The effect of orientation of square perforations on the heat transfer enhancement from a fin subjected to natural convection

The heat transfer dissipation from a horizontal rectangular fin embedded with square perforations of two orientations under natural convection is numerically investigated. The parameters considered in this investigation are the geometrical dimensions and the orientations of the perforation. A comparison between heat dissipation of the fin with variable orientations of the perforations is presented. It is found that the heat dissipation enhancement from a fin with square perforation parallel to the fin base was more than that of fin with inclined square perforation. The problem of this study was numerically solved using the variational approach finite element technique.     

Effect of viscous dissipation on the heat transfer in sinusoidal profile finned dissipators

In the present work, the efficiency of finned heat dissipators cooled by laminar flow is studied. The analysis is carried out by varying certain sizing parameters in correspondence with different viscous dissipation conditions. The velocity distribution in the fluid and the temperature distribution in the dissipator and in the fluid are determined by means of a finite element method. The model allows to study the variation of the heat transfer coefficient due to the fluid dynamic conditions imposed by the fin profile. Lastly, a comparison between the optimum fin shapes obtained under different viscous dissipation effects is carried out.     

Enhancement of natural convection heat transfer from a fin by triangular perforation of bases parallel and toward its tip

This study examines the heat transfer enhancement from a horizontal rectangular fin embedded with triangular perforations （their bases parallel and toward the fin tip） under natural convection. The fin＇s heat dissipation rate is compared to that of an equivalent solid one. The parameters considered are geometrical dimensions and thermal properties of the fin and the perforations. The gain in the heat transfer enhancement and the fin weight reduction due to the perforations are considered. The study shows that the heat dissipation from the perforated fin for a certain range of triangular perforation dimensions and spaces between perforations result in improvement in the heat transfer over the equivalent solid fin. The heat transfer enhancement of the perforated fin increases as the fin thermal conductivity and its thickness are increased.     

Entry region of louvered fin heat exchangers

The dominant thermal resistance for most compact heat exchangers occurs on the gas side and as such an understanding of the gas side flowfield is needed before improving current designs. Louvered fins are commonly used in many compact heat exchangers to increase the surface area and initiate new boundary layer growth. For this study, detailed flowfield measurements were made in the entry region of several louvered fin geometries whereby the louver angle, ratio of fin pitch to louver pitch, and Reynolds number were all varied. In addition to mean velocity measurements, time-resolved velocity measurements were made to quantify unsteady effects.

The results indicated larger fin pitches resulted in lower average flow angles in the louver passages and longer development lengths. Larger louver angles with a constant ratio of fin pitch to louver pitch resulted in higher average flow angles and shorter development lengths. As the Reynolds number increased, longer development lengths were required and higher average flow angles occurred as compared with a lower Reynolds number case. Time-resolved velocity measurements indicated some flow periodicity behind the fully developed louver for a range of Reynolds numbers. The Strouhal number of these fluctuations was constant for a given louver geometry, but the value increased with increasing fin pitch.     

Two-dimensional performance of convecting-radiating fins of different profile shapes

A finite element approach is used to investigate the two-dimensional performance of convecting-radiating fins of rectangular, trapezoidal, triangular, and concave parabolic shapes. The heat transfer rate depends on fin size parameter α, Biot numberBi, radiation-conduction parameterN _r , and environment temperatures θ_∞ and θ _r . Numerical results for the heat transfer rate and the error due to one-dimensional assumption are presented and discussed for each geometry. The highest heat dissipation is achieved with the concave parabolic shape and the lowest with the rectangular shape with the trapezoidal and triangular shapes falling in between. The maximum error of +144 percent is noted for a short and thick rectangular fin (α=1) and ?47 percent for a long thin triangular fin (α=20).     

Analysis of heat transfer in a partially wet radial fin assembly during dehumidification

This paper presents the analysis of heat transfer in a partially wet annular fin assembly during the process of dehumidification. In past studies, both fully dry and fully wet fins have been analyzed. New analytical formulation leading to a closed-form solution has been developed for a partially wet fin, which is most common in dehumidifier coil operation during air conditioning. The parameters that influenced the heat transfer rate in the finned tube structure are ratio of fin and wall thermal conductivities, ratio of fin thickness to fin pitch, ratio of wall thickness to fin pitch, ratio of fin length to fin pitch, cold fluid Biot number, ambient Biot number, the relative humidity and dry bulb temperature of the incoming air, and the cold fluid temperature inside the coil. Calculations were carried out to study the performance of the heat exchanger. The computed results included the temperature distribution in the wall and the fin and the fin efficiency.     

