Could pressure washers solve the Australia bushfires problem?

[RobertGC]

TL;DR Summary

Can pressure washers throw water stream thousands of meters into the air?

The JetLev water pack puts out about 60 psi but can lift a 400 pound weight 30 feet in the air.

A lot of water can be provided by just those water jet pack units, 1,000 gallons per minute, providing 400 pounds of force, all of that powered by a 200 hp pump that trails behind remaining in the water:



According to the formulas, you can get 10 meters height of a water stream for each bar(atm) of additional pressure. There are pressure washers than can put out 4,500 psi, 300 bar. Then theoretically they could send a water stream 3,000 meters in the air, 3 km(!)

Then could we use these with a water source such as rivers, creeks, and lakes to put out fires kilometers away?

Pressure washers for home use only put out a few gallons per minute. But we could combine thousands of them for this purpose.

Has anyone tried simply pointing a pressure washer straight up at its highest pressure setting, that is, not as a spray, to see how high the water stream can go?

 

[berkeman]

I don't think the limiting factor is water pressure -- it's getting the water source close to the fire.

 

[anorlunda]

Also quantity of water. 1 one inch rainfall dumps about 17 million gallons of water per square mile. 5 days ago, there were about 32,000 square miles on fire. A 1 inch rainfall in one hour might or might not be enough to put those fires out. Let's say 3 inches in one hour to be safe.

Put those numbers in your calculator and see how many pumps you would need.

 

[Baluncore]

In Australia, bush fires spread when there are high winds. Those fires run through the tree canopy with spot fires jumping several kilometres ahead of the main fire front. Catastrophic fires cannot be controlled when they occur.

Most fire brigades in Australia have vehicles fitted with similar pumps to a JetLev. Those tanker vehicles can only protect local structures where sufficient defensive preparations have been made before the fire season. They are used to extinguish small fires or hot spots at calmer times, so as to prevent catastrophic fires starting when the high winds return.

Fires are a natural part of the environment. Stable forests and grasslands develop naturally by selecting flora and fauna species that inherently reduce the intensity of fires. Fires become a problem when we change those ecosystems, or the climate. Both are changing now.

 

[256bits]

Summary:: Can pressure washers throw water stream thousands of meters into the air?

Then theoretically they could send a water stream 3,000 meters in the air, 3 km(!)

Theoretically, using projectile motion in a frictionless air.

That's a problem, though, as the air does provide friction acting against the jet flow. In addition, there can be aeration of the jet, increasing its evaporation rate. Perhaps after the 3 km as you suggest, depending upon the jet size, there would be little water, if any, left to put out a fire.

Just a lookup, I found this
https://www.flow3d.com/wp-content/u...ucket-of-Cakmak-1-Diversion-Weir-and-HEPP.pdf
for a spillway "jet"
The distance reached by a real jet with air entrainment, versus the theoretical jet, is on average 16% reduction in horizontal distance for this study. Table 2.

Although directly not applicable, since the air entrainment is induced into the stream in the study, that might be an engineering challenge to overcome for a 3km jet.

 

[Baluncore]

A simple nozzle will throw an arch of water some distance, but the water column will quickly break up and fall as droplets.
A laminar flow nozzle can throw an arch of water that does not break up so quickly in flight. It will throw to a significantly greater height and distance.

 

[anorlunda]

Fires are a natural part of the environment.

I learned that the same applies to Central Florida. Scrub pines and scrub oaks, both about 2 m tall, work together to create crowning fires once every 30-50 years. The crowning fires kill trees taller than 2m, that could block sunlight from reaching the scrub species.

The forest service began putting those fires out. To compensate, they need to clear cut every 30-50 years. But that still leaves the majority of the areas not clear cut covered with tall trees rather than scrub trees.

 

[Baluncore]

The forest service began putting those fires out. To compensate, they need to clear cut every 30-50 years.

That may be their excuse.

Here it requires significantly more water to grow a new forest than it took to maintain the stable old forest. When a forest is cleared and replanted it becomes a dry monocultural fire hazard. The once continuous flowing streams from the valleys cease. The soil becomes so dry that any fire consumes all, including the organic components of the soil. Then it rains on the ash bed and mineral soil, resulting in flash floods with severe erosion, choking waterways and reservoirs, reducing the reliable water supply and hydroelectric generation. All for the love of cheaper cardboard.