Card 6e - Thermal Coupling Request (free convection)

The following NEARC options of the Card 6e are associated with free convection and hydraulic elements.

Parameters: L, N1S, N1F, N1D, N2S, N2D, HN1, KODE, EXP, P1, VX, VY, VZ

Additional available free convection options are the Card 6a NEARF and FREE convection options.

The N1 elements must be shell elements. Except for the NEARC10, CONCYL, CONSPH, CAVITY, and CAVITYH options, the N2 elements may be 2-node hydraulic elements or 1-node AMBIENT elements.

The fluid is assumed to be a gas, and the free convection conductance is computed with:

where:

  • h is the computed free convection heat transfer coefficient.
  • HN1 is a constant multiplier.
  • ATC(N1) is the area of the overlap of N1 onto N2.

L

L is the code AREA (or 11)

The NEARx (recommended) options connect the N1 elements to the nearest of the N2 elements.

KODE = NEARC6

NEARC6 (or 3100): For this option, a characteristic element is defined, and TMG automatically selects the correlation appropriate for the characteristic element's geometry from the following correlation types:

  • top surface of a horizontal flat plate
  • top surface of an angled flat plate
  • one side of a vertical flat plate
  • horizontal rods
  • vertical rods
  • angled rods
  • spheres

For the NEARC6 option, the relative vertical positions of the N1 and N2 elements are important. Free convection is driven by gravity, therefore the N1 elements must be hotter than the N2 elements and be positioned below them, or they must be cooler and above them.

EXP is the characteristic element whose shape determines the correlation type and characteristic length. EXP should be a planar, spherical, or beam element with the shape of the full convecting surface on which N1 is located. EXP may also be the code SELF, in which case the characteristic element is N1 itself.

KODE = NEARC9

NEARC9 (or 3104): This option assumes free convection upward from the bottom surface of a hot horizontal plate, or downward from the top surface of a cold plate.

The relative vertical positions of N1 and N2 are important. Free convection will only occur if N1 is hotter than N2 and is below it, or is colder and above it.

EXP is the characteristic element whose shape determines the correlation type and characteristic length. EXP should be a planar, spherical, or beam element with the shape of the full convecting surface on which N1 is located. EXP may also be the code SELF, in which case the characteristic element is N1 itself.

KODE = NEARC10

NEARC10 (or 3105): This option models recirculation between two closely spaced parallel plates boxed in at their edges, whose areas are large compared to the distance separating them (e.g., two circuit boards).

N1 and N2 must both be horizontal or vertical. If they are otherwise oriented, a warning message is printed and a vertical or horizontal assumption is made.

The recirculating fluid properties are defined on the Card 5a AMBIENT elements.

EXP is the characteristic element whose shape determines the correlation type and characteristic length. EXP should be a planar, spherical, or beam element with the shape of the full convecting surface on which N1 is located. EXP may also be the code SELF, in which case the characteristic element is N1 itself.

KODE = NEARC16

NEARC16 (or 3500): This is the preferred option for most applications. It is similar to NEARC6, except that the relative vertical position of the N2 and N1 elements is not taken into account. The N2 element is considered to "surround" the N1 elements, therefore free convection will always occur.

If N1 is a horizontal plate colder than N2, the NEARC9 correlation is used, i.e., the cold air will flow downwards from the top surface of the plate.

EXP is the characteristic element whose shape determines the correlation type and characteristic length. EXP should be a planar, spherical, or beam element with the shape of the full convecting surface on which N1 is located. EXP may also be the code SELF, in which case the characteristic element is N1 itself.

KODE = NEARC19

NEARC19 (or 3504): This is similar to the NEARC9 option, except that the relative vertical position of N1 and N2 is not taken into account. Free convection will always occur, since N2 is considered to "surround" N1.

If N1 is colder than N2, the NEARC6 correlation (convection from the top surface of a plate) is used.

EXP is the characteristic element whose shape determines the correlation type and characteristic length. EXP should be a planar, spherical, or beam element with the shape of the full convecting surface on which N1 is located. EXP may also be the code SELF, in which case the characteristic element is N1 itself.

KODE = NEARCIN

NEARCIN (or 3107): Free convection couplings from the inside surface of a box N1 to an internal hydraulic element N2 are calculated.

The orientation of the surface normal of N1 with respect to the gravity vector determines the correlation used.

If the convecting surface is the roof of a box (the surface normal points downward), the NEARC6 correlation is used, and N2 is assumed to lie below N1. Convection will occur if N1 is colder than N2.

If the convecting surface is the floor of a box (the surface normal points upward), the NEARC6 correlation is used, and N2 is assumed to be above N1. Convection will occur if N1 is warmer than N2.

If the convecting surface is the wall of a box (the surface normal points sideways), the NEARC16 correlation is used. Convection in this case will always occur.

EXP is the characteristic element whose shape determines the correlation type and characteristic length. EXP should be a planar, spherical, or beam element with the shape of the full convecting surface on which N1 is located. EXP may also be the code SELF, in which case the characteristic element is N1 itself.

KODE = NEARCOUT

NEARCOUT (or 3108): Free convection couplings from the outside surfaces of a box N1 to a surrounding fluid (hydraulic element N2) are calculated.

The orientation of the surface normal of N1 with respect to the gravity vector determines the correlation used.

If the convecting surface N1 is the bottom of a box (the surface normal points downward), the NEARC19 correlation is used. Convection will always occur.

If the convecting surface is the roof or side of a box (the surface normal points sideways or upward), the NEARC16 correlation is used. Convection will always occur.