Computation of the 3-D Unsteady Flow Past Deforming Geometries

A 3-D incompressible unsteady flow solver based on simple finite elements with adaptive remeshing and grid movement for both moving and deforming surfaces is described. We demonstrate the combination of adaptive remeshing techniques with the incompressible flow solver with the computation of flow past an eel in 2-D and a blue-fin tuna in 3-D. The flow past a swimming tuna was computed for two extreme cases of the caudal fin frequency and swimming speed. A grid refinement study was performed and a grid converged solution for the force produced by the caudal fin was obtained.     

Application of nanofluids to a heat pipe liquid-block and the thermoelectric cooling of electronic equipment

Microprocessor power dissipation is constantly increasing. An increase in microprocessor size has also resulted in higher heat fluxes. The growth of information technology has rapidly increased over the past few years, causing an increase in the demand for a microprocessor that has a very high computing ability. The previous generation of central processing units (CPU) had 1.17 billion transistors planted in it, which indicates that a significant amount of heat was generated. The total heat dissipation resulting from a high end CPU is approximately 110-140 W, which will increase if the CPU voltage and frequency increase. Conventional air-cooled cooling systems are no longer adequate to remove these heat fluxes. For a number of applications, direct air-cooling systems will have to be replaced or enhanced by other high performance compact cooling techniques. In this study, the application of nanofluids as the working fluid on a heat pipe liquid-block combined with thermoelectric cooling is investigated. The type and effect of volume concentrations of nanofluids, coolant temperature, and thermoelectricsystem as heat pumps of a PC on the CPU’s temperature are considered. The results obtained from this technique are compared to those from other conventional cooling techniques. The heat pipe liquid-block combined with the thermoelectric system has a significant effect on heat transfer from the CPU. The higher thermal performance heat pipe liquid-block and thermoelectric cooled system with nanofluids proved its potential as a working fluid.     

Unsteady thermal response of a porous fin under the influence of natural convection and radiation

In this study, the effects of transient thermal performance of a rectangular porous fin in the presence of radiation and natural convection heat transfer are considered. The porous fin allows the flow to infiltrate through it and solid–fluid interaction takes place. This study is performed using Darcy’s model to formulate heat transfer equation. To study the thermal performance, three types of cases are considered, namely, long fin, finite length fin with insulated tip and finite length fin with tip exposed. The effects of the porosity parameter S_h, radiation parameter G and the temperature ratio C_T on the dimensionless transient temperature distribution and heat transfer rate are discussed.     

Measurements of steady-state heat dissipation from miniaturized horizontally-based straight rectangular fin arrays

Experiments have been conducted to investigate the effects of miniaturizing the base plate dimensions of horizontally-based straight rectangular fin arrays on the steady state heat dissipation performance. The variation of the steady-state heat dissipation rates per unit base area and the average heat dissipation coefficients within a limited fin base excess temperature above the ambient temperature (from 20 to 50 °C) have been studied as integral aluminum alloy fin arrays were miniaturized by changing the ratio of the base width to length from 0.51 to 1.96 for two inter-fin spacing distances of 3 mm and 11 mm. The miniaturization process have been initiated from a square-based array of 49 × 49 mm (maximum base area of 24.51 × 10^–4m²) and terminated at a square-based array of 25 × 25 mm (minimum base area of 6.25 × 10^–4m²) with rectangular-based arrays of varying intermediate areas in between. Relevant non-dimensional parameters formulated by earlier similarity analyses for large fin arrays with comparable inter-fin-spacing distances and fin heights have been found inadequate for generalizing the results. Modifications to correlations proposed for large fin arrays have been made by including the effect of varying the value of the base width to length ratio parameter to correlate the data for miniaturized fin arrays. Two types of correlations for miniaturized horizontally-based straight rectangular fin arrays, one which used the inter-fin separation distance as the prime geometric parameter, and the other, which employed half the fin length, have been presented, on the basis of the experimental conditions of this investigation.An erratum to this article can be found at     

