Internal Longitudinal Fins Research Articles

Modeling and parametric analysis of an adsorber unit for thermal energy storage

The dynamic model of an adsorber unit used as thermal energy storage device immersed in water is presented. The system operates with the silica-gel/water pair and is capable of storing the thermal energy received from the surrounding water (e.g., excess heat input from a hot water storage tank), in order to give it back later to the water as adsorption heat. The model was developed following a lumped parameter approach implemented in MATLAB® code. The performance of the absorber unit was assessed by a set of parametric tests under different geometric configurations and temperature conditions. The mass of adsorbent was found to have a higher impact on the thermal energy exchange than the surface contact area between metal and adsorbent. An improved finned adsorber, with 27 internal longitudinal fins and 120 external annular fins, resulted in a heat output to the water 2.3 times higher than with a similar finless adsorber. Moreover, the evaporation temperature effect was found to be much higher than the condensation temperature effect. This device seems to be an attractive solution to include, for instance, in solar hot water systems in order to fulfill the thermal energy needs during periods of low solar radiation.

Study on turbulent flow and heat transfer performance of tubes with internal fins in EGR cooler

In this paper, flow and heat transfer performances of the tubes with internal longitudinal fins in Exhaust Gas Recirculation (EGR ) cooler were investigated by three-dimension computation and experiment . Each test tube was a single-pipe structure, without inner tube. Three-dimension computation was performed to determine the thermal characteristics difference between the two kinds of tubes, that is, the tube with an inner solid staff as a blocked structure and the tube without the blocked structure. The effects of fin width and fin height on heat transfer and flow are examined. For proving the validity of numerical method, the calculated results were compared with corresponding experimental data. The tube-side friction factor and heat transfer coefficient were examined. As a result, the maximum deviations between the numerical results and the experimental data are approximately 5.4 % for friction factor and 8.6 % for heat transfer coefficient, respectively. It is found that two types of internally finned tubes enhance significantly heat transfer. The heat transfer of the tube with blocked structure is better, while the pressure drop of the tube without blocked structure is lower. The comprehensive performance of the unblocked tube is better to applied in EGR cooler.

Complex turbulent flow and heat transfer characteristics of tubes with internal longitudinal plate-rectangle fins in EGR cooler

Complex flow and heat transfer characteristics of the tubes with internal longitudinal plat-rectangle fins in EGR (Exhaust Gas Recirculation) cooler are investigated by experiment. Each internally finned tube is single-tube structure. The effects of internal fin width, inscribed circle diameter, wave number and upwind distance on heat transfer performance are examined. The range of internal fin width is from 2.5 mm to 3.5 mm, inscribed circle diameter selects 5 mm, 7 mm and 9 mm, and wave number gets 3, 4, 5. The heat transfer coefficient, friction factor and Nusselt number in the fully developed region are obtained. The experimental results show that the friction factor increased with the increase of wave number, while it decreases with the increase of internal fin width and inscribed circle diameter. When 4.4 mm ≤ Dh ≤ 4.9 mm, dins = 7 mm (dins/Di = 50%) and N = 4, the heat transfer enhancement effects of internally finned tubes should be the best. Moreover, general correlations are proposed to describe the characteristics of the fin configuration for 1689 ≤ Re ≤ 5076, 4.05 mm ≤ Dh ≤ 14 mm. In addition, when manufacturing the internally finned tube, it is better to select large upwind distance.

Experimental and numerical determination of heat transfer coefficient between oil and outer surface of monometallic tubes finned on both sides with twisted internal longitudinal fins

Results of thermal investigations of monometallic tubes finned on both sides used in heat exchangers are presented in this article. Investigated tubes differ in twist and inclination angles of internal fins. In experiments a transform oil was cooled and air was a coolant. Heat transfer coefficient values for the inner side of the tube based on correlation equations from literature were compared with the experimental and numerical ones. The aim of this research is to specify the meaning of correlation equations for determination of heat transfer coefficients of tubes finned on both sides with twisted longitudinal internal fins. The change in heat flux in a tube when the twist angle of the internal fins varies is shown. Results of computations are presented in the form of useful drawings, which can be readily applied in practice.

