LINK34

Convection Link

LINK34 Element Description

LINK34 is a uniaxial element with the ability to convect heat between its nodes. The element has a single degree of freedom, temperature, at each node point. The convection element is applicable to a 2-D (plane or axisymmetric) or 3-D, steady-state or transient thermal analysis.

If the model containing the convection element is also to be analyzed structurally, the convection element should be replaced by an equivalent (or null) structural element. The element may have a nonlinear film coefficient which may also be a function of temperature or time. See LINK34 in the Mechanical APDL Theory Reference for more details about this element.

Figure 34.1: LINK34 Geometry

LINK34 Input Data

The geometry and node locations for this convection element are shown in Figure 34.1: LINK34 Geometry. The element is defined by two nodes, a convection surface area, two empirical terms, and a film coefficient. In an axisymmetric analysis the convection area must be expressed on a full 360° basis. The empirical terms n (input as EN) and CC determine the form of the convection equation in conjunction with KEYOPT(3).

The convection function is defined as follows:

q = h_f*A*E*(T(I) - T(J))

where:

q = heat flow rate (Heat/Time)

h_f = film coefficient (Heat/Length²*Time*Deg)

A = area (Length²)

T = temperature (this substep) (Deg)

E = empirical convection term =

T_p = temperature (previous substep) (Deg)

n = empirical coefficient (EN)

CC = input constant

Note: E = F if n and CC = 0.0. F = 1.0 unless KEYOPT(3) = 2. If KEYOPT(3) = 3, E equals the larger of IT_p(I) - T_p(J)Iⁿ or CC/h_f.

A special option obtained with KEYOPT(3) = 2 allows an alternate input for h_f and an input scale factor (F). This option uses the VAL1 field of the SFE command with KVAL = 0 for the h_fvalue and KVAL = 2 for the F value. If the h_fvalue is zero (or blank), the HF material property is used for h_f. If the F value is zero (or blank) or negative, a value of 1.0 is assumed for F. Note, the F value input in this field will ramp within a load step if KBC = 0. An SFE command must be included (even if the values are left blank) for all LINK34 elements having KEYOPT(3) = 2.

Heat generation rates may be input as element body loads at the nodes. The node J heat generation rate HG(J) defaults to the node I heat generation rate HG(I).

A summary of the element input is given in "LINK34 Input Summary". A general description of element input is given in Element Input.

LINK34 Input Summary

Nodes

I, J

Degrees of Freedom

TEMP

Real Constants

AREA - Convection surface area

EN - Empirical coefficient

CC - Input constant

Material Properties

MP command: HF

Surface Loads

Convections --: 1 - Alternate input of HF and F if KEYOPT(3) = 2 (see text above)

Body Loads

Heat Generation --: HG(I), HG(J)

Special Features

Birth and death

Nonlinearity if real constant EN is not equal to zero or if KEYOPT(3) = 3

KEYOPT(2)

Evaluation of film coefficient:

0 --: Use average of T(I) and T(J) to evaluate HF
1 --: Use greater of T(I) or T(J) to evaluate HF
2 --: Use lesser of T(I) or T(J) to evaluate HF
3 --: Use differential |T(I) - T(J)| to evaluate HF

KEYOPT(3)

Film coefficient and scale factor:

0 --: Standard element input and empirical term
2 --: Use alternate input for HF and F (input with SFE command)
3 --: Use discontinuous empirical term

LINK34 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 34.1: LINK34 Element Output Definitions

The heat flow rate is in units of Heat/Time and is positive from node I to node J. In an axisymmetric analysis, the heat flow is on a full 360° basis. 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 34.1: LINK34 Element Output Definitions

Name	Definition	O	R
EL	Element Number	Y	Y
NODES	Nodes - I, J	Y	Y
XC, YC	Location where results are reported	Y	1
H	Film coefficient (includes empirical term)	Y	Y
AREA	Input area	Y	Y
TEMP	Temperature at node I and node J	Y	Y
HEAT RATE	Heat flow rate from node I to node J	Y	Y

Available only at centroid as a *GET item.

Table 34.2: LINK34 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 34.2: LINK34 Item and Sequence Numbers:

Name: output quantity as defined in the Table 34.1: LINK34 Element Output Definitions
Item: predetermined Item label for ETABLE command
E: sequence number for single-valued or constant element data
I,J: sequence number for data at nodes I and J

Table 34.2: LINK34 Item and Sequence Numbers

Output Quantity Name	ETABLE and ESOL Command Input
Output Quantity Name	Item	E	I	J
HEAT RATE	SMISC	1	-	-
TEMP	SMISC	-	2	3
H	NMISC	1	-	-
AREA	NMISC	2	-	-

LINK34 Assumptions and Restrictions

If T_p(I) = T_p(J) and n are nonzero, the first term of E is defined to be zero.
Since all unspecified nodal temperatures are initially set to the uniform temperature, a nonzero value of n may result in no heat flowing through the element in the first substep of a thermal solution.
Nodes may or may not be coincident.
The element is nonlinear if n is nonzero or KEYOPT(3) = 3. However, the solver always assumes the element is nonlinear and, therefore, always performs an iterative solution. (Only 2 iterations are performed if the element is linear.)

LINK34 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.
Nonlinearity is not available (real constant EN can not equal 0 and KEYOPT(3) can not equal 3).

ANSYS Mechanical Premium

Birth and death is not available.