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The review paper presents the various passive methods used in the heat exchanger in detail with their advantages and disadvantages over the active methods. The paper studies the experimental and numerical studies of twist tape as an insert due to its retrofit capability and easy handling advantages. The experimental studies are categorized based on the geometrical parameter of the twist tape insert. The twisted tape with similar geometries is compiled in the same section. For example, twist tape with a clockwise twist, anticlockwise twist, alternate twist, or twist tape with a twist and no twist in the same section. It is a concise form that basically illustrates the studies based on similar geometrical parameters. The study covers both experimental and numerical studies and presents the advantages of experimental and numerical studies over one another. There is a section that shows statistical analysis of the Nusselt number and friction factor for various swirl flow inserts with comparison to the plain tube. The selection of twist tape inserts for the heat exchanger depends upon the cost and feasibility at the required point of application of the heat exchanger. This is done by comparing the thermal performance factor of the insert in the heat exchanger. The thermal performance factor of a particular insert in a tubular heat exchanger must be greater than 1, to justify its capability as a good insert. Finally, future recommendations are suggested to further carry out the work in this domain. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Polytechnic is the property of Journal of Polytechnic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Thermal engineering experiments were carried out with laboratory water-to-water tube-in-tube heat exchangers of the same design parameters with smooth and profiled inner tubes. The tubes were profiled by confuser–diffuser constrictions of the flow section of the inner channel, which were formed by the deformation of their walls and placed along the length at a step that was constant and equal for all profiled tubes. The obtained results showed a dependence of the heat transfer enhancement in the tube channel on the Reynolds and Prandtl numbers, with the dependence on the latter being much stronger than that on the former, at least in cases where the heat carrier is water. [ABSTRACT FROM AUTHOR]

The results of thermal engineering experiments on a water–water tubular heat exchanger of the tube-in-tube type with heat transfer intensified by periodic confuser–diffuser elements arranged along the channel length at a step equal to the doubled inner diameter of the inner tube are compared with the results of experiments on a similar smooth-tube heat exchanger and the results of calculations by the criterial models of B.S. Petukhov, S.S. Kutateladze, W. Nusselt, and M.A. Mikheev. The comparison showed that the ratio of heat transfers in the tube channels of the intensified and smooth-tube heat exchangers, being a function of the Reynolds and Prandtl numbers, depends on the latter to a much higher extent. As a consequence, at least for water as a medium where the Prandtl number depends on temperature, the intensification of heat transfer is determined not only by the profiling parameters, but also by the parameters of the heat transfer process itself. In addition, the comparison demonstrated that the replacement of experimental data on smooth-tube heat exchangers by the results of calculation by the criterial models worsens the accuracy of estimates and leads to an increase in deviations with an increase in the Reynolds number Re. [ABSTRACT FROM AUTHOR]

Vapor compression refrigeration (VCR) systems operating in hot climates suffer from high condenser temperatures that reduce their performance. One interesting approach being investigated to improve VCR performance is incorporating phase change materials (PCMs) into VCR systems that have not yet been expanded experimentally. So, this work experimentally studies the effect of using tubular PCM heat exchanger to cool the VCR condenser. The impact of two PCMs types suitable for warm climate conditions: SP24 and SP26, and combination of them on the VCR energy and exergy performance is investigated for two inlet ambient air temperatures. The impact on the exit air and PCMs temperatures, and VCR unit's pressure-enthalpy curve, VCR coefficient of performance, and power consumption is also examined. The results show that PCM-equipped systems significantly enhance the VCR exergy efficiency and coefficient of performance, especially at higher ambient temperature. Compared to the system without PCM, the power consumption can be reduced by up to 10.4% with PCM, while the exergy efficiency and coefficient of performance can be improved by 13.7% and 13.4%, respectively. While PCM SP24 provides the best performance, PCM SP26 has longer effective cooling period. A combination of SP24 and SP26 balances the performance and effective cooling period.

