Improvement In Heat Transfer Rate Research Articles

Heat Transfer from a Hybrid Pulsating and Swirling Air Jet Impingement

With decrease in size of electronic equipment’s, effective heat removal is a major challenge these days. Present work focuses on implementation of a novel hybrid method which helps attain heat transfer enhancement. An experimental investigation is carried out to study effect of pulse air jet on local heat transfer distribution of a flat surface. Effect of nozzle to plate distance (z/d = 2 to 6), Reynolds number (5000 to 9000), pulsating frequency (f = 0.07 to 2.03 hz) and Strouhal number (Sr = 6.7e-5 to 0.0029) are studied with constant nozzle diameter. Thin foil technique is used to estimate local heat transfer characteristics using IR thermal infrared imaging technique. Nusselt number distribution is plotted for all the cases using information got from IR image. It is observed that at lower frequency rate and low Strouhal number heat, transfer rate is more effective. A novel hybrid method to improve heat transfer rate is introduced in this study using Pulse combined with swirl technique. This method involves introducing swirler of specified twist ratio into nozzle subjected to air pulse. Experiments show that this novel hybrid method improves heat transfer rate at all the above-mentioned conditions.

Modelling, Analysis and Entropy Generation Minimization of Al2O3-Ethylene Glycol Nanofluid Convective Flow inside a Tube

Entropy generation is always a matter of concern in a heat transfer system. It denotes the amount of energy lost as a result of irreversibility. As a result, it must be reduced. The present work considers an investigation on the turbulent forced convective heat transfer and entropy generation of Al2O3-Ethylene glycol (EG) nanofluid inside a circular tube subjected to constant wall temperature. The study is focused on the development of an analytical framework by using mathematical models to simulate the characteristics of nanofluids in the as-mentioned thermal system. The simulated result is validated using published data. Further, Genetic algorithm (GA) and DIRECT algorithm are implemented to determine the optimal condition which yields minimum entropy generation. According to the findings, heat transfer increases at a direct proportion to the mass flow, Reynolds number (Re), and volume concentration of nanoparticles. Furthermore, as Re increases, particle concentration should be decreased in order to reduce total entropy generation (TEG) and to improve heat transfer rate of any given particle size. A minimal concentration of nanoparticles is required to reduce TEG when Re is maintained constant. The highest increase in TEG with nanofluids was 2.93 times that of basefluid. The optimum condition for minimum entropy generation is Re = 4000, nanoparticle size = 65 nm, volume concentration = 0.2% and mass flow rate = 0.54 kg/s.

Investigation of newly designed Alternate Perforated V-Notch (APVN) twisted tape with heat transfer characteristics

Swirl device is seen as a path to enhance the efficiency of a thermal switch. Swirl device with fabricated form of porosity and v-cuts twisted tape (tt) inner pipe insert helps to augment performance by improving the heat transfer (U) coefficient. This work is related to the thermal performance factor (TPF), friction factor (ff) and Nusselt (NNu) number in the inner tube inserted with a innovative design of Alternate Perforated V-Notch (APVN) tape having twisted ratio 6.25 incorporating porosity amount of Rp = 1.087% and width (w/W) ratio = 0.333, were investigated features to improve heat transfer rate. Enhancement in turbulent generation of the primary flow into the secondary flow with this design. Experiment test was performed on a pipe in pipe tubes of (d) internal diameter of 0.013 m with test section length of 0.9 m. Temperature of the warm water had kept constant at 60 °C within the Reynolds number range of 2246–16,224. The heat exchanger with empty tube (without tt) and the input of normal twisted tape (tt) has been checked. In addition to the investigated range, NNu, ff and TPF in the tube with APVN twisted tape insertion were observed (Rp - ratio) 1.833–2.276, 2.155–4.549 and 1.84–1.778 times more than the values of empty tube. The presented work is very useful in the field of energy conservation through maximum transfer of heat in the industrial process.

