Multidimensional and Unsteady Simulation of Fin-and-Tube Heat Exchangers

This article presents a model for the analysis of fin-and-tube heat exchangers, focusing on the heat conduction processes within the finned tube bundle. A cutting cell discretization has been proposed for the fins to adapt to the tubes shape, while the tubes have been discretized in axial and angular directions to consider complex heat transfer coefficient variations. A set of results is given on fin efficiency and transient response comparing with well-established methods. A full-scale condenser is also analyzed as an illustrative result, detecting important thermal bridges through the fins.     

Thermal Performance of Elliptical Fin-and-Tube Heat Exchangers with Vortex Generator under Various Inclination Angles

Elliptical fin-and-tube heat exchangers are commonly used in air conditioning,heating,refrigeration industries,and ventilation.This study numerically investigates the effect of vortex generators on the performance of elliptical fin-and-tube heat exchanger under different inclination angles.In this study,air flow that is in the transitional regime is selected as the working fluid.Reynolds numbers at the inlet are varied in a range of 1300 to 2100,and the shear stress transport k-ωturbulence model is selected to solve the non-closure of basic turbulence equations.The ellipticity ratios of the tubes which are used for the analysis are between 0.6 and 1.0,and the inclination angles are varied from 15°to 75°.The effects of different inclination angles of vortex generators on the Colburn factor j,friction factor f,and efficiency index j/f are analyzed.The friction and Colburn factors are observed to increase with increasing vortex generator inclination angles.It is found that the efficiency factors for a 15°vortex generator inclination angle at 0.6,0.7,0.8,and 0.9 ellipticity ratios improve compared to the corresponding cases with no vortex generator.However,the vortex generator cannot improve the efficiency factor of the circular tube heat exchanger.The 3 D CFD method employed by this study has great potential for use in optimally designing the arrangement of the vortex generators to enhance the performance of heat exchangers.     

Performance Prediction of Compact Fin-and-Tube Heat Exchangers in Maldistributed Airflow

An experimental study of a fin-and-tube heat exchanger was performed in two different configurations (single and three-screen mode). To this end, a test rig was constructed to evaluate the heat transfer capacity on the air side and water side. A wide range of Reynolds numbers on the air side was investigated. A series of measurements was performed with uniform inlet flow conditions. These served to determine the heat transfer correlation for the fin type using the Wilson plot method. No correlation was available, as the fin is an adapted inclined louvered type. To validate these results, a thorough uncertainty analysis was performed. Parallel to the experiments, a simulation program was written, designed to take non-uniform flow into account. The program is based on a local (section by section) analysis scheme. To validate the program, a series of non-uniform measurements was performed. Results showed that the program is able to predict the impact of non-uniform inlet flow conditions. The numerical code can be used as a design tool to develop more efficient heat exchangers.     

Thermal and Fluid Dynamic Simulation of Automotive Fin-and-Tube Heat Exchangers,Part 2: Experimental Comparison

A detailed model for the simulation of automotive fin-and-tube heat exchangers previously developed by the authors (Part 1) has been experimentally validated for a wide range of geometries and boundary conditions. Some of this experimental information was collected in an academic testing unit, while a second group of experiments was conducted in the experimental set-up of an industrial partner. The data cover a wide range of operational conditions and analyze the effect of most influential geometric parameters. The paper presents the experimental units and shows the comparison between numerical predictions and experimental values. The numerical calculations have been carried out using the most suitable available air-side heat transfer and friction correlations. Although the comparison is reasonably accurate, the deviations appearing among the predictions using different correlations indicate that further research work is still necessary to describe in a more accurate way the fundamental behavior of the louver fin geometry.     

改进粒子群算法在管壳式换热器优化设计中的应用

以管壳式换热器每年的总费用作为目标函数,采用含随机扰动算子的改进粒子群算法(IPOS)对其进行了优化.在优化设计模型中,采用Bell-Delaware法描述壳侧流体,优化变量选择管程数、换热管内径和外径及间距、管布置方式、封头类型、流体分配方式、密封条数、壳程压降和管程压降.对采用IPOS算法得到的优化结果与相关文献的结果进行了比较.结果表明:IPOS算法具有全局收敛、计算精度高、稳定性好的特点,并能获得约束条件下管壳式换热器的最优设计方案.     

