Main Help → All Commands → MPM Boundary Conditions → HeatFlux
The HeatFlux
command applies heat fluxes to surfaces near particles (which are expected to be on the surface) in MPM calculations.
It applies a flux to all particles selected by a ParticleBC block.
HeatFlux (mode),(face),(style),(value),<(time)>
where the parameters depend on the type of heat flux being applied. The two types of flux boundary conditions, which depend on (mode)
, are as follows.
This condition applies a surface flux in heat flux units for transport rate of heat per unit area. A positive value is flux into the material while a negative value is flux out of the material. The parameters are:
(mode)
must be "external"
to indicate it is an external heat flux.(face)
specifies the particle surface that is on the edge and has the flux. In 2D, imagine a box around the initial particle. Surfaces 1 to 4 are the four edges of the box in the order bottom, right, top, and left (with normals (0,-1), (1,0), (0,1), and (-1,0)). In 3D, imagine a cube around the initial particle. Surfaces 1 to 4 are same as for 2D (now with normals (0,-1,0), (1,0,0), (0,1,0), and (-1,0,0)), 5 in the bottom z surface (normal = (0,0,-1)), and 6 is the top z surface (normal = (0,0,1)).(style)
specifies the style of the applied heat flux. The setting depends on two parameters specified by arguments (value)
and (time)
. If either argument is not supplied, they are set to zero. The standard units are heat flux units for (value)
and alt time units for (time)
(but the units may change depending on the (style) setting).This version calculates the heat flux from a function of the particle temperature. The parameters are:
(mode)
must be "coupled"
to indicate it is a coupled heat flux.(face)
must be the boundary face with the flux (see above).(style)
must be function
.(value)
must be the function
for the the applied flux. It is entered as a a user-defined function of t
and entered as quoted text. At each time step, the variable t
will be replaced by the particle temperature. The function should evaluate to the desired flux in heat flux units. The function can additionally depend on particle position (x
, y
, z
, D
, T
, R
, or Z
in length units), and/or clockwise particle rotation (q
in radians).
(time)
- if supplied, the coupled flux will be applied starting at the entered time (in alt time units).Two uses of this flux condition are to implement convective and/or radiative boundary conditions. In convective cooling or heating, the function could be
function = h*(T0 - t)
where h
is heat transfer coefficient (in heat flux units/K), T0 is a reservoir temperature, and t
is used for surface particle temperature. In radiative cooling or heating, the flux function could be the Stefan-Boltzman law:
function = σ*ε*(T04 - t4)
where σ = 5.6704e-8 W/(m^2 K^4) is the Stefan-Boltzman constant and ε (<1) is the emissivity. In these functions, the physical terms should be replaced by their numerical values. If desired, however, they could also be functions themselves, such as to have h
be a function of t
or surface particle temperature. They cannot, however, depend on time, because t
is used here for particle temperature instead of time.