Experimental Study for the Movement of Liquid Droplets on the Surface with Gradient Surface Energy

By using the chemical vapor deposition (CVD), a surface with gradient surface energy is fabricated based on the treated silicon chip. The dodecyltrichlorosilane (C_(12)H_(25)Cl_3Si) and Octrytrichlorosilane (C_(8)H_(17)Cl_3Si) are used as the source of silanization. By using the measurement of sessile drop method, the surface with gradient surface energy was characterized by measuring the contact angle of small water which lied on the surface of the treated silicon chip. The experiment shows the liquid droplets are driven to move from hydrophobic to hydrophilic zone on the gradient surface which is placed horizontally, the diameter of the droplets are 1~3 mm, and the single droplet reached the maximum velocity of up to 0.9 m/s. Based on the experimental results, the mechanical of the movement of the liquid droplet on the gradient surface is researched.     

Analysis of the Temperature Limit of Dynamic Water Intake of Open loop Surface Water Source Heat Pump Systems

Energy consumption of water intake is one of the key factors for energy saving in the application of the open loop surface water heat pump system. An energy efficiency ratio coupling model for open loop surface water source heat pump systems was established on the basis of the energy consumption model for the water intake and the heat pump units. According to energy saving rate and regulation of energy consumption of water intake, dynamic temperature limits of water intake in different water supply temperature of cooling tower and different pump head were proposed so as to find a calculation method of temperature limits of water intake of open loop surface water heat pumps. Moreover, the energy saving rate of surface water source heat pump systems compared with traditional air conditioning systems under various condition was also calculated.     

CONDENSATION HEAT TRANSFER ON THE THREE-DIMENSIONAL EXTENDED SURFACE TUBE ATTACHED BY A POROUS DRAINAGE STRIP

An experimental study was carried out for the condensation heat transfer on the three dimensional extended surface tube attached by a porous drainage strip. The results show that the combination of the three dimensional extended surface and the porous drainage strip is the effective method enhancing condensation heat tiansfer on the horizontal tube. The change of the shape arid depth of the axial grooves results in a 10% vaitation of condensation heal transfer coei ficienls. In the range of the experiments, for aocohol as the working fluid, the enhancement is up to 152%, and for water, 185% as compared with the horizontal low-finned tube.     

Numerical investigation of bubble deformation and flow field characteristics of subcooled boiling during condensation

The mass and energy transfer model of bubble condensation in subcooled boiling flow is established. The bubble condensation process is numerically simulated by VOF model. The bubble deformation and flow field characteristics are also obtained. The result agrees well with previous results. The results indicate that bubble shapes will change and are significantly influenced by the bubble initial diameter and the subcooled degree in condensation process. The bubble deformation will appear more sharply with increasing subcooled degree or initial diameter. The bubble will break when the subcooled degree and initial diameter reach a certain value at later phase.     

槽式太阳能集热器传热模型及性能分析

槽式太阳能集热器一维和二维传热数学模型是一组非线性代数方程,为改进求解的稳定性和计算精度,将槽式太阳能集热器一维和二维传热模型的求解看作有约束优化问题,建立了集热器传热过程求解的有约束优化数学模型,应用MATLAB软件优化函数fmincon进行求解。分析了传热流体入口温度及太阳能辐射热流密度变化对集热器性能的影响。采用fmincon函数求解集热器传热过程,计算速度快,计算过程稳定。分析表明,传热流体温度变化对集热器效率的影响大于太阳能辐射热流密度对集热器效率的影响。     

GGH heat transfer enhancement and a new type heat exchangerin the desulphurization system of wet flue gas

This paper conducts in-tube heat transfer experiments in a three dimensional fin tube with 102 mm outer diameter.Compared with the smooth tube,the heat transfer enhancement ratio is between 1.65 and 1.7,and the pressure drop ratio is between 1.65 and 1.7.Based on the analysis of the heat transfer and tube surface temperature,a new type heat exchanger is put forward.Moreover,the design and calculation method is explored.The engineering example indicate that not only the tube surface temperature is higher than the smooth tube,but also the quantity of heat is increased by about 20% than the smooth tube.Compared with other types,the new type heat exchanger has a overall better performance.     

Computation Method and for Thermal Transmittance of Glass Curtain walls Appllcation

The heat conduction characteristic of glass curtain wall was investigated. Based on one dimensional steady heat conduction theory, the numerical calculation model of glass system thermal transmittance was set up by using insulating glass as an example. Based on two dimensional steady heat conduction theory and finite element method, both the thermal transfer matrix and temperature load array of 3 DOFs triangular element were derived. Then the revised formulas about the heat transfer matrix and temperature load array under the boundary conditions of constant heat flux, heat convective, radiation and coupled of them were also derived. Then the numerical calculation models of glass curtain wall frame and linear thermal transmittance were set up. The program TJCW based on the Visual C++ and ObjectARX was developed for calculating the thermal transmittance of glass curtain wall and was validated by contrast with the results calculated by thermal software LBNL. Finally, TJCW program was used to calculate and check the thermal transmittance of glass curtain wall in a practical project. The results indicate that the thermal transmittance of glass curtain wall can be calculated correctly by adopting the presented model, and the program based on this model can be used in energy conservation calculation and analysis in the actual projects.     

