Heat Flow Characteristics Research Articles

곡면 델타 윙렛 와류발생기를 이용한 핀 휜의 열전달 및 유동 특성 개선

A numerical analysis was carried out to investigate the effects of curved delta winglet vortex generator on the heat transfer and flow characteristics of pin fin arrays. The steady RANS simulation has been performed with κ-ω SST turbulence model by using Fluent 18.0. The effects of the curved delta winglet vortex generators installed upstream of each pin of the staggered array 8 row pins were confirmed, and the cases where the curved delta winglet vortex generators were located on one endwall(Case 1) and on both endwalls(Case 2) were considered. The results showed that the curved delta winglet vortex generators induce the generation of mixed vortices that reduce the size of the wake region of the pin and improve the heat transfer of the pins. In addition, the pressure loss is reduced due to the effect of decreasing the size of wake occurring in the pin, and this tendency becomes stronger as the Reynolds number increases. As a result, the thermal performance factor(η) increases according to the Reynolds number, and when the Reynolds number is 30000, η of Case 1 and Case 2 increased by 11.3% and 12.2%, respectively, compared to the baseline.

Performance improvement and thermodynamic assessment of microchannel heat sink with different types of ribs and cones

The present study aims to investigate the performance of microchannel heat sink via numerical simulations, based on the first and second law of thermodynamics. The heat transfer and flow characteristics of rectangular microchannel heat sinks have been improved by adding six different types of surface enhancers. The cross-sections include rectangular, triangular, and hexagonal-shaped ribs and cones. The cones have been created from the same cross-sections of ribs by drafting them at an angle of 45° orthogonal to the base, which is expected to decrease the pressure drop, dramatically. The performance of ribs and cones has been evaluated using different parameters such as friction factor, wall shear stress, entropy generation rate, augmentation entropy generation number, thermal resistance, and transport efficiency of thermal energy. The results of the present study revealed that the novel effect of coning at an angle of 45° reduces frictional losses (Maximum pressure drop reduced is 85%), however; a compromise on thermal behavior has been shown (Maximum Nusselt number reduced is 25%). Similarly, the application of coning has caused a significant reduction in wall shear stress and friction factor which can lead to reducing the pumping power requirements. Moreover, triangular ribs have more ability to transfer thermal energy than rectangular and hexagonal ribs. Furthermore, it has been examined in the present study that the trend of total entropy generation rate for triangular ribs decreases up to Re = 400 and then increases onwards which means that thermal losses are more significant than frictional losses at lower Reynolds number. However, frictional losses dominate over thermal losses at higher Reynolds numbers, where vortex generation takes place, especially in triangular ribs.

Experimental Investigation of Heat Transfer and Flow Characteristics of Split Natural Cooling System for Data Center Based on Micro Heat Pipe Array

This paper presents a new type of split natural cooling system that maximizes the use of natural cold energy to significantly reduce the power consumption of the air conditioning system in data centers. A split natural cooling system module, which consisted of indoor and outdoor heat exchanger based on micro heat pipe arrays connected by liquid circulation system, was selected for experimental research. The heat transfer process and flow characteristics were analyzed under different outdoor environment temperatures, air and water flow rates, and different ratios of heat transfer components (N) of indoor and outdoor heat exchangers. To improve the utilization of natural cold energy, two kinds of heat dissipation conditions, namely room and heat channel-based, were proposed. The indoor temperature of two conditions at 28 °C and 38 °C were simulated in the laboratory at constant temperature-humidity, respectively. Results indicated that the air flow rate had a greater influence on the heat transfer performance than the water flow rate. The pressure drop of the air and water sides was at a lower level, and the fitting curve of the pressure drop was obtained to provide a reference for the heat exchanger design and equipment selection. When the ratio of heat transfer components (N) of the indoor and outdoor heat exchanger was approximately 0.75, the split natural cooling system showed optimal comprehensive performance. Under heat channel-based conditions, the maximum heat transfer rate reached 12.4 kW, and the maximum energy efficiency ratio was 17.15; the maximum heat transfer rate and the maximum energy efficiency ratio increased by 42.5% and 22.64% compared with the room-based condition, respectively. The fitting curve of the energy efficiency ratio was calculated under different outdoor temperatures at two heat dissipation conditions.

