32mm inlet restrictor effect on HP

How many horsepower is possible on a 1.8 L 4 cylinder turbo engine with a 32mm inlet restrictor?

I'm sure there are a million other factors involved here, but I'm just looking for a rough estimate. 250-300hp?

---

Michael LeCompte

pikespeakgtx Wrote:
-------------------------------------------------------
> How many horsepower is possible on a 1.8 L 4
> cylinder turbo engine with a 32mm inlet
> restrictor?
The same as any other size engine with a 32mm restrictor.
>
> I'm sure there are a million other factors
> involved here, but I'm just looking for a rough
> estimate. 250-300hp?

Sure, why not?

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Anything is possible.

My 2 liter with 32mm hole and safe tuning only makes around 190hp at the wheels on pump gas. And I leave it like that.

---

Ted Mendham
www.rensport.net

That seems to be the standard answer, Michael, based on theoretical airflow limits, etc. But there are other factors involved in the overal 'power' performance level that rally engine builders have worked around.

Is 250HP enough for what you want to do? Like get in to trouble with a rally car?

Regards,
Mark B.

Guessing here:
PGT/P4 mandates a 32mm hell hole in the US, right?
Mazda 1.8 liter?

Do you want a dyno chart to show off, and/or do ya wanna get in trouble in a rally car?
;-)

---

Ted Mendham
www.rensport.net



Edited 1 time(s). Last edit at 01/29/2008 04:05PM by tedm.

Are there boost limitations in the rules as well? couldn't you just run some sort of hellishly gigantoid pressure if you can afford it?

I'm not really up on airflow dynamics and all the uber-scientific principles involved, but if you're forced to a specific size, is there a terminal limit to the airflow? As in, a pressure level beyond which no more volume of air will pass?

Then, is this limitation in the airflow larger than the limitation induced by the ability of the head and cams?

What's the overall target power for the vehicle? With a 323, even with the extra mass of the AWD and a cage, even 150whp will be rip-stomping fun. 200 will make your face hurt from smiling all the time. 250 will require a hans device just to keep your neck from snapping off when you hit the gas, and 300 will bankrupt you because of the diapers needed to protect your suit when you crap your pants.



--sarge

---

---** To be in compliance with the Anarchy **---
Jorden R. Kleier
Baraboo, Wisconsin, USA
1990 Mazdog Protege 4WD
1973

SgtRauksauff Wrote:
-------------------------------------------------------
> Are there boost limitations in the rules as well?
> couldn't you just run some sort of hellishly
> gigantoid pressure if you can afford it?

No
>
> I'm not really up on airflow dynamics and all the
> uber-scientific principles involved, but if you're
> forced to a specific size, is there a terminal
> limit to the airflow? As in, a pressure level
> beyond which no more volume of air will pass?

Ain't really high faluting science, all you need to think of is good ol'Daniel Bernoulli
From Wikipedia, the free encyclopedia
Jump to: navigation, search
Daniel Bernoulli
Daniel Bernoulli

Daniel Bernoulli (Groningen, February 8, 1700 – March 17, 1782) was a Dutch-born mathematician who spent much of his life in Basel where he died. A member of a talented family of mathematicians, physicists and philosophers, he is particularly remembered for his applications of mathematics to mechanics, especially fluid mechanics, and for his pioneering work in probability and statistics.

Continued from:
* Bernoulli's principle
From Wikipedia, the free encyclopedia
Jump to: navigation, search

Bernoulli's equation redirects here; see Bernoulli differential equation for an unrelated topic in ordinary differential equations.

In physics, hydraulics and fluid dynamics, Bernoulli's Principle states that for an incompressible fluid (e.g. most liquids), with no work being performed on the fluid, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's gravitational potential energy.[1] Bernoulli's Principle is named in honor of Daniel Bernoulli.

Bernoulli's Principle is equivalent to the principle of conservation of energy. This states that the sum of all forms of mechanical energy in a fluid along a streamline is the same at all points on that streamline. This requires that the sum of kinetic energy and potential energy remains constant. If the fluid is flowing out of a reservoir the sum of all forms of energy is the same on all streamlines because in a reservoir the energy per unit mass (the sum of pressure and gravitational potential ρgh) is the same everywhere. [2]

Fluid particles are subject only to pressure and their own weight. If a fluid is flowing horizontally and along a section of a streamline the speed increases it can only be because the fluid on that section has moved from a region of higher pressure to a region of lower pressure; and if its speed decreases, it can only be because it has moved from a region of lower pressure to a region of higher pressure. Consequently, within a fluid flowing horizontally, the highest speed occurs where the pressure is lowest, and the lowest speed occurs where the pressure is highest.
Contents
[hide]

* 1 Incompressible flow equation
o 1.1 Simplified form
* 2 Compressible flow equation
o 2.1 Compressible flow in fluid dynamics
o 2.2 Compressible flow in thermodynamics
* 3 Derivations of Bernoulli equation
o 3.1 Incompressible fluids
o 3.2 Compressible fluids
* 4 Real World Application
* 5 A common misconception about wings
o 5.1 Stick and Rudder
o 5.2 Understanding Flight
o 5.3 Equal transit-time fallacy
* 6 References
* 7 See also
* 8 External links

[edit] Incompressible flow equation

In most circumstances liquids can be considered to be of constant density, regardless of pressure. For this reason liquids can be considered to be incompressible and the flow of liquids can be described as incompressible flow. Bernoulli performed his experiments on liquids and his equation is valid only for incompressible flow.

