HEAT TRANSFER IN TUBES FITTED WITH TRAPEZOIDAL-CUT AND PLAIN TWISTED TAPE INSERTS

Experimental investigation of heat transfer and friction factor characteristics of a circular tube fitted with plain twisted tapes (PTT) and trapezoidal-cut twisted tapes (TTT) with twist ratios y = 2.0, 4.4, and 6.0 was carried out. The experimental data obtained from plain tube and PTT were verified with the standard correlation to ensure the validation of experimental results. The experimental results revealed that heat transfer rate, friction factor, and thermal enhancement factor in the tube equipped with TTT were significantly higher than in the tube fitted with PTT and the plain tube. The additional disturbance and secondary flow in the vicinity of the tube wall generated by the TTT compared to that induced by the PTT was determined as the reason for enhancement. Subsequently, an empirical correlation was also formulated to match with experimental results with ±6% and ±5% variation respectively for Nusselt number and the friction factor.     

水平微肋管内流动蒸发换热特性的实验研究

为了研究微肋管结构尺寸及工况等对管内流动蒸发性能的影响,对4种微肋管和1根9.52 mm光管进行了实验,4根微肋管中管外径为9.52 mm和7 mm的各2根,所用工质为R22.实验中质量流速变化范围为90～400kg•m^-2•s^-1,所选工况为：蒸发温度7℃,入口干度15%～20%,出口过热度5～6℃.获得了蒸发换热性能随质量流速的变化,讨论了微肋结构尺寸和管径等对蒸发换热性能的影响.两根9.52mm微肋管的传热系数比光管分别分别提高了130%和180%,而其内表面积只比光管分别增加了40%和70%.     

螺旋扁管换热器传热与阻力性能

对不同结构的螺旋扁管管内传热及流体阻力性能进行实验研究,并与光管比较,选出传热与流阻综合性能较好的管型。同时对2台螺旋扁管换热器及1台外螺纹螺旋扁管换热器进行壳程传热与流阻实验研究。根据实验结果给出了管、壳程传热膜系数与阻力系数的经验关联式。     

HEAT TRANSFER AND FLUID FLOW IN A NONISOTHERMAL CONSTRAINED VAPOR BUBBLE

A Constrained Vapor Bubble (CVB) with a relatively large Bond number formed by partially underfilling liquid in an evacuated cavity is capable of high thermal conductance. Il operates on the principle of closed loop phase-change along with capillarity to circulate the working fluid. Analytical investigations were conducted to compare with existing experimental data. A steady-state fluid flow model combined with a two-dimensional heat transfer model was developed and solved to yield key operating parameters ( i.e., temperature and liquid meniscus curvature) of the CVB. The modeling results of the outside wall temperature in the evaporator were found to agree well with the measured experimental data. An area average heat transfer coefficient was used to characterize the heat transfer on the inside wall of the evaporator. The value of this heat transfer coefficient was found to increase with the heat flow rate. The fluid flow model with the heat transfer model in the evaporator to provide the energy balance was used successfully to fit the experimental curvature data. The mass flow rate in the bottom corners of the CVB was found to be higher than that in the top corners due to the gravitational body force.     

HEAT TRANSFER AND FLUID FLOW IN A NONISOTHERMAL CONSTRAINED VAPOR BUBBLE

A Constrained Vapor Bubble (CVB) with a relatively large Bond number formed by partially underfilling liquid in an evacuated cavity is capable of high thermal conductance. Il operates on the principle of closed loop phase-change along with capillarity to circulate the working fluid. Analytical investigations were conducted to compare with existing experimental data. A steady-state fluid flow model combined with a two-dimensional heat transfer model was developed and solved to yield key operating parameters ( i.e., temperature and liquid meniscus curvature) of the CVB. The modeling results of the outside wall temperature in the evaporator were found to agree well with the measured experimental data. An area average heat transfer coefficient was used to characterize the heat transfer on the inside wall of the evaporator. The value of this heat transfer coefficient was found to increase with the heat flow rate. The fluid flow model with the heat transfer model in the evaporator to provide the energy balance was used successfully to fit the experimental curvature data. The mass flow rate in the bottom corners of the CVB was found to be higher than that in the top corners due to the gravitational body force.     

FINITE ELEMENT ANALYSIS FOR LAMINAR FLOW AND HEAT TRANSFER IN FINITE ROD BUNDLES

This investigation deals with the application of finite element method to solve the thermohydraulic problem of laminar fully developed flow in the interior and wall sub-channels of finite fuel rod bundles. A variational principle has been used for the solution of the momentum and energy equations. Wall shear stress and temperature distributions, ?Re and Nusselt numbers are obtained for the sub-channels of different configurations. The results are compared with solutions generated by collocation and finite difference methods.     

