifold

Development of an effective battery thermal management system (BTMS) is crucial for increasing the lifetime of electrochemical batteries and their reliable operation for various energy systems such as electric vehicles (EVs) and energy storage systems (ESSs). Liquid cooling can be a promising thermal management strategy for high energy density batteries due to its high heat transfer coefficient. However, conventional liquid cooling modules for large-scale battery packages require a high pumping power due to a long and serpentine flow path. They also induce a high-temperature deviation of battery cells since the coolant temperature gradually increases from inlet to outlet. Here, we introduce an energy-efficient liquid cooling module incorporating manifold flow distributors connected to a porous metal layer. The thermohydraulic performances of BTMS are investigated using both numerical and experimental platforms for the battery package composed of 24 pouch-type cells. The total energy capacity and heat generation of the package are determined to be ∼6.9 kWh and 504 W, respectively. The cooling module is designed to minimize the vortex generation within the cooling path, maximizing heat exchange area, and minimizing heat spreading resistance. The developed liquid cooling module shows ∼12.9 % higher temperature uniformity and 7.4 % lower maximum cell temperature compared to the straight channel-based module utilizing the same flow rate. The proposed liquid cooling strategy provides ∼43.3 °C of the maximum cell temperature with below 2 °C of temperature deviation by consuming only 3 L/min, which is ∼4.2 times lower flow rate compared to that of previously reported straight channel-based BTMS. This work will help develop energy-efficient electrochemical battery-based energy systems including EVs and ESSs.

Analysis of the meteorological factors affecting the short-term increase in O3 concentrations in nine global cities during COVID-19

Surface ozone (O3) is a major air pollutant around the world. This study investigated O3 concentrations in nine cities during the Coronavirus disease 2019 (COVID-19) lockdown phases. A statistical model, named Generalized Additive Model (GAM), was also developed to assess different meteorological factors, estimate daily O3 release during COVID-19 lockdown and determine the relationship between the two. We found that: (1) Daily O3 significantly increased in all selected cities during the COVID-19 lockdown, presenting relative increases from −5.7% (in São Paulo) to 58.9% (in Guangzhou), with respect to the average value for the same period in the previous five years. (2) In the GAM model, the adjusted coefficient of determination (R2) ranged from 0.48 (Sao Paulo) to 0.84 (Rome), and it captured 51–85% of daily O3 variations. (3) Analyzing the expected O3 concentrations during the lockdown, using GAM fed by meteorological data, showed that O3 anomalies were dominantly controlled by meteorology. (4) The relevance of different meteorological variables depended on the cities. The positive O3 anomalies in Beijing, Wuhan, Guangzhou, and Delhi were mostly associated with low relative humidity and elevated maximum temperature. Low wind speed, elevated maximum temperature, and low relative humidity were the leading meteorological factors for O3 anomalies in London, Paris, and Rome. The two other cities had different leading factor combinations.

Numerical investigation of thermal performance of a combined heat sink with various microchannel shapes

The influence of channel shape on a combined heat sink of three different channel forms is investigated numerically in this work. The channel shapes considered were the trapezoidal, inverse trapezoidal and hexagonal microchannel shapes. The goal of this study was to compare and identify the combined microchannel shape that performed best under conditions of high uniform heat flux. The thermal performance of the combined heat sink was assessed using two criteria: lowest maximum temperature and lowest temperature elevation on the bottom of the combined heat sink where heat is applied. The uniform heat flux applied to the bottom of the combined heat sink was elevated from 100 𝑊/𝑐𝑚2 to1000 𝑊/𝑐𝑚2. For the maximum heat flux of 1000 𝑊/𝑐𝑚2and lowest pressure drop of 10kPa considered, in terms of temperature elevation on the bottom of the heat sink where heat is applied, the trapezoidal combined microchannel heat sink outperformed other channel shapes. When the minimized overall maximum temperature is considered, the hexagonal combined microchannel heat sink was the best combined heat sink.

