Investigation Of Natural Convection Flow Research Articles

Numerical investigation of natural convection flow inside a square enclosure filled with different nanofluids by using two-phase Eulerian–Eulerian model: A new correlation for Nusselt number

Numerical investigation of natural convection flow inside a square enclosure filled with different nanofluids by using two-phase Eulerian–Eulerian model: A new correlation for Nusselt number

Experimental investigation of natural convection flow in a laterally heated vertical cylindrical enclosure

Vertical cylindrical enclosures are used in the crystal growth industry as crystal growth reactors. Gallium nitride crystals are grown in ammonothermal growth reactors that requires temperatures in the range of 600–1000 K (620–1340 °F) and pressures in the range of 1000–6000 bar (14,504–87,022 psi). The process conditions make any experimental measurements difficult, in particular, flow pattern visualization and velocity measurements. A geometrically similar transparent reactor and similar fluid dynamic conditions for crystal growth were used in the process of experimental observation and measurement of the flow. Boundary and fluid temperatures along with velocity vectors were recorded. The flow proved to be oscillating in nature with steady and uniform time-averaged patterns. Fluid temperatures showed a higher standard deviation in the mixing region suggesting that the fluctuations are stronger at this location. Flow patterns and fluid temperatures indicated that the heat transfer between the two sections is driven by conduction and advection.

Numerical Investigation of Natural Convection Flow in a Hexagonal Enclosure Having Vertical Fin

Numerical study of natural convection flow in a hexagonal enclosure with a single vertical fin attached to its heated bottom wall has been carried out. Finite element method based Galerkin weighted residual technique is used to solve the governing equation. The horizontal walls of the enclosure are kept at constant high temperature while the inclined walls are kept at constant cold temperature. A vertical heated fin is attached to the hot bottom wall with a length at a position from the left surface having thickness . The Prandlt number for the flow inside the enclosure is 0.71. The results of the problem are presented in graphical and tabular forms and discussed. The fin efficiency and temperature distribution were examined. The numerical results indicate the strong influence of the mentioned parameters on the flow structure and heat transfer as well as temperature. A set of graphical results are presented in terms of streamlines, isotherms contour, temperature profiles, velocity profiles, local Nusselt number and average Nusselt number. The obtained results indicated that the heat transfer rate increases with the increase of Rayleigh number in a hexagonal enclosure. The results are validated comparing with the published works.

Visualization and investigation of natural convection flow of CO2 in aqueous and oleic systems

Optimal storage of carbon dioxide (CO2) in aquifers requires dissolution in the aqueous phase. Nevertheless, transfer of CO2 from the gas phase to the aqueous phase would be slow if it were only driven by diffusion. Dissolution of CO2 in water forms a mixture that is denser than the original water or brine. This causes a local density increase, which induces natural convection currents accelerating the rate of CO2 dissolution. The same mechanism also applies to carbon dioxide enhanced oil recovery. This study investigates a set of high pressure visual experiments, based on the Schlieren technique, in which we observe the effect of gravity-induced fingers when sub- and super-critical CO2 at in situ pressures and temperatures is brought above the liquid, i.e., water, brine or oil. A short but comprehensive description of the Schlieren set-up and the transparent pressure cell is presented. The Schlieren set-up is capable of visualizing instabilities in natural convection flows; a drawback is that it can only be practically applied in bulk flow, i.e., in the absence of a porous medium. All the same many features that occur in a porous medium also occur in bulk, e.g., unstable gravity fingering. The experiments show that natural convection currents are weakest in highly concentrated brine (25 w/w% NaCl solution) and strongest in oil, due to the higher and lower density contrasts respectively. Therefore, the set-up can screen aqueous salt solutions or oil for the relative importance of natural convection flows. The Schlieren pattern consists of a dark region near the equator and a lighter region below it. The dark region indicates a region where the refractive index increases downward, either due to the presence of a gas liquid interface, or due to the thin diffusion layer. The experiments demonstrate the initiation and development of the gravity induced fingers.

