Experimental Studies on Thermal Performance and Flow Resistance of Heat Exchangers with Helical Baffles

In this study, the shell-side heat transfer performance and flow resistance of the shell-and-tube heat exchangers with third-symmetrical, quarter-symmetrical, quarter-unsymmetrical helical baffles and segmental baffles were experimentally obtained. Except for the baffles, these heat exchangers had the same geometrical configuration and number of tubes. Cold and hot water were used as working fluids in the shell and the tube side, respectively. The experiments were done with the cold water volumetric flow rate ranging between 3 and 7 m³/h and the hot water volumetric flow rate constant at 5.5 m³/h. The results show that the heat exchanger with segmental baffles has higher shell-side heat transfer performance and flow resistance than those with helical baffles. Among the three helical baffles used, the third-symmetrical helical baffle offers the highest shell-side heat transfer performance and flow resistance. The quarter-unsymmetrical helical baffle offers the lowest shell-side flow resistance. Its performance of shell-side heat transfer is also the lowest one but close to that of the quarter-symmetrical helical baffle, so the quarter-unsymmetrical helical baffle provides the best conversion efficiency in all heat exchangers mentioned. Compared with the segmental baffle, the shell-side Nusselt numbers that the third-symmetrical, the quarter-symmetrical, and the quarter-unsymmetrical helical baffle offer decrease on the average by about 26%, 37%, and 38%, respectively, and the corresponding shell-side Euler numbers they provide decrease on the average by about 33%, 49%, and 55%, respectively. Thus, the relative shell-side conversion efficiencies increase by about 9%, 25%, and 39% on the average, respectively.     

Experimental investigation of the influence of the cross flow in the nozzle region on the shell-side heat transfer in double-pipe heat exchangers

In shell-and-tube heat exchangers, the shell-side fluid flow enters and leaves through nozzles which are mounted on the shell wall. The cross-flow in the nozzle region has an impact on the shell-side pressure drop and heat transfer. The influence on the heat transfer is investigated by means of experiments with four double-pipe heat exchangers.The results show that the influence is greater, the shorter the heat exchangers are, and the smaller the ratio of the free cross sectional areas of the nozzle to that of the shell-side. A correlation suitable for predicting the heat transfer coefficient is presented in this paper. The correlation consists of the Nusselt number for the flow in the nozzle region and that for the flow in the annulus.     

Most Frequently Used Heat Exchangers from Pioneering Research to Worldwide Applications

Heat exchangers contribute significantly to many energy conversion processes. Applications range from power production, petroleum refining and chemicals, paper and pharmaceutical production, to aviation and transportation industries. A large percentage of world market for heat exchangers is served by the industry workhorse, the shell-and-tube heat exchanger. Recent developments in other exchanger geometries have penetrated in various industry applications; however, the shell-and-tube exchanger by far remains the industry choice where reliability and maintainability are vital. Over the years, significant research and development efforts are devoted to better understand the shell-side geometry. New geometries are introduced for performance enhancement and to improve reliability. The pioneering work published by J. Nemcansky et al. in the Trans. Institute of Chemical Engineers in May, 1990, on helical baffles paved the way to a major shift from a conventional understanding of baffles in a shell-and-tube heat exchanger. Helical baffles serve as guide vanes for shell-side flow as compared to creating flow channels with conventional segmented baffles. In the past decade, ABB Lummus Heat Transfer has extended the understanding of the helical baffle geometry through extensive testing and development. CFD flow simulation studies have further confirmed the helical baffle advantage. Industry feedback on operating Helixchanger® heat exchangers—the shell-and-tube heat exchangers with helical baffles—has demonstrated low fouling characteristics as well as a higher conversion of shell-side pressure drop to heat transfer. In this paper, the characteristics of this novel Helixchanger heat exchanger are discussed. Examples from early installations in the power industry to the major applications in the petro-chemical and refining industries are presented, illustrating the advantages in reducing fouling and increasing reliability while achieving lower total life cycle costs.     

