Turbulent Free Convection Heat Transfer Research Articles

The Study of the Effects of Radiation And Blowing from the Wall of a Vertical Channel on the Turbulent Free Convection Heat Transfer

This article investigates the effects of radiation and blowing from a wall on a turbulent heat transfer in vertical channels with asymmetrical heating. The equations involved were numerically solved with three turbulent models including Spalart Allmaras, R-N-G k-e with Standard Wall Function wall nearby model, R-N-G k-e with Enhanced Wall Treatment wall nearby model and Ray Tracing radiation techniques. The results were compares with experimental data and appropriate methods were selected for turbulent modeling. The problem of Rayleigh number, Reynolds, radiation parameters and Prandtl were solved and the effects of these parameters on the flow lines, lines of constant temperature, radiation, convection, heat transfer caused by blowing and the total heat transfer were determined.

Prediction of Local Heat Transfer in a Vertical Cavity Using Artificial Neutral Networks

A time-averaging technique was developed to measure the unsteady and turbulent free convection heat transfer in a tall vertical enclosure using a Mach–Zehnder interferometer. The method used a combination of a digital high speed camera and an interferometer to obtain the local time-averaged heat flux in the cavity. The measured values were used to train an artificial neural network (ANN) algorithm to predict the local heat transfer. The time-averaged local Nusselt number is needed to study local phenomena, e.g., condensation in windows. Optical heat transfer measurements were made in a differentially heated vertical cavity with isothermal walls. The cavity widths were W=12.7 mm, 32.3 mm, 40 mm, and 56.2 mm. The corresponding Rayleigh numbers were about 3×103, 5×104, 1×105, and 2.7×105, respectively, and the enclosure aspect ratio (H/W) ranged from A=18 to 76. The test fluid was air and the temperature differential was about 15 K for all measurements. ALYUDA NEUROINTELLIGENCE (version 2.2) was used to generate solutions for the time-averaged local Nusselt number in the cavity based on the experimental data. Feed-forward architecture and training by the Levenberg–Marquardt algorithm were adopted. The ANN was designed to suit the present system, which had 4–13 inputs and one output. The network predictions were found to be in a good agreement with the experimental local Nusselt number values.

On the laminar and turbulent free convection heat transfer from a vertical plate over the entire range of Prandtl numbers

In a number of papers, Arpaci et al. (Int. J. Heat Mass Transfer, 29, 1071 (1986); 40, 3819 (1997) obtained equations for the laminar and turbulent heat transfer in free convection from a vertical plate over the entire range of Prandtl numbers. The objective of the present paper is to note that their approach for the laminar case is similar to that of Ruckenstein (AIChE Journal, 26, 850 (1980). Their treatment of the turbulent case differs from that of Ruckenstein and Felske (J. Heat Transfer, 102, 773 (1980) and arguments are brought to demonstrate that the latter is more plausible than the former.

Turbulent Free Convection Heat Transfer to Drag-Reducing Fluids From Arbitrary Geometric Configurations

The problem of turbulent free convection heat transfer from curved surfaces to drag-reducing fluids has been investigated using the Nakayama-Koyama solution methodology. The surface wall temperature is allowed to vary in the streamwise direction in an arbitrary fashion and calculations are carried out for the turbulent free convection about the horizontal circular cylinder and the sphere for the sake of illustration.

Turbulent free convection heat transfer to power-law fluids from arbitrary geometric configurations

The problem of turbulent free convection heat transfer from curved surfaces to non-Newtonian power-law fluids has been investigated using the Nakayama-Koyama solution methodology. The scheme is designed to deal with bodies of arbitrary geometric configurations and hence can be viewed as a generalized version of the Shenoy-Mashelkar approach for turbulent free convection heat transfer from a flat vertical plate to a power-law fluid. The surface wall temperature is allowed to vary in the streamwise direction in an arbitrary fashion, and calculations are carried out for the turbulent free convection about the horizontal circular cylinder and sphere for illustrative purposes. Available theoretical and experimental data have been compared with the predictions of the present analysis and the comparison of results has been found to be reasonably good.

Turbulent Free Convection Heat Transfer from Vertical Parallel Plates : Effect of Entrance Bell-Mouth Shape

The streamwise development of turbulence in the free convection flow between vertical parallel plates (5m long and various spacings B) was experimentally studied. To control inlet disturbance, a bell-mouth entrance was installed at the lower end of the vertical parallel plate channel. The turbulent quantity profiles (velocity, intensity, turbulent heat flux and kinetic energy production) were measured in the vertical channel at heights X (110, 820, 1690, 2630 and 3840mm) and at spacings B of 50, 100 and 200mm. The streamwise development of intensity profiles of vertical velocity and the beginning of the transition seem to be closely related to the development vertical velocity profiles through buoyancy effects. The measured profiles of the turbulent kinetic energy production and the turbulent heat fluxes seem to clarify the characteristics of turbulence intensity.

Turbulent free convection heat transfer to air from vertical parallel plates.

Turbulent free convection heat transfer to air from vertical parallel plates (height of 5000 mm and spacings B of 50, 100 and 200 mm) were studied experimentally. Turbulence quantities (intensities and correlations of fluctuating temperature and velocities, and turbulent shear stress) in the induced flow between the parallel plates were measured using LDV and fine thermocouples at height X (=820, 1690, 2630 and 3840 mm). The measured streamwise variations of the turbulence quantities, which were affected by the inlet disturbances in the upstream flow region, demonstrated that there were three types of flow regions corresponding to the laminar, transition and turbulent regions of the free convection boundary layer on a single vertical plate. The characteristics of the turbulence quantity profiles in each flow region were consistent with those of the local Nusselt number distributions on heated plates, calculated from the vertical distributions of temperature on it.

An analysis of turbulent free convection about bodies of arbitrary geometrical configurations

A general solution method is suggested for the prediction of the turbulent free convection heat transfer from curved surfaces. The method which may be viewed as a generalized version of the Eckert-Jackson method for the isothermal plate, is designed to deal with bodies of arbitrary geometrical configurations. The surface wall temperature is also allowed to vary in the streamwise direction in an arbitrary fashion. For the illustrative purpose, the calculations are carried out for the turbulent free convection about the horizontal circular cylinder, and the results are compared with the existing empirical formula. The flow transition from laminar to turbulent is also predicted by matching the laminar and turbulent solutions.

A new approach to the analysis of turbulent free convection heat transfer

The principle of surface renewal is utilized in the analysis of fully turbulent free convection. The present analysis together with a previous surface renewal ased analysis of combined forced and free convection associated with supercritical fluids demonstrate the potential usefulness of the surface renewal approach in modelling buoyancy influenced turbulent convection processes.

Turbulent free convection heat transfer from a flat vertical plate to a power law fluid

Turbulent free convection heat transfer from a flat vertical plate to a power law fluid

An Analysis of Turbulent Free Convection Heat Transfer from a Vertical Surface

In the analysis of the turbulent free convection two different solutions are obtained ; one has a fundamental assumption that the temperature and velocity distributions in the boundary layer respectively take similar figures along the flow, and the other has a fundamental assumption that the laminar sublayer takes a Reynolds number 160. The former corresponds to the transient turbulent boundary layer and the latter to the ordinary turbulent boundary layer. Then referring to the experimental results, the most appropriate dimensionless heat transfer coefficients are represented.