Heat Transfer Augmentation and Entropy Generation Analysis of a Helically Coiled Tube with Internal Longitudinal Fins

AbstractHeat transfer augmentation and entropy generation were investigated for a helically coiled tube with internal longitudinal fins. The Nusselt number, friction factor, thermal‐hydraulic performance ratio, and augmentation entropy generation number were calculated and analyzed. The results indicated that the internal longitudinal fins enhance the secondary flows and increase the temperature gradient near the tube wall, which in turn increase the heat transfer. It was found that the helically coiled tube with internal longitudinal fins provides the best integrated performance over the range of computed Dean numbers. The Nusselt number rised by 20–35 % with a corresponding 27–56 % increase of the friction factor. The computed results indicated that augmentation entropy generation numbers are approximately changed between 0.012 to 0.132 levels, i.e., the novel helically coiled tube with internal longitudinal fins is more efficient than that without internal fins.

Numerical Simulation of Laminar Heat Transfer in Aluminium Circular Tube With Internal Longitudinal Fins

This paper presents a numerical simulation of laminar heat transfer in circular tube flows with internal longitudinal fins using finite difference numerical code. Three types of fin models with three different half included angle are considered. Two types of fluids (coolants), namely, water and engine oil, have been considered. Aluminium is considered as tube/fin materials. The variation of thermal conductivity of the tube materials, fluids and viscosity of the fluids with the temperature are taken into account in the solution procedure. The outer surface of the tube is exposed to constant heat flux. Steady, laminar flow and heat transfer is assumed. Reynolds numbers equal to 1,500 are used in this study. The flow is assumed to be fully developed locally, but thermally undeveloped. The governing equations are discretized using finite difference scheme. The momentum equation for the fluid and the energy equations for the fluid and the tube wall are solved simultaneously and iteratively.

A Numerical Investigation of Flow and Mixed Convection Inside a Vertical Eccentric Annulus

In this article, mixed convection heat transfer is numerically studied in a vertical eccentric annulus. For this purpose, full Navier-Stokes equations along with energy equations are solved in a 3-D orthogonal grid using a bipolar cylindrical coordinate system and finite-volume method based on the SIMPLE algorithm. To investigate the flow and heat transfer in the presence of gravity, the inner wall of the annulus is kept at a constant temperature while the outer wall is assumed to be insulated. The effect of different governing nondimensional parameters consisting of dimensionless eccentricity (E), radius ratio (N), and mixed convection parameter (Gr/Re) on the flow and temperature field are studied in detail. The numerical results obtained are in good agreement with the previous numerical works. Furthermore, the flow and heat transfer field in the presence of internal longitudinal fins on the inner wall of the annulus are studied compared with the finless case. The amount of augmented heat transfer due to internal fins is also discussed.

Numerical study of laminar fluid flow in a curved elliptic duct with internal fins

The fully developed laminar incompressible flow inside a curved duct of elliptical cross-section with four thin, internal longitudinal fins is studied using the improved CVP method. We present numerical results for the friction factor and an investigation of the effect of the fin height and the Dean number on the flow. It is found that the friction factor increases for large fins and for high Dean numbers and that in some cases, it has a strong dependence on the cross-sectional aspect ratio. The thermal results show that the heat transfer rate is enhanced by the internal fins and that it depends on the aspect ratio.

Convective heat transfer and pressure drop of annular tubes with three different internal longitudinal fins

AbstractPressure drop and heat transfer characteristics of air in three annular tubes with different internal longitudinal fins were investigated experimentally at uniform wall heat flux. The tested tubes have a double‐pipe structure with the inner blocked tube as an insertion. Three different kinds of fins, plain rectangle fin, plain rectangle fin with periodical ridges and wave‐like fin, were located peripherally in the annulus. The friction factor and Nusselt number can be corrected by a power‐law correction in the Reynolds number range tested. It was found that the tube with periodical ridges on the plain fin or with wave‐like fin could augment heat transfer; however, the pressure drop was increased simultaneously. In order to evaluate the comprehensive heat transfer characteristics of the tested tubes, two criteria for evaluating the comprehensive thermal performance of tested tubes were adopted. They are: 1) evaluating the comprehensive heat transfer performance under three conditions: identical mass flow, identical pumping power, and identical pressure drop; 2) the second law of thermodynamics, i.e., the entropy generation. According to the two different evaluating methods, it was found that the tube with wave‐like fins provided the most excellent comprehensive heat transfer performance among the three tubes, especially when it was used under higher Reynolds number conditions. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(1): 29–40, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20186

