Entropy parameters for heat exchanger design

A general expression for entropy generation in counter-current heat exchangers is developed. It is applicable to incompressible liquids and perfect gases. Two new entropy generation numbers are defined, N_M and N_Q. The analysis is applied to an air-air counter-current heat exchanger. The three entropy generation numbers, N_S, N_M and N_Q, have a different variation with NTU at the various values of the capacity flow rate ratio employed in the calculations.     

Optimum design parameters of a heat exchanger

In this study, the effects of the longitudinal and lateral seperations of consecutively enlarged-contracted arranged fin pairs, widths of the fins, angle of attack, heights of fins and flow velocity on the heat and pressure drop characteristics were investigated using the Taguchi experimental-design method. Nusselt number and friction factor were considered as performance parameters. An L₁₈(2¹13⁷) orthogonal array was selected as an experimental plan for the eight parameters mentioned above. First of all, each goal was optimized, separately. Then, all the goals were optimized together, considering the priority of the goals, and the optimum results were found to be fin width of 15 mm, angle of attack of 15°, fin height of 100 mm, span-wise distance between fins of 20 mm, stream-wise distance between fins of 10 mm, span-wise distance between slices of 20 mm, stream-wise distances between slices of 20 mm at a flow velocity of 4 m/s.     

Experimental investigation of heat transfer in a triple tube heat exchanger with coiled spring inserts

Experiments have been performed to investigate the effect of coiled spring inserts on heat transfer, pressure drop, and performance parameters of a triple tube heat exchanger (TTHX). Three different spring inserts having a pitch of 5, 10, and 15 mm are used and the diameter of the spring wire is taken as 1 mm. The experiments were carried out under a turbulent flow regime, with water as a working medium in parallel and counter flow configurations. The variation in different performance characteristics like heat transfer coefficient, Nusselt number, and effectiveness have been compared at various Reynolds numbers ranging between 4000 and 16,000 in the considered flow patterns. The Nusselt number of TTHX with the lowest pitch spring is found to be higher than that of the plain TTHX by 57.27% at Re = 4000 for the counter flow configuration. Both the thermal performance factor and effectiveness increased as the pitch of the spring insert was decreased. The effectiveness of TTHX with the lowest pitch spring insert is found higher than that of the plain TTHX by 43.84% in the counter flow pattern.     

一种新型换热器流动特性的实验研究

螺旋折流板换热器是将折流板布置成与管束有某个倾斜角度 ,流体在壳程沿着螺旋折流板呈螺旋状流动的一种新型换热器。在对几个影响螺旋折流板换热器流动特性的因素进行了实验研究后 ,本文对实验结果进行了论述和分析。     

Numerical investigation on the multi-objective optimization of a shell-and-tube heat exchanger with helical baffles

An improved method combining numerical simulation with multi-objective genetic algorithm (MOGA) was applied to study the flow and heat transfer characteristics of shell-and-tube heat exchanger with helical baffles (STHXsHB). It overcomes the dependence on empirical correlations. The helix angle and overlapped degree of helical baffles were chosen as optimization parameters, while the overall heat transfer coefficient K and pressure drop ΔP of STHXsHB were optimized by MOGA. The results showed that both overall heat transfer coefficient K and pressure drop ΔP varied adversely with the helix angles. The pressure drop ΔP was favorably affected by the overlapped degrees. The overall heat transfer coefficient K did not vary significantly with the overlapped degree. Three optimum configurations were obtained by the MOGA to maximize the overall heat transfer coefficient K and minimize the shell-side pressure drop ΔP. Compared with the original heat exchanger, the overall heat transfer coefficient K increased averagely by 28.3%, while the average pressure drop reduced averagely by 19.37%.     

