Inlet Air Velocity Research Articles

Optimization of the Cooling Performance of Symmetric Battery Thermal Management Systems at High Discharge Rates

An air cooling battery thermal management system (BTMS) is widely used in electric vehicles (EVs). In this work, numerical simulation is used to provide a greater understanding of the system efficiency of T-type symmetric air cooling BTMS (T-BTMS) and its coupled systems. For T-BTMS, the method of the coefficient of variation (MCV) is applied to evaluate the schemes with different inlet flow rates and battery clearances. It is found that optimum cooling performance and energy consumption are achieved at an internal clearance of 3 mm and an inlet air velocity of 6 m·s–1. Further improvements in cooling performance can be realized by introducing heat transfer fins into the module. Increasing the number of fins can improve cooling performance but results in higher energy consumption. To further improve the cooling performance at high battery discharge rates, a coupled system with air cooling and liquid cooling is proposed. It is found that, at high discharge rates, the coupled system gives better cooling performance and lower energy consumption compared to uncoupled systems. When the battery module is fully discharged at the rate of 4 C, the maximum temperature of the coupled system is below the critical value of 45 °C and the maximum temperature difference is less than 5 °C.

Simulation study on coupled heat and moisture transfer in grain drying process based on discrete element and finite element method

In present article, the soybean packed bed was generated based on the Discrete Element Method, and the distribution of radial porosity and airflow path of the packed bed were analyzed. The porosity distribution of the packed bed is not uniform, and it is larger near the wall. However, it is lower near the central axis, resulting in a larger airflow tortuosity in this area. Based on the thermal non-equilibrium principle, the double-diffusion heat and moisture transfer model of grain pile was developed. The double-diffusion model was verified and validated using experimental data from the relative literature on soybean thin-layer drying, and the mean relative deviation was 1.74–4.47% between the simulated and the experimental results. The model was applied to the drying process of soybean packed bed, and the influence of drying air temperature and inlet air velocity on drying was analyzed. It was shown that the moisture transfer rate of soybean is mainly affected by the drying air temperature and the moisture content of soybean. At constant air temperature of 35 °C, 45 °C, 55 °C, and 65 °C, and drying air relative humidity of 17%, 21%, 25%, and 30%, respectively, the drying rates were 0.086, 0.089, 0.093, and 0.098%(d.b.)/min, respectively (within the first 10 min). The drying with the stepwise temperature makes the drying rate curve abnormal. Compared with the constant temperature drying at 45 °C, when the drying air temperature changes from the initial value of 55 °C and 35 °C to the end value of 40 °C and 65 °C, respectively. It was observed that drying the packed bed moisture content to 14.5%(d.b.) saves time as much as 80, 110, and 130 min.

Experimental Investigation Utilizing Thermal Image Technique to the Heat Transfer Enhancement Using Oscillated Fins

Heat transfer around a flat plate fin integrated with piezoelectric actuator used as oscillated fin in laminar flow has been studied experimentally utilizing thermal image camera. This study is performedfor fixed and oscillated single and triple fins. Different substrate-fin models have been tested, using fins of (35mm and 50mm) height, two sets of triple fins of (3mm and 6mm) spacing and three frequenciesapplied to piezoelectric actuator (5, 30 and 50HZ). All tests are carried out for (0.5 m/s and 3m/s) in subsonic open type wind tunnel to evaluate temperature distribution, local and average Nusselt number (Nu) along the fin. It is observed, that the heat transfer enhancement with oscillation is significant compared to without oscillation for low air inlet velocity. Higher thermal performance of triple fins is obtained compared to the single rectangular fin, also triple fins with (height=50mm and finspacing=3mm) gives better enhancement as compared to other cases. This work shows that the piezoelectric actuator when mounted on the rectangular fins shows great promise for enhancing the heat transfer rate.

