3-D 20-Node Thermal Solid

Compatible Products: – | – | – | Enterprise | Ent PP | Ent Solver | –Pro | Premium | Enterprise | Ent PP | Ent Solver | –

SOLID90 Element Description

SOLID90 is a higher order version of the 3-D eight node thermal element (SOLID70). The element has 20 nodes with a single degree of freedom, temperature, at each node. The 20-node elements have compatible temperature shapes and are well suited to model curved boundaries.

The 20-node thermal element is applicable to a 3-D, steady-state or transient thermal analysis. See SOLID90 in the Mechanical APDL Theory Reference for more details about this element. If the model containing this element is also to be analyzed structurally, the element should be replaced by the equivalent structural element (such as SOLID186).

Figure 90.1:  SOLID90 Geometry

SOLID90 Geometry

SOLID90 Input Data

The geometry, node locations, and the coordinate system for this element are shown in Figure 90.1: SOLID90 Geometry. The element is defined by 20 node points and the material properties. A prism-shaped element may be formed by defining duplicate K, L, and S; A and B; and O, P, and W node numbers. A tetrahedral-shaped element and a pyramid-shaped element may also be formed as shown in Figure 90.1: SOLID90 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 90.1: SOLID90 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). If all corner node heat generation rates are specified, each midside node heat generation rate defaults to the average heat generation rate of its adjacent corner nodes.

For phase change problems, use KEYOPT(1) = 1 (diagonalized specific heat matrix).

A summary of the element input is given in "SOLID90 Input Summary". A general description of element input is given in Element Input.

SOLID90 Input Summary


I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z, A, B

Degrees of Freedom


Real Constants


Material Properties

MP command: KXX, KYY, KZZ, DENS, C, ENTH

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), HG(Q), HG(R),
HG(S), HG(T), HG(U), HG(V), HG(W), HG(X), HG(Y), HG(Z), HG(A), HG(B)
Special Features

Birth and death


Specific heat matrix:

0 -- 

Consistent specific heat matrix

1 -- 

Diagonalized specific heat matrix

SOLID90 Output Data

The solution output associated with the element is in two forms:

Convection heat flux is positive out of the element; applied heat flux is positive into the element. 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 90.1:  SOLID90 Element Output Definitions

ELElement NumberYY
NODESNodes - I, J, K, L, M, N, O, PYY
MATMaterial numberYY
XC, YC, ZCLocation where results are reportedY2
HGENHeat generations HG(I), HG(J), HG(K), HG(L), HG(M), HG(N), HG(O), HG(P), HG(Q), ..., HG(Z), HG(A), HG(B)Y-
TG:X, Y, Z, SUMThermal gradient components and vector sum at centroidYY
TF:X, Y, Z, SUMThermal flux (heat flow rate/cross-sectional area) components and vector sum at centroidYY
FACEFace label1-
NODESCorner nodes on this face1-
AREAFace area11
HFILMFilm coefficient1-
TAVGAverage face temperature11
TBULKFluid bulk temperature1-
HEAT RATEHeat flow rate across face by convection11
HEAT RATE/AREAHeat flow rate per unit area across face by convection1-
HFLUXHeat flux at each node of face1-
HFAVGAverage film coefficient of the face-1
TBAVGAverage face bulk temperature-1
HFLXAVGHeat flow rate per unit area across face caused by input heat flux-1

  1. Output only if a surface load is input

  2. Available only at centroid as a *GET item.

Table 90.2: SOLID90 Item and Sequence Numbers lists output available through the ETABLE command using the Sequence Number method. See Creating an Element Table in the Basic Analysis Guide and The Item and Sequence Number Table in this reference for more information. The table uses the following notation:


output quantity as defined in the Table 90.1: SOLID90 Element Output Definitions


predetermined Item label for ETABLE command


sequence number for solution items for element Face n

Table 90.2:  SOLID90 Item and Sequence Numbers

Output Quantity NameETABLE and ESOL Command Input

SOLID90 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 90.1: SOLID90 Geometry or may have the planes IJKL and MNOP interchanged.

  • The condensed face of a prism-shaped element should not be defined as a convection face.

  • The specific heat and enthalpy are evaluated at each integration point to allow for abrupt changes (such as melting) within a coarse grid of elements.

  • If the thermal element is to be replaced by a SOLID186 structural element with surface stresses requested, the thermal element should be oriented such that face IJNM and/or face KLPO is a free surface.

  • A free surface of the element (i.e., 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.

  • An edge with a removed midside node implies that the temperature varies linearly, rather than parabolically, along that edge.

  • See Quadratic Elements (Midside Nodes) in the Modeling and Meshing Guide for more information about the use of midside nodes.

  • Degeneration to the form of pyramid should be used with caution.

  • The element sizes, when degenerated, should be small in order to minimize the field gradients.

  • Pyramid elements are best used as filler elements or in meshing transition zones.

SOLID90 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 

  • Birth and death is not available.

ANSYS Mechanical Premium 

  • Birth and death is not available.

Release 18.2 - © ANSYS, Inc. All rights reserved.