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Heat transfer equipment has been used in many different domestic and industrial applications. There has been a concentrated effort to create a heat exchanger design that will reduce energy requirements while saving materials and other costs. Increasing the effective heat transfer surface area or creating turbulence are two common ways to improve heat transfer and hence lower thermal resistance. The thermal Performance Factor is the ratio of the difference in heat transfer rate to the difference in friction factor and serves as a metric to assess the efficiency of heat transfer enhancement technologies. Different types of twisted tubes are used in many heat transfer improvement devices. geometrical parameters of the twisted tube encompassing the aspect ratio, twist ratio, twist direction, twist length, etc. impact the heat transfer. For Instance, oval pipes with unequal twist pitches have a thermal performance factor (1.75) and equal twist pitches have a thermal performance factor (1.98). furthermore, the thermal performance factor of the twisted tube with oval dimples is equal to 1.19 compared with the twisted tube without dimples. The thermal performance factor of the twisted tube with oval dimples is equal to 1.38 compared with the straight tube, with another improvement to the twisted tube that improves the heat transfer properties by disrupting the thermal boundary layer and destabilizing it. This paper presents a comprehensive investigation of passive heat transfer devices (twisted tubes) and their relative merits in a myriad of commercial applications. [ABSTRACT FROM AUTHOR]

The article discusses the results of a study of the influence of flow twisting on convective heat transfer in banks of twisted tubes. The author claims that the method of artificial turbulization of flow by twisting the latter by twisted tube allows an individual to reduce the overall dimensions and mass of heat exchanging apparatuses owing to heat transfer enhancement. The author suggests dimensionless relations that correlate the data of various authors. In conclusion, the author claims that the heat transfer from twisted tubes and spirally finned rods depends on their position in a bank.

To explore the impact of intersecting surface shape on the thermal-fluid behaviors in the twisted tube (TT) under the two conditions of equal area and equal perimeter of intersecting surfaces, a 3D simulation method is used to examine the convection heat transfer characteristics of fluids with different viscosities in TTs with typical symmetrical cross sections at low Reynolds number (Re) according to experimental verification. The results manifest that the regularly helical deformation of the TTs induces secondary flows in the perpendicular direction of the main flow, leading to a better convection heat transfer performance. In the Re range of 650– 1550 with water, the twisted triangular tube produced with equal cross-sectional perimeter exhibits the topmost convection heat transfer performance, with a comprehensive performance evaluation factor of heat transfer (PEF) of 1.85– 1.87. As for the equal cross-sectional perimeters with engine oil, the twisted elliptical tube shows the highest PEF of 1.39– 1.40 as the Re is below 1100. When the Re exceeds 1100, the twisted triangular tube displays the supreme PEF of 1.33– 1.37. For the equal cross-sectional areas with water and engine oil, the twisted elliptical tube presents the utmost PEF of 1.32– 1.47. [ABSTRACT FROM AUTHOR]

In the present work, three dimensional numerical study is conducted to investigate the heat transfer and flow characteristics of twisted tubes of different cross section shapes with the Reynolds number ranging from 50 to 2000. The constant wall temperature condition is used in the simulation analysis. The numerical results of twisted square tube are compared with the available previous experimental data. The results indicate that the heat transfer performance of twisted tube is enhanced compared with the smooth tube, while the pressure drop increases as well. One of the key findings is that the transition point of twisted square tube from laminar flow to turbulent flow is identified and located at Re = 500. It is also found that the cross section shape has little effect on the heat transfer of twisted tubes, while it has great influence on the flow pattern. The results also reveal that the twist pitch has remarkable effects on the heat transfer performance of twisted tubes. In addition, the maximum value of PEC of 2.69 is obtained in twisted pentagon tube with twist pitch ratio of 0.17, and the Reynolds number of 350. These results are significant because it will contribute to the development of compact twisted tube heat exchangers. [ABSTRACT FROM AUTHOR]

