Vertical Fin Research Articles

Effects of Microstructure on the Conjugated Mixed Forced and Free Convection-Conduction Analysis of Heat Transfer in a Vertical Plate Fin

A conjugated convection-conduction analysis has been made for a vertical plate fin which exchanges heat with its micropolar fluid environment by mixed forced and free convection. The analysis is based on a one-dimensional model for the plate fin whereby the heat conduction equation for the fin is solved simultaneously with the conservation equations for mass, momentum, angular momentum, and energy in the micropolar fluid boundary layer adjacent to the fin. The local heat transfer coefficient is not specified in advance but is one of the results of the numerical solutions. Numerical results of the overall heat transfer rate, the local heat transfer coefficient, the local heat flux, and the fin temperature distribution for Pr = 5 are presented for various values of Δ (dimensionless material parameter), Nc (conjugated convection-conduction parameter), and Ω (buoyancy parameter).

The effect of prandtl number on conjugate heat transfer in porous media

The problem of conjugate mixed convection heat transfer from a vertical plate fin embedded in a porous medium is studied numerically for various fluids. Approximate solutions for the problem are based on the local nonsimilarity method. Results are provided for the controlling parameters in the following ranges: 0.05 ≤ Pr ≤ 5.5 , 0.0 ≤ Ncc ≤ 2.0 , and 0.0 ≤ Ω ≤ 2.0. The effects of Prandtl number on fin temperature distribution, local heat transfer coefficient, local heat flux, and fin efficiency are examined. The results indicate strong effects of both Prandtl number and conduction-convection parameter.

CONJUGATE MIXED CONVECTION HEAT TRANSFER ANALYSIS OF A PLATE FIN EMBEDDED IN A POROUS MEDIUM

The problem of mixed convection flow about a vertical plate fin embedded in a porous medium, taking into consideration the interaction between conduction in the fin and convection in the surrounding fluid, has been analyzed. It was found that the governing parameters for the problem are the Prandtl number Pr, the mixed convection parameter ω, and the convection-conduction parameter Ncc. The results of the analysis were found to be similar to those of the classical fluids. In particular, at a high value of the convection-conduction parameter Ncc, the local heat transfer coefficient is found to decrease first, attain a minimum value, and then increase in the stream-wise direction. This behavior can be attributed to the enhanced buoyancy force resulting from an increase in the wall-to-fluid temperature difference along the stream-wise direction. The total heat transfer rate was found to decrease with increasing Ncc.

Orientation effects on natural convection/radiation heat transfer from pin-fin arrays

The heat transfer characteristics of highly populated pin-fin arrays have been investigated for three different orientations in the gravity field: (1) horizontal fins and vertical baseplate, (2) vertical fins and horizontal downfacing baseplate, and (3) vertical fins and horizontal upfacing baseplate. Experiments were performed in air to measure the combined natural convection and radiation heat transfer, and the radiation was determined analytically. Parametric variations were also made of the number of fins and of the baseplate-to-ambient temperature difference. In general, among the three orientations, the vertical upfacing fin array yielded the highest heat transfer rates, followed by the horizontal fin array and the vertical downfacing fin array. With an increase in the number of fins for fixed values of the other parameters, the heat transfer rate increased at first, attained a maximum, and then decreased, thereby defining an optimal fin population. The fractional contributions of radiation to the combined-mode heat transfer were generally in the 25–40% range, with the larger contributions occurring at the smaller baseplate-to-ambient temperature differences. Comparison of the pin-fin results with those for plate fins tends to encourage the use of pin fins.

Heat transfer performances of vertical rectangular fins protruding from rectangular bases: Effect of fin length

The effects of increasing the fin length from 250 to 375 mm on (i) the steady-state rate of heat loss and (ii) the optimal uniform fin separation of vertical rectangular fins protruding from a horizontal or a vertical rectangular base, have been investigated experimentally. A constant base temperature, 40 (±0·3)°C above that of the ambient environment, was used.

The Influence of Lateral Mass Flux on Conjugate Natural Convection from a Vertical Plate Fin in a Saturated Porous Medium

The effects of lateral surface mass transfer on the natural convection boundary layer about a vertical plate fin with solution-determined thermal boundary conditions (or fin temperature distributions) in a fluid-saturated porous medium were studied numerically. It was found that the governing parameters for the problem are the convection-conduction parameter N/sub cc/ and the lateral mass flux parameter f/sub w/. The nonsimilar solutions were obtained by the local nonsimilarity method and were carried out up to the third level of truncation. The effects of mass flux on fin temperature distribution, boundary-layer thickness, local heat transfer coefficient, local heat flux, and total heat transfer rate are presented and discussed.

Conjugate free convection from long vertical plate fins embedded in a porous medium at high Rayleigh numbers

Analyses are made for steady conjugate free convection about a vertical fin embedded in a porous medium at high Rayleigh numbers. Two types of heat sources at the fin base are considered: a plate heat source and a circular heat source. With the thin-fin approximation for the fin and the boundary-layer approximation for the convective fluid, similarity solutions are obtained for the free convection boundary-layer flow adjacent to a long vertical plate fin with its conductivity-thickness product varying as a power function of distance from the specified origin. Analytical expressions are obtained for the local surface heat flux, local Nusselt number and thermal boundary-layer thickness along the fin. A numerical example, with plots of streamlines and isotherms, is presented for a constant cross-section vertical plate fin heated by a plate heat source and embedded in a porous medium.

