Study of Flow and Heat Transfer in an Ejector-Driven Swirl Anti-Icing Chamber

The formation of ice on the leading edge of aircraft engines is a serious issue,as it can have catastrophic consequences.The Swirl Anti-Icing(SAI)system,driven by ejection,circulates hot fluid within a 360°annular chamber to heat the engine inlet lip surface and prevent icing.This study employs a validated Computational Fluid Dynamics(CFD)approach to study the impact of key geometric parameters of this system on flow and heat transfer characteristics within the anti-icing chamber.Additionally,the entropy generation rate and exergy efficiency are analyzed to assess the energy utilization in the system.The research findings indicate that,within the considered flow range,reducing the nozzle specific areaφfrom 0.03061 to 0.01083 can enhance the ejection coefficient by over 60.7%.This enhancement increases the air circulating rate,thereby intensifying convective heat transfer within the SAI chamber.However,the reduction inφalso leads to a significant increase in the required bleed air pressure and a higher entropy generation rate,indicating lower exergy efficiency.The nozzle angleθnotably affects the distribution of hot and cold spots on the lip surface of the SAI chamber.Increasingθfrom 0°to 20°reduces the maximum temperature difference on the anti-icing chamber surface by 60 K.

Thermal Feature Analysis of a New Hot-Air Anti-Icing Structure

Ice accretion on surfaces of the aircraft and engine is a serious threat to the flight safety.In this paper,a novel hot air anti-icing method is proposed based on the porous foam.Taking the NACA0012 airfoil as an example,the traditional thermal protection structure is proved to exist the deficiency in balancing the heat exchange caused by route loss of the heat.By dividing the hot chamber into multiple regions to fill with various foam metal,flow resistance characteristics and heat transfer characteristics for this protection mode are analyzed in order to derive the maximized benefit in anti-icing process.The calculation results reveal that,under the same condition,the region filled with foamed copper not only improves the temperature uniformity on the anti-icing area,but also achieves a better protection effect for enhancing heat transfer between the tube and the hot gas,averagely above 20℃higher than it without porous foam filling in surface temperature.Additionally,the minimum mass flow rate of the protection hot air is reduced by 16.7%.The gratifying efficiency of the porous filler in fortifying heat transfer confirms the potential of replacing the efficient but complex heat transfer design with simple structure filled with foam metal.

Hot air treatment activates defense responses and induces resistance against Botrytis cinerea in strawberry fruit

The effect of hot air（HA, 45°C, 3.5 h） treatment on reducing gray mold caused by Botrytis cinerea in strawberry fruit and the possible mechanisms were investigated. The results showed that HA treatment significantly reduced lesion diameter and enhanced activities of chitinase（CHI）, β-1,3-glucanase and phenylalanine ammonia-lyase（PAL） in strawberry fruit. Total phenolic contents were also increased by HA treatment. The activities of antioxidant enzymes including superoxide dismutase（SOD）, catalase（CAT） and ascorbate peroxidase（APX） were higher in HA treated strawberry fruit than those in control. Expression of three defense related genes such as CAT, CCR-1 allele and PLA6 was greatly induced in HA treated strawberry fruit with or without inoculation by B. cinerea. In addition, the in vitro experiment showed that HA treatment inhibited spore germination and tube growth of B. cinerea. These results suggested that HA treatment directly activated disease resistance against B. cinerea in strawberry fruit without priming response and directly inhibiting growth of B. cinerea.

Comparative studies on the hot corrosion behavior of air plasma spray and high velocity oxygen fuel coated Co-based L605 superalloys in a gas turbine environment

An improvement in the corrosion resistance of alloys at elevated temperature is a factor for their potential use in gas turbines. In this study, Co Ni Cr Al Y has been coated on the L605 alloy using air plasma spray(APS) and high-velocity oxygen fuel(HVOF) coating techniques to enhance its corrosion resistance. Hot corrosion studies were conducted on uncoated and coated samples in a molten salt environment at 850°C under cyclic conditions. Thermogravimetric analysis was used to determine the corrosion kinetics. The samples were subjected to scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction for further investigation. In coated samples, the formation of Al2O3 and Cr2O3 in the coating acts as a diffusion barrier that could resists the inward movement of the corrosive species present in the molten salt. Coated samples showed very less spallation, lower weight gain, less porosity, and internal oxidation as compared to uncoated sample.HVOF-coated sample showed greater corrosion resistance and inferred that this is the best technique under these conditions.