Investigation of Heat Transfer from Convective and Radiative Stretching/Shrinking Rectangular Fins

We study the efficiency of shrinking/stretching radiative fins to improve heat transfer rate. To evaluate the competence of suggested fins, the influence of shrinking/stretching, thermogeometric parameters, surface temperature, convection conduction, radiation conduction, and Peclet number is investigated. The problem is solved numerically using a shooting method. To validate the numerical solution, the results are compared with the solution of a differential transform method. Temperature distribution increases with a rise in convection and radiation conduction parameters when Peclet number, stretching/shrinking, ambience, and surface temperatures are raised. The temperature of the fin’s tip increases as ambient temperature, Peclet number, and surface temperature increase, and decreases for enhanced radiation and convection conduction parameters. Radiation and convection cause the efficiency of the fin to increase for shrinking and decrease for stretching, which shows an important role in heat transfer analysis in mechanical engineering. The formulated model is also studied analytically, and the result is compared to numerical solution, which shows qualitatively good agreement.

Lattice Boltzmann-based numerical analysis of nanofluid natural convection in an inclined cavity subject to multiphysics fields

This research conducts a study of natural convection heat transfer (NCHT) in a nanofluid under a magnetic field (MF). The nanofluid is in a cavity inclined at an angle of 45°. The MF can take different angles between 0° and 90°. Radiative heat transfer is present in the cavity in volumetric form. There are two hot semicircles, similar to two half-pipes, on the bottom wall. The top wall is kept cold. The side walls and parts of the bottom wall, except the pipes, have been insulated. The lattice Boltzmann method has been used for the simulation. The studied parameters are the Rayleigh number (in the range 103–106), magnetic field angle, radiation parameter (in the range 0–2), and nanoparticle volume fraction (in the range 0–5%). The generated entropy has been studied as the NCHT. The results indicate that adding nanoparticles improves heat transfer rate (HTR). Moreover, the addition of volumetric radiation to the cavity enhances the Nusselt number by 54% and the generated entropy by 12.5%. With an augmentation in the MF angle from 0° to 90°, HTR decreases and this decrease is observed mostly at higher Rayleigh numbers. An augmentation in the Ra increases NCHT and entropy generation. Indeed, a rise in the Ra from 103 to 106 increases HTR by almost sixfold.

Thermal and Flow Analysis of Different Shaped Pin Fins for Improved Heat Transfer Rate

In this paper, a micro pin fin heat sink is numerically investigated with four fins geometries (circular, elliptical, square, and drop shape) at two types of arrangement styles, inline and staggered arrangement. The hydrodynamic and thermal characteristics of different fin geometries and two arrangement styles have been compared under the exact value of Reynolds number and constant wall temperature thermal boundary conditions. The Reynolds number was sweeping in the range of (400-2800) to ensure the fluid flow velocity impact in the pin fin performance. The results obtained indicate that a longitude pin fin dropped with increasing Reynolds number at a distributed temperature. Also, the circler Pin fin reaches the lowest temperature comparison to the rest of the three-pin fin types. Generally, according to the extracted, Nusselt number for different geometries increased versus increasing the Reynolds number. Observe that the elliptical fin shape yields the highest Nusselt number at all Reynolds numbers. Moreover, the elliptical pin fin ejects the highest heat transfer rate, which indicates the pin fin performance. Furthermore, skin friction has a significant function with variation in Reynolds number.

Analysis of Ventilated Disc Brake Using Ansys with Computer Aided Manufacturing

Safety is the most important parameter while developing a modern vehicle. A vehicle capable of high acceleration must decelerate quickly as well. Disc brakes are used in modern vehicles to reduce stopping distance. On application of brakes, the disc is subjected to thermal and structural stresses. The brakes fail to slow down or stop the vehicle if they become too hot. In this study, we attempt to understand the existing disc brake rotors in use in the automobile industry and improve on their design in order to enhance heat dissipation. The currently used disc brakes are studied to understand their design. This knowledge is further used to design a useful disc brake. The aim of this paper is to improve heat transfer rate by designing disc rotors and selecting suitable material.

