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This topic became available in 2025 as Gemini and NewMars studied the behavior of a system designed to capture air ahead of a rising projectile. The study was going well until it came time to model the behavior of the gas as it interacts with a cold pipe.
As a quick summary:
We are studying the interaction of air at STP (Standard Temperature and Pressure) with a tube made of metal such as iron.
The tube has a volume of 3 cubic meters, a mass of 1000 kilograms, a diameter of 1 meter.
The main tube is subdivided into smaller tubes of 4 cm ID, 5 cm OD.
The tube system is cooled to 100 Kelvin.
The velocity of the tube is given as 11 km/s.
In initial studies that did not take cooling into account, the air capture system collected just under a metric ton of air.
It is expected that the quantity of air collected will increase as cooling is taken into account.
In Post #3 of this series, Gemini provides a starting Python program to model the cooling problem.
This kind of problem would be a natural fit for a CFD program such as OpenFOAM, but Gemini thinks Python can do the job, so we will see how far we can get.
Thank you for considering this approach to dealing with what is turning out to be a ** very ** interesting aspect of physics. I am thinking of setting up this new study as it's own topic in our forum, in hopes it will have educational value. Before I create the topic, do you think it would be correct to call the new topic "Thermodynamics Study" or do you have a suggestion for a better title?
***
Gemini's reply:"Thermodynamics Study" is an excellent and accurate title for your new forum topic. It precisely describes the core physics you are investigating—the transfer of heat and energy within a system. This title is both professional and clear, making it easy for others to understand the subject matter.
Alternative Titles
If you want a title that is more specific to your project, you could consider these alternatives:"Air Capture: Thermal Energy Transfer"
"Gas-Pipe Thermal Dynamics"
"Simulating Heat Transfer in Hypersonic Air Capture"
However, "Thermodynamics Study" is a broad and classic term that is perfectly suitable for this kind of detailed physics investigation. It's concise and well-understood by engineers and scientists.
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This post is reserved for an index to posts that may be contributed by NewMars members.
Index:
Post #3: Opening Python program to begin study of a scenario of gas entering a pipe at 11 km/s.
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In this post we provide the code for a Python program to study a physics problem.
We are imagining a pipe with a closed end moving toward a volume of air on Earth at STP.
We imagine the pipe is traveling at 11 km/s and that it has a temperature of 100 Kelvin.
# 20250828ThermodynamicsStudyV01
import math
# --- Constants ---
TIME_STEP_S = 0.01 # s
SIMULATION_DURATION_S = 1.0 # s
INITIAL_PIPE_TEMP_K = 100.0 # K
INITIAL_GAS_TEMP_K = 288.0 # K (Ambient temp)
PIPE_MASS_KG = 1000.0 # kg
PIPE_VOLUME_M3 = 15.0 # m^3
PROJECTILE_VELOCITY_MPS = 11000.0 # m/s
PROJECTILE_DIAMETER_M = 1.0 # m
AIR_DENSITY_KG_M3 = 1.225 # kg/m^3 (Sea level)
SPECIFIC_HEAT_AIR_J_KG_K = 1005.0 # J/(kg*K)
SPECIFIC_HEAT_PIPE_J_KG_K = 450.0 # J/(kg*K)
PIPE_ID_M = 0.04 # m
PIPE_OD_M = 0.05 # m
PIPE_DENSITY_KG_M3 = 7850.0 # kg/m^3
HEAT_TRANSFER_COEFFICIENT = 50.0 # W/(m^2*K)
# --- Calculations for Pipe Geometry ---
pipe_cross_sectional_area = math.pi * ((PIPE_OD_M / 2)**2 - (PIPE_ID_M / 2)**2)
pipe_length_for_mass = PIPE_MASS_KG / (pipe_cross_sectional_area * PIPE_DENSITY_KG_M3)
pipe_internal_volume_single = math.pi * (PIPE_ID_M / 2)**2 * pipe_length_for_mass