THERMODYNAMIC ANALYSIS AND PERFORMANCE EVALUATION OF CONVECTIVE HEAT TRANSFER THROUGH DUCTS

A second law analysis is carried out on convective heat transfer in fully developed region with constant wall temperature through circular, trianglar and rectangular ducts. Besides, the entropy generation rate expression is obtained and the loss rate of available energy in convective heat transfer processes is defined as well. At the same time, the influence of initial temperature difference between fluid and wall as well as the influence of fluid friction on the loss rate of available energy is discussed. Then, the thermodynamic performances of several typical ducts are compared. Finally , the optimum initial temperature difference with the minimum loss rate of available energy is also obtained.     

水平荷载作用下斜坡刚性桩非线性分析

在综合分析现有水平荷载作用下桩基分析方法的基础上,建立了考虑桩侧土体受力状态的斜坡刚性桩力学模型;根据极限平衡原理,建立横向荷载作用下斜坡刚性桩弯矩和应力平衡方程;引入考虑斜坡影响的p-y曲线方法,提出了综合考虑桩侧土体极限承载力与水平抗力系数沿深度呈线性增加的侧向极限承载力与土体抗力承载力系数计算方法,同时,将该方法应用于计算实例,通过与已有有限元和理论计算方法对比分析,计算结果验证了本文方法的合理性与可行性;并利用该方法,分析了斜坡坡角、桩土接触面系数以及地基水平抗力系数对斜坡刚性桩承载特性的影响因素。分析表明:斜坡的坡角、桩土接触面系数对侧向荷载作用下斜坡刚性桩的荷载位移曲线影响明显,而桩侧土的抗力系数对侧向荷载作用下斜坡刚性桩的荷载位移曲线影响不明显。     

Convection Heat Transfer Coefficient Distribution Over the Single Rectangle Fin Surface

Rectangle fin is widely used in different kinds of heat exchangrs. Convection heat transfercoefficient distribution over the fin surface is one of the theorehcal problems in research on enhancement of heat transfer. In this paper, a tube with an attached rectangular fin is used for a model and thefin surface is divided into a network of nodes by the finite difference techinque. When the wind velocityis u= 4. 5 m/s. the temperature distribution of discretization is obtained by experimental measurement,then the convection heat transfer coefficient of all nodes are soved by using the methed of inverse heatconduction problem. Through checking with heat balance methed, the results show that the solution cancorrectly express the actual heat transfer situation.This result is useful to experimental research onenhancement of heat transfer for finned for heat exchangers.     

Pressure Drop and Evaporative Heat Transfer Characteristics of Air-water Bubbling Flow

A new kind of evaporative heat transfer experiment for the cooling process of condensers is conducted. The test coil is immersed in an air-water bubbling layer. The air-water two-phase flow passes through the heating tubes of the coil. Due to the motion of the air bubbles in the water, a thin water film forms on the surface of the heating tubes. As the air bubbles passing by the tubes the water is evaporated into the air. The tubes of coil reject heat to the water film, and the evaporation of the water film then rejects heat to the air bubble stream. This heat transfer mode significantly increases the heat transfer coefficient between tubes and air. The consumption of the power of a water pump can be decreased. Moreover, the airflow rate required is less than that of an air-cooled condenser.The pressure drop of air through air-water bubbling layer and the heat transfer between the tubes and water are experimentally investigated in the paper. The results show that the factors affecting the pressure drop and the heat transfer coefficient involve the pore geometry of sieve plate, the height of the air-water bubbling layer, the air flow rate through the sieve plate and the heat flux of tubes. The heat transfer coefficient between tube and water is two times larger than that of falling film of water on the outer surface of tube.     

太阳能制冷机组通风系统中粮库温度的系统分析

针对不同的粮库内部太阳能制冷机组空调分布形式,利用CFD计算软件,采用标准k-e模型对粮库内部的大空间气流组织的非稳定特性进行三维数值模拟,分别比较了集中辐射式分布和沿四壁周向式分布两种形式的粮食表面附近的截平面的速度和温度分布,模拟结果显示:采用集中辐射式分布的模型流场扰动范围大,换热效果好,温度场分布均匀,整体降温效果好.由此可以看出流体计算技术在研究空调换热空间速度场和温度场分布的巨大作用,为空调的设计运行参数提供了重要依据,从而可以选用换热效果更好的空调分布形式.     

Experimental Study on Refrigeration Performance of Fin-tube With Circular Hole Under the Frost Condition

The performance of heat transfer of fin-tube with circular hole is better than fin-tube without hole if there is no frost,but what is the situation if under the frost condition.Tthe comparison study on performance of heat transfer and refrigeration is carriedout under the frost condition for the heat exchanger with three kinds of fins: circular and half circular hole,circular hole,plane form.The experiment process is finished through the refrigeration system of icebox.In the course of experiment,the influence of frost process to the diameter of circular hole;is analyzed The real refrigeration amount,heat transfer coefficient and real refrigeration coefficient of the three kinds of fins are compared;compare the effect of energy saving of enforced fins is given.The fin efficiency is calculated method and make out the real convection coefficient to disclose the situation of heat transfer of fins is lnade out.Results: compared with plane form fin,the following results are for fin-tube with circular hole: average heat transfer coefficient rise 11.53%,convection coefficient rises 18.84%,real refrigeration coefficient rises 6.83%,virtual refrigeration amount rises 6.02%,electricity saving is 6.39%.Fin-tube with circular hole is the best form for the three kinds of fins.     