Assessment of Thermal Performance of Non-Evaporative Cooling System Assisted with TEC Models at High Temperature Climate

In this work, a non-evaporative cooling system is used with an assisted thermoelectric cooler (TEC) devices module. The system was proposed as an alternative cooling system in the high temperature climate to overcome the high energy consumption of traditional air-conditioning compression cycle. The open source Open FOAM V.9 was used to solve the transient effect of 3D model of indirect non-evaporative cooling system. The primary air temperature was set to 319 . While, the air flow was tested under four different air inlet velocities: 0.75 m/s, 1 m/s, 1.25 m/s, and 1.5 m/s. the validation shows good and acceptable agreement in COP values of the system with both experimental and theoretical works from literature within an error between (12.9 % and 9.5 %). Results show that the temperate difference value on a slice through the length of the air channel starts to decrease as velocity increasing. For example, at the last timesteps of each velocity, the temperature difference reaches about (~10 oK) when velocity is (0.75 m/s) starting from the first quarter of the channel, while the same difference in temperature not reached until the half way of the channel from the channel inlet when velocity is (1.5 m/s). Revealing that even though the percentage increase in the velocity is about 50%, the change in the temperature difference value between the inlet and outlet of the channel is about 1.2%. The local Nusselt number shows that steady state heat transfer reached very quickly as the velocity increased (i.e., at 0.75 m/s at 12s while for 1.5 m/s at 4s). Notwithstanding, as the time processed the ( increases for all cases but becomes lower as the velocity increased. .

Computational study on hybrid air-PCM cooling inside lithium-ion battery packs with varying number of cells

Rising global pollution index, together with transportation vehicles as one of the major contributors, has prompted researchers to focus on clean and renewable sources of energy. Electric vehicles (EVs) with rechargeable lithium-ion battery offer a promising option to develop clean energy vehicles. However, in order to bring off an optimal performance, a specified temperature range must be chosen for the operation of these batteries. Here, we numerically investigated a battery thermal management system (BTMS) utilizing encapsulated phase change material (PCM) combined with forced convective air cooling using the coupled electrochemical-thermal modelling. Commercial SONY 18650 type lithium-ion cells were taken in two arrangements, namely, inline and staggered. PCM encapsulation of thickness 0–3 mm over the cells was used. Broadly, the influence of increasing cell number (N) on the cooling performance and thermal uniformity has been delineated at discharging rates of 1C, 2C and 5C. A scrupulous analysis of temperature and velocity distribution, cell temperature (average and maximum), and thermal uniformity plots have been reported. Typically, for N = 8, a significant reduction of ~33 K in average temperature was seen at 5C discharge rate and air inlet velocity of Uin = 0.2 m/s when only a thin layer (1 mm) of PCM is applied on the cells. Moreover, a simple predictive correlation is established for a priori estimation of the average and maximum cell temperature in the gamut of pertinent parameters. Lastly, for an optimization viewpoint, a comparative analysis of results is presented based on different location of PCM encapsulation.

Computational fluid dynamics analysis of the airflow field inside a cyclone of a combine harvester with adjustable blocks

Existing combine harvesters used for rapeseed still have challenges. To simplify the structure of the harvester and reduce losses a new type of cyclone is proposed as a cleaning device. It has several spiral arranged adjustable magnetic blocks fitted at the bottom of the cyclone to disrupt and reduce any dead zone in the airflow field. To establish the effect of altering the dead zone of the airflow field, the motion of a single rapeseed in the cyclone was analysed based on the kinematics and dynamics. A simulation model of the cyclone, based on computational fluid dynamics, was established to optimise the arrangement of the magnetic blocks within the cyclone. The influences of helix angle, distance and spiral number of the magnetics blocks on the airflow were explored through a single-factor simulation experiment, which determined the optimal number of spirals as 4. Subsequently, the air velocity of the inlet and materials other than grain (MOG) at the outlet were added as factors to carry out the Box-Behnken designed experiment. Results showed the optimal combination of parameters were an inlet air velocity 4.2 m s−1, a MOG outlet air velocity 27.4 m s−1, a helix angle 64.2° and distance between magnetics blocks 52.4 mm. Bench tests and field experiment were conducted to validate the performance of the cleaning device under the optimum conditions. The results showed that the average cleaning ratio and loss ratio of the rapeseed were 88.96% and 4.12%, respectively.

