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.     

Heat transfer and pressure drop performance of twisted oval tube heat exchanger

Twisted oval tube heat exchanger is a type of heat exchanger that aims at improving the heat transfer coefficient of the tube side and also decreasing the pressure drop of the shell side. In the present work, tube side and shell side heat transfer and pressure drop performances of a twisted oval tube heat exchanger has been experimentally studied. The tube side study shows that the tube side heat transfer coefficient and pressure drop in a twisted oval tube are both higher than in a smooth round tube. The shell side study shows that the lower the modified Froude number Fr_M, the higher the shell side heat transfer coefficient and pressure drop. In order to comparatively analyze its shell side performance of the heat exchanger, a rod baffle heat exchanger with similar size of the twisted oval tube heat exchanger is designed and its performance is calculated with Gentry's method. The comparative study shows that the heat transfer coefficient of the twisted oval tube heat exchanger is higher and the pressure drop is lower than the rod baffle heat exchanger. In order to evaluate the overall performance of the twisted oval tube heat exchanger, a performance evaluation criterion considering both the tube side and shell side performance of a heat exchanger is proposed and applied. The analyze of the overall performance of the twisted oval tube shows that the twisted oval tube heat exchangers works more effective at low tube side flow rate and high shell side flow rate.     

Shell side heat transfer characteristics with an eggcrate support plate for water in parallel flow

The shell side heat transfer and pressure drop for water in parallel flow with an eggcrate support plate were experimentally investigated in order to obtain higher performance for the heat exchanger in a boiling water reactor power plant. The following three conclusions were reached. (1) The shell side heat transfer characteristics with the eggcrate support plate were twice as large as those of the shell side parallel flow. An equation using the Reynolds number of the eggcrate support plate could predict the heat transfer coefficient. (2) The shell side pressure drop characteristics with the eggcrate support plate were about five to six times as large as those of shell side parallel flow. (3) The enhancement constant of heat transfer with the eggcrate support plate, using Colburn's j‐factor and friction factor f, was the same as that of the ROD‐baffle type, and was about two times as large as that of the segmental baffle type. © 2000 Scripta Technica, Heat Trans Asian Res, 29(2): 91–112, 2000     

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 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.     

Computation of thermal properties of CMSP shell and tube heat exchanger using different types of helical baffles

This paper investigates the flow and thermal properties of a combined multiple shell pass (CMSP)-shell and tube heat exchanger (STHE) with the provision of unilateral ladder-type helical baffle (ULHB) and continuous helical baffle (HB) in the outer shell pass of the heat exchanger. Two CMSP-STHEs with ULHB and HB, respectively, are compared with the traditional STHE having segmental baffles (SG-STHE) using the computational fluid dynamics method. The computational outcomes are validated with the empirical correlations of the Kern and Esso method. The Reynolds-averaged Navier–Stokes-based standard k–ω turbulence model accurately predicts the heat transfer (HT) rate and pressure drop. The computed results of HT rate, pressure drop, and logarithmic mean temperature difference corresponding to various mass flow rates (m) for three STHEs are presented. The results show that the overall HT rate of CMSP (ULHB)-STHE and the CMSP (HB)-STHE at the same mass flow rate are nearly 28.3% and 14.8% larger than that of traditional SG-STHE, respectively. Furthermore, the overall area-weighted average pressure drop (ΔP) of CMSP (HB)-STHE is smaller than that of SG-STHE by 26.5% at the same mass flow rate (m) and for CMSP (ULHB)-STHE it is larger by 2% than that of traditional STHE. Based on the above results, it is concluded that the CMSP (ULHB)-STHE is a suitable replacement for the conventional SG-STHEs.     

The latent heat recovery from boiler exhaust flue gas using shell and corrugated tube heat exchanger: A numerical study

The excessively increasing environmental concerns along with reducing fossil fuel resources introduce the trend of increasing the efficiency of boiler via implementing waste heat recovery. In the present study, the potential of latent heat recovery is investigated in the middle‐size boiler exhaust flue gas using the shell and corrugated tube heat exchanger. The main purpose of the present study is efficiency growth in flue gases using latent heat recovery of the steam energy. The heat recovery analysis is evaluated by a validated computational fluid dynamics model by a commercial software. For this study, the effect of different tube arrangements, number of tubes, and flow direction in the shell on heat transfer and pressure drop were investigated. The results showed that in‐line arrangement of the tubes in the shell presents better thermal performance and also high pressure drop among the other arrangements. As a result, by considering the thermal performance and pressure drop, radial arrangement shows higher performance. According to the obtained results from Section 2 of the present study, by considering the radial arrangement of tubes in the shell, as the number of tube rises, the thermal performance declines.     

