compound numbers

You have time and time again stated to everyone and yourself the fact that mass flow is dependent on fluid density, and volumetric flow is independent of density. This is true and i agree with that statement.

M(dot) = V(dot)*rho

You have to density compensate the mass flow to show the true flow through the second compressor.

Again, the fluid density changes with temperature and pressure, and thus the mass flow will change.

Mass flow is shown on the maps for the simple reason of convention. Other compressors move fluids where the end user needs to know the physical amount of fluid being moved. You don't care about that, so why all the fuss?

We are indeed on the same page conceptually.

Your tone and quips are unnecessary and detract from the conversation.
 
CSM diesel said:
You have time and time again stated to everyone and yourself the fact that mass flow is dependent on fluid density, and volumetric flow is independent of density. This is true and i agree with that statement.

M(dot) = V(dot)*rho

You have to density compensate the mass flow to show the true flow through the second compressor.

Again, the fluid density changes with temperature and pressure, and thus the mass flow will change.

Mass flow is shown on the maps for the simple reason of convention. Other compressors move fluids where the end user needs to know the physical amount of fluid being moved. You don't care about that, so why all the fuss?

We are indeed on the same page conceptually.

Your tone and quips are unnecessary and detract from the conversation.
Click to expand...


For that I apologize. I wasn't blessed with same level of patience that many seem to have.

What you should realize, is that the argument by some has actually been that mass flow is technically correct for the compressor, and while this very well may be, everything I have seen, and what I have shared here stands is staunch opposition of that. Hence the fact that I couldn't just throw up my hands and bow to mass flow, although that would certainly be easier than arguing.
 
On that note, would you be interested in the math behind all this? Compressible flow and all the gritty details? Mass flow becomes much more necessary then... Dealing with possible sonic flows and stagnation.
 
CSM diesel said:
On that note, would you be interested in the math behind all this? Compressible flow and all the gritty details? Mass flow becomes much more necessary then... Dealing with possible sonic flows and stagnation.
Click to expand...

Math behind what? Centrifugal compression?
 
CSM diesel said:
compressable flow. Local speeds of sound, mach numbers, and maximum local mass flow.
Click to expand...

Skip the others and just jump straight to "maximum local mass flow" if you will. Because I am still interested to see how a maximum mass flow can occur without reference to the volume of media, or at the very least, the size of the flowable area. I imagine that fluid density can readily increase without any inherent flow limit right up to the point of phase change.

The others seem pretty straight-forward. Having a mass flow limit for a fluid like air without referencing volume, whether directly or indirectly with temperature and pressure still seems strange to me.
 
I have an unrelated question for both of you. Out of curiosity, are either of you wearing a pocket protector that contains at least one mechanical pencil?

I know Cliff is.
 
RonA said:
I have an unrelated question for both of you. Out of curiosity, are either of you wearing a pocket protector that contains at least one mechanical pencil?

I know Cliff is.
Click to expand...

I'm wearing a Swamps Diesel T-shirt with no pocket, sitting here eating a bag of cool ranch doritos and wishing it would stop RAINING so I could get back to work.
 
Charles said:
Skip the others and just jump straight to "maximum local mass flow" if you will. Because I am still interested to see how a maximum mass flow can occur without reference to the volume of media, or at the very least, the size of the flowable area. I imagine that fluid density can readily increase without any inherent flow limit right up to the point of phase change.

The others seem pretty straight-forward. Having a mass flow limit for a fluid like air without referencing volume, whether directly or indirectly with temperature and pressure still seems strange to me.
Click to expand...

This isn't A la carte. They are all necessary to arrive at what you desire.

Assuming isentropic and adiabatic conditions... (one, two, skip a few...)

p2/p1=(t2/t1)^k/(k-1) or p2/p1 = (rho2/rho1)^k


we arrive at.... (again skipping lots of boring stuff im sure no one cares about)

a = (kp/rho)^.5 or a = (kRT)^0.5 speed of sound

a(ft/sec) ~ 49(T(Rankine))^0.5

^dimensional formula for those who dont like lots of variables.

moving on to mach(Ma)... skipping lots of steps and several correlations that make this all possible, we arrive at these little guys: (using k = 1.4)

Ma = V / a

T(not)/T = 1+0.2Ma^2

rho(not)/rho = (1+0.2Ma^2)^2.5

p(not)/P = (1+0.2Ma^2)^3.5

you can use temp the easiest for this (T(not), rho(not) & p(not) are stagnation numbers) you can measure T, rho, and P

Ma^2 = 5*(T(not)/T-1)

solve for Ma. If you are b/w 0.3 and 0.8 you are good to go and subsonic.

From mach, we can simplify the ideal gas law to:

rho V A = rho* V* A* (* = sonic conditions)

skipping lots again...

A/A* = (1/Ma) ((1+0.2Ma^2)^3/1.728)
knowing your mach # you can find the area ratio to where sonic conditions will exist. The one listed above is for areas. you know your flow areas.

finally moving to choke conditions... skipping steps again

Mdot MAX = (0.6847 P(not) A*) / SQRT(R T(not))
and now local conditions:

Mdot MAX = (0.6847 P(not) A) / SQRT(R T(not))


Just use the formulas in bold.