Modification of a 240 kWth grate incineration system for oxyfuel combustion of wood chips

The objective of this work is the application of the oxyfuel combustion technology for grate incineration systems to increase the CO2 concentration in the flue gas for higher efficiency when processing the gas for storage or utilization. Therefore, an experimental 240 kWth moving grate combustion facility has been modified to allow the investigation of the combustion behavior under various oxyfuel conditions. Subsequent to the modification, combustion experiments with dried wood chips under air and several oxyfuel atmospheres have been performed. During oxyfuel operation, the oxygen concentration in the gas supply streams towards the furnace has been set to 30 vol.-% dry with recycled flue gas being the rest of the gas composition. The oxygen distribution between primary and secondary zone has been varied (30%/70%, 40%/60%). Additionally, one case with increased oxygen concentration in the primary zone (40 vol.-% dry) has been investigated. The results show that oxyfuel grate incineration of the given fuel in this setup is feasible. However, the combustion behavior differs significantly between air and oxyfuel conditions in the investigated cases. The CO2 concentration in the dry flue gas could be increased to around 73 vol.-% with 5.7 vol.-% excess O2. Compared to the reference air cases the emission rates of CO were also increased during oxyfuel operation. However, it seems manageable given enough excess oxygen (∼7 vol.-% dry). Although the temperature at the end of the furnace is comparable among the cases, oxyfuel combustion leads to lower maximum temperatures along the combustion chamber. Differences between 150 °C and 200 °C have been measured among corresponding air and oxyfuel cases. Also, the temperatures of the grate and inside the fuel bed are reduced during oxyfuel operation even in the case with increased O2 concentration leading to the impression that the thermal strain on the grate is lower compared to air operation with the same fuel throughput.

Understanding Growth-Induced Trends in Local Climate Zones, Land Surface Temperature, and Extreme Temperature Events in a Rapidly Growing City: A Case of Bulawayo Metropolitan City in Zimbabwe

Assessment of the responses of the urban thermal environment to climate is important, especially because of their possible influence on low- and high-temperature extreme events. This study assessed the combination of remotely sensed land surface temperature (LST) and local climate zones (LCZs) with in situ air temperature-retrieved extreme temperature indices. It aimed to assess the effect of urban growth on the three-dimensional thermal environment in the Bulawayo metropolitan area, Zimbabwe. LST and LCZ were derived from the Landsat data for 1990, 2005, and 2020, while extreme temperature indices and trends were derived from daily minimum and maximum temperature data from a local weather station. Results showed that the built LCZ expanded at the expense of vegetation-based LCZ. Average LST for each LCZ increased from 1990 to 2020, which was attributed to background warming, while the expansion of high LST areas was associated with LCZ transitions. Although average minimum temperature decreased, cool nights increased, warmest nights remained unchanged, and the lowest minimum increased, the highest minimum temperatures decreased, but the trends were not statistically significant (p &amp;gt; 0.05). Indices of daytime warming showed significant changes, which includes an increase in average maximum temperature (p = 0.002), increase in lowest maximum temperature (p = 0), increase in the number of very warm days (p = 0.004), and decrease in the number of cool days (p = 0). The significant increase in daytime extremes was attributed to an increase in highly absorbing LCZ and daytime pollution due to industrial activities. The study also concluded that development in water areas or siltation of water bodies has a greater warming effect than other LCZ changes. The findings show that development needs to consider potential effects on the thermal environment and temperature extremes.

