4.71 MASS71 Thermal Mass

In a steady-state solution the element acts only as a temperature dependent heat source or sink. Other elements having special thermal applications are the COMBIN14 and COMBIN40 elements. These elements, which are normally used in structural models, may be used for thermally analogous situations.

If the model containing the thermal mass element is also to be analyzed structurally, the thermal element should be replaced by an equivalent structural element (such as MASS21)

Figure 4.71-1 MASS71 Thermal Mass

4.71.1 Input Data

The heat generation is applied directly as a nodal load and is not first multiplied by the volume. Thus, if KEYOPT(3)=0 (i.e., when using the specific heat matrix), the heat generation rate must be adjusted to account for the volume. For an axisymmetric analysis the heat generation rate should be input on a full 360° basis. A temperature dependent heat generation rate of the following polynomial form may be input:

where T is the absolute temperature from the previous substep. The constants, A₁ through A₆, should be entered as real constants. If any of the constants A₂ through A₆ are non-zero, KEYOPT(4) must be set to 1. Also, if temperatures are not absolute, the offset conversion [TOFFST] must be specified. Alternately, the heat generation expression may be defined as a temperature dependent material property (QRATE) with the MP commands.

A summary of the element input is given in Table 4.71-1. A general description of element input is given in Section 2.1.

Table 4.71-1 MASS71 Input Summary

Element Name	MASS71
Nodes	I
Degrees of Freedom	TEMP
Real Constants	CON1 see KEYOPT(3),A1, A2, A3, A4, A5, A6 (constants for temperature function)
Material Properties	QRATE, DENS, C, ENTH if KEYOPT(3)=0 or QRATE if KEYOPT(3) = 1
Surface Loads	None
Body Loads	None (heat generation rates may be defined as a function of temperature by using real constants A1,A2,... or by the QRATE material property definition.)
Special Features	Nonlinear if heat generation is defined as a function of temperature, Birth and death
KEYOPT(3)	0 - Interpret CON1 as volume (with either DENS and C or ENTH supplied as material properties)
KEYOPT(4)	0 - No temperature dependent heat generation (required if all real constants A2-A6 are zero) 1 - Include temperature dependent heat generation (required if any real constants A2-A6 are non-zero)

4.71.2 Output Data

• nodal temperatures included in the overall nodal solution
• additional element output as shown in Table 4.71-2

The following notation is used in Table 4.71-2:

A colon (:) in the Name column indicates the item can be accessed by the Component Name method [ETABLE, ESOL] (see Section 2.2.2). The O and R columns indicate the availability of the items in the file Jobname.OUT (O) or in the results file (R), a Y indicates that the item is always available, a number refers to a table footnote which describes when the item is conditionally available, and a - indicates that the item is not available.

Table 4.71-2 MASS71 Element Output Definitions

Name	Definition	O	R
EL	Element number	Y	Y
NODE	Node I	Y	Y
CENT: X, Y, Z	Center location XC, YC, ZC	-	Y
TEMP	Element (node) temperature	Y	Y
HEAT RATE	Heat generation rate into node	Y	Y

Table 4.71-3 lists output available through the ETABLE command using the Sequence Number method. See Chapter 5 of the ANSYS Basic Analysis Procedures Guide and Section 2.2.2.2 of this manual for more information. The following notation is used in Table 4.71-3:

Name - output quantity as defined in the Table 4.71-2

Item - predetermined Item label for ETABLE command

E - sequence number for single-valued or constant element data

Name	Item	E
HEAT RATE	SMISC	1
TEMP	SMISC	2

4.71.3 Assumptions and Restrictions

4.71.4 Product Restrictions

ANSYS/Thermal

The birth and death special feature is not allowed.