Enhanced heat transfer study of thermoelectric generation system based on bidirectional coupling simulation

ABSTRACT To improve the performance of thermoelectric generator (TEG) for recovering the waste heat of thermaI fluid, a fluid-thermoelectric multiphysics numerical model is developed by using a bidirectional-coupled simulation method. The interaction between the thermal fluid and the TEG system is considered in this method and the numerical model is experimentally validated. Two numerical models of TEG systems with straight fins and corrugated fins are established, respectively. The temperature and potential distributions of the TEG at different inlet velocities and temperatures are analyzed. The results show that the corrugated fins can enhance the convective heat transfer, thereby improving the output characteristics of TEG. The developed model can predict the output characteristics of TEG system accurately. The error between the simulated and experimentally measured open-circuit voltage does not exceed 2.41%. Increasing the inlet air velocity and temperature improves the TEG hot side temperature, thus increasing its output power. Compared with the TEG system with straight fins, the heat transfer coefficient of the thermal fluid in the TEG system with corrugated fins was improved by about 10%. The output power and conversion efficiency were also improved by 18.9% and 0.12%, respectively, at a higher inlet velocity of 5.36 m/s.

Theoretical study on the wetting rate in wet channel of dew-point evaporative cooler based on Marangoni effect

Dew-point evaporative cooler is widely concerned as a fresh air precooling system, for its high efficiency, energy saving and environmental protection. A mathematical model for a plate-type counter flow dew-point evaporative cooler is developed in the paper, in which the film shrinkage induced by the Marangoni effect is taken in account. The results show that the model based on Marangoni effect has a higher accuracy compared to the model with wetting rate σ = 100%, in which the Average Relative Deviation from the experiment decreases by 15.8%. The wettability distribution characteristics are investigated. Along the air flow, the transverse contraction distance of film is varied, which mostly depends on the evaporation process. The higher inlet air temperature, the lower inlet air humidity, the higher velocity of inlet air, the larger channel gap, and the higher ratio of working air to inlet air would cause the higher Marangoni number and lower wetting rate. Further, a constant value of wetting rate 96.2% is recommended to simplify the calculation, while the Average Relative Deviation of the simulated results compared to the actual process is only 0.47%.

Parametric effects of ring-shaped phase change module on the temperature regulation of ultra-low carbon shallow geothermal ventilation system

As one of the most representative geothermal systems, shallow geothermal ventilation (SGV) system has been widely used with the advantages of simple configuration and low operation cost. However, this system is characterized by relatively large temperature fluctuations at the outlet in many application scenarios, which will reduce the thermal comfortable of the delivery outlet air temperature. The existing model development of horizontal buried-pipe SGV system tends to ignore the vertical buried-pipe part of the air inlet and outlet, and only considers the heat transfer model of horizontal buried-pipe, which may affect the accuracy of the developed model to a certain extent. Based on these, this study proposes a SGV system integrating the ring-shaped phase change material (RSPCM) module, and develops the dynamic heat transfer model considering the vertical part of the air inlet and outlet of the system. In this study, firstly, a relevant field experimental testbed is built and the developed dynamic model is verified with good agreement based on the experimental data, which has a maximum relative error of 4.83 %. In addition, the effects of RSPCM and its different parameters on the thermal performance of SGV system are investigated based on the developed model. The results show that RSPCM arranged at the air outlet can regulate the outlet temperature fluctuation of the SGV system and improve the comfort of the air supply temperature to a certain extent. When the inlet air velocity is 1 m/s, the temperature fluctuation at the outlet is 1.73 °C for the system comprising RSPCM, while the corresponding temperature fluctuation at the outlet is 2.10 °C for the system without RSPCM. The effect of thermal conductivity on the PCM's temperature regulation ability is not obvious enough for the proposed system application. Therefore, in practice, by increasing the thermal conductivity of RSPCM is not an optimal and feasible way when considering the economic cost. The RSPCM thickness is increased to a certain level and then this measure will not have much effect to improve the system's thermal performance. For this system structure and operating conditions, a more suitable RSPCM thickness should be about 20 mm, and the RSPCM with a phase-change temperature of 24 °C has a relatively good temperature regulation capability. The RSPCM has a better temperature regulation capability for the system outlet temperature when it is located at the outlet position. This study provides a novel research possibility for the application of SGV in buildings, and can also provide theoretical guidelines for designers and constructors in practice to apply SGV systems.