Numerical study of heat transfer enhancement of finned flat tube bank fin with vortex generators mounted on both surfaces of the fin

Tube bank fin heat exchanger is one of the most compact heat exchangers, and it is widely used in industry equipments. The flat tube bank fin heat exchangers with vortex generators (VGs) have significant good heat transfer performance, and are used as radiators of locomotive. Here, we study heat transfer enhancement of a new fin where VGs are mounted on both surfaces of the fin. The heat transfer performance of this pattern is evaluated by a numerical method, and the results are compared with those obtained, under identical mass flow rate, when the VGs are mounted only on one surface of the fin. The results reveal that using this new pattern the height of VGs can be reduced and still obtain satisfactory heat transfer enhancement, while the pressure drop is reduced. The results also reveal that if VGs on one surface of the fin is determined, the locations where VGs are mounted on other surface of the same fin are very important, with configurations studied in this paper, depending on the value of Reynolds number, there exists an optimum location with which best heat transfer performance can be obtained.     

Performance analysis and optimization of convective annular fins with internal heat generation

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.     

Heat transfer from convecting-radiating fins of different profile shapes

A finite difference method is used to predict the performance of convecting-radiating fins of rectangular, trapezoidal, triangular, and concave parabolic shapes. The analysis assumes one-dimensional, steady conduction in the fin and neglects radiative exchange between adjacent fins and between the fin and its primary surface. For the range of thermal and geometrical parameters investigated, the variation of heat transfer rate and the fin efficiency with other profile shapes was found to be within 11 percent of the rectangular shape. The effect of profile shape is most pronounced when the Biot number,Bi, and radiation number,N _r, are small compared to unity. Because of several limiting assumptions, the results would be used only for preliminary analysis and design particularly when a fin assembly is involved rather than an individual fin.     

Nodeless variable finite element method for heat transfer analysis by means of flux-based formulation and mesh adaptation

Based on flux-based formulation, a nodeless variable element method is developed to analyze two-dimensional steady-state and transient heat transfer problems. The nodeless variable element employs quadratic interpolation functions to provide higher solution accuracy without necessity to actually generate additional nodes. The flux-based formulation is applied to reduce the complexity in deriving the finite element equations as compared to the conventional finite element method. The solution accuracy is further improved by implementing an adaptive meshing technique to generate finite element mesh that can adapt and move along corresponding to the solution behavior. The technique generates small elements in the regions of steep solution gradients to provide accurate solution, and meanwhile it generates larger elements in the other regions where the solution gradients are slight to reduce the computational time and the computer memory. The effectiveness of the combined procedure is demonstrated by heat transfer problems that have exact solutions. These problems are: (a) a steady-state heat conduction analysis in a square plate subjected to a highly localized surface heating, and (b) a transient heat conduction analysis in a long plate subjected to a moving heat source. The English text was polished by Yunming Chen.     

Experimental investigation of heat transfer and flow pattern from heated horizontal rectangular fin array under natural convection

This paper presents results of the experimental study conducted on heated horizontal rectangular fin array under natural convection. The temperature mapping and the prediction of the flow patterns over the fin array with variable fin spacing is carried out. Dimensionless fin spacing to height (S/H) ratio is varied from 0.05 to 0.3 and length to height ratio (L/H) = 5 is kept constant. The heater input to the fin array assembly is varied from 25 to 100 W. The single chimney flow pattern is observed from 8 to 12 mm fin spacing. The end flow is choked below 6 mm fin spacing. The single chimney flow pattern changes to sliding or end flow choking at 6 mm fin spacing. The average heat transfer coefficient (h_a) is very small (2.52–5.78 W/m² K) at 100 W for S = 5–12 mm. The h_a is very small (1.12–1.8 W/m² K) at 100 W for 2–4 mm fin spacing due to choked fin array end condition. The end flow is not sufficient to reach up to central portion of fin array and in the middle portion there is an unsteady down and up flow pattern resulting in sliding chimney. The central bottom portion of fin array channel does not contribute much in heat dissipation for S = 2–4 mm. The h_a has significantly improved at higher spacing as compared to lower spacing region. The single chimney flow pattern is preferred from heat transfer point of view. The optimum spacing is confirmed in the range of 8–10 mm. The average heat transfer results are compared with previous literature and showed similar trend and satisfactory agreement. An empirical equation has been proposed to correlate the average Nusselt number as a function of Grashof number and fin spacing to height ratio. The average error for this equation is ?0.32 %.     