Heat exchanger design: Thermal performances of rectangular fins protruding from vertical or horizontal rectangular bases

An experimental investigation of the steady-state rates of heat transfer from an array of vertical rectangular fins of 3 mm thickness and 250 mm length, protruding 60 mm perpendicularly upwards from a 250 mm × 190 mm horizontal rectangular base, is reported. For constant (to ±0·1°C) base temperatures between 40°C and 80°C, in an ambient environment of 20±0·2°C, the optimal separation of the parallel fins, corresponding to the maximum rate of heat loss, is 10·5±1·0 mm. The effects of the extent of the fin protrusions on the thermal performances of such vertical fins, on the same base, which was arranged to be either vertical or horizontal, have been studied. The experiments were performed with three different fin protrusions, namely 32 mm, 60 mm and 90 mm, for a base temperature of 40°C above that of the ambient environment. The steady-state rate of heat dissipation from the fin array increased slightly less than linearly with the fin protrusion for both orientations, but the relationship became closer to linear as the fin spacing was increased. A comparison of the abilities to dissipate heat to the room air from the same geometrical configuration having a rectangular fin array but positioned with vertical fins on a vertical base, vertical fins protruding upwards from a horizontal base, or horizontal fins on a vertical base, has been made. The orientation with vertical fins protruding upwards from the horizontal base, is the preferred option because of the relatively high rates of heat transfer that can then be achieved.

Heat exchanger design: Optimal uniform separation between rectangular fins protruding from a vertical rectangular base

Steady-state rates of heat loss, from an array of 3 mm thick, 250 mm long, horizontal rectangular duralumin fins extending 60 mm perpendicularly out of a 250 mm × 190 mm vertical rectangular duralumin base, have been measured. With the base, at a uniform temperature of between 40°C and 80°C, in a 20°C ambient environment, two separations of the parallel fins, corresponding to maxima in the rate of heat loss versus fin separation curves ensued, respectively at 12 ± 1 mm and 38 ± 1 mm. The use of the latter maxima (i.e. the optimal separation) leads to the higher rate of heat loss. The heat transfer performances of vertical and horizontal rectangular fin arrays on a vertical rectangular base are compared: using the same geometrical configuration and identical base temperatures in both cases, the vertical fin orientation has the more rapid, steady-state heat loss.

Heat exchanger: Optimal separation for vertical rectangular fins protruding from a vertical rectangular base

An experimental investigation of the steady-state rates of heat transfer from an array of vertical rectangular 3 mm thick fins, extending 60 mm perpendicularly out of a 250 mm high vertical rectangular base, is reported. For base temperatures between room temperature (∼ 15°C) and 100°C, the optimal separation of the parallel fins, corresponding to the maximum rate of heat loss, is 10 ± 1 mm.

Heat Transfer Enhancement in a Paraffin Wax Thermal Storage System

Heat transfer enhancement in a thermal storage system consisting of vertically arranged fins between a heated and cooled horizontal finned-tube arrangement is reported. The high thermal expansion coefficient and low viscosity of paraffin wax, at temperatures above 50°C, are utilized to induce natural convection in the liquid phase even at small thicknesses. The experimental data on the rate of production of liquid as a function of time and temperature of the hot surface is presented. The photographs of the melted zone indicate a naturally buoyant flow induced in the neighborhood of the vertical fins causes a rapid melting of the solid wax and a downdraft along the cooler solid phase surface. The heat transfer coefficient at the interface is calculated from experimentally determined instantaneous locations of the moving boundary.

Flight Service Evaluation of Composite Components on Bell 206L and Sikorsky S‐76 Helicopters

Progress on two programs to evaluate composite structural components in flight service on commercial helicopters is described. Thirty-six ship sets of composite components that include the litter door, baggage door, forward fairing, and vertical fin were installed on Bell Model 206L helicopters that are operating in widely different climatic areas. Four horizontal stabilizers and ten tail rotor spars that are production components on the S-76 helicopter were tested after prescribed periods of service to determine the effects of the operating environment on their performance. Concurrent with the flight evaluation, specimens from materials used to fabricate the components were exposed in ground racks and tested at specified intervals to determine the effects of outdoor environments. Results achieved from 14,000 hours of accumulated service on the 206L components, tests on a S-76 horizontal stabilizer after 1600 hours of service, tests on a S-76 tail rotor spar after 2300 hours service, and two years of ground based exposure of material coupons are reported.

