Flow and Heat Transfer Characteristics of a Cross-Flow Heat Exchanger with Elliptical Tubes
TL;DR: In this article, the effect of variation of longitudinal and transverse pitch-to-diameter ratios for a cross-flow heat exchang was investigated for heat transfer and fluid flow.
Abstract: Numerical investigations of heat transfer and fluid flow have been carried out to study the effect of variation of longitudinal and transverse pitch-to-diameter ratios for a cross-flow heat exchang...
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TL;DR: In this paper , an approach is developed to determine the effective length of the heat exchanger and the temperature of the cold coolant (oil) at its outlet in the case of a strong dependence of oil viscosity on temperature.
Abstract: The heating of oil and oil products is widely used to reduce energy losses during transportation. An approach is developed to determine the effective length of the heat exchanger and the temperature of the cold coolant (oil) at its outlet in the case of a strong dependence of oil viscosity on temperature. Oil from the Uzen field (Kazakhstan) is considered as a heated coolant, and water is considered as a heating component. The method of the log–mean temperature difference, modified for the case of variable viscosity, and the methods of computational fluid dynamics (CFD) are used for calculations. The results of the numerical calculations are compared with the data obtained on the basis of a theoretical approach at a constant viscosity. When using a theoretical approach with a constant or variable viscosity, the heat transfer coefficients to cold and hot coolants are found using criterion dependencies. The Reynolds-averaged Navier–Stokes (RANS) and a turbulence model that takes into account the laminar–turbulent transition are applied. In the case of variable oil viscosity, a transition from the laminar flow regime to the turbulent one is manifested, which has a significant effect on the effective length of the heat exchanger. The obtained results of the CFD calculations are of interest for the design of heat exchangers of a new type, for example, helicoid ones.
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TL;DR: In this paper, the authors investigated heat transfer through natural convection using a series of experiments and computational modeling using Computational Fluid Dynamics (CFD) simulations in a one-meter b...
Abstract: The present work investigates heat transfer through natural convection using a series of experiments and computational modeling using Computational Fluid Dynamics (CFD) simulations in a one-meter b...
Cites background from "Flow and Heat Transfer Characterist..."
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TL;DR: In this article , numerical simulation of the transverse air flow around a tube bundle with a diameter of 5 mm is carried out, where pipe sizes ranged from 0.1 to 0.5 mm.
Abstract: Currently, the problem of heat removal and recovery in transport is relevant. Of the many existing designs of heat exchangers, about 80% are shell-and-tube heat exchangers. In this work, numerical simulation of the transverse air flow around a tube bundle with a diameter of 5 mm is carried out. The bundle is formed by pipes with a diameter of 0.1 to 0.5 mm. For each pipe diameter, a bundle model with different packing porosity was created. Porosity ranged from 0.7 to 0.95. The calculations were carried out in the ANSYS software package (v. 19.2). The influence of pipe diameter and packing porosity on the heat flow and pressure drop was analyzed.
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TL;DR: In this article, a performance evaluation plot has been proposed, which takes the ratios of heat transfer enhancement and friction factor increase as its two coordinates, where the quadrant of the coordinate where both (Nue/Nu0), (fe/f0) are greater than 1.
Abstract: On the basis of the existing performance evaluation criteria analysis and four assumptions, a performance evaluation plot has been proposed in this paper. This plot takes the ratios of heat transfer enhancement and friction factor increase as its two coordinates. The quadrant of the coordinate where both (Nue/Nu0), (fe/f0) are greater than 1.0 can be divided into four regions. In Region 1 heat transfer is actually deteriorated based on identical pumping power, in Region 2 heat transfer is enhanced based on identical pumping power but deteriorated based on identical pressure drop, in Region 3 heat transfer is enhanced based on identical pressure drop but the increase in friction factor is larger than the enhancement of heat transfer at identical flow rate, and in Region 4 heat transfer enhancement ratio is larger than friction factor increase ratio based on identical flow rate. For some techniques which lead to the reduction of both heat transfer rate and friction factor, the proposed plot is still applicable. Different enhanced techniques for the same reference one can be easily and clearly compared for their effectiveness when enhancement study is based on energy-saving. Five practical examples are provided to show the functions of the plot. 2008 Elsevier Ltd. All rights reserved.
