My dumb question of the day...what is “pressure recovery”?

[hoffman900]

I think one has to remember, there are multiple instances in these engines where this occurs. 1) the carburetor Venturi 2) the MCSA (pushrod pinch for a lot of you) 3) the valve seat / valve (which is in constant flux).

Plenty of places for loss of total pressure.

[GARY C]

I think one has to remember, there are multiple instances in these engines where this occurs. 1) the carburetor Venturi 2) the MCSA (pushrod pinch for a lot of you) 3) the valve seat / valve (which is in constant flux).

Plenty of places for loss of total pressure.

Unfortunately most any info available on these subjects are based on opinion or computer models that do not hold true in real world comparisons and the real world examples published leaves one to conclude that a lot of the #'s floating around out there really don't matter as much as we are lead to believe.

It seems most are willing to claim how important some of these things are but can never give one a direct answer to what one needs for a given application and the few that are willing to give a direct requirement for an application are eaten alive by those not willing to answer.

This is not directed at you hoffman, you have been one of the few here to answer some of these things even with my stupid questions, but it just seems that at any given time there are 3 or more threads claiming how important something is and 3 or more threads asking about those exact things and maybe i the critical thread itself, yet none of those asking about a specific combination or situation will ever get an answer.

[naukkis79]

What the equation is saying is - you can convert pressure into velocity and back again. If there are no losses (due to friction, excessive turbulence etc), the final pressure in the cylinder (assumed stagnant) will be atmospheric because the air was initially at that pressure and zero velocity before entering the intake. In fact (again assuming no losses) the "total" pressure (static + dynamic) should equal atmospheric at any cross section along the intake tract.

"Pressure recovery" is simply describing how much of the total pressure is retained in the transition from maximum velocity near the valve seat and "zero" velocity in the cylinder. If there were no losses (perfect design), the total pressure would be the same at both points.

Nope. If you have one liter air at some pressure you can convert that pressure to velocity and pressure again. With pipe with open end to atmosphere(unlimited amount of air) there's constant pressure accelerating air in pipe, so in pipe air can have both near atmospheric pressure and up to mach speed.

And result is, if there's a cylinder with full vacuum connected with pipe to atmosphere, when that pipe is opened cylinder will be filled to much higher pressure than atmospheric before flow is reversing. Resulting pressure in cylinder is about energy in intake pipe flow and pressure recovery capability, how efficiently that energy is converted to pressure.

[SpeierRacingHeads]

BERNOULLI 101

http://speierracingheads.com/bernoulli-101.html

[naukkis79]

Bernoulli says that you can convert amount of air, like one liter one bar pressure of air to flow which energy is same, and if there's no losses, by stopping that flow recover back to one liter one bar pressure of air.

When there is unlimited amount of one bar pressurized air that pressure can accelerate air to much higher speed than what one liter is able which again is recoverable to fixed amount, like one liter to much higher pressure than one bar. There's nothing against physics laws, just higher volume of low pressure air converted to flow energy which can be converted to lower volume of higher pressure air.

[SpeierRacingHeads]

Bernoulli says that you can convert amount of air, like one liter one bar pressure of air to flow which energy is same, and if there's no losses, by stopping that flow recover back to one liter one bar pressure of air.

When there is unlimited amount of one bar pressurized air that pressure can accelerate air to much higher speed than what one liter is able which again is recoverable to fixed amount, like one liter to much higher pressure than one bar. There's nothing against physics laws, just higher volume of low pressure air converted to flow energy which can be converted to lower volume of higher pressure air.

What accelerates that air? HEAT

[naukkis79]

What accelerates that air? HEAT

Pressure differentials.

[rebelrouser]

Might be better explained through an old Stanford University video of Flow Visualization. Focus on minute 13 through 22 for the diffuser part since the air exiting the valve seat area and going into the chamber is a lot like air going through a diffuser. The point here is that you don't want the exit walls at such a large angle so as to cause the flow to stall. The video doesn't give us an ideal wall angle, but suggests it's much closer than people think. Hence, in developing flow past the intake valve angle, the top angle and the chamber wall should be right up close to the actual flow path for max intake flow.

great video thanks for sharing

[SpeierRacingHeads]

What accelerates that air? HEAT

Pressure differentials.

Your saying just simply because of area, that is what accelerates the air?

Once its at the apex of the venturi the pressure drops and the temp drops with it. A perfect example of the conservation of energy. The total energy stayed the same it just transformed into other forms. The heat energy was used to accelerate the air! Once the air slows down and the pressure rises the heat is absorbed giving back the working fluid its pressure. The cause of all this change is,,, wait for it,,, AREA.

[68corvette]

What accelerates that air? HEAT

Do you mean that without heat there is not pressure?

[hoffman900]

Not entirely true, there is a reason an electric car holds the record up Pikes Peak now.

Temperature (and other things) drives the spacing of the molecules which controls the mass in a given volume (density). Obviously the more mass you have in a given volume, the more weight (mass * gravity) it will have and exert a great amount of pressure, everything below it.

[SpeierRacingHeads]

What accelerates that air? HEAT

Do you mean that without heat there is not pressure?

No, I'm saying pressure recovery is about area. And heat is an accelerator.

What you do with that area is up to the porter. BUT you better be doing something with the heat as well.

My opinion and it doesn't appear some agree.

It's all good.

[mk e]

Heat rise is what you get when the pressure is not recovered, it is the inefficiency in the system. The goal is to fill the cylinder not make heat.