Bernoulli's equation is sometimes valid for the flow of gases provided that there is no transfer of kinetic or potential energy from the gas flow to the compression or expansion of the gas. If both the gas pressure and volume change simultaneously, then work will be done on or by the gas. In this case, Bernoulli's equation can not be assumed to be valid. However if the gas process is entirely isobaric, or isochoric, then no work is done on or by the gas, (so the simple energy balance is not upset). According to the gas law, an isobaric or isochoric process is ordinarily the only way to ensure constant density in a gas. Also the gas density will be proportional to the ratio of pressure and absolute temperature, however this ratio will vary upon compression or expansion, no matter what non-zero quantity of heat is added or removed. The only exception is if the net heat transfer is zero, as in a complete thermodynamic cycle, or in an individual isentropic (frictionless adiabatic) process, and even then this reversible process must be reversed, to restore the gas to the original pressure and specific volume, and thus density. Only then is the original, unmodified Bernoulli equation applicable. In this case the equation can be used if the velocity of the gas is sufficiently below the speed of sound, such that the variation in density of the gas (due to this effect) along each streamline can be ignored. Adiabatic flow at less than Mach 0.3 is generally considered to be slow enough.

The original form of Bernoulli's equation[3] is:

{v^2 \over 2}+gh+{p\over\rho}=\mathrm{constant}

where:

v\, is the fluid velocity at a point on a streamline
g\, is the acceleration due to gravity
h\, is the height of the point above a reference plane
p\, is the pressure at the point
\rho\, is the density of the fluid at all points in the fluid

The following assumptions must be met for the equation to apply:

* The fluid must be incompressible - even though pressure varies, the density must remain constant.
* The streamline must not enter the boundary layer. (Bernoulli's equation is not applicable where there are viscous forces, such as in the boundary layer.)

The above equation can be rewritten as:

{\rho v^2 \over 2}+\rho gh+p=q+\rho gh+p=\mathrm{constant}

where:

q = \frac{\rho v^2}{2} is dynamic pressure

The above equations suggest there is a velocity at which pressure is zero and at higher velocities the pressure is negative. Gases and liquids are not capable of negative absolute pressure, or even zero pressure, so clearly Bernoulli's equation ceases to be valid before zero pressure is reached. The above equations use a linear relationship between velocity squared and pressure. At higher velocities in liquids, non-linear processes such as (viscous) turbulent flow and cavitation occur. At higher velocities in gases the changes in pressure become significant so that the assumption of constant density is invalid.

[edit] Simplified form

In many applications of Bernoulli's equation, the change in the \rho\,gh term along streamlines is zero or so small it can be ignored. This allows the above equation to be presented in the following simplified form:

p + q = p_0\,

where p_0\, is called total pressure, and q\, is dynamic pressure[4]. Many authors refer to the pressure p\, as static pressure to distinguish it from total pressure p_0\, and dynamic pressure q\,. In Aerodynamics, L.J. Clancy writes: "To distinguish it from the total and dynamic pressures, the actual pressure of the fluid, which is associated not with its motion but with its state, is often referred to as the static pressure, but where the term pressure alone is used it refers to this static pressure."[5]

The simplified form of Bernoulli's equation can be summarized in the following memorable word equation:

static pressure + dynamic pressure = total pressure[6]

Every point in a steadily flowing fluid, regardless of the fluid speed at that point, has its own unique static pressure p, dynamic pressure q, and total pressure p0.

The significance of Bernoulli's principle can now be summarised as "total pressure is constant along a streamline." Furthermore, if the fluid flow originated in a reservoir, the total pressure on every streamline is the same and Bernoulli's principle can be summarised as "total pressure is constant everywhere in the fluid flow." However, it is important to remember that Bernoulli's principle does not apply in the boundary layer.

[edit] Compressible flow equation

Bernoulli developed his principle from his observations on liquids, and his equation is applicable only to incompressible fluids, and compressible fluids at very low speeds (perhaps up to 1/3 of the sound velocity in the fluid). It is possible to use the fundamental principles of physics to develop similar equations applicable to compressible fluids. There are numerous equations, each tailored for a particular application, but all are analogous to Bernoulli's equation and all rely on nothing more than the fundamental principles of physics such as Newton's laws of motion or the First Law of Thermodynamics.