It is known that the results of calculations for various criterial models of convective heat transfer may differ from each other, which, according to existing ideas, is usually associated with different operating conditions of the heat exchangers under study. In the work, thermal engineering experiments are carried out with a laboratory water-to-water tubular heat exchanger of the "pipe-in-pipe" type with smooth tubes at normal pressure and moderate temperatures at various inlet temperatures of the heat carriers and their flow rates. The results of the experiment are compared with the results of calculations based on the models of B.S. Petukhova, S.S. Kutateladze, Nusselt, and M.A. Mikheev. The comparison shows that the discrepancies between the experiment and the models, as well as between the models themselves, stem not only from experimental inaccuracies, but also from inaccuracies in the models themselves. [ABSTRACT FROM AUTHOR]

Copyright of Eurasian Physical Technical Journal is the property of E.A. Buketov Karaganda University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The processing of dimple on the outer wall of tube will produce corresponding protrusion dimple on the inner wall. The turbulent flow and heat transfer performance of a tubular heat exchanger containing a dimpled inner tube is studied numerically. The results show that the main reason for the enhancement of heat transfer ability of the dimple is the flow vortex in the concave dimple and the shock to the wall induced by the protrusion dimple. Compared with the smooth wall of the tube, the maximum enhancement of heat transfer was 1.94 times in concave dimple and 2.74 times in protrusion dimple. By comparing the heat transfer performance, flow resistance, and comprehensive heat transfer factor of the tube and shell of different sizes of exchange heat pipe, it is determined that the combination of inner and outer wall dimple size of 10–15 mm is a structure with better comprehensive heat transfer performance. [ABSTRACT FROM AUTHOR]

Since it is known that the results of calculations for various criterial models of convective heat transfer may differ from each other, we compare the experimental data on heat transfer obtained in experiments on laboratory water-to-water tubular heat exchangers with smooth tubes of three different diameters at normal pressure and moderate temperatures with the results of calculations for the criterial models of B.S. Petukhova, S.S. Kutateladze, Nusselt, and M.A. Mikheev. The experiments are carried out on a two-dimensional flow grid of a tube and inter-tube channel, which makes it possible, in accordance with the previously developed method, to construct the longitudinal profiles of the heat-exchange parameters. The results of processing of the experimental data using the method of average values and the longitudinal profiles demonstrate good agreement when compared with each other. It is found that the deviations of the experimental data from the results of calculations using criterial models are systematic in nature; depend on the range of the defining parameters, i.e., the Reynolds and Prandtl numbers Re–Pr in which they are compared; increase with increasing Re number; and, depending on the Pr numbers, have an extremum. [ABSTRACT FROM AUTHOR]

This paper aims to present a numerical study on heat transfer enhancement of a tubular heat exchanger inserted with novel anti-clockwise clockwise twisted (ACCT) tape. Twelve different combinations of ACCT tapes are investigated; including tapes with four twist ratios (x/b) and three twist angles (θ) in a turbulent flow zone (4000 ≤ Re ≥ 24000). Parametric analysis is carried out to understand the flow characteristics. The results revealed that the proposed insert develops multiple vortices in the flow, increasing the turbulent kinetic energy. The Nusselt number, friction factor and thermal performance factor (TPF) of the tube with ACCT tapes increases with the increasing twist angle and the decreasing twist ratio. The highest enhancement of the Nusselt number and friction factor by 2.98 and 6.86 times is achieved for ACCT tapes with x/b = 3.0, θ = 90° and Reynolds number of 4000. The TPF is above unity for all the considered cases, with the highest being 1.54, verifying that use of the ACCT tapes is an efficient technique. Further by selecting the appropriate twist angle and twist ratio for the ACCT tape, a beneficial balance between increased heat transmission rate and friction factor can be achieved. [ABSTRACT FROM AUTHOR]

The processing of dimple on the outer wall of tube will produce corresponding protrusion dimple on the inner wall. The turbulent flow and heat transfer performance of a tubular heat exchanger containing a dimpled inner tube is studied numerically. The results show that the main reason for the enhancement of heat transfer ability of the dimple is the flow vortex in the concave dimple and the shock to the wall induced by the protrusion dimple. Compared with the smooth wall of the tube, the maximum enhancement of heat transfer was 1.94 times in concave dimple and 2.74 times in protrusion dimple. By comparing the heat transfer performance, flow resistance, and comprehensive heat transfer factor of the tube and shell of different sizes of exchange heat pipe, it is determined that the combination of inner and outer wall dimple size of 10–15 mm is a structure with better comprehensive heat transfer performance.

