BobOk, here goes
Ok, first
I'll agree with you regarding methanol and water being much better for the liquid side of the cooling equation of computers from a thermal standpoint.
Hmmmm... where to start regarding the rest... too much for one post
Note: all comments are geared towards the cooling systems at hand - low viscosity, low temperature, newtonian fluids. (the term 'low' being relative - temps under 80C and viscosities such that the liquids are considered "thin" compared to "thick" fluids like oil)
* and the winner is *
Viscocity
The kinematic viscosity is the important value
Dynamic viscosity
alone is of lesser importance.
First a little piece of info you may not know.
Kinematic viscocity and
Dynamic viscocity can be related to one another through a material's
density. Here's the relationship:
Kinematic viscosity
v (Greek letter nu)
Dynamic viscocity
u (Greek letter mu)
Density
p (Greek letter rho)
v =
u/
p
In the case of thermal designs using liquid, there are 3 important and inter-related issues:
The
Reynold's number (an indicator of flow type - from fully laminar to extremely turbulent) for the fluid flow - this affects directly both the
frictional losses and the film coefficient.
Frictional losses through the system - this affects the final
mass flow rate (which subsequently also affects the
velocity of the flow).
The
Film Coefficient (also called the convection heat-transfer coefficient) - in this realm, a measure of the
heat transfer between the fluid coolant and the solids it passes through (both block and rad in this case).
Here are the fluid characteristics which are used to calculate each of these 3 very important values:
Reynold's Number - this is a dimensionless number (no units of measure associated with it) that is a relationship between the inertial forces and the viscous forces in fluid flow. The characteric of the fluid used to calculate this number is the
kinematic viscosity.
Frictional losses - the number of friction factor correlations in unreal, but - they all use the same flow properties, the differences are in how they handle the geometry of the channel the fluid flows within.
For
laminar flows, it's pretty straightforward - it depends
only on the Reynold's number. For
turbulent flows, it depends upon both the Reynold's number
and on the surface features and geometry of the channel the fluid flows through. No
direct fluid properties are used - these are taken into account through the use of the Reynold's number.
These frictional losses are usually discussed in terms of
head and are what determine what the flow rate through the system is for a given pump. The flow rate of course also determines the velocity of the flow at any point in the system.
Film coefficient - this is the 'ultimate' value that determines the heat flux from the solid (water block in this case) to the fluid flow and from the fluid flow to the solid (heat exchanger, radiator, heater core). The basic equation for the heat transfer is as follows:
Q/A = h * (Tw - Tf) where
Q/A is heat flux per area,
h is the film coefficient,
Tw is the Wall temperature, and
Tf is the Fluid temperature.
The film coefficient is calculated from the following characteristics of the fluid flow - the thermal conductivity of the fluid, the Reynold's number for the flow, and the Prandtl number (another dimensionless value that characterizes convection - it relates the hydrodynamic and thermal boundary layers, linking velocity and temperature and is equal to the
kinematic viscocity divided by the thermal diffusivity).
Hopefully, you can now see why kinematic viscosity is the "important" viscosity as it were
.
ps. Be careful around here about asking for Avatars and labels - just ask ECU Pirate, lol
