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File: Weed.jpg (9 KB, 232x217)
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Can I use an electric weed torch as an air supply for a forge?
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>>2295046
does it blow air
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Yeah they blow air that's like 1200 F
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>>2295046
I've never used one, but if it blows air it'll work at least somewhat.
The temperature of the air doesn't really matter afaik. All the heat comes from your fuel. Maybe for high performance smelting work or something, but just making coal burn hotter all you care about is increasing the oxygen supply.
What you want is a controllable high volume of low speed air flow. A purpose made forge blower is best but anything that moves air can work. I've got a hair dryer wired to a regular household dimmer switch and it's fine, easily gets hot enough to burn steel if I'm not careful. Adjustment is a little imprecise and the air velocity is higher than is ideal for the volume so I need a deeper bed of coals if I want to make sure all the oxygen is consumed to minimize scale formation, but it works more than well enough for my needs.
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>>2295046
Aren't they highly inefficient
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>>2295074
if you have the right volume of air but the velocity is too high, what you need to do is increase the cross sectional area of your setup. If you change the velocity of air flow through a pipe you're necessarily going to change the volume of airflow by the same amount. You cannot change one without changing the other until your airflows become compressible, but that doesn't start happening until you hit very high velocities nearing the speed of sound.
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>>2295046
>>2295058
>>2295066
the air doesn't have to be hot faggot, that's what the fuel is for
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>>2295092
>He doesn't know about preheating his air
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>>2295080
inefficiency is just bitch talk for "I didn't get as much done in the time I wanted to"
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>>2295074
>The temperature of the air doesn't really matter afaik
This is correct. It's just about introducing more oxygen. Use of heated air is a waste. A thrift store hairdryer on cool (or with the heating element clipped) is perfect.
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>>2295046
dude weed lmao
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do americans really smoke weed out of power tools
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>>2295485
It kills weeds by cooking them.
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>>2295074
fpbp
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>>2295193
Sounds like melanated talk for "I'm lazy and accept trash results"
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File: index.jpg (261 KB, 1229x1326)
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>>2295490
Not really.
If you're burning the weeds out then you aren't killing the root at all, it has enough energy in reserve to keep growng back several times over.

What your supposed to do is just gently wilt the leaves. This way the root will blow its entire load trying to repair the leaves instead of growing new ones.
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>>2295178
Hot air is less dense which reduces the oxygen density as anyone with a basic education should know.

Why do you mongs imagine charge cooling is used to boost HP?

Want to succeed? Copy success until you actually learn enough to invent something effective.

Why do you people think giving your fire less oxygen will increase heat output?
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>>2296623
Engines are limited by heat more than anything, charge cooling is primarily to counteract the heat generated by compression, by my understanding. Obviously expansion is a big part of that, but it's not really a comparable scenario.
In a forge you want as much heat as possible. Preheating an air supply is standard practice in industrial furnaces. https://www.energy.gov/sites/prod/files/2014/05/f16/et_preheated.pdf
Worth doing on a small scale forge? Not likely, but it's a much closer analogue than ICE
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Dad started a fire other lawn with the propane version a decade ago. Didn't stop him from burning giant black ugly ass holes 8n the lawn for no reason tho. Just fucking pull out the dandelion man
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>>2295710
>you aren't killing the root at all
this
in Germany the city workers use hot water boilers, they look like diesel heated pressure washers without the pump, the hot water flows in the cracks down to the root.
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>>2296674
>Engines are limited by heat more than anything
Engines are hard limited by the cylinder volume, i.e. how much air you can shove in there per cycle. Turbochargers heat air when compressing it, so if you cool it back down it becomes more dense and you can push more of it (by mass) into the cylinder under the same pressure to burn more fuel and extract more energy.
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>>2297162
Yeah, that's why they fit turbos with charge cooling in industrial furnace settings instead of preheating heat exhangers
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>>2295046
>Can I use an electric weed torch as an air supply for a forge?
I used a blowdryer, really your imagination is the limit anon.
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>>2297214
https://energy.gov/sites/prod/files/2014/05/f16/et_preheated.pdf

51% fuel savings maximum

When making heat is the goal, you always preheat so you don't waste fuel heating up the relatively cold intake air as well as the furnace
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>>2297214
Indeed charge cooling reduces efficiency because you essentially dump outside part of the energy supplied by the compressor, but in piston engines densifying the charge to extract more power from the same cylinder volume (as well as keeping it cool to prevent knocking) is more important than chasing efficiency when you're turbocharging the engine.
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>>2297234
Yes except we're not talking about an IC engine here, we're talking about heating a furnace
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>>2296623
That's only relevant in a heat engine where you're using expanding gas to do work. A forge only cares about more heat, so preheating the fuel and oxidizer works well and actual industrial forges do it.
You lack a fundamental understanding of the actual processes at work. lrn2physics
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>>2297252
The primary fuel is already accomplishing this, the airflow in this case is to provide more oxygen to increase the burn rate. The biggest problem I see with this is the longevity of the heating element. Like any heat gun, they work but are they really designed to be operated for extended periods?

