3-D Thermal
Solid
SOLID70 Element Description
SOLID70 has a 3-D thermal conduction capability. The element has eight nodes with a single degree of freedom, temperature, at each node. The element is applicable to a 3-D, steady-state or transient thermal analysis. The element also can compensate for mass transport heat flow from a constant velocity field. If the model containing the conducting solid element is also to be analyzed structurally, the element should be replaced by an equivalent structural element (such as SOLID185). See SOLID90 for a similar thermal element, with mid-edge node capability.
An option exists that allows the element to model nonlinear steady-state fluid flow through a porous medium. With this option, the thermal parameters are interpreted as analogous fluid flow parameters. For example, the temperature degree of freedom becomes equivalent to a pressure degree of freedom. See SOLID70 in the Mechanical APDL Theory Reference for more details about this element.
SOLID70 Input Data
The geometry, node locations, and the coordinate system for this element are shown in Figure 70.1: SOLID70 Geometry. The element is defined by eight nodes and the orthotropic material properties. A prism-shaped element, a tetrahedral-shaped element, and a pyramid-shaped element may also be formed as shown in Figure 70.1: SOLID70 Geometry. Orthotropic material directions correspond to the element coordinate directions. The element coordinate system orientation is as described in Coordinate Systems. Specific heat and density are ignored for steady-state solutions. Properties not input default as described in the Material Reference.
Element loads are described in Nodal Loading. Convection or heat flux (but not both) and radiation may be input as surface loads at the element faces as shown by the circled numbers on Figure 70.1: SOLID70 Geometry.
Heat generation rates may be input as element body loads at the nodes. If the node I heat generation rate HG(I) is input, and all others are unspecified, they default to HG(I).
The nonlinear porous flow option is selected with KEYOPT(7) = 1. For this option, temperature is interpreted as pressure and the absolute permeability of the medium are input as material properties KXX, KYY, and KZZ. Properties DENS and VISC are used for the mass density and viscosity of the fluid. Properties C and MU are used in calculating the coefficients of permeability as described in the Mechanical APDL Theory Reference. Temperature boundary conditions input with the D command are interpreted as pressure boundary conditions, and heat flow boundary conditions input with the F command are interpreted as mass flow rate (mass/time).
A mass transport option is available with KEYOPT(8). With this option the velocities VX, VY, and VZ must be input as real constants (in the element coordinate system). Also, temperatures should be specified along the entire inlet boundary to assure a stable solution. With mass transport, you should use specific heat (C) and density (DENS) material properties instead of enthalpy (ENTH).
A summary of the element input is given in "SOLID70 Input Summary". A general description of element input is given in Element Input.
SOLID70 Input Summary
- Nodes
I, J, K, L, M, N, O, P
- Degrees of Freedom
TEMP
- Real Constants
Mass transport effects (KEYOPT(8) = 1): VX - X direction of mass transport velocity VY - Y direction of mass transport velocity VZ - Z direction of mass transport velocity - Material Properties
MP command: KXX, KYY, KZZ, DENS, C, ENTH, VISC, MU (VISC and MU used only if KEYOPT(7) = 1.
Do not use ENTH with KEYOPT(8) = 1).
- Surface Loads
- Convection or Heat Flux (but not both) and Radiation (using Lab = RDSF) --
face 1 (J-I-L-K), face 2 (I-J-N-M), face 3 (J-K-O-N), face 4 (K-L-P-O), face 5 (L-I-M-P), face 6 (M-N-O-P)
- Body Loads
- Heat Generations --
HG(I), HG(J), HG(K), HG(L), HG(M), HG(N), HG(O), HG(P)
- Special Features
- KEYOPT(2)
Evaluation of film coefficient:
- 0 --
Evaluate film coefficient (if any) at average film temperature, (TS + TB)/2
- 1 --
Evaluate at element surface temperature, TS
- 2 --
Evaluate at fluid bulk temperature, TB
- 3 --
Evaluate at differential temperature |TS-TB|
- KEYOPT(4)
Element coordinate system defined:
- 0 --
Element coordinate system is parallel to the global coordinate system
- 1 --
Element coordinate system is based on the element I-J side
- KEYOPT(7)
Nonlinear fluid flow option:
- 0 --
Standard heat transfer element
- 1 --
Nonlinear steady-state fluid flow analogy element
Note: Temperature degree of freedom interpreted as pressure.
- KEYOPT(8)
Mass transport effects:
- 0 --
No mass transport effects
- 1 --
Mass transport with VX, VY, VZ
SOLID70 Output Data
The solution output associated with the element is in two forms:
Nodal temperatures included in the overall nodal solution
Additional element output as shown in Table 70.1: SOLID70 Element Output Definitions
Convection heat flux is positive out of the element; applied heat flux is positive into the element. If KEYOPT(7) = 1, the standard thermal output should be interpreted as the analogous fluid flow output. The element output directions are parallel to the element coordinate system. A general description of solution output is given in Solution Output. See the Basic Analysis Guide for ways to view results.