基于翅片管式热交换器的优化设计研究

以一种特定管翅式热交换器的翅片形式为研究对象,提出了一种针对翅片结构的优化换热方法。该方法主要针对翅片侧换热系数和整体传热随翅片结构改变的变化规律,并采用传热系数和压降相结合的评价方法,针对管翅式热交换器的翅片高度、翅片厚度及翅片间距进行优化。经计算得出了热交换器的总传热系数在控制单一变量或多个变量下的最优值范围。     

Experimental investigation of heat transfer enhancement in a double pipe heat exchanger with a twisted inner pipe

In the present work, an experimental investigation is conducted to address the influence of inner pipe twisting on the overall performance of a double pipe heat exchanger. With the fluid to fluid heat exchange, both parallel and counter flow directions are examined as well. In addition to the original elliptical pipe, three pipes with different numbers of twisting (3, 5, and 7 twists per unit length) constructed from the elliptical pipe are considered where the heat transfer rate and pressure drop are addressed. All tests are carried out in the turbulent flow regime where the Reynolds number (Re) ranging from 5000 to 26,000 and water is used as the working medium. The obtained outcomes show that for both flow directions, there is an enhancement in the heat exchanger overall performance with all considered twisting pipes. The maximum enhancement in the Nusselt number is found to be 1.8 for the parallel flow and around 2.2 for the counter flow compared with the original pipe. The inner pipe with 7 twists, however, improves the overall performance the most, where a maximum performance enhancement factor of 1.63 and 1.9 are observed at Reynolds number of 26,000 in the parallel and counter flow configurations, respectively.     

A design optimization tool of earth-to-air heat exchanger using a genetic algorithm

Advancement in genetic algorithm (GA) optimization tools for design applications, coupled with techniques of soft computing, have led to new possibilities in the way computers interact with the optimization process. In this paper, the concept of goal-oriented GA has been used to design a tool for evaluating and optimizing various aspects of earth-to-air heat exchanger behavior. A new optimization method based on GA is applied as a generative and search procedure to optimize the design of earth-to-air heat exchanger. The GA is used to generate possible design solutions, which are evaluated in terms of passive heating and cooling of building, using a detailed thermal analysis of non air-condition building environment The results from the simulations are subsequently used to further guide the GA search to find the high-energy solutions for optimized design parameters. The specific problem addressed in this study is the sizing of earth-to-air heat exchanger in a non air-conditioned residential building. The developed algorithm is suitable for the calculation of the outlet air temperature and therefore of the heating and cooling potential of the earth-to-air heat exchanger system. This methodology is applicable to a wide range of design optimization problems like choice of building such as green house, solar house, or heating and cooling of buildings by mechanical system.     

Optimization of heat exchangers with vortex-generator fin by Taguchi method

A comparative study of effects of attack angle, length of vortex generator, height of vortex generator, fin material, fin thickness, fin pitch and tube pitch on fin performance of vortex-generator fin-and-tube heat exchanger is conducted by numerical method. The parameters of vortex-generator fin-and-tube heat exchangers are optimized by the Taguchi method. Eighteen kinds of models are made by compounding levels on each factor, and the heat transfer and flow characteristics of each model are analyzed. The results show that these six factors (fin pitch, longitudinal tube pitch, transverse tube pitch, length of vortex generator, height of vortex generator, and attack angle of vortex generator) have great influences on the JF-factor. The fin material and fin thickness have trifling effects on the JF-factor. The two optimal conditions (A1B3C3D2E1F2G1H3 and A2B2C2D3E1F2G1H3) are acquired, and the reproducibility of the results is verified by two analytical results.     

Computational and statistical analysis on the U-tube heat exchanger with different passes configuration: Taguchi method

In the present study, the passive technique of heat transfer in which single pass and double passes are included in a simple U-tube heat exchanger is analyzed. The computational fluid dynamics (CFD)-based parametric analysis is carried out to optimize the parameters affecting the temperature drop and heat transfer achieved from the U-tube heat exchanger. ANSYS Fluentv20 is used for the CFD analysis, and the RNG k-ɛ model and energy equation were considered to define the turbulence and heat transfer phenomena. The Taguchi method is used to formulate the experimental work and analyze the working parameters of the U-tube heat exchanger, such as hot and cold mass flow rate and hoRenew Energyt inlet temperature and cold inlet temperature. For the U-tube heat exchanger, four operating parameters are considered at four different levels in the Taguchi method. The best combination of parameters for achieving a maximum temperature drop is A₄B₁C₂D₃, and it is A₃B₄C₁D₂ in case of heat transfer. A U-tube single-pass heat exchanger is more effective as compared with other U-tube heat exchangers (zero- and double-pass). Experimental results are provided to validate the suitability of the purpose of the approach.     

