多孔介质模型在管壳式换热器数值模拟中的应用

本文详细讨论了多孔介质模型在管壳式换热器数值模拟中的应用,开发了一套能自动生成多孔介质特性参数的通用程序。该程序主要基于三维交错网格及SIMPLE算法,然后运用该模型,采用改进的κ-ε模型和壁面函数法,对换热器壳侧的湍流流动进行了数值模拟。计算结果与换热器冷态实验结果符合良好,表明该模型和计算方法是切实可行的。     

组合式多壳程螺旋折流板管壳式换热器数值模拟研究

本文采用数值模拟方法对内壳程为非连续螺旋折流板的组合式螺旋折流板和单壳程弓形折流板管壳式换热器壳侧流动换热特性进行对比研究,结果表明:相同壳程质量流量和相同换热量条件下,组合式两壳程螺旋折流板换热器的压损比弓形折流板换热器降低14.6%;相同壳程质量流量条件下,组合式两壳程螺旋折流板换热器单位压降下换热量比弓形折流板换热器提高10.8%.     

螺旋折流板换热器层流流动与换热的数值模拟

应用多孔介质和分布阻力模型对一螺旋折流板管壳式换热器的壳侧层流流动与换热进行了三维数值模拟,并与该换热器的实验研究结果进行了对比分析,符合程度良好.证明了该方法能有效地模拟螺旋折流板换热器的流动和换热特性.     

螺旋折流片换热器壳侧传热与流动的数值模拟

提出了一种强化管壳式换热器壳侧传热的螺旋折流片式换热器新方案,该方案在部分管子上套上螺旋折流片,不仅强化传热,而且对相邻管子形成支撑;利用FLUENT流体计算软件对同心套管螺旋折流片式换热段的壳侧流场、温度场进行了数值模拟,并讨论了螺旋角对其强化传热和阻力性能的影响。结果显示螺旋折流片诱导的涡旋流动对于减薄边界层,促进近壁流体与主流区流体的动量和质量交换进而强化传热有明显的作用,传热系数可比光管提高约40％-100％,但其流动阻力也将增大。     

双壳程连续螺旋折流板换热器的数值模拟

本文提出了一种新型的双壳程连续螺旋折流板换热器。采用数值模拟方法对双壳程、单壳程连续螺折流板换热器,以及弓形折流板换热器壳侧流动与传热持性进行了对比研究。结果表明,同质量流量和对流换热系数近似相等的情况下,双壳程连续螺旋折流板换热器壳程压降比弓形折流板换热器低17.7%～23.5%,同质量流量和壳程压降近似相等的情况下,其对流换热系数比单壳程连续螺旋折流板换热器高7.1%～12.6%。     

弓形折流板换热器中折流板对换热器性能的影响

本文采用Bell-Delaware换热器设计方法研究了传统弓形折流板换热器加热轻油时在不同管束排列角度下,改变换热器壳侧折流板间距以及改变折流板的窗口高度对管壳式换热器的壳体内径、换热管数目、壳侧换热系数及壳侧压降的影响.     

阶梯式螺旋折流板换热器流动与传热特性研究

针对现有的螺旋折流板换热器加工较为复杂,并且非连续型螺旋折流板的相邻折流板间存在漏流的问题,提出了一种新型阶梯式螺旋折流板换热器。通过数值模拟的方法对阶梯式螺旋折流板换热器和弓形折流板换热器进行对比,研究其壳程流动与传热特性。结果表明,阶梯式螺旋折流板换热器能够使壳侧流体呈近似螺旋状流动,综合性能优于弓形折流板换热器,速度分布更加均匀。     

低温发电用翅片管换热器传热特性的数值模拟分析

为了深入研究低温余热发电系统用翅片管换热器的传热特性,文中建立了翅片管换热器计算模型,对工质R123在翅片管换热器内的传热性能进行数值模拟,比较管内工质R123在不同流速与温度时的换热特性,利用最小二乘法原理,对烟气侧和工质侧的换热关联式进行了拟合,得到了二者的换热准则方程,此外,利用实验方法对模拟结果进行验证。     

新型管壳式换热器三维流场分析

本文应用周期性简化模型，对弓型、杆式以及H型壳程支撑结构的管壳式换热器壳程内的流动特性进行了分析。对于其对应的三种典型流态，反映在壳程内流体流动方面的主要差别是壳程内横向流速度分量的不同，且三种流态各自在不同流量下的横向流速度分量与纵向流速度分量之比几乎均为一定值。具有不同管束支撑结构的管壳式换热器壳程内流体阻力降与传...     