Summary: Stationary solar collector such as flat‐plate collector is a thermal device, which traps solar energy and converts it into heat that can be used in industrial and domestic applications such as water heating. Flat‐plate collector thermal performance enhancement is investigated in this research paper. Two cross‐sectional geometries of the tube in the heat exchanger were investigated; a normal circular tube and a twisted tube were used in the experiment. The aim of the twisted tube exchanger is to enhance the performance of heat transfer of the tubes and to reduce the shell pressure drop; flat‐plate solar collector is the used application to study the heat exchanger performance. Both twisted tubes heat exchanger and normal circular tubes heat exchanger were examined in the same location and conditions with the same solar collector, both were used in the heat exchanger to study their effect, with two different working fluids, which are distilled water and multiwalled carbon nanotube (MWCNT)/water nanofluid. The system shows an increase in the performance when twisted tubes were used in the system compared with the circular tubes in both distilled water and MWCNT/water nanofluid by 12.8% and 12.5%, respectively, with an improvement by 34% for twisted tubes with MWCNT compared with normal circular tubes with distilled water. [ABSTRACT FROM AUTHOR]

The numerical research aims to investigate the heat transfer performance difference between the twisted tube and the smooth tube at the same hydraulic diameter. The effect of the major/minor axis ratios on the fluid-flow inside the twisted oval tube is studied in the Reynolds number range of 3000-11000, and the integral thermal-hydraulic effectiveness of twisted oval tubes is evaluated. The results show that the twisted wall induces secondary flow perpendicular to the mainstream direction. The vortices are rapidly generated in the pipe-line when the fluid enters the twisted tube section from the upstream section. As the fluid develops further, the vortices converge to form a spiral flow. Numerical simulations indicate that the average Nusselt number of twisted oval tube with a major/minor axes ratio of 1.70 increases by 18.7-35.5%, while the pressure drop increases by 59.9-61.3% compared to smooth oval tube. Furthermore, as the major/minor axes ratio increases from 1.18-2.48, the average Nusselt number experiences an increase of 26.7-38.2%. The twisted tubes within the major/minor axes ratio range of 1.40-1.96 demonstrate superior integral thermal-hydraulic performance compared to other pipes. [ABSTRACT FROM AUTHOR]

In the present investigation, the exergy of an innovative technique involving the integration of curved helical tubes with twisted passages was experimentally presented. This technique aims to improve the thermofluid characteristics by involving the swirl intensity of fluid flow in a twisted tube helical coil (TTHC). Six identical geometries with different pitch ratios of 36 mm, 54 mm, and ∞ (smooth/no twisted) were experimentally explored at two different inner tube profiles of triangular and square cross-sections in counter flow arrangements. The experimental runs were carried out at 10,300 ≤ Rei ≤ 37,800 and 2400 ≤ Reo ≤17,600 for both the inner and annulus fluids, respectively. The results showed that the Nusselt number, Nu, increased by 39.6% and 41.5% for triangular and square inner twisted cross-section profiles, respectively, at a of 36 mm at the expense of increasing f by 37.6% and 60.7%, respectively. The results also showed that the thermal performance factor reached 1.3 and 1.25 for a of 36 mm for the triangular and square inner twisted tube profiles, respectively. A comprehensive study is performed to analyze the TTHC from thermal, frictional, and exergetic viewpoints. New correlations for expecting the annulus Nuo and fo are presented. [ABSTRACT FROM AUTHOR]

The effect of a twisting parameter on heat transport in a square-sectioned twisted tube was studied. One definition of a twisting parameter is the ratio of the hydraulic diameter to the length of the tube at the point when it completed a full 360-degree twist. The twist parameters that were selected are 5, and they were compared to the Double Twisted Square Tube heat exchanger (DTSTHE). Transient flow was taken into account when evaluating the sets of Reynolds numbers. On the other hand, there are four different concentration volumes of nano fluid amounts of 0.005, 0.01, 0.025, and 0.04 for turbulent flow, and the Reynolds number ranges from 5,000 to 25,000. An examination was conducted into the effect of the twist parameter on the convective heat transfer coefficient through turbulent flow. The finite volume approach and the conventional − turbulence model were used to conduct numerical simulations of three-dimensional, steady-state incompressible flow in body-fitted coordinates. It was found that as the twist parameter is decreased, the heat transmission coefficient increases. What this means for the created span-wise swirling flow is unclear. With increasing distance from the tube center towards the walls, the whirling causes the cross-flow velocity vectors to increase. The boundary layer has good thermal properties because it thins out at the tube wall as the near-wall velocity increases. Internal thermal balance is further improved by spinning since it increases the mixing process. A higher Reynolds number, along with larger velocity components, results in a higher heat transfer coefficient. [ABSTRACT FROM AUTHOR]