Electrolyte Role on the Thermal Runaway Characteristics of LFP Chemistry

Lithium-ion batteries have become the power source of choice in grid storage applications and electric powertrains, given its high energy density and extended cycle life. However, lithium-ion batteries carry significant safety risks and are a growing hazard due to thermal runaway that can be caused by overheating, cell deformation, overcharging and short-circuits. It is well understood that thermal runaway occurs when the self-heating rate in the cell exceeds the heat dissipation out of the cell. This self-heating is the product of undesired side-reactions in the cell, such as SEI decomposition or oxygen evolution from the cathode, triggered by abuse conditions that then result in thermal runaway. The key to inhibiting thermal runaway is to modify the cell such that the self-heating rate under abuse conditions is significantly reduced.These risks are believed to be mitigated by compromising energy density with safety through the choice of lithium iron phosphate (LFP) as the cathode. LFP is known to demonstrate lower rates of self-heating and achieve lower maximum temperatures during thermal runaway relative to mixed metal oxide cathodes (NMCs). LFP has other reported advantages over NMCs, such as superior cycle life, rate capability, no questionably sourced metals, and significantly lower cost. However, the safety aspect of LFP is only relative to their less stable metal oxide competitors, as LFP cells are still known to evolve oxygen and enter thermal runaway, particularly in larger cells and packs. This concern will increase in the near future as the next obvious battery design choice will be to pair LFP with silicon dominant anodes or lithium metal to create cells with energy densities on par with conventional metal oxide chemistries. There is a need to reduce cell self-heating without further compromising energy density. Therefore our approach is to modify the electrolyte system to reduce the overall cell self-heating rate. This is a tunable, drop-in solution to addressing the need for improving battery safety.We report an alternative electrolyte design to improve the robustness of the SEI and overall stability of the electrolyte system, which carries significance in improving cycle life and abuse tolerance in LFP chemistries in both conventional graphite and silicon-dominant anodes. These electrode pairings are investigated in coin cells, 2 Ah and 30 Ah pouch cells. The choice of electrolyte formulation is shown to impact the abuse tolerance of cells on both the material level, i.e. the electrolyte-electrode interaction and on the cell level.We evaluate the thermal profiles of delithiated LFP paired with lithiated graphite and silicon combined with electrolyte via differential scanning calorimetry (DSC). Our findings suggest that the primary driver of thermal instability in LFP systems arises from the anode in both graphite as well as silicon. The presented electrolyte systems demonstrate reduced overall energy and peak heat flow in the thermal profiles. These findings correlate electrolyte choice with lower self-heating rates in an accelerating rate calorimeter (ARC) heat-wait-seek test on LFP pouch cells. This approach carries significance in not just safer cells but also in enabling next-generation lithium-ion battery technology premised on low-cost cobalt-free cathodes.

Can diagnostic and imaging recommendations from the 2011 AAP UTI guidelines be applied to infants

In 2011, the American Academy of Pediatrics (AAP) published guidelines regarding diagnosis and management of children 2-to-24-months-old with initial febrile urinary tract infection (fUTI). Available data were insufficient to determine whether evidence from studies of 2-to-24-month-olds applies to those <2-months-old, so they were excluded. This study aimed to 1) compare demographic, clinical, imaging and outcomes between patients <2-months-old and those 2-to-24-months-old hospitalizedwith fUTI, and 2) assess whether diagnostic and imaging recommendations of the AAP 2011 guidelines apply to those <2-months-old. A cohort study of patients ≤24-months-old hospitalized at a children's hospital with fUTI from 2016 to 2018 was conducted. Data were collected via a prospectively generated electronic medical record note template, supplemented with retrospective chart review. Primary outcomes included differences in demographics, clinical presentation, urine culture results, and imaging utilization/results by age group. Secondary outcomes included surgical procedures, UTI recurrence, and 90-day all-cause readmissions and emergency department (ED) revisits. Univariate and bivariate statistics were utilized to compare age groups. Overall, 137 patients were included (median age 70 days, 55.5% male [92.1% uncircumcised], 53.3% Hispanic/Latino, 89.8% 1st fUTI). There were no demographic differences between groups, except children <2-months-old were more frequently male (71.2 vs 43.6%, p=0.002). The Summary Table compares clinical factors and imaging utilization byage. There were no differences in urinalysis or urine culture results between groups. Patients <2-months-old had shorter fever duration, lower maximum temperature, and lower white blood cell counts. Voiding cystourethrograms (VCUGs) were recommended and obtained more frequently in patients <2-months-old, but there were no differences in renal and bladder ultrasound (RBUS) or VCUG results between age groups. There were no differences in UTI recurrence (13.6% of <2-months-old vs 14.1% of 2-to-24-months-old, p=1.00) or fUTI recurrence (13.6 vs 7.7%, p=0.40) within 1 year, 90-day readmission (6.8 vs 6.4%, p=1.00), or 90-day ED revisit (22.0 vs 20.5%, p=1.00). There were minimal differences between the <2-months-old and 2-to-24-months-old age groups in demographics, laboratory (including microbial) or imaging results, or clinical outcomes. Patients <2-months-old were more frequently male and less ill. These data support applying urinalysis and urine culture diagnostic criteria, and universal RBUS, from the AAP guidelines to patients <2-months-old. Given utilization differences, applicability of VCUG guideline recommendations requires further clarification for patients <2-months-old. Laboratory testing and RBUS recommendations from the AAP guidelines may be safely applied to infants <2-months-old. Further studies are needed to clarify optimal VCUG recommendations.