纵流壳程换热器壳程近壁区流场和温度场数值研究

对新型纵流壳程换热器壳程近壁局部区域的流场和温度场进行了数值模拟研究,总结了换热器横截面内各换热管壁面对流传热系数与换热管距壳体轴心距离的关系,分析了近壁区域非规则流道内流体对流传热系数较壳体中心主流区内规则流道大的原因,为换热器壳程内关键局部区域流体流动和传热状况的改善以及进一步的结构优化提供了直观依据.提出的纵流壳程换热器周期性全截面计算模型,为发现和解决换热器中与局部位置流体流动和传热细节相关的深层次问题提供了良好的辅助手段.     

新型制冷机冷凝器壳侧的传热强化研究

针对现行制冷机冷凝器的不足 ,设计了适用于冷凝传热的新型折流杆冷凝器的壳程内部结构 ,并分析了其传热强化机理。在重力控制条件下 ,对不同内部支承结构与管束组合的冷凝器进行了传热实验研究 ,得到了水蒸汽在冷凝器壳侧的冷凝传热特性曲线。采用冷凝传热强化因子的概念 ,建立了预测该种折流杆冷凝器壳侧冷凝传热膜系数的计算公式 ,为折流杆冷疑器在制冷系统中的设计应用提供了理论依据。     

Evaluation of Nusselt number and effectiveness for a vertical shell-coiled tube heat exchanger with air bubble injection into shell side

Air bubble injection was employed to increase the heat transfer rate (Nusselt number) of a vertical shell and coiled tube heat exchanger in this article. Hot and cold water flowed into the coil side and shell side of heat exchanger, respectively, and air bubbles were injected inside the shell side of heat exchanger via a memorable method. Bubbles' vertical movement due to buoyancy forcing through the heat exchanger can enhance the heat transfer rate by mixing the thermal boundary layer, increasing the turbulence level of the fluid flow and increasing the shell-side fluid Reynolds number.     

热储周围岩石热补偿对增强型地热系统采热过程的影响

采用自行开发的增强型地热系统(EGS)地下热流动过程三维动态模拟软件,模拟不同地质条件下EGS的长期运行过程,分析热储周围岩体的热补偿对产热温度以及热储内岩石、流体温度演化的影响.该数值模型视热储为等效多孔介质,采用两个能量方程分别描述流体和岩石的温度场,深入探究岩石与循环流体之间的换热过程.研究发现,热储周围岩体的热补偿作用与热储内流场形态强烈相关,且并不总是提高EGS的生产温度.在深度方向上有较大的优势流动的热储中,热补偿作用在EGS运行早期甚至会降低采出流体的温度.随着EGS的运行,热储温度持续降低,热补偿将对热能开采的影响将逐渐转向正面,对生产流体温度的提高效果增强.     

Maximum power output of a class of irreversible non-regeneration heat engines with a non-uniform working fluid and linear phenomenological heat transfer law

Maximum power output of a class of irreversible non-regeneration heat engines with non-uniform working fluid, in which heat transfers between the working fluid and the heat reservoirs obey the linear phenomenological heat transfer law [q ∝ Δ(T ⁻¹)], are studied in this paper. Optimal control theory is used to determine the upper bounds of power of the heat engine for the lumped-parameter model and the distributed-parameter model, respectively. The results show that the maximum power output of the heat engine in the distributed-parameter model is less than or equal to that in the lumped-parameter model, which could provide more realistic guidelines for real heat engines. Analytical solutions of the maximum power output are obtained for the irreversible heat engines working between constant temperature reservoirs. For the irreversible heat engine operating between variable temperature reservoirs, a numerical example for the lumped-parameter model is provided by numerical calculation. The effects of changes of reservoir’s temperature on the maximum power of the heat engine are analyzed. The obtained results are, in addition, compared with those obtained with Newtonian heat transfer law [q ∝ Δ(T)].     