A Comparative Assessment of RODbaffle Shell-and-Tube Heat Exchangers

The shell-and-tube heat exchanger (SBE), with its tubes held in plate baffles to produce cross flow of the shell-side fluid, has recently been modified to produce a RODbaffle heat exchanger (RBE) free from tube failure due to vibration. The results showed slightly enhanced heat transfer coefficients with significant reductions in pressure loss, leading to reduced cost of exchangers and in some instances smaller exchangers.     

Numerical modeling and experimental validation of heat transfer and flow resistance on the shell side of a shell-and-tube heat exchanger with flower baffles

CFD simulation has become a powerful and popular tool for the thermal hydraulic design and analysis of heat exchangers. However, the computation load is usually too heavy to simulate a whole shell-and-tube heat exchanger (STHX) applying the traditional modeling method. In the present study, a numerical model based on the concepts of porosity and permeability is developed to obtain the shell-side thermal hydraulic performances. In this model, the distributed resistances and heat sources, as well as the distributed turbulence kinetic energy and its dissipation rate are introduced to account for the impacts of tubes on the fluid. The numerical model is solved over Re = 6813–22,326 for the shell side of a STHX with flower baffles, and reasonable accuracy is demonstrated by the comparison with test data (maximum relative deviation within 15%). With this model, the velocity and temperature fields, together with the distribution of convective heat transfer coefficient, are obtained and presented to help analyzing the underlying mechanism of shell-side thermal augmentation. The present work shows that this model is economic and effective in the thermal hydraulic design and analysis of a whole device.     

Double Perforated Impingement Plate in Shell-and-Tube Heat Exchanger

This article presents a solution to a chronic problem causing repeated tube failure at shell-and-tube heat exchangers. The problem is related to the fouling process on the tubes' surface, which accumulates downstream from the impingement plate at the exchanger inlet nozzle within the first tube rows due to low velocity and vortices production. In fouling services, the suspended deposits, fouling, accumulates on the tubes' surface downstream from the impingement plate, causing under-deposit corrosion, raising the tubes' surface temperature due to lack of cooling, and accelerating fouling process. Under-deposit corrosion attacks tubes and causes repeated tube failure, costing a lot of money in terms of material, maintenance, and production losses. Normal practice of extending tube life and delaying their failure is to upgrade the tubes' metallurgy. So the article objective is to present an economical solution option through modifying the impingement plate in the shell-and-tube heat exchangers where the impingement plate is recommended by the Tubular Exchanger Manufacturers Association (TEMA). The impingement modification is to replace the solid conventional impingement plate with double spaced plates having offset holes, called double perforated impingement plates (DPIP). The objective of this work can be met by comparing the simulation of the shell-side inlet flow distribution around the conventional and modified (DPIP) impingement plates and ensuring enhancement of the flow pattern distribution at the area behind the impingement plates. Since experimental work in flow investigation is time-consuming and costly, computational fluid dynamics (CFD) Fluent software was implemented as a cost-effective helpful tool to conduct the simulation for comparison purposes. The modified impingement plate, DPIP, will destroy vortices created behind the conventional plate, retarding fouling accumulation. DPIP will enhance shell-side flow distribution downstream from the impingement plate and will stop fouling accumulation on the tubes to prevent under-deposit corrosion.     

Heat transfer characteristics of a temperature-dependent-property fluid in shell and coiled tube heat exchangers

An experimental investigation was performed to study the heat transfer characteristics of temperature-dependent-property engine-oil inside shell and coiled tube heat exchangers. For this purpose, a well-instrumented set-up was designed and constructed. Three heat exchangers with different coil pitches were selected as the test section for counter-flow configuration. Engine-oil was circulated inside the inner coiled tube, while coolant water flowed in the shell. All the required parameters like inlet and outlet temperatures of tube-side and shell-side fluids, flow rate of fluids, etc were measured using appropriate instruments. An empirical correlation existed in the previous literature for evaluating the shell-side Nusselt number was invoked to calculate the heat transfer coefficients of the temperature-dependent-property fluid flowing in the tube-side of the heat exchangers. Using the data of the present study, an empirical correlation was developed to predict the heat transfer coefficients of the temperature-dependent-property fluid flowing inside the shell and coiled tube heat exchangers.     