[edit] Compressible flow in fluid dynamics

A useful form of the equation, suitable for use in compressible fluid dynamics, is:

\left(\frac {\gamma}{\gamma-1}\right)\frac {p}{\rho} + \frac {v^2}{2} + gh = constant[7] (constant along a streamline)

where:

\gamma\, is the ratio of the specific heats of the fluid
p\, is the pressure at a point
\rho\, is the density at the point
v\, is the speed of the fluid at the point
g\, is the acceleration due to gravity
h\, is the height of the point above a reference plane

In many applications of compressible flow, changes in height above a reference plane are negligible so the term gh\, can be omitted. A very useful form of the equation is then:

\left(\frac {\gamma}{\gamma-1}\right)\frac {p}{\rho} + \frac {v^2}{2} = \left(\frac {\gamma}{\gamma-1}\right)\frac {p_0}{\rho_0}

where:

p_0\, is the total pressure
\rho_0\, is the total density

[edit] Compressible flow in thermodynamics

Another useful form of the equation, suitable for use in thermodynamics, is:

{v^2 \over 2}+ gh + w =\mathrm{constant}[8]

w\, is the enthalpy per unit mass, which is also often written as h\, (which would conflict with the use of h\, for "height" in this article).

Note that w = \epsilon + \frac{p}{\rho} where \epsilon \, is the thermodynamic energy per unit mass, also known as the specific internal energy or "sie."

The constant on the right hand side is often called the Bernoulli constant and denoted b\,. For steady inviscid adiabatic flow with no additional sources or sinks of energy, b\, is constant along any given streamline. More generally, when b\, may vary along streamlines, it still proves a useful parameter, related to the "head" of the fluid (see below).

When the change in gh\, can be ignored, a very useful form of this equation is:

{v^2 \over 2}+ w = w_0

where w_0\, is total enthalpy.

When shock waves are present, in a reference frame moving with a shock, many of the parameters in the Bernoulli equation suffer abrupt changes in passing through the shock. The Bernoulli parameter itself, however, remains unaffected. An exception to this rule is radiative shocks, which violate the assumptions leading to the Bernoulli equation, namely the lack of additional sinks or sources of energy.

[edit] Derivations of Bernoulli equation

[edit] Incompressible fluids

The Bernoulli equation for incompressible fluids can be derived by integrating the Euler equations, or applying the law of conservation of energy in two sections along a streamline, ignoring viscosity, compressibility, and thermal effects.

The simplest derivation is to first ignore gravity and consider constrictions and expansions in pipes that are otherwise straight, as seen in Venturi effect. Let the x axis be directed down the axis of the pipe.

The equation of motion for a parcel of fluid on the axis of the pipe is

m \frac{dv}{dt}= -F
\rho A dx \frac{dv}{dt}= -A dp
\rho \frac{dv}{dt}= -\frac{dp}{dx}

In steady flow, v = v(x) so

\frac{dv}{dt}= \frac{dv}{dx}\frac{dx}{dt} = \frac{dv}{dx}v=\frac{d}{dx} \frac{v^2}{2}

With ρ constant, the equation of motion can be written as

\frac{d}{dx} \left( \rho \frac{v^2}{2} + p \right) =0

or

\frac{v^2}{2} + \frac{p}{\rho}= C

where C is a constant, sometimes referred to as the Bernoulli constant. It is not a universal constant, but rather a constant of a particular fluid system. We deduce that where the speed is large, pressure is low and vice versa. In the above derivation, no external work-energy principle is invoked. Rather, the work-energy principle was inherently derived by a simple manipulation of the momentum equation.
A streamtube of fluid moving to the right. Indicated are pressure, height, velocity, distance (s), and cross-sectional area.
A streamtube of fluid moving to the right. Indicated are pressure, height, velocity, distance (s), and cross-sectional area.

Applying conservation of energy in form of the work-kinetic energy theorem we find that:

the change in KE of the system equals the net work done on the system;
W=\Delta KE. \;

Therefore,

the work done by the forces in the fluid + decrease in potential energy = increase in kinetic energy.

The work done by the forces is

F_{1} s_{1}-F_{2} s_{2}=p_{1} A_{1} v_ {1}\Delta t-p_{2} A_{2} v_{2}\Delta t. \;

The decrease of potential energy is

m g h_{1}-m g h_{2}=\rho g A _{1} v_{1}\Delta t h_{1}-\rho g A_{2} v_{2} \Delta t h_{2} \;

The increase in kinetic energy is

\frac{1}{2} m v_{2}^{2}-\frac{1}{2} m v_{1}^{2}=\frac{1}{2}\rho A_{2} v_{2}\Delta t v_{2} ^{2}-\frac{1}{2}\rho A_{1} v_{1}\Delta t v_{1}^{2}.

Putting these together,

p_{1} A_{1} v_{1}\Delta t-p_{2} A_{2} v_{2}\Delta t+\rho g A_{1} v_{1}\Delta t h_{1}-\rho g A_{2} v_{2}\Delta t h_{2}=\frac{1}{2}\rho A_{2} v_{2}\Delta t v_{2}^{2}-\frac{1}{2}\rho A_{1} v_{1}\Delta t v_{1}^{2}

or

\frac{\rho A_{1} v_{1}\Delta t v_{1}^{ 2}}{2}+\rho g A_{1} v_{1}\Delta t h_{1}+p_{1} A_{1 } v_{1}\Delta t=\frac{\rho A_{2} v_{2}\Delta t v_{ 2}^{2}}{2}+\rho g A_{2} v_{2}\Delta t h_{2}+p_{2} A_{2} v_{2}\Delta t.

