板式换热器性能的数值模拟

建立了人字形板式换热器冷热双流道的流体流动与传热计算模型,利用计算流体力学软件对5组不同速度工况下换热器内流体的流动和传热进行了数值模拟,分析了换热器流道内的速度场、温度场和压力场.结果表明:数值模拟得到的板式换热器进、出口温差和压降与试验测量值的误差均小于6%;换热器内流体的流动和传热存在明显的不均匀性,导致其进、出口的另一侧出现明显的传热"死区";换热器的总传热系数和流道阻力均随着流体流速的增大而增大.     

板式间接蒸发冷却换热器的层流特性研究

间接蒸发冷却换热器与传统空调相比具有环保与节能的优点。由于蒸发冷却过程的传热传质机理复杂,本文针对板式间接蒸发冷却换热器,建立了三维稳态传热传质数学模型,并确定了合适的边界条件。通过数值模拟得到了压力场、温度场和浓度场的分布,并讨论了通道间距、速度、温度以及相对湿度等因素对换热效果的影响,为间接蒸发冷却换热器的设计提供了理论指导。     

板式间接蒸发冷却器热工特性的实验研究

对自行研制设计的间接蒸发冷却换热试件开展了实验，研究了影响换热器换热性能的因素。结果表明：板式间接蒸发冷却器换热效率随二次空气入口的速度升高、一次空气入口的温度、二次空气入口的湿球温度升高而变大，随一次空气入口的速度变大而变小。实验结果对于深入认识间接蒸发冷却器的换热机理及开展换热器的优化设计有着很大的指导意义。     

螺旋套管换热器传热特性研究

根据螺旋套管换热器的结构特点及传热特性,建立了水一水蒸气的流动与传热的三维几何模型.利用Fluem时不同工况下的螺旋套管进行了数值模拟,得出了湍流状态下螺旋套管内流体的温度场、速度场和压力场;利用搭建的螺旋套管换热器试验台,得出多种工况下的传热系数,为螺旋套管换热器的设计计算提供了依据.同时将试验结果和数值模拟结果进行...     

管壳式换热器壳侧气液两相流动和传热的数值模拟研究

采用数值模拟方法,使用FLUENT对管壳式换热器壳侧的两相流动及相变传热进行了模拟计算.根据壳侧流体流动特点,选定合适的湍流模型、两相流模型为混合物模型,并根据汽水转化公式编写了自定义函数UDF来描述相变过程质和量的传递.对管壳式换热器壳侧的流体介质换热发生相变并产生气液两相流动进行了三维的数值模拟研究.得到了管壳式换热器壳程的速度场、温度场、压力场及气液各相的分布情况,对壳侧气液两相流动及相变换热进行了分析.对具有相变情况下的管壳式换热器的结构设计起到参考指导作用.     

一种用于船舶烟气冷却的喷雾螺旋管冷却器的传热特性研究

船舶使用的主动降噪设备需要连接到排烟支管,但高温烟气会缩短设备的使用寿命。为了降低烟气温度,建立了冷却器喷雾冷却的数值模型对支管冷却器的运行工况进行优化,通过数值模拟分析喷射压差与喷雾半角对冷态以及热态性能的影响。结果表明：最佳喷雾半角为60°,喷射压差为1.5 MPa时,冷却器性能最佳;采用液滴蒸发效率与逃逸质量分析冷却器内液滴的流动特性,根据模拟结果进行二次回归式拟合,喷雾压差和喷射半角与蒸发效率相关系数分别为0.19和0.56,其相对于逃逸质量的相关系数为0.25和0.72,喷嘴工作参数应选取较高的喷雾半角和较低的喷射压差。     

LHP圆盘式蒸发器三维传热与流动分析

通过补充相变蒸发界面传热传质热力学关系式,构建了回路热管(loop heat pipe,LHP)圆盘式蒸发器的流动与传热多区域耦合分析三维数学物理模型,并基于FLUENT软件对某种甲醇-不锈钢平板型蒸发器内的流动与传热情况进行了数值求解。数值分析结果表明,蒸发器内的传热与流动受几何结构影响明显,表现出较强的方向差异;不同热负荷条件下,补偿腔内流体的流动与传热特性呈现出较大差别,受到回流液速度和温度、毛细芯界面蒸发质量流量、毛细芯反向导热和侧壁漏热等多种因素共同影响。计算方法和研究结果,可以为平板型蒸发器内流动与传热特性的定量分析提供依据。     

基于CFD分析的板式换热器流体分配性能影响的研究

利用CFD软件对某板式换热器内流体流动进行了数值模拟,发现板式换热器流道数目和角孔低槽对板式换热器流体分配有很大的影响。模拟结果表明:在一定流速下,通道数目大于39以后,流动状况开始恶化,开始出现部分流道没有流体分配的状况;流道数目大于20以后,随着角孔低槽直径的增大,通道内流量分配状况也会发生急剧恶化。     

一种基于太阳能与蒸发冷却的新型新风处理机组

新风负荷约占空调能耗的30％,减少新风处理能耗对降低空调能耗有重要作用.本文提出了一种将太阳能空气集热器与间接蒸发冷却器相结合的新型新风处理机组,夏季采用间接蒸发冷却器对新风预冷,喷淋水以循环水为主,利用冷凝水作为其补充水,降低了喷淋水的水温,并利用室内排风作为间接蒸发冷却器的二次空气,提高了换热效率;冬季采用太阳能空...     