三叶膨胀管换热器壳程强化传热的数值研究

三叶膨胀管是一种新型强化传热管,针对纵向流换热器特点,设计了三种不同管束结构参数的三叶膨胀管自支撑纵向流换热器。应用FLUENT软件及Realizable k-ε湍流模型,对三种不同结构参数的三叶膨胀管换热器壳程强化传热特性展开了数值模拟,并通过与实验数据的对比,验证了计算模型的可靠性。计算了不同壳程介质流速下,三叶膨胀管换热器壳程的换热系数与压降值,并获得了壳程流体流线以及相应的温度场、速度场和二次流分布图。结果发现,在壳程水流速一致的情况下,管束横向间距越大的三叶膨胀管换热器,壳程拥有更高的综合换热性能和更低的压降值,但相应地,换热系数也更低。流场分析显示,壳程流体流线呈现出三维纵向旋流形态,二次流的出现改变了速度场和温度场分布,二次流的强度随着管束横向间距的减小而增大。     

Numerical Investigation of the Effect of Baffle Orientation on Heat Transfer and Pressure Drop in a Shell and Tube Heat Exchanger With Leakage Flows

The commercial CFD code FLUENT is used to investigate the effect of baffle orientation and of viscosity of the working fluid on the heat transfer and pressure drop in a shell-and-tube heat exchanger in the domain of turbulent flow. The shell-and-tube heat exchanger considered follows the TEMA standards and consists of 76 plane tubes with fixed outside diameter, which are arranged in a triangular pitch. Two baffle orientations as well as leakage flows are considered. In order to determine the effect of viscosity on heat transfer and pressure drop, simulations are performed for the working fluids air, water, and engine oil with Prandtl numbers in the range of 0.7 to 206. For each baffle orientation and working fluid, simulations are performed using different flow velocities at the inlet nozzle. Heat transfer and pressure drop are reported in order to describe the performance of vertically and horizontally baffled shell-and-tube heat exchangers. The heat transfer coefficient is described as modified shell-side Nusselt number, which is defined similar to the VDI method.     

Comparative study of mechanical and chemical methods for surface cleaning of a marine shell‐and‐tube heat exchanger

In this article, experimental analysis is done on shell‐and‐tube heat exchanger of a marine vessel for removal of fouling using optimum surface‐cleaning techniques. The main objective is to compare the performance of the heat exchanger before and after maintenance. Two identical deteriorated systems of heat exchangers are taken and real‐time analysis is conducted. The log data are taken before and after undergoing maintenance for the two systems. Two different cleaning techniques are used, namely, chemical cleaning and mechanical cleaning. Detailed calculations are made for the shell‐and‐tube heat exchanger. From the obtained data, comparisons are made for different parameters on the tube side such as friction factor, heat transfer coefficient and pressure drop, as well as total heat transfer rate on the shell side. From the analysis and comparison, it was found that greater heat transfer takes place for the tubes cleaned using the chemical cleaning method than for tubes cleaned by the mechanical cleaning method. Pressure drop is found to be less for chemical cleaning method than mechanical cleaning method. This indicates that the fouling effect is reduced for tubes cleaned by the chemical cleaning method, and furthermore these tubes remain corrosion‐resistant for longer periods of time.     

