共查询到20条相似文献,搜索用时 31 毫秒
1.
Cihat Arslanturk 《Heat and Mass Transfer》2011,47(2):131-138
Although tapered fins transfer more rate of heat per unit volume, they are not found in every practical application because
of the difficulty in manufacturing and fabrications. Therefore, there is a scope to modify the geometry of a constant thickness
fin in view of the less difficulty in manufacturing and fabrication as well as betterment of heat transfer rate per unit volume
of the fin material. For the better utilization of fin material, it is proposed a modified geometry of new fin with a step
change in thickness (SF) in the literature. In the present paper, the homotopy perturbation method has been used to evaluate
the temperature distribution within the straight radiating fins with a step change in thickness and variable thermal conductivity.
The temperature profile has an abrupt change in the temperature gradient where the step change in thickness occurs and thermal
conductivity parameter describing the variation of thermal conductivity has an important role on the temperature profile and
the heat transfer rate. The optimum geometry which maximizes the heat transfer rate for a given fin volume has been found.
The derived condition of optimality gives an open choice to the designer. 相似文献
2.
A combination of uniform-thickness annular fins evenly spaced on a tube is a common extended-surface heat exchanger configuration. An analytical model is developed and is verified by comparing total heat transfer predicted by the model to available experimental data. A direct-pattern search technique is applied to the model to optimize the fin/ tube geometry. Optimum dimensions and spacing of fins are established to provide the maximum free convection heat transfer from a fin/tube combination. The optimum arrangement is dependent on fin thermal conductivity, tube diameter, volume of fin material per unit length of tube, and temperature difference between the tube and the surrounding air. Calculated results indicate that a fin in the optimum fin/tube system is shorter and thicker than an isolated fin optimized for minimum material (with no consideration of the effects of fin spacing). 相似文献
3.
杨翔翔 《应用数学和力学(英文版)》1988,9(3):267-278
Circular fins are used extensively in heat exchange devices to increase the heat transfer. For economic purposes, the traditional
approach to the optimization of fins consists of minimizing the comsumption (investment) of fin material for the excution
of a specified heat transfer task. The minimum weight cooling fin has optional profile to be a concave parabola. Therefore,
the optimum geometric dimensions of circular fins of parabolic profile with variable thermal parameters are studied. The effect
of the two pertinent physical parameters-thermal conductivity variation parameter α and the index of the heat transfer coefficient
variationm upon the optimum geometric dimensions is also studied. The results pressented can be used as the design guideline for engineering
practice. 相似文献
4.
The steady-state natural convection heat transfer from aluminum vertical rectangular fins extending perpendicularly from vertical rectangular base was investigated experimentally. Thirty different fin configurations were tested. Experiments were performed for fin lengths of 250 and 340 mm. Fin thickness was kept fixed at 3 mm. Fin height and fin spacing were varied from 5 to 25 mm and 5.75 to 85.5 mm, respectively. Five heat inputs ranging from 25 to 125 W were supplied for all fin configurations, hence; the base-to-ambient temperature differences were measured in order to evaluate the heat transfer rates from fin arrays. The results of experiments have shown that the convective heat transfer rate from fin arrays depends on geometric parameters and base-to-ambient temperature difference. The separate roles of fin height, fin spacing and base-to-ambient temperature difference were investigated. It was found that, for a given base-to-ambient temperature difference, the convective heat transfer rate from fin arrays takes on a maximum value as a function of fin spacing and fin height and an optimum fin spacing value which maximizes the convective heat transfer rate from the fin array is available for every fin height. These measurements were to extend data obtained earlier from aluminum fin-arrays using the same experimental system and method (Yüncü and Güvenç in Heat Mass Transfer 37:409–416, 2001). Data collated from earlier and present work cover the range of fin spacing from 4.5 to 85.5 mm. The fin length range was from 100 to 340 mm, the fin height from 5 to 25 mm and the number of fins per array 3 to 34. The range of base-to-ambient temperature difference was quite extensive, from 30 to 150 K. These results indicate that the optimum fin spacing is between 6.1 and 11.9 mm, for the fin arrays employed in the earlier and present work. A scale analysis is performed in order to estimate the order-of-magnitude of optimum fin spacing at a given fin length and base-to-ambient temperature difference. From the scale analysis, correlations to evaluate the optimum fin spacing value and the corresponding maximum convective heat transfer rate at a given fin length and base-to-ambient temperature difference were obtained. 相似文献
5.