Experimental study of heat transfer enhancement in an asymmetrically heated rectangular duct with perforated baffles

The paper presents results of an experimental study of heat transfer and friction in rectangular ducts with baffles (solid or perforated) attached to one of the broad walls. The duct has width-to-height ratio of 7.77; the baffle pitch-to-height ratio is 29; the baffle height-to-duct height ratio is 0.495. The Reynolds number of the study ranges from 2850 to 11500. The baffled wall of the duct is uniformly heated while the remaining three walls are insulated. These boundary conditions correspond closely to those found in solar air heaters. Over the range of the study, the Nusselt number for the solid baffles is 73.7–82.7% higher than that for the smooth duct, while for the perforated baffles, it ranges from 60.6–62.9% to 45.0–49.7%; decreasing with the increase in the open area ratio of these baffles from 18.4% to 46.8%. The friction factor for the solid baffles is found to be 9.6–11.1 times of the smooth duct, which decreased significantly for the perforated baffles with the increase in the open area ratio; it is only 2.3–3.0 times for the perforated baffles with open area ratio of 46.8%. Performance comparison with the smooth duct at equal pumping power shows that the baffles with the highest open area ratio give the best performance.     

Dendritic fins optimization for a coaxial two-stream heat exchanger

This paper documents the fundamental relation between the maximization of global performance and the maleable (morphing) architecture of a flow system with global constraints. The example is the coaxial two-stream heat exchanger with flow through a porous bed in the annular space. It is shown that the constraints force the design toward heat exchangers with finite axial length, where additional improvements are derived from installing high-conductivity fins across the porous bed. The maximization of global performance is achieved through the optimization of the configuration of plate fins. Configurations with radial fins are optimized analytically and numerically. Configurations with branched fins are optimized numerically. It is shown that the best configuration (radial vs. branched) depends on the size of the heat exchanger cross-section. When the size is small, the best is the radial pattern. When the size exceeds a certain threshold, the best configuration is the optimized branched tree of fins.     

Experimental investigation of single phase convective heat transfer coefficient in a corrugated plate heat exchanger for multiple plate configurations

Corrugated plate heat exchangers have larger heat transfer surface area and increased turbulence level due to the corrugations. In this study, experimental heat transfer data are obtained for single phase flow (water-to-water) configurations in a commercial plate heat exchanger for symmetric 30°/30°, 60°/60°, and mixed 30°/60° chevron angle plates. Experiments were carried out for Reynolds number ranging from 500 to 2500 and Prandtl number from 3.5 to 6.5. Experimental results show significant effect of chevron angle and Reynolds number on the heat transfer coefficient. Based on the experimental data, a correlation to estimate Nusselt number as a function of Reynolds number, Prandtl number and chevron angle has been proposed.     

An experimental investigation of heat transfer enhancement for a shell-and-tube heat exchanger

For the purpose of heat transfer enhancement, the configuration of a shell-and-tube heat exchanger was improved through the installation of sealers in the shell-side. The gaps between the baffle plates and shell is blocked by the sealers, which effectively decreases the short-circuit flow in the shell-side. The results of heat transfer experiments show that the shell-side heat transfer coefficient of the improved heat exchanger increased by 18.2–25.5%, the overall coefficient of heat transfer increased by 15.6–19.7%, and the exergy efficiency increased by 12.9–14.1%. Pressure losses increased by 44.6–48.8% with the sealer installation, but the increment of required pump power can be neglected compared with the increment of heat flux. The heat transfer performance of the improved heat exchanger is intensified, which is an obvious benefit to the optimizing of heat exchanger design for energy conservation.     

Correlations and optimization of a heat exchanger with offset-strip fins

The thermo-flow characteristics of a heat exchanger with offset-strip fins are numerically investigated for various fin geometries and working fluids. Previous correlations underestimate f values in the laminar and turbulent regimes and overestimate j values in the laminar regime, as the blockage ratio increase. Therefore, new correlations, which apply to offset-strip fins with blockage ratios of greater than 20%, are presented. Even though the working fluid was changed, the f values did not vary. However, the j values differed according to the working fluid. New j correlations were suggested as functions of the Prandtl number. Design variables of the offset-strip fins in a fuel cooler were optimized by using the correlations and the design of experiment. As a result, the JF factor of the optimized offset-strip fin was enhanced by 24% compared with that of the reference offset-strip fin.     