Augmented artificially roughened solar air heaters

The use of baffles, fins, ribs, and grooves in the solar air heater (SAH) improves heat transfer (HT). Various efforts were made to improve heat transfer rates through duct using these components. As a result, significant pressure drop has also been observed due to these components. This article attempts to describe and conclude experimental investigations on the influence of ribs with a variety of designs on heat transfer (HT) and fluid flow (FF). It also outlines prior developed Nusselt number (Nur) and friction factor (fr) correlations. This comparative review was done to comprehend the findings of various experiments on SAHs with varying absorber surface roughness. This study aims to investigate the effects of artificial roughness on the friction and heat transfer properties of the duct.

Computational Analysis of Conventional and Helical Finned Shell and Tube Heat Exchanger Using ANSYS-CFD

The summary of the proposed work is to compare the rate of heat transfer, logarithmic mean temperature difference (LMTD) and effectiveness (ε) for a conventional shell and tube heat exchanger with and without helical finned surfaces on tube side of heat exchanger. It is shown that the inlet velocity of cold fluid at the tube side varies, while the inlet velocity of hot fluid at the shell side remains constant. The percentage variations of heat transfer rates with theoretical and simulation methods are compared. The geometry is modelled in ANSYS design modeler and analysis have been carried out in ANSYS-CFD. The inlet velocity of shell side hot fluid is varied in both types of heat exchangers. The proposed work is tested for two configurations of counter flow heat exchanger (conventional and helical finned surfaces) under different shell side inlet velocities of fluids. Helical finned tube heat exchanger with counter flow has a higher LMTD than a conventional counter flow heat exchanger. Variation in heat transfer rates and heat transfer coefficients were observed in heat exchanger influenced by shell side hot fluid velocity. The study shows that helical finned tube surfaces have improved heat transfer rates, LMTD, effectiveness (ε) and overall heat transfer coefficients compared to the conventional heat exchangers.

Heat transfer enhanced by angle-optimized fan-shaped porous medium in phase change thermal energy storage system at pore scale

High-thermal-conductivity porous medium can effectively improve the heat transfer rate of solid-liquid phase change in thermal energy storage system, enhancing the usage efficiency of renewable energy. In this paper, the fan-shaped porous medium was applied to accelerate heat transfer rate of phase change material in thermal energy storage, and the corresponding heat transfer performance affected by Rayleigh number, porosity and angle of porous medium during melting and solidification process was investigated. The results showed that the porous medium can reduce heat accumulation and improve heat transfer rate. Compared with the pure PCM, the complete melting time was shortened by 51.2% after inserting 150° porous medium with porosity of 0.5, when the Rayleigh number was 105. In addition, there was an optimal angle according to the melting rate and energy storage density. When the Rayleigh number was 5 × 105, the optimal angle of porous medium is 180°. Besides, the heat transfer effect was significantly improved by the porous medium with larger angle during solidification process.

Enhanced Water Nucleation and Growth Based on Microdroplet Mobility on Lubricant-Infused Surfaces.