超临界R134a水平圆管内冷却换热模拟研究

采用增强壁面函数的标准k-ε模型对超临界R134a水平圆管内冷却换热进行了模拟研究.分析了管内不同截面上流体温度、速度和湍动能的分布情况及对应关系。研究了质量流量和浮升力对换热系数的影响。结果表明,流体速度随着温度的降低而减小,并且最大速度处对应着最高温度和最小湍动能.换热系数随着质量流量的增加而增大,其峰值出现在准临界温度附近。浮升力在似液体区的影响较大,对流体换热起到增强的效果。     

地热换热器的传热分析

本文综述了作者近年来在地热换热器传热模型方面的研究:提出了分析竖直埋管地热换热器钻孔内的传热过程的准三维模型,考虑流体工质在深度方向上的温度分布,给出钻孔内热阻的解析表达式;求得有限长线热源在半无限大介质中的瞬态温度响应解析解;导得了有渗流时无限大介质中线热源温度响应的解析解。以上工作改进和深化了国际上现有的地热换热器传热模型,并已应用于工程设计和模拟。     

高温吸热管内超临界CO2传热特性的数值模拟

研究超临界CO2在高温吸热管内的传热特性是将其应用于聚光太阳能热发电技术中的基础.本文对此进行了数值模拟研究,分析了流体温度、流动方向、系统压力、质量流率和热流密度对对流传热系数和Nu数的影响.结果表明:高温区(800—1050 K)的对流传热系数和Nu数受流动方向和系统压力的影响均很小,但都随着质量流率的增大以及热流密度的减小而明显增大;而随着流体温度的升高,对流传热系数近似线性增大,Nu数则近似线性减小.另外,本文研究发现在高温区可忽略浮升力对传热的影响,而由高热流密度引起的流动加速效应会明显恶化传热.最后,选取了八种管内超临界流体传热关联式与模拟结果进行对比,发现使用基于热物性修正的关联式对高温区传热数据预测的结果优于使用基于无量纲数修正的关联式得到的结果,且其中预测效果最优的关联式得到的计算结果与模拟结果之间的平均绝对相对偏差为8.1%.     

Impact of Internal Heat Source on Mixed Convective Transverse Transport of Viscoplastic Material under Viscosity Variation

This communication addresses the impact of heat source/sink along with mixed convection on oblique flow of Casson fluid having variable viscosity. Similarity analysis has been utilized to model governing equations, which are simplified to set of nonlinear differential equations. Computational procedure of shooting algorithm along with 4th order Range-Kutta-Fehlberg scheme is opted to attain the velocity and temperature distributions. Impact of imperative parameters on Casson fluid flow, temperature, significant physical quantities such as skin friction, local heat flux and streamlines are displayed via graphs.     

Impact of Internal Heat Source on Mixed Convective Transverse Transport of Viscoplastic Material under Viscosity Variation

This communication addresses the impact of heat source/sink along with mixed convection on oblique flow of Casson fluid having variable viscosity. Similarity analysis has been utilized to model governing equations, which are simplified to set of nonlinear differential equations. Computational procedure of shooting algorithm along with 4 th order Range-Kutta-Fehlberg scheme is opted to attain the velocity and temperature distributions. Impact of imperative parameters on Casson fluid flow, temperature, significant physical quantities such as skin friction, local heat flux and streamlines are displayed via graphs.     

Heat Transfer in an Upper Convected Maxwell Fluid with Fluid Particle Suspension

An analysis is carried out to study the magnetohydrodynamic (MHD) flow and heat transfer characteristics of an electrically conducting dusty non-Newtonian fluid, namely, the upper convected Maxwell (UCM) fluid over a stretching sheet. The stretching velocity and the temperature at the surface are assumed to vary linearly with the distance from the origin. Using a similarity transformation, the governing nonlinear partial differential equations of the model problem are transformed into coupled non-linear ordinary differential equations and the equations are solved numerically by a second order finite difference implicit method known as the Keller-box method. Comparisons with the available results in the literature are presented as a special case. The effects of the physical parameters on the fluid velocity, the velocity of the dust particle, the density of the dust particle, the fluid temperature, the dust-phase temperature, the skin friction, and the wall-temperature gradient are presented through tables and graphs. It is observed that, Maxwell fluid reduces the wall-shear stress. Also, the fluid particle interaction reduces the fluid temperature in the boundary layer. Furthermore, the results obtained for the flow and heat transfer characteristics reveal many interesting behaviors that warrant further study on the non-Newtonian fluid flow phenomena, especially the dusty UCM fluid flow phenomena.