Optimization of a conducting cooling fin with a heat sink using optimality criterion

An optimality criterion is used to obtain a minimum volume design of a conducting fin with an arbitrarily located heat sink whose volume is a design variable. The finite element method is used for the analysis. The effect of the heat sink as an active cooling device on the optimum volume of the fin is studied     

Natural convection heat transfer from a thin rectangular fin with a line source at the base — a finite difference solution

This paper presents an analysis of the problem of a thin fin of finite thermal conductivity, with an isothermal line source at the base, dissipating heat to the surrounding air by natural convection. The horizontal surface to which the fin is attached is adiabatic so that heat is dissipated only through the fin. The temperature and velocity distributions in the field, the temperature profile in the fin, local Nusselt numbers along the fin and the average heat transfer coefficient of the fin are obtained by solving the governing equations in the field and the heat transfer equation in the fin simultaneously, using an explicit unsteady Finite Difference formulation leading to the steady state result. Numerical experiments are performed to study the influence of parameters namely the fin height, temperature of the heating source and the fin material on the average heat transfer coefficient. Comparison is made with fins of infinite thermal conductivity and the vertical isothermal flat plate.     

Unsteady conjugate problem of a dissipative fluid in a horizontal channel with a periodic variation temperature

The unsteady two-dimensional transient heat transfer problem referring to a fully laminar flow developing in a parallel-plane channel exposed to a periodic variation surface temperature with distance is numerically studied. The effects of channel thickness, Péclet number, wall-to-fluid conductivity ratio, thermal diffusivity ratio, angular frequency and the viscous dissipation parameter are determined in the solutions. The non-linear equations are discretized by means an implicit finite difference scheme and the electric analogy to the resulting system is applied to convert these equations into a network-electrical model that was solved using a computer code (electric circuits simulator). In this scheme, only spatial discretization is necessary, while time remains as a real continuous variable, and its programming does not require manipulation of the sophisticated mathematical software that is inherent in other numerical methods. The network simulation method, which satisfies the conservation law for the heat flux variable and the uniqueness law for temperature, also permits the direct visualization of the local and/or integrated transport variables at any point or section of the medium.     

Unsteady flow and heat transfer adjacent to the sidewall wall of a differentially heated cavity with a conducting and an adiabatic fin

The unsteady natural convection flow adjacent to the finned sidewall of a differentially heated cavity is numerically investigated through comparisons between the cases with a conducting fin and an adiabatic fin. The results show that the flow and temperature structures in the transition to a periodic flow induced by a conducting fin are considerably different from those by an adiabatic fin. Based on the present numerical results, the temporal development and spatial structures of the flow adjacent to the finned sidewall are described, and instabilities are characterized. It is found that the conducting fin improves the transient convective flows in the cavity and enhances heat transfer across the cavity (by up to 52% in comparison with the case without a fin).     

Steady mixed convection flow of Maxwell fluid over an exponentially stretching vertical surface with magnetic field and viscous dissipation

The steady mixed convection flow and heat transfer from an exponentially stretching vertical surface in a quiescent Maxwell fluid in the presence of magnetic field, viscous dissipation and Joule heating have been studied. The stretching velocity, surface temperature and magnetic field are assumed to have specific exponential function forms for the existence of the local similarity solution. The coupled nonlinear ordinary differential equations governing the local similarity flow and heat transfer have been solved numerically by Chebyshev finite difference method. The influence of the buoyancy parameter, viscous dissipation, relaxation parameter of Maxwell fluid, magnetic field and Prandtl number on the flow and heat transfer has been considered in detail. The Nusselt number increases significantly with the Prandtl number, but the skin friction coefficient decreases. The Nusselt number slightly decreases with increasing viscous dissipation parameter, but the skin friction coefficient slightly increases. Maxwell fluid reduces both skin friction coefficient and Nusselt number, whereas buoyancy force enhances them.