Role of Three-Dimensional Swirl in Forced Convection Heat Transfer Enhancement in Wavy-Plate-Fin Channels

The influence of swirl flow on enhanced forced convection in wavy-plate-fin cores has been investigated. Three-dimensional computational simulations were carried out for steady-state, periodically developed flow of air (Pr ~ 0.71) with channel walls subject to constant-uniform temperature and flow rates in the range 50 = Re = 4000. The recirculation that develops in the wall troughs and grows to an axial helix is scaled by the Swirl number Sw. As Sw increases, tornado-shaped vortices appear in the wave trough region mid-channel height, then extend longitudinally to encompass majority of the flow channel. As shown by the local wall-shear and heat transfer coefficient variations, the boundary-layer thinning upstream of the wave peak assists to intensify the momentum and heat transfer. However, the flow recirculation in wave trough impedes the local heat transfer at low Sw due to flow stagnation but promotes it at high Sw because of swirl-augmented fluid mixing. Swirling flows also create pressure drag that contributes substantively to the overall pressure loss. Its proportion grows as Sw, corrugation severity, and fin spacing increases to as much as 80% of the total pressure drop. The fin-wall curvature-induced secondary circulation nevertheless produces significantly enhanced convection, and more so in flows with higher Sw. It is quantified by Ff (or j), which is seen to increase log-linearly as fin corrugation aspect ratio and/or fin spacing ratio increases; the influence of cross-section aspect ratio is found to be marginal.

Flow and Heat Transfer Simulation Analysis of 3D Compact Heat Exchanger

Compact heat exchangers (CHEs) are one of the most commonly used heat exchangers in the industry due to their superior advantages over other types of heat exchangers. Various geometric (fin spacing, tube inclination angle, etc) and process (such as flow velocity, temperature, etc) parameters affect the performance of such compact HEs. This research aims to examine the effects of fin spacing, tube inclination angle, and airflow velocity on heat transfer and pressure drop performance of CHE in both inline and staggered configurations. A three-dimensional (3D) numerical method with the aid of Ansys FLUENT software was carried out for the laminar flow condition. Based on the obtained results, the highest average heat transfer coefficient was observed at 120° for both tube arrangements while the lowest average pressure drop penalty is at 30°. Therefore, the recommended inclination angle when high heat transfer is needed is at 120° while if the pumping power is the major problem, 30 °or 150° is recommended. based on the London area goodness factor (j/f), 30° and 150° show the highest value for both configurations. The j/f factor decreases with the increase of Reynolds number for both configurations. In addition, 120° shows the lowest j/f which can be due to the high pressure drop.

Investigation of the effects of geometrical parameters, eccentricity and perforated fins on natural convection heat transfer in a finned horizontal annulus using three dimensional lattice Boltzmann flux solver

Purpose The purpose of this paper is to investigate the effects of geometrical parameters, eccentricity and perforated fins on natural convection heat transfer in a finned horizontal annulus using three-dimensional lattice Boltzmann flux solver. Design/methodology/approach Three-dimensional lattice Boltzmann flux solver is used in the present study for simulating conjugate heat transfer within an annulus. D3Q15 and D3Q7 models are used to solve the fluid flow and temperature field, respectively. The finite volume method is used to discretize mass, momentum and energy equations. The Chapman–Enskog expansion analysis is used to establish the connection between the lattice Boltzmann equation local solution and macroscopic fluxes. To improve the accuracy of the lattice Boltzmann method for curved boundaries, lattice Boltzmann equation local solution at each cell interface is considered to be independent of each other. Findings It is found that the maximum heat transfer rate occurs at low fin spacing especially by increasing the fin height and decreasing the internal-cylindrical distance. The effect of inner cylinder eccentricity is not much considerable (up to 5.2% enhancement) while the impact of fin eccentricity is more remarkable. Negative fin eccentricity further enhances the heat transfer rate compared to a positive fin eccentricity and the maximum heat transfer enhancement of 91.7% is obtained. The influence of using perforated fins is more considerable at low fin spacing although some heat transfer enhancements are observed at higher fin spacing. Originality/value The originality of this paper is to study three-dimensional natural convection in a finned-horizontal annulus using three-dimensional lattice Boltzmann flux solver, as well as to apply symmetry and periodic boundary conditions and to analyze the effect of eccentric annular fins (for the first time for air) and perforated annular fins (for the first time so far) on the heat transfer rate.