The present investigation focuses on the thermal performance of a fully wet stretching/shrinking longitudinal fin of exponential profile coated with a mechanism like a conveyer belt. The modeled equation is non-dimensionalized and solved by applying the Runge-Kutta-Fehlberg(RKF) method. The effects of parameters such as the wet parameter, the fin shape parameter, and the stretching/shrinking parameter on the heat transfer and thermal characteristics of the fin are graphically analyzed and discus... 相似文献
6.
This paper presents an analysis of the compound effect of finite temperature differences and fluid friction on the existence
of an optimum laminar flow regime in singly connected micro channels with complex free flow area cross sections. A widespread
conviction has been established that the two competing irreversibility sources in a channel flow with heat transfer lead to
the existence of an optimum flow regime. The results presented in this paper clearly shows the opposite. When an objective
function is represented by the entropy generation rate per unit heat capacity rate of the fluid stream, the thermodynamic
optimum flow regime represents a rather rare occurrence in the laminar region of irregularly shaped ducts. The presence of
an extremum is more probable for very small diameters, the ones of an order of magnitude of O(≤10−3 m). The analysis is performed for selected ranges of relevant geometric, flow, and thermal parameters of a set of straight
micro channels with irregular free flow area cross-sections. The following geometries of the free flow area cross section
were investigated: (i) sine duct, (ii) circular duct, (iii) elliptical duct, (iv) moon-shaped ducts, and (v) four-cuspped
duct. The range of Reynolds numbers has been established between O(102) and O(104). The existence of the objective function minimum is confirmed for ducts with an irregular cross section only for very small
hydraulic diameters. These minima are relatively weak, and as a general rule, the sets of optimum parameters are close to
the onset of turbulence or possibly even in the transitional or turbulent regions.
Received on 10 November 1998 相似文献
7.
Experimental studies on flow visualization and heat transfer measurements of finned surface in a narrow duct were carried
out to understand the flow behavior and its effect on heat transfer. In this experiment, short rectangular fins were attached
to a surface (endwall) with having inclination angle of 20° and exposed to air flow. Several flow visualization results reveal
that horse shoe vortex was formed just at the front of the fin whereas the main longitudinal vortex was formed by the side
top edge of the fin. Some important features of the vortex structure, size and flow reattachment positions were noticed from
the smoke flow visualization. Detailed heat transfer distributions were discussed from the thermal image. Nusselt number shows
that the finned surface achieved average heat transfer enhancement at a factor of four times than that of without fins. 相似文献
8.
《ournal of non Newtonian Fluid Mechanics》2001,96(1-2):341-370
We extend to the realm of complex fluids and finite durations the classical problem of extremum work delivered from (or consumed by) the nonequilibrium system composed of a complex fluid, a perfect thermal machine and the environment or an infinite reservoir. The fluid constitutes a valuable resource of a finite flow or amount “a finite resource”, and work production (consumption) takes place sequentially, in stages of “endoreversible” thermal machines. At each stage, heat and mass transfer takes place in boundary layers which play the role of resistances in the system model. For the fluid at flow, total specific work is extremized at constraints which take into account dynamics of heat and mass transport and rate of work generation. Finite rate limits are obtained for the work production and consumption, which provide stronger bounds that those predicted by classical thermodynamics. Optimal work functions, which incorporate an inevitable minimum of the entropy production are found as functions of end states, duration and (in discrete processes) number of stages. Formal analogies between the entropy production expressions for work-assisted and conventional mass transfer operations help formulate optimization models. 相似文献
9.