A new technique was proposed and implemented through an experimental model to improve the absorber tube of a parabolic trough collector, which was connected to a twisted tube and resulted in a heat transfer enhancement. The enhancement increased the capacity of the tube to absorb solar energy by improving the convective transfer between the inner surface of the absorber tubes and the heat transfer fluid. The new design was dependent on overlapped and reverse flow, which was validated through five receiver tube (R t) models, each one consisting of two types of overlapped flows. The first was a flow through inner twisted tubes (single (STT), dual (DTT), and triple (TTT) twisted tubes), with different hydraulic diameters. The second was a reverse flow through an outer round tube, with both concentric tubes joined at one side by a bayonet end cap. For each R t , the inlet flow from the central or peripheral tubes was assessed. The results showed a remarkable increase in heat transfer enhancement for most STT models and a greater heat transfer in TTT that was overlapped than for a plain tube collector. The enhancement was accompanied by an increase in the pressure difference that was higher for TTT than STT. For each model, the efficiency of the collector and pressure losses was estimated, and the Nusselt number (Nu) and an efficiency evaluation criterion were calculated. [ABSTRACT FROM AUTHOR]

The results of investigations in the field of hydrodynamics and heat transfer in fast reactors and an accelerator-controlled system with liquid-metal coolants are presented. Physical phenomena, effects, regularities, and characteristics of the velocity and temperature fields in the flow path and core of fast reactors are analyzed. The data of investigations on a sodium model of a large-module steam generator and a fragmented lead model of a steam generator with twisted tubes are presented. The results of investigations on a model of a fast neutron reactor tank demonstrate the temperature stratification with stagnant and recirculation formations, internal waves at stratified interfaces, temperature fluctuations, thermal fatigue of structural materials, and a decrease in the service life of equipment. It is shown that the boiling process of liquid metals in fuel rod assemblies has a complex structure and is characterized by both stable (bubble, disperse-annular) and pulsating (slug) modes with significant parameter fluctuations, which cause a heat transfer crisis. The heat transfer is investigated, a cartogram of the flow regimes of a two-phase flow of liquid metals in fuel rod assemblies is constructed, the effect of fuel rod surface roughness on heat transfer and boiling regimes is investigated, and the possibility of long-term cooling of the core during sodium boiling in the case of a "sodium cavity" above the reactor core is substantiated. The characteristics of the process of degradation of the fuel assembly simulator of the core of fast reactors during the thermal interaction of uranium-containing fuel simulators with static sodium and their dependence on the parameters and design of the system are determined. The problems of thermophysical investigations for a high-temperature sodium reactor for hydrogen production are presented. [ABSTRACT FROM AUTHOR]

Study of the heat transfer performance of twisted tubes have been limited to forced convective conditions (inertia-dominated flow) without studying the effect of different isothermal wall temperature (buoyancy force). Therefore, this work investigated the flow and heat transfer behavior of a twisted square tube of a varying pitch length at different mixed convective regimes. The model continuity, momentum, and energy equations were solved using the finite volume technique. The numerical model setup was validated using experimental results and a satisfactory result was achieved. The result shows that the twisted square tube performs better than the smooth tube subjected to the same conditions. The heat transfer rate and drag coefficient increase with decreasing twist pitch length. In addition, the result shows that increment of buoyancy force, while inertia force is kept constant leads to a high reduction of drag as compared to increasing inertia force, while buoyancy force is kept constant. Overall, a 15% increase (at Ri=1) is obtained in the drag coefficient and a 13% increase (at Ri=0.5) is obtained in the heat transfer rate in the 100 mm twist pitch length as compared to the 600 mm twist pitch length. [ABSTRACT FROM AUTHOR]

The high thermal efficiency of supercritical water makes it a promising alternative to water cooled reactors. This study employs numerical analysis, utilizing the SST k-ω turbulence model, to investigate the heat transfer performance of supercritical water (SCW) in various tube configurations and fluid flow conditions across Reynolds numbers ranging from 8,000 to 20,000. This research examines how different geometrical parameters, such as the helical direction, number of lobes, and cross-sectional shape, impact the flow physics and heat transfer performance of different spiral tubes. The outcomes specify that increasing the lobed number in the tube improves the heat flux by about 5%–16%. Furthermore, introducing two direction changes in the twisted tube will cause a slight increase (about 20%) on heat transfer enhancement. Finally, the sensitivity analysis of heat flux and Nusselt number to each of the effective parameters in the heat transfer of supercritical water in twisted tubes has been accomplished and the Response Surface Method (RSM) utilizes the central composite design (face-centered) approach. According to the findings of these two studies, it has been established that the Reynolds number of the fluid flow is the most influential parameter in determining the extent of heat transfer. Specifically, it exerts an effectiveness of 26% and 76% on the Nusselt number and heat flux, respectively. Furthermore, the inscribed circle diameter of tube by 8% effectivity and minor axis length by 5% effectivity on heat flux are more effective than others. [ABSTRACT FROM AUTHOR]

