Biagio Morrone

NUMERICAL ANALYSIS OF PARTIALLY HEATED VERTICAL PARALLEL PLATES IN NATURAL CONVECTIVE COOLING

This paper addresses the significance of adding insulated extensions to a parallel-plate channel in which the plates receive a uniform heat flux and a natural convection airflow is responsible for the cooling. The wall temperatures may decrease or increase, depending on whether the channel extensions are appended at the inlet or at the exit of the channel. The full elliptic conservation equations are solved numerically in an I-type composite computational domain. For the two cases treated, the pertinent results are reported in terms of wall temperature profiles, induced mass flow rates, and pressure profiles. The insulated extension placed downstream of the heated part implies a reduction of the maximum wall temperature. This effect is less relevant as the Rayleigh number increases. In addition, correlations have been obtained between the induced mass flow rate as well as the maximum wall temperatures and the Rayleigh number and the extension ratio in the investigated range of parameters.

Heat transfer enhancement by the chimney effect in a vertical isoflux channel

Abstract The ease of thermal control by means of air natural convection stimulates the investigation of configurations with the aim at improving the thermal performance. The effect of adding adiabatic extensions downstream of a vertical isoflux symmetrically heated channel has been experimentally analyzed. Optimal configurations have been identified through the measured wall temperature profiles, with reference to the extension and expansion ratios ( L / L h and B / b ) of the insulated extensions. Conspicuous maximum wall temperature reductions have been achieved by means of these optimal configurations. In details, percent increases of the heat transfer rate (i.e., average channel Nusselt number) were of order 10–20% depending on the channel aspect ratio, L h / b , and imposed wall heat flux. In any case, quite large extensions should be added to enhance the heat transfer rate, i.e. about 3.0 times the height of the channel, while the optimal expansion ratio was nearly 2.0 for all the configurations. Composite correlations between the average Nusselt number and the maximum dimensionless wall temperatures and Ra * , the Rayleigh channel number, B / b and L / L h parameters, in the 1.5⩽ L / L h ⩽4.0,1.0⩽ B / b ⩽4.0 and 10 2 ⩽ Ra * B / b ⩽5.0×10 6 ranges, have been evaluated.

Optimum plate separation in vertical parallelplate channels for natural convective flows: incorporation of large spaces at the channel extremes

Abstract This paper addresses the problem of optimizing the plate separation of an open, parallel-plate channel that is cooled by natural convection air flow. The plates are symmetrically heated by uniform heat flux. The I-shaped computational domain comprised two subdomains: the actual physical domain between the plates, and two large rectangular reservoirs placed upstream of the entrance and downstream of the exit. The aggregate subdomains accommodated the diffusion phenomena by momentum and energy that occur outside the channel. The full elliptic Navier-Stokes and energy equations are solved numerically in the composite domain. Correlations of the optimal values of the plate spacing as a function of the GrL number and of the induced mass flow rate, as well as thermal and velocity profiles, are presented for air.

Quasi-steady-state three-dimensional temperature distribution induced by a moving circular gaussian heat source in a finite depth solid

Abstract An analytical solution to the three-dimensional quasi-stationary problem in a finite depth and width solid with a circular Gaussian moving heat source at the body surface is developed and analyzed. The temperature distribution and the axial coordinate at which the maximum midplane temperature is achieved are presented as a function of Peclet number, solid thickness and width. The dependence of the maximum midplane temperature on the process parameters is highlighted. Combinations of process parameters for which the solution to the three-dimensional problem can be approximated by those to simpler models are pointed out.

Experimental Analysis of Thermal Instability in Natural Convection Between Horizontal Parallel Plates Uniformly Heated

An experimental investigation of natural convection between horizontal, heated, parallel plates in air was carried out by visualizing the flow and measuring the air temperature. Grashof numbers, based on the plate spacing, varied in the 1.22×10 5 -1.06×10 6 range. Flow patterns and probable onset of secondary motions were observed for three heating modes: (1) both plates heated, (2) upper plate heated and lower one unheated, and (3) upper plate unheated and lower one heated. The main flow pattern resembled a C shape (C loop) for all modes. In fact, the flow penetrated inside the cavity close to the leading edge of the lower plate and exited from the upper part, by reversing its motion between the plates. When the lower plate was heated, flow visualization showed that secondary flows were added to the C loop main flow. Such secondary structures arose as thermals, then changed into longitudinal vortices and, in the upper region of the open-ended cavity, a chaotic motion was detected. The existence of these structures was confirmed by measurements of instantaneous temperature values