Experiments were performed to investigate the effect of duct height on heat transfer enhancement of a surface affixed with arrays (7 × 7) of short rectangular plate fins of a co-rotating type pattern in the duct. An infrared imaging system is used to measure detailed distributions of the heat transfer at the endwall along with the fin base. An infrared camera of TVS 8000 with 160 × 120 point In–Sb sensor was used to measure the temperature distributions in order to calculate the local heat transfer coefficients of the representative fin regions. Pressure drop and heat transfer experiments were performed for a co-rotating fin pattern varying the duct height from 20?50 mm. The friction factor calculated from the pressure drop shows that comparatively larger friction occurs for the smaller duct cases and the friction factor slowly decreases with increasing Reynolds number. The effect of duct height on the area-averaged heat transfer results show that heat transfer initially increases with duct height and then finally decreases with increasing the duct height. Detailed heat transfer analysis and iso-heat transfer coefficient contour gives a clear picture of heat transfer characteristics of the overall surface. The relative performance graph indicates that a 25 mm duct is the optimum duct height for the highest thermal performance. In addition, a significant thermal enhancement, 2.8?3.8 times the smooth surface, can be achieved at lower Reynolds number with a co-rotating fin pattern in the duct. 相似文献
10.
Suhil Kiwan 《Transport in Porous Media》2007,67(1):17-29
This work introduces a simple method of analysis to study the performance of porous fins in a natural convection environment.
The method is based on using energy balance and Darcy’s model to formulate the heat transfer equation. The thermal performance
of porous fins is then studied for three types of fins: long fin, finite-length fin with insulated tip and a finite-length
fin with tip exposed to a known convection coefficient. It is found from the analysis that the effect of different design
and operating parameters such as: Ra number, Da number, thermal conductivity ratio, Kr and length thickness ratio on the temperature
distribution along the fin is grouped into one newly defined parameter called S_H. The effect of the variation of S_H on the
porous fin thermal performance is established. The effect of varying the fin length and thermal conductivity ratio on the
heat transfer rate from the fin is investigated and compared with that for a solid fin at certain conditions. It is found
that the heat transfer rate from porous fin could exceed that of a solid fin. It is also found that increasing the fin length
and effective thermal conductivity enhances the heat transfer from the fin up certain limit, where a further increase in these
parameters adds no improvement to the fin performance.
On Leave from Jordan University of Science and Technology, Irbid-Jordan 相似文献
11.
In this study, a steady, fully developed laminar forced convection heat augmentation via porous fins in isothermal parallel-plate
duct is numerically investigated. High-thermal conductivity porous fins are attached to the inner walls of two parallel-plate
channels to enhance the heat transfer characteristics of the flow under consideration. The Darcy–Brinkman–Forchheimer model
is used to model the flow inside the porous fins. This study reports the effect of several operating parameters on the flow
hydrodynamics and thermal characteristics. This study demonstrates, mainly, the effects of porous fin thickness, Darcy number,
thermal conductivity ratio, Reynolds number, and microscopic inertial coefficient on the thermal performance of the present
flow. It is found that the highest Nusselt number is achieved at fully filled porous duct which requires the highest pumping
pressure. The results show that using porous fins requires less pumping pressure with comparable high heat augmentation weight
against fully filled porous duct. It is found that higher Nusselt numbers are achieved by increasing the microscopic inertial
coefficient (A), the Reynolds number (Re), and the thermal conductivity of the porous substrate k
2. The results show that heat transfer can be enhanced (1) with the use of high thermal conductivity fins, (2) by decreasing
the Darcy number, and (3) by increasing microscopic inertial coefficient. 相似文献
12.
