Kontron VMP3 - Manual (Page 128)

System Considerations VMP3
Page 6 - 4 © 2005 Kontron Modular Computers GmbH ID 29230, Rev. 01
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P R E L I M I N A R Y
6.1.2 System Environment
The VMP3 system environment plays the major role in determining the thermal management
concept to be applied to the VMP3. Generally speaking, there are two basic types of system
environments: open and closed.
Open environments use ambient air convectional cooling as their main instrument of system
thermal management. Closed environments rely heavily on conductional cooling as their first
line of system thermal management. Closed systems may also be of a hybrid nature where
convectional cooling is used on top of conductional cooling. The initial means of cooling the
VMP3 is convectional.
Convection
(Free and Forced)
The cooling of a body by means of the use of a fluid (liquid or gas) whose temper-
ature is lower.
Convectional cooling always requires that some fluid is moved over a body and
that the fluid temperature is lower than that of the body to be cooled.
Free convection relies on the buoyancy of the fluid caused by the transfer of heat
from the body to be cooled to the fluid. This results in a very minimal amount of
fluid flow which, depending on the temperature of the fluid and the amount of fluid
available, may be sufficient to cool the body. In the case of the VMP3, the fluid
would be ambient air.
Forced convection relies on the forceful movement of a fluid across a body caused
by the application of external energy. Again in the case of the VMP3, the fluid
would be ambient air which is forced over the heat sink of the VMP3.
Radiation The transfer of heat from a body by means of thermal radiation.
The VMP3 is not designed for radiation cooling.
Ambient Air The air occupying the immediate space surrounding a body to be cooled.
For cooling to take place using ambient air, the ambient air must pass over the
body to be cooled and the ambient air temperature must be lower than that of the
body to be cooled.
Ambient Air Temperature The temperature of the ambient air surrounding the body to be cooled.
When applied to convectional cooling, it is the temperature of the ambient air
directly prior to its flowing over the body to be cooled.
Air Flow Movement of ambient air across a body to be cooled.
The flow of ambient air is critical to convectional thermal management in particular
if the ambient air is recycled (reflowed over the body to be cooled). Continuous
recycling without cooling of the ambient air will quickly lead to overheating. In
addition, the cooling effect of air flow in itself is limited. It requires a minimum
velocity in order to have any cooling effect at all, and above a given velocity no fur-
ther increase in real cooling effect is achieved.
Heat Spreader A mechanism to achieve a rapid transfer of heat away from one body to another.
Heat Sink A mechanism to achieve a (rapid) transfer of heat away from a body and to act as
a transport medium to another body or fluid.
Heat Pipe A special form of heat spreader which employes both conduction and convection
in a discrete body to achieve a rapid transfer of heat from one body to another or
to a fluid.
Table 6-1: Thermodynamics Terminology as Relating to the VMP3
TERM DEFINITION