The Element Output Definitions table uses the following notation:
A colon (:) in the Name column indicates that the item can be accessed by the Component Name method (ETABLE, ESOL). The O column indicates the availability of the items in the file Jobname.OUT. The R column indicates the availability of the items in the results file.
In either the O or R columns, “Y” indicates that the item is always available, a number refers to a table footnote that describes when the item is conditionally available, and “-” indicates that the item is not available.
Table 70.1: SOLID70 Element Output Definitions
| Name | Definition | O | R |
|---|---|---|---|
| EL | Element Number | Y | Y |
| NODES | Nodes - I, J, K, L, M, N, O, P | Y | Y |
| MAT | Material number | Y | Y |
| VOLU: | Volume | Y | Y |
| XC, YC, ZC | Location where results are reported | Y | 3 |
| HGEN | Heat generations HG(I), HG(J), HG(K), HG(L), HG(M), HG(N), HG(O), HG(P) | Y | - |
| TG:X, Y, Z, SUM | Thermal gradient components and vector sum at centroid | Y | Y |
| TF:X, Y, Z, SUM | Thermal flux (heat flow rate/cross-sectional area) components and vector sum at centroid | Y | Y |
| FACE | Face label | 1 | - |
| AREA | Face area | 1 | 1 |
| NODES | Face nodes | 1 | - |
| HFILM | Film coefficient at each node of face | 1 | - |
| TBULK | Bulk temperature at each node of face | 1 | - |
| TAVG | Average face temperature | 1 | 1 |
| HEAT RATE | Heat flow rate across face by convection | 1 | 1 |
| HEAT RATE/AREA | Heat flow rate per unit area across face by convection | 1 | - |
| HFAVG | Average film coefficient of the face | - | 1 |
| TBAVG | Average face bulk temperature | - | 1 |
| HFLXAVG | Heat flow rate per unit area across face caused by input heat flux | - | 1 |
| HFLUX | Heat flux at each node of face | 1 | - |
| PRESSURE GRAD | Total pressure gradient and its X, Y, and Z components | 2 | - |
| MASS FLUX | Mass flow rate per unit cross-sectional area | 2 | - |
| FLUID VELOCITY | Total fluid velocity and its X, Y, and Z components | 2 | - |
Available only at centroid as a *GET item.
Table 70.2: SOLID70 Item and Sequence Numbers lists output available through the ETABLE command using the Sequence Number method. See The General Postprocessor (POST1) in the Basic Analysis Guide and The Item and Sequence Number Table in this reference for more information. The following notation is used in Table 70.2: SOLID70 Item and Sequence Numbers:
- Name
output quantity as defined in the Table 70.1: SOLID70 Element Output Definitions
- Item
predetermined Item label for ETABLE command
- FCn
sequence number for solution items for element Face n
SOLID70 Assumptions and Restrictions
The element must not have a zero volume. This occurs most frequently when the element is not numbered properly.
Elements may be numbered either as shown in Figure 70.1: SOLID70 Geometry or may have the planes IJKL and MNOP interchanged.
A prism or tetrahedron shaped element may be formed by defining duplicate node numbers as described in Degenerated Shape Elements.
The specific heat and enthalpy are evaluated at each integration point to allow for abrupt changes (such as for melting) within a coarse grid.
Because the element is linear, the heat flux distribution is piecewise constant and, hence, the accuracy is low if the mesh is too coarse. To obtain a more accurate heat flux, increase the mesh density.
If the thermal element is to be replaced by a SOLID185 structural element with surface stresses requested, the thermal element should be oriented such that face I-J-N-M and/or face K-L-P-O is a free surface.
A free surface of the element (that is, not adjacent to another element and not subjected to a boundary constraint) is assumed to be adiabatic.
Thermal transients having a fine integration time step and a severe thermal gradient at the surface will also require a fine mesh at the surface.
If KEYOPT(8) > 0, unsymmetric matrices are produced.
When mass flow is activated (KEYOPT(8)=1), the element Peclet number should be less than 1:
Pe = ρ*v*L*Cp/(2*k) <1.0
Where L is an element length scale based on the element geometry. See SOLID70 in the Mechanical APDL Theory Reference for more details.
SOLID70 Product Restrictions
When used in the product(s) listed below, the stated product-specific restrictions apply to this element in addition to the general assumptions and restrictions given in the previous section.
ANSYS Mechanical Pro
This element does not have the mass transport or fluid flow options. KEYOPT(7) and KEYOPT(8) can only be set to 0 (default).
Birth and death is not available.
ANSYS Mechanical Premium
This element does not have the mass transport or fluid flow options. KEYOPT(7) and KEYOPT(8) can only be set to 0 (default).
Birth and death is not available.