Use of segmental baffle in shell and tube heat exchanger for nano emulsions

Among the heat exchangers (HE), the shell and tube type is being widely used in different applications like oil, chemical, and power plant Industries. The incorporation of segmental baffles (SB) improves the HE capacity from higher temperature fluid to lower temperature fluid. Nanofluids can be effectively used to enhance the heat transfer rate. In this study, numerical simulations have been carried out in a shell and tube heat exchanger (STHX). Among HE design methods, Tubular Exchanger Manufacturers Association (TEMA) standard is being used for better design by many researchers. In this paper, the computational fluid dynamics analysis was carried out with Al₂O₃, CuO, and SiO₂ nanofluids amid 1, 3, and 5 vol. % with water emulsion to enhance the heat transfer coefficient of STHX. The nanofluid has been used in the cold fluid of the HE and on the other side hot water is used. From the results, it is noticed that with the increase of Nanofluids, the value of heat transfer coefficients is found to be increasing. The overall heat transfer coefficient has been enhanced for Al₂O₃, CuO, and SiO₂ about 10.41%, 12.27%, and 9.56%, respectively, at 0.22 kg/s for the 5 vol. % addition. It is also depicted that the pressure drop is increasing with the incorporation of nanofluids.     

折流板换热器壳程流场数值模拟与结构优化

基于多孔介质与分布阻力的概念,采用FLUENT软件对单弓形折流板换热器的壳侧流场进行了三维数值模拟,模拟结果与实验结果吻合较好。在此基础上针对折流板换热器壳程压降大、能耗高,存在传热死区等的缺点,提出了壳程流场的改进方案,通过数值模拟可以看到壳程流场改进后不仅具有压降低、场协同性能好、基本无传热死区等特点,而且在一定程度上还提高了管束抗流体诱导振动的性能。     

Investigation on the heat transfer characteristics of propylene glycol–water mixture in the shell side of a spiral‐wound heat exchanger

The heat transfer characteristics of propylene glycol–water (PG–W) mixture (10%, 20%, and 30% propylene glycol) on the shell side of a spiral‐wound heat exchanger (SWHE) were investigated experimentally. Among the SWHE selected, there are 18 twined tubes with a diameter of 8 mm. PG–W mixture is on the shell side and water is on the tube side. The results show that the heat transfer coefficient of PG–W mixture flowing downwards is higher than upwards under countercurrent conditions. The heat transfer coefficient decreases with the increasing of concentration of PG–W mixture. When the inclination angle of the SWHE is 90°, the heat transfer coefficient of PG–W mixture is the largest; and when the inclination angle is less than 90°, the heat transfer coefficient decreases with the decrease of inclination angle. The inclination angle has a great effect on the heat transfer coefficient at a high concentration. The fitting correlation equations between Nu, Re, Pr, and inclination angles of SWHE are established.     

Numerical and experimental study of a shell and tube heat exchanger for different baffles

In the present work, the shell and tube heat exchanger (STHX) is designed based on The Tubular Exchanger Manufacturers Association standards with hot fluid (water) flowing on the shell side and cold fluid on the tube side. A comparison is made between the Nusselt number and friction factor obtained from numerical and experimental results of segmental baffles (SBs) and helical baffles (HB) with different baffle inclinations. The results show that SB provided a higher Colburn factor (j_s) when compared with HBs STHXs (20°, 30°, 40°, and 50°), but shell side pressure drop is lower for 40° HBs STHXs for the same shell side fluid flow rates.     

Multi-objective optimization of shell and tube heat exchangers

The effectiveness and cost are two important parameters in heat exchanger design. The total cost includes the capital investment for equipment (heat exchanger surface area) and operating cost (for energy expenditures related to pumping). Tube arrangement, tube diameter, tube pitch ratio, tube length, tube number, baffle spacing ratio as well as baffle cut ratio were considered as seven design parameters. For optimal design of a shell and tube heat exchanger, it was first thermally modeled using ε–NTU method while Bell–Delaware procedure was applied to estimate its shell side heat transfer coefficient and pressure drop. Fast and elitist non-dominated sorting genetic algorithm (NSGA-II) with continuous and discrete variables were applied to obtain the maximum effectiveness (heat recovery) and the minimum total cost as two objective functions. The results of optimal designs were a set of multiple optimum solutions, called ‘Pareto optimal solutions’. The sensitivity analysis of change in optimum effectiveness and total cost with change in design parameters of the shell and tube heat exchanger was also performed and the results are reported.     

