Alternative Design Approach for Plate and Frame Heat Exchangers Using Parameter Plots

The simultaneous design and specification of heat exchangers of the plate-and-frame type is analyzed. A pictorial representation of the design space is used to guide the designer toward the selection of the geometry that best meets the heat duty within the limitations of pressure drop. The design space is represented by a bar plot where the number of thermal plates is plotted for three conditions: (1) for fully meeting the required heat load, (2) for fully absorbing the allowable pressure drop in the cold stream, and (3) for fully absorbing the allowable pressure drop in the hot stream. This type of plot is suitable for representing the design space, given the discrete nature of the plate geometrical characteristics, such as effective plate length and plate width. Applications of the use of bypasses as a design strategy are also presented.     

Alternative Sizing Methodology for Compact Heat Exchangers of the Spiral Type

A rapid sizing methodology for compact heat exchangers of the spiral plate type is presented. The methodology allows for the determination of the exchanger geometry such that full pressure drop utilization is achieved on both streams. This is done by considering plate width and plate spacing as continuous variables. The resulting values are the basis for selecting the final exchanger dimensions according to standard dimensions. The design approach makes use of empirical correlations for the calculation of heat transfer coefficient and friction factor based on average curvature. The approach is demonstrated using two case studies.     

板式通风换热器的研究进展

新风系统中的余热回收是重要的建筑节能技术之一。板式通风换热器因其结构简单、经济且与建筑一体化程度好等优点,已得到广泛应用。本文首先简述了板式通风换热器的特点,然后系统地介绍了目前国内外的试验和理论研究现状,最后展望其发展和应用前景。     

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。     

Thermodynamic and Economic Optimization of Plate Fin Heat Exchangers Using the Bees Algorithm

This study presents the successful application of the bees algorithm (BA) for optimal design of a cross‐flow plate fin heat exchanger by offset strip fins. The ε – NTU method is used to approximate the heat exchanger effectiveness and pressure drop. Two different objective functions including the minimization of total annual cost (sum of investment and operational costs) and total number of entropy generation units for certain heat duty required under given space constraints are considered as targets of optimization separately. Based on the applications, seven design parameters (heat exchanger length at hot and cold sides, fin height, fin frequency, fin thickness, fin‐strip length, and number of hot side layers) are selected as optimization variables. Two examples from the literature are presented to illustrate the efficiency and accuracy of the proposed algorithm. Results showed that the BA can detect an optimum configuration with higher speed (short computational time) and accuracy compared to the imperialist competitive algorithm (ICA) and the genetic algorithm (GA). © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 43(5): 427–446, 2014; Published online 3 October 2013 in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21087     

Improved Water Utilization with Plate Heat Exchangers

Cooling water costs can often be reduced by utilizing impure sources of water, such as the sea. The use of seawater generally involves a closed-cycle freshwater primary circuit, a type of cooling that, although saving on water, requires special design techniques in order to optimize the process. These techniques are discussed and examples are given of large and small installations currently in operation.     

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.     

板式换热器颗粒污垢特性的实验研究

以纳米氧化镁颗粒溶液为实验工质,进行了板式换热器颗粒污垢特性的实验研究,分析了颗粒质量浓度、颗粒粒径、流速和低温介质温度对颗粒污垢热阻的影响.结果表明:板式换热器颗粒污垢无明显诱导期存在,结垢速率和污垢热阻渐进值均随颗粒质量浓度的增大而增大,且增大幅度逐渐减小;颗粒粒径对污垢热阻的影响较明显,在相同质量浓度下,颗粒粒径越小,结垢速率越快,且污垢热阻越大;流速对污垢热阻的影响较为复杂,高流速下的结垢速率略大于低流速下,且高流速下达到稳定时的污垢热阻渐进值小于低流速下;低温介质温度对颗粒污垢热阻的影响不明显.     