Mathematical Modeling and Effect of Various Hot-Air Drying on Mushroom(Lentinus edodes)

An experimental study was performed to determine the characteristics and drying process of mushroom （Lentinus edodes） by 6 different hot-air drying methods namely isothermal drying, uniform raise drying, non-uniform raise drying, uniform intermittent drying, non-uniform intermittent drying and combined drying. The chemical composition （dry matter, ash, crude protein, crude fat, total sugars, dietary fiber, and energy）, color parameters （L, a＊, b＊, c＊, and h~） and rehydration capacities were determined. Among all the experiments, non-uniform intermittent drying reached a better comprehensive results due to the higher chemical composition, better color quality associated with high bright （26.381＋5.842）, high color tone （73.670＋2.975）, low chroma （13.349a：3.456） as well as the highest rehydration （453.76% weigh of dried body）. Nine kinds of classical mathematical model were used to obtained moisture data and the Midili-kucuk model can be described by the drying process with the coefficient （R2 ranged from 0.99790 to 0.99967）, chi-square （X2 ranged from 0.00003 to 0.00019） and root mean square error （RMSE ranged from 0.000486 to 0.0012367）.

Influence of hot air sintering on dioxin emission

Sintering pot tests with hot air were conducted. Air recovery from exhaust gas from the sintering plant. The effects was heated by using a resistance furnace to simulate heat of the process parameters, such as temperature of hot air, oxygen enrichment, coke consumption and bed depth, on quality of products, energy consumption and dioxin emission were investigated. Good results were obtained under the following conditions ： 200℃ hot air, no oxygen enrichment, lime with high CaO, thinner bed and addition of accelerant.

An Experimental Study on the Performance of Storage Pulverizing System after Renovation of Importing Hot Air

A thermal power plant of Sinopec has 9 boilers, which generally have problems of high exhaust gas temperature and high flying ash carbon content. In order to improve the adaptability of coals, the stability of coal powder ignition, the burn-off rate of pulverized coals and the boiler efficiency, a series of renovation projects about importing hot air into mill exhauster are proposed. For the sake of verifying the renovation effects, an efficiency performance test is conducted on the renovated #5 boiler. The test result shows that the boiler heat efficiency has improved by 0.4% and it operates more safely and reliably after the renovation. At last, this paper recommends an optimized operation mode.

Effects of Chemical Osmotic Pretreatment on Drying Characteristics and Quality of Blueberry under Hot Air Drying

In order to study the effects of chemical osmotic pretreatment on the characteristics and quality of blueberry under hot air drying,fresh blueberries were pretreated with 2.5 g/100 mL K2CO3+0.6 g/100 mL olive oil,and 5.0 g/100 mL K2CO3+0.6 g/100 mL olive oil at(45±0.5)℃,respectively.The changes of water content,rehydration,hardness,microstructure,color difference,active ingredient anthocyanin,total phenol and DPPH radical scavenging capacity of dried blueberries in different treatment groups under hot air drying were compared and analyzed.The results showed that the dehydration rates of blueberries vary greatly according to the type of pretreatments when the samples were dried to the same water content with hot air.Specifically,the dehydration rate of dried blueberries pretreated by 5.0%K2CO3 solution was the highest,followed by 2.5%K2CO3 osmotic pretreatment and lastly the control group;the corresponding dehydration time was 10,14 and 20h,respectively.The physical qualities of dried blueberries,involving the browning degree,color difference,rehydration and microstructure,were significantly different between the chemical osmotic pretreatment group and the control group(P<0.05).The chemical osmotic pretreatment of K2CO3 solution increased the dehydration rate of the samples,shortened the drying time and maintained the quality of blueberries dried with hot air.There was no significant difference between the physical quality of dried blueberries pretreated by 2.5%and 5.0%K2CO3 solution(P>0.05),whereas there was significant difference in drying time and nutrient quality which is characterized by total phenols,anthocyanins,DPPH radical scavenging rate,soluble total sugar(P<0.05).Conclusion:5.0%K2CO3 osmotic pretreatment combining with hot air drying can improve the dehydration rate,shorten the drying time and maintain the physical and nutritional quality.

