Horizontal Rectangular Fin Array Research Articles

Numerical validation of natural convection heat transfer with horizontal rectangular fin array using straight knurling patterns on fins—correlation for Nusselt number

AbstractNatural convection heat transfer from horizontal rectangular fin array with various knurling patterns has been studied experimentally by the present authors to investigate the effect of knurl‐produced surface roughness of fin on the heat transfer rate. The parameters like knurling height from base, knurling depth, fin spacing, and supply wattage were considered for parametric study. In the present paper, numerical method (CFD) is used to simulate natural convection phenomena with knurled fins and results are validated with the experimental data available from literature. The numerical results show similar trends compared with experimental data and one can use this method to study various fin configurations for knurling patterns. The flow patterns from experiments and numerical method are compared for different supply wattages and fin spacing to back up the conclusion. It is also observed that the variation in nondimensional roughness depth and spacing (D kn/H and S/H) have more effect on Nusselt number than roughness height parameter (H kn/H). Further, the method is extended to study numerically large number of fin configurations with knurling patterns to gather sufficient data for Nusselt number with respect to fin geometric parameters as above and establish correlation for heat transfer coefficient for such type of fins.

Experimental Investigation of Heat Transfer by Natural Convection with Perforated Pin Fin Array

The main objective of this experimental study is to quantify and compare the natural convection heat transfer enhancement of perforated fin array with various fin spacing, perforation angle, perforation diameter, pitch of perforation and heater inputs. The variables for this natural convection cooling with the help of finned surfaces are orientation and geometry. In this study, the steady state heat transfer from the solid fin and perforated fin arrays are measured. The present study establishes optimized fin setup for various parameters of fin geometry and its effect on heat transfer results. The results obtained are matched well and showed similar trend and satisfactory agreement for heat transfer under natural convection. From all results it is concluded that the heat transfer rate for the fins of perforation with constant pitch and 4 mm diameter with 45° geometry of perforation is optimum fin and the array of this fin with 10 mm spacing is best suited horizontal rectangular fin array.

Enhancement of Natural Convection Heat Transfer from Horizontal Rectangular FIN Arrays : A Review

Enhancement of Natural Convection Heat Transfer from Horizontal Rectangular FIN Arrays : A Review

Enhancement of natural convection heat transfer from horizontal rectangular fin arrays with perforations in fin base

The overall convection heat transfer coefficients for long horizontal rectangular fin arrays are low because the surfaces in the inner region are poorly ventilated. In this study, we introduce perforations through the fin base to improve ventilation with cold air from below the fin base. Aluminum fin arrays with length L = 380 mm or 104 mm, fin height H = 38 mm, fin thickness tf = 1 mm, and fin spacing S = 10 mm are analyzed numerically with a temperature difference of 55 K between the fin base and the surroundings. Since the flow associated with horizontal rectangular fin arrays longer than about 100 mm tends to be unsteady, an unsteady model is adopted. In the main part of the present study, we analyze a single channel with multiple equal-length, equally spaced rectangular perforations which cover the full width of the fin spacing and have a total perforation length of L/2 or L/4. In addition, a multi-channel analysis is conducted for a selected fin array configuration with the uniform heat applied on the bottom surface at the middle part and longitudinal perforations arranged on the fin base outside the heated region. The perforations, especially located in the inner region, improve ventilation and heat transfer performance significantly. The patterns with more distributed shorter perforations exhibit better improvements. The overall heat transfer coefficients can be more than twice as large as that without perforations for long fin arrays. The flow fields and the longitudinal distributions of the height-averaged local heat flux from fin surface are analyzed to describe the effects of fin-base perforations.

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 (ha) is very small (2.52–5.78 W/m2 K) at 100 W for S = 5–12 mm. The ha 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 ha 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 %.

Enhanced performance of horizontal rectangular fin array heat sink using assisting mode of mixed convection

Experimental study of heated horizontal rectangular fin array (HRFA) under natural and assisting mode of mixed convection is presented in this paper. Mainly two type of flow patterns are encountered in case of HRFA namely: (i) single chimney flow pattern (L/H⩽5) and spacing about 8–10mm, (ii) sliding chimney flow pattern L/H>5 and small spacing less than 6mm or so. It was envisaged to use mixed convection in its assisting mode to convert sliding chimney to single chimney flow pattern and take advantage of large area (A), due to small S and favorable flow to augment heat dissipation rate from the fin array. The mixed convection heat transfer has been investigated for a wide range of Rayleigh numbers and different fin spacings and flow velocities. The constant heat flux boundary condition is present with air as surrounding fluid. Experiments are conducted for Rayleigh numbers 4×104⩽Ra⩽3×105, Reynolds numbers 80⩽Re⩽1500 and Richardson number 0.08⩽Ri⩽5. Dimensionless fin spacing to height (S/H) ratio is varied from 0.05 to 0.3 and L/H=5 is kept constant. A fan developed upward velocity in the range between 0.05⩽V⩽0.5m/s. Assisting mode results of mixed convection are compared with natural convection for various heater inputs and Ri numbers. The average heat transfer coefficient has increased up to 69.46% at cost of very small energy input (0.3–0.65W). At small spacing (S=2–5mm), a large surface area is available to dissipate. The optimum spacing region becomes wider (S≈4–6mm) under mixed convection as compared to natural convection (S≈8–10mm). An empirical equation has been developed to correlate the average Nusselt number as a function of Re, Gr and S/H within uncertainty of ±10%.