Numerical simulation of a shell-and-tube latent heat thermal energy storage unit

A theoretical model was developed to predict the transient behavior of a shell-and-tube storage unit with the phase change material (PCM) on the shell side and the heat transfer fluid (HTF) circulating inside the tubes. The multidimensional phase change problem is tackled with an enthalpy-based method coupled to the convective heat transfer from the HTF. The numerical predictions are validated with experimental data. A series of numerical experiments are then undertaken to assess the effects of various thermal and geometric parameters on the heat transfer process and on the behavior of the system. Results show that the shell radius, the mass flow rate, and the inlet temperature of the HTF must be chosen carefully in order to optimize the performance of the unit.     

Heat Transfer Enhancement in Shell-and-Tube Heat Exchangers Using Porous Media

A numerical simulation has been carried out to investigate the heat transfer enhancement in a shell-and-tube heat exchanger using a porous medium inside its shell and tubes, separately. A three-dimensional geometry with k-? turbulent model is used to predict the heat transfer and pressure drop characteristics of the flow. The effects of porosity and dimensions of these media on the heat exchanger's thermal performance and pressure drop are analyzed. Inside the shell, the entire tube bundle is wrapped by the porous medium, whereas inside the tubes the porous media are located in two different ways: (1) at the center of the tubes, and (2) attached to the inner wall of the tubes. The results showed that this method can improve the heat transfer at the expense of higher pressure drop. Evaluating the method showed that using porous media inside the shell, with particular dimension and porosity can increase the heat transfer rate better than pressure drop. Using this method inside the tubes leads to two diverse results: In the first configuration, pressure loss prevails over the heat transfer augmentation and it causes energy loss, whereas in the second configuration a great performance enhancement is observed.     

“Zero Fouling” Self-Cleaning Heat Exchanger

Conventional shell and tube heat exchangers sometimes have to use two severely fouling process streams, one in the tubes and one in the shell. This paper presents the design of a self-cleaning heat exchanger that applies the self-cleaning mechanism in the tubes of two parallel bundles handling the fouling process streams. For the transfer of heat between both bundles, a small circulating flow of conditioned water is used as an intermediate fluid, a fraction of which evaporates on the outside of the tubes of the high-temperature bundle and condenses on the outside of the tubes of the low-temperature bundle. This novel design, which consists of two parallel bundles in one shell, experiences very high film coefficients at the outside surface of both tube bundles and does not suffer from any fouling. Therefore, it is referred to as a “zero fouling” self-cleaning heat exchanger. In this paper, a conventional severely fouling crude oil preheater will be compared with a zero fouling self-cleaning heat exchanger for the same service.     

Experimental determination of shell side heat transfer coefficient and pressure drop for an oil cooler shell-and-tube heat exchanger with three different tube bundles

In this paper, the heat transfer coefficient and pressure drop on the shell side of a shell-and-tube heat exchanger have been experimentally obtained for three different types of copper tubes (smooth, corrugated and with micro-fins). Also, experimental data has been compared with theoretical data available. Correlations have been suggested for both pressure drop and Nusselt number for the three tube types. A shell-and-tube heat exchanger of an oil cooler used in a power transformer has been modeled and built for this experimental work in order to investigate the effect of surface configuration on the shell side heat transfer as well as the pressure drop of the three types of tube bundles. The bundles with the same geometry, configuration, number of baffles and length, but with different external tube surfaces inside the same shell were used for the experiment. Corrugated and micro-fin tubes have shown degradation of performance at a Reynolds number below a certain value (Re < 400). At a higher Reynolds number the performance of the heat exchanger greatly improved for micro-finned tubes.     

Detailed equipment design in heat exchanger networks synthesis and optimisation

In heat exchanger network synthesis, important features like pressure drop and fouling effects are usually neglected. In this work a new methodology is proposed to include these effects in grassroots as in retrofit designs. Heat exchangers are detailed designed during the heat exchanger network synthesis. Pinch analysis is used to obtain the heat exchangers network with the maximum energy recovery, and a new systematic procedure is proposed to the identification and loop breaking. Bell–Delaware method for the shell side is used to design the heat exchangers. An example of the literature was studied and the results show differences between heat exchangers, with and without the detailed design, relative to heat transfer area, fouling and pressure drop. The great contribution of this work is that individual and global heat transfer coefficients are always calculated, in despite of the current literature, where these value are assumed in the design step. Moreover, the methodology proposed to the heat exchangers design assures the minor heat exchanger according to TEMA standards, contributing to the minimisation of the heat exchanger network global annual cost. Finely, the new heat exchanger network considering pressure drops and fouling effects presents values more realistic then those one neglecting the equipment detailed design.     