PCM emulsions have attracted considerable interest as the media for thermal energy storage (TES) owing to their high thermal storage capacity, desirable fluidity and thermal conductivity. However, the direct transportation of PCM emulsions in TES systems for both charging and discharging is rarely reported. In this work, a PCM-in-water nano-emulsion was prepared with n-hexadecane and suitable surfactants for cooling energy storage at a charging and discharging temperature range of 20–5 °C and 5–15 °C, respectively. It was applied to a tubular heat exchanger system to evaluate its TES performance for a cooling panel of 0.2 m2 total surface area. The thermal storage performance was notably increased with the flow rate of emulsion through the exchanger tube. The volumetric thermal storage capacity of charging was 50% higher than that of water. The cooling energy could be rapidly released in the discharging process, 79% of the stored energy at averaging 25 W during most of the discharging period. The emulsion remained stable throughout the test period. Overall, the results demonstrated that the PCM nano-emulsion has the unique characteristics of high static stability, and high energy releasing efficiency and the promising potential for air-conditioning application in buildings.

A serpentine tube heat exchanger is physically constrained by its bend radius. The U-tube bend section of a tubular heat exchanger is thus interesting broadly in terms of fluid flow and heat transfer. This paper presents the tube size dependence of heating profile of this U-tube as is commonly encountered in the design of pasteurizers. Analytical and computational modeling were employed in investigating the heat capacity, heat flux, heating rate and energy use of a U-tube at increasing diameters 9.52, 12.70, 19.05 and 25.40 mm, each at constant 1 mm thickness. SolidWorks 2016 was used in geometric modeling while Ansys v16 was used for transient thermal computational fluid dynamics simulation of the conduit (SS316L) and the product (coconut water). The initial conditions were 5,000 W m-2 K--1 convective heat supply at 95°C and 92°C surface temperature for the conduit and the product, respectively. Both the tube and the product were initially at 30°C. The tube, whose heating profile was independent of size, reached 90°C in 2.1 s. For the product, as the tube size increases, the heat capacity increases exponentially (Qp = 108.3e0.1831x), the heat flux drops down 57% within 40 s, while both the heating rate (Tt =60s = -48ln(x) + 183.65) and the energy use (Qu = -29.65lnx + 235.36) drops logarithmically. These results are beneficial to designers and engineers in sizing of heaters, minimizing fouling and optimizing energy efficiency as well as pasteurizer processing capacity. [ABSTRACT FROM AUTHOR]

• Coupling PCMs with an air conditioner condenser for its performance is studied experimentally. • Rising PCM quantity from 7 to 11 kg, reduces air conditioner consumption by 7.8 % and 10.4 %, respectively. • Integrating 11 kg PCM yields 0.5 °C room temperature reduction compared with air conditioners without PCM. • The higher system performance is achieved for 4 h of system working during the day time. • Enhancing the PCM's lower thermal conductivity using nanoparticles for more system performance could be studied. Air conditioning systems are vital for modern comfort but consume a substantial portion of global energy, contributing to environmental concerns and rising energy costs. PCMs can store and release energy during phase transitions, making them promise to reduce cooling loads. This study endeavors to empirically investigate the influence of integrating hybrid Phase Change Materials (PCMs), specifically PCMSP24E and PCMSP26E, with a real vapor compression refrigeration system. The primary focus is on assessing the consequential effects on the energy consumption of the refrigeration system and the interior environmental conditions within a building, including temperature and relative humidity. The energy usage of the split air conditioner wherein the outdoor unit is attached to PCMs tube heat exchanger for precooling the incoming air is investigated. Experiments reveal that PCM precooling effectively reduces the ambient air temperature entering the air conditioning condenser, leading to substantial energy savings. Increasing the PCM quantity enhances the system performance and refrigeration unit power saving. With 11 kg of PCMs, energy consumption by the air conditioning system decreases by 10.4 %, and indoor air temperature and relative humidity reduce by 0.5° and 5 %, respectively. Hence, PCM integration ensures a more consistent indoor temperature profile, enhancing occupant comfort and reducing temperature fluctuations. [ABSTRACT FROM AUTHOR]

