Enhancement Of Natural Convection Heat Transfer Research Articles

Investigation of a natural convection heat transfer enhancement of a different shaped pin fin heat sink for different vertical fin spacing

Investigation of a natural convection heat transfer enhancement of a different shaped pin fin heat sink for different vertical fin spacing

Turbulent natural convection heat transfer enhancement of nanofluids

This study investigates the enhancement of heat transfer for the fluid with the addition of nano-particles in a two-dimensional rectangular cavity. Thermo-physical properties of such fluids and volume fraction of nano-particles in those fluids and its heat transfer characteristics are studied. ANSYS Fluent code is utilized for this purpose. Validation of the computational model has been carried out against the benchmark data available from the literature. A heat transfer correlation in terms of the Nusselt number (Nu) average as a function of Grashoff number and volume fraction of the nano-particles in the base fluid for the turbulent flow is developed and formulated in this study.

Natural convection heat transfer enhancement using bubble injection between vertical parallel plates

We experimentally study natural convection heat transfer enhancement using bubble injection between a vertical heated plate and a flow guiding plate in water. While heat transfer is more than tripled with bubble injection, the introduction of the flow guiding plate parallel to the heated plate further increases heat transfer by up to 12% despite attenuating the wall-normal liquid fluctuating velocity. We attribute further heat transfer enhancement to increased wall-parallel liquid velocity driven by bubbles rising at high speeds. We also perform temperature calculations incorporating experimentally measured mean liquid velocities, which permit a quantitative evaluation of the wall-parallel mean liquid velocity and wall-normal liquid fluctuating velocity contributions to heat transfer. The calculations show that the fractional contribution of wall-parallel mean liquid velocity with bubble injection to heat transfer is high, especially in the upstream region of the heated section, and the presence of the flow guiding plate near the heated wall increases the contribution by up to 30% compared with the case without the plate.

Experimental study of natural convection heat transfer enhancement in a square cavity filled with nanofluid using magnetic effects

Researchers in heat transfer are paying close attention to nanofluids because of their potential as high-performance thermal transport media. In light of natural convection's enormous significance, the addition of nanoparticles significantly enhances the thermophysical properties of the nanofluids compared to the base fluid. In this study, experimental work was used to evaluate the influence of CuO nanoparticles on natural convection with magnetohydrodynamic (MHD) flow in a square cavity. The cavity’s left and right vertical walls were maintained at different temperatures, and the top and bottom walls of the cavity were insulated. This experimental study applied a horizontal magnetic field with uniform strength. Results were obtained for a variety of Hartmann numbers ranging from 0–300, Rayleigh numbers going from 2.76E+8 to 6.89E+8, and solid volume fractions ranging from 0 to 1.5%Vol. Results showed that the heat transfer coefficient and Nusselt number values decreased with the increase in the values of the Hartmann number, except for the heat transfer coefficients at Ha=100 and 150 are larger than the heat transfer coefficients at Ha= 0. The maximum heat transfer coefficient and Nusselt number enhancement were 40.8% and 28.5%, respectively, at a 1.5% volume concentration of CuO-water nanofluid, Ra= 6.7E+8 and Ha=100 compared with pure fluid (water) at Ha=0.

Experimental study of natural convection heat transfer enhancement in a square cavity filled with nanofluid using magnetic effects

Experimental study of natural convection heat transfer enhancement in a square cavity filled with nanofluid using magnetic effects

Geometry contributions to natural convection heat transfer enhancement by the chimney effect

Natural convection heat transfer enhancement continues to be an evolving problem in the design of passive safety systems in nuclear engineering. Increasing heat rejection rates guarantees safety and higher heat duty. This study numerically investigated the influence of the geometry of an adiabatic extension appended downstream of a vertical heated cylinder. Four geometries comprising straight, diffuse, hyperboloid, and compound adiabatic extensions were studied. Nusselt number ratios, temperature distribution ratios, and mass flow rates were presented. Results showed that the compound extension geometry exuded high heat transfer enhancement capabilities by the chimney effect, and reduced wall temperature by up to 16% for the range of parameters studied. These findings are presented as a contribution to the design improvements of air-cooled passive systems, especially in advanced nuclear reactors.

Natural Convection Heat Transfer Enhancement Using Bubble Injection between Vertical Parallel Plates

Natural Convection Heat Transfer Enhancement Using Bubble Injection between Vertical Parallel Plates

Natural Convection Heat Transfer Enhancement of Circular Obstacle within Square Enclosure

Natural Convection Heat Transfer Enhancement of Circular Obstacle within Square Enclosure

Numerical simulation and optimization of natural convection heat transfer enhancement in solar collectors using electrohydrodynamic conduction pump

This study investigated the application of electrohydrodynamic conduction pumping for heat transfer enhancement between two 45-degree diagonal plates containing a dielectric fluid, while there is a constant volume heat density inside the inner wall. A numerical simulation was performed to determine the optimum dimensional configuration of electrodes and to clarify how the heat transfer in the fluid between the electrodes is influenced by the electric field magnitude and volume heat density. At low applied voltages, a small flow vortex near the electrodes traps the heat and creates an obstacle blocking the natural convection, which leads to decreasing the efficiency of heat transfer. When the applied voltage is increased to 16kV, the heat trap begins to separate from the wall, which decreases the wall temperature and leads to a faster heat transfer. Therefore, the heat transfer efficiency suddenly increases. In comparison with the case without the electric field, the use of EHD technique can increase the efficiency of heat transfer through the operating fluid almost twice. This configuration of the electrohydrodynamic pump can be used for increasing the efficiency of solar collectors.