Numerical analysis of heat transfer and flow characteristics of a precooler with a methanol cracking reaction

For hydrocarbon-fueled turbojet engines with a precooling technology, the precooling technology with a low-temperature endothermic fuel is a great potential way to solve the problem of sharp reduction of the specific impulse caused by the insufficient heat sink of the hydrocarbon fuel. To study the heat transfer and flow characteristics of a precooler with a fuel endothermic reaction, methanol is chosen as the low-temperature endothermic fuel, and the numerical model of a precooler of tube bank arranged in-line is built, which considers the methanol with a cracking reaction. The results indicate that the methanol cracking reaction can enhance the cooling effect to the air by increasing the heat transfer temperature difference. When the cracking rate is not more than 20%, the cooling effect to the air increases and the cracking rate decreases with the methanol mass flow rate. When the longitudinal pitch-to-diameter ratio varies between 1.25 and 2.50, the cooling effect and the cracking rate increase with its increase, which is not conducive to the compactness of the precooler. When the transverse pitch-to-diameter ratio varies between 1.25 and 2.00, the cooling effect and cracking rate increase with its decrease but bring significant pressure loss.

Research on Fault Diagnosis of Switchgear Based on Temperature Cloud Image Technology

In the process of power system operation, contact aging, partial discharge and overcurrent faults are the main causes of switch cabinet faults. At the same time, it is difficult to install sensors inside the switch cabinet due to its closed operation. In this paper, in order to solve the over current problem of switchgear, according to the principle of high current heating, the thermal flow model of power switchgear is established, and the characteristics of heat flow inside the switchgear are studied. The infrared temperature detector is designed to collect the surface temperature cloud map of the switchgear. Combined with the internal heat flow law of the switchgear, the over current phenomenon in the switchgear is judged, so as to judge the operation state of the switchgear. In order to verify the correctness of the theory proposed in this paper, the operation state of the fault switch cabinet is designed for detection and comparative analysis. The test results show that the heat change caused by the over-current fault can be accurately fed back to the surface of the switch cabinet, which can be used as an effective means to diagnose the fault of the switch cabinet.

Heat Flow Characteristics of Ferrofluid in Magnetic Field Patterns for Electric Vehicle Power Electronics Cooling

The ferrofluid is a kind of nanofluid that has magnetization properties in addition to excellent thermophysical properties, which has resulted in an effective performance trend in cooling applications. In the present study, experiments are conducted to investigate the heat flow characteristics of ferrofluid based on thermomagnetic convection under the influence of different magnetic field patterns. The temperature and heat dissipation characteristics are compared for ferrofluid under the influence of no-magnet, I, L, and T magnetic field patterns. The results reveal that the heat gets accumulated within ferrofluid near the heating part in the case of no magnet, whereas the heat flows through ferrofluid under the influence of different magnetic field patterns without any external force. Owing to the thermomagnetic convection characteristic of ferrofluid, the heat dissipates from the heating block and reaches the cooling block by following the path of the I magnetic field pattern. However, in the case of the L and T magnetic field patterns, the thermomagnetic convection characteristic of ferrofluid drives the heat from the heating block to the endpoint location of the pattern instead of the cooling block. The asymmetrical heat dissipation in the case of the L magnetic field pattern and the symmetrical heat dissipation in the case of the T magnetic field pattern are observed following the magnetization path of ferrofluid in the respective cases. The results confirm that the direction of heat flow could be controlled based on the type of magnetic field pattern and its path by utilizing the thermomagnetic behavior of ferrofluid. The proposed lab-scale experimental set-up and results database could be utilized to design an automatic energy transport system for the cooling of power conversion devices in electric vehicles.

The flow and heat transfer characteristics of DPF porous media with different structures based on LBM

AbstractTo study the flow and heat transfer characteristics of diesel particulate filter wall porous media, Lattice Boltzmann Method (LBM) is used to simulate and analyze different structures in this article. On studying the heat transfer and flow characteristics of regular structures such as parallel and staggered structures, it is proved that the distribution of porous media structure has an effect on the heat transfer and flow characteristics. The effects of different structure distributions on the flow and heat transfer characteristics are analyzed by studying the complex structures such as random structure and the structure of Quartet Structure Generation Set (QSGS). The influences of different fiber diameters on the parameters under the parallel arrangement, the staggered arrangement, and the random arrangement is considered. The flow and heat transfer characteristics of the QSGS structure and Sierpinski carpets structure are also considered. Under the same porosity, different fiber diameters have effect on dimensionless permeability coefficient, pressure gradient, and filtration efficiency. The different structures of porous media affect the temperature and pressure distribution. For the relatively complex structure, the flow resistance is greater. The increase in Re will reduce the temperature gradient, and with the increase in Re, the flow in the structure will be more uniform.