After dividing by Δt, ρ and A1v1 (= rate of fluid flow = A2v2 as the fluid is incompressible):

\frac{v_{1}^{2}}{2}+g h_{1}+\frac{p_{1}}{\rho}=\frac{v_{2}^{2}}{2}+g h_{2}+\frac{p_{2}}{\rho}

or, as stated in the first paragraph:

\frac{v^{2}}{2}+g h+\frac{p}{\rho}=C (Eqn. 1)

Further division by g\, produces the following equation. Note that each term can be described in the length dimension (such as meters). This is the head equation derived from Bernoulli's Principle:

\frac{v^{2}}{2 g}+h+\frac{p}{\rho g}=C (Eqn. 2a)

The middle term, h\,, can be called an elevation head, although height is used throughout this discussion. h_{elevation}\, represents the internal energy of the fluid due to its height above a reference plane.

A free falling mass from a height h\, (in a vacuum) will reach a velocity

v=\sqrt{{2 g}{h}}, or when we rearrange it as a head: h_{v}=\frac{v^{2}}{2 g}

The term \frac{v^2}{2 g} is called the velocity head, expressed as a length measurement. It represents the internal energy of the fluid due to its motion.

The hydrostatic pressure p is defined as

p=\rho g h \,, or when we rearrange it as a head: \psi=\frac{p}{\rho g}

The term \frac{p}{\rho g} is also called the pressure head, expressed as a length measurement. It represents the internal energy of the fluid due to the pressure exerted on the container.

When we combine the head due to the velocity and the head due to static pressure with the elevation above a reference plane, we obtain a simple relationship useful for incompressible fluids.

h_{v} + h_{elevation} + \psi = C\, (Eqn. 2b)

If we were to multiply Eqn. 1 by the density of the fluid, we would get an equation with three pressure terms:

\frac{\rho v^{2}}{2}+ \rho g h + p=C (Eqn. 3)

We note that the pressure of the system is constant in this form of the Bernoulli Equation. If the static pressure of the system (the far right term) increases, and if the pressure due to elevation (the middle term) is constant, then we know that the dynamic pressure (the left term) must have decreased. In other words, if the speed of a fluid decreases and it is not due to an elevation difference, we know it must be due to an increase in the static pressure that is resisting the flow.

All three equations are merely simplified versions of an energy balance on a system.

[edit] Compressible fluids

The derivation for compressible fluids is similar. Again, the derivation depends upon (1) conservation of mass, and (2) conservation of energy. Conservation of mass implies that in the above figure, in the interval of time \Delta t\,, the amount of mass passing through the boundary defined by the area A_1\, is equal to the amount of mass passing outwards through the boundary defined by the area A_2\,:

0= \Delta M_1 - \Delta M_2 = \rho_1 A_1 v_1 \, \Delta t - \rho_2 A_2 v_2 \, \Delta t.

Conservation of energy is applied in a similar manner: It is assumed that the change in energy of the volume of the streamtube bounded by A_1\, and A_2\, is due entirely to energy entering or leaving through one or the other of these two boundaries. Clearly, in a more complicated situation such as a fluid flow coupled with radiation, such conditions are not met. Nevertheless, assuming this to be the case and assuming the flow is steady so that the net change in the energy is zero,

0= \Delta E_1 - \Delta E_2 \,

where ΔE1 and \Delta E_2\, are the energy entering through A_1\, and leaving through A_2\,, respectively.

The energy entering through A_1\, is the sum of the kinetic energy entering, the energy entering in the form of potential gravitational energy of the fluid, the fluid thermodynamic energy entering, and the energy entering in the form of mechanical p\,dV work:

\Delta E_1 = \left[\frac{1}{2} \rho_1 v_1^2 + \phi_1 \rho_1 + \epsilon_1 \rho_1 + p_1 \right] A_1 v_1 \, \Delta t

where \phi=gh\,, g\, is acceleration due to gravity, and h\, is height above a reference plane

A similar expression for ΔE2 may easily be constructed. So now setting 0 = ΔE1 − ΔE2:

0 = \left[\frac{1}{2} \rho_1 v_1^2+ \phi_1 \rho_1 + \epsilon_1 \rho_1 + p_1 \right] A_1 v_1 \, \Delta t - \left[ \frac{1}{2} \rho_2 v_2^2 + \phi_2\rho_2 + \epsilon_2 \rho_2 + p_2 \right] A_2 v_2 \, \Delta t

which can be rewritten as:

0 = \left[ \frac{1}{2} v_1^2 + \phi_1 + \epsilon_1 + \frac{p_1}{\rho_1} \right] \rho_1 A_1 v_1 \, \Delta t - \left[ \frac{1}{2} v_2^2 + \phi_2 + \epsilon_2 + \frac{p_2}{\rho_2} \right] \rho_2 A_2 v_2 \, \Delta t

Now, using the previously-obtained result from conservation of mass, this may be simplified to obtain

\frac{1}{2}v^2 + \phi + \epsilon + \frac{p}{\rho} = {\rm constant} \equiv b

which is the Bernoulli equation for compressible flow.