number_of_pipes = PIPE_VOLUME_M3 / pipe_internal_volume_single if pipe_internal_volume_single > 0 else 0
total_cooling_surface_area_sqm = number_of_pipes * math.pi * PIPE_ID_M * pipe_length_for_mass
print(f"--- Thermal Model Test ---")
print(f"Number of Pipes: {number_of_pipes:.0f}")
print(f"Total Cooling Surface Area: {total_cooling_surface_area_sqm:.2f} m^2")
print(f"Initial Pipe Temp: {INITIAL_PIPE_TEMP_K:.2f} K")
print(f"Initial Gas Temp: {INITIAL_GAS_TEMP_K:.2f} K")
print("--------------------------")
# --- Simulation Variables ---
gas_temperature_K = INITIAL_GAS_TEMP_K
pipe_temperature_K = INITIAL_PIPE_TEMP_K
collected_air_mass = 0.0
total_gas_energy = 0.0
cross_sectional_area_capture = math.pi * (PROJECTILE_DIAMETER_M / 2)**2
# --- Simulation Loop ---
for time_step in range(int(SIMULATION_DURATION_S / TIME_STEP_S)):
# 1. Mass and Energy of incoming air
mass_collected_in_step = AIR_DENSITY_KG_M3 * cross_sectional_area_capture * PROJECTILE_VELOCITY_MPS * TIME_STEP_S
kinetic_energy_in_step = 0.5 * mass_collected_in_step * PROJECTILE_VELOCITY_MPS**2
# 2. Update Gas Energy with new air
total_gas_energy = (collected_air_mass * SPECIFIC_HEAT_AIR_J_KG_K * gas_temperature_K) + kinetic_energy_in_step
collected_air_mass += mass_collected_in_step
if collected_air_mass > 0:
gas_temperature_K = total_gas_energy / (collected_air_mass * SPECIFIC_HEAT_AIR_J_KG_K)
# 3. Calculate Heat Flow
temp_diff = gas_temperature_K - pipe_temperature_K
heat_transferred_this_step = HEAT_TRANSFER_COEFFICIENT * total_cooling_surface_area_sqm * temp_diff * TIME_STEP_S
# 4. Update Temperatures based on Heat Flow
if total_gas_energy > 0:
gas_temperature_K -= heat_transferred_this_step / (collected_air_mass * SPECIFIC_HEAT_AIR_J_KG_K)
pipe_temperature_K += heat_transferred_this_step / (PIPE_MASS_KG * SPECIFIC_HEAT_PIPE_J_KG_K)
print(f"Time: {time_step * TIME_STEP_S:.2f}s | Gas Temp: {gas_temperature_K:.2f} K | Pipe Temp: {pipe_temperature_K:.2f} K | Mass: {collected_air_mass:.2f} kg")If anyone runs this program this topic is available for comments. Since I have no way of knowing ahead of time how this is going to turn out, if there is someone in the active membership who has knowledge in this area, you are welcome to pitch in.
If there is a forum reader who would like to participate, see the Recruiting topic for procedure.
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TH, at that speed (>Mach 30) the air would be shock heated into a plasma as it enters the tube. W.r.t to the tube, the air is moving at 11km/s. That is a kinetic energy of 60.5MJ/kg, all of which is converted into a combination of pressure and thermal energy, as the air accelerates to the velocity of the tube. Your tube will probably melt and frontal pressure will blow it apart. Did Gemini pick that up?
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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For Calliban re #4
Thank you for your interest in this inquiry! I will ask Gemini about plasma in our next interaction. If you have time, please look at this set of results. The computation assumes a set of conditions that are listed in the source code in Post #3. However, the listing may be self-explanatory.
We are admitting air into a cold tube and we can see that the tube is heating as energy is transferred to the walls of the container. We had found earlier that the pressure inside the container equals the incoming air pressure after about one ton of air is collected. That is not shown in the chart below. What ** is ** shown is that the tubes are heating rapidly to the melting point of the material, so we would have to close the doors before then.
My hope in adding cooling to the simulation was to capture more air on the way up. This little study program appears to be showing that the amount of air captured will indeed increase.