Artificial neural network techniques to predict the moisture ratio content during hot air drying and vacuum drying of Radix isatidis extract

Background:To predict the moisture ratio of Radix isatidis extract during drying.Methods:Artificial neural networks were designed using the MATLAB neural network toolbox to produce a moisture ratio prediction model of Radix isatidis extract during hot air drying and vacuum drying,where regression values and mean squared error were used as evaluation indexes to optimize the number of hidden layer nodes and determine the topological structure of artificial neural networks model.In addition,the drying curves for the different drying parameters were analyzed.Results:The optimal topological structure of the moisture ratio prediction model for hot air drying and vacuum drying of Radix isatidis extract were“4-9-1”and“5-9-1”respectively,and the regression values between the predicted value and the experimental value is close to 1.This indicates that it has a high prediction accuracy.The moisture ratio gradually decreases with an increase in the drying time,reducing the loading,initial moisture content,increasing the temperature,and pressure can shorten the drying time and improve the drying efficiency.Conclusion:Artificial neural networks technology has the advantages of rapid and accurate prediction,and can provide a theoretical basis and technical support for online prediction during the drying process of the extract.

Animal-Fats Biodiesel as a Heating Fuel for Agricultural Hot Air Heaters

Biodiesel （BD） was made from animal-fats reacting with methanol and potassium hydroxide in the laboratory. The biodiesel made in the laboratory was sent to K-petro, the government agency to inspect the quality of animal-fats biodiesel, of which generally the quality was acceptable for heating oil for agricultural hot air heater. Kinematic viscosity and calorific values of the biodiesels were measured. BD20（K）, kerosene based biodiesel, showed 18 cSt at -20 ~C. It seems that BD100 can not be suitable for heating fuel under some temperature. As BD content increased calorific value decreased up to 40,000 J/g for 100% BD （BD100） while, light oil calorific value was 45,567 J/g, showing difference of 5,567 J/g （about 12% difference）, Several different fuels including BD20 （biodiesel 20% ＋ light oil 80%）, BD50 （biodiesel 50% ＋ light oil 50%）, BD100 （biodiesel 100%） and light oil were prepared and tested for fuel combustion qualities for agricultural hot air heater and their combustion performances were compared and analyzed. Flame dimensions of biodiesels and light oil were almost same shape at the same combustion condition in the burner of the hot air heater. Generally, CO2 amounts of BDs were greater than light oil, but the differences were so small that it is hard to tell there was significant difference between the BDs combustion and light oil.

Measurements of Absolute Atomic Nitrogen Density by Two-Photon Absorption Laser-Induced Fluorescence Spectroscopy in Hot Air Plasma Generated by Microwave Resonant Cavity

For the first time, absolute densities of atomic nitrogen in its ground state (N4S) have been measured in hot dry and humid air plasma columns under post-discharge regime. The determination of space-resolved absolute densities leads to obtain the dissociation degrees of molecular nitrogen in the plasma. The hot plasmas are generated inside an upstream gas-conditioning cell at 600 mbar when the air gas flow is directly injected at 10 slm in a microwave resonant cavity (2.45 GHz, 1 kW) placed in the downstream side. Density measurements based on laser induced fluorescence spectroscopy with two-photon excitation (TALIF), are more particularly performed along the radial and axial positions of the plasma column. Calibration of TALIF signals is performed in situ (i.e. in the same gas-conditioning cell but without plasma) using an air gas mixture containing krypton. Optical emission spectroscopy is considered to estimate the rotational gas temperature by adding a small amount of H2 in dry air to better detect OH (A-X) spectra. The rotational temperatures in humid air plasma column (50% of humidity) are larger than those of dry air plasma column by practically 30% near the nozzle of resonant cavity on the axis of the plasma column. This is partly due to attachment heating processes initiated by water vapor. A maximum of the measured absolute nitrogen density is also observed near the nozzle which is also larger for humid air plasma column. The obtained dissociation degrees of molecular nitrogen in both dry and humid air plasma along the air plasma column are lower than the cases where only thermodynamic equilibrium is assumed. This is characteristic of the absence of chemical and energetic equilibria not yet reached in the air plasma column dominated by recombination processes.