[edit] Real World Application

* The carburetor used in many reciprocating engines contains a venturi to create a region of low pressure to draw fuel into the carburetor and mix it thoroughly with the incoming air. The low pressure in the throat of a venturi can be explained by Bernoulli's Principle - in the narrow throat, the air is moving at its fastest speed and therefore it is at its lowest pressure.

* The velocity of a fluid can be measured using a devices such as a Venturi meter or an orifice plate, which can be placed into a pipeline to reduce the diameter of the flow. For a horizontal device, conservation of mass shows that for an incompressible fluid, the reduction in diameter will cause an increase in the fluid velocity. Subsequenty Bernoulli's principle then shows that there must be a decrease in the pressure in the reduced diameter region. This phenomenon is known as the Venturi effect.

* The drain rate for a tank with a hole or tap at the base can be calculated directly from Bernoulli's equation, and is found to be proportional to the square root of the height of the fluid in the tank.""

See?

But this is where it gets exciting:
Venturi effect
From Wikipedia, the free encyclopedia
Jump to: navigation, search
For other uses, see Venturi (disambiguation).
in a diagram, the pressure in "1" conditions is higher than "2", and the relationship between the fluid speed in "2" and "1" respectively, is the same as for pressure.
in a diagram, the pressure in "1" conditions is higher than "2", and the relationship between the fluid speed in "2" and "1" respectively, is the same as for pressure.

The Venturi effect is an example of Bernoulli's principle, in the case of incompressible flow through a tube or pipe with a constriction in it. The fluid velocity must increase through the constriction to satisfy the equation of continuity, while its pressure must decrease due to conservation of energy: the gain in kinetic energy is supplied by a drop in pressure or a pressure gradient force. The effect is named after Giovanni Battista Venturi, (1746–1822), an Italian physicist.

The limiting case of the Venturi effect is choked flow, in which a constriction in a pipe or channel limits the total flow rate through the channel, because the pressure cannot drop below zero in the constriction. Choked flow is used to control the delivery rate of water and other fluids through spigots and other valves.

Referring to the diagram to the right, using Bernoulli's equation in the special case of incompressible fluids (such as the approximation of a water jet), the theoretical pressure drop (P1 − P2) at the constriction would be given by \frac{\rho}{2}(v_2^2 - v_1^2).

[edit] Experimental apparatus
This is a Venturi tube demonstration apparatus built out of PVC pipe and operated with a vacuum pump.
This is a Venturi tube demonstration apparatus built out of PVC pipe and operated with a vacuum pump.

* Venturi Tubes

The simplest apparatus, as shown in the photograph and diagram, is a tubular setup known as a Venturi tube or simply a venturi. Fluid flows through a length of pipe of varying diameter. To avoid undue drag, a venturi tube typically has an entry cone of 30 degrees and an exit cone of 5 degrees.

A venturi can also be used to mix a fluid with air. If a pump forces the fluid through a tube connected to a system consisting of a venturi to increase the water speed (the diameter decreases), a short piece of tube with a small hole in it, and last a venturi that decreases speed (so the pipe gets wider again), air will be sucked in through the small hole because of changes in pressure. At the end of the system, a mixture of fluid and air will appear.

* Orifice plate

Venturi tubes are more expensive to construct than a simple orifice plate which uses the same principle as a tubular scheme, but the orifice plate causes significantly more permanent energy loss.

In Chronic Aortic Regurgitation, after the initial large stroke volume is released, the Venturi effect draws walls together, transiently obstructing flow causing a Pulsus Bisferiens.

[edit] Practical uses

The Venturi effect is visible in:

* the capillaries of the human circulatory system, where it indicates aortic regurgitation
* large cities where wind is forced between buildings.
* inspirators that mix air and flammable gas in barbecues, gas stoves, Bunsen burners and Airbrushes.
* water aspirators that produce a partial vacuum using the kinetic energy from the faucet water pressure
* Steam siphon using the kinetic energy from the steam pressure to create a partial vacuum
* atomizers that disperse perfume or spray paint (i.e. from a spray gun)
* foam firefighting nozzles and extinguishers
* carburetors that use the effect to suck gasoline into an engine's intake air stream.
* Protein skimmers, a filtration device for saltwater aquaria.
* In automated pool cleaners that use pressure-side water flow to collect sediment and debris.
* The modern day barrel of the clarinet, which uses a reverse taper to speed the air down the tube, enabling better tone, response and intonation.
* Compressed air operated industrial vacuum cleaners
* Venturi scrubbers used to clean flue gas emissions
* Injectors (or sometimes called ejectors) used to add chlorine gas in water treatment chlorination systems
* Sand blasters use the effect to draw fine sand in and mix it with air
* Emptying bilge water from a moving boat through a small waste gate in the hull. The air pressure inside the moving boat is greater than the water sliding by beneath.
* A SCUBA diving regulator may use the effect to assist the flow of air once it starts flowing.
* modern vaporisers use the venturi effect to optomise efficiency
* the Venturi mask used in medical oxygen therapy


A simple way to demonstrate the Venturi effect is to squeeze and release a flexible hose that is normal shape: the partial vacuum produced in the constriction is sufficient to keep the hose collapsed.