Numerical Study of Air Flow and Distribution of Temperature in A Room with Dislocation Ventilation and A Chilled Ceiling

In the present study, numerical analysis has been employed to investigate the distribution of velocity and temperature of the air in space conditioned with corrugated ceiling radiant cooling panels (RCP). The model of the study is a three-dimensional room with dimensions of (5.0*4.0*3.2) m. The initial and boundary conditions of the models are set to start the simulation in which the mean cooling panel temperature (Tmp) is (15 °C), where Tmp must not be lesser than that variety to avoid the danger of water vapor condensation on the surface of panels and tubes. The air inlet temperatures Tin is taken as (15, 20, and 25) °C and inlet velocities Vin are (1 and 0.5) m/s with an outdoor air temperature of (40 °C). Ansys Fluent software is considered in this study to simulate the flow field under the influence of several factors including outdoor air temperature, mean panel temperature, air inlet velocity, and temperature. The outcomes show an improvement in the overall cooling capacity and the mixed convection heat transfer. Many of the calculated outcomes were displayed as velocity vectors and temperature contour diagrams. Numerical studies assist in using the chilled ceiling technique for cooling aims in Iraqi weather for its simplicity, easiness, and better comfort presentation.

Methane migration and explosive fringe localisation in retreating longwall panel under varied ventilation scenarios: a numerical simulation approach

Methane-based inflammable underground coal mine environment has led to catastrophic losses in the past. Migration of methane from the working seam and desorption region above and below the seam causes explosion hazard. In this study, the computational fluid dynamics (CFD)-based simulations of a longwall panel in a methane-rich inclined coal seam of the Moonidih mine in India established that the ventilation parameters greatlyinfluence themethane flow in the longwall tailgate and porous medium of the goaf. The field survey and CFD analysis revealed that methane accumulation on the "rise side" wall of the tailgate is attributable to the geo-mining parameters. Further, the turbulent energy cascade was observed to impact the distinct dispersion pattern along the tailgate. The numerical code was used to investigate the changes in ventilation parameters made to dilute the methane concentration in the longwall tailgate. Methane concentration in the tailgate outlet decreased from 2.4 to 1.5% as the inlet air velocity increased from 2 to 4m/s. The oxygen ingress into the goaf increased from 0.5 to 4.5 lps as thevelocity was increased, causing the explosive zone in the goaf to expand from 5 to 100m. Amongst all velocity variations, the lowest level of gas hazard was observed at an inlet air velocity of 2.5m/s. This study, thus, demonstrated the ventilation-based numerical method to assess the coexistence of gas hazard in the goaf and longwall workings. Moreover, it provided impetus to the necessity of novel strategies to monitor and mitigate the methane hazard in U-type longwall mine ventilation.

Investigating the thermal performance of air-cooling system integrated with TEC modules: Transient numerical simulation

The current study represents a developed 3-D numerical transient model to a complete indirect non-evaporative cooling system integrated with an assisted TEC unit using OpenFOAM V.9 source code. The TEC model was developed using a hand-written code as a source added to the energy equation. The primary air temperature was a criterion to compare between three cases of environment's temperature: low mode (299 K), medium mode (309 K), and high mode (319 K). A new dimensionless factor called by Heat Flux Ratio (HFR) is derived to evaluate the thermal performance. In addition, wall heat flux and temperature difference along the vertical air channel were the parameters used for comparison. The complete system was constructed and validated according to number of experimental and theoretical studies from literature. Furthermore, all cases were tested under five different air inlet velocities: 0.75 m/s, 1 m/s, 1.25 m/s, 1.5 m/s, and 1.75 m/s. Results show that HFR values increase as time increases. In addition, it was found that HFR increases with the reduction in the velocity. Moreover, it was found that higher temperature difference can be reached at the lowest velocity (0.75 m/s) while the minimum difference would be at the highest velocity (1.75 m/s) with the error between modes doesn't pass (2.5%). On the other hand, the highest wall heat flux approached at the highest velocity (1.75 m/s) and vice versa where the error doesn't exceed (2.85%) between the modes. Finally, the validation shows good and acceptable agreement in COP values of the system with both experimental and theoretical works form literature where the error is ranged between (20.3% and 3.64%).