Fluid flow and heat transfer investigations in shell and dimple heat exchangers

Heat transfer and pressure drop characteristics are investigated here using experimental and analytical techniques for a dimple plate heat exchanger. The analysis uses the log mean temperature difference method (LMTD) in all its calculations. Whilest the shell side flow highly resembles the flow over a rough or wavy plate, the tube side passage in these represents the flow over short hexagonal tube banks with the flowing across the sectional areas between the hexagons having the shape of a benzene ring. Local and global experimental measurements are carried out around the heat exchanger. Furthermore, analytical models for both sides of the heat exchanger were obtained from the literature. Reasonable cross match between experimental and analytical results could be obtained. Copyright © 2005 John Wiley & Sons, Ltd.     

Numerical investigation on combined multiple shell-pass shell-and-tube heat exchanger with continuous helical baffles

A combined multiple shell-pass shell-and-tube heat exchanger (CMSP-STHX) with continuous helical baffles in outer shell pass has been invented to improve the heat transfer performance and simplify the manufacture process. The CMSP-STHX is compared with the conventional shell-and-tube heat exchanger with segmental baffles (SG-STHX) by means of computational fluid dynamics (CFD) method. The numerical results show that, under the same mass flow rate M and overall heat transfer rate Q_m, the average overall pressure drop Δp_m of the CMSP-STHX is lower than that of conventional SG-STHX by 13% on average. Under the same overall pressure drop Δp_m in the shell side, the overall heat transfer rate Q_m of the CMSP-STHX is nearly 5.6% higher than that of SG-STHX and the mass flow rate in the CMSP-STHX is about 6.6% higher than that in the SG-STHX. The CMSP-STHX might be used to replace the SG-STHX in industrial applications to save energy, reduce cost and prolong the service life.     

Evaporation performance of a new plate‐type heat exchanger with winding tubes on plate surfaces (estimation of performance of the heat exchanger)

A method for evaluating and predicting the performance of a newly developed plate‐type heat exchanger as an evaporator for water‐refrigerant systems such as chillers has been developed. The main component of the developed heat exchanger consists of plates packed together in a casing with winding tubes connected to both sides of the plates. Refrigerant flows inside the tubes, and water flows in the space between the plates. A herringbone‐like pattern is formed in this space by the cross sections of the winding tubes. The newly developed method estimates evaporation performance of the developed heat exchanger using new empirical correlations. There are correlations for heat transfer and pressure drop in winding‐tube banks on the water side, and correlation for the pressure drop on the refrigerant side. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(4): 245–257, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20009     

Thermal modeling of a shell and tube type evaporator with R404A

In this study, the two‐phase heat‐transfer coefficient of R404A inside horizontal tubes is analyzed through the evaporator's overall heat‐transfer coefficient, obtained using the effectiveness—Number of Transfer Units thermal design approach. This method constitutes an approximation that can be used in the evaporator's thermal design with an attempt to break some of the initial assumptions established in the heat exchanger thermal design method development. For the analysis, an experimental refrigeration system that is commercially available is built up with a shell and tube evaporator. All the experiments are performed at different evaporator pressures (270, 570 kPa), evaporator temperatures (?20, 0°C) and cooling water temperatures (20, 40°C). For these parameters, overall heat‐transfer coefficient of the heat exchanger is found in the range of 0.05–0.35 kW °C^?1. Copyright © 2010 John Wiley & Sons, Ltd.     

Experimental study of Fe2O3/water and Fe2O3/ethylene glycol nanofluid heat transfer enhancement in a shell and tube heat exchanger

Heat transfer characteristics of Fe₂O₃/water and Fe₂O₃/EG nanofluids were measured in a shell and tube heat exchanger under laminar to turbulent flow condition. In the shell and tube heat exchanger, water and ethylene glycol-based Fe₂O₃ nanofluids with 0.02%, 0.04%, 0.06% and 0.08% volume fractions were used as working fluids for different flow rates of nanofluids. The effects of Reynold's number, volume concentration of suspended nanoparticles and different base fluids on the heat transfer characteristics were investigated. Based on the results, adding nanoparticles to the base fluid causes a significant enhancement of the heat transfer characteristics and thermal conductivity. This enhancement was investigated with regard to various factors; concentration of nanoparticles, types of base fluids, sonication time and temperature of fluids. In this paper, the effect of Fe₂O₃ nanoparticles on the thermal conductivity of base fluids like ethylene glycol and water was studied. The thermal conductivity measurement was made for different concentrations and temperatures. As the concentration of the nanoparticles increased, there was a significant enhancement in thermal conductivity and overall heat transfer due to more interaction between particles. It was also observed that there was an improvement in the thermal conductivity of the base fluid as the temperature increased. The measurements also showed that the pressure drop of nanofluid was higher than that of the base fluid in a turbulent flow regime. However, there was no significant increase in pressure drop at laminar flow.     