Analysis of Condensation in Porous Wall Exposed to Hot Humid Climate

According to the work of Motakef and EI-Masri, the wall was divided into dry-wet-dry zones. Based on the heat and moisture transfer through porous media, considering the vapour condensation as a vapour sink, water source and heat source, coupled heat and moisture equations for wet zone were established. Closed-form analytical expressions for the condensation rate, moisture content and the time when critical moisture content value reached are obtained. It is indicated that the condensation rate exhibits a strong dependence on the temperature difference of the two sides of wet zone, and the maximum condensation rate value is reached at the boundary of wet zone close to lower temperature.     

Simulation and experiment for warp characteristic of wet multiple disc clutches

Based on the real size and constrain of the wet clutch, the friction pair of temperature, stress fields coupling model, and the heat convection coefficient model are established. The transient thermal-structural coupling and the thermoelastic instability of the phenomenon of friction discs generated in overload tests are numerically simulated and analyzed with ANSYS/LS-DYNA. Additionally, the distribution of the hot spots in the circle direction and surface of the friction discs are revealed, the distribution of the stress and strain caused by the thermoelastic instability is analyzed and tested. The results show that hot spots and contact pressure are mutual promotion. The thermal expansion and stress concentration caused by temperature gradient lead to steel disc warp. The heat fading caused by the thermoelastic instability leads to steel disc failure.     

COMBINED HEAT TRANSFER OF TURBULENT NATURAL CONVECTION AND SURFACE RADIATION IN AN OPEN CAVITY

A numerical study is carried out for the combined heat transfer of turbulent natural convection and surface radiation in an two-dimensional open square cavity with only one heated wall. The results show that the radiation significantly affects the velocity and temperature fields,and it can reduce the turbulent natural convection heat transfer as well as enhance it. For different Rayleigh number and temperature difference ratio,the overall heat transfer rates and the portion of radiation present different variation patterns.     

Study on Heat Transfer Characteristics in Waste Gas of the Exchanger

By the calculation and experiment,analysed the heat transfer characteristies in waste gas of the high temperature exchanger.The results which the reasonable vertical and horizontal distances were obtained,these turned out that the metallic rediation net was the effectve method intensified heat transfer in hot waste gas.The infulence of the velcity and temperature of waste gas on the multiple heat transfer caefficrent of the exchanger was studied by the experiment data.     

Thermal Radiation Effects on Smoke-flow in Atrium Fires

The field models for smoke flow in atrium, takings into account strong buoyancy, turbulence, radiation exchange and wall heat losses are developed according to the characteristics of the atrium fire. Realistic combustion processes in the burning fuel have not been included. A six-flux radiation model is included in a general mathematical model for fires, which are taking as a volumetric heat source, It is applied to the predictions of fire smoke development in a small-scale atrium. In order to avoid complicated radiation exchange models, radiation heat loss effects are combined to the wall heat loss. A General-purpose compute program PHOENICS has been developed to meet this need. Results of numerical calculations based on the field model are compared with test data for a fire in the small-scale atrium test facility. The resullts indicate that radiation transfer has the minor effects, due to the relatively low temperatures encountered. The method that the effect of radiation is included in the calculation of wall heat transfer losses by using maximum heat transfer coefficient is feasible. The field model used in the present study is not good enough, which a turbulent combustion sub-model must be included.     

Experimental Studies of Forced Convective Heat Transfer and Pressure Drop of Ethylene Glycol in Tubes with Three Dimensional Internally Extended Surface

In this paper,the reSults are presented from experimental investigation on heattransfer performance in seven copper tu bes with three dimensional internally extended surface(3-DIEST)varying in axial pitch,circumferential pitch,height, width and arrangement form of fins. The forced con vective heat transfer and pressure drop of ethylene glycol flowing in the 3-DLESTShave been tested in the Revnolds number range from 250 to 6,000 and the Prandtl number rangefrom 60 to 90.The average stanton number in the most superior 3-DIEST can be increased about2.4times in the laminar flow.and4.5 times in the transitional flow and turbulent flow as com-pared with that in the smooth tube. And the friction factor between fluid and tube wall can be 1.7times in laminar flow. and 4 times in transitional flow andturbulent flow inside the 3-DIEST as much as those inside the smcoth tube.     

ANALYSIS AND CALCULATION OF CONDENSATION HEAT TRANSFER ON HORIZONTAL LOW-FINNED TUBE ATTACHED BY A POROUS DRAINAGE STRIP

An analytical model was proposed for the condensation heat transfer on the horizontal low-finned tube attached by a porous drainage strip, and compared with the experimental data with a good agreement. The permeability of the porous drainage strip was also experimentally determined.