In this study, thermodynamic analysis was performed for tubular heat exchanger, shell and tube heat exchanger, and plate heat exchanger. The performances of these 3 types of heat exchangers were experimentally tested. The cold water flow rate of the heat exchanger test zone was kept constant at 1.5 L / min, while the hot water flow rate was set at 0.8 L / min, 1.6 L / min and 2.4 L / min. The hot water tank temperature was selected as 50 ° C, 60 ° C and 70 ° C. The experiments were conducted in both counter flow and parallel flow. As a result of the experiments, it was observed that increasing temperature and flow rate increased the power taken from the heat exchanger. The heat exchanger type with the highest amount of heat transfer from the test zone is the shell and tube heat exchanger, and the tubular heat exchanger type has the lowest performance. [ABSTRACT FROM AUTHOR]

Failure analysis of a tubular oil heat exchanger made up of admiralty brass in an industrial unit was investigated. In the oil exchanger, circulating water is used as a coolant inside the brass tubes to reduce the temperature of oil flowing inside the brass shell. The causes of failure of the leaked admiral tubes were investigated performing various visual and microscopic examinations. Chemical analysis of the corrosion scales and its phase analysis with x-ray diffraction and microstructural examinations by optical and scanning electron microscopy were carried out. The study revealed that tube material was suffering from extensive de-zincification and under-deposit pitting. [ABSTRACT FROM AUTHOR]

This paper presents the comparison of static and dynamic neural network (NN), model to predict the exit temperature of the heat exchangers. Feed forward NN was used as a static network while Time delay NN was used for a dynamic network. Experimental data was collected from a shell and tube heat exchanger to provide sufficient data processing, namely training, test and validation data to develop the models. The static and dynamic network models of the heat exchanger have been developed using Matlab. The performances of the models were evaluated by their statistical validity using the correlation co-efficient and the mean squared error. For time series predictions, the dynamic NN has shown better results than the static NN. [ABSTRACT FROM AUTHOR]

Metallic inserts have been receiving considerable interest in recent research as a means of enhancing passive thermal performance. Nevertheless, little research has been conducted on Y-shaped inserts with different perforations. The purpose of this study is to seek out optimum performance in terms of heat transfer employing hexagonal, trapezoidal, kite, and hybrid shapes with Perforation Indexes (PI) of 10%, 20%, and 30%. While conducting the analyses, air is utilized as the working fluid, using Reynolds numbers (Re) ranging from 3000 to 21000. The findings demonstrate that Nusselt number (Nu) values of up to 225 can be achieved at Re = 21000 for trapezoidal designs with a PI of 20%. In contrast, such case seems to have the lowest friction factor (f) of 0.07, yielding in the most optimized thermal performance. With PI = 10%, hexagonal perforations have the maximum f of 0.24, making it particularly prone to pressure drop. When compared to the smooth tube, Nu improved up to 6.15 times and f enhanced up to 5.03 times. The trapezoidal configuration with PI = 20% yielded the highest thermal performance factor, a TPF of 3.68, making it the best optimal case in terms of both thermal and hydraulic performance. [ABSTRACT FROM AUTHOR]

Modeling of the process of thermal fluidization of a ventilated granular bed by means of a heat exchanger in the form of horizontal tubes positioned inside the bed is carried out. [ABSTRACT FROM AUTHOR]

The problem of synthesis of feedback control for objects with distributed parameters using continuous monitoring of the phase state of an object at its definite points is considered and illustrated by the example of control of the process of heating a tubular heat exchanger in its steam jacket. To solve the problem, it is proposed to use first-order numerical methods. Formulas for components of the gradient of an objective functional in the space of the parameters being optimized are derived. The results of the made numerical experiments are presented. [ABSTRACT FROM AUTHOR]