Venturi tubes are also used to measure the speed of a fluid, by measuring pressure changes at different segments of the device. Placing a liquid in a U-shaped tube and connecting the ends of the tubes to both ends of a venturi is all that is needed. When the fluid flows though the venturi the pressure in the two ends of the tube will differ, forcing the liquid to the "low pressure" side. The amount of that move can be calibrated to the speed of the fluid flow.

[edit] See also

* Bernoulli's principle
* Choked flow
* Venturi injector
* Orifice plate
* Bunsen burner

This article does not cite any references or sources. (December 2007)
Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed.
Retrieved from "http://en.wikipedia.org/wiki/Venturi_effect";

Categories: Fluid dynamics | Articles lacking sources from December 2007 | All articles lacking sources


Now this is the exciting bit:
Choked flow
From Wikipedia, the free encyclopedia
Jump to: navigation, search

Choked flow of a fluid is a fluid dynamic condition caused by the Venturi effect. When a flowing fluid at a certain pressure and temperature flows through a restriction (such as the hole in an orifice plate or a valve in a pipe) into a lower pressure environment, under the conservation of mass the fluid velocity must increase for initially subsonic upstream conditions as it flows through the smaller cross-sectional area of the restriction. At the same time, the Venturi effect causes the pressure to decrease. Choked flow is a limiting condition which occurs when the mass flux will not increase with a further decrease in the downstream pressure environment.

For homogenous fluids, the physical point at which the choking occurs for adiabatic conditions is when the exit plane velocity is at sonic conditions or at a Mach number of 1.[1][2][3] It is most important to note that the mass flow rate can still be increased by increasing the upstream stagnation pressure.

The choked flow of gases is useful in many engineering applications because the mass flow rate is independent of the downstream pressure, depending only on the temperature and pressure on the upstream side of the restriction. Under choked conditions, valves and calibrated orifice plates can be used to produce a particular mass flow rate.

If the fluid is a liquid, a different type of limiting condition (also known as choked flow) occurs when the Venturi effect acting on the liquid flow through the restriction decreases the liquid pressure to below that of the liquid vapor pressure at the prevailing liquid temperature. At that point, the liquid will partially "boil" into bubbles of vapor and the subsequent collapse of the bubbles causes cavitation. Cavitation is quite noisy and can be sufficiently violent to physically damage valves, pipes and associated equipment. In effect, the vapor bubble formation in the restriction limits the flow from increasing any further.[4][5]
Contents
[hide]

* 1 Mass flow rate of a gas at choked conditions
o 1.1 Choking in change of cross section flow
* 2 Thin-plate orifices
* 3 Minimum pressure ratio required for choked flow to occur
* 4 See also
* 5 References
* 6 External links

[edit] Mass flow rate of a gas at choked conditions

All gases flow from upstream higher stagnation pressure sources to downstream lower pressure sources. There are several situations in which choked flow occurs, such as: change of cross section (as in a convergent-divergent nozzle or flow through an orifice plate), Fanno flow, isothermal flow and Rayleigh flow.

[edit] Choking in change of cross section flow

Assuming ideal gas behavior, steady state choked flow occurs when the ratio of the absolute upstream pressure to the absolute downstream pressure is equal to or greater than [ ( k + 1 ) / 2 ] k / ( k - 1 ), where k is the specific heat ratio of the gas (sometimes called the isentropic expansion factor and sometimes denoted as γ ).

For many gases, k ranges from about 1.09 to about 1.41, and therefore [ ( k + 1 ) / 2 ] k / ( k - 1 ) ranges from 1.7 to about 1.9 ... which means that choked flow usually occurs when the absolute source vessel pressure is at least 1.7 to 1.9 times as high as the absolute downstream pressure.

When the gas velocity is choked, the equation for the mass flow rate in SI metric units is: [1][2][3][6]

Q\;=\;C\;A\;\sqrt{\;k\;\rho\;P\;\bigg(\frac{2}{k+1}\bigg)^{(k+1)/(k-1)}}

where the terms are defined in the table below. If the density ρ is not known directly, then it is useful to eliminate it using the Ideal gas law corrected for the real gas compressibility:

Q\;=\;C\;A\;P\;\sqrt{\bigg(\frac{\;\,k\;M}{Z\;R\;T}\bigg)\bigg(\frac{2}{k+1}\bigg)^{(k+1)/(k-1)}}

so that the mass flow rate is primarily dependent on the cross-sectional area A of the hole and the supply pressure P, and only weakly dependent on the temperature T. The rate does not depend on the downstream pressure at all. All other terms are constants that depend only on the composition of the material in the flow.
where:
Q = mass flow rate, kg/s
C = discharge coefficient, dimensionless (usually about 0.72)
A = discharge hole cross-sectional area, m²
k = cp/cv of the gas
cp = specific heat of the gas at constant pressure
cv = specific heat of the gas at constant volume
ρ = real gas density at P and T, kg/m³
P = absolute upstream stagnation pressure, Pa
M = the gas molecular mass, kg/kmole (also known as the molecular weight)
R = Universal gas law constant = 8314.5 (N·m) / (kmole·K)
T = absolute gas temperature, K
Z = the gas compressibility factor at P and T, dimensionless

The above equations calculate the steady state mass flow rate for the stagnation pressure and temperature existing in the upstream pressure source.