For the first time, this study reports the results of numerical investigation of conjugate convection from a finned channel. The computational domain of investigation consists of a horizontal channel with vertical rectangular fins being mounted on outside of the channel. The equations governing two-dimensional, steady, incompressible, constant property laminar flow have been solved for the fluid flowing outside the channel. In doing this, Boussinesq assumption is assumed to be valid for the fluid flowing outside the channel along the fins. For the fluid flowing inside the channel, flow is assumed to be turbulent with forced convection as the mode of heat transfer. From a large volume of numerically generated data correlations have been proposed for (1) Nusselt number and (2) Entropy generated by the system. These correlations are finally used to obtain thermodynamic optimum where in we seek a solution with minimum total entropy generation rate for varying heat duties, by using the state-of-the art Genetic algorithms. 相似文献
13.
A numerical study of the effects of the number and distribution of fins on the storage characteristics of a cylindrical latent heat energy storage system (LHESS) was conducted. Due to the low thermal conductivity of phase change materials (PCMs) used in LHESS, fins were added to the system to increase the rate of heat transfer and charging. Finite elements were used to implement the developed numerical method needed to study and solve for the phase change heat transfer (melting of PCM) encountered in a LHESS during charging. The effective heat capacity method was applied in order to account for the large amount of latent energy stored during melting of the PCM and the moving interface between the solid and liquid phases. The effects of increasing the number and distribution of fins on the melting rate of the PCM were studied for configurations having between 0 and 27 fins for heat transfer fluid (HTF) velocities of 0.05 and 0.5?m/s. Results show that the overall heat transfer rate to the PCM increases with an increase in the number of fins irrespective of the HTF velocity. It was also observed that the total amount of energy stored after 12?h increases nearly linearly with the addition of fins up to 12 fins; further addition of fins increasing the total energy stored by ever smaller amounts. 相似文献
14.
Cihat Arslanturk 《Heat and Mass Transfer》2009,45(4):519-525
Correlation equations for optimum design of annular fins with temperature-dependent thermal conductivity are obtained in the
present work. The nonlinear fin equation which is associated with variable thermal conductivity condition is solved by Adomian
decomposition method that provides an analytical solution in the form of an infinite power series. The optimum radii ratio
of an annular fin which maximizes the heat transfer rate has been found as a function of Biot number and the fin volume for
a given thermal conductivity parameter describing the variation of the thermal conductivity. The fin volume is fixed to obtain
the dimensionless geometrical parameters of the fin with maximum heat transfer rate. The data from the present solutions is
correlated for a suitable range of Biot number and the fin volume. The simple correlation equations presented in this work
can assist for thermal design engineers for optimum design of annular fins with temperature-dependent thermal conductivity. 相似文献
15.
P.K. Papadopoulos P.M. Hatzikonstantinou 《International Journal of Heat and Fluid Flow》2008,29(2):540-544
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. 相似文献
16.
This paper presents the comparative studies on the effect of duct height on heat transfer and flow behavior between co-angular
and co-rotating type finned surface in duct. Experiments were performed to investigate the effect of duct height on heat transfer
enhancement of a surface affixed with arrays (7 × 7) of short rectangular plate fins of a co-angular and a co-rotating type
pattern in the duct. An infrared imaging system with the camera of TVS 8000 was used to measure the temperature distributions
to calculate the local heat transfer coefficients of the representative fin regions. Pressure drop and heat transfer experiments
were performed for both types of fin pattern varying the duct to fin height ratio (H
d/H
f) of 2.0–5.0. The friction factor calculated from the pressure drop shows that friction factor decreases with increasing the
duct to fin height ratio (H
d/H
f) regardless of fin pattern and this is expected because the larger friction occurs for smaller duct to fin height ratios.
Detailed heat transfer distribution gives a clear picture of heat transfer characteristics of the overall surface as well
as the influence of the duct height. In addition, different flow behavior and flow structure developed by both patterns were
visualized by the smoke flow visualization technique. 相似文献
17.