NATURAL CONVECTION BETWEEN PARALLEL PLATES WITH CONJUGATE CONDUCTIVE EFFECTS

This article deals with the conjugate conductive and convective heat transfer in a vertical channel with finite thickness conductive parallel plates. The investigation is carried out numerically by solving the full elliptic Navier-Stokes and energy equations with the finite volume method in a composite I-shaped domain. The results are reported as functions of the main geometrical (B/b and L/b) and thermal (K and Ra*) parameters, for a Prandtl number of 0.71 (i.e., air). The results show that the thinner the plate the more uniform the heat flux distribution along the plate. As the thickness of the plate increases, the heat flux distribution is less uniform and at the inlet corner the temperatures present much higher values than at the infinitely thin plate. Lower plate thermal conductivity implies a more uniform heat flux distribution and lower temperature increments than the infinitely thin plate. The dependence of the heat flux and temperature distributions along the solid-fluid interface is stronger than the lower the Ra* value.

Numerical Investigation of the Natural Convection Flows for Low-Prandtl Fluids in Vertical Parallel-Plates Channels

Laminar natural convection of metallic fluids (Pr«1) between vertical parallel plate channels with isoflux heating is investigated numerically in this work. The full elliptic Navier-Stokes and energy equations have been solved with the combination of the stream function and vorticity method and the finite-volume technique. An enlarged computational domain is employed to take into account the flow and thermal diffusion effects. Results are presented in terms of velocity and temperature profiles. The investigation also focuses on the flow and thermal development inside the channel; the outcomes show that fully developed flow is attained up to Ra=10 3 , whereas the thermal fully developed condition is attained up to Ra=10 4 . Further, correlation equations for the dimensionless induced flow rate, maximum dimensionless wall temperatures, and average Nusselt numbers as functions of the descriptive geometrical and thermal parameters covering the collection of channel Grashof numbers 1.32× 10 3 ≤ Gr/A ≤ 5.0 × 10 6 and aspect ratios 5≤A≤15. Comparison with experimental measurements has been presented to assess the validity of the numerical computational procedure.

Meshless approach for computing the heat liberation from annular fins of tapered cross section

This technical note addresses an extremely simple computational procedure for solving the complex quasi-one dimensional heat equation with variable coefficients that governs the temperature change in annular fins of hyperbolic profile cooled by a fluid. The salient feature of the computational procedure is the convenient linkage of the finite-difference method with a meshless approach. Using a very coarse mesh, accurate estimates for the temperature distribution and heat liberation from annular fins of hyperbolic profile have been obtained by hand solving small systems of three algebraic equations.

Thermal Analysis of Solids at High Peclet Numbers Subjected to Moving Heat Sources

A three-dimensional heat transfer model has been developed to obtain the conductive thermal field inside a brick-type solid under a moving heat source with different beam profiles. The problem in quasi-steady state has been approximated by neglecting the axial diffusion component; thus, for Peclet numbers greater than 5, the elliptic differential equation becomes a parabolic one along the motion direction. The dependence of the solution on the radiative and convective heat losses has been highlighted. Thermal fields are strongly dependent on different spot shapes and on the impinging jet; this situation allows control of the parameters involved in the technological process.

A Review of Hydrogen-Natural Gas Blend Fuels in Internal Combustion Engines

In the last ten years, the number of natural gas (NG) vehicles worldwide has rapidly grown with the biggest contribution coming from the Asia-Pacific and Latin America regions (IANGV, 2011). As natural gas is the cleanest fossil fuel, the exhaust emissions from natural gas spark ignition vehicles are lower than those of gasoline-powered vehicles. Moreover, natural gas is less affected by price fluctuations and its reserves are more evenly widespread over the globe than oil. In order to increase the efficiency of natural gas engines and to stimulate hydrogen technology and market, hydrogen can be added to natural gas, obtaining Hydrogen Natural Gas blends, usually named as HCNG.