This work introduces a heat exchanger design approach for units using combined twisted tape and twisted tube heat transfer enhancement technology. In design and retrofit, the use of these systems is characterized by heat transfer enhancement on both sides of the unit. It is shown that the rate of increase of heat transfer is much higher than in single twisted tubes leading to improved designs. Thermal and hydraulic experimental published data on these types of surfaces are employed in developing the design approach. In the case of design, an area reduction of up to 32.2 % with a length reduction of 31.4 % for the same pressure drop levels is achieved. In the case of retrofit, the use of a combined twisted tube and twisted tape led to a heat load increase of 29.2 % with an increment of 40.4 % in pressure drop. The methodology is demonstrated in a case study from the open literature. [ABSTRACT FROM AUTHOR]

The thermal and fluid physiognomies of a double twisted tube heat exchanger was examined numerically. Twisted engineering is a wide-use method to improve heat transfer in heat exchangers. A counter-flow mode utilizing hot water in the inner tube and cold air in the outer tube was considered. This study aims to progress the thermal performance of the double tube heat exchanger by using twisted tubes instead of plane tubes. The heat exchanger was (1m) length, outer diameter (0.05m) and inner diameter (0.025m), both with a thickness (0.004m). It was tested for different values of twist ratios (Tr= 5, 10, and 15 respectively) and Reynolds numbers (Re=5000 to 30000). The Navier - Stockes and energy equations besides the turbulence model in demand for modelling this physical problem. ANSYS Fluent code was used for the numerical simulation. The results showed that the twisted tube heat exchanger showed increasing heat transfer compared with a plain tube heat exchanger. It was found that the cold outlet temperature, pressure drop and effectiveness are increased as the twist ratio increases. [ABSTRACT FROM AUTHOR]

Twisted structures have been commonly used to improve heat transfer in tubular heat exchangers operating at regular pressures. However, their behavior under supercritical operating conditions remains unknown, and the thermal and hydraulic characteristics of a precooler equipped with twisted structures in a supercritical carbon dioxide (SCO 2) cycle have not been studied before. For this reason, 3D simulations are conducted to explore the flow and heat transfer of SCO 2 in a precooler featuring both twisted tubes and twisted tapes. Furthermore, four non-uniform configurations are designed for each twisted structure. The obtained results indicate that for SCO 2 in a gas-like state, the use of twisted tubes is more suitable, whereas, for SCO 2 in a liquid-like state, the use of twisted tapes is more appropriate. Twisted configurations exhibit a heat transfer coefficient ranging from 1.11 to 1.48 times higher than that of the straight mini-tube. Non-uniform structures can help control and tailor turbulence levels according to SCO 2 's thermophysical properties variations. The results reveal that shorter twist pitches at the beginning of the flow path in non-uniform twisted tubes and in the middle section for twisted tapes provide the best overall performance, with significant heat transfer enhancement and a relatively low pressure drop penalty. • The performance of a precooler with novel twisted structures is studied for SCO 2 power cycle. • Twisted structures improve the thermal performance of the precooler by 11–48 %. • The hydraulic performance can vary based on the twisted structure and flow conditions. • The twisted tube case with shorter initial twist lengths shows the best overall performance. • The twisted tape case with shorter twist lengths in the middle is the standout top performer. [ABSTRACT FROM AUTHOR]

