SOLID70

3D Thermal Solid

SOLID70 Element Description

Although this element is available for use in your analysis, Ansys, Inc. recommends using a current-technology element such as SOLID278.

SOLID70 has a 3D thermal conduction capability. The element has eight nodes with a single degree of freedom, temperature, at each node. The element is applicable to a 3D, steady-state or transient thermal analysis. The element can also account for heat transfer by a mass flow with a prescribed velocity field (see Mass Transport (Advection) in the Theory Reference). 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.

Figure 70.1: SOLID70 Geometry

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 Element 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

Birth and death

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 letter or 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	-

Output if a surface load is input
Output if KEYOPT(7) = 1
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

Table 70.2: SOLID70 Item and Sequence Numbers

Output Quantity Name	ETABLE and ESOL Command Input
Output Quantity Name	Item	FC1	FC2	FC3	FC4	FC5	FC6
AREA	NMISC	1	7	13	19	25	31
HFAVG	NMISC	2	8	14	20	26	32
TAVG	NMISC	3	9	15	21	27	33
TBAVG	NMISC	4	10	16	22	28	34
HEAT RATE	NMISC	5	11	17	23	29	35
HFLXAVG	NMISC	6	12	18	24	30	36

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.
Mass flow (activated by KEYOPT(8)=1) is restricted to the condition that the element Peclet number (Pe) must be less than 1:

where is the magnitude of the velocity vector, is an element length scale along the velocity vector direction, and , , and are the density, specific heat, and equivalent thermal conductivity of the fluid. If , an error is printed, and you will have to reduce the mesh size and run again (see Galerkin Formulation in the Thermal Analysis Guide).
Note: Mass transport for the current-technology element SOLID278 is not restricted by Pe.

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).