Experimental study of thermal performance improvement in a cross‐flow heat exchanger by using copper foam

AbstractIn this study, copper foam was used as a porous medium in place of traditional aluminum fins. A comparison between the two heat exchangers—one with fins and the other with copper foam—was conducted under various conditions. The air inlet velocity ranged from 0.9 to 9.3 m/s, and the water inlet temperature ranged from 10°C to 18°C. Different water flow rates were tested. A comparison was made between the performance of copper foam and aluminum fins by calculating several parameters, including thermal resistance, heat exchanger effectiveness, Colburn factor, Nusselt number, friction factor, and area goodness factor (AG). The experimental results showed that at low air velocities, the heat transfer coefficient for both types of heat exchangers was almost equal. However, at high air velocities, the copper foam exhibited a higher heat transfer coefficient. The Colburn factor was higher for the heat exchanger with copper foam than in the conventional fins, where it was equal to 0.1959 for the copper foam and 0.1186 for the fins. On the other hand, the AG was higher in the case of fins than in the heat exchanger with copper foam.

Design optimization of Air-Cooled Li-ion battery thermal management system with Step-like divergence plenum for electric vehicles

Air-cooled Battery Thermal Management System (BTMS) technology has been proven and is frequently employed to regulate the distribution of temperature in a battery pack of an electric vehicle. In this study, a step-like divergence plenum was introduced to a standard Z-type BTMS to alter its airflow distribution pattern and thus improve its cooling effectiveness. The impacts of the number and length of steps in the divergence plenum on the cooling responses of the BTMS were investigated using a validated Computational Fluid Dynamics (CFD) method. Analysis of 1-step, 3-step, 4-step, and 7-step BTMS models were conducted and findings showed that the step quantity has a significant impact on the battery pack's ability to dissipate heat. For a step length of 30 mm, a 7-step case model offered the best system’s maximum temperature of 324.9 K and cell temperature difference of 1 K which were both 3.94 K and 5.93 K, respectively lower than that of the standard Z-type model. Furthermore, the step case models were optimized by observing the impacts of their step length on system's thermal performance. The outcomes showed that there was a substantial impact of the step length on cooling performance for all case models. For instance, a 4-step case model with a 45 mm step length offered a reduction in maximum temperature of 3.61 K and maximum temperature difference of 6.01 K when compared to the standard Z-type model. Finally, the behaviour of each case model was examined under increasing inlet air velocity and it shows that at higher airflow velocity, the 7-step case model performed substantially well than other investigated cases.

Mixed Seeds of Oat and Vetch Based on DEM-Fluent Coupling Motion Simulation in a Venturi Tube

The gas–solid flow of mixed seeds of oat and vetch in the air-blowing venturi tube was simulated numerically by means of a coupling approach of the discrete element method (DEM) and computational fluid dynamics (CFD). In the gas–solid coupling model, EDEM software was used to depict the discrete particle phase, and ANSYS Fluent software was used to describe the continuous gas phase. The effects of the seed entry angle and inlet air velocity on the uniformity of mixed seed supply were studied and analyzed from the angle of airflow field variation and mixed seeds movement characteristics. The simulation results showed that the seeding angle has a great influence on the seed movement in the tube and affects the pressure and velocity gradient of the airflow field. If the seed insertion angle is too large, the number of collisions between the seed and the tube wall will increase, and the phenomenon of seeds retention and disordered jumping will occur. The inlet air velocity mainly affects the outlet air velocity and seed velocity and has little effect on the change in airfield. With the increase in inlet air velocity, the greater the velocity and force of the seeds, the closer the mixed seeds collide with the wall to the outlet pipe. At high inlet airflow velocity, there is a great disparity in the movement speed between the seeds, resulting in uneven spacing between the seeds. The results showed that under the conditions of 60° seed entry angle and 35~40 m/s inlet air velocity, the airflow field distribution in the tube was uniform and the seed movement was continuous and uniform.