Crosslinked polyethylene: A review on the crosslinking techniques, manufacturing methods, applications, and recycling

AbstractOne of the most used resins in the plastics industry is polyethylene (PE). Although PE has good impact resistance and ductility, its low maximum use temperature and mechanical strength limit some commercial development, especially for load‐bearing applications. To get better overall performances, crosslinking is performed to improve the chemical, mechanical, and thermal properties of PE. Although PE can be crosslinked by using various chemical and physical methods, this makes the resulting polymers more difficult to recycle since a three‐dimensional (3D) network is created. In this review, we first describe the different crosslinking techniques for PE to manufacture crosslinked PE (XLPE) parts. Then, as more than half of the XLPE‐based products are disposed directly after use, we present several options to reuse and recycle these products to overcome this environmental issue and find a sustainable solution. A focus is made on mechanical recycling and de‐crosslinking techniques for XLPE to generate recycled‐XLPE (r‐XLPE). Finally, a conclusion is presented on the current situation and research gaps that must be filled by future works.

Моделювання умов отримання наноструктур в алюмінієвих сплавах при дії іонізуючого випромінювання

The use of laser radiation as a source of ionizing radiation to obtain nanostructured and submicrostructured layers on aluminum alloys requires the determination of the necessary technological parameters. Therefore, a theoretical study of ionizing radiation on aluminum alloy AK8 was conducted according to the previously proposed model. When choosing the region in the material of the aluminum alloy, where nanostructures can be formed under the action of ionizing radiation, apply different lengths of ions. Because of the theoretical study of the formation of nanostructures in the surface layer of the aluminum alloy AK8, the temperature distribution in the zone of ionizing radiation at different depths of the material was obtained. Temperature fields for different heat flux densities q1 = 106 W/m2 and q2 = 105 W/m2 were also constructed. The obtained temperature fields for heat flux q1 showed that with increasing depth of the material, the temperature decreases from 2480 to 650 K. The values of maximum temperatures on the material surface are slightly higher than necessary to obtain nanostructures at lower depths maximum temperatures decrease to nanostructures can be realized. Simultaneously, under the action of heat flux q2 = 105 W/m2, the maximum surface temperature decreased to values of 1950 K, and at depth it was 550 K. and was equal to 106 K/s at q2. All these confirmed the possibility of creating conditions for the formation of nanostructures. Due to the temperature range obtained from the calculated temperature fields, the depths of the aluminum alloy where nanostructures can be formed were determined. Studies of the effect of laser radiation spot size on the surface of the material on the formation of nanostructures were also conducted, which showed that when exposed to a spot size of 3 · 103 to 10-3 m, the possibility of nanostructures is significantly reduced, while reducing the spot size to 10-4 m leads to a significant increase in the possibility of forming nanostructures. To estimate the possible volume of nanostructures, the dependence of the nanocluster size on the heat flux density in the range from 107 to 1010 W / m2 and its action time in the range from 10-9 to 10-3 s were considered. The dependence of the maximum temperature on the heat flux density and the time of its action is also constructed. All this allows you to choose the technological parameters of laser radiation to obtain nanostructured layers on aluminum alloys, and the ability to determine the size of nanostructures allows you to predict the physical and mechanical characteristics of the surface layers of processing materials. These studies may be of interest to specialists in strengthening the surfaces of aluminum alloys and further studies of nanostructures.

Investigation of heat transfer, melting and solidification of phase change material in battery thermal management system based on blades height

This paper deals with the Battery thermal management system (BTMS) of a battery pack with three cylindrical batteries using the passive method. For this purpose, the area around the batteries is filled with PCM. This analysis is performed in two-dimensional mode, transient and by cutting in the longitudinal direction of the batteries. There are a number of blades on the batteries. By changing the height of the blades installed on the batteries in the range of 1 to 4 cm, the BTMS is examined. For numerical solution, the Finite element (FEM) is used to solve the equations. The results of this study showed that the values of the average heat transfer coefficient (HETC) from the battery to the PCM as well as the temperature of the batteries were strongly dependent on time and both parameters increased with increasing time. Using a shorter blade instead of a long blade creates a higher average HETC in batteries, so using a 1 cm blade instead of a 4 cm blade more than doubles the average HETC. The battery in the middle of the other two batteries requires more thermal management than the other two batteries due to the higher temperature. Increasing the height of the blades has also reduced the average temperature of the battery pack, and all three batteries have a lower maximum temperature. Also at high times, especially 50 min after the start of the battery life, the use of battery blades has created more molten PCM around the batteries.