Ultrasounds Used as Promoters of Heat-Transfer Enhancement of Natural Convection in Dielectric Fluids for the Thermal Control of Electronic Equipment

We present an experimental investigation of the effect of ultrasound application to increase the heat-transfer coefficient for natural convection of a dielectric fluid. An experimental analysis is carried out to estimate the increase of the convective heat-transfer coefficient between an electronic board and a refrigerant fluid, the Fluorinert Electronic Fluid FC-72. For this purpose, an experimental apparatus composed of an electronic board, its electronic control circuit, and data acquisition systems have been designed and implemented. The data collected appear to confirm in some situations of practical interest the enhancement effect of the convective heat-transfer coefficient in connection with the use of ultrasound. The most favorable condition was observed with the fluid in quite low subcooled conditions.

Natural convection heat transfer enhancement of different nanofluids by adding dimple fins on a vertical channel wall

Abstract In this numerical study, natural flow and heat transfer of nanofluids with Al2O3, TiO2, Cu and CNT nanoparticles in a vertical channel with dimpled fins at Rayleigh number (Ra) of Ra = 3.25 × 107 to Ra = 1 × 108 are investigated by using the finite volume method. The obtained results revealed that, using CNT in volume fractions of 2% and 4% leads to significant heat transfer and at φ = 6%, using TiO2 nanoparticles has a great effect on Nu number enhancement. Also, using solid nanoparticles in base fluid causes more uniform heat transfer distribution, especially in areas close to heated surface and by adding more volume fraction in base fluid, temperature level reduces. In general, according to temperature contours, reduction of wall temperature depends on the increase of Ra and volume fraction and the type of solid nanoparticles.

Numerical investigation of heat transfer enhancement and entropy generation of natural convection in a cavity containing nano liquid-metal fluid

Investigation of natural convection heat transfer enhancement and entropy generation of nano liquid-metal fluid in a differentially heated cavity is carried out for three types of nanofluids, copper-Ga (CuGa), diamond-Ga (Diam-Ga) and carbon nanotubes-Ga (CNTGa), in which Grashof number varies from 104 to 106 and nanoparticles volume fraction from 0.01 to 0.15. The nanofluid flow is simulated by the two-phase mixture model. The studied results show that the convective intensity, heat transfer and local entropy generation increase with the increase of Grashof number. The average Nusselt number of nano liquid-metal fluid increases monotonically with increasing of Grashof number and nanoparticles volume fraction, and the total entropy generation also increases monotonically. The heat transfer performance of CNT-Ga is the highest, that of Diam-Ga is the second and the CuGa is the lowest.

Natural convection heat transfer enhancement in new designs of plate-fin based heat sinks

Experimental investigation was conducted to measure the convective heat transfer coefficient and thermal performance of plate fins and plate cubic pin-fins heat sinks, under natural convection regime. The investigation was conducted for Rayleigh number from 8 × 106 to 9.5 × 106 and input heat of 10 W to 120 W. The fin spacing and fin numbers are varied between 5–12 mm and 5–9, respectively. The results demonstrated that plate cubic pin-fins heat sinks have lower thermal resistance and higher heat transfer, compared to plate fins heat sinks. Heat transfer enhancement of new-designed heat sinks is about 10–41.6% higher, compared to normal pin-fins. Increasing fin spaces in all types of studied heat sinks cause lower thermal resistance. But, increasing fin numbers does not cause better heat transfer. The best heat sink design was a plate cubic pin–fin heat sink with 7 fins and 8.5 mm fin spacing. Finally, empirical equations have been developed to correlate the average Nusselt number as a function of number of fin plates, fin spacing to height ratio as well as Rayleigh (and consequently Grashof) number.

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.

CFD Analysis of Steady Laminar Natural Convection Heat Transfer from a Pin Finned Isothermal Vertical Plate

AbstractHeat transfer behavior with both the conductive and nonconductive fins have been analyzed by examining variations of the local and average Nusselt numbers in two‐dimensional flow. The main objective of this study is to quantify and compare the natural convection heat transfer enhancement of fin array with different fin aspect ratio and at different angles of inclination. It is found that significant heat transfer augmentation is obtained for both conductive and nonconductive fins. For conductive fins 20% higher augmentation factor is obtained when the fin aspect ratio is 6, angle of inclination is 60° and the pitch‐to‐length ratio is 0.2. For nonconductive fins, 10% higher augmentation factor is obtained when fin aspect ratio is 8, angle of inclination is 45° and pitch‐to‐length ratio at 0.5. A general correlation has been developed to predict the average Nusselt number and heat transfer augmentation factor for conductive and nonconductive fin arrays as a function of different fin configurations.