Research and Development of Hot Primary Air Heater for Coal-Fired Boilers in Power Plant

The reasons of introducing cold air into pulverizer are analyzed for boilers with large capacity and high parameters. The temperature rises of the exhaust gas are calculated when varying the amount of the cold air. The hot primary air heater, a new technology, is developed to eliminate the cold air from the pulverized coal system. The applications, advantages and disadvantages are introduced in detail for the new device and system. It is concluded that introducing cold air into pulverizer is one of the major factors that causes the exhaust gas temperature of boilers with large capacity to be high. The amount of the cold air could be reduced signif icantly, even to zero in some cases by adopting the hot primary air heater, which drops the exhaust gas temperature of the boiler effectively. The hot primary air heater, which could play part roles of the steam-air heater or the hot air recirculation system, could also be used to adjust the exhaust gas temperature within the range of 20 ℃ by controlling the flow rate of the cooling medium. Moreover, the startup period of the steam-air heater or the hot air recirculation system will be shortened, which is a unique advantage of the hot primary air heater among the measures to drop the exhaust gas temperature.

Study and Application of W-Flame Boiler Startup Aided by Adjacent Hot Primary Air

In this paper,the designed features of a W-flame coal-fired boiler are introduced.A scheme of joint primary air for two boilers is made and technical measures are also taken based on corresponding analyses and studies.The scheme and the measures provide a reference for technicians to improve the efficiencies and reduce the startup costs of other similar large boilers.

Hot Air Generator Using Natural Convection Flow in a Heated Channel

Hot air producing is one of the most important engineering applications in recent years.It is a technique used in various thermodynamic systems,such as home heating systems,food dryers.One of the main problems impeding the spread of hot air producing technology is the lack of homogeneity of the heat flow coming from hot air generators as well as an inadequate flow rate.The most of the existing hot air generators require to be supported by systems that can increase the low volumetric flow and the air temperature of these generators,through increasing the speed of the flow of air emitted or lifting the drawer Heat,which contributes to raising the overall cost.However,to improve the thermal and dynamic quality of the hot air flow produced by the generator,a numerical investigation of the free convection flow inside two different configurations is presented in this thesis.The primary objective of this work is to predict the behavior of the flow inside tow configurations,the first one consists of a vertical cylinder with heated walls,and the second configuration is an open-ended vertical cylinder with a hot disc placed at the entrance(configuration A,configuration B).This work characterizes through the examination of this flow,the variables that control an air emission with high flow rate and a high and homogeneous temperature to represent the appropriate criteria that should be respected to obtain a hot air generator overcoming the previously mentioned constraints.Furthermore;the results of this work show the influence the boundary conditions and Rayleigh number on the resulting flow.

从hot air谈起

What he said was just a lot of hot air. 若将这句话中的hot air理解成“热空气”就错了,因为它的意思是“大话,吹牛皮”。hot在和其他一些词连用时,也容易引起误解,须根据上下文来认真判断。如:The problem is a hot potato.(这是个棘手的问题。)

苹果丁冷冻-热风联合干燥体积收缩机制

为降低冻干苹果能耗,同时获得具有良好外观的脱水产品,该研究将冷冻-热风联合干燥应用于苹果脱水加工,并从水分迁移角度探究此过程中产品的收缩机制。选取4个水分转换点(干基含水率分别为1.00、0.76、0.53和0.33 g/g)对苹果进行联合干燥处理,并对脱水产品的收缩率、质构特性、微观结构、孔隙分布及样品在热风干燥阶段的水分迁移与分布进行测定及分析。结果表明,联合干燥样品的收缩情况显著(P<0.05)优于单一热风干燥样品,且转换点对样品收缩率影响较大(收缩率6%~45%),当转换点干基含水率低于0.53 g/g时,联合干燥样品没有出现明显的体积收缩现象。随着转换点干基含水率的升高,样品的收缩程度增大,并出现不同程度的中心塌陷,且孔隙率逐渐减小,但相应能耗降低。产品收缩主要发生在热风干燥过程的升速阶段,在此阶段样品自由水含量大幅减少,结合水与不易流动水未发生明显改变,样品内部水分在湿度差的作用下向表面迁移,这是导致联合干燥样品发生体积收缩的关键机制。该研究结果可为冷冻-热风联合干燥高效生产良好外观的脱水苹果提供数据支撑及理论参考。