Twisted bundle heat exchangers performance evaluation by CFD (CJ12/5054)

Shell and tube heat exchanger with single twisted tube bundle in five different twist angles, are studied using computational fluid dynamics (CFD) and compared to the conventional shell and tube heat exchanger with single segmental baffles. Effect of shell-side nozzles configurations on heat exchanger performance is studied as well. Heat transfer rate and pressure drop are the main issues investigated in the paper. The results show that, for the same shell-side flow rate, the heat transfer coefficient of heat exchanger with twisted tube bundle is lower than that of the heat exchanger with segmental baffles while shell-side pressure drop of the former is even much lower than that of the latter. The comparison of heat transfer rate per unit pressure drop versus shell-side mass flow rate shows that heat exchanger with twisted tube bundle in both cases of perpendicular and tangential shell-side nozzles, has significant performance advantages over the segmental baffled heat exchanger. Optimum bundle twist angles for such exchangers are found to be 65 and 55° for all shell side flow rates.     

Experimental Performance Comparison of Shell-Side Heat Transfer for Shell-and-Tube Heat Exchangers with Different Helical Baffles

In this study, experiments were carried out to study the effects of baffle overlap proportion on the shell-side flow resistance and heat transfer performance of the shell-and-tube heat exchangers with helical baffles (STHXsHB). Three STHXsHB with an overlap proportion of 10% and helix angles of 20°, 30°, and 40° were tested. Comparisons were made of the experimental data of the STHXsHB with the same helix angles but 50% overlap proportion. The theory of entransy dissipation was employed to evaluate the irreversible loss in STHXsHB with different helix angles and overlap proportions. The results indicated that both the baffle overlap proportion and the helix angle have a great effect on the shell-side flow resistance and heat transfer. For a given helix angle, the comprehensive performance of STHXsHB with small overlap proportion is always better than that with large overlap proportion at the same mass flow rate or Reynolds number on the shell side. However, for the same heat transfer area, working conditions, and helix angle, the STHXsHB with large baffle overlap proportion has less irreversibility in the heat exchange process, according to the theory of entransy dissipation. In addition, experimental results demonstrated that the configuration of the relatively large helix angle and baffle overlap proportion is the preferred alternative in STHXsHB.     

An Analytical Technique of Transient Phase-Change Material Melting Calculation for Cylindrical and Tubular Containers

In this study, an analytical model for a class of heat storage that utilizes latent heat of a phase-change material (PCM) is developed. Two basic shell-and-tube configurations are considered, one in which the PCM melts inside the tubes while the heat transfer fluid (HTF) flows in the shell along it, and the other in which HTF flows inside the tubes while PCM melts outside. A system of partial differential equations, which describes heat transfer and melting of the PCM and heat transfer in the HTF, is derived with some simplifying assumptions, while still capturing and preserving the essential features of the processes involved. These equations are solved analytically, yielding the overall heat exchange parameters, like instantaneous heat transfer rate, stored energy, and overall operation time of the system. The present work shows that the use of the proposed analytical technique and its modifications for the practical PCM arrangements is beneficial. Proper application of the model makes it possible to obtain the parameters of a real PCM melting process in the form of algebraic formulas, both for the transient values of variables over time, and for the overall process characteristics. A comparison with the results of numerical calculations of transient melting, made using computational fluid dynamics, confirms the validity of analytical findings and allows to assess the degree of accuracy of the results of our analytical method in various practical cases.     

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.