Air Flow Analysis for Protective Clothing Ventilation Elements with and Without Constant Cross-Section Area Opening

Abstract In this paper a ventilation element is designed with the constant cross-sectional area of 3.14 mm2 with the outer ring, to study the efficiency of ventilation at three different inlet air velocities (2, 5 and 8 m/s). There are five different cases analysed in the study, in which four cases are with different coordinate values of outer ring and core while the fifth case is studied with ventilation element without outer ring. The results of all five cases are analysed and compared to see the efficiency of ventilation element design. These ventilation elements are attached at ventilation hole at the inner part of the protective jacket. The attached ventilation element increases mechanical strength of the clothing by covering ventilation hole and restricting direct access of insects to the body. Moreover, ventilation elements permit smooth flow of air inside jacket. The objective is to determine which element’s geometrical configuration results in the minimum flow energy losses in the cell flow channel from the inlet to the outlet, which are represented by the pressure difference. Flow energy losses increase with increasing pressure difference (ΔP), and the body cooling reduces if the flow is weakened or there is of lost energy. SolidWorks Flow Simulation is used to calculate the pressure, temperature, and heat flux for the simplified elliptical model of the human body with a protective jacket. The obtained results are compared and analysed to study the concept of constant cross-sectional area in the design of ventilation elements with and without outer ring. The pressure and temperature difference for each case are calculated for the comparison and the obtained results show that the element design without outer ring provides better overall results and less flow energy loss in the cell flow channel than that of element design with outer ring.

Defrosting Characteristics of the Cockpit Windshield of Manned Airships

Frost covering of the cockpit windshield will seriously obstruct the driver’s vision and even affect flight safety of the low-altitude manned airship. To solve the problem, this paper proposes a rapid defrosting strategy using hot gas injection method. The influences of the air inlet type, air temperature, air velocity and air angle on the defrosting characteristics of the transparent windshield are investigated and the defrost characteristics of the manned airship are obtained by fluid dynamics simulation. The result shows: (1) Defrosting effect of single inlet is not as good as double inlets. The defrosting area of the double inlet is relatively large, mainly concentrated at both ends of the windshield. (2) The effect of air supply temperature on defrosting effect of windshield surface is more significant when double air supply inlets are used. But when the air supply temperature reaches a certain value and continues to rise, the defrosting time does not change much, so there is an optimal air supply temperature range. (3) The higher the air supply velocity is, the shorter the phase transformation time of frost layer is and the faster the melting velocity is. Considering energy consumption and defrosting characteristics, the optimal air supply velocity is about 6 m/s. (4) When the angle between the air supply direction and the horizontal plane of the bridge near the windshield is 100°, the frost layer has the shortest melting time.

Investigation of the Effect of Air Inlet Position and Velocity on Battery Cooling Performance in Electric Vehicles