三维变形管换热器在压缩机中间冷却器中的应用研究

中间冷却器是提高压缩机效率的一种重要设备,在对三维变形管换热器的结构和传热特点进行介绍的基础上,对其在压缩机中间冷却器中的应用进行了可行性分析。采用三维变形管换热器对中石化某年产100万吨延迟焦化装置用富气压缩机中间冷却器进行了技术改造,并进行了实际运行测试和考核分析。结果表明:三维变形管换热器有效解决了管束的振动问题,在换热面积减少37. 4%、气体阻力降低36. 9%的情况下,气体出口温度达到生产工艺要求,起到了良好的节能节材效果。     

Effect of Operating Parameters on the Heat Transfer and Liquid Film Thickness of Revolving Heat Pipe

This paper presents a study on the effects of operating parameters on the liquid film thickness and heat transfer of revolving heat pipe. The effects of speed, radius of rotation, evaporator and condenser temperatures, and mass of the working fluid are considered. Also, the effects of these parameters on the maximum heat transfer and minimum mass of the working fluid supplied to the heat pipe are considered. A simplified theoretical model is presented to estimate the heat transfer and the liquid film thickness. The theoretical model is used to determine the driven forces on the control volume. The system of equations associated with the heat pipe model is solved using the fourth-order Runge–Kutta method through a numerical code written in MATLAB. The results show that the heat transfer increases by decreasing the mass of the working fluid and increasing the temperature difference through the heat pipe. They also show that the liquid film thickness increases with the decrease in temperature difference and with increase in the mass of fluid. The maximum heat transfer increases with the increase in the rotation speed. The minimum mass of the working fluid supplied to the heat pipe increases with the increase in temperature difference and with the decrease in the rotation speed.     

Finite-volume modelling of heat and mass transfer during convective drying of porous bodies – Non-conjugate and conjugate formulations involving the aerodynamic effects

In this study, a numerical procedure is outlined and representative results for heat and mass transfer during convective drying of porous bodies are presented. The Luikov model was implemented and applied both on individual samples of construction materials and agricultural products, as well as on a drying-chamber scale, with parallel flow of a hot air stream over rectangular slabs which represent the product to be dried. In the latter case the configuration is an experimental dryer in which the heat source is a solar air collector with evacuated tubes. A general approach was developed that allows a selection between modelling of phenomena either in the drying solid only, or considering an extended simulation domain encompassing, apart from the solid body, the flow of air as well. In the second case, the solution of the flow field is pursued along with a conjugate heat/mass transfer problem coupling the solid and fluid phenomena and in both cases phase change (evaporation) was taken into account. For the numerical simulation, the finite-volume method was used. The validation of the model was based on experimental and numerical results from the literature and results from simulations that were conducted in the pursuit of the energetic optimization of an experimental solar dryer of NCSR “Demokritos” are presented. In the latter case, the effect of the particular flow field features developing for a single and a double-plate configuration on the heat/mass transport and drying rates is demonstrated. Such a methodology could be used to analyze the transport phenomena in any type of convective dryer, including those utilizing solar energy as the heat source.     

管内强化传热结构及其性能分析

强化传热一直是工程中节能降耗的有效措施,本文阐述了各种管内强化传热结构及其性能特点,并用场协同原理和数值模拟方法分析了其强化传热机理。数值分析表明,管内壁面的凸起对流体产生扰流作用,减薄和破坏了液体边界层,管内插入物促进了流体的湍动,加速流体的径向混合,这都有利于提高流体的传热强度。     

Application issues of the streamline,heatline and massline for conjugate heat and mass transfer

Functions and lines have been extensively used to visualize two-dimensional fluid, heat and mass transportation structures. However, some ambiguities related to streamlines, heatlines and masslines still exist, especially for conjugate heat and mass transfer in anisotropic media. Present work aims to clarify these issues from numerical viewpoints, mainly including diffusion coefficient of transportation function at the interface of different media, different numerical approaches for solving visualization functions, non-dimensional forms of heatfunction and massfunction matching the spatial Nusselt and Sherwood numbers. The numerical procedures and code routines for the primitive conserved variables and the functions are illustrated through visualizing fluid, heat and solute transportations of double diffusive natural convection in square enclosures with massive walls or center-inserted body.     