FINITE ELEMENT ANALYSIS FOR LAMINAR FLOW AND HEAT TRANSFER IN FINITE ROD BUNDLES

This investigation deals with the application of finite element method to solve the thermohydraulic problem of laminar fully developed flow in the interior and wall sub-channels of finite fuel rod bundles. A variational principle has been used for the solution of the momentum and energy equations. Wall shear stress and temperature distributions, ƒRe and Nusselt numbers are obtained for the sub-channels of different configurations. The results are compared with solutions generated by collocation and finite difference methods.     

管壳式换热器壳程流动和传热的三维数值模拟

提出了一种管壳式换热器壳程单相流动和传热的三维模拟方法 .用体积多孔度、表面渗透度、分布阻力和分布热源来考虑壳程复杂几何结构造成的流道缩小和流动阻力、传热效应 ,通过数值求解平均的流体质量、动量、能量守恒方程 ,得到壳程流动和换热的分布 .用该方法对一实验换热器进行了流动和传热的模拟 ,计算结果和实验结果吻合良好 .     

MASS TRANSFER THROUGH PERMEABLE WALLS: A NEW INTEGRAL EQUATION APPROACH FOR CYLINDRICAL TUBES WITH LAMINAR FLOW

Mass transfer through cylindrical semipermeable walls is analyzed. The solution is obtained in terms of integral equations. Despite the existence of a non-homogeneous boundary condition on the semipermeable wall, the solution thus obtained is particularly advantageous since the associated eigenvalue problem is independent of the Sherwood number. This parameter takes into account the main conductances at the tube wall.

The approach is applied to the case of mass transfer from the interior of a capillary tube with semipermeable walls to an external fluid. The flow in the tube is laminar, and the external flow is assumed turbulent.

The mathematical methodology employed provides a framework to develop numerical schemes of fast and sure convergence.     

含扭曲带管内流动与传热的数值模拟

以空气为介质(Pr=0.698),通过数值模拟的方法在Re=300～800的范围内对含扭曲带管内周期性充分发展的层流流动进行了模拟分析,说明了不同Re、扭曲比y、纽带厚度δ和翅片系数C_fin对Nu、速度环量和阻力系数的影响,并通过对Nu和速度环量之间的关系进行了分析,得出在含扭曲带管内强化换热流动中决定换热能力的物理量——速度环量.     

LAMINAR FLOW HEAT TRANSFER WITH INLINE MIXERS INSERTS

Heat transfer coefficients were measured for heat transfer to a Newtonian fluid flowing in laminar flow through a tube with inline mixer inserts. Kenics “Static” mixer and Ross LPD mixer inserts were studied as heat transfer augmentation devices. The mixer inserts were in the inner tube of a concentric tube heat exchanger. Steam was condensed in the annulus of the exchanger. Significant heat transfer enhancement was obtained with both inserts at the expense of even greater pressure drop increases. The use of the Ross mixer insert gave greater augmentation than did the use of the kenics insert. An analysis using the analogy between momentum and heat transfer allowed the prediction of heat transfer coefficients from pressure drop measurements. The predicted coefficients were in good agreement with experimentally measured heat transfer coefficients for laminar flow.     

LAMINAR FLOW HEAT TRANSFER WITH INLINE MIXERS INSERTS

Heat transfer coefficients were measured for heat transfer to a Newtonian fluid flowing in laminar flow through a tube with inline mixer inserts. Kenics “Static” mixer and Ross LPD mixer inserts were studied as heat transfer augmentation devices. The mixer inserts were in the inner tube of a concentric tube heat exchanger. Steam was condensed in the annulus of the exchanger. Significant heat transfer enhancement was obtained with both inserts at the expense of even greater pressure drop increases. The use of the Ross mixer insert gave greater augmentation than did the use of the kenics insert. An analysis using the analogy between momentum and heat transfer allowed the prediction of heat transfer coefficients from pressure drop measurements. The predicted coefficients were in good agreement with experimentally measured heat transfer coefficients for laminar flow.     

STEADY LAMINAR FLOW IN TWO SUCCESSIVE BIFURCATIONS

The steady-state vorticity transport equation was solved numerically for inspiratory flow in two-dimensional models of two successive bifurcations. Streamlines and velocity distributions were obtained for Reynolds numbers ranging from 1 to 800. For both symmetric and asymmetric airway models, the calculated axial velocity profiles in the parent channels of the second bifurcations are asymmetric.     

STEADY LAMINAR FLOW IN TWO SUCCESSIVE BIFURCATIONS

The steady-state vorticity transport equation was solved numerically for inspiratory flow in two-dimensional models of two successive bifurcations. Streamlines and velocity distributions were obtained for Reynolds numbers ranging from 1 to 800. For both symmetric and asymmetric airway models, the calculated axial velocity profiles in the parent channels of the second bifurcations are asymmetric.     