• Numerical simulation of steam-liquid two-phase flow with swirling flow in different twisted tubes is carried out. • The volume fraction, velocity and temperature distribution are studied under the influence of swirling flow. • Un-uniform of the circumferential heat transfer coefficient is studied. • The absolute vorticity flux and secondary flow intensity of twisted tubes are quantitatively analyzed. • Comparison between two-fluid three flow field with the droplet model and EE+GENTOP concept is carried out. The Eulerian-Eulerian (EE) simulation approach + GENeralized TwO Phase (GENTOP) concept and two-fluid three-flow field with droplet were used to simulate the heat and mass transfer. Analysis encompassed the examination of steam and liquid phase distributions, as well as flow pattern transitions. Heat transfer enhancements were quantified using a comprehensive heat transfer factor. The disturbance intensity of the secondary flow was characterized by the absolute vortex flux. Results revealed a correlation between the intensity of the secondary flow and axial length, indicative of progressive fluid disturbance enhancement. Additionally, the maximal motion of the steam phase vortex was observed both near the wall and channel center. The EE+GENTOP concept exhibited superior capability in reproducing multi-scale flow including small-scale dispersed bubbles and large-scale continuous steam (coalescence and break-up). For investigations into the entrainment and deposition of liquid droplets in annular flow, the selection of a two-fluid three-flow field with the droplet model is recommended. [ABSTRACT FROM AUTHOR]

• A simulation study on the sub-cooled water flow boiling in vertical tubes. • Twisted tubes offer better heat transfer but result in higher pressure drop. • Twisted tube wall causes spiral flow of the fluid inside the tube. • Centrifugal force has an important effect on the phase distribution in twisted tubes. Twisted elliptical tubes possess superior heat transfer performance due to their unique geometry. It is necessary to further explore their potential applications in high-efficiency heat transfer devices. This study conducted a numerical simulation investigation to analyze the flow boiling heat transfer characteristics of subcooled water inside twisted elliptical tubes. The results show that the spiral flow inside twisted elliptical tube causes the fluid with relatively small vapor volume fraction to tend to distribute near the wall, while also increases turbulence intensity and promotes interactions among bubbles. Moreover, increasing the aspect ratio of the twisted elliptical tube can effectively improve the heat transfer coefficient and has a relatively small impact on the pressure drop of the fluid in the tube. Simulation data show that when the aspect ratio increases from 1.41 to 1.80, the heat transfer coefficient of the pipe increases by 15.21 %, while the pressure drop increases by 3.34 %. [ABSTRACT FROM AUTHOR]

The convective heat transfer and flow resistance properties of water flowing through a twisted trilobed tube (TTT) with Reynolds numbers that ranged from 10,000 to 40,000 were examined in this work. Specifically, we examined how the tip circle radius (r), straight length (l), transition radius (R), and twist pitch (S) influenced the heat transfer and flow resistance in the tube. Our results showed that the TTT had an average Nusselt number (Nu) that was 30% higher than that of a plain tube, while the friction coefficient (f) increased by 39%. We also presented temperature and velocity field distributions and explained the enhanced heat transfer process using the field synergy principle. Furthermore, we found that a larger tip circle radius (r) and straight length (l), as well as a smaller transition radius (R) and twist pitch (S), led to better overall heat transfer performance of the TTT. Among the different cases evaluated, Case 7 had the highest overall heat transfer performance with a PEC of 1.37. The unusual structure of the TTT caused a rotating motion, which resulted in secondary and spiral flows that increased the synergy through the velocity and temperature fields. Finally, our research found a correlation with the Nusselt number (Nu) as well as the friction coefficient (f). [ABSTRACT FROM AUTHOR]

Heat transfer characteristics of graphene oxide (GO)/turbine oil as a non‐Newtonian nanofluid are assessed both experimentally and numerically in this paper. To do so, 0.2, 0.3, 0.5, and 1 mass percent (wt%) of GO is homogeneously dispersed in the base liquid. First, the specific heat capacity, thermal conductivity, viscosity, and density of the synthesized nanofluids are measured using standard laboratory methods. After that, constants of the shear stress equation are determined through the nonlinear regression of the rheology data on the power law model. Finally, the heat transfer from turbine blades with a constant surface temperature to the coolant nanofluid is investigated using mathematical modeling. The results suggest that while the nanofluid density, viscosity, and thermal conductivity increase by increasing the nanoparticle concentration by 0.57%, 7.07%, and 18.89% in succession, respectively, and its specific heat capacity decreases by 0.54%. Moreover, both the convective heat transfer coefficient and the temperature profile in the considered nanofluids depend on the average velocity and Reynolds number. Furthermore, the convective heat transfer coefficient increases by 5.5%, 9.5%, 14%, and 17% in exchange for 0.2, 0.3, 0.5, and 1 wt% of GO nanoparticles in the base liquid, respectively. [ABSTRACT FROM AUTHOR]

