- #1
jesmitter
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How long does it take for 500 degree F - 1000 psi steam to move through 24" of 3/16 ID pipe and fill a 1 cubic inch volume cylinder to 1000 psi? Can it be modeled mathematically or with the help of Steam Tables?
Thermodynamics Question About Steam
- Thread starter jesmitter
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- Steam Thermodynamics
In summary, the conversation discusses the process of designing and building a single cylinder steam engine and determining its RPM limit. The main concerns are the flow/volume limit through 3/16" stainless steel tubing and the fill time required for the cylinder to be completely filled with steam at full pressure (1000 psi). It is possible to model this process mathematically using a Moody chart and simplifying assumptions, such as an instant valve opening and ignoring pressure drop and the speed of sound in the steam. The suggested approach is to start with a simple model and gradually add variables to make it more accurate.
- #2
anorlunda
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That sounds like a school assignment. Is it?
- #3
jesmitter
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No, I am trying to characterize a single cylinder steam engine that I want to design and build to see what the RPM limit will be.
- #4
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What is in the tube and cylinder before you start?
- #5
jesmitter
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The 3/16" tube is connected to an electronically controlled steam valve at the cylinder which will open at top dead center of the piston inside the cylinder. So, the tube will theoretically be filled with steam produced by the boiler (assume an unlimited steam supply), at least for the first cycle. Then as the RPM increases, the tubing will reach its limit caused by the diameter of the tubing causing "steam Starvation". In addition, the cylinder has a fill time that may not be satisfied by the amount of steam that the tubing can supply at the higher RPM. These are the unknown variables I'm trying to figure out -
1. What is the flow/volume limit through 3/16" stainless steel tubing?
2. What is the "fill time" required for the cylinder to completely fill with steam at full pressure (1000 psi)?
1. What is the flow/volume limit through 3/16" stainless steel tubing?
2. What is the "fill time" required for the cylinder to completely fill with steam at full pressure (1000 psi)?
Last edited:
- #6
jrmichler
Mentor
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Yes, it can be modeled. You can calculate pressure drop vs flow rate through pipe for any Newtonian fluid, gas or liquid, using a Moody chart (search the term). However, that calculation only works for steady state flow. Your application will only have steady state flow at extremely low speed.
At any speed over about 10 to 100 RPM, a flow calculation will need to include the time to move the valve from closed to open, the volume of the tube, and the position of the piston. I once wrote a simulation for a high speed air cylinder. That simulation accurately predicted acceleration, deceleration, and presence/absence of bouncing. The simulation treated the valve as a variable orifice, and the connecting tube as a dead volume lumped with the piston position. Your case has a very long tube, which adds a complicating factor.
I suggest start with simplifying assumptions:
1) Valve opens instantly.
2) Piston at TDC, not moving.
3) Ignore pressure drop down the length of the tube.
4) Valve starts to open at TDC.
5) Ignore the speed of sound in the steam.
Then the only pressure drop in the system is the ##C_V## or equivalent orifice area of the valve. Then you can calculate the initial flow rate through the valve. Calculate the time for the downstream pressure to increase about 10%, then recalculate the flow rate at that time step until downstream pressure is almost equal to supply pressure. This can be done with a spreadsheet.
When you get that iterative calculation working, it's easy to add sophistication. Based on your results, decide which simplifying assumption you want to remove. If, for example, the time to fill the tube with steam is about equal to the valve opening time, that would be a good variable to add to your model.
IMPORTANT: Start as simple as possible, then add only one variable at a time.
At any speed over about 10 to 100 RPM, a flow calculation will need to include the time to move the valve from closed to open, the volume of the tube, and the position of the piston. I once wrote a simulation for a high speed air cylinder. That simulation accurately predicted acceleration, deceleration, and presence/absence of bouncing. The simulation treated the valve as a variable orifice, and the connecting tube as a dead volume lumped with the piston position. Your case has a very long tube, which adds a complicating factor.
I suggest start with simplifying assumptions:
1) Valve opens instantly.
2) Piston at TDC, not moving.
3) Ignore pressure drop down the length of the tube.
4) Valve starts to open at TDC.
5) Ignore the speed of sound in the steam.
Then the only pressure drop in the system is the ##C_V## or equivalent orifice area of the valve. Then you can calculate the initial flow rate through the valve. Calculate the time for the downstream pressure to increase about 10%, then recalculate the flow rate at that time step until downstream pressure is almost equal to supply pressure. This can be done with a spreadsheet.
When you get that iterative calculation working, it's easy to add sophistication. Based on your results, decide which simplifying assumption you want to remove. If, for example, the time to fill the tube with steam is about equal to the valve opening time, that would be a good variable to add to your model.
IMPORTANT: Start as simple as possible, then add only one variable at a time.
1. What is the definition of steam in thermodynamics?
Steam in thermodynamics is defined as the gaseous phase of water, which is formed when water is heated to its boiling point and undergoes a phase change from liquid to gas. It is a common working fluid in many thermodynamic systems.
2. How does steam produce work in a steam engine?
In a steam engine, steam is produced by heating water in a boiler. The steam then expands and pushes against the pistons, causing them to move and produce mechanical work. This work can then be used to power machinery or generate electricity.
3. What is the difference between saturated steam and superheated steam?
Saturated steam is steam that is at the same temperature as its boiling point for a given pressure. Superheated steam, on the other hand, is steam that has been heated to a temperature above its boiling point for a given pressure. This results in a higher energy content and can be used for more efficient work in certain applications.
4. How does the enthalpy of steam change during a phase change?
During a phase change from liquid to gas, the enthalpy of steam remains constant. This is because the energy being added is used to break the bonds between water molecules and turn them into gas, rather than increasing the temperature.
5. Can steam be used to transfer heat in a thermodynamic system?
Yes, steam is often used as a heat transfer fluid in thermodynamic systems. It has a high specific heat capacity, meaning it can absorb a lot of heat energy, and it can also be easily controlled and transported through pipes. This makes it a popular choice for heating and cooling applications in industries such as power generation and HVAC systems.
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