Encyclopaedia Index

CONJUGATE heat transfer

The term conjugate heat transfer is used to describe processes which involve variations of temperature within solids and fluids, due to thermal interaction between the solids and fluids. A typical example is the heating or cooling of a solid object by the flow of air in which it is immersed.

To cause PHOENICS to simulate such flows, the user should:

  1. solve for temperature directly, by SOLVE(TEM1), which command activates harmonic averaging of the exchange coefficients;
  2. specify the locations of the solids by the use of CONPOR with a negative blockage factor, and create the thermal link between solid and fluid by activating the automatic wall functions on the solid surfaces (see CONPOR);
  3. specify the material in each cell by store(prps), followed by appropriate initialisation of PRPS with FIINIT and patch statements.

Convergence of the TEm1 equation may be accelerated by specifying whole-field solution for TEM1 (see SOLUTN), and by using the block correction technique described in the entry on BLOK.

An example of conjugate heat transfer may be found in Library case 460.

As compared with the conjugate-heat-transfer capability of PHOENICS 1.5, the current PHOENICS is improved several respects:-

  1. An ASCII file houses now the library of materials, which can therefore be easily customised/expanded by the user. Material properties can now be constant or dependent on other properties. They can also be read from Q1 directly by EARTH.
  2. Boundary conditions (including thermal links) at the fluid-solid interface are set up automatically.
  3. Heat-transfer coefficients can be optionally calculated and printed out by Earth.

Conjugate heat-transfer in the general menu

A new menu option now enables users to simulate conjugate-heat-transfer problems, solving for temperature directly instead of enthalpy. As part of this feature, a library of material properties can be accessed from the menu to assign properties to fluid and solid parts of the domain; users themselves can add materials to this library. Appropriate solution-control devices (viz the block-correction feature, solving whole-field for temperature, and harmonic averaging of conductivities) are activated automatically.