Using ice slurry can assist the energy saving in cooling systems. Ice slurries are used as secondary refrigerant in large cooling systems. They are mixtures of tiny ice particles in water and an antifreezing agent. The cooling can be stored in ice particles during off-peak conditions and released during peak condition. The stored cooling in ice slurry must be delivered to the desired system through a heat exchanger. Successive U-bend pipes commonly exist in tubular heat exchangers. However, this configuration has not been investigated yet for ice slurries. The present study aims to investigate the heat transfer of these mixtures in successive in-plane U-bends as part of heat exchangers. Mass transfer between ice slurry and fluid is the main important part of this problem which is considered in the present study. For the simulation of ice slurry, the Eulerian two-fluid numerical method is used along with the consideration of mass transfer between two phases and the kinetic theory of granular flow for ice particles viscosity. Nusselt number and pressure drops are mainly studied for different geometric configurations. The length between two bends are changed from 50 to 400 mm and the radius of curvatures of the bends are changed from 50 to 100 mm. The results of the study indicated that the average Nusselt number increases with the radius of curvature and distance between two U-bend pipes. Two successive U-bends neutralize each other's centrifigual effects, then ice particles have chances to rearrange and reduce the wall temperature in each bend. This effect is more prominent in higher distances between two bends and higher radii of curvature. At low radius of curvatures, the variation of distance between two bends has stronger effect on heat transfer of the system; in such a way that by doubling the distance between two bends, the Nusselt number increases 4.1% and 1.5% respectively for radius of curvatures 50 mm and 100 mm. Also it was shown that by increasing the radius of curvature and distance between two U-bend pipes the skin friction coefficient increases. It can be seen that by increasing the ratio of the distance between two bends to the radius, the performance evaluation criterion (PEC) increases. [ABSTRACT FROM AUTHOR]

The present study improves the thermal-hydraulic performance of a circular tube equipped with a delta winglet vortex generator by providing a numerical model, investigating the effect of two additional parameters, and developing a support vector regression (SVR) for prediction and optimization. The additional parameters are the angle of attack and SiO 2 concentration, while the data on the variation of thermohydraulic parameters with pitch and blockage is already available in the literature. The boundary layer disruption and swirling flow caused by the delta winglet result in heat transfer enhancement. The presence of such inserts also increases the pressure drop in the heat exchanger. The nanofluid further enhances heat transfer by boosting the thermophysical properties of the fluid. The hybrid method, CFD-SVR, is carried out for turbulent water flow at Reynolds numbers ranging from 4200 to 16200. The delta winglets are in pair arrangement with ten angles of attack from 25 ∘ to 70 ∘ with 5 ∘ increments. The addition of SiO 2 with volumetric concentrations varies from φ = 0 to 0.5% has been explored. The diameter of the tube (D) is 50 mm, while the pitch ratio (P/D) and blockage ratio (B/D) vary from 1 to 3 and 0.1 to 0.2, respectively. Finally, the data of this study and the previously published experimental data were fed into an SVR to find the best possible arrangement of delta winglet for a tubular heat exchanger. The highest achieved thermal enhancement factor (TEF) was found to be 2.18 with α = 25°, P R = 0.83, B R = 0.13, and φ = 0.5% at the least Re number. [Display omitted] [ABSTRACT FROM AUTHOR]

The aim of this paper was to study the influence of a double tube heat exchanger (DTHX) on thermo-hydraulic performance, considering 21 different shell–tube configurations including smooth and corrugated inner and outer tubes. In order to emulate the behavior of high-viscosity food-industry fluids, a 60°brix solution of water and sugar was used as the Heat Transfer Fluid (HTF). A total of 504 experimental tests were carried out, varying the flow velocity (Reynolds number) and the shell corrugation parameters (helix pitch P and groove depth d). The results from three different shells, one smooth and two corrugated shells, and seven different inner tubes, one smooth and six corrugated with a groove depth between 0.5 mm and 1.2 mm are presented. The comparison of the three shells with an inner smooth tube shows significant heat transfer rate enhancements using a light groove depth (CC1) in the outer tube of the DTHX, increasing both the average efficiency and the P E C indicator (Performance evaluation criteria) by 5% compared with the smooth shell. No improvements are found when a higher groove depth (CC2) in the outer tube of the DTHX is used. Regarding the results with different inner tubes, the tubes with the highest groove depth in the tested range (between 0.5 and 1.2 mm), CO11 and CO12 (with a groove depth of 1.1 and 1.2 mm, respectively), show the best results, regardless of the type of shell. Corrugated tube CO12 shows the best results in terms of efficiency, with an average increment of 19% compared with the smooth inner tube. Regarding P E C , CO11 shows an average increment of 9% in the analyzed P E C indicator compared with the smooth inner tube. • The thermo-hydraulic performance of a double tube heat exchanger was evaluated. • 21 different shell–tube configurations were experimentally tested. • The shell with a groove depth of 0.6 mm increases 5.5% the heat transfer coefficient. • The inner tube C012 gets a increase of 19% in the thermal efficiency. [ABSTRACT FROM AUTHOR]