Experimental Investigation on Port-to-Channel Flow Maldistribution in Plate Heat Exchangers

Experiments have been conducted to analyze the flow and pressure distribution in a plate heat exchanger by measuring local port pressure distribution in a commercial plate heat exchanger. Flow rate in channel and channel pressure drops are evaluated by measuring the pressure inside the inlet and exit ports at different locations for different port dimensions. In these experiments, the measurement of pressure is done without disturbing the fluid flow inside the port. This technique also offers the option of manipulating port size without changing the plate characteristics. Direct experimental measurement provides the scope for eliminating other effects, such as gasket, end losses, and improper wetting of channels from the flow maldistribution effect. The measurements indicate the existence of non-uniform flow distribution that increases with flow rate and decreases with port diameter. Results clearly show that it is important to consider the flow maldistribution for better design of plate heat exchangers.     

顺排与叉排套片式换热器的热力性能对比研究

套片式换热器的管束排列形式一般都是叉排,顺排非常少见。由于顺排形式的套片式换热器通常比叉排的流动阻力更小,因而对一些流动阻力有限制的场合,可以考虑使用顺排形式的套片式换热器。为论证这一点,对某种结构形式的顺排套片式换热器和叉排套片式换热器的热力性能进行了对比研究。为便于对比、分析,两个换热器试件的纵向管间距及管排数设计成相等。结果显示:两个试件的热力性能非常接近。分析表明,在某些应用场合,套片式换热器排列成顺排是更合适的选择。图7参6     

CFD Simulation of Heat Transfer and Pressure Drop in Compact Brazed Plate Heat Exchangers

In this paper, the thermal and hydraulic characteristics of corrugated fluid channels of compact brazed plate heat exchangers (BPHE) are investigated by computational fluid dynamics (CFD) simulations using the commercial CFD software ANSYS CFX 14.0. The influence of geometry parameters of the corrugated pattern such as chevron angle and corrugation pitch on the BPHE performance is investigated on small fluid section geometries. The influence of various types of wall heat transfer boundary conditions on the simulation results is also studied. An entire fluid channel is simulated using various turbulence models in the Reynolds number range of 300 to 3000. The CFD predictions are also validated using data obtained from laboratory experiments. The simulations of the entire fluid channel underpredict heat transfer and pressure drop by 20–30% and 10–35%, respectively. The results from the small fluid sections suggest that the CFD simulations can be used as a reasonably effective tool in determining the relative performance variation of various plate patterns.     

Exergetic Optimization of Shell-and-Tube Heat Exchangers Using NSGA-II

In this article, a multi-objective exergy-based optimization through a genetic algorithm method is conducted to study and improve the performance of shell-and-tube type heat recovery heat exchangers, by considering two key parameters, such as exergy efficiency and cost. The total cost includes the capital investment for equipment (heat exchanger surface area) and operating cost (energy expenditures related to pumping). The design parameters of this study are chosen as tube arrangement, tube diameters, tube pitch ratio, tube length, tube number, baffle spacing ratio, and baffle cut ratio. In addition, for optimal design of a shell-and-tube heat exchanger, the method and Bell–Delaware procedure are followed to estimate its pressure drop and heat transfer coefficient. A fast and elitist nondominated sorting genetic algorithm (NSGA-II) with continuous and discrete variables is applied to obtain maximum exergy efficiency with minimum exergy destruction and minimum total cost as two objective functions. The results of optimal designs are a set of multiple optimum solutions, called “Pareto optimal solutions.” The results clearly reveal the conflict between two objective functions and also any geometrical changes that increase the exergy efficiency (decrease the exergy destruction) lead to an increase in the total cost and vice versa. In addition, optimization of the heat exchanger based on exergy analysis revealed that irreversibility like pressure drop and high temperature differences between the hot and cold stream play a key role in exergy destruction. Therefore, increasing the component efficiency of a shell-and-tube heat exchanger increases the cost of heat exchanger. Finally, the sensitivity analysis of change in optimum exergy efficiency, exergy destruction, and total cost with change in decision variables of the shell-and-tube heat exchanger is also performed.     