Comparative Assessment of Different Turbulence Models to Estimate Thermo-Fluid Characteristics of an Infrared Suppression (IRS) Device

AbstractThe accurate computation to predict the heat transfer and flow characteristics in an IRS system is challenging because of the complex designs of thermo-fluid dynamics, such as the entrainment of cold atmospheric air and mixing with the hot exhaust from the gas turbine housed in naval or cargo ships. This study considers the IRS device with four cylindrical funnels stacked one above the other. This study aims to find the suitable turbulence model(s) for numerical modeling of the IRS device. The Reynolds number based on the nozzle diameter is varied between 3527 and 7231 (laboratory-scale) and 4×105 to 5×105 (real-scale) as per the availability of the experimental data. Eight turbulence models, viz., standard k−ε, RNG k−ε (with standard wall function and enhanced wall functions), realizable k−ε, low Reynold number (LRN) Launder-Sharma k−ε, low Reynold number (LRN) Yang-Shi k−ε, standard k−ω, k−ω SST, v2−f are used to model the complex entrainment and mixing process inside the IRS device. The LRN-LS model estimates the thermos-fluid dynamics quite accurately for the lower Reynolds number range (laboratory-scale IRS), and SST k−ω model predicts accurately for higher Reynolds number values (real-scale IRS). We believe that the present study would help further the numerical modeling of IRS devices.

Numerical investigation on heat transfer and flow characteristics of supercritical methane in a horizontal tube

The main component of liquefied natural gas (LNG) is methane. The regasification process of LNG is usually under a supercritical condition. In this paper, a three-dimensional model is established to study the heat transfer and flow mechanism of supercritical methane in a heating process. The special physical properties of supercritical methane are compiled and imported through user-defined database. The standard k–ε model with the standard wall function is selected for simulation. The results show that deterioration of heat transfer occurs on the upper surface of the channel, which is most evident when the bulk temperature approaches the pseudocritical temperature. And the heat transfer coefficient increases first and then decreases along the channel with the bulk temperature rising. The peak value appears near the pseudocritical temperature. The pressure also has a great influence on heat transfer and flow. Besides, the buoyancy effect is strong near the pseudocritical point, leading to nonuniform distribution of temperature and density on the cross section, and causing significant radial circulation. The heat transfer deterioration can be effectively reduced by using special structures such as fins to hinder the buoyancy.

Investigation of thermohydraulic characteristics of a novel triple concentric pipe minichannel heat exchanger

In this paper, a novel triple concentric pipe minichannel heat exchanger (TCPMHE) is presented and built, which is a combination of concentric pipe heat exchanger and minichannel heat transfer technology. A range of experimental investigations are further systematically performed by varying the volume flow rate of hot water (Vh), inner annulus size (Si) and hot fluid inlet temperature (th, i) to evaluate the heat transfer and flow characteristics of TCPMHE. And the results are comprehensively compared with the double concentric pipe minichannel heat exchanger (DCPMHE), aiming to offer some references for the concentric pipe heat exchanger and minichannel heat transfer technology in further industry application. Results indicate that the friction factor (f) values for both DCPMHE and TCPMHE are almost equal under the same operating conditions. Although the Nusselt number (Nu) values of DCPMHE are 21.8%-50.7% higher than those of TCPMHE, the effectiveness (ε) values of TCPMHE are all much higher than those of DCPMHE under the same conditions, and the enhancing factor (η) ranges from 1.45 to 1.65. Compared with the DCPMHE, the volumetric heat transfer capacity of the TCPMHE is improved by up to 65.4% at Si = 0.5 mm, th,i = 60 ℃ and Vh = 209 L·h−1. In addition, the dimensionless correlations for inner annulus hot fluid Nu, ε, and f of TCPMHE were established, and the maximum deviations are ± 8%, ± 5% and ± 11% for Nu, f, and ε, respectively, which indicates that the predicted values from the correlations agree well with the measured results.