Experimental and numerical estimation of slip coefficient in a partially porous cavity

The paper reported an experimental investigation of natural convection flow in a two-dimensional cavity partially filled with a vertical porous layer. The porous layer consisted of circular cylindrical rods installed horizontally along the left wall of the cavity in a regular array. The porosity and permeability were kept constant but the Rayleigh number varied to simulate different flow conditions. The range of Rayleigh number was from 2.806×104 to 1.053×106. A saline solution having a refractive index similar to that rods and cavity was selected as the working fluid. Particle Image Velocimetry was used to conduct detailed velocity measurement in the cavity, in particular the velocity in the porous and at the porous/fluid interface. From the measurement, the value of slip velocity at the interface was determined. It was found that the slip velocity made dimensionlessly by the shear rate at the interface was independent of interfacial height in mostly flow region, and also the slip coefficient. As a result, an average slip coefficient, defined as a mean value of the coefficient along the direction of interfacial height, was presented in a range of 0.307 through 2.53 for the experiment.

Natural convection along a wavy vertical plate to non-Newtonian fluids

A numerical investigation of natural convection flow along irregular vertical surfaces in non-Newtonian fluids is reported. A wavy vertical surface is used as an example to show the heat transfer mechanism near such surfaces. The results demonstrate that with an increase of flow index, the axial velocity increases, but the velocity boundary layer becomes thinner. The difference between the velocity in the crests and the troughs is indiscernible. The boundary layer around nodes is getting thicker compared to that of the crests and the troughs. When the natural convection boundary layer grows thick, the amplitude of the local Nusselt number gradually decreases. The effects of Prandtl number, flow index and surface amplitude in non-Newtonian fluids are also discussed in detail.

A study of natural convection in non-Newtonian fluids induced by a vertical wavy surface

A numerical investigation of natural convection flow along irregular vertical surfaces is reported. A transformation method is applied to the problem of natural convection under the assumption of a large Grashof number. A vertical wavy surface is used as an example to demonstrate the advantages of the transformation method, and to show the heat transfer mechanism near such surfaces. Surface non-uniformities on the boundary layer flow induced by a constant was temperature, semi-infinite surface are investigated. Also the effects of Prandtl number, flow index, and surface amplitude in Non-Newtonian fluids are discussed. When possible, the comparison of the numerical results shows a good agreement. The amplitude is proportional to the amplitude of a wavy surface. The results demonstrate that the local heat flux along a wavy surface is smaller than that of a flat surface. The frequency of the wavy surface is half that of the local heat transfer rate. The amplitude of the local Nusselt number gradually decreases downstream where the natural convection boundary layer grows thick.

Natural convection liquid immersion cooling of a heat source flush mounted on a conducting substrate in a square enclosure

A numerical investigation of natural convection flow and heat transfer due to a rectangular heat source flush mounted on a substrate in a liquid-filled square enclosure was conducted. A finite volume model that accounts for the coupled conduction within the substrate and heat source and the natural convection in the liquid was utilized for a wide range of Rayleigh and Prandtl numbers. Little reduction in maximum temperatures was observed when substrate to fluid and component to fluid thermal conductivity ratios were increased beyond 10 and 25, respectively. Computed temperatures using the present model compared favorably with an existing experimental study.

Natural convection arising from a heat generating substrate-mounted protrusion in a liquid-filled two-dimensional enclosure

An investigation of natural convection flow and heat transfer arising from a substrate-mounted protruding heat source immersed in a liquid-filled square enclosure is reported. The model considers heat transfer within the protrusion and substrate and the coupled natural convection in the fluid. Numerical predictions are obtained for a wide range of appropriate Rayleigh and Prandtl numbers and substrate to fluid thermal conductivity ratios that may be encountered in liquid-immersion cooling of electronic components. For many situations of interest prescribing simplistic heat transfer conditions at the solid surfaces is found inappropriate. Increasing the Rayleigh number beyond 106 and the substrate thermal conductivity beyond 100 times that of the liquid produces only a marginal decrease in the maximum temperatures. Computed protrusion surface temperatures compare favorably with available experimental results for a similar configuration.

An experimental investigation of natural convection flow on an inclined surface

A thermocouple and two hot-film anemometer probes in the form of an “inverted V” were used to investigate the boundary region flow formed over an inclined surface dissipating a uniform heat flux. Temperature and the longitudinal and transverse components of velocity were measured. A single longitudinal vortex system arises. It causes a spanwise variation of the temperature and velocity fields, which results in a spanwise variation of heat transfer. The spanwise mean-flow variation, or vortex system, arises first downstream for angles greater than 11°. Our local measurements permit detailed comparison with well-established disturbance mechanisms in vertical flows. Frequency filtering of periodic disturbances is again found. The beginning of transition is postulated in terms of disturbance magnitude. The location is found to depend on the distance from the leading edge, in addition to the Grashof number, in the same way as in vertical flows.