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。     

Plate Heat Exchangers: Calculation Methods for Singleand Two-Phase Flow

Plate heat exchangers were first developed about 100 years ago but have won increasing interest during the last two decades, primarily due to the development of methods of manufacturing brazed plate heat exchangers. This type of heat exchanger offers very good heat transfer performance in single-phase flow as well as in evaporation and condensation. Part of the reason is the small hydraulic diameters, typically being less than 5 mm. Other advantages of plate heat exchangers are the extremely compact design and the efficient use of the construction material. In spite of their long use, the calculation methods for predicting heat transfer and pressure drop are not widely known. It is the purpose of this article to present such calculation methods for single-phase flow and for flow boiling and to discuss some of the specifics of this type of heat exchangers.     

等流速法在板式换热器传热试验中的应用

在换热器的传热性能试验中,对流换热系数的测定是一个重要的组成部分。对于板式换热器而言,用等雷诺数法来获得其对流换热系数是比较合适的一种方法,但对试验过程的控制要求比较高。文中阐述了一种修正的等雷诺数方法－－等流速法,它使试验过程的控制十分方便,通过实例,介绍了该方法的具体应用。     

多股流换热器自动最优控制过程的模拟

为了模拟多股流换热器自动控制过程，应用特别适用于“多输入．多输出”系统的状态空间方法。该方法的调节依据是状态参数的反馈，状态参数不仅包括输出参数，还包括输出参数变化的速度和加速度及高阶导数等。利用实验所得的动态特性，导出了多股流换热器的状态方程和输出方程，并用动态规划方法对其自动最优控制过程进行了模拟。给出了一个四股流换热器自动最优控制过程模拟实例。结果表明：状态空间方法和动态规划方法可有效地应用于多股流换热器的最优反馈控制设计。图4表2参8     

Two-Phase Flow Visualization in Chevron and Bumpy Style Flat Plate Heat Exchangers

Adiabatic flow visualization in a chevron plate, a 1:1 aspect ratio bumpy plate, and a 2:1 aspect ratio bumpy plate heat exchangers were investigated for vertical upward flow with R134a. Qualities ranging from 5% to 90% and mass fluxes of 60, 90, and 125 kg/m²-s were investigated. The flow visualization experiments were conducted at a 10°C inlet temperature. Four flow regimes were observed for the flat plate geometries investigated: bubbly flow, rough annular flow, smooth annular flow, and mist flow. The four flow regimes are mapped out on a mass flux versus quality basis for each geometry. The chevron geometry was seen to undergo flow transitions at lower qualities and mass fluxes than the bumpy plate geometries, and the 2:1 aspect ratio bumpy plate geometry was seen to undergo flow transitions at lower qualities and mass fluxes than the 1:1 aspect ratio bumpy plate geometry.     

新型板式凝汽器传热特性及优化研究

为了提高板式凝汽器的换热效果,设计了一种椭圆通道板式凝汽器,入口蒸汽进入4个椭圆管束通道,在相变冷凝过程中,体积不断减少,先后进入3个椭圆管束通道、2个椭圆管束通道,随后从单个椭圆管束通道中排出凝结液,简称为4-3-2-1型。通过FLUENT软件在蒸汽流量68.3 m3/h、温度140 ℃,循环冷却水流量为3 487.14 kg/h及温度20 ℃条件下,模拟并分析了短长轴比和板间距对传热性能的影响。结果表明,对于4-3-2-1型椭圆通道板式凝汽器,板束椭圆通道短长轴比为0.6、板间距为10 mm时,其综合传热性能最佳。为了验证新型板式凝汽器通道布置的合理性,对比了4-3-2-1型、4-2-2-2型和4-4-1-1型3种凝汽器的传热性能,当循环冷却水流速在0.08~0.32 m/s范围内,4-3-2-1型板束通道结构传热性能优于其他两种板束结构,更易使水蒸气发生相变凝结。     

等雷诺数法在板式换热器传热试验中的应用

在换热器的传热性能试验中,对流换热系数的测定是重要的一个组成部分,对流换热系数的测定方法有很多种,但都有各自的应用范围和条件。对于板式换热器而言,用等雷诺数法来获得其对流换热系数是比较合适的一种方法,文中介绍了等雷诺数法的原理及其在板式换热器中的应用。通过实例,介绍了具体的试验及计算方法。