And there ya have it.... Your free education on compressible flow.

:Cheer:


FML
 
Last edited:
CSM diesel said:
This isn't A la carte. They are all necessary to arrive at what you desire.

Assuming isentropic and adiabatic conditions... (one, two, skip a few...)

p2/p1=(t2/t1)^k/(k-1) or p2/p1 = (rho2/rho1)^k


we arrive at.... (again skipping lots of boring stuff im sure no one cares about)

a = (kp/rho)^.5 or a = (kRT)^0.5 speed of sound

a(ft/sec) ~ 49(T(Rankine))^0.5

^dimensional formula for those who dont like lots of variables.

moving on to mach(Ma)... skipping lots of steps and several correlations that make this all possible, we arrive at these little guys: (using k = 1.4)

Ma = V / a

T(not)/T = 1+0.2Ma^2

rho(not)/rho = (1+0.2Ma^2)^2.5

p(not)/P = (1+0.2Ma^2)^3.5

you can use temp the easiest for this (T(not), rho(not) & p(not) are stagnation numbers) you can measure T, rho, and P

Ma^2 = 5*(T(not)/T-1)

solve for Ma. If you are b/w 0.3 and 0.8 you are good to go and subsonic.

From mach, we can simplify the ideal gas law to:

rho V A = rho* V* A* (* = sonic conditions)

skipping lots again...

A/A* = (1/Ma) ((1+0.2Ma^2)^3/1.728)
knowing your mach # you can find the area ratio to where sonic conditions will exist. The one listed above is for areas. you know your flow areas.

finally moving to choke conditions... skipping steps again

Mdot MAX = (0.6847 P(not) A*) / SQRT(R T(not))
and now local conditions:

Mdot MAX = (0.6847 P(not) A) / SQRT(R T(not))


Just use the formulas in bold.

And there ya have it.... Your free education on compressible flow.

:Cheer:


FML
Click to expand...



This will take me quite some time to grasp, as there is little if any conception given, and little variable declaration. I will probably have to wait until after work today when I can look up the portions I need before I can start to work deciphering through it. Although just off-the-cuff I did find it humerous that area was mentioned in relation to the last section on maximum flow. I specifically stated that I expected that flowable area would rear it's head. Without working through the equations and uncovering the conception behind them I can't say at present, but I will say that I will not be shocked if I learn that the choke is still volume flow dependent.

Even though it is little more than a pile of equations, thank you for that. Now I hope to work through them later today.
 
I will do the algebra and fill in the blanks after i get off of this job and drive back to civilization.
 
You can get computer programs to calculate the compressiblity values. Those formula works. The map does change for the different suction pressure. Mass flow at the inlet is the same at the discharge. Actual volume (flow) ACFM at the suction isn't the same at the discharge. The mach number determines where the choke line is, and the engine will start to push the Air/fuel ratio as it takes more work to generate more air.

They just rate the maps at mass flow (lbs/min) cause that way turbochargers are done. Most people just run them as a single and the manufacturer usually just provides numbers for 14.73 psi ambient pressure. You guys are basically saying the say thing, just a different way. Everything is based off the fan laws used in centrifugal compressors.
 
Mike Holmen said:
You can get computer programs to calculate the compressiblity values. Those formula works. The map does change for the different suction pressure. Mass flow at the inlet is the same at the discharge. Actual volume (flow) ACFM at the suction isn't the same at the discharge. The mach number determines where the choke line is, and the engine will start to push the Air/fuel ratio as it takes more work to generate more air.

They just rate the maps at mass flow (lbs/min) cause that way turbochargers are done. Most people just run them as a single and the manufacturer usually just provides numbers for 14.73 psi ambient pressure. You guys are basically saying the say thing, just a different way. Everything is based off the fan laws used in centrifugal compressors.
Click to expand...

Fan laws! I remember those, brings me back to my HVAC days:kick:

ScreenShot053.jpg
 
yeah, them make things real easy.

got an old "Fan Engineering" book from Buffalo Forge Company here in the office.

Another of my best references is the "Crane 410"
 
I wanted to share this with you guys.
Compressor Maps | www.TurboneticsInc.com - Boosting Since 1978 | turbochargers, intercoolers, wastegates, blow-off valves, controls, boosting systems, turbo kits, forced induction parts & accessories
TurboByGarrett.com - Turbo Tech101

It kinda helps in turbo selection. Lots of reading but very good information.

The trick is to try different combos if you have patient to try them all:rockwoot:. I've try to adjust things just to see what I can feel for a difference. I'm trying to see the difference between running really large turbos vs. small turbo. Some stuff is obvious, I want to see where the truck will perform at top power but still have the best spool-up. I want to build the perfect twin set for 500rwhp. I had a buddy tell me this weekend, but you could just run a decent single and forget twins.:doh:
 
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