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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]

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]

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]

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]

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]