If the gas is being released from a closed high-pressure vessel, the above steady state equations may be used to approximate the initial mass flow rate. Subsequently, the mass flow rate will decrease during the discharge as the source vessel empties and the pressure in the vessel decreases. Calculating the flow rate versus time since the initiation of the discharge is much more complicated, but more accurate. Two equivalent methods for performing such calculations are explained and compared online.[7]

The technical literature can be very confusing because many authors fail to explain whether they are using the universal gas law constant R which applies to any ideal gas or whether they are using the gas law constant Rs which only applies to a specific individual gas. The relationship between the two constants is Rs = R / M.

Notes:

* The above equations are for a real gas.
* For a monatomic ideal gas, Z = 1 and ρ is the ideal gas density.
* kmole = 1000 moles = 1000 gram-moles = kilogram-mole

[edit] Thin-plate orifices

The flow of real gases through thin-plate orifices never becomes fully choked. The mass flow rate through the orifice continues to increase as the downstream pressure is lowered to a perfect vacuum, though the mass flow rate increases slowly as the downstream pressure is reduced below the critical pressure.[8] "Cunningham (1951) first drew attention to the fact that choked flow will not occur across a standard, thin, square-edged orifice."[9]

[edit] Minimum pressure ratio required for choked flow to occur

The minimum pressure ratios required for choked conditions to occur (when some typical industrial gases are flowing) are presented in Table 1. The ratios were obtained using the criteria that choked flow occurs when the ratio of the absolute upstream pressure to the absolute downstream pressure is equal to or greater than [ ( k + 1 ) / 2 ] k / ( k - 1 ) , where k is the specific heat ratio of the gas.

Table 1
Gas k = cp/cv Minimum
Pu/Pd
required for
choked flow
Hydrogen 1.410 1.899
Methane 1.307 1.837
Propane 1.131 1.729
Butane 1.096 1.708
Ammonia 1.310 1.838
Chlorine 1.355 1.866
Sulfur dioxide 1.290 1.826
Carbon monoxide 1.404 1.895

Notes:

* Pu = absolute upstream gas pressure
* Pd = absolute downstream gas pressure
* k values obtained from:
1. Perry, Robert H. and Green, Don W. (1984). Perry's Chemical Engineers' Handbook, 6th Edition, McGraw-Hill Company. ISBN 0-07-049479-7.
2. Phillips Petroleum Company (1962). Reference Data For Hydrocarbons And Petro-Sulfur Compounds, Second Printing, Phillips Petroleum Company.

[edit] See also

* Accidental release source terms includes mass flow rate equations for non-choked gas flows as well.
* Orifice plate includes derivation of non-choked gas flow equation.
* Laval nozzles are Venturi tubes that produce supersonic gas velocities as the tube and the gas are first constricted and then the tube and gas are expanded beyond the choke plane.
* Rocket engine nozzles discusses how to calculate the exit velocity from nozzles used in rocket engines.

[edit] References

1. ^ a b Perry's Chemical Engineers' Handbook, Sixth Edition, McGraw-Hill Co., 1984.
2. ^ a b Handbook of Chemical Hazard Analysis Procedures, Appendix B, Federal Emergency Management Agency, U.S. Dept. of Transportation, and U.S. Environmental Protection Agency, 1989. Handbook of Chemical Hazard Analysis, Appendix B Click on PDF icon, wait and then scroll down to page 391 of 520 PDF pages.
3. ^ a b Methods For The Calculation Of Physical Effects Due To Releases Of Hazardous Substances (Liquids and Gases), PGS2 CPR 14E, Chapter 2, The Netherlands Organization Of Applied Scientific Research, The Hague, 2005. PGS2 CPR 14E
4. ^ Valve Sizing Calculations Scroll to discussion of liquid flashing and cavitation.
5. ^ Control Valve Handbook Search document for "Choked".
6. ^ Risk Management Program Guidance For Offsite Consequence Analysis, U.S. EPA publication EPA-550-B-99-009, April 1999. Guidance for Offsite Consequence Analysis
7. ^ Calculating Accidental Release Rates From Pressurized Gas Systems
8. ^ Section 3 -- Choked Flow
9. ^ Forum post on 1 Apr 03 19:37

[edit] External links



>
> Then, is this limitation in the airflow larger
> than the limitation induced by the ability of the
> head and cams?
>
> What's the overall target power for the vehicle?
> With a 323, even with the extra mass of the AWD
> and a cage, even 150whp will be rip-stomping fun.
> 200 will make your face hurt from smiling all the
> time. 250 will require a hans device just to keep
> your neck from snapping off when you hit the gas,
> and 300 will bankrupt you because of the diapers
> needed to protect your suit when you crap your
> pants.
>
>
>
> --sarge

Your stuff ever arrive?
>
>
>
>
> ---** To be in compliance with the Anarchy **---
> Jorden R. Kleier
> Baraboo, Wisconsin, USA
> for RallyX an '88 Buick Electra Estate Wagon and
> for paved TSD/Gimmick, an '85 Volvo 744tic.
> 1973

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.