Effects of heat and mass transfer on the peristaltic flow of hyperbolic tangent fluid in an annulus

This article deals with the influence of heat and mass transfer on peristaltic flow of a hyperbolic tangent fluid in an annulus. The two dimensional equations of tangent hyperbolic fluid are simplified by making the assumptions of long wave length and low Reynolds number. Exact solutions are evaluated for both heat and concentration field, while analytical and numerical solutions are carried out for velocity profile. Comparison of both the solution is presented through graph and table. The expressions for pressure rise, temperature, concentration field and pressure gradient are sketched for various embedded parameters and interpreted.     

Impact of activation energy and gyrotactic microorganisms on flow of Casson hybrid nanofluid over a rotating moving disk

Many models of various non-Newtonian fluid flows for different geometries are available for analyzing the mass and heat transfer. Nevertheless, for researchers, it is challenging to choose the most suitable model for a specific geometry. Here, we have adopted a modified Buongiorno model to explore the impact of activation energy on the Casson hybrid nanofluid flow over an upward/downward-moving rotating disk filled with the gyrotactic microorganisms. Moreover, the external magnetic field can establish the magnetic effect, which normalizes the features of heat, mass transfer, and fluid flow. Here, we used silver and copper as nanoparticles suspended in human blood as the carrier fluid. The modeled partial differential equations are converted to ordinary differential equations by opting suitable similarity variables. The numerical solutions of these reduced equations are attained by means of Runge–Kutta–Fehlberg fourth-fifth-order method by adopting a shooting scheme. An investigation of the attained outcomes reveals that the flow field is affected appreciably by the activation energy, bioconvection, and magnetic effect. Peclet and concentration difference numbers diminish the microorganism's profile. A rise in values of the Brownian motion parameter leads to an increase in the rate of heat transfer.     

Numerical simulation of fluid flow and convection heat transfer in sintered porous plate channels

Fluid flow and convective heat transfer of water in sintered bronze porous plate channels was investigated numerically. The numerical simulations assumed a simple cubic structure formed by uniformly sized particles with small contact areas and a finite-thickness wall subject to a constant heat flux at the surface which mirrors the experimental setup. The permeability and inertia coefficient were calculated numerically according to the modified Darcy’s model. The numerical calculation results are in agreement with well-known correlation results. The calculated local heat transfer coefficients on the plate channel surface, which agreed well with the experimental data, increased with mass flow rate and decreased slightly along the axial direction. The convection heat transfer coefficients between the solid particles and the fluid and the volumetric heat transfer coefficients in the porous media predicted by the numerical results increase with mass flow rate and decrease with increasing particle diameter. The numerical results also illustrate the temperature difference between the solid particles and the fluid which indicates the local thermal non-equilibrium in porous media.     

A study on the heat and mass transfer properties of multiple pulsating impinging jets

In order to explore the potential effect of unsteady intermittent pulsations on the heat and mass transfer rate of multiple impinging jets, a numerical study is performed on a two-dimensional pulsating impinging jet array under large temperature differences between jet flows and impingement wall when the thermo-physical properties can change significantly in the flow domain. Computational fluid dynamic approach is used to simulate the flow and thermal fields of multiple pulsating impinging jets. The numerical results indicate a significant heat transfer enhancement due to intermittent pulsation over a wide range of conditions. The oscillatory flow periodically alters the flow patterns in contrast to steady jets, which can eliminate the formation of a static stagnation point and enhance the local Nusselt number along the impingement wall between adjacent jets. Examination of the velocity field shows that the instantaneous heat transfer rate on the target surface is highly dependent on the hydrodynamic and thermal boundary layer development with time.     

土壤水热耦合模型在三江源冻土活动层水热变化中的应用

为揭示青海三江源区水文活动规律,描述季节性冻土分布区内冻、融变化过程中土壤内部热量交换和水分迁移等物理过程,采用有限体积法离散热传导方程和非饱和土壤水运动方程并对其进行耦合求解,建立了冻土区土壤水热耦合模型。利用2005～2007年间9个测站的土壤水热观测资料,从不同角度分析了冻土活动层内的土壤水热特征,对土壤融化深度、表层土壤温度及表层土壤含水量等变化过程的模拟验证结果表明,该模型的模拟结果符合当地的水热运动规律。并定量分析检验了模型方法的有效性,揭示了三江源区的土壤水热运动规律,为该地区的生态系统服务提供了有力的支持。     

Optimized mass flux ratio of double-flow solar air heater with EHD

The numerical study of laminar forced convection inside double-flow solar air heater with electrohydrodynamic technique is investigated by finite difference method. The electric field is generated by the wire electrodes charged with DC high voltage. The mathematical modeling of computational fluid dynamics includes the interactions among electric field, flow field, and temperature field. It can be perceived that augmented heat transfer with presence of an electric field increases with the supplied voltage but decreases with the total mass flux. The optimized mass flux ratio is expressed incorporating with concerning parameter comprising of the electrode arrangement, the number of electrodes, the total heat flux at an absorbing plate, and the channel geometry.