Convective heat transfer and pressure drop of a tube with internal longitudinal fins

AbstractThe fluid flows and heat transfer characteristics of a tube with internal longitudinal fins were investigated experimentally and numerically. The realizable turbulence model was adopted to simulate the problem, whose results indicate a good agreement with the measured data. Compared with the circular annulus tube, it was shown that the internal longitudinal finned tube provides excellent heat transfer performance greater than those of the circular annulus tube, with a great increase of simultaneous pressure drops. Furthermore, there exists a critical Reynolds number, about 1500, when the Reynolds number is less than the critical value, and the Nusselt number of an internal longitudinal finned tube will be smaller than that of a circular annulus tube in laminar flow. On the other hand, the transition Reynolds number for a tube with internal longitudinal fins from laminar to turbulent is greatly decreased due to the existence of internal longitudinal fins. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(2): 57–65, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20147

Numerical Investigation of the Thermally Developing Flow in a Curved Elliptic Duct With Internal Fins

The hydrodynamically fully developed and thermally developing flow inside a curved elliptic duct with internal longitudinal fins is studied numerically. The duct is subjected to the uniform temperature boundary condition on its wall and fins. The local and mean Nusselt numbers are examined for various values of the Dean and Prandtl numbers, the cross-sectional aspect ratio, and the fin height. The characteristics of the optimum duct, which achieves enhanced heat transfer rates combined with low friction losses, are determined in terms of the aspect ratio and the fin height.

An analysis of entropy generation through a circular duct with different shaped longitudinal fins for laminar flow

The present study focuses on the entropy generation analysis in a circular duct with internal longitudinal fins of different shape for laminar flow. Three different fin shapes are chosen for the analysis: Thin, triangular and V-shaped fins. Calculations are performed for various dimensionless lengths and number of fins, dimensionless temperature difference and fin angle for triangular and V-shaped fins. It is found that the number of fins and dimensionless length of the fins for both thin fins and triangular fins, and the fin angle for triangular and V-shaped fins have significant effect on both entropy generation and pumping power. Further, both entropy generation and pumping power also are influenced by dimensionless temperature difference.

Numerical Analysis of Fully Developed Flow in Curved Square Ducts With Internal Fins

The laminar incompressible flow in a curved square duct with two or four internal longitudinal fins is studied numerically with the SIMPLE method. The results show an increase of the friction factor depending on the fin height and the Dean number. The visualization of the flow reveals the existence of complex flow patterns in the transverse plane of the channel, where up to ten vortices are found to form. The effect of the curvature on the friction factor is examined and a functional relation for the latter is developed in terms of the Dean number and the fin height.

Heat transfer for laminar flow in internally finned pipes with different fin heights and uniform wall temperature

An analysis is presented for fully developed laminar convective heat transfer in a pipe provided with internal longitudinal fins, and with uniform outside wall temperature. The fins are arranged in two groups of different heights. The governing equations have been solved numerically to obtain the velocity and temperature distributions. The results obtained for different pipe-fins geometries show that the fin heights affect greatly flow and heat transfer characteristics. Reducing the height of one fin group decreases the friction coefficient significantly. At the same time Nusselt number decreases inappreciably so that such reduction is justified. Thus, the use of different fin heights in internally finned pipes enables the enhancement of heat transfer at reasonably low friction coefficient.