Review on Heat Transfer Enhancement by Rectangular Fin

Heat generation of engineering appliances has bad effect in handling the system can cause the trouble, short life cycle of machines, frequent maintenance requirements and low reliability of systems. The passive cooling technique has been widely used to solve such problems. This review work summarizes the heat transfer enhancement technique in a rectangular fin with economic way. So many research about the enhancement of heat transfer by rectangular fins experimentally and numerically and found very significant result. In this review, various types of rectangular fin structures are studied simultaneously. It is revealed through reviewing the related literature that the highest value of equivalent heat transfer enhancement is found the increase in average heat transfer performance of inverted triangular notched fin 50.51% as compared with plane rectangular fin and the perforated fin total heat transfer rate increased by 38.9% compared to regular fin. Furthermore, by reduction of the optimal fin spacing, heat flux can be changed by 20% in standard rectangular fin when compared with regular fin spacing. Also cooling performance of the inclined rectangular fin with 60° of tilt angle is seen to be as 6% higher than solid rectangular fin. This article can be considered as a benchmark in the practical application for enhances the heat transfer rates.

Effect of condensate flow rate, surface tension, density and vapor velocity on condensate retention of wire wrapped tubes

Simulated condensation has been conducted on three wire wrapped tubes having same root diameter but different fin spacing of 1.5mm, 2mm and 2.5mm. Different fluids (Ethanol, Ethylene Glycol and Water) are used for condensation by providing them to the tubes through tiny holes in inter-fin spacing on the top of the surface of tubes. The major parameters are to be controlled in this research are fin spacing, vapor velocity, condensate flow rate and ratio of surface tension to density of the fluid. Obtained results show that flooding angle (calculated from the top of the tube to the level where fluid fills the fin) rises by increasing fin spacing. Also, retention angles increase by reducing ratio of surface tension to density of fluid. Acute flooding angles at zero air velocity and zero flow rate, elevates by increasing air velocity. However, obtuse flooding angles at static conditions drop by reducing air velocity. An interesting result is obtained regarding retention angle which remains almost even for the higher condensation flow rates until the tube gets inundated with condensation. Moreover, critical flow rates for all the tubes against using different working fluids are measured. Results obtained for static conditions have good correspondence with already available authentic data for flooding angle. Pictures showing condensate retention angles have been included in this paper.

Dynamic numerical study on phase change thermal storage heat transfer

Targeted at the poor heat transfer effect of the phase change thermal storage heat exchanger due to the low thermal conductivity of the phase change material, a fin-tube type phase change thermal storage heat exchanger has been proposed in the study. A 2-D model of the phase-change heat storage unit was established, and the dynamic heat transfer law of the melting and solidification of the phase change material, and the influence of the fin structure size on the heat storage/release performance of the heat exchanger were numerically analyzed. The results show that in the area close to the tube wall, the smaller the fin spacing, the larger the thickness, the faster the phase change heat storage/release speed, and the better heat transfer effect. In the central area of the phase change material, the greater the fin spacing and thickness, and the better the heat transfer effect of the phase change heat storage/release. The area close to the outer wall has the smallest temperature change, and the heat storage/release effect is the worst. Therefore, the use of energy storage heat exchangers with gradual fin thickness and spacing is an effective method to improve the heat transfer efficiency of existing equipment. In addition, in order to improve the heat exchange effect of the edge area of the phase change, its structure could be changed or the heat exchange form can be increased.

Experimental and Numerical Investigation of Natural Convection Heat Transfer From Horizontal Rectangular Plate Fin Pin Fin Arrays

Fins are commonly employed for cooling of electronic equipment, compressors, Internal Combustion engines and for heat exchange in various heat exchangers. In short fin (length to height ratio, L/H = 5) arrays used for natural convection cooling, a stagnation zone forms at the central portion and that portion is not effective for carrying away heat. An attempt is made to modify plate fin heat sink geometry (PFHS) by inserting pin fins in the channels formed between plate fins and a plate fin pin fin heat sink (PFPFHS) is constructed to address this issue. An experimental setup is developed to validate numerical model of PFPFHS. The three-dimensional elliptic governing equations were solved using a finite volume based computational fluid dynamics (CFD) code. Fluent 6.3.26, a finite volume flow solver is used for solving the set of governing equations for the present geometry. Cell count based on grid independence and extended domain is used to obtain numerical results. Initially, the numerical model is validated for PFHS cases reported in the literature. After obtaining a good agreement with results from the literature, the numerical model for PFHS is modified for PFPFHS and used to carry out systematic parametric study of PFPFHS to analyze the effects of parameters like fin spacing, fin height, pin fin diameter, number of pin fins and temperature difference between fin array and surroundings on natural convection heat transfer from PFPFHS. It is observed that it is impossible to obtain optimum performance in terms of overall heat transfer by only concentrating on one or two parameters. The interactions among all the design parameters must be considered. This thesis presents Experimental and Numerical study of natural convection heat transfer from horizontal rectangular plate fin and plate fin pin fin arrays. The parameters of study are fin spacing, temperature difference between the fin surface and ambient air, fin height, pin fin diameter, number of pin fins and method of positioning pin fins in the fin channel. Experimental set up is validated with horizontal plate standard correlations. Results are generated in the form of variation in average heat transfer coefficient (ha), base heat transfer coefficient (hb), average Nusselt number (Nua) and base Nusselt number (Nub). Total 512 cases are studied numerically and finally an attempt is made to correlate the Nusselt Number (Nu), Rayleigh Number (Ra), increase in percentage by inserting pin fins (% Area), ratios like spacing to height (S/H) and L/H obtained in the present study.