Abstract: An experimental study was conducted to investigate the effect of advanced surfaces on the ammonia absorption process in tubular bubble absorbers using NH3/LiNO3 as a working pair at operating conditions of interest for absorption chillers. The tubular bubble absorber is a vertical double-pipe heat exchanger in which absorption takes place in the inner tube. In order to compare the effect of surface enhancement, a smooth tube and an internally micro-finned tube were tested. The inner tube of the absorber is made of aluminium and has an outer diameter of 8.0mm and the micro-finned tube has internal helical micro-fins measuring 0.3mm in length. The effect of tube length on absorption was also studied using two tube lengths (1 and 3m) and two tube diameters (8 and 9.5mm). Our results show that the absorption rate achieved with the micro-finned tube is up to 1.7 times higher than with the smooth tube at a solution mass flow rate of 40kgh−1. We also found that absorption mass flux increases when tube diameter is reduced and decreases when tube length is increased. [Copyright &y& Elsevier]

Abstract: The classic conservative approach for thermal process design can lead to over-processing, especially for laminar flow, when a significant distribution of temperature and of residence time occurs. In order to optimize quality retention, a more comprehensive model is required. A model comprising differential equations for mass and heat transfer is proposed for the simulation of the continuous thermal processing of a non-Newtonian food in a tubular system. The model takes into account the contribution from heating and cooling sections, the heat exchange with the ambient air and effective diffusion associated with non-ideal laminar flow. The study case of soursop juice processing was used to test the model. Various simulations were performed to evaluate the effect of the model assumptions. An expressive difference in the predicted lethality was observed between the classic approach and the proposed model. The main advantage of the model is its flexibility to represent different aspects with a small computational time, making it suitable for process evaluation and design. [Copyright &y& Elsevier]

A regenerative gas turbine cycle with two particular tubular recuperative heat exchangers in parallel is considered for multi-objective optimization. It is assumed that tubular recuperative heat exchangers and its corresponding gas cycle are in design stage simultaneously. Three objective functions including the purchased equipment cost of recuperators, the unit cost rate of the generated power, and the exergetic efficiency of the gas cycle are considered simultaneously. Geometric specifications of the recuperator including tube length, tube outside/inside diameters, tube pitch, inside shell diameter, outer and inner tube limits of the tube bundle and the total number of disc and doughnut baffles, and main operating parameters of the gas cycle including the compressor pressure ratio, exhaust temperature of the combustion chamber and the air mass flowrate are considered as decision variables. Combination of these objectives anddecision variables with suitable engineering and physical constraints (including NOx and CO emission limitations) comprises a set of mixed integer non-linear problems. Optimization programming in MATLAB is performed using one of the most powerful and robust multi-objective optimization algorithms, namely non-dominated sorting genetic algorithm. This approach is applied to find a set of Pareto optimal solutions. Pareto optimal frontier is obtained, and a final optimal solution is selected in a decision-making process. [ABSTRACT FROM AUTHOR]

Abstract: Continuous hydrothermal flow synthesis processes are of interest for the manufacture of nanoparticle metal oxides. In such processes, nanoparticle nuclei (in a slurry) which are initially formed, may continue to grow and agglomerate to generate larger particles as they pass through the synthesis apparatus. These processes can widen the size distribution and also affect the ultimate particle shape in the recovered product. Therefore, fast cooling or quenching the initial nanoparticle slurry using a highly efficient heat exchanger may minimise or stop further crystallisation/agglomeration processes. This may be achieved by optimising the design of the heat exchanger based on detailed examination of flow patterns and heat transfer profiles using a computational fluid dynamics (CFD) modelling approach. The predicted flow and heat transfer patterns in the heat exchanger can also provide detailed information for the identification of any heat transfer deterioration or hot spots where further reactions may occur. This paper employs a CFD modelling approach to simulate the heat transfer processes in a tubular heat exchanger of a continuous hydrothermal flow synthesis system and also to examine the effect of various operating conditions, including inlet temperature and flowrate of hot slurry and inlet flowrate of cooling water, on the fluid and thermal features in the heat exchanger. The simulated results show that the predicted temperature and heat transfer coefficient are in good agreement with experimental measurements. [Copyright &y& Elsevier]