EXP is the characteristic element whose shape determines the correlation type and characteristic length. EXP should be a planar, spherical, or beam element with the shape of the full convecting surface on which N1 is located. EXP may also be the code SELF, in which case the characteristic element is N1 itself.

KODE = PLATE

PLATE (or 3801): A free convection coupling from the top/bottom/both side(s) of element(s) N1 on a plate is created to hydraulic or AMBIENT element N2.

  • EXP is the characteristic length = area/perimeter of the plate. Alternatively, EXP may be the code SELF, in which case the vector components VX, VY, and VZ, as well as the characteristic length are calculated from the geometry of the group N1.
  • N1D may be 0 or the material ID of the convecting fluid. If it is zero, the fluid properties are obtained from the HYDENV Card.
  • P1 may be the code TOP, BOTTOM, or BOTH, indicating the side of the plate that convects. If P1 is BOTH, two separate thermal couplings are created, one from each side of the plate.
  • VX, VY, VZ are the directional components of the vector of the surface normal of the plate.

KODE = PLATEH

PLATEH (or 3802): A free convection coupling from the top/bottom/both side(s) of element(s) N1 on a horizontal plate is created to hydraulic or AMBIENT element N2.

  • N1D may be 0 or the material ID of the convecting fluid. If it is zero, the fluid properties are obtained from the HYDENV Card.
  • EXP is the characteristic length = area/perimeter of the plate. Alternatively, EXP may be the code SELF, in which case the vector components VX, VY, and VZ, as well as the characteristic length are calculated from the geometry of the group N1.
  • P1 may be the code TOP, BOTTOM, or BOTH, indicating the side of the plate that convects. If P1 is BOTH, two separate thermal couplings are created, one from each side of the plate.
  • VX, VY, VZ are the directional components of the vector of the surface normal of the plate.

KODE = SPHERE

SPHERE (or 3803): A free convection coupling from element(s) N1 on the surface of a sphere is created, convecting to hydraulic/AMBIENT element N2.

  • N1D may be 0 or the material ID of the convecting fluid. If it is zero, the fluid properties are obtained from the HYDENV Card.
  • EXP is the diameter of the sphere.

KODE = CYLINDER

CYLINDER (or 3804): A free convection coupling from element(s) N1 on the surface of a cylinder is created, convecting to hydraulic/AMBIENT element N2.

  • N1D may be 0 or the material ID of the convecting fluid. If it is zero, the fluid properties are obtained from the HYDENV Card.
  • EXP is the diameter of the cylinder.
  • P1 must be the length of the cylinder.
  • VX, VY, VZ are the directional components of the axis vector of the cylinder.

KODE = INCCHNL

INCCHNL (or 3805): A free convection coupling from the element(s) N1 on the inner surface of either wall of an inclined open parallel plate channel is created, convecting to hydraulic element N2.

  • N1D may be 0 or the material ID of the convecting fluid. If it is zero, the fluid properties are obtained from the HYDENV Card.
  • EXP is the distance between the walls of the channel.
  • P1 is the length of the channel.
  • VX, VY, VZ are the directional components of the vector of the surface normal of the walls of the channel.

KODE = CAVITY

CAVITY (or 3806): A free convection coupling from the element(s) N1 on one wall of an inclined closed parallel plate cavity is created, convecting to the nearest element N2 on the other wall of the cavity.

  • N1D may be 0 or the material ID of the convecting fluid. If it is zero, the fluid properties are obtained from the HYDENV Card.
  • EXP is the distance between the walls of the cavity. If VX is the code SELF, then P1, VX, VY, VZ are automatically calculated from the elements N1.
  • P1 is the length of the cavity.
  • VX, VY, VZ are the directional components of the vector of the surface normal of the walls of the cavity.

KODE = CAVITYH

CAVITYH (or 3807): A free convection coupling from the element(s) N1 on one wall of a horizontal closed parallel plate cavity is created, convecting to the nearest element N2 on the other wall of the cavity.

  • N1D may be 0 or the material ID of the convecting fluid. If it is zero, the fluid properties are obtained from the HYDENV Card.
  • EXP is the distance between the walls of the cavity. If VX is the code SELF, then P1, VX, VY, VZ are automatically calculated from the elements N1.
  • P1 is the length of the cavity.

KODE = CONCYL

CONCYL (or 3808): A free convection coupling from the element(s) N1 on the outer cylinder of two concentric horizontal cylinders is created, convecting to the nearest element N2 on the inner cylinder.

  • N1D may be 0 or the material ID of the convecting fluid. If it is zero, the fluid properties are obtained from the HYDENV Card.
  • EXP is the diameter of the outer cylinder.
  • P1 is the diameter of the inner cylinder.

KODE = CONSPH

CONSPH (or 3809): A free convection coupling from the element(s) N1 on the outer sphere of two concentric spheres is created, convecting to the nearest element N2 on the inner sphere.

  • N1D may be 0 or the material ID of the convecting fluid. If it is zero, the fluid properties are obtained from the HYDENV Card.
  • EXP is the diameter of the outer sphere.
  • P1 is the diameter of the inner sphere.

Code examples

AREA WALL 0 0 AIR 0 1 NEARC6 101
$ FREE CONVECTION CONDUCTANCES FROM THE WALLS OF A BOX
$ TO THE AIR THE CHARACTERISTIC ELEMENT IS ELEMENT 101
AREA BOARD1 0 0 BOARD2 0 1 NEARC10 SELF
$ FREE CONVECTION CONDUCTANCES CALCULATED BETWEEN
$ TWO BOARDS