用模拟退火算法改进管壳式换热器的优化设计

介绍了一种由两级管壳式换热器组成的换热器系统的优化设计数学模型，数学模型属于典型的有约束非线性规划问题。目前对有约束非线性规划问题还没有通用的求全局最优解的算法。转轴直径搜索可行方向法(DSFD方法)是一种比较有效的求解有约束非线性规划问题的算法。但它只能得到局部最优解。将模拟退火(Simulated Annealing)算法结合DSFD算法，构成了一种DSFD—SA—DSFD算法。在应用模拟退火算法的同时引入了罚函数法．将有约束非线性问题转化为无约束非线性问题。计算结果表明，DSFD—SA—DSFD算法能较快得到换热器优化问题的最优解，克服了单纯用DSFD算法只能得到局部最优解和单纯用SA算法效率不高的缺点。图3表11参8     

A New Approach to Correlate the Frictional Performance of Fin-and-Tube Heat Exchangers in Wet Conditions

This study presents a new approach to correlate the frictional performance of fin-and-tube heat exchangers in "completely wet" and "partially wet" conditions by using "completely dry" data. A total of 22 samples of uncoated plain fin-and-tube heat exchangers are used to develop the associated frictional correlation. The developed correlation is capable of predicting the frictional performance of "completely wet" and "partially wet" conditions with a mean deviation of 7.2%.     

Conjugated Heat Transfer Simulation of a Fin-and-Tube Heat Exchanger

Heat transfer and pressure drop of a fin-and-tube heat exchanger are studied by taking into account the conjugated heat transfer between the flow and the fin. The temperature distribution of the fin is calculated in respect to the convective heat transfer of the air flowing through the tube bank channel. Contemporary enhancement methods emphasize the importance of local turbulence augmentation which effects the convective heat transfer. In this paper, the importance of conjugated heat transfer, where the temperature of the flow and fin are coupled together is emphasized and compared with a constant surface temperature boundary condition simulation and experiment, which are found in the literature.     

Design of Regenerative Heat Exchangers

Rotary regenerators are used widely for energy recovery, both in industrial and air-conditioning applications, because of the advantages they have over other types of heat exchangers. In this study, a mathematical model for the design of rotary regenerators is presented. The method is valid for all kinds of channel geometries that form the matrix of a rotary regenerator and can be used for all rotational speeds. The validity of the method is tested with the experimental and numerical results available for rotational speeds between 0.05 and 7 rev/min. A good agreement between the model and the experimental numerical results is obtained. The method presented can therefore be recommended for the safe design of rotary regenerators.     

Parallel-Flow Heat Exchangers with Ambient Thermal Interaction

A mathematical model is developed to study the performance of a parallel-flow heat exchanger in which both fluid streams are interacting thermally with the surroundings. The fluid temperatures are found to be dependent on the magnitude of the ambient temperature relative to fluid inlet temperatures, the ratios of conductances between the fluids and the ambient and the interfluid conductance, the ratio of minimum to maximum fluid capacities, and the number of transfer units, NTU, for the heat exchanger. Two heat exchanger effectiveness criteria, one each for the hot and cold fluids, are used to study performance. The effectiveness is found to be adversely affected by increasing conductance ratios, increasing NTU, and increasing temperature difference between the ambient and the fluid of interest. For very high values of the conductance ratios, the heat exchanger will not perform as expected and both fluid temperatures will approach that of the ambient. The parallel-flow arrangement is compared to counterflow and is found to be less effective under the external heat transfer condition.     