154 citations
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TL;DR: In this paper, heat transfer characteristics and flow behaviors have been made clear for an elliptic cylinder of axis ratio 1 : 3, where the testing fluid was air and the Reynolds number ranged from about 8000 to 79000.
Abstract: Heat transfer characteristics and flow behaviors have been made clear for an elliptic cylinder of axis ratio 1 : 3. The testing fluid was air and the Reynolds number ranged from about 8000 to 79000. The angle of attack α was varied from 0° to 90°. The local and overall heat transfer features are clarified in relation to the flow behaviors around the cylinder. The critical Reynolds number is detected, where the heat transfer and flow characteristics change drastically. It is found that the mean heat transfer coefficient is at its highest at α = 60°–90° over the whole Reynolds number range studied and also that even the lowest value of the mean heat transfer rate is still higher than that for a circular cylinder. Effects of the axis ratio of the elliptic cylinder are also discussed in comparison with previous works.
126 citations
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TL;DR: In this article, the authors investigated the thermofluid characteristics of the elliptic tube bundle in crossflow and showed that increasing the angle of attack clockwise until 90° enhances the convective heat transfer coefficient considerably.
Abstract: In this work, the thermofluid characteristics of the elliptic tube bundle in crossflow have been investigated. Experimental and numerical investigations of the turbulent flow through bundle of elliptic tubes heat exchanger are carried out with a particular reference to the circular tube bundle. The investigation covers the effects of key design parameters of Reynolds numbers (5600–40,000), minor-to-major axis ratios (0.25, 0.33. 0.5 and 1) and flow angles of attack (0–150°). Five bundles of elliptic tube heat exchangers with different axis ratios were designed and manufactured in staggered manner. Numerical CFD modeling using finite volume discretization method was conducted to predict the system performance extensively. Four methods were presented to resort a metric that expresses the thermal performance criteria of the elliptic tube bundle. The results indicated that, increasing the angle of attack clockwise until 90° enhances the convective heat transfer coefficient considerably. The maximum thermal performance under constraint of a fixed pumping power or a mass flow rate was obtained at a zero angle of attack and the minimum thermal performance occurred at an angle of attack equals 90°. The best thermal performance of the elliptic tube heat exchanger was qualified with the lower values of Reynolds number, axis ratio and angle of attack.
119 citations
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TL;DR: In this paper, three types of finned-tube configurations have been investigated under dry and wet conditions for different values of inlet frontal velocity ranging from 2 to 7 m/s: two elliptic finned tubes with staggered and in-line arrangements and one circular finned tube with staggered arrangement.
Abstract: Fluid flow and heat transfer over a 4-row. elliptic, finned-tube heat exchanger having an axis ratio of 2.83:1 are studied experimentally and numerically. Three types of finned-tube configurations have been investigated under dry and wet conditions for different values of inlet frontal velocity ranging from 2 to 7 m/s: two elliptic finned tubes with staggered and in-line arrangements and one circular finned tube with staggered arrangement. The experimental results indicate that the average heat transfer coefficient of an elliptic finned lube is 35–50% of the corresponding circular finned tube having the same tube perimeter, while the pressure drop for an elliptic finned-tube bank is only 25–30% of the circular finned-tube bank configuration. Three-dimensional numerical results of a laminar model for dry coils are also presented and are compared with the experimental data.
94 citations
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TL;DR: In this article, an experimental investigation has been made to clarify the heat transfer characteristics of an elliptic cylinder of axis ratio 1 : 2, where the testing fluid was air and the Reynolds number ranged from about 5000 to 90000.
Abstract: An experimental investigation has been made to clarify the heat transfer characteristics of an elliptic cylinder of axis ratio 1 : 2. The testing fluid was air and the Reynolds number ranged from about 5000 to 90000. The angle of attack α was varied from 0°to 90°. The local heat transfer behavior is clarified and it is quite different from that of a circular cylinder. In the region of α>40°, the heat transfer rate from the upstream surface, on which a laminar boundary layer develops, becomes lower than that from the downstream surface in the separated flow region. The mean heat transfer coefficient Num depends upon the angle of attack along with the Reynolds number. It is found that Num is the highest for α=75° to 90° and is the lowest for α=30° over the whole Reynolds number range studied. The mean heat transfer rate from the elliptic cylinder investigated in the present work is higher than that from the circular cylinder at all the angles of attack over the Reynolds number range studied.
58 citations
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