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This numerical study examines the thermal-hydraulic performance of helical coil heat exchangers (HCHEs) using twisted tubes versus conventional circular tubes. The effects of Reynolds number (Re = 10,000 to 100,000), pitch length (11, 7.2, 5.5, 3.6 mm), and twisted tube orientation (co-current, counter-current) on heat transfer efficiency and pressure drop were investigated. The results show that higher Reynolds numbers can reduce the Resistance factor by approximately 25 % and improve heat transfer by approximately 35 %. An optimal pitch length of 5.5 mm was found to balance enhanced heat transfer and manageable pumping costs. Twisted tubes demonstrate significant performance advantages at lower Re, with 20–33 % higher Performance Evaluation Criterion (PEC) values compared to circular tubes. However, the benefit diminishes at higher Re, with less than 10 % PEC increase. Implementing counter-current twisted tube configurations leads to approximately 13 % higher Nusselt number and 11 % higher Resistance factor, resulting in a 10 % overall PEC improvement. These findings highlight the superior thermal-hydraulic performance of twisted tubes in HCHE applications, especially at lower Reynolds numbers. Future work could explore different fluids, advanced optimization, energy analysis, cost assessment, and additional geometric parameters to further enhance twisted tube heat exchanger design and performance.

Abstract In this article, the forced convective turbulent flow of a shear-thinning non-Newtonian nanofluid through twisted tubes with elliptical cross sections is numerically studied and analyzed at various Reynolds numbers. The base fluid of the studied nanofluid is 0.5% carboxymethyl cellulose solution in water (which has non-Newtonian behavior of shear-thinning), and it contains copper oxide nanoparticles. Two types of twisted tubes are considered: finned tubes and unfinned ones. The finite volume method is utilized, and the two-equation model of k-ε has been applied to analyze the flow characteristics of the turbulent problem. The computational results demonstrate an excellent agreement with respect to already published reports, which is a testament to our reasonable and correct procedure. The effects of pipe wall twisting on the average Nusselt number have been investigated. The achievements demonstrate a powerful secondary and rotating flow is formed with the tube surface twisting. This secondary flow causes better mixing and increases the average Nusselt number. The increase is up to 45% for the unfinned case and 62% for the finned case in comparison with the tube without projections. In addition, the coefficient of friction in these pipes increases to 62% and 104% for the unfinned and finned tubes, respectively. It is also observed that by increasing the length of the fin and adding nanoparticles up to 1.5%, the highest value of the performance evaluation criterion (i.e. 1.78) in the twisted finned tube could be achieved, which occurred at the Reynolds number of 4000. The combination of present geometry and the working fluid of shear-thinning non-Newtonian CMC-based nanofluid is the main novelty of this work, and the results can be applicable and reliable in the relevant industries. [ABSTRACT FROM AUTHOR]

Highlights Rheological properties of food waste slurry were tested and modeled Pilot test of twisted tube heat exchanger validated the CFD-based simulations Twisted hexagonal tubes exhibited better performance at low-temperature differences Heat-transfer enhancement was due to strong and continuous shear effect close to tube walls Twisted hexagonal tubes exhibited better performance at low-temperature differences Heat-transfer enhancement was due to strong and continuous shear effect close to tube walls

Supercritical water (SCW) as fluid with enough potential abilities such as high thermal efficiency can be replaced in water cooling systems. However, helical pipes are the most common type of swirl generators used for heat transfer enhancement, and their geometrical parameters contribute significantly to the compactness and efficiency of heat exchangers. In this study, for the Reynolds ranges of 8000–20000, a numerical study is performed to investigate SCW flow within circular tube, twisted oval tube and twisted multi-lobe tubes. Effects of such parameters as cross-section shapes and lobed numbers on heat transfer performance and flow physics of different spiral tubes were investigated. Results indicated SCW has a contradictory behavior with ordinary water. The results showed that twisted tri-lobed tubes had higher average Nusselt number than circular tube and twisted oval tube, which was 53% and 41%, respectively. Also in these tubes the larger radius of connecting arc and the smaller length of major axis conclude the higher amount like 4%-6% of heat flux due to the enhancement of swirling fluid flow in the pipe and the heat flux. By increasing the number of lobes, the swirling flow rate that is bounded by the lobes will increase. [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]

