Uncoupling the Conjugate Heat Transfer Problem in a Horizontal Plate Under the Influence of a Laminar Flow

The conjugate heat transfer process of cooling a horizontal plate in steady state condition is studied. The model considers both solid and fluid regions in Cartesian coordinates. The problem was solved analytically, considering the fluid flowing in a laminar condition and hydrodynamically developed before any interaction with the heated body. The height of the fluid considered was enough to allow the generation of a thermal boundary layer without any restriction. The conservation of mass, momentum and energy equations were considered to turn the problem into a non dimensional form. The heated body presented a constant heat flux at the bottom side, and convective heat transfer at the top side in contact with the fluid. The other two boundary conditions are adiabatic. The energy equation was considered in the solid to turn it into a non dimensional form. The interface temperature was obtained from a regression using the Chebyshev polynomial approximation. As the problem deals with the cooling of a electronics components, the solution presents the mathematical solution of the energy equation for the solid, including the isothermal lines. The non dimensional form allows a thorough analysis of the problem, considering the influence of the different parameters in the conjugate heat transfer problem. The solution is compared with numerical solution of different problems, and the parameters considered are Reynolds number, plate thickness, Prandtl number, and solid thermal conductivity. The results obtained present isothermal lines, local Nusselt number, and average Nusselt number.

Application of Various Combustion Models to a Generic Combustor

The flow-field of a generic gas combustor with interior and exterior conjugate heat transfers was numerically studied. Results obtained from three combustion models, combined with the re-normalization group (RNG) k-ε turbulence model, discrete ordinates radiation model, and partial equilibrium NOx model are presented and discussed. The numerical results are compared with a comprehensive database obtained from a series of experimental tests. The flow patterns and the recirculation zone length are excellently predicted, and the mean axial velocities are in fairly good agreement with the experimental measurements, particularly at downstream sections for all three combustion models. The mean temperature profiles are also fairly well captured by the probability density function (PDF) and eddy dissipation (EDS) combustion models. The EDS-finite-rate combustion model fails to provide acceptable temperature field. In general, the PDF shows some superiority over the EDS and EDS-finite-rate models. NOx levels predicted by the EDS model are in reasonable agreement with the experimental measurements.

Experimental Validation of Computer Models for Food and Polymer Extrusion

The accuracy and validity of the mathematical and numerical modeling of extruders for polymers and for food are considered in terms of experimental results obtained on typical full-size single and twin-screw extruders. The fluid is treated as non-Newtonian and with strong temperature-dependent properties. The chemical conversion of food during extrusion is also considered. The numerical modeling is employed for steady-state transport, for a range of operating conditions. Following grid-independence studies, the results obtained are first considered in terms of the expected physical behavior of the process, yielding good agreement with observations presented in the literature. The results are then compared with detailed and qualitative experimental results available from previous investigations to evaluate their accuracy. Good agreement with experimental data is obtained, lending strong support to the mathematical and numerical models.

A Comparison Between Three- and Two-Dimensional Thermal Finite Element Analysis of the Gas Metal Arc Welding Process

Predictions of transient temperature distributions in welding can help the selection of welding process parameters that minimize residual stresses. A three-dimensional (3D) thermal finite element model of bead-on-plate gas metal are welding (GMAW) is presented and is used to evaluate a cross-sectional, two-dimensional (2D) counterpart model. While the thermomechanical problem of welding is 3D in nature, it is shown that the 2D model can provide temperature field predictions comparable to those of the 3D model, even though the 2D model tends to predict peak temperatures higher than those of the 3D model. Both types of model predictions are compared to welding test measurements.

A Novel Transition-Sensitive Conjugate Methodology Applied to Turbine Vane Heat Transfer

A documented numerical methodology for conjugate heat transfer was employed to predict the metal temperature of an internally-cooled gas turbine vane at realistic operating conditions. The conjugate heat transfer approach involves the simultaneous solution of the flow field (convection) and the conduction within the metal vane, allowing a solution of the complete heat transfer problem in a single simulation. This technique means better accuracy and faster turn-around time than the typical industry practice of multiple, decoupled solutions. In the present simulations, the solid and fluid zones were coupled by energy conservation at the interfaces. In the fluid zones, the Reynoldsaveraged Navier-Stokes equations were closed with a three-equation, eddy-viscosity model, developed in-house and previously documented, with the capability to predict laminar-to-turbulent boundary-layer transition. The single-point model is fully-predictive for transition and requires no problem-dependent user inputs. For comparison, a simulation was also run with a commercially available Realizable k-ε turbulence model. A high-quality, unstructured gird was employed in both cases. Numerical predictions for midspan temperature on the airfoil surface are compared to data from an open-literature experiment with the same geometry and operating conditions. The new model captured transition of the initially laminar boundary layer to a turbulent boundary layer on the suction surface. The results with the new model show excellent agreement with measured data for surface temperature over the majority of the airfoil surface. The new model showed a marked improvement over the Realizable k-ε model in all regions where laminar boundary layers exist, highlighting the importance of accurately modeling transition in turbomachinery heat transfer simulations.

Energy Efficient Refrigerators: The Effect of Door Gasket and Wall Insulation on Heat Transfer

The energy efficiency of refrigerators not only depends on the efficiency of the various components used in the cycle but also on their thermodynamics cycle efficiency as well the thermal efficiency of the cabinet housing the components. Efficiency improvements to the thermodynamics cycle and refrigerator components have been the subject of various papers published in the open literature. Not many researchers have looked at reducing the heat leakage into the refrigerator cabinet with the explicit objective of reducing the power consumption of the unit and hence improving its thermal efficiency. This paper is based on an experimental study of this topic, and includes information on the experimental rig used and the results obtained. This research was performed in two stages: The first stage was focused on improving the energy efficiency by changing wall insulation while the second stage was to study the heat transfer through the doors’ gaskets. For the first part, a domestic refrigerator was instrumented with many thermocouples and heat flux meters to measure the inside and outside air temperatures and the heat transfer through the wall of the unit, respectively. These measurements were taken under different environmental conditions as well as different insulation thickness in the walls of the cabinet. For the second part, using a specially designed and manufactured experimental rig, various door gaskets were placed between a warm and a cold chamber and heat transfer through the gasket was measured. The results showed that by adding 30 mm polystyrene insulation to the walls of the refrigerator, the heat transfer through the walls reduced by around 35%. The power consumption data agreed very well with the measured heat flux through the walls. The percentage heat transfer through the doors’ gaskets was confirmed to be about 13% of the total heat transferred into the unit.

A Mass Transport Model for CVD Coating of Optical Fibers

Carbon coated optical fibers are produced by the chemical vapor deposition process which includes multi-species mass transport with chemical reactions. A proper numerical model of this process will help elucidate the basic mechanisms and optimize the process to improve coating quality. A heat transfer model has been developed in our research group. We are now developing an applicable chemical kinetics model to include mass transport with gas phase and surface reactions. Several different chemical reactor models have been tried, including a continuous-stirred tank reactor (CSTR) model, a plug flow reactor (PFR) model and a multi-component diffusion model with the Maxwell-Stefan approximations. We found that in reactor conditions with well-mixed or large mass Peclet number, the CSTR and PFR models validate well with experimental results. But a multi-component gas diffusion model is needed for low mass Peclet number conditions. The model has been extended to a wider range of temperatures necessary for this optical fiber coating process.