The thermal analysis performance of evaporative fluid coolers (EFCs) is improved by replacing plain tubes by twisted oblong tubes. Results of the system are assessed by a rapid design algorithm (RDA) and compared to conventional plain-tube EFCs and other traditional algorithms including the effectiveness number of transfer units ( ϵ-NTU). Based on the RDA, a relationship between heat transfer coefficients, pressure drops, heat transfer area, and mass transfer coefficient is derived. Using the maximum allowable pressure drops in this algorithm, the minimum required heat transfer area can be determined. The algorithm is validated by comparing the plain-tube EFC design with twisted-tube design. The RDA-designed EFCs with twisted tubes provide higher efficiency compared with the traditional designs with plain tubes in such that the new design needs a lower heat transfer area for a given heat load. [ABSTRACT FROM AUTHOR]

The Lead-cooled Fast Reactors (LFRs) are fast neutron spectrum reactors cooled by molten lead or lead alloys, which are recommended as one of candidates for the next generation of nuclear reactors due to high performance in sustainability, thermal-hydraulics, and security features. As the critical equipment linking the primary circuit and secondary circuit in LFR, the performance of the main heat exchanger plays a significant role in the operating efficiency of the reactor. In order to improve the heat transfer efficiency and optimize the temperature distribution between the coolant in the primary circuit and secondary circuit of LFR, the flow and heat transfer characteristics of fluids in twisted elliptical tube are investigated in the present study, since the specific spiral cross flow is expected occurring in both inside of the tubes and the interfering area outside the tubes. Theoretical calculation is conducted firstly based on the periodical unit model of the twisted tube heat exchanger. Then the numerical simulation is carried out to study the characteristics of fluid and heat transfer in both shell and tube sides. The results show that the cross flow in twisted tubes improves the overall heat transfer performance of the heat exchanger by strengthening the mixing and turbulence of working fluid. Compared with straight tubes, the entire performance evaluating factor of twisted tubes is around 1.596 times. The theoretical and numerical studies are helpful to the design of the main heat exchanger in LFR. [ABSTRACT FROM AUTHOR]

To investigate the heat transfer characteristics of a car radiator involved nanofluids, we used GAMBIT & FLUENT softwares and calculated the effective physical parameters using some famous models as a single-phase mixture. Carbon nanotubes and boron nitride nanotubes have been used in less than 1% volume concentration in flat and twisted tubes. Our results show that nanofluids application in a twisted tube gives a great enhancement in the thermal performance in comparison of the flat tube. [ABSTRACT FROM AUTHOR]

This study explored the heat transfer performance of a decaying swirl flow generated by a four‐lobed swirl generator with simulations and experiments. In the experimental studies, the thermal performance of a swirl generator was compared with that of a circular tube, indicating that the printed swirl generator provided better heat transfer performance than the printed circular tube. Further experiments were performed over a range of Reynolds numbers with different lengths of post‐swirl, circular pipe to assess the decay of swirl, downstream. Here, for shorter lengths of post‐swirl, circular pipe, the thermal improvement was maintained, but this advantage was lost with longer circular pipe runs. In numerical studies, the effect of various pitch‐to‐diameter (PD) ratios of the swirl pipe, including the actual swirl pipe (in-swirl) as a part of the heat exchanger or excluding it (ex-swirl), and the effect of different post‐swirl section lengths were investigated. The heat transfer rate and pressure drop increased with the reduction of the PD ratio, and the in‐swirl arrangements gave higher thermal enhancement and similar pressure loss compared with the ex‐swirl arrangements. The PD6 in‐swirl arrangement gave the highest thermal enhancement for all the geometries. Applying the swirl intensity and the field synergy principle confirmed these results, showing that any thermal enhancement created by swirl generators disappeared rapidly after exiting the swirl tube. In addition, the field synergy principle was more suited to explain the thermal enhancement effect of the decaying swirl flow instead of swirl intensity. This study demonstrates that by optimising the post‐swirl pipe length, overall heat transfer performance can be increased by around 5% with a pressure drop of less than 16%. [ABSTRACT FROM AUTHOR]

