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This topic is intended to focus upon a specific physics problem.
The context for this inquiry is ongoing work on kbd512's Optical Plane space vessel in early 2025.
As we proceed to analyze the components of the space vessel, the nature and performance of the Heating subsystem is in focus.
In Post #3 of this topic I will paste a transcript with Google's Gemini.
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This post is reserved for an index to posts that may be contributed by NewMars members over time.
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Post #3: Transcript of conversation with Gemini about how to model Flow through a pipe.
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This post reports on an inquiry of Google's Gemini in an attempt to learn/discover how to model the flow of hydrogen gas through a pipe while that pipe is heated by external energy sources.
Conversation with Gemini
How to Model Flow through Pipe - Hi Gemini! Thanks for all your help with previous requests. For this one, we are looking at flow of hydrogen through a pipe that is 240 meters long. We are delivering thermal energy to the hydrogen at the rate of 6000 watts per 38 millimeters, for a total of 40 megawatts. The average flow rate is 1 kg/s, but the actual flow rate through the pipe will probably be lower, because we expect the diameter of the pipe to be less than the exit port diameter. Are you aware of any existing software that can help us model this situation? We are looking for pressure at every meter along the pipe. The speed of sound of hydrogen is in the thousands of meters per second depending upon temperature, so I would expect convection to transfer pressure throughout the pipe but I'm not able to see data one way or another.
***Hey there! Absolutely, let's dive into modeling the flow of hydrogen through your pipe. It sounds like a fascinating project!
You're right, there are several software options available that can definitely help you simulate this scenario and get a handle on the pressure profile along the 240-meter pipe. Here are a few categories and specific examples of software commonly used for this type of fluid dynamics modeling:
Computational Fluid Dynamics (CFD) Software:
CFD software is specifically designed to simulate fluid flow, heat transfer, and related physical processes. They solve complex equations numerically to predict fluid behavior within defined geometries.
ANSYS Fluent: This is a very powerful and widely used commercial CFD software. It offers extensive capabilities for modeling various flow regimes, heat transfer mechanisms (including convection from your thermal energy input), and complex geometries. You can define the pipe dimensions, the heat flux along its length, the inlet conditions (like flow rate or pressure), and then simulate the flow to obtain pressure, temperature, and velocity profiles throughout the pipe. It handles compressible flows, which is important given the potential for significant temperature changes in your hydrogen.
COMSOL Multiphysics: Another robust commercial software package that excels in multiphysics simulations, including fluid flow and heat transfer. Its strength lies in its ability to couple different physical phenomena. You can model the heat addition to the hydrogen and its effect on the fluid properties (like density and viscosity), which in turn affects the flow and pressure.
OpenFOAM: This is an open-source CFD software that is highly flexible and customizable. While it might have a steeper learning curve compared to commercial options, it's incredibly powerful and free to use. It has a large community and many solvers suitable for compressible flows and heat transfer.
STAR-CCM+: A high-end commercial CFD software known for its advanced modeling capabilities and efficient handling of large-scale simulations. It's well-suited for complex thermal-fluid problems.
Pipe Flow Specific Software:
While CFD software offers the most detailed analysis, some software is more specifically tailored for pipe flow calculations:
AFT Fathom: This software focuses on incompressible and compressible flow analysis in pipe networks. It's designed for engineers who need to analyze pressure drop, flow distribution, and heat transfer in piping systems. You can input your pipe geometry, fluid properties, and heat input to determine the pressure profile.
PIPE-FLO: Similar to AFT Fathom, PIPE-FLO is designed for the analysis and design of piping systems. It can handle compressible fluids and heat transfer and provide pressure and temperature profiles along the pipe.
Regarding your questions about flow rate and pressure propagation:
Impact of Diameter Difference: You're spot on to consider that a larger pipe diameter compared to the exit port will likely result in a lower actual flow rate through the pipe for a given upstream pressure. The restriction at the exit will create a backpressure that influences the flow within the pipe. The software mentioned above allows you to define the pipe geometry accurately and account for such constrictions.
Convection and Pressure Transfer: The speed of sound in hydrogen is indeed high, especially at higher temperatures. This means that pressure changes propagate relatively quickly through the fluid. Convection, the transfer of heat through fluid motion, will play a significant role in distributing the thermal energy you're adding along the pipe. As the hydrogen heats up, its density will change, influencing the flow and pressure. The CFD software will explicitly model these convective heat transfer effects and their impact on the pressure field.
How to approach modeling this:
Define your geometry: Accurately input the length and diameter of your pipe into the software. If you have details about the exit port diameter, you can include that in your model as a boundary condition.
Specify fluid properties: Hydrogen's properties (density, viscosity, thermal conductivity, specific heat) are temperature-dependent. Most CFD software has built-in property databases for common fluids, including hydrogen, and can account for these variations with temperature.
Apply boundary conditions: You'll need to define the inlet conditions (e.g., mass flow rate of 1 kg/s, or a specific inlet pressure and temperature). You'll also need to define the outlet condition (e.g., pressure at the exit).Implement the heat source: You'll need to define the thermal energy input. The 6000 watts per 38 millimeters translates to a heat flux per unit length. You'll need to distribute this heat flux appropriately along the 240-meter length in your model. Be mindful of the total power of 40 megawatts and ensure consistency in your input.
Run the simulation: The software will then solve the governing equations (Navier-Stokes for fluid flow, energy equation for heat transfer) to give you the flow field, temperature field, and pressure field within the pipe.
Post-process the results: You can then extract the pressure at every meter along the pipe, as well as visualize other parameters like temperature and velocity distributions.
Important Considerations:
Compressibility: Given the potential for significant temperature changes and high flow velocities, it's crucial to use a compressible flow model in your chosen software.
Turbulence: Depending on the flow velocity and pipe diameter, the flow might become turbulent. You'll need to choose an appropriate turbulence model within the CFD software if this is the case.
Accuracy vs. Computational Cost: More complex models (e.g., with detailed turbulence modeling or very fine mesh resolution) will provide more accurate results but will also require more computational resources and time. You'll need to find a balance based on your needs.
I hope this gives you a good starting point! Exploring the capabilities of the software options mentioned above will be the next step in setting up your simulation. Good luck with your modeling!
Sources and related content
Computational Fluid Dynamics (CFD) Simulation Software - SimScaleAn introduction to CFD: what, why and how - Femto Engineering
Ansys Fluent | Fluid Simulation Software
ANSYS Fluent Tutorial: Pipe Flow Simulation Plotting and Exporting Temperature and Velocity Profiles - YouTube
Compressible Flows Tutorial with Ansys Fluent
www.ansys.com
***
thank you for your thorough and careful analysis of our request, and for your suggestions of ways to proceed! Best wishes to you as you attempt to assist all your other customers!
***You're most welcome! It was my pleasure to help you think through this. Best of luck with your hydrogen flow modeling – I hope you get some fascinating insights! If any other questions bubble up as you work on it, don't hesitate to ask. Have a great day!
If there is anyone in the readership who is not already a member, and who would like to help with this problem, Please see the Recruiting topic for procedure.
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