# Calculation of Pressure in a Cylinder with an orifice on its surface

• Sandeep8719
In summary, the conversation discussed calculating the pressure profile inside a cylinder with an orifice, using matlab and assuming compressible ideal gas and isentropic flow. The method involved calculating mass flow rate and using energy balance and ideal gas equation to find new temperature and pressure. The issue of the pressure inside the cylinder becoming higher than the surrounding pressure was also discussed, with suggestions to research published information and solve the problem analytically before using software. Concerns were raised about relying on software without a strong understanding of the science and system being modeled.
Sandeep8719
I want to calculate the pressure profile inside a cylinder whose initial pressure is less than the outside pressure and has a orifice on its surface to flow air through it. Air is a considered as compressible ideal gas and mass flow rate across a orifice is assumed isentropic. Also the temperature is assumed same initially in cylinder and surroundings.

I am generating the pressure profile inside the cylinder as a function of time using matlab, the method i followed is I took a small delta_t and calculated the massflow rate using available compressed mass flow rate formula and find the net mass flown into the cylinder and I found the new temperature using the energy balance for open system and using ideal gas equation I found the new pressure.

Now the problem is after some time the pressure inside the cylinder becomes more than the surrounding pressure, Is it possible to have that kind of situation or am I doing something wrong?

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Is this a homework problem?

No i am working on ic engines suction modelling i face same kind of problem over there

(1) The gas dynamics of engines has been researched in great depth and over many years . You should easily be able to find published information which will tell you exactly how to deal with this type of problem .

(2) You would find it very instructive to solve your problem analytically before trying to set it up on MATLAB .

(3) I really worry about the trend which seems to be becoming almost universal now of people trying to solve problems with MATLAB , FEA and other types of solver software when they haven't a clue about the science basics or any real idea of how to set up a realistic model of the system they are dealing with .

Chestermiller and BvU

## 1. What is the formula for calculating pressure in a cylinder with an orifice on its surface?

The formula for calculating pressure in a cylinder with an orifice on its surface is P = (Q*A)/C, where P is the pressure, Q is the flow rate, A is the area of the orifice, and C is the coefficient of discharge.

## 2. How is the coefficient of discharge determined for an orifice?

The coefficient of discharge is determined experimentally by measuring the actual flow rate through the orifice and comparing it to the theoretical flow rate. It can also be calculated using the orifice diameter and the fluid properties.

## 3. What factors affect the pressure in a cylinder with an orifice?

The pressure in a cylinder with an orifice is affected by the flow rate, the area of the orifice, the coefficient of discharge, and the properties of the fluid, such as density and viscosity.

## 4. Can the pressure in a cylinder with an orifice be calculated for any fluid?

Yes, the pressure can be calculated for any fluid as long as the properties of the fluid are known and the appropriate formula is used.

## 5. How can the pressure be adjusted in a cylinder with an orifice?

The pressure in a cylinder with an orifice can be adjusted by changing the flow rate, the area of the orifice, or the properties of the fluid. These changes can be made manually or by using valves or regulators.

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