Assessment of thermal performance of hybrid nanofluid flow in a tilted porous enclosure by imposing partial magnetic fields

A novel approach of implementation of a partial active magnetic field in a slanting porous cavity packed with hybrid nanofluid has a significant influence on the various types of passive controlling of the transport phenomena. The magnetohydrodynamic (MHD) flow coupled with other multiphysics comes across widespread applications in health and medical science, electronics, others. Imposing magnetic field, treatment of tumor tissues is a promising technique, which needs an in-depth analysis of thermal performance. In this context, the present study explores a novel implementation of the partial magnetic field induced on a differentially heated inclined porous square enclosure containing Cu−Al2O3/water hybrid nanofluid. The partial magnetic field is imposed using varying effective width and the allocation impacts of this partial magnetic field on the inclined cavity have been investigated systematically. The width, as well as positional impacts of the applied partial magnetic fields, has been scrutinized thoroughly. The coupled transport equations are used for the solution by the finite volume technique (FVM) for a selective range of variables like Darcy-Rayleigh number (Ram), Hartmann number (Ha), Darcy number (Da), the concentration of hybrid nanofluid (ζ) and cavity angle (γ). The investigation exposes that the partial magnetic fields with cavity inclination have substantial effects on the heat transport mechanism. The study indicates that adjusting the position and width of the imposed magnetic fields, cavity angle, and involved pertinent parameters can significantly modulate the local as well as global transport phenomena under the multi-physical scenario. This technique allows less reduction in heat transfer, which is ∼15% (with partial magnetic field) and ∼30% (with whole domain magnetic field) relative to the no-magnetic field. Highlights The impact of a partially active magnetic field on thermal convection in a typical porous inclined cavity packed with a hybrid nanofluid is analyzed. The positional shifting and width of the spatially active magnetic field for the various parameters are illustrated using streamlines, isotherms, heatlines, and Nusselt numbers. The orientation of the enclosure under the partial magnetic fields significantly alters the overall thermal performance of the enclosure. The magnetic field intensity, porous structure permeability, volume concentrations of hybrid nanoparticles comprehensively persuade fluid and heat flow features. With this technique reduction in heat transfer is less, which is ∼ 15% (with partial magnetic field), and ∼ 30% (with whole domain magnetic field) relative to the no-magnetic field.

Heat Transfer of Ferrofluid in Fluted Tubes with an Electromagnetic Field

The present study considers the effects of the electromagnetic field and pulsating flow on nanofluids heat transfer and flow characteristics in the three-start helically fluted tube. The experiments are performed using anofluids with the Reynolds number varying from 8000 to 13000, and with an Fe3O4/water nanofluids (Ferrofluid) concentration of 0.005% by volume with and without an electromagnetic field effect. The measured results are verified with the predicted results from the proposed correlations and the published experimental results. As a result of the disturbed flow boundary layer, higher swirling Brownian motion, higher local thermal conductivity, and the mixing of turbulent intensity, the heat transfer performance also increases. For a given pulsating flow of 30 Hz, the Nusselt number enhancement increases significantly to 137.7% and 156.7% for the helical depth ratios of 0.028 and 0.093, respectively. The helically fluted tube with a helical depth ratio of 0.093 and a helical pitch ratio of 0.93 yields the highest Nusselt number improvement. The Nusselt number under the electromagnetic field effect increases by 19.0% and 14.4% for the pulsating flow of 30 Hz and 20 Hz, respectively. Finally, a comprehensive evaluation index is applied to estimate thermo-hydraulic performance. It is found that the comprehensive evaluation index increases with the increasing Reynolds number at first and then decreases as the Reynolds number increases further.

Simulation study on optimal structure of circular corrugated finned tube

The heat transfer experiment of circular finned tube is carried out, and the numerical simulation is carried out with the same model and boundary conditions to verify the accuracy of the model. The heat transfer and flow characteristics on the air side of staggered corrugated finned tubes and equidistant corrugated finned tubes are simulated. The relationships between the number of corrugations, the height of corrugations and the air heat transfer and pressure drop on the shell side are obtained. The results show that the corrugated finned tube with optimized structure will achieve beneficial results instead of the flat finned tube, and the equidistant corrugated finned tube is better than the staggered corrugated finned tube.