Parametric study on the dynamic behavior of natural convection from horizontal rectangular fin arrays

A parametric study on the dynamic natural convection from long horizontal fin arrays (L=128, 254 and 380mm) is made using a 3-D unsteady numerical analysis. The investigated range of height H is 6.4–38mm and that of spacing S is 6.4–20mm. Increasing L tends to enhance the oscillating sliding-chimney flow, whereas increasing S weakens it. The time-averaged overall convection heat transfer coefficients h¯ are larger for high and short fin arrays, due to the stronger buoyancy and thinner boundary layers. The h¯–S relation exhibits a steep drop when S is narrowed below a threshold, which is larger for lower and longer fins. The optimum fin spacing Sopt occurs near the threshold S, below which the benefit of increasing heat transfer area surrenders to the decrease of h¯ caused by excessive viscous drag. The heat transfer rate per unit base area Q/Ab decreases with increasing L and decreasing H. The predicted dependence of Sopt on H and L agrees well with experimental results and is explained based on numerical results of flow and heat transfer characteristics. The present predictions of Nu agree well with the correlations in the literature which use S as the characteristic length.

Numerical Analysis of Inverted Notched Fin Array Using Natural Convection

Geometry and orientation plays an important role in natural convection heat transfer. For horizontal rectangular fin array a chimney flow pattern is developed due to density difference. This flow pattern creates a stagnant zone near central bottom region. That portion does not contribute much towards heat dissipation. This area is removed from fins and they became inverted notched fins. This modified geometry reduces material cost, material weight without hampering heat transfer rate. Numerical models are prepaid to investigate heat transfer characteristics in plane fins and inverted notched fins. This investigation is also extended over different types of notches and their effectiveness comparison. Fin spacing, fin height, fin length, heater input, percentage of area removed in the form of inverted notch are the parameters under consideration. This analysis is done numerically using CFD package (Fluent). It is found that the heat transfer coefficient of inverted notch fin array is 25% to 35% higher as compared with normal fin array. Also we found that the triangular shape notch gives better result than trapezoidal and rectangular shape notch.

Dynamic characteristics of natural convection from horizontal rectangular fin arrays

Abstract This work numerically analyzes the dynamic behavior of natural convection from horizontal rectangular fin arrays. Unsteady simulations are conducted for different fin lengths of L = 56–500 mm with fin heights of H = 6.4 and 38 mm and a fixed fin spacing of 6.4 mm. With a decreasing H/L ratio, the flow pattern evolves from a steady single-chimney to an oscillating sliding-chimney flow in which cold air is drawn downward from the upper ambience. For both fin heights, the average convection heat transfer coefficient decreases with increasing fin length. It first drops steeply and then decreases mildly beyond a certain length when the sliding-chimney flow occurs. The effect of the downward flow on heat transfer is weaker for high fins because the penetration depths are limited by the thicker boundary layers developed in the high channels. The predicted average Nusselt numbers agree well with the experimental data in the literature. For an intense sliding-chimney flow pattern from long and low fin arrays, an unsteady simulation yields higher average convection heat transfer coefficients than those using a steady-state simulation.

Convection Heat Transfer from Horizontal Rectangular Fin Array having Triangular Perforations

Convection Heat Transfer from Horizontal Rectangular Fin Array having Triangular Perforations

Laminar free convection underneath a downward facing hot fin array

A combined analytical, numerical and experimental study was conducted to investigate the problem of natural convection underneath a horizontal rectangular hot fin array. This subject has not been explored before. The purpose of the investigation was to provide useful and reliable heat transfer coefficients. In addition to the experimental and numerical results, a useful approximate closed form analytical solution is offered. The analytical solution clearly reveals the dependence of the Nusselt number on the Rayleigh number, the Prandtl number and the fin's height to spacing ratio. Optimum analyses were conducted to determine the minimum fin height that provides the necessary cooling capability of a specified array base area. In this context it is shown that the optimal fin spacing varies within a narrow range which depends primarily on the array length. Those findings have important industrial application because they impact both the cost and size of cooling finned surfaces.

A three dimensional numerical study on natural convection heat transfer from short horizontal rectangular fin array

Steady state natural convection heat transfer in a longitudinally short rectangular fin array on a horizontal base is numerically investigated. The problem is three dimensional laminar natural convection heat transfer with open boundaries. A finite difference code based on vorticity-vector potential approach is developed to solve the governing equations. The steady behaviour of the flow and temperature distributions is obtained from the solution of transient form of the governing equations. Results are compared with the available experimental results in the literature. A good agreement is seen between the numerical and reported experimental results. Flow configurations occurring in the channel of the fin arrays with different geometrical parameters, (fin length, fin height and fin spacing) are analysed. Based on the obtained results, two types of flow patterns are observed. The mechanisms of the flows are discussed and flow patterns are plotted to support the discussion. The study is limited to Rayleigh number based on fin spacing, ranging from 120 to 39000. The fin length and fin height are varied from 2 to 20 and 0.25 to 7-fin spacing, respectively.

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.

Natural Convection Heat Transfer From Horizontal Rectangular Fin Arrays

Average heat-transfer coefficients are presented for fin arrays positioned with the base oriented horizontally. The flow field associated with the natural convection from the fin arrays was investigated and used as a model to find parameters to generalize the data. The proposed correlation overcomes the inadequacy of parameters available previously for horizontal rectangular fins.