Conceptual optimization of a rotary heat exchanger with a porous core

The present article numerically optimizes the thermal performance of a rotary heat exchanger (RHEx) where its internal structure is modeled as a porous medium. The objective is to maximize the RHEx's heat transfer rate per unit of frontal surface area (q″). The flow velocity through the porous matrix respects Darcy's law. Two thermal conditions between the solid matrix and the fluid are considered: (i) local thermal equilibrium – LTE and (ii), non-local thermal equilibrium – NLTE. The numerical calculations, which are implemented using a finite volume formulation, allow us to optimize two design variables, the length L of the heat exchanger and the porosity φ. The numerical results show that the figure of merit is substantially affected by both design variables and that optimal values of L and φ can be obtained. The numerical experiments also show that the optimum porosity is not a function of the pressure difference driving the flow across the RHEx. The study ends by addressing the effects of the porosity distribution and differential periods between the hot and cold sides of RHEx on the figure of merit. The numerical results are supported by a scale analysis.     

Optimal design analysis of a tubular heat exchanger network with extended surfaces using multi-objective constructal optimization

The present work aims to investigate the influence of extended surfaces (fins) on the multi-objective optimization of a tubular heat exchanger network (THEN). An increase in the heat transfer area using various extended surfaces (fins) to enhance the performance of the heat exchanger was used while considering the effectiveness and total heat transfer area as two objective functions. In addition to the simulation of simple fins, a new set of fins, called constructal fins, was designed based on the constructal theory. Tubular heat exchanger network design parameters were chosen as optimization variables, and optimization results were achieved in such a way as to enhance the effectiveness and decrease the total heat transfer area. The results show the importance of constructal fins in improving the objective functions of heat exchangers. For instance, the simple fins case enhances the effectiveness by up to 5.3% compared to that without fins (usual heat exchanger) while using constructal fins, in addition to the 7% increment of effectiveness, reduces the total heat transfer area by 9.47%. In order to optimize the heat exchanger, the heat transfer rate and cold fluid temperature must increase, and at the same time, the hot exiting fluid temperature should decrease at the same constant total heat transfer area, which is higher in the constructal fins case. Finally, optimized design variables were studied for different cases, and the effects of various fins were reported.     

The application of field synergy number in shell-and-tube heat exchanger optimization design

In the present work the field synergy principle is applied to the optimization design of the shell-and-tube heat exchanger with segmental baffles. The field synergy number which is defined as the indicator of the synergy between the velocity field and the heat flow is taken as the objective function. The genetic algorithm is employed to solve the heat exchanger optimization problems with multiple design variables. The field synergy number maximization approach for heat exchanger optimization design is thus formulated. In comparison with the initial design, the optimal design leads to a significant cost cut on the one hand and an improvement of the heat exchanger performance on the other hand. The comparison with the traditional heat exchanger optimization design approach with the total cost as the objective function shows that the field synergy number maximization approach is more advantageous.     

Optimization of the design parameters of Parallel-Plain Fin heat sink module cooling phenomenon based on the Taguchi method

This paper presents an effective method for predicting and optimizing the cooling performance of Parallel-Plain Fin (PPF) heat sink module based on the Taguchi method. The numerical simulative analyses of PPF heat sink module have been constructed to understand the affecting situation of its related modeling parameters. The design parameters evaluated are the outline design of the heat sink module and the wind capacity of fan, and the highest temperature (or thermal resistance) of this module is considered as the performance characteristics. Taguchi method for design of experiment (DOE) and the analysis of variance (ANOVA) are employed to efficiently seek the combination of optimized design parameters. From the numerical simulative analyses, the optimum design parameters to obtain the lowest value of the highest temperature (or thermal resistance) are found, which is the target of this research.     

Experimental investigation of header configuration improvement in plate–fin heat exchanger

Flow characteristics in the header of a plate–fin heat exchanger have been investigated by means of Particle Image Velocimetry (PIV). A series of velocity vector and streamline graphs of different cross-sections are obtained in the experiment. The experimental results indicate that performance of fluid maldistribution in a conventional header is very serious, while the improved header configuration with a punched baffle can effectively enhance the uniformity of flow distribution. The flow maldistribution parameter and the ratio of the maximum velocity to the minimum in a plate–fin heat exchanger decreases by installing the punched baffle. Further heat exchange experiments indicate that the temperature is distributed more uniformly in the improved heat exchanger core and the heat exchanger effectiveness can be effectively enhanced. The conclusion of this paper is of great significance in the optimum design of plate–fin heat exchanger.