The default setting of Off causes the simulation to be adiabatic, and does not solve for any heat transfer effects.
When Heat Transfer is set to On, conduction are convection are solved for. To include internal radiation, check the Radiation box on the Radiation group. If Joule heating boundary conditions (current and/or voltage) are applied, heat transfer must be enabled.
In a forced convection analysis, the flow and heat transfer can be solved separately because the flow does not depend on the temperature distribution. An often used technique is to compute the flow solution prior to computing the thermal distribution. Unlike a buoyancy-driven solution, the flow and heat transfer solutions are decoupled from one another.
This approach reduces the overall analysis time for the following reasons:
Auto Forced Convection automates this technique. To automatically stage a forced convection analysis into separate flow and heat transfer stages, select the following options on the Settings task dialog:
The following occurs after pressing the Solve button:
If the Stop button is pressed during the flow-only portion, the analysis will stop after the current iteration, and will not run the automatic heat-transfer stage.
To change the number of thermal-only iterations, enable this flag on the Flag Manager:
where # is the number of thermal-only iterations the Solver should run.
Example of running with Automatic Forced Convection
Enable Radiation to include surface-to-surface radiation effects in a heat transfer analysis. Radiation is typically most relevant when the field temperatures are very high. If the global temperature differentials are below 70-80 C, radiation typically has very little effect. Note that simulations with radiation enabled take longer to run. It is important to balance the additional time required with the objectives of the simulation. If accuracy is important, and the temperatures are high enough, then enabling Radiation is helpful. If, however, the objective is to obtain comparative results (as in conceptual design iterations), then the objective may not warrant the additional time required by the Radiation solver.
The radiation model is a non-participating model, meaning that radiation occurs between the walls and the fluid medium (the air) is not directly affected by the radiation. When radiation is activated, the start-up processing of the analysis will generally take longer due to the view factor calculation.
Radiative heat transfer through transparent media is supported, as well as geometric symmetry. The radiation model computes radiative heat transfer to moving solids and moving surfaces, and is the basis of the solar heating model. The radiation model has very rigorous “book-keeping” to keep track of the radiative energy balance, and reports the amount of heat transfer due to radiation and the radiative energy balance for each part in a model. The result is that reciprocity is enforced, to ensure that the radiative heat transfer between parts with large size differences is computed accurately.
The radiation model is designed for use with all of the supported geometry types: two and three dimensional Cartesian and axisymmetric about the X and Y axes.
Be sure to set the emissivity of the walls and solids (in the Materials dialog). Emissivity set as a fluid property is automatically applied to all contacting wall surfaces. Because the radiation model is non-participating, emissivity values set on fluid materials are not relevant to the fluids. Emissivity set on a solid material overrides any specified value on the contacting fluid.
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