Bu çalışmada, hava giriş konumu ve hızının, hesaplamalı akışkanlar dinamiği (HAD) simülasyonları kullanılarak elektrikli araçlarda (EA'lar) nikel-metal hidrür (Ni-MH) batarya paketinin soğutma performansı üzerindeki etkisi incelenmiştir. EA'lara olan talebin artması, araçların güvenliğini sağlamak için gelişmiş batarya soğutma performansına ihtiyaç duyulmasına neden olmuştur. Ni-MH batarya takımının soğutma performansı, batarya takımının 0 ila 60 mm arasında değişen giriş konumları ve sabit çıkış konumu ile hem U hem de Z kanalı geometrilerinde analiz edilmiştir. Hava giriş hızları 2 ila 6 m/s arasında değişmektedir. Sonuçlar, hava giriş konumu arttıkça sıcaklık değerlerinin düştüğünü, ancak 30 mm'lik giriş konumundan sonra düşüşün önemsiz hale geldiğini göstermektedir. Bu, hava akışını batarya takımını tamamen dolaştırmaya ve ısı transfer hızını artırmaya yönlendirmenin, hızı artırmaktan daha etkili olduğunu göstermektedir. En iyi soğutma performansının sırasıyla 316,86-327,75 K ve 316,27-317,46 K sıcaklık değerleri ile hem U hem de Z tipi kanallar için, 30 ve 60 mm giriş konumunda ve 6 m/s hızında olduğu bulunmuştur. Ek olarak, Z-tipi kanalın U-tipi kanaldan yaklaşık %6 daha fazla ısıyı dağıttığı görülmüştür. Çalışmanın sonuçları, EA’larda batarya ısıl yönetim sistemlerinin (BIYS) enerji verimliliğini artırmak için kullanılabilir. Havayı daha düşük hızlarda yönlendirerek, soğutma sisteminin enerji tüketimi azaltılabilir ve gerekli soğutma performansı korunabilir. Bu, sonuçta EA'ların menzilinin artmasına ve performansının gelişmesine yol açacaktır. Ek olarak, çalışma aynı zamanda EA’larda soğutma performansını optimize etmek ve araçların genel enerji verimliliğini artırmak için kullanılabilecek batarya paketi düzeninin tasarımı hakkında da fikir vermektedir.

Experimental and numerical investigations of heat transfer characteristics of vertical falling film heat exchanger in data center cabinets

To reduce the energy consumption in data centers, this paper proposes a novel structure that integrates a cabinet with a vertical falling film heat exchanger in data center to perform natural evaporative cooling. First, an experimental setup is built to verify the heat and mass transfer characteristics of a falling film in a vertical tube and to obtain the mass transfer coefficient 0.05. Then, the characteristics of tube length direction and heat and mass transfer are analyzed using compiled user-defined functions for different parameters of moist air and water in the tube. The maximum growth rates of heat transfer coefficient and mass transfer rate are 67.65% and 55.23% at increasing inlet moist air Rema,i, respectively. Finally, the heat transfer characteristics of the falling film heat exchanger with staggered and in-line are compared for inlet air velocities in the range of 1–3.5 m·s−1. The corresponding results demonstrate that the heat flow rate, heat transfer coefficient, and overall heat transfer performance PEC of the staggered are better than those of the in-line as the inlet air velocity of the heat exchanger continues to increase. The maximum PEC of the staggered heat exchangers is 40.07% higher than that of the in-line heat exchangers.

Hybrid battery thermal management by coupling fin intensified phase change material with air cooling

Phase change material (PCM) based passive battery thermal management (BTMS) is a promising strategy for controlling lithium-ion battery temperature during operation. However, the drawbacks of low thermal conductivity and poor secondary heat dissipation of PCM still need to be addressed. Herein, the metal fin intensified PCM system coupling with air cooling is proposed for battery thermal management. The effects of PCM thickness, metal fin diameter and number, air inlet velocity, and airflow temperature on the performance of the proposed BTMS are numerically investigated. Results indicate that the novel hybrid BTMS exhibits a superior cooling performance than fin-air BTMS without PCM and PCM-air BTMS without fins, reducing the maximum battery temperature by 18.6% and 3.2%, respectively. The embedded fins can improve the heat dissipation of the battery and PCM. Increasing air velocity can help recover the PCM latent heat but consume additional power. The proposed BTMS is investigated and optimized considering the cooling performance and power consumption tradeoff. The optimal design has a 1.0mm PCM thickness, 162fin numbers, and a 3.0mm fin diameter. Under such an optimal design, battery temperature can be controlled below the desired value of 40°C with less power consumption. The run-out of PCM latent heat is also effectively prevented in continuous cycle operation with an air velocity of 2.0m/s. This study can provide new insights into an advanced BTMS design for next-generation battery systems with high charging and discharging rates.