where in turn is the thermal conductivity, and is the von Karman constant equal to 0.41.

The computational result should be checked so that the distance between the computational fluid domain and the wall, w, is almost everywhere small compared to any geometrical quantity of interest. The distance w is available as a postprocessing variable on boundaries.

References for the Non-Isothermal Flow and Conjugate Heat Transfer Interfaces

1.D.C. Wilcox, “Turbulence Modeling for CFD,” 2nd ed., DCW Industries, 1998.

2.Jonas Larsson, “Numerical Simulation of Turbulent Flows for Turbine Blade Heat Transfer”, Doctoral Thesis for the Degree of Doctor of Philosophy, Chalmers University of Technology, Sweden, 1998.

3.R.L. Panton, “Incompressible Flow”, 2nd ed., John Wiley & Sons, Inc., 1996.

4.W.M. Kays, “Turbulent Prandtl Number — Where Are We?”, ASME Journal of Heat Transfer, 116, pp. 284–295, 1994.

5.B. Weigand, J.R. Ferguson, and M.E. Crawford, “An Extended Kays and Crawford Turbulent Prandtl Number Model,” International Journal of Heat and Mass Transfer, vol. 40, no. 17, pp. 4191–4196, 1997.

6.D. Lacasse, È. Turgeon, and D. Pelletier, “On the Judicious Use of the k— Model, Wall Functions and Adaptivity”, International Journal of Thermal Sciences, vol. 43, pp. 925–938, 2004.

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13

H e a t T r a n s f e r B r a n c h

This chapter describes the physics interfaces in the Heat Transfer branch () in the Model Wizard. As with all other physical descriptions simulated by COMSOL Multiphysics, any description of heat transfer can be directly coupled to any other physical process. This is particularly relevant for systems based on fluid-flow, as well as mass transfer. The interfaces also allows you to account for heat sources and sinks, such as energy evolving from chemical reactions. The Mechanisms for Modeling Heat Transfer in the CFD Module helps you choose the best one to start with.

In this chapter:

•The Heat Transfer Interfaces and The Heat Transfer Interface

•Out-of-Plane Heat Transfer Features

•The Heat Transfer in Porous Media Interface

•Out-of-Plane Heat Transfer Theory

•Theory for the Heat Transfer in Porous Media Interface

•The Non-Isothermal Flow and Conjugate Heat Transfer, Laminar Flow Interfaces and The Non-Isothermal Flow and Conjugate Heat Transfer, Turbulent Flow Interfaces are described in the fluid flow chapter.

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T h e M e c h a n i s m s f o r M o d e l i n g H e a t T r a n s f e r i n t h e C F D M o d u l e

Heat Transfer is an important part of simulating fluid flow. Fluid flow has such an important effect on heating and cooling operations that it is difficult to simulate such without a complete description of how the flow is applied. Furthermore, the physical and thermodynamic properties of fluids are highly-affected by temperature such that flow can vary greatly in systems with temperature gradients.

While, the standard COMSOL Multiphysics package includes physics interfaces for simulating heat transfer through conduction and convection, the CFD Module provides extra functionality for simulating heat transfer in turbulent flow through The Non-Isothermal Flow and Conjugate Heat Transfer, Turbulent Flow Interfaces. The module also provides extra functionality for simulating heat transfer in porous media through The Heat Transfer in Porous Media Interface.

In this section:

•Selecting the Right Interface

•The Heat Transfer Interface Options

•Coupling to Other Physics Interfaces

Selecting the Right Interface

The Heat Transfer branch () included with this module has a number of subbranches to use to describe momentum transport. One or more of them can be added from the Model Wizard; either by themselves or in collaboration with other physics interfaces such as mass transfer, or even chemical reactions. Being a multiphysics interface, it contains the physics for modeling fluid-flow, which can be laminar, turbulent, and Stokes flow, as well as heat transfer through convection and conduction.

Several of the interfaces vary only by one or two default settings (see Table 13-1), which are selected at the Model Wizard level, or from a check box or drop-down list on the individual interfaces. The interfaces in the Non-Isothermal Flow and Conjugate

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Heat Flow branches relate to each other based on selections made from these drop-down lists in the Settings window (Figure ).

The Conjugate Heat Transfer interface is, by default in the Heat Transfer branch, set up to model heat transfer throughout a fluid in collaboration with a solid where heat is transferred by conduction. If a liquid regime is chosen in the Default model list, then the interface is renamed Non-Isothermal Flow, which is the same interface as Conjugate Heat Transfer but with different default settings as in Table 13-1.

For the Non-Isothermal Flow and Conjugate Heat Transfer branches, all the interfaces have the same interface identifier (nitf), where the differences are based on the default settings in the Physical Model section on the Settings window, and by what is required to model that type of heat transfer (see Table 13-1). Also, for all the

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interfaces, the Neglect initial term (Stokes flow) check box is not selected by default.

TABLE 13-1: THE NON-ISOTHERMAL FLOW PHYSICAL MODEL DEFAULT SETTINGS*

*For all the interfaces, the Neglect Initial Term (Stokes Flow) check box is not selected by default.

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