Numerical simulations were performed with the open-source CFD software OpenFOAM to investigate the ability of several configurations of short-length twisted tube geometries with non-circular cross section connected to tubes with circular cross section to induce a swirling flow. The heat transfer and the pressure drop linked to the generated swirling flow are also calculated. The swirling flow is modeled using a k-ω SST turbulence model with a low-Reynolds approach. It is shown that a short-length twisted tube with an elliptical cross section (STE) is able to generate a swirling flow, but its intensity greatly depends on its twist pitch and its aspect ratio. The lower the aspect ratio, the higher the swirl intensity. For a Reynolds number ranging from 10,000 to 100,000, the results reveal that compared to a plain tube, the STE with the lowest aspect ratio achieves enhancing the heat transfer from 22 to 90% at the cost of an increased pressure drop of, respectively, 63 and 129%. The second part of the study is focused on a short-length twisted tube with a three-lobed cross section, and the results reveal that the generated swirling flow is even more intense than with the STE and that the heat transfer enhancement goes from 30 to 105% at the cost of an increased pressure drop from 137 to 180%. [ABSTRACT FROM AUTHOR]

Heat exchangers used in the composition of large-capacity energy conversion systems for space applications must be able to operate at high temperatures (above 1000 K) and at high (several MPa) values of pressure difference between the “hot” and “cold” heat carrier/coolant channels. This is why especially demanding strength and stiffness requirements are posed to the heat-transfer matrix of these devices, a circumstance that precludes almost completely the use of well-known compact and light plate-and-fin devices with 50-100-μm-thick foil fins. The article presents the results from experimental investigations into the thermal and hydraulic characteristics of alternative versions of heat-transfer elements involving the use of different heat transfer enhancement methods. Experimental investigations of heat transfer and hydrodynamics were carried out for three types of heat-transfer surfaces: a tubular one composed of small-diameter (3 mm) thin-walled tubes deformed over the cross-section perimeter and length (twisted tubes), a plate one finned with pins having a diamond-shaped cross section (2 × 2 mm in cross section and 4 mm in height), and a plate one composed of thin-walled 0.2-mm-thick plates with the surface formed by oppositely directed truncated cones with saddle-like bridges (a biconvex stamped plate). After processing and analyzing the experimental data obtained for these heat-transfer surfaces, dimensionless dependences for the Nusselt number and the pressure-drop coefficient on the Reynolds number were constructed. The dimensionless formulas obtained for twisted tubes and for the pin-finned surface are compared with the well-known correlations. It is shown that the use of twisted tubes instead of round ones results in improving the heat transfer intensity by more than 20% with the hydrodynamic indicators worsened by 50%. The use of the pin-finned plate surface improves the heat transfer intensity by more than a factor of two as compared with using a staggered tube bundle. [ABSTRACT FROM AUTHOR]

Thin-walled tubes are light in weight and has shown good energy absorption potential. Geometry of such tubes is a key in deformation modes and energy absorption under impact loading. Energy absorption can further be enhanced by implementing improved geometrical configurations. In the present investigation, crushing and energy absorption behavior of twisted aluminum tubes are test simulated under impact loading. The nonlinear finite element simulation is carried out using commercially available software ABAQUS ® . The analysis is carried out with three different thicknesses and three different velocities for twisted tubes. Different modes of deformation, load-displacement curve are developed and analyzed. The investigation shows that energy absorption marginally decreases with increase in velocity whereas, it increases with increase in thickness of the tubes. The tubes deform in concertina mode and value of maximum first peak force is evaluated for various thicknesses and impact velocities. This study helps in design of the crush tubes in automotive sector wherein sudden rise of peak force is undesirable from passenger safety viewpoint. [ABSTRACT FROM AUTHOR]

We establish various Hardy-type inequalities for the Dirichlet Laplacian in perturbed periodically twisted tubes of non-circular cross-sections. We also state conjectures about the existence of such inequalities in more general regimes, which we support by heuristic and numerical arguments. [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]

Abstract: We show that a twist of a three-dimensional tube of uniform cross-section yields an improved decay rate for the heat semigroup associated with the Dirichlet Laplacian in the tube. The proof employs Hardy inequalities for the Dirichlet Laplacian in twisted tubes and the method of self-similar variables and weighted Sobolev spaces for the heat equation. [ABSTRACT FROM AUTHOR]