Simulation of Natural Convection Heat Transfer Enhancement by Nanoparticles in an Open-Enclosure Using Lattice Boltzmann Method

A numerical analysis is performed to investigate the laminar, free convection flow in an Open Enclosure Using Lattice Boltzmann Method (LBM) in the presence of Carbon nanotube and Cu nanoparticles. The problem is studied for different volume fractions of nanoparticles, and aspect ratio of the cavity for various Rayligh numbers. The volume fraction of added nanoparticles to water (as base fluid) is lower than 1% to make dilute suspensions. The study presents a numerical treatment based on LBM to model convection heat transfer of Carbon nanotube based nanofluids. Results show that adding a low value of Carbon nanotube to the base fluid led to significant enhancement of convection rate. Results show that adding nanoparticles to the base fluid enhances the rate of natural convection in a cavity. Make a comparison between Carbon nanotube and Cu-nanoparticles shows that the Carbon nanotube-nano- particle has better performance to enhance convection rate at comparison with Cu- nanoparticles.

Natural convection heat transfer enhancement using nanofluid and time-variant temperature on the square enclosure with diagonally constructed twin adiabatic blocks

A finite difference based two dimensional numerical investigation of laminar natural convection inside the closed square enclosure filled with copper–water nanofluid and two diagonally placed adiabatic blocks is presented by vorticity–stream function approach. The left and right walls are assumed as hot and the top wall is kept as cold. The temperature of bottom wall varies sinusoidal over time. The variables considered in the present study are Rayleigh number (104 to 106), volumetric fraction of copper particles (0 < ϕ < 4%), amplitude (0 < a < 0.5) and the period (0.001 < τ < 0.8). The periodic results of fluid flow are elucidated with Streamlines, Isotherms and Nusselt number. The combined effect of nanofluid and time-variant temperature at the bottom wall suppresses the hydrodynamic blockage effect of solid blocks and enhanced the convective heat transfer. The time-averaged local Nu is increased by a maximum of 11% when comparing with pure fluid.

An experimental investigation of natural convection heat transfer enhancement from perforated rectangular fins array at different inclinations

The main objective of this experimental study is to quantify and compare the natural convection heat transfer enhancement of perforated fin array with different perforation diameter (4–12mm) and at different angles of inclination (0–90°). 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 increase in the heat transfer coefficient was achieved with perforated fins of 12mm perforation diameter at the angle of orientation 45°, which shows about 32% enhanced heat transfer coefficient as opposed to the solid fin array with nearly 30% saving in material by mass.

Effects of properties variations of Al2O3–EG–water nanofluid on natural convection heat transfer in a two-dimensional enclosure: Enhancement or deterioration?

Heat transfer enhancement or deterioration of variable properties Al2O3–EG–water nanofluid natural convection in a differentially heated rectangular cavity has been investigated numerically. A finite volume approach has been utilized to solve the governing equations for a Newtonian fluid. The influences of the pertinent parameters such as Rayleigh number, Ra, in the range of 103–107 and nanoparticles volume fraction from 0 to 0.04 have been studied. The results verified by making overall comparison with some existing experimental results have shown that for Ra = 103, for which conduction heat transfer is dominant, the average Nusselt number increases as nanoparticles volume fraction increases, but contradictory with the constant properties cases it decreases for higher Ra values. This reduction, which is associated with the increased viscosity, is more severe at Ra = 104 and the least deterioration in heat transfer occurs for Ra = 107. This is due to the fact that the Brownian motion enhances as Ra increases; thus at Ra = 107 the improved conductivity becomes more important than viscosity enhancement. To clarify the contradictory reports existing in the literature on the natural convection heat transfer enhancement or deterioration of nanofluids, a scale analysis performed showed that unlike methods of evaluating the base fluid Ra have led to such differences.

Natural Convection Heat Transfer Enhancement in a Differentially Heated Parallelogrammic Enclosure Filled With Copper-Water Nanofluid

Laminar natural convection of a nanofluid consists of water and copper in a differentially heated parallelogrammic enclosure has been studied numerically using the finite volume method (FVM). Governing equations are solved over a wide range of Rayleigh numbers (104 ≤ Ra ≤ 106), skew angles (−60 deg ≤ Φ ≤ +60 deg), aspect ratios (0.5 ≤ AR ≤ 4), and solid volume fractions (0 ≤ φ ≤ 0.2). Effects of all these parameters on flow and thermal fields are presented in form of streamline, isotherm contours and average Nusselt number. It is shown that the heat transfer rate increases remarkably by the addition of copper-water nanofluid and the shape of the convection vortices is sensitive to the skew angle variation.