In the present article, a novel coaxial with shell-and-tube (CWST) heat exchanger is developed and simulated using Ansys-Fluent®, and its results are compared with those of the shell-and-tube heat exchanger from which it is derived. The geometry of this new exchanger was given, specifying the different types of fluids it can contain and their circulations, and a theoretical calculation based on the NTU method (number of transfer units method) is used to validate the simulations. In order to be able to analyse the phenomena occurring inside this exchanger, the fluid temperature, pressure, and velocity distribution figures are given with the evolutionary curve of some performance parameters (the heat, the pressure losses, the ratio between heat and pressure losses, the heat flux and the overall heat transfer coefficient) as a function of the cold fluid volume rate. At the end the various advantages it can give to enhance the efficiency of heat transfer, to reduce manufacturing and operating costs, as well as its potential for further research on the improvement of the design were explained. [ABSTRACT FROM AUTHOR]

The purpose of this study is to experimentally enhance the heat exchange rate of the shell and helical coil tube heat exchanger by mixing water with aluminum oxide (Al2O3) nanoparticles, as well as to explore the effect of inlet thermal parameters on the performance of the heat exchanger. A test rig was constructed to investigate the influence of particle concentration, and inlet temperatures on the performance of nano-fluid. Parameters such as Nusselt number, pressure drop, performance evaluation criteria (PEC) are considered to rate the performance of the nano-particle with the heat exchanger. In this study a wider range of particle concentration is considered, which varies from 0.0%-0.75%. Experiments with and without nanoparticles are carried out under identical working conditions. By analyzing the experimental data, it was found that nanoparticles significantly improve the coefficient of heat transfer inside the helically coiled tube. From sensitivity analysis, it is obseerved that there is a slight decrease in Nusselt number of the nano-fluid with increase in inlet temperatures of the nano-fluid and the cooling water. Furthermore, it is concluded that an 8.5% increase in PEC value is observed with increase in particle concentration from 0.15% to 0.75%. [ABSTRACT FROM AUTHOR]

In the present article, heat transfer enhancement by three-start spirally twisted tube combination with triple-channel twisted tape is studied numerically using RNG k-ε turbulence model. Influences of the tape width ratio ( w/D = 0.1, 0.25, 0.34 and 0.5) and tube/tape arrangement (belly-to-belly and belly-to-neck arrangements) are described. The numerical results of a twisted tube without tape and a circular plain tube are also given for comparison. The results are reported in terms of velocity field, temperature field, turbulent kinetic energy, local Nusselt number distribution, average Nusselt number, pressure loss and thermal performance factor. It is found that heat transfer and friction factor increase with tape width ratio. At a given tape width, the systems in belly-to-neck arrangement are more efficient for heat transfer enhancement than the ones in belly-to-belly arrangement. The three-start spirally twisted tubes with twisted tapes in belly-to-neck arrangement at w/D = 0.1, 0.25 and 0.34 give higher Nusselt numbers than the twisted tube without tape up to 1.2%, 21% and 36%, respectively. The twisted tubes with triple-channel twisted tape in belly-to-belly arrangement provide higher Nusselt numbers than the twisted tube without tape up to 1.23%, 6.7%, 10% and 17%, respectively. The superior heat transfer of the combined devices in belly-to-neck arrangement (especially at large w/D ) is attributed to the stronger interaction between the swirling flows induced by the tubes and those induced by the tapes. Moreover, the systems in belly-to-neck arrangement cause lower friction loss than the ones in belly-to-belly arrangement. Thus, the systems in belly-to-neck arrangement yield higher thermal performance factors. Among the studied cases, the twisted tube combined with triple-channel twisted tape in belly-to-neck arrangement at w/D = 0.34 possesses the maximum thermal performance of 1.32 at Reynolds number of 5000. [ABSTRACT FROM AUTHOR]

This article employs a plate with V-shape ribs inside a tube as turbulator to augment the heat transfer rate. The utilized vortex generators are double-winglets arranged in a V-shape placed on both sides of the plate. The proposed system's suggested working fluids are water-based hybrid nanofluids, including Al2O3–Cu/water, Cu–CuO/water, and Cu–TiO2/water. This work involves a numerical evaluation of the effects of the type and volume concentration of the examined hybrid nanofluids on the enhancement of heat transfer. The experimental results are used to validate the numerical model. It is worth mentioning that all the obtained numerical results are compared with the simple tube, without any turbulator (vortex generator) and in the presence of water instead of the hybrid nanofluids. Based on the numerical results, it can be concluded that all employed hybrid nanofluids showed improved thermal performance compared to pure water. Furthermore, the differences between the models are more substantial for higher Reynolds numbers than for lower Reynolds numbers. In Re = 30,000, the Cu–TiO2/water exhibits the lowest thermal performance improvement (augmentation of about 0.3%), while the Cu–CuO/water at Re = 50,000 exhibits the largest thermal performance improvement (augmentation of approximately 5.7%), in the case of ∅1 = ∅2 = 0.5%. For ∅1 = ∅2 = 1%, the Cu–TiO2/water at Re = 30,000 has the lowest thermal performance improvement (augmentation of around 1.1%), while the Cu–CuO/water at Re = 50,000 has the most thermal performance improvement (augmentation of roughly 8.7%). According to the augmentation of around 2.8% at Re = 30,000 for Cu–TiO2/water and approximately 10.8% at Re = 50,000 for Cu–CuO/water, the thermal performance increase in the scenario of ∅1 = ∅2 = 1.5% is the lowest. In Conclusion, the Cu–CuO/water hybrid nanofluid with a volume concentration of ∅1 = ∅2 = 1.5% has the greatest thermal performance value of all the hybrid nanofluids studied. [ABSTRACT FROM AUTHOR]