Risk-Based Design Margin Selection for Heat Exchangers

For more than a quarter century, business and industry have used risk-based matrices to quantify probability and consequences in decision making. However, this tool has not yet been applied to the heat exchanger design process. Adding a design margin to the calculated size of an exchanger is common practice. This margin represents the added heat exchanger area necessary to provide confidence that the exchanger will operate as required throughout its run cycle. An assumption is made that the additional area will not have a deleterious impact on performance. This report introduces the concept of a risk-based design margin selection process as a quantitative aid in separating the individual components that comprise the uncertainty in heat exchanger design. In addition, it provides a technique to help the designer determine a reasonable, cost-effective margin to apply to the heat exchanger. Two example cases show the application of the procedure.     

板式换热器在供热系统中的应用

本文介绍板式水－水换热器的基本特点,详述了它的计算、设备选型、组合方式和应注意问题。     

Effect of Waffle Height on the Air-Side Performance of Wavy Fin-and-Tube Heat Exchangers under Dehumidifying Conditions

An experimental study was carried out to examine the effect of the waffle height on air-side performance of typical fin-and-tube heat exchangers under dehumidifying conditions. The waffle heights examined in the present study are 1.18 and 1.58 mm, respectively. A total of 12 samples of heat exchangers, including eight having wavy fin and four having plain fin configurations were tested. The test results indicated that the effect of waffle height on the heat transfer enhancement ratio, compared to the plain-fin counterpart, is pronounced only for smaller fin pitch and larger waffle height, while its effect on the pressure drop is very pronounced throughout the test range, and is almost two times higher than in dry conditions.     

Application of Transient Analysis Methodology to Quantify Thermal Performance of Heat Exchangers

A transient testing technique is developed to evaluate the thermal performance of industrial-scale heat exchangers. A Galerkin-based numerical method with a choice of spectral basis elements to account for spatial temperature variations in heat exchangers is developed to solve the transient heat exchanger model equations.

Testing a heat exchanger in the transient state may be the only viable alternative where conventional steady-state testing procedures are impossible or infeasible. For example, this methodology is particularly suited to the determination of apparent fouling levels in component cooling water system heat exchangers in nuclear power plants. The head load on these so-called component coolers under steady-state conditions is too small to permit meaningful testing. An adequate heat load develops immediately after a reactor shutdown when the exchanger inlet temperatures are highly time-dependent. The application of the analysis methodology is illustrated herein with reference to an in-situ transient testing carried out at a nuclear power plant. The method, however, is applicable to any transient testing application.     

Single- and Multi-Objective Design Optimization of Plate-Fin Heat Exchangers Using Jaya Algorithm

This paper explores the use of Jaya algorithm for the single- and multi-objective design optimization of plate-fin heat exchangers (PFHEs). Design of PFHEs involves a number of geometric and physical parameters with high complexity. The general design approaches are based on trial and error and become tedious and time consuming and do not guarantee the achievement of an optimal design. Therefore, advanced optimization algorithms are preferred. The Jaya algorithm is a newly developed simple algorithm and it does not have any algorithmic-specific parameters to be tuned and this aspect reduces the designer's effort in tuning the parameters to arrive at the optimum value of the objective function. The Jaya algorithm is proposed for the design optimization of PFHEs by minimizing the total surface area of heat transfer, total annual cost, and total pressure drop of the system and maximizing the effectiveness. Seven design parameters are considered which are imposed by constraints on the design. Single- as well as multi-objective design optimization is carried out using the proposed algorithm. The results obtained by Jaya algorithm are compared with the results of latest reported algorithms. These comparisons revealed that the Jaya algorithm can be successfully applied for the design optimization of PFHEs.     

一种多股流换热器综合性能优化设计方法

在综合考虑了体积、重量和阻力等因素的基础上,对多股流换热器进行通道排列和优化设计,并运用无量纲分析法,自定义了syn因子、syn线等用以评价换热器综合性能的指标。详细分析了应用syn因子综合优化翅片结构的过程,与实际的设计结果比较表明：该方法适用于多股流换热器的综合性能优化设计。     

基于遗传算法的热管换热器优化设计

在对热管传热和热阻的关系进行分析的基础上,利用遗传算法进行优化得到了最合适的翅片间距和翅片高度.算例表明这种优化是准确有效的,达到了优化热管换热器性能的目的.     

