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.
Turn Radiation On to include surface-to-surface radiation effects in a heat transfer analysis. Radiation is typically most relevant when the field temperatures are very high. 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.
Use the Gravity Vector for buoyancy driven flows (natural convection). Because most natural convection analyses occur on Earth, all that is required to set up gravity is to make sure the Earth is selected as the Gravity Method (it is by default) and to indicate the direction of gravity in your model with a unit vector. For example, if your model is constructed such that “down” is in the negative Y direction, then the unit vector for gravity should be:
0,-1,0
For buoyancy driven flows on other planets (or where the gravity is different from that on Earth), select Componets as the Gravity Method, and enter the magnitude (in the analysis units) and the direction of the gravity vector.
A gravity vector is not needed for forced convection flows.
To include gravity as a force acting on a moving solid, assign a driving or resistive force equal to the force imparted from gravity. The gravitational force may be added to an additional driving or resistive force, if necessary. It is not necessary to specify a gravity vector on the Solve dialog for moving solids unless flow buoyancy is simulated.
Related Topics