Improvements in heat exchanger thermal efficiency are crucial for achieving energy use and cost reductions. The use of nanofluids and the rotation of the exchanger inner tube may enhance heat transfer and exchanger efficiency. In this work, after having performed experiments on such a heat exchanger, a three dimensional numerical model was developed to simulate the transitional forced convection flow of a horizontal double-tube heat exchanger, with the aim of obtaining insight into the effects of the inner tube rotation, fluid flow rate and type of nanofluid employed. It was found that an increase in the nanoparticle concentration up to 3% increased the exchanger efficiency. Al2O3, Al2O3-Cu and Cu-water nanofluids were studied, with the Cu-water being the fluid with the best performance (19.33% improvement). Heat transfer was enhanced with inner tube rotation up to 500 rpm (41.2%). Nevertheless, pressure drop and friction values were increased due to both phenomena, leading to higher pumping power values for the operation of the heat exchanger. Hence, a balance between the performance and pumping power increase must be considered when modifications are made on a heat exchanger. The development of the numerical model might help in further optimizing, redesigning and scaling up heat exchangers. [ABSTRACT FROM AUTHOR]

The energetic and exergetic enactments of the plate heat exchanger (corrugated) were studied theoretically using a hybrid nanofluid. Alumina–silver (Al–Ag) and magnesia–silver (Mg–Ag) nanoparticles were mixed in the propylene glycol–water brine and ethylene glycol–water brine solutions. Here, two cases were dealt with, one with a given flow rate and the other with a given area and concentration. The effect of nanoparticle concentration and hybrid nanofluid flow rate was studied on different parameters. It was observed that the overall heat transfer coefficient, pressure drop, pumping power, non-dimensional exergy destruction, entropy generation rate, and irreversibility rise with the flow rate. In contrast, the irreversibility distribution ratio reduces with the flow rate. Moreover, the trend reversed with the nanofluid volume concentration up to 0.5% concentration was observed, which can be treated as a critical parameter. In studied ranges, propylene glycol brine performs better than ethylene glycol brines. The alumina–silver combination is found to be better than the magnesia–silver combination. Increasing the flow rate is suggested as a better option than increasing the nanoparticle concentration for a given area. [ABSTRACT FROM AUTHOR]

The cross-wave primary surface recuperator (CW-PSR) is a dependable option as a recuperator for micro gas turbines (MGT). The micro CW-PSR studied in this paper is composed of 171 stacked curved plates, with each plate containing 33 micro heat transfer channels with equivalent diameters of less than 1 mm. In this study, the influence of bending curvature on the thermal performance of CW-PSR plates is investigated through three-dimensional numerical simulation with fluid–solid–thermal coupling. The results indicate that the variation in bending curvature studied can result in a noteworthy 8% difference in the total heat transfer coefficient of CW-PSR plates. A direct correlation between heat transfer capacity and secondary flow strength is derived mathematically, explaining the mechanism by which secondary flow enhances heat transfer. By employing this relationship, a comprehensive analysis of CW-PSR plates with diverse bending curvatures is conducted, effectively showcasing how curvature influences the secondary flow pattern and enhances the channel's heat transfer capacity. In addition, this paper considers the comprehensive influence of the size parameters of the heat transfer unit and the bending curvature of the heat transfer plate on the heat transfer and flow characteristics of the CW-PSR, and a dominant mathematical expression is obtained, which can be used for the design of similar heat exchangers of the same type. [ABSTRACT FROM AUTHOR]