Fin Pattern Effects on Air-Side Heat Transfer and Friction Characteristics of Fin-and-Tube Heat Exchangers with Large Number of Large-Diameter Tube Rows

Air-side heat transfer and friction characteristics of nine kinds of fin-and-tube heat exchangers, with a large number of tube rows (6, 9, and 12, respectively) and large diameter of tubes (18 mm), are experimentally investigated. The test samples consist of three types of fin configurations: plain fin, slit fin, and fin with delta-wing longitudinal vortex generators. The working fluid in the tube is steam. Results show that when the number of tube is larger than 6, the heat transfer and friction performance for three kinds of fins is independent of the number of tube rows, and slit fin provides higher heat transfer and pressure drop than the other two fins. The heat transfer and friction factor correlations for all the heat exchangers were acquired with Reynolds numbers ranging from 4000 to 10000. The air-side performance of heat exchangers with plain fin, slit fin, and longitudinal vortex-generator fin were evaluated under three sets of criteria, and the results showed that the heat exchanger with slit fin has better performance than that with vortex-generator fin, especially at high Reynolds numbers.     

Thermal Analysis of Vertical Ground Exchangers of Heat Pumps

The heat rate absorbed from the ground by a vertical ground exchanger of a heat pump unit is considered. The aim is to investigate the time variation of this energy rate for a set of parameters. The analyzed set of alternatives encompasses arrangements of the exchanger tubes, values of the temperature of the heat carrier, thermal parameters of the ground, periodic operation of the compressor, and, when appropriate, different values of seepage velocity. To achieve this goal, the transient temperature distributions in the soil surrounding the ground exchanger are evaluated. The calculations are carried out using both PATRAN-THERMAL, a commercial finite volume code, and FEMCONV, an in-home FEM package. Characteristic features of the latter are discussed briefly along with some results of simulations for a ground exchanger with tube-in-tube (Field-type) elements. It is shown that in every case, the heat rate absorbed from the ground depends on the season and reaches the minimum value in the second part of winter. As expected, a strong influence of the arrangement of the exchanger tubes and the motion of moisture is observed. It is shown that if the prices of the electric energy are variable during a day, it may be profitable to operate an HP unit compressor in a periodic regime. The approximate values of the heat pump unit coefficient of performance, defined as the ratio of heat output of HP and compressor driving power, are evaluated. It is pointed out that this coefficient depends on the heat carrier temperature, and therefore this temperature may also be a subject of optimization calculations.     

Numerical Investigation on Thermal Performance Design of Cryogenic Compact Heat Exchangers with Serrated-Fin Channels

Abstract

Traditional empirical formulas of Colburn heat transfer factors will lead to a design deviation for cryogenic heat exchangers. This paper employs the computational fluid dynamics (CFD) technique to numerically study the thermal performance of cryogenic compact heat exchangers (CCHEs). To obtain more precise convective heat transfer coefficients, the heat transfer performance of CCHE with serrated fin channels is analyzed considering various cryogenic fluid properties, fin materials and the axial heat conduction (AHC), and a heat transfer deterioration rate is proposed to investigate the effect of AHC on the heat transfer performance of CCHEs. For the simulation design, a quasi-one-dimensional calculation model is developed to obtain the temperature and pressure fields of the whole heat exchanger using the previous CFD results of the finned channels to avoid the deviation caused by traditional empirical formulas. Finally, a case study for a CCHE in a practical system is designed and analyzed by the proposed approach. The results suggest that cryogenic conditions have a significant effect on the design performance of heat exchangers, especially when considering the influences of fluid properties, materials, and AHC. For different cryogenic fluids, accurate heat transfer factors should be selected for the design calculations, and materials with high thermal conductivity will increase the effect of AHC and deteriorate the performance of the CCHE.