Direct cooling of a planar magnetic converter using dielectric liquid forced convection enabled by additive manufacturing

Power densification of magnetic converters has encountered a fundamental challenge due to the inability to effectively remove heat produced by power losses. State-of-the-art thermal management technologies for planar printed circuit board (PCB) transformers are limited by the inability to substantially improve the overall thermal conductance from the transformer to the cold plate. Furthermore, a lack of thermal management technologies capable of reducing temperature gradients in these devices exists. Direct liquid cooling reduces the number of thermal resistances from hot spot to coolant, resulting in lower maximum temperatures and reduced thermal gradients. Here, we study the thermal-hydraulic performance of a PCB planar transformer cooled using a polymer additively manufactured (AM) housing and single-phase internal flow with Novec 7300 and pure ethylene glycol. Computational fluid dynamics simulations were used to identify hot spots, quantify temperature gradients, and characterize pressure drop. Experiments in a custom-made setup quantified the maximum temperature and pressure drop with different flow rates (0.4–4 LPM) of Novec 7300 and ethylene glycol. Both working fluids showed better thermal-hydraulic performance when compared to results found in literature which implements cold-plates. Analysis reveals that selection between both fluids is guided by flow rate, pressure drop and pumping power, such that if low pressure drop is a priority, Novec 7300 is a better choice, and if low pumping power and flow rate are a priority, ethylene glycol is better. Our results show that direct liquid cooling can reduce thermal resistance by up to 80% using an 80% lower pressure drop when compared to a cold-plate benchmark. As a result, the developed AM-enabled thermal management technology can potentially improve the reliability of the converter, provide an alternative for high temperature heat recovery, and facilitate further converter power densification.

Consideration of graphene material in PCM with aluminum fin structure for improving the battery cooling performance

Phase change material (PCM) based battery thermal management system (BTMS) provides even heat distribution and lower maximum temperature, but it suffers from low thermal conductivity. In this study, the impact of graphene additive on PCM was analyzed by presenting three experiments with various structures to solve PCM's low thermal conductivity problem. The results demonstrate that there is no positive impact of graphene additive in the first and third structures. The PCM-graphene additive between the second structure's fins significantly improves the battery heat transfer by allowing the battery to cool down 1500 seconds earlier than the graphene-free structure. Moreover, a thermal equivalent circuit model was derived for the second structure because of its enhanced performance. It is shown that the model works accurately and proves its ability to control not only temperature fluctuations but also transient behavior of the battery. This model provides that the battery temperature can be analyzed without experimentation for different charge-discharge scenarios in lithium-ion batteries with a shorter computation time.

Modeling and optimization of turbulent flow through PEM fuel cell cooling channels filled with metal foam- a comparison of water and air cooling systems

One of the proposed methods to improve the performance of a proton exchange membrane fuel cell is using metal foam within the channels. Here, we performed a 3D numerical simulation and studied the effect of structural properties of metal foam on the system performance. Also, we used artificial neural network to predict three criteria, i.e., maximum temperature, temperature uniformity index, and pressure drop, together with Genetic Algorithm for system optimization. Obtained results indicate that using metal foam can improve the temperature uniformity in the cell, so that maximum temperature and temperature uniformity index are decreased about 1.785 K and 0.7 K, respectively, while resultant increase in overall pressure drop of the system is only about 4.4%. The same amount of maximum temperature reduction is possible by increasing the flow rate; however, this scheme puts 60% more pressure drop upon the system. Moreover, we compared the performance of air- and water-cooling systems and found that for a given pressure drop, the maximum temperature as well as temperature uniform index of an air-cooling system is lower than that of a water-cooling system, while for the same system parasitic power, a system with water coolant has more uniform temperature distribution with lower maximum temperature.