Numerical study on enhanced heat transfer and flow characteristics of supercritical hydrogen rocket engine's chamber wall using cylindrical ribs structure

One of the most critical issues in supersonic flight is the thermal protection of the rocket engine combustion chamber. The ribs' construction can improve heat transfer and coolant flow characteristics significantly. Ansys fluent was used to investigate the supercritical hydrogen fuel flow and heat transfer characteristics. Ribs spacing of 10 mm, 5 mm, and 2.5 mm were compared to determine the optimal spacing required to achieve maximum cooling influence and lower pressure drop to safeguard the overheated structure and lower the temperature of the walls. Compared to the smooth channel, the thermal performance factor and pressure drop of the 5 mm spacing increased by 32.5% and 16.64%, respectively, while the maximum temperature reduced by 12.07%. Therefore, the cylindrical rib construction with a 5 mm spacing is perfect for improving heat transfer, has acceptable pressure drops, and reduces thermal stratification inside the channel.

Rheological Modeling of Metallic Oxide Nanoparticles Containing Non-Newtonian Nanofluids and Potential Investigation of Heat and Mass Flow Characteristics.

Nanofluids have great potential due to their improved properties that make them useful for addressing various industrial and engineering problems. In order to use nanofluids on an industrial scale, it is first important to discuss their rheological behavior in relation to heat transfer aspects. In the current study, the flow characteristics of nanofluids are discussed using a mathematical model that is developed by fundamental laws and experimental data. The data are collected in the form of viscosity versus shear rate for different homogeneous ethylene glycol- (EG) based nanofluids, which are synthesized by dispersing 5–20% nanoparticle concentrations of SiO2, MgO, and TiO2 with diameters of (20–30 nm, 60–70 nm), (20 nm, 40 nm), and (30 nm, 50 nm), respectively. The data are fitted into a rheological power-law model and further used to govern equations of a physical problem. The problem is simplified into ordinary differential equations by using a boundary layer and similarity transformations and then solved through the numerical Runge–Kutta (RK) method. The obtained results in the form of velocity and temperature profiles at different nanoparticle concentrations and diameters are displayed graphically for discussion. Furthermore, displacement and momentum thicknesses are computed numerically to explain boundary-layer growth. The results show that the velocity profile is reduced and the temperature profile is raised by increasing the nanoparticle concentration. Conversely, the velocity profile is increased and the temperature profile is decreased by increasing the nanoparticle diameter. The results of the present investigation regarding heat and mass flow behavior will help engineers design equipment and improve the efficacy and economy of the overall process in the industry.

Effect of side-wall ribs on heat transfer and flow characteristics in internal cooling passage of gas turbine blade

Abstract The effect of the side-wall ribs on the heat transfer and flow characteristics in the blade internal cooling passage was conducted by both experiments and CFD calculations, and its optimal shape, arrangement and further development were investigated. It is necessary for the side-wall ribs to optimize the shape for the purpose of not increasing the total pressure loss as much as possible. In this study, Λ and V shaped side-wall ribs with aspect ratio of 1.0 were numerically and experimentally investigated. In addition, with the aim of reducing the total pressure loss, the side-wall ribs with slit which were modified by removing the central part of the Λ and V shaped ribs and those combinations were investigated. As a result, it was confirmed that the combination of V and V shaped with slit were promising and multi-objective optimization using a genetic algorithm was conducted for it. The design parameters were the angle of attack (AoA) for both V shaped with slit and V shaped side-wall ribs, the slit width of V shaped and the height of ribs. The objective functions were Nusselt number, total pressure loss coefficient and thermal performance. The optimized shape has the highest thermal performance, although there exists a strong trade-off relationship between heat transfer coefficient and total pressure loss coefficient. Moreover, the effect of aspect ratio was investigated with considering the vortices distributions in the three-dimensional space. In this study, two kinds of aspect ratio, W/H=0.5 and 2.0 were numerically investigated. As a result, it was found that W/H=0.5 is the best with respect to thermal performance due to pressure loss reduction because the interaction of vortices were suppressed. In conclusion, the side-wall ribs promote the reattachment of separated cooling air flow and the high heat transfer coefficient region can be expanded and the thermal performance can be improved.