Lubricant-infused surfaces (LISs) can promote stable dropwise condensation and improve heat transfer rates due to a low nucleation free-energy barrier and high droplet mobility. Recent studies showed that oil menisci surrounding condensate microdroplets form distinct oil-rich and oil-poor regions. These topographical differences in the oil surface cause water microdroplets to rigorously self-propel long distances, continuously redistributing the oil film and potentially refreshing the surface for re-nucleation. However, the dynamic interplay between oil film redistribution, microdroplet self-propulsion, and droplet nucleation and growth is not yet understood. Using high-speed microscopy, we reveal that during water condensation on LISs, the smallest visible droplets (diameter: ∼1 μm, qualitatively representing nucleation) predominantly emerge in oil-poor regions due to a lower nucleation free-energy barrier. Considering the significant heat transfer performance of microdroplets (<10 μm) and transient characteristic of microdroplet movement, we compare the apparent nucleation rate density and water collection rate for LISs with oils of different viscosities and a solid hydrophobic surface at a wide range of subcooling temperatures. Generally, the lowest lubricant viscosity leads to the highest nucleation rate density. We characterize the length and frequency of microdroplet movement and attribute the nucleation enhancement primarily to higher droplet mobility and surface refreshing frequency. Interestingly and unexpectedly, hydrophobic surfaces outperform high-viscosity LISs at high subcooling temperatures but are generally inferior to any of the tested LISs at low temperature differences. To explain the observed nonlinearity between LISs and the solid hydrophobic surface, we introduce two dominant regimes that influence the condensation efficiency: mobility-limited and coalescence-limited. We compare these regimes based on droplet growth rates and water collection rates on the different surfaces. Our findings advance the understanding of dynamic water-lubricant interactions and provide new design rationales for choosing surfaces for enhanced dropwise condensation and water collection efficiencies.

Characterisation of a plate heat exchanger chevron type with carbon-based nanofluids under pulsed condition

In industrial-thermal applications, pulsating flow along with carbon-based nanofluids is a well adopted active method, although not in plate heat exchangers (PHEs). The performance of a PHE with carbon-based nanofluids was experimentally evaluated by superimposing pulsating flow along with steady-state flow. The results demonstrated that the use of GNP-water, hybrid GNP/MWCNT-water, and MWCNT-water nanofluids with volume fractions ranging from 0.01% to 0.1% in a steady-state flow led to improved average heat-transfer rates of 1.34, 1.27, and 1.25, respectively. Furthermore, implementation of pulsating flow enhanced the average heat-transfer rate, in comparison to that of the steady-state flow in the same nanofluids, in the range of 10.9%–28.2%, 9%–25.4%, and 7.1%–14.8%, respectively. Pulsating flow in nanofluids improved heat-transfer rate more than it did in pure water owing to the enhancement of the Brownian motion of the suspended carbon-based nanoparticles. In the considered volume fractions from 0.01% to 0.1%, the pulsating flow condition increased the pressure drop by a factor of 1.48, 1.49, and 1.62 for the MWCNT-water, hybrid GNP/MWCNT-water, and GNP-water nanofluids, respectively, in comparison to pure water. The experimental results indicated that the pulsating flow had a more profound influence on the improvement of heat-transfer rate and pressure drop in the case of GNP-based nanofluid than in the others. This could be attributed to the unique platelet shape of the GNP nanoparticles and consequently the higher Brownian motion. The improvement in the heat-transfer rate, obtained through implementation of the pulsating flow condition, outweighed the cost of increase in pressure drop in all the cases. Among the nanofluids considered, the hybrid GNP/MWCNT-water nanofluid exhibited the best overall performance of 1.2.

Effect of Nanofluids on the Enhancement of Boiling Heat Transfer: A Review

Boiling heat transfer can play a vital role in the two-phase flow applications. The analysis of the boiling hat transfer enhancement is of importance in such applications and the enhancement can be mostly conducted by using various active and passive techniques. One type of passive techniques is the enhancement of heat transfer by nanofluids. This article presents an extensive review on the effect of different nanofluids on the enhancement of heat transfer coefficient (HTC) and critical heat flux (CHF) for both pool as well as flow boiling. Nanoparticles addition to a working fluid is done arbitrarily to improve the thermophysical properties which in turn improves heat transfer rate. Numerous works have been done in the studies on nanofluid boiling. Among various nanoparticles, the most frequently used nanoparticles are Al2O3 and TiO2. In the case of binary nanoparticles, the most commonly used combination is Al2O3 and TiO2. After reviewing the relevant literatures, it is found that for pool boiling, the maximum HTC is increased to 138% for TiO2 nanoparticles and the maximum CHF is increased to 274.2% for MWCNTs. Conversely, in flow boiling the maximum HTC is increased to 126% for ZnO nanoparticles and the maximum CHF increased to as 100% for GO nanoparticles. In addition, when two or more nanoparticles in succession or binary nanofluids are used the CHF in pool boiling increased up to 100% for Al2O3 and TiO2 as well as the CHF in flow boiling increased up to 100% for Al2O3, ZnO, and Diamond. Though the information of the coefficient of heat transfer and the critical heat flux varied for different nanofluids and vary from experiment to experiment for each of the nanofluids. This variation happens because the coefficient of heat transfer and the critical heat flux in boiling is dependent upon several factors.