Experimental Investigation of Heat Transfer Enhancement in Solid Cylindrical & Cylindrical with Perforated Fins in Staggered & in Inline Arrangements

In this project investigates the heat transfer enhancement in solid cylindrical and cylindrical with perforated fins in inline and staggered arrangement in rectangular channel. The channel had a cross-sectional area of 250- 100 mm2. The experiments covered the following range: Reynolds number 13,500–42,000, the clearance ratio (C/H) 0, 0.33 and 1, the inter-fin spacing ratio (Sy/D) 1.944 and 3.417. Nusselt number and Reynolds number were considered as performance parameters. Correlation equations will be developed for the heat transfer and friction factor. Computational Fluid Dynamics analysis is done by using ANSIS FLUENT 14.5 software. The Numerical and computational analysis shows that the use of the cylindrical perforated pin fins leads to heat transfer enhancement than the solid cylindrical fins. Heat transfer Enhancement varies depending on the clearance ratio and inter-fin spacing ratio. Validation of Numerical and Computational Analysis will be done.

Numerical study for heat transfer enhancement using CuO water nanofluids through mini-channel heat sinks for microprocessor cooling

Water cooled heat sinks are becoming popular due to increased heat generation inside the microprocessor. Timely heat removal from microprocessor is the key factor for better performance and long life. Heat transfer enhancement is reached either by increasing the surface area density and/or by altering the base fluid properties. Nanoparticles emerge as a strong candidate to increase the thermal conductivity of base fluids. In this research, the thermal performance of mini-channel heat sinks for different fin spacing (0.2 mm, 0.5 mm, 1 mm, and 1.5 mm) was investigated numerically using CuO-water nanofluids with volumetric concentration of 1.5%. The numerical values computed were than compared with the literature and a close agreement is achieved. We recorded the minimum base temperature of chip to be 36.8?C for 0.2 mm fin spacing heat sink. A reduction of 9.1% in base temperature was noticed using CuO-water nanofluids for 0.2 mm fin spacing as compared to previously experimental estimated value using water [1]. The drop percentage difference in pressure between water and CuO-water nanofluids was 2.2-13.1% for various fin spacing heat sinks. The percentage difference in thermal resistance between water and CuO-water nanofluids was computed 12.1% at maximum flow rate. We also observed uniform temperature distribution for all heat sinks.

Numerical Study of a New Solar Vacuum Tube Integrating with Phase Change Material

In this work, a new solar vacuum tube (SVT) integrating with phase change material is introduced and numerically investigated. The mathematical model and the numerical solution of phase change heat transfer is introduced. The heat transfer of the solar energy collection system during the energy storage process is simulated. Solid-liquid phase change characteristics of the SVT with paraffin inside is analyzed. Optimization analysis of fin structure parameters (fin thickness and fin spacing) in the vacuum tube is conducted. The results showed that the metal fin has a great effect on the phase change heat transfer of paraffin in SVTs. The closer the paraffin is to the fins, the more uniform the paraffin temperature is and the sooner the paraffin melts. As the fin thickness increases and the spacing between the fins decreases, the melting time of the paraffin decreases. Meanwhile, the effect of fin spacing on the overall heat transfer performance of the phase change energy storage tube is larger than the effect of the fin thickness. When the fin thickness is 2 mm, the melting time of paraffin with a fin spacing of 80 mm is 21,000 s, which is almost three times of that with a fin spacing of 10 mm (7400 s). Therefore, decreasing fin spacing is an effective way of enhancing phase change heat transfer. When the total fin volume is constant, a SVT with small fin space and small fin thickness performs better in heat transfer performance.