MODELING OF HEAT TRANSFER OF UPWARD ANNULAR FLOW IN VERTICAL TUBES

This article presents the modeling of heat transfer of upward annular flow in a smooth tube and a spirally internally ribbed tube. First, analytical models of two-phase flow dynamics and heat transfer of annular flow in flow boiling were derived from the liquid film momentum and energy equations for smooth tubes. Combined with empirical correlations for liquid droplet entrainment and deposition rates in annular flow, modeling of heat transfer of upward annular flow in the smooth tube was conducted. The predicted heat transfer coefficients of annular flow agree with the experimental results very well for the smooth tube. Based on the heat transfer model for smooth tubes, a simplified annular flow heat transfer model for the spirally internally ribbed tube was proposed by modifying the interfacial friction factor. The predicted heat transfer coefficients by the modified heat transfer model for the spirally internally ribbed tube agree with the experimental results to some extent. It is suggested that the heat transfer model for the spirally ribbed tube be further improved by modifying the correlations for liquid droplet entrainment and deposition rates in annular flow, which should describe the feature of annular flow in the spirally internally ribbed tube. Extensive experimental data are needed for this purpose.     

MODELING OF HEAT TRANSFER OF UPWARD ANNULAR FLOW IN VERTICAL TUBES

This article presents the modeling of heat transfer of upward annular flow in a smooth tube and a spirally internally ribbed tube. First, analytical models of two-phase flow dynamics and heat transfer of annular flow in flow boiling were derived from the liquid film momentum and energy equations for smooth tubes. Combined with empirical correlations for liquid droplet entrainment and deposition rates in annular flow, modeling of heat transfer of upward annular flow in the smooth tube was conducted. The predicted heat transfer coefficients of annular flow agree with the experimental results very well for the smooth tube. Based on the heat transfer model for smooth tubes, a simplified annular flow heat transfer model for the spirally internally ribbed tube was proposed by modifying the interfacial friction factor. The predicted heat transfer coefficients by the modified heat transfer model for the spirally internally ribbed tube agree with the experimental results to some extent. It is suggested that the heat transfer model for the spirally ribbed tube be further improved by modifying the correlations for liquid droplet entrainment and deposition rates in annular flow, which should describe the feature of annular flow in the spirally internally ribbed tube. Extensive experimental data are needed for this purpose.     

HEAT TRANSFER TO NON-NEWTONIAN LIQUIDS FLOWING THROUGH HORIZONTAL TUBES

Experimental and analytical investigation of heat transfer to single phase flow of pseudoplastic fluids under constant heat flux condition was carried out. Experimental data for laminar flow heat transfer in the thermally developing region over a wide range of rheological properties ( n from 0.54 to 0.84 and K from 0.07 to 2.41 Nsⁿ/m²) in 0.028 and 0.057 m diameter pipes were collected. Enhancement in heat transfer rate due to natural convection and temperature dependent rheotogy was observed. The temperature dependent viscosity effect is a function of flow behavior index and it contributes more towards heat transfer enhancement than natural convection does. A correlation (confidence level ±15%) for the entire set of data is also presented.     

螺旋槽管中单相水与油湍流摩擦阻力与传热特性

对单相水与油分别在4根不同几何参数的螺旋槽管中湍流摩擦阻力与传热特性进行了试验研究。以动量传递与热量传递的模拟理论为基础,由试验结果的关联得到了动量传递粗糙度函数（R函数）与热量传递粗糙度函数（G函数）的表达式,并与前人工作进行了比较。针对油的Pr随温度变化较大的特性,提出了改进的强化传热性能评价方法,并据此对1号与2号试验管进行了评价。研究结果可用于换热器设计及优化螺旋槽管几何参数。     

空气横掠波纹管束的流动与传热性能

引　言管壳式换热器是石油化工行业应用十分广泛的换热设备 ,它具有易于制造、耐压高等特点 .但是普通管壳式换热器换热效率低 ,因此开发高效传热元件对管壳式换热器的进一步推广应用具有十分重要的意义 .采用翅片管换热器可以大大强化换热 ,但是阻力也增加很多 ,并且容易积垢 ,影响使用 .近年来开发的波纹管换热器由于加工方便、易于制造而越来越受到人们的重视[1～ 4 ] .但对于流体横掠波纹管束时流动传热性能的研究却少见报道 .本文对如图 1所示的波纹管束组成的换热器进行了实验测定 ,研究了 3种排数的阻力与换热规律 ,为设计换热器提供…     

ANALYTICAL STUDY OF HEAT TRANSFER TO LAMINAR FLOW OF NON-NEWTONIAN FLUIDS IN ANNULUS

An analytical study is made of the problem of laminar flow heat transfer to pseudoplastic fluids in a concentric circular tube annulus. The solution is obtained for simultaneously developing velocity and temperature profiles and constant wall heat flux. Constant property results are presented for different values of flow behavior index, n, and several inner to outer tube radius ratios and Prandtl numbers. Variable property solutions, with strongly temperature-dependent consistency index are obtained. The effect of viscous dissipation on the results of heat transfer is also presented.