Heat transfer analysis for conjugate free convection‐conduction in a vertical plate fin

Heat transfer analysis for conjugate free convection‐conduction in a vertical plate fin

Enhancing heat transfer rates from closed-sided, open-topped heat exchangers, each having vertical rectangular fins extending upwards from a horizontal base

The almost two-dimensional steady-state rates of heat loss from arrays of uniformly-spaced vertical rectangular fins, extending upwards—in otherwise stagnant air—from horizontal heated bases, have been measured. (The vertical air gaps between the fins were closed at their sides, by insulated vertical end-barriers.) The effects of various combinations of height, thickness and spacing of the fins, for different base temperatures (in the range 40 to 100°C), have been studied. For the configuration considered, in a normal ambient environment (∼ 20°C), there is an optimal fin spacing (⋍ 16 mm) corresponding to the greatest steady-state rate of free convective/conductive heat loss through the air from the finned system, and this is almost independent of the temperature of the heat exchanger base (in the range 40–100°C). At this optimal spacing for base temperatures not greater than 50°C, the convective/conductive heat transfer rate from the array increases with the fin height up to about 60 mm, so that it would be uneconomic to employ taller fins if convection/conduction is dominant compared with radiation. If the radiation contribution is also considered, then the optimal spacing corresponding to the maximum total steady-state rate of heat loss through the air is somewhat less than the optimal spacing for which, under the same temperature conditions, the maximum steady-state rate of convective/conductive heat leak occurs. The greater the emissivity of the heat exchanger surfaces, the narrower the optimal uniform gaps between the fins. A two-dimensional finite-difference computer program has been composed to predict the temperature distribution throughout the heat exchanger for a stipulated ambient environmental temperature and experimentally-determined distribution of the heat transfer coefficient over the surfaces of the exchanger. This enables, for instance, any hot spots to be located prior to a proposed design being built.

A study of the ship induced roll-yaw motion of a heavy towed fish

The lateral motions of roll, yaw and sway of a heavy towed fish are investigated. Perturbation lateral ship motion propagates down the cable as a damped wave and non-dimensional tables are provided that allow the attenuation of the motion to be estimated. The tables are supplemented by a short BASIC computer program for calculations outside the tabular range. Three-dimensional dynamic simulation of the Bath Mk 3 Sonar Fish is used to establish the effects of fish weight, towstaff length and vertical fin size on the amplitude of rolling and yawing motion. It is shown that very careful adjustment of fin size can reduce the amplitude of yawing motion by a factor of about 3. It is also shown that attaching the cable to the fish with a towstaff free to pivot only in pitch improves the towing properties of the fish and reduces the amplitude of rolling motion.

Similarity solution for conjugate natural convection heat transfer from a long vertical plate fin

Presentation d'une solution de similitude pour le transfert de chaleur conjugue par convection naturelle d'une ailette verticale de longueur infinie. Resultats complets pour une ailette plane a conductivite uniforme en fonction du nombre de Prandtl du fluide

Conjugate mixed convection heat transfer from a vertical rectangular fin

A numerical investigation of the heat transfer from a rectangular fin by combined forced and natural convection is presented. Results are given for buoyancy parameters in the range of 0 ⩽ Gr/Re 2 ⩽ 2 and convection - conduction parameters in the range of 0 ⩽ √ Re k fL/k sb ⩽ 10 . The results are compared with the conventional fin theory and it is found that concerning the fin efficiency, the latter produces acceptable results although it is not strictly correct.

A class of backward free-convective boundary-layer similarity solutions

This paper presents a class of backward free-convective boundary-layer similarity solutions. It is shown that these boundary layers can be produced along slender downward-projecting slabs of prescribed thickness variation, which are infinitely long. It is pointed out that these solutions can be used to describe free convective flows along vertical fins which have received attention in the literature before. An important result is that the temperature along a downward-projecting fin of constant thickness varies in proportion to the inverse of the seventh power of the shifted longitudinal coordinate.

CONJUGATE NATURAL CONVECTION HEAT TRANSFER FROM A HORIZONTAL CYLINDER WITH A LONG VERTICAL LONGITUDINAL FIN

Abstract Conjugate heat transfer by steady laminar natural convection from an isothermal circular cylinder with one infinitely long vertical plate fin has been studied by a finite-difference numerical procedure. Interactions between the fin and cylinder boundary layers are determined through the elliptic nature of the solution technique. Heat transfer from both the fin and the cylinder is less than predicted, disregarding the complex interactions. A fin of low conductance reduces the total heat transfer below the free-cylinder value. Fins of large conductance enhance the total heat transfer by a few percent. Heat transfer correlations have been developed to predict local and total heat transfer rates for both the fin and the cylinder as a function of the three governing dimensionless parameters: Rayleigh number, Prandtl number, and fin conduction parameter.

Effect of vibration on natural convection heat transfer from vertical fin arrays

The effect of vibration on natural convection heat transfer from vertical rectangular fin arrays of different fin spacings and fin lengths was investigated experimentally. It was seen that up to a certain threshold value of the product of amplitude and frequency (15 mm/s), the imparting of vibration did not have any significant effect on heat transfer from the fin array: Beyond this value, however, the heat transfer rate increased considerably with the increase in the intensity of vibration, the maximum increase obtained being 250% when the vibrational energy input was 90 W.