[myv65]

I'm certain not everyone will agree with my statements. So be it. Here's an engineer's take on the situation and why BigBen2k has the right idea.

You can look at a radiator as basically a series of thermal resistances. You have to get thermal energy from the fluid to the tubing. You have to convey that thermal energy from the tubing to the fins. You have to dissipate that thermal energy from the fins to air. Along the way you run into interface resistances between the tubing and fins as well as the potential for fouling of the tubing via scale and crud in your fluid.

The only part of the picture that fluid flowrate can affect is energy exchange from the fluid to the tubing walls. Convective energy exchange is defined by the equation q = h * A * delta-T where "q" is energy, "h" is convective coefficient, "A" is surface area, and delta-T is the local temperature differential between the fluid and tubing wall. For you calculus knobs out there, we're actually talking heat flux integrated across the entire surface area where delta-T is a function of position.

"A" is fixed by our radiator. If we assume for a moment that "q" is fixed, ie no change in energy dissipation versus flow, then we recognize that h * delta-T must be a constant. "h" is a function of many things, but the dominant factor for a given fluid that determines this is the fluid's velocity. If velocity goes up, "h" goes up with it. This tells us that delta-T should drop as velocity increases.

If this is true (and it is), then higher flowrate would be better provided you could get it without adding more energy to the system. Therein lies the rub. You can't get more velocity without putting more energy into the system. So now the question becomes, "How do I find the radiator's sweet spot?"

The only practical answer is through experimentation. Qualitatively, you can describe the process, but quantitatively is another story.

"h" does not increase linearly with velocity. "h" tends more to a fractional power on the order of velocity ^ (1/2). This means that increasing velocity by a factor of ~4 is required to double the convection coefficient. Power required to generate flow doesn't go up linearly either. Unfortunately, it requires ~ 4 times the pressure to double the flow. Translation: At some point, power that you put in goes up more quickly than the benefit you gain from higher convection.

Let's also remember that flowrate * delta-T (fluid in vs fluid out of radiator) is constant for a constant energy input to the system.

In the real world, this means that at very low flow rates, the fluid leaving the radiator will be practically at ambient temperature, but must be pretty darn warm entering. This is obviously not ideal. At extremely high flow rates, it takes so much energy to push the flow around our loop that the fluid will be almost a constant temperature going through the radiator, but that constant will be well above ambient. In the "sweet spot", flow is high enough for good velocity, yet not so high that copious excess energy gets dumped into the fluid to pump it around.

The differences are pretty minor and it isn't like there's a sharp point defining the optimum flow rate. You will find that radiator dissipation is more like a gentle hill with a gradual drop in performance from its peak.

Where you'll get bit is if the radiator is simply too small or the airflow rate too low to dissipate the necessary power.

Cova,

I'll also be brutally blunt. Virtually zero of the pump's ineffiency gets released from the housing as heat. What you feel when the casing gets hot is the motor's ineffiency. I am sorry that you will no doubt find this offensive, but I'll take the concerted agreement of all those that work in the pump field over the unstudied opinion of an anonymous pump user any day.

At some point I gotta say, sorry, but that's simply the way things are. If after all the explanation in the other thread you still disagree, that is certainly your call. But if you wish to continue believing this try finding some hard data to back up the position. Other than heresay from others without solid background, you will find nothing.