Edited 1 time(s). Last edit at 01/29/2008 05:28PM by john vanlandingham.

Dyno numbers? ehh doesn't really matter to me. Safe tune is what matters most. besdies, I can't brag to my buddies back home about 250hp...They wouldn't bat an eyelash. They're racing that nopi tuner import drag racing bizness for Lucas Oil with 1500 rwhp supra's and solaras.

I do want to get into trouble though... But honestly I REALLY can't afford to wrap it around a tree, and I have to drive it accordingly.

Thing is I bought the car and now I need to decide what to do with it.

One thing I've learned really quickly here is that full on Rally is probably way too fucking expensive for me right now. But I'm thinking of giving it a shot or at least building the car so it can get logbooked. Make sure the build is going in a direction toward being actually useful in a series and not just a car you sunk a whole lot of money into and now you can't do anything with it. Or land in an an open class against guys who have super deep pockets.

I was looking at the NASA rulebook. And in the California rally series there's a CRS GT class... It's like a performance stock class except it allows awd and turbo cars. And it's not an open class where I'll likely get stomped. And maybe they'll be fewer cars in this niche class and I'll stand a chance of doing reasonably well.


In reality, I'm thinking more of a hillclimb/rallyX/AutoX car.

There's an autoX club in my area... There's the Hoopa Hillclimb once a year, and about 4 rallyX's close by. And always Pikes Peak. I've had a fascination with the mountain since I went as a kid. I took the car up Pikes Peak last summer a few times, but not during the race. I was able to go between practice and before they let the public back out on the road because I worked at the event. I'd like to race it, but it's like what? $1500 just to enter. Thats more than 20 percent of what I have invested in the whole car.

I love to rally back home on the farm , we have a little track setup, some jumps we made with a bobcat and trails through the woods. The cost of tearing shit up out there is enough, without having to pay for stage notes, entry fees, etc... Plus we can drink beer.

I'm getting started now on real live, graduating college, and I want driving and building rally cars to be my hobby and passion for the rest of my life. I'd do it for a living if they right opportunity came along, but I see that option as a long shot...So I'm doing what I can little by little.

---

Michael LeCompte

If you want to rally NOW! and money is a problem than don't build, buy a turnkey car. Especially so if you are new to the sport. Sell the ride you are thinking of building and find a cheap 2WD car which can be had for 4 to 5k. Then you can accumulate knowledge on how to build a car while rallying instead of building without having particpated. Then when you are ready to build and have a good knowledge base through experience, sell the cheap FWD car for 4k to 5k and have at it....

I completely understand the desire to build your own car from the get go, but without first hand experiernce or hands on support from other experienced builders its a bad idea.

(just my 2 cents)



Edited 1 time(s). Last edit at 01/29/2008 07:08PM by Eddie Fiorelli.

I hear you loud and clear. I guess the real rally fun will come when I have lots of disposable income. For now it'll be the occasional hillclimb, and some rallyX / autoX duty, and my fun mobile.

Thing is, I'd never sell this car. Ever.

It'll probably never see real rally duty. It's a great car for the back-roads around here. I live near some of the most killer scenic highways. Sometimes I hit up the lost coast, Old PHC highway 1, sometimes 299 toward redding, highway 30 toward red bluff which goes down to 1 lane at some points. There are tons and tons of roads and fire trails mostly roughly paved, some gravel, they wind back up through the mountains and through the redwood forest service land. Some snow and ice once you get up high enough. I throw the snowboards in the back and bomb backcountry and use the car as a chairlift.

---

Michael LeCompte

If it will never see "real" rally duty, why install a restrictor?!? Turn up the boost and drive the car.

---

Ted Mendham
www.rensport.net

SgtRauksauff Wrote:
>
> I'm not really up on airflow dynamics and all the
> uber-scientific principles involved, but if you're
> forced to a specific size, is there a terminal
> limit to the airflow? As in, a pressure level
> beyond which no more volume of air will pass?

Yes, based on steady conditions. Simple flow restrictors are not perfect in regulating flow, but they give a first order limit to maximum flow. They are used in dishwashers and washing machines to regulate the amount of fill water in a given amount if time, despite varying water line pressures. Same theory for engines; but I sure would like to understand some of the tricks developed to fool them by a few top rally teams.

>
> Then, is this limitation in the airflow larger
> than the limitation induced by the ability of the
> head and cams?

Yep.

Regards,
Mark B.

absolutely... 16psi and away I go.

---

Michael LeCompte

John, that made me laugh out loud. Then I spent a few minutes reading.

And no, nothing's arrived yet. When did you send them? Do you gots a trackin' number?


--sarge

---

---** To be in compliance with the Anarchy **---
Jorden R. Kleier
Baraboo, Wisconsin, USA
1990 Mazdog Protege 4WD
1973