Quote:
Originally posted by EMC2
Bob
Ok, 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 
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i had some help with this, several chemists, a PhD in chemical engineering, and a couple of mechanical engineers. all of whom pointed at the dynamic viscosity as being the measurement most relavant to what we're doing in computer cooling. this might be a technical issue, as the kinematic viscosity of methanol also vastly oustrips antifreeze (or ethylene glycol if you like) but to break the differences down between them into laymans terms as i understand them, dynamic viscosity measures the amount of resistance or drag a liquid moving through a tube or capillary deals with (or a hose such as the ones we're using in cooling computers) and kinematic viscosity measures the amount of drag or resistance a solid object encounters when moving through a liquid (such as dropping a ball in a bucket of liquid). airplanes, cars, buildings and submarines measure the kinematic viscosity because the object is moving through a liquid (air or water in this case). measuring the amount of resistance or drag of oil in a pipe however (for example) will use the figures found in the dynamic viscosity ratings.
i am purposely using laymans terms so everyone can understand this and the differences between them. am very familiar with reynolds numbers and laminar flow coefficients.
in the end, both apply in some regard i suppose, and i have no doubt your knowlege of this is quite comprehensive as you've demonstrated. but i'm going to stand by my figures and the means in which it's measured. i feel it's the best way to represent the differences and directly provide us with the most accurate figures for a comparison that is relavant to what we're doing. thanks though for the time and energy you spent putting into this though. very informative.