Honestly this sounds like a decent experiment. Does preheating forced air produce better results? It may even be detrimental due to how gasses expand under heat. Chilled air would have a higher density of oxygen.
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>>2297252
>except we're not talking about an IC engine here,
The post I was replying to did.
Preheating in industrial furnaces serves a different purpose. Air is mostly nitrogen and there's only so much energy in common fuel types, so the temperature you can possibly reach by just burning it with air is often not quite high enough for things like melting metals for example. But if you somehow preheat the air without using the oxygen it contains (using electric heater or heat exchanger) before introducing fuel, you can raise the final temperature without having to switch to oxygen or more exotic and expensive fuel with higher specific heat of combustion.
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>>2297042
>in Germany
I need to kill 6 gorillion weeds in 5 years. You think this will work?
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>>2297042
Ahh yes Germans and their overly engineered autistic shit
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>>2297299
>Like any heat gun, they work but are they really designed to be operated for extended periods?

Depends highly on the gun. The lifetime of a heating element is proportionate to both the ratio of its surface area to volume (e.g. how thick the wire it's made of is) and how hot it is at operating temperature.

There's a parameter called "watt density" used in designing heating elements, which is a simple power-to-surface-area ratio. An acceptable range for watt density is extremely dependent on the configuration of the heater. A kiln expected to get to around 2000°F with a coiled heating element sitting in channels would normally be in the neighborhood of 13-15W/in^2. A heating element sitting in a stream of forced air (such as in a space heater or hair dryer) could easily be well over 50W/in^2, depending on how much airflow it's getting.

If you wanted to go full autismal on it, you could take apart the heat gun, measure the heating element, power draw, and airflow, then determine from that whether the heating element is at a reasonable watt density for long life.

Perhaps way easier is to just look at the color of the heating element when it's running. If it doesn't glow, it's going to basically last forever. If it gets dull red, it will likely last for a few decades. Orange, a few years. Yellow, probably not very long. White, something has gone very wrong and the element is actively melting.


Unless the element is being driven pretty hard, however, it almost doesn't even matter. The shitty brushed motor powering the fan is almost certainly going to fail before the element does.
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>>2297299
>Does preheating forced air produce better results? It may even be detrimental due to how gasses expand under heat. Chilled air would have a higher density of oxygen.

To expand on what >>2297321 pointed out, the combustion of a fuel/air mix adds a fixed amount of energy to the products of the reaction. The ratio of fuel/air required for a stoichiometric mix does not change, regardless of actual mass flow rate. In other words, the amount of heat added per unit mass of fuel/air doesn't change. If the fuel/air mix expands, all that really means is that you require a higher mass flow (in practical terms, velocity/airspeed) to move the same amount of combustion product through the system.

As the amount of energy added to the combustion products is fixed per unit mass, that means that the actual temperature of the combustion products are dependent on how much heat the reaction releases and the temperature the reactants were before they were burned. If, for example, you have a fuel/air mixture that produces a temperature of 3600°F when the fuel/air started at 70°F (this is typical for a propane/air flame), you can get that same mixture to produce a 4000°F flame if you preheat that mixture to 470°F.
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>>2297667
(cont'd.)

Since the amount of energy transferred to the workpiece per unit fuel burned is heavily dependent on the temperature difference between the workpiece and burned gasses around it, this can make a huge difference in efficiency of a furnace/forge. If, say, you're trying to melt iron with propane, the temperature difference between the melting point iron and flame is only about 800°F. Were you to add another 800°F to the air/fuel mix before it was burned (which is perfectly doable), you could double that difference, effectively putting twice as much heat into the iron for the same amount of fuel consumed. This doesn't quite work out to using only half the fuel, as the relatively temperature difference decreases when the iron isn't at its melting point, but the savings is significant. It also greatly decreases the amount of time required to heat up your melt/workpiece to working temperature, too.

That's why some people use hair dryers/heat guns as blowers. The preheated air makes the overall system more efficient. That being said, a far better way to do it is to harvest the hot gasses being blown out of the furnace/forge and pass them through a heat exchanger. The vast majority of the heat being put into these heating devices (we're talking like 80% or more) is just being blown right back out of them. Recapturing some of that heat and using it to pre-heat the incoming air results in a radical increase in efficiency. A gas-powered melting furnace, for example, can cut its fuel use to just a third of what it was before with a well-made heat exchanger. The only downside is the obvious one: It's more complicated than just sticking a hair dryer on the intake.
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>>2297677
>That's why some people use hair dryers/heat guns as blowers
I'm really skeptical that a hair dryer on the intake of a simple forge would make any noticeable difference. People just use them because they're convenient.
Maybe on a wood fired forge that struggles to hit welding heats, using a good heat gun that blows a couple hundred c could make a significant difference, but the real advantage is just that they're a decently high performance ducted fan you can get for 2.50$ at thrift stores.
Particularly if you're just forging and not trying to backyard cast iron a simple hairdryer is more than enough to burn your steel into a useless lump if you stop paying attention to it for a minute.
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why? it's a huge waste of electricity compared to a regular blower, and probably won't push enough air anyways
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>>2296674
i'd say maximum compression ratios are the biggest hindrance to engine performance
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>>2297611
they have to use shit like this because all herbicides are outlawed for use on pavement.



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