Experimental study on the effect of porous medium on performance of a single tube heat exchanger: A CO2 case study

An experimental study on single‐phase laminar forced convection in a single porous tube heat exchanger is presented. Parametric studies are conducted for different inlet pressures, different mass flow rates, and different porosities to evaluate the effects of particle diameter and Reynolds number on the heat transfer and friction factor. The Nusselt number and friction factor are developed for efficient design of a porous heat exchanger based on the present configuration. Heat is transferred to the walls of the heat exchanger by natural convection mode. Gravel sand with different porosities is used as a porous medium during the tests. The flow of carbon dioxide as a working fluid in the porous medium is modeled using the Brinkman–Forchheimer‐extended Darcy model. A dimensionless performance parameter is developed in order to be used in evaluating the porous tube heat exchanger based on both the heat transfer enhancement and the associated pressure drop. The study covers a wide range of inlet pressures (P_i), mass flow rates ( ), porosity of gravel sand (ε), and particle diameters (d_m) which ranged 34.5 ≤ P_i ≤ 43 bars, 8 ?? 10^?5 ≤ ≤ 16 ?? 10^?5 kg/s, 34.9% ≤ ε ≤ 44.5%, 1.25 ≤ d_m ≤ 5.15 mm, respectively. This study revealed that a smaller particle diameter can be used to achieve higher heat transfer enhancement, but a larger particle diameter leads to a more efficient performance based on heat transfer enhancement. The average heat transfer coefficient of carbon dioxide decreases when the porosity increases. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21059     

Experimental and numerical study of convective heat transfer and fluid flow in twisted oval tubes

Twisted oval tube heat exchanger is a type of heat exchanger aims at decreasing the pressure drop of the shell side. In the present study, heat transfer and pressure drop performances of twisted oval tube have been studied experimentally and numerically. The experimental study of the twisted oval tube shows that heat transfer process can be enhanced but also with an increasing of pressure drop when compared with the smooth round tube. The effects of geometrical parameters on the performance of the twisted oval tube have been analyzed numerically. The result reveals that the heat transfer coefficient and friction factor both increase with the increasing of axis ratio a/b, while both decrease with the increasing of twist pitch length P. The influence of a/b and P on the overall performance of the twisted oval tubes are also studied. Aiming at obtaining the heat transfer enhancement mechanism of the twisted oval tube, secondary flow, total velocity and temperature distributions of flow section are given. From the analysis it can be concluded that the emergence of twist in the twisted oval tube results in secondary flow. It exists in the form of spiral flow when a/b is big, but in the form of up and down when a/b is small. It is this secondary flow that changes the total velocity and temperature distributions of the twisted oval tube when compared with a smooth oval tube with the same sectional geometric parameters. Then the synergy angle between velocity vector and temperature gradient is reduced and the heat transfer process is enhanced.     

Development and validation of helical‐coil‐in‐fluted‐tube gas cooler for CO2 heat pump water heaters

A segmented approach [1] for the CO₂ helical‐coil‐in‐fluted‐tube gas cooler is developed. The CO₂ helical‐coil‐in‐fluted‐tube gas cooler consists of helically coiled tube and fluted tube. It is fabricated by twisting a straight copper tube to form helically coiled tube and embedded in the groove of the fluted tube. The available heat transfer and pressure drop correlations for the supercritical CO₂‐side and water‐side are provided to simulate the gas cooler. The simulation is compared with a detailed set of experimental data, for given the inlet conditions. The predicted data matches well with the experimental data with absolute average deviations of 1.15, 4.6 and 4.7% for the CO₂ pressure drop, gas cooler exit temperature and hot water temperature, respectively. Based on the good matches between measured data and predicted data, the detailed thermodynamic processes of gas cooler parameters are predicted and analyzed. Furthermore, different arrangements of the gas cooler within the original package dimensions are simulated and better performance of the gas cooler is obtained under the structural parameters of the 3‐row fluted tube with the inner diameter 12 mm. Copyright © 2010 John Wiley & Sons, Ltd.