This paper reports an experimental study of free convection heat transfer from rectangular fin-arrays on a horizontal base.
An experimental set-up was constructed and calibrated, 15 sets of fin-arrays and a base plate without fins were tested in
atmosphere. Fin height was varied from 6 mm to 26 mm, fin spacing was varied from 6.2 mm to 83 mm. The base-to-ambient temperature
difference was also varied independently and systematically with the power supply to heater ranging from 8 W to 50 W. Fin
length and fin thicknesses were fixed at 100 mm and 3 mm, respectively. The experimental program was conducted so as to clearly
delineate the separate roles of fin height, fin spacing and base-to-ambient temperature difference. It was found that for
a given base-to-ambient temperature difference the convection heat transfer rate from fin-arrays takes on a maximum value
as a function of fin spacing and fin height. For a given base-to-ambient temperature difference the enhancement of the convection
heat transfer rate of fin-arrays relative to that for base plate without fins is strongly dependent on the fin spacing to
fin height ratio and number of fins. A correlation was also presented relating the convection heat transfer rate of fin-arrays
relative to that for base plate without fins with the relevant non-dimensional parameters.
Received on 7 August 1997 相似文献
18.
A numerical study of the effects of the thermal fluid velocity on the storage characteristics of a cylindrical latent heat
energy storage system (LHESS) was conducted. Due to the low thermal conductivity of phase change materials (PCMs) used in
LHESS, fins were added to the system to increase the rate of heat transfer and charging. Finite elements were used to implement
the developed numerical method needed to study and solve for the phase change heat transfer (melting of PCM) encountered in
a LHESS during charging. The effective heat capacity method was applied in order to account for the large amount of latent
energy stored during melting of the PCM and the moving interface between the solid and liquid phases. The effects of the heat
transfer fluid (HTF) velocity on the melting rate of the PCM were studied for configurations having between 0 and 18 fins.
Results show that the overall heat transfer rate to the PCM increases with an increase in the HTF velocity. However, the effect
of the HTF velocity was observed to be small in configurations having very few fins, owing to the large residual thermal resistance
offered by the PCM. However, the effect of the HTF velocity becomes more pronounced with addition of fins; since the thermal
resistance on the PCM side of the LHESS is significantly reduce by the large number of fins in the system. 相似文献
19.
Experimental study of convective heat transfer from a rotating finned tube in transverse air flow 总被引:1,自引:0,他引:1
The convective heat transfer from fins to air has been evaluated using rotating annular fins subjected to an air flow parallel
to the fins. The fin cooling is studied using infrared thermography. The thermal balance in a fin during its cooling process
allows us to obtain the heat transfer coefficient from the temperature time evolution of the fin. Moreover, Particle Image
Velocimetry allows us to obtain the flow field in the mid-plane between two fins. The influence of the fin spacing on the
convective heat transfer is studied for various velocities of the superposed air flow and various fin rotational speeds. These
tests were carried out for air flow Reynolds numbers (based on the shaft diameter and the velocity of the superposed air flow)
between 2550 and 18200 and rotational Reynolds numbers (based on the shaft diameter and the peripheral speed) between 800
and 2.9 × 104, for different fin spacings.
Received: 14 May 1999/Accepted: 8 October 1999 相似文献
20.
An analysis of the thermal performance for convective annular fins, having a general trapezoidal profile and internal heat generation, is presented. The solution of the optimal problem is also given when either the heat dissipation rate or the volume of the fin is specified. The results are expressed in suitable nondimensional variables that are specified by the problem, and presented graphically. The effect of the fin's profile and thermal conductivity upon the optimum dimensions is discussed. It is shown that the presence of heat generation reduces the ability of the fin to convect heat. Furthermore, certain limiting values of the heat generation that may be imposed on the fin for a feasible optimization are also derived. 相似文献