3-D Thermal Surface Effect

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SURF155 Element Description

SURF155 can be used for various load and surface-effect applications. The element is applicable to 3-D thermal analyses. It can be overlaid onto an edge of any 3-D thermal solid element. Various loads and surface effects can exist simultaneously.

Figure 155.1:  SURF155 Geometry

SURF155 Geometry

SURF155 Input Data

The element is defined by two to four node points and by the material properties. The nodes for this element must share the nodes of the underlying solid element. An extra node (away from the base element) can be used for convection effects.

See Nodal Loading for a description of element loads. Convections or heat fluxes can be input as surface loads on the element.

The convection surface conductivity matrix calculation uses the film coefficient (input on the SFE command with KVAL = 0 and CONV as the label). If the extra node option is used, its temperature becomes the bulk temperature. If the extra node is not used, the CONV value input with KVAL = 2 becomes the bulk temperature. The convection surface heat flow vector calculation uses the bulk temperature. On a given face, either a heat flux or a convection can be specified, but not both simultaneously.

Setting KEYOPT(7) = 1 multiplies the evaluated film coefficient by the empirical term |TS-TB|n, where TS is the element surface temperature, TB is the fluid bulk temperature, and n is an empirical coefficient (real constant ENN).

Convections and heat fluxes are multiplied by an area to obtain the heat flows. KEYOPT(12) determines whether the current area or the original area is selected for the calculation.

A film coefficient specified by the SFE command can be modified by activating the user subroutine USERCV with the USRCAL command. USERCV can be used to modify the film coefficient of a surface element with or without an extra node. It can be used if the film coefficient is a function of temperature and/or location.

Heat generation rates are input on a per unit volume basis and can be input as an element body load at the nodes, using the BFE command. Element body loads are not applied to other elements connected at the same nodes. The node I heat generation HG(I) defaults to zero. The node J heat generation defaults to HG(I). The heat generation load vector calculation uses the heat generation rate values.

As an alternative to using the BFE command, you can specify heat generation rates directly at the nodes using the BF command. For more information on body loads, see Body Loads in the Basic Analysis Guide.

When KEYOPT(4) = 0, 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.

Following is a summary of the element input. A general description of element input is given in Element Input. For axisymmetric applications see Harmonic Axisymmetric Elements.

SURF155 Input Summary

I, J if KEYOPT (4) = 1, and KEYOPT (5) = 0
I, J, K if KEYOPT (4) = 1, and KEYOPT(5) = 1
I, J, K if KEYOPT (4) = 0, and KEYOPT(5) = 0
I, J, K, L if KEYOPT (4) = 0, and KEYOPT(5) = 1
Degrees of Freedom


Real Constants
See Table 155.1: SURF155 Real Constants for more information.
Material Properties
MP command: DENS, C, ENTH
Surface Loads
Convections -- 

face 1 (I-J) if KEYOPT(8) > 1

Heat Fluxes -- 

face 1 (I-J) if KEYOPT(8) = 1

Body Loads
Heat Generation -- 

HG(I), HG(J); also HG(K) if KEYOPT(4) = 0

Special Features

Birth and death


Midside nodes:

0 -- 

Has midside node

1 -- 

No midside node


Extra node for convection calculations:

0 -- 

No extra nodes

1 -- 

Has extra node (optional if KEYOPT(8) > 1)

KEYOPT(6) (used only if KEYOPT(5) = 1 and KEYOPT(8) > 1)

Use of bulk temperatures:

0 -- 

Extra node temperature used as bulk temperature

1 -- 

Adiabatic wall temperature used as bulk temperature


Empirical term:

0 -- 

Do not multiply film coefficient by empirical term.

1 -- 

Multiply film coefficient by empirical term |TS-TB|n.


Heat flux and convection loads:

0 -- 

Ignore heat flux and convection surface loads (if any)

1 -- 

Include heat flux, ignore convection

Use the following to include convection (ignore heat flux):

2 -- 

Evaluate film coefficient hf (if any) at average film temperature, (TS +TB)/2

3 -- 

Evaluate hf at element surface temperature, TS

4 -- 

Evaluate hf at fluid bulk temperature, TB

5 -- 

Evaluate hf at differential temperature, | TS - TB |


Film coefficient matrix key:

0 -- 

Program determines whether to use diagonal or consistent film coefficient matrix (default).

1 -- 

Use a diagonal film coefficient matrix.

2 -- 

Use a consistent matrix for the film coefficient.

Table 155.1:  SURF155 Real Constants

1 - 6(Blank)--
8 - 12(Blank)--
13ENNEmpirical coefficient
14 - 15(Blank)--

SURF155 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. 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 155.2:  SURF155 Element Output Definitions

ELElement NumberYY
EXTRA NODEExtra node (if present)YY
MATMaterial numberYY
XC, YCLocation where results are reportedY6
VN(X, Y)Components of unit vector normal to center of element-Y
MASSMass of Element-1
HGENHeat generations HG(I), HG(J), HG(K)2-
HEAT GEN. RATEHeat generation rate over entire element (HGTOT)22
HFLUXInput heat flux at nodes I, J3-
HEAT FLOW RATEInput heat flux heat flow rate over element surface area (HFCTOT)33
HFILMFilm coefficient at each face node44
TBULKBulk temperature at each face node or temperature of extra node44
TAVGAverage surface temperature44
CONV. HEAT RATEConvection heat flow rate over element surface area (HFCTOT)44
CONV. HEAT RATE/AREAAverage convection heat flow rate per unit area4-

  1. If dens > 0

  2. If heat generation load is present

  3. If KEYOPT(8) = 1

  4. If KEYOPT(8) > 1

  5. If KEYOPT(6) = 1 and KEYOPT(8) > 1

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

Table 155.3: SURF155 Item and Sequence Numbers lists output available via the ETABLE command using the Sequence Number method. (See The General Postprocessor (POST1) and The Item and Sequence Number Table for more information.) The following notation is used in the table:


output quantity


predetermined Item label for the ETABLE command


sequence number for single-valued or constant element data


sequence number for data at nodes I and J

Table 155.3:  SURF155 Item and Sequence Numbers

Output Quantity NameETABLE and ESOL Command Input

SURF155 Assumptions and Restrictions

  • The element must not have a zero length.

  • If real constant AREA is defined for the element, the element volume is greater than zero. If BF, BFE, or BFUNIF commands are issued under this circumstance, heat generation loads are activated, and the damping matrix is activated based on the density and specific heat of the element. In order to have heat generation but no damping from the element, set density and specific heat to small values.

SURF155 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.