Experimental investigation on influence of metal based additives on performance, combustion and emission parameters of diesel engine

A biodiesel substitute for regular diesel is widely seen as having greater social advantages, such as decreasing greenhouse gas emissions and sustaining rural agriculture economies, than conventional diesel fuel. As a natural fuel, biodiesel has a variety of feedstocks such as vegetable oils and animal fats. A biodegradable material made from fatty acid esters such as methyl and ethyl. Oils such as palm oil, soya bean oil, sunflower oil, etc., produce the majority of today's biodiesel fuels due to their eco-friendliness and sustainability.. Transesterification of waste chicken fat oil to produce biodiesel in a 1:1 ratio, followed by testing the performance and emission characteristics of a C.I engine running on the biodiesel. There will be three distinct proportions of B10, B20, and B30 blends of biodiesel with diesel and 100 ppm of metal oxide (sio and nio) additive in order to improve fuel ignition and cold starting. When using Conventional Diesel at 180 bar, performance measures such as Brake Power (BP), Brake Specific Fuel Consumption (BSFC), and NOx, HC, and CO emission characteristics of the stated engine at 1500 rpm are analysed. The B20 Biofuel sample was shown to be the most efficient and economical compared to the other two samples, B10 and B30. Nickle oxide and silicon oxide nanoparticles in the B20 blend are particularly interesting due to their features such as improved heat transfer rate.

A Numerical Simulation Study to Improve Heat Transfer Rate in a Double Pipe Heat Exchanger using Different ways.

In this work the thermo hydraulic performance of double pipe heat exchanger made of stainless-steel with inner and outer diameters are (11.43 and 16.83cm) respectively, 0.305cm thickness and150cm length, studied numerically by using Solid Works 2016 package. It is used to the purpose of preheat heavy fuel oil flow in the outer pipe by hot air flow inside the inner one. Helical tape with different pitches (11, 14, and 17) cm the inner side of the inner tube and helical fin with different fin spaces (10, 20, and 30) cm over the inner tube are used as an enhancement heat transfer device. The study was conducted with specific identifiers, Reynold’s number (Re) values are (31668, 47361, 63008, 78589) for air side (inner tube), oil inlet temperature is (313) K and flow with rate of oil (0.1 and 0.06 kg/s). The results were first verified by using both the inner helical tape and outer helical fin separately and comparing the results of them with the plain tube, and then combining each of the helical tape and helical fin together and indicating the improvement in heat transfer rate, the result show that the maximum heat transfer is (4559.726 W) obtained by merged the helical tape with smaller pitch (11 cm) and helical fin with low fin pitch (10 cm) at oil flow rate (0.1 kg/s) as compared with (2052.385W) for plain tube, the maximum enhancement percentage in heat transfer rate and overall heat transfer coefficient were is (122.167 % and 142.941%) at the same conditions. The maximum enhancement in Nusselt number (Nu) and convection heat transfer coefficient were (224.572 % and 129.523 % W/m2. K) respectively were achieved by using helical tape with pitch (11 cm). At higher Reynolds number, the higher-pressure drop for air side is (7437.8 pa) obtained when using minimum pitch for helical tape and it is (1086.26 pa) for oil side by using helical fin with pitch (10 cm).