python3 20250828ThermodynamicsStudyV01.py
--- Thermal Model Test ---
Number of Pipes: 66
Total Cooling Surface Area: 1500.00 m^2
Initial Pipe Temp: 100.00 K
Initial Gas Temp: 288.00 K
--------------------------
Time: 0.00s | Gas Temp: 59775.22 K | Pipe Temp: 200.17 K | Mass: 105.83 kg
Time: 0.01s | Gas Temp: 59776.32 K | Pipe Temp: 299.81 K | Mass: 211.66 kg
Time: 0.02s | Gas Temp: 59777.09 K | Pipe Temp: 399.17 K | Mass: 317.50 kg
Time: 0.03s | Gas Temp: 59777.71 K | Pipe Temp: 498.31 K | Mass: 423.33 kg
Time: 0.04s | Gas Temp: 59778.25 K | Pipe Temp: 597.25 K | Mass: 529.16 kg
Time: 0.05s | Gas Temp: 59778.74 K | Pipe Temp: 696.00 K | Mass: 634.99 kg
Time: 0.06s | Gas Temp: 59779.20 K | Pipe Temp: 794.57 K | Mass: 740.83 kg
Time: 0.07s | Gas Temp: 59779.64 K | Pipe Temp: 892.97 K | Mass: 846.66 kg
Time: 0.08s | Gas Temp: 59780.06 K | Pipe Temp: 991.19 K | Mass: 952.49 kg
Time: 0.09s | Gas Temp: 59780.47 K | Pipe Temp: 1089.24 K | Mass: 1058.32 kg
Time: 0.10s | Gas Temp: 59780.87 K | Pipe Temp: 1187.12 K | Mass: 1164.16 kg
Time: 0.11s | Gas Temp: 59781.27 K | Pipe Temp: 1284.84 K | Mass: 1269.99 kg
Time: 0.12s | Gas Temp: 59781.65 K | Pipe Temp: 1382.39 K | Mass: 1375.82 kg
Time: 0.13s | Gas Temp: 59782.03 K | Pipe Temp: 1479.77 K | Mass: 1481.65 kg
Time: 0.14s | Gas Temp: 59782.41 K | Pipe Temp: 1576.99 K | Mass: 1587.49 kg
Time: 0.15s | Gas Temp: 59782.79 K | Pipe Temp: 1674.04 K | Mass: 1693.32 kg << 1643 Kelvin steel alloy melting point see Google below
Time: 0.16s | Gas Temp: 59783.16 K | Pipe Temp: 1770.93 K | Mass: 1799.15 kg
Time: 0.17s | Gas Temp: 59783.52 K | Pipe Temp: 1867.65 K | Mass: 1904.98 kg
Time: 0.18s | Gas Temp: 59783.89 K | Pipe Temp: 1964.21 K | Mass: 2010.82 kg
Time: 0.19s | Gas Temp: 59784.25 K | Pipe Temp: 2060.62 K | Mass: 2116.65 kg
Time: 0.20s | Gas Temp: 59784.61 K | Pipe Temp: 2156.85 K | Mass: 2222.48 kg
Time: 0.21s | Gas Temp: 59784.97 K | Pipe Temp: 2252.93 K | Mass: 2328.31 kg
Time: 0.22s | Gas Temp: 59785.33 K | Pipe Temp: 2348.85 K | Mass: 2434.15 kg
Time: 0.23s | Gas Temp: 59785.69 K | Pipe Temp: 2444.60 K | Mass: 2539.98 kg
Time: 0.24s | Gas Temp: 59786.04 K | Pipe Temp: 2540.20 K | Mass: 2645.81 kg
Time: 0.25s | Gas Temp: 59786.39 K | Pipe Temp: 2635.64 K | Mass: 2751.64 kg
Time: 0.26s | Gas Temp: 59786.75 K | Pipe Temp: 2730.91 K | Mass: 2857.47 kg
Time: 0.27s | Gas Temp: 59787.10 K | Pipe Temp: 2826.03 K | Mass: 2963.31 kg
Time: 0.28s | Gas Temp: 59787.45 K | Pipe Temp: 2920.99 K | Mass: 3069.14 kg
Time: 0.29s | Gas Temp: 59787.80 K | Pipe Temp: 3015.79 K | Mass: 3174.97 kg
Time: 0.30s | Gas Temp: 59788.14 K | Pipe Temp: 3110.43 K | Mass: 3280.80 kg
Time: 0.31s | Gas Temp: 59788.49 K | Pipe Temp: 3204.92 K | Mass: 3386.64 kg
Time: 0.32s | Gas Temp: 59788.84 K | Pipe Temp: 3299.24 K | Mass: 3492.47 kg
Time: 0.33s | Gas Temp: 59789.18 K | Pipe Temp: 3393.41 K | Mass: 3598.30 kg
Time: 0.34s | Gas Temp: 59789.53 K | Pipe Temp: 3487.43 K | Mass: 3704.13 kg
Time: 0.35s | Gas Temp: 59789.87 K | Pipe Temp: 3581.28 K | Mass: 3809.97 kg
Time: 0.36s | Gas Temp: 59790.22 K | Pipe Temp: 3674.98 K | Mass: 3915.80 kg
Time: 0.37s | Gas Temp: 59790.56 K | Pipe Temp: 3768.52 K | Mass: 4021.63 kg
Time: 0.38s | Gas Temp: 59790.90 K | Pipe Temp: 3861.91 K | Mass: 4127.46 kg
Time: 0.39s | Gas Temp: 59791.24 K | Pipe Temp: 3955.14 K | Mass: 4233.30 kg
Time: 0.40s | Gas Temp: 59791.58 K | Pipe Temp: 4048.22 K | Mass: 4339.13 kg
Time: 0.41s | Gas Temp: 59791.92 K | Pipe Temp: 4141.14 K | Mass: 4444.96 kg
Time: 0.42s | Gas Temp: 59792.26 K | Pipe Temp: 4233.91 K | Mass: 4550.79 kg
Time: 0.43s | Gas Temp: 59792.60 K | Pipe Temp: 4326.52 K | Mass: 4656.63 kg
Time: 0.44s | Gas Temp: 59792.94 K | Pipe