Heat Transfer Characteristics and Pressure Drop of U-type Channel in Vacuum Distillation Process for Titanium Sponge

Blockage of the U-type channel exacerbates the intermittency of production, and clarifying the channel heat transfer characteristics and pressure drop is an effective way to address this problem. The channel heat transfer and flow characteristics of the fluid in the channel are experimentally investigated in this study. According to the experiments, the heat transfer coefficient is between 59.95 and 200.29 W/m2⋅K and increases with the flow velocity and fluid temperature. Because the pressure drop is usually accompanied by a change in the energy loss of the fluid, the energy loss is evaluated experimentally. The results demonstrate that the friction loss in the straight tube section accounts for 80% of the energy loss. A bent tube of 90° is recommended instead of a right-angle tube to reduce the pressure drop. A dimensionless relation regarding the Nusselt number is presented to predict the heat transfer characteristics. We provided proposals to address the problem of blockage of the U-type channel, this is helpful to reduce production energy consumption and improve the quality of titanium sponge.

Heat transfer and flow characteristics of straight-type PCHEs with rectangular channels of different widths

Printed circuit heat exchanger (PCHE) is considered to be the most promising heat exchangers in the supercritical CO2 Brayton cycle. The heat transfer and flow characteristics in straight-type PCHEs with rectangular channels of different widths were numerically investigated in this paper. With the increase of rectangular channel width, the average heat transfer coefficients in the cold side decrease first and then increase, while the average heat transfer coefficients in the hot side always increase. The increase of rectangular channel width can effectively increase the heat transfer rate per unit volume and reduce the pressure drop at the same mass flux. However, the changes of heat transfer rate per unit volume and pressure drop tend to be gentle with the width increase. Furthermore, the overall performance evaluation of PCHEs with rectangular channels of different widths was performed. The overall performance evaluations of rectangular channels in the hot side of PCHEs are enhanced compared with the semicircular channel, and the enhancement becomes more and more significant with the increase of mass flux. While the overall performance evaluations of the rectangular channels in the cold side are not as good as that of the semicircular channel. The channel width should be appropriately increased in the hot channel design of straight-type PCHEs to reduce flow resistance and improve overall performance evaluation. The sharp corners of the PCHE channel cross-sections should be eliminated to reduce the heat transfer deterioration zone.

Numerical investigation of 2D double-diffusive convection in rectangular cavities with different aspect ratios: Heat and mass transfer and flow characteristics

In this paper, the dynamical behavior of two-dimensional double-diffusive convection is numerically investigated using a high-accuracy numerical method. The process of flow transition in the presence of buoyancy is studied in detail, and the effects of the fluid properties and geometric parameters on the flow characteristics and heat and mass transfer are discussed. The results show that, as the buoyancy ratio increases from 0 to 2, the flow undergoes a complex series of transitions, from a steady, temperature-dominated state to periodic motion, then chaotic motion, back to periodic motion, and finally back to a steady, concentration-dominated state. At a fixed buoyancy ratio, when the Prandtl number Pr is less than 1, the flow changes from periodic or chaotic to steady with increasing Pr, and the heat and mass transfer efficiencies oscillate with an increasing trend. When Pr≥1, the flow is steady, and the heat and mass transfer remain nearly constant. For low Rayleigh numbers, the heat and mass transfer efficiencies increase monotonically with increasing Lewis number, but the flow is always in a steady state. For high Rayleigh numbers, the flow transitions from steady to periodic or chaotic via a supercritical Hopf bifurcation with increasing Lewis number, and the heat and mass transfer efficiencies oscillate with an increasing trend. In the range of aspect ratios considered in this study, the heat and mass transfer efficiencies exhibit an overall decay with increasing aspect ratio.

Design and Analysis of a New Cooling Structure for Interior Permanent Magnet Synchronous Motor with Built-in Fan

Aiming at the overheating problem of interior permanent magnet synchronous motor (IPMSM) for compressors due to the limitation of working environment, a new type of IPMSM with built-in fan based on the axial ventilation cooling structure is proposed. Firstly, an axial fan is installed inside the rotor without affecting the electromagnetic performance of motor, and the air velocity distribution and temperature distribution characteristics inside motor are analysed by computational fluid dynamics (CFD). Secondly, the influence of the position of the inlet and outlet on the heat flow distribution is analyzed. Finally, for the problem that the heat dissipation effect of the ventilation slots on casing is not obvious, the ventilation slots are removed and the air outlets are installed on front cover. And the results of heat flow characteristics show that this cooling structure is optimal.