Application of Cylindrical Fin to Improve Heat Transfer Rate in Micro Heat Exchangers Containing Nanofluid under Magnetic Field

In this study, the convective mode heat transfer phenomena of bi-phase elasticoviscous (non-Newtonian) nanofluid is quantified by forcefully flowing it through a specially designed microchannel test section. The test section, which is rectangularly cross-sectioned and annexed internally with cylindrical needle ribs is numerically investigated by considering the walls to be maintained at a constant temperature, and to be susceptible to a magnetizing force field. The governing system-state equations are numerically deciphered using control volume procedure and SIMPLEC algorithm. With the Reynolds number (Re) varying in the turbulent range from 3000 to 11,000, the system-state equations are solved using the Eulerian–Eulerian monofluid Two-Phase Model (TPM). For the purpose of achieving an apt geometry based on the best thermo-hydraulic behavior, an optimization study must be mandatory. The geometry of the cylindrical rib consists of h (10 × 10−3, 15 × 10−3, 20 × 10−3), p (1.0, 1.5), and d (8 × 10−3, 10 × 10−3, 12 × 10−3), which, respectively, defines the height, pitch, and diameter of the obstacles, with the dimensions placed within the braces being quantified in mm. The results demonstrated that the magnetic field leads to an enhanced amount of average Nusselt number (Nuav) in contrast with the occurrence at B = 0.0. This is due to the that the magnetic field pushes nanoparticles towards the bottom wall. It was found that B = 0.5 T has the maximum heat transfer compared with the other magnetic fields. The channel with h = 15 μm height leads to the maximum value of Nuav at all studied Re for constant values of d and h. The channel with p = 1.5 μm results in the maximum value of Nuav at all studied Re for constant values of d and h. The microchannel with d = 8 μm, p = 1.5 μm, and h = 15 μm in the presence of the magnetic field with B = 0.5 T is the best geometry in the present work.

Time-dependent Blasius–Rayleigh–Stokes flow conveying hybrid nanofluid and heat transfer induced by non-Fourier heat flux and transitive magnetic field

Increasing behavior of thermal performance and improvement of heat transfer rate with the growing consequence of hybrid nanofluid is used in the advantages of cooling and heating processes. The current paper addresses to see the impact of non-Fourier heat flux on Blasius–Rayleigh–Stokes flow conveying the hybrid nanofluid through a plate by comprising the significance of the magnetic effect, nothing is known on the significance of magnetic (Fe3O4) and non-magnetic (Al2O3) hybrid nanoparticles. Appropriate variables are utilized to transfigure nonlinear partial differential equations into a nonlinear system of ordinary differential equations. Bvp4c approach is implemented to get the numerical solution of the converted system of ordinary differential equations. The results are interpreted through graphs to inspect the flow behavior of pertaining parameters involved in the problem. It is examined that the temperature enhances due to hybrid nanoparticles while the velocity reduces. In addition, the acute angle accelerates the velocity but decelerates the temperature. Moreover, to check the efficiency and reliability of the proposed technique, the outcomes of the considered problem are compared with the previously available outcomes and found to be in a favorable agreement.

Vapor stem bubbles dominate heat transfer enhancement in extremely confined boiling