A simulation model of the fouling behaviour of an arbitrary heat treatment device for milk, instancing tubular heat exchangers, is described. The final target is to examine new processing technologies in order to lengthen the processing time between two cleaning cycles whilst maintaining product quality. For this purpose a hybrid model of the fouling process in tubular heat exchangers was developed, combining deterministic differential equations with cognitive elements. The model allows the calculation of both processing and product behaviour throughout the whole heat exchanger. Pressure drop, temperature distribution and the chemical and biological effects of the heat treatment on the product can be calculated, so that the fouling behaviour and the expected product quality can be estimated. In order to validate the process model measured data from an industrial UHT plant were used. The calculated temperature profiles and pressure drops were in reasonable agreement with the experimental data. The deviation of calculated to measured values ranges between 10% and 20% for pressure, between 5% and 10% for temperature. [ABSTRACT FROM AUTHOR]

A comparative experimental study to examine the hydrothermal behaviors of the double tube heat exchanger with various modified twisted tape and wire coil inserts is performed using Al 2 O 3 +MWCNT hybrid nanofluid. The investigation is performed for Reynolds number of 8000–40000, nanofluid flow rate of 5–25 lpm and volume concentration of 0.01%. The effects of using various enhancers (V-cut twisted tapes and tapered wire coils) and hybrid nanofluid on the hydrothermal characteristics are assessed for different enhancer arrangements such as different twist ratios, V-cut depth ratios, V-cut width ratios, converging type (C-type) wire coil, diverging (D-type) wire coil and converging-diverging type (C-D type) wire coil. The test reveals that the pressure drop and heat transfer coefficient increase with reducing twist ratio, increasing depth ratio and reducing width ratio. D-type wire coil exhibits higher heat transfer performance with the penalty of pressure drop than that of other arrangements. V-cuts twisted tape of minimum twist ratio, maximum depth and width ratios yields maximum PEC and FOM. V-cut twisted tapes show a higher performance index than the tapered wire coil as the augmentation in pressure drop is slightly significant. D-type wire coil shows the minimum value of entropy generation among all other arrangements. • Performance of concentric tube heat exchanger is studied with inserts using hybrid nanofluid. • Experiment is performed for various V-cut twisted tape and tapered wire coil configurations. • D-type wire coil exhibits higher heat transfer performance with the penalty of pressure drop. • V-cut twisted tapes show higher hydrothermal performance as compared to tapered wire coil. • D-type wire coil exhibits minimum value of entropy generation among all the arrangements. [ABSTRACT FROM AUTHOR]

Effects of insertion of a straight tape mounted with double-sided V-baffles used as a longitudinal vortex generator (LVG) on turbulent convection heat transfer behaviors in a constant heat-fluxed tube in the Reynolds number (Re) range of 4120 to 25,800 are experimentally and numerically investigated. In the present experiment, the V-baffles at a fixed attack angle (α = 30°) were placed on the tape with two arrangements: V-apex pointing downstream and upstream (hereinafter called "V-down" and "V-up"). The V-down and up tapes with three baffle height ratios, (R B = b / D = 0.20, 0.15, 0.10) and pitch ratios, (R P = P / D = 1.5, 1.0, 0.5) were tested. Data of the current smooth or plain tube were also examined for comparison. The experimental results have shown that the employ of the V-down tape generally yields higher heat transfer, friction loss and thermal performance than that of the V-up one. A new derived thermal-performance enhancement factor (TEF) is proposed. The maximum TEF of the V-down tape is around 2.07 at R B = 0.15, R P = 1.0 and is, in average, about 1.4% higher than the V-up one having its peak of 2.04. A 3D numerical V-baffled-tube flow model was also simulated to examine the fluid flow and heat transfer patterns. The numerical validation was seen in close agreement with available experimental data. Numerical heat transfer contours and flow structures were also reported. • A novel V-baffled tape is introduced for performance improvement in a tubular heat exchanger. • The insertion of V-down tape yields superior thermal performance over the V-up. • Thermal characteristics in the tubular heat exchanger are experimentally and numerically examined. • Optimum parameters of V-baffled tapes and their correlations are reported. [ABSTRACT FROM AUTHOR]