热风加热沥青路面冲击射流共轭传热特性

为提高热风加热沥青路面的就地再生加热效果,基于热风冲击射流对流换热和沥青路面内部导热的共轭传热过程,建立了热风加热沥青路面的冲击射流共轭传热理论模型,选取有限容积法得到了共轭传热模型的通用离散方程,采用压力-速度耦合半隐式算法(semi-implicit method for pressure linked equations,SIMPLE)获得了整个求解域内温度场分布,选取平均热流密度和平均换热系数反映沥青路面加热效果,通过正交试验研究了热风出口速度和热风出口温度对路面加热效果的影响程度。仿真和试验结果表明:理论计算与实验温度场分布趋势吻合度高,两者平均误差为8.4%;平均热流密度和平均换热系数在加热初期均从最大值急剧下降,而后下降幅度逐渐减小趋于平衡,两者的仿真计算与实验结果趋势相同,平均误差分别为6.4%和7.8%;热风出口速度和热风出口温度对平均热流密度均有显著影响,热风出口速度对平均换热系数有显著影响,热风出口温度对平均换热系数的影响相较于平均热流密度指标表现为不显著。研究结果为后续沥青路面就地热再生热风加热温度控制和加热器设计提供了理论依据。

辣椒的干燥特性和力学性能试验研究

为了降低辣椒在干燥及运输过程中的破损率,提高辣椒的干燥品质,对辣椒进行热风干燥的同时,进行拉伸和三点弯曲力学性能试验研究,并分析了辣椒的干燥特性和力学特性。试验结果表明:当干燥温度为45、60、75℃时,水分有效扩散系数分别为1.160096×10^(-10)、1.713660×10^(-10)、2.380429×10^(-10),随温度升高而升高。由阿伦尼乌斯公式计算得出辣椒活化能为22.0769kJ/mol,表明干燥过程中从辣椒中出去1mol的水分所需的最低能量是22.0769kJ。在75℃干燥温度下的辣椒拉伸力学性能试验中,随着加热时间的增加,平均最大载荷不断增大,加热300min后平均最大载荷曲线开始下降与前面干燥特性吻合,表明辣椒在前300min快速升温,降水速度快,表面自由水失去多,整体韧性增强导致所需载荷增大,干燥后期辣椒含水率较低,脆性增加,拉伸所需最大载荷降低;45℃干燥温度下,随着加热时间的增加,平均最大载荷变化不大。在不同含水率辣椒的三点弯曲试验中,含水率为14%时最大承受载荷约为3.5N,含水率为10%时最大承受载荷为约2.5N,含水率为6%时最大承受载荷约为1.1N,表明随着含水率的减小辣椒所能承受的最大载荷和压缩位移逐渐减小,辣椒抗压能力下降。研究结果可为提高辣椒干燥品质、降低运输过程中的破损提供理论依据。

铁棍山药片热风干燥过程中传热传质规律

[目的]探明热风干燥过程中铁棍山药片的传质情况,以及干燥空间和山药片的传热情况。[方法]选用7种薄层干燥数学模型对山药片热风干燥曲线进行拟合,找出最适传质动力学模型;测定不同温度下山药的导热系数和比热容,在此基础上利用ANSYS软件模拟热风干燥过程中干燥空间温度场变化和山药片温度变化。[结果]Modified Page模型能准确预测不同热风温度条件下山药片的水分变化情况(R2为0.998 96~0.999 86)。热风干燥过程中干燥室空间温度总体呈水平面上距进出风口近处温度高,远处温度稍低,竖直面上呈上高下低的状态,但温差均不大。热风干燥过程中山药片中心处温度最低,外表面温度最高,内外层温差逐渐缩小,前期温度变化较快而后期缓慢,实测值与模拟值间的温差最大达7.75℃,最小仅为0.07℃,说明模拟结果准确度较高。[结论]Modified Page模型和ANSYS软件能够准确模拟热风干燥过程中山药片的传热传质。

牛大力热风干燥工艺参数优化

热风干燥有利于提高鲜制牛大力干燥时的干燥速率和产品品质。为此,对新鲜的牛大力进行单因素热风干燥实验,结果表明:干燥过程中热风温度越高、切片厚度越薄时,牛大力的干燥速率越快;而热风温度过高时,牛大力切片表面会发生褐化和裂纹。结合响应面优化分析方法,建立各因素与指标值之间的回归分析模型。由响应面优化分析和实验结果可知:当热风温度为50~60℃、切片厚度为3~7 mm和热风风速为0.5~1.5 m/s时,牛大力热风干燥的最佳干燥参数为:热风温度60℃,切片厚度5 mm,热风风速1.116 m/s。