Dyno load control

[Moriniman]

I've been thinking about a possible water brake Dyno installation with a limited water supply. To lower the water consumption, I was considering using a temperature controller on the output valve.

A bit of research found the following patent; US-5,834,654

It uses both valves to control the load quickly, but uses an offset between the valves for temperature control.

[Tony]

If water is in very short supply, IMHO, a much better solution would be to build a cooling tower, and a storage tank (or cooling tower sump) large enough to absorb sudden water temperature changes going back into the dyno.

There should essentially be no water loss from a cooling tower, except through evaporation. It will still consume a surprising amount of water, but nothing like a total loss system.

The main advantage is that you can then design your water brake to have a water flow high enough so that temperature rise or boiling is never going to be an issue.

All you need is one variable speed pump to run the entire system, dyno and cooling tower. No other flow control system is needed, just one pump. The dyno itself will generate the massive pressure to spray a fine mist of water into the cooling tower.

[86rocco1]

We use about a 750L storage tank for our dyno and recirculate the water, larger would of course be better but our tests are almost always fairly short duration tests so heat buildup in the tank hasn't been an issue, at least not to date.

[106-1194218389]

[86rocco1]

Heat's definitely an issue, all that engine power doesn't just disappear it goes into the water as heat. I've calculated the cooling load required for our dyno, they're rather significant and quite frankly, I'm surprised we've never had problem, I guess the metal tank and pipes dissipate more heat than you'd think. But if we were to do extended testing I'm quite certain our current set-up would need to be upgraded.

[Moriniman]

I don't really have room for a cooling tower and there are serious implications about Legionella.

I've got the offer of a Froude DPX-0 which uses sluice gates between the rotor and the stator plates whilst remaining full of water. The manual talks about four gallons (imp.) per horsepower per HOUR, which is a very much lower water consumption that most other types. The DPX is quite bulky and the sluice gates take quite a lot of effort to operate, so it would be harder to automate. The minimum torque is also rather high. To go lower you have to open the drain valve and lower the water charge, just as you would with most other water brakes.

Making a much more compact Stuska/L&S style absorber with a simpler control system has its attractions, but the large water flow required does have it's problems. Reading up, it's possible to retrict the outlet water flow, but you then get the penalty of a sluggish response. The water charge in the absorber is related to the difference between the water coming in and the water going out. Conventionally the outlet is fixed (smaller) and the inlet controlled. It seemed to me that simultaneosly controlling both would allow a faster fill and faster emptying, but also a lower throughput of water.

[86rocco1]

4 gallon per HP per hour doesn't seem right. How do they dissipate all the heat?

Consider this, 1 HP equal approximately 740 watts, if you put a 740 watt immersion heater into a 4 gallon bucket of water, the water would start to boil in MUCH less than an hour. In fact, if the bucket were very well insulated, it would start to boil in about 8 minutes, and after 1 hour, all of the water would have been vaporized.

[Tony]

It is pretty easy to work out.

In Imperial units, one horsepower = 42.44 BTU/minute.
1BTU raises one pound of water by one degree Fahrenheit.

In metric units, one horsepower = 10.68 calories/minute
One calorie raises 1cc of water by one degree Celsius.

Four imperial gallons of water (not US gallons) weighs forty pounds.
If you feed one horsepower into that for one hour, it would raise the temperature 1.061 degrees per minute, or roughly 64 degrees Fahrenheit in an hour. That is doable.

But 1Hp is not a lot of power.

50Hp = 200 gallons per hour
500Hp = 2,000 gallons per hour

That is rather a lot of water.

[86rocco1]

[Tony]

Yes, you are quite right. I never bothered to work it out in metric.
If I had, the mistake in the units would have been glaringly obvious.

Water is great stuff for absorbing heat, but a lot of heat still requires a great volume of water.