A study of heat transfer effectiveness of circular tubes with internal longitudinal fins having tapered lateral profiles

This paper presents a finite-difference based numerical simulation of steady, laminar heat transfer in circular tubes fitted with four identical longitudinal fins having tapered lateral profiles. The lateral view of the tip of each fin is a circular arc. The tube is exposed to constant heat flux. The temperature dependence of thermal conductivity and viscosity has been taken into account. The flow is assumed to be locally fully developed but thermally undeveloped. The momentum equation for the fluid and energy equations for the fluid and the tube wall with/without fins are solved iteratively and simultaneously. At each axial location, bulk velocity, bulk temperature of the fluid and Effectiveness which is an indicator of the enhancement of heat transfer due to addition of fins are calculated. A parametric study of effectiveness vs. axial distance for various combinations of fin materials and coolants reveals interesting results. The velocity profiles, friction factors and comparisons with respect to constant property solutions have also been discussed.

Heat transfer for non-Newtonian laminar flow in internally finned pipes with uniform temperature

An analysis is presented for fully developed laminar convective heat transfer of non-Newtonian power-law fluids in pipes with internal longitudinal fins and uniform outside wall temperature. The governing momentum and energy equations have been solved numerically, with the influence of fin conductance. The distributions of fin temperature, fluid temperature and local heat flux (both at finned and unfinned surfaces) are presented. These are shown to be strongly dependent on finned pipe geometry, fluid flow behavior index and the fin conductance. Values of overall Nusselt number indicated significant heat transfer enhancement over finless pipes. The flow behavior index affects the no. of fins which maximizes the overall Nusselt number.

Conjugate heat transfer in solar collector panels with internal longitudinal corrugated fins—Part I: Overall results

Conjugate heat transfer in solar collector panels with internal longitudinal corrugated fins—Part I: Overall results

ANALYSIS OF COMBINED NATURAL AND FORCED CONVECTION IN VERTICAL SEMICIRCULAR DUCTS WITH RADIAL INTERNAL FINS

A numerical analysis of combined natural and forced convection is conducted for the fully developed laminar flow and heat transfer in a vertical semicircular duct with radial, internal longitudinal fins. Accurate solutions for heating upward flow are obtained by the finite difference method based on a fine grid, while the hydraulic and thermal conditions of the fins are ascertained. The results represent a range of Rayleigh numbers and various values of fin lengths and number of fins. The fully developed f Re and Nu values for pure forced convection in the finned semicircular duct are also documented. It is found that both the friction factor and the Nusselt number in the finned tube increase as the Rayleigh number increases. The effect of buoyancy is significant in semicircular ducts with short fins. By comparing the results of finless ducts with those of finned ducts, it was concluded that heat transfer in combined natural and forced convection in the semicircular duct is dramatically enhanced by using ...

Numerical Analysis on Fully Developed Laminar Forced Convective Heat Transfer in Circular Tube with Internal Longitudinal Fins.

Fully developed laminar forced convective heat transfer in a circular tube with internal longitudinal fins is analyzed by using the finite difference method under two kinds of thermal boundary conditions at the outer tube wall (i. e., constant wall temperatures and uniform heat fluxes). Extended Nusselt numbers based on the outer wall temperature are compared for a wide range of geometrical parameters and the following results are obtained : (1) For small values of the ratio of tube-material-to-fluid thermal conductivities heat transfer augmentation by fins is not effective. (2) When the thermal conductivity ratio lies in the order of 100, the effect of the wall thickness on the heat transfer coefficient can be neglected. Furthermore in the case that the ratio is greater than 500, the thermal resistance of the fin can be ignored in respect to the heat transfer.

Tubular heat exchangers with internal longitudinal fins for metal hydride reaction beds.

The purpose of this study is to clarify the effects of internal longitudinal fins for annular metal hydride reaction beds. Twenty-one kinds of cylindrical tubes with stainless steel internal fins were filled with metal hydride powders (LaNi5). Experimental investigation and numerical analysis were carried out for annular reaction beds (length : 150mm, inner diameter : 40mm) and the relationships between the internal fin geometries and the reaction rates were clarified. In addition to fin geometries, the thermal conductivity and the thermal capacity of the fins were determined to be important factors determining the heat exchanger performance.