Boiling has long been sought as the heat dissipation mechanism for a wide variety of compact thermal management applications owing to low-resistance heat transport, high heat flux limits, and surface isothermalization. This work aims to elucidate the thermofluidic transport mechanisms of boiling in extremely confined gaps through experimental measure of the temporal evolution of heat fluxes and surface temperatures during deionized water boiling, as well as high-speed visualization of bubble formation. The flow visualizations reveal small residual pockets of vapor, termed ‘stem bubbles’ herein, that remain on the boiling surface through a pinch-off process where vapor escapes through the edges of the confined heated region. These stem bubbles act as seeds for vapor growth in the next phase of the boiling process. These bubbles dictate the boiling performance for extremely confined boiling as defined based on a dimensionless ratio of the gap spacing to capillary length (Bo≤ 0.35 - 0.5). This conclusion is supported by the enhanced thermal response of the surface compared to nucleate boiling. Because activation of nucleation sites is not required for stem bubble boiling, phase change occurs at a reduced surface superheat at a given heat flux compared to nucleate boiling. Criteria for the dimensionless confinement gap spacing are identified to harness this improved heat transfer rate of the stem bubble boiling regime. This new understanding of boiling in extremely confined gaps offers a new direction to design compact two-phase thermal management solutions through using the unique enhancements provided by the vapor stem bubble boiling regime.

Bioconvection transport of magnetized Walter's B nanofluid across a cylindrical disk with nonlinear radiative heat transfer

Nanotechnology plays a crucial role in the main innovation development of the modern age in the latest technology. In recent times, researchers are concentrated to build up various algorithms to increase their heat transfer rate. One of the approaches that have conquered this deficiency is to significantly raise the thermal properties of regular fluids by manifestation of nanoparticles in host fluids. In this article, a numerical study is developed to investigate the bio convective transport of Walter's B nanofluid past a cylindrical disk in the presence of thermophoretic and Brownian diffusions. Additionally, non-linear thermal radiation, variable thermal conductivity and motile microorganisms are also considered. The Buongiorno model is used to explore the nanofluid features with motile microorganisms. The constituted normalized system of modeled flow equations is condensed into dimensionless system of differential form by adopting appropriate similarity variables. The ordinary systems are elucidated through bvp4c technique in MATLAB software. Characteristics of flow parameters against velocity field, temperature distribution, volumetric concentration of species and microorganism's profile are discussed. From the results we observed that velocity field is reduced for larger magnetic parameter. It is noticed that developing values of mixed convection parameter raises the velocity field. It is analyzed that temperature distribution of Walter's B fluid upsurge for variable thermal conductivity parameter. Temperature field intensifies for thermal Biot number. It is perceived that solutal field of species diminishes for larger Brownian motion parameter. The microorganism field is found to decay with Peclet and bioconvective Lewis numbers. The current proposed model is more useful in the field of engineering. The improvement in heat transfer rate is current issue in the world. Nanofluids have high thermal efficiency therefore such fluids are more useful to improve the heat transfer rate.

Experimental investigation of orientation and geometry effect on additive manufactured aluminium LED heat sinks under natural convection

The continued adaptation of light-emitting diodes (LEDs) presents challenges for heat dissipation. LEDs are considered to be high power density devices, as such effective thermal management is imperative for extended usage. In this study, new design considerations such as adapting middle fin, fin height gradient towards the centre of the heat sink, along with fin perforations and a spiral cut out of the central pillar have been incorporated into heat sinks to assist convection. The heat sinks were manufactured out of aluminium alloy (AlSi10Mg) using the selective laser melting (SLM) method. The effects of orientation on the heat transfer of different heat sink geometries were experimentally studied under natural convection conditions. The performance of six different geometries with 6, 8 and 10 long fins (6LF, 8LF and 10LF) with and without middle fins were evaluated under three different heat flux conditions (471.57 W/m2, 943.14 W/m2 and 1257.52 W/m2) for 10 different orientation angles (0°–90°). The higher fin density heat sinks are found to have lower orientation dependency. The convective fluid flow of the higher fin density geometries is significantly hindered by the overlapping of thermal boundary layers. The increase in the Rayleigh number has the most significant effect on the 6LF heat sink. The overall Nusselt number correlations for the 6LF, 8LF and 10LF heat sinks with short fins are 0.2748Ra0.3425,0.3868Ra0.2747 and 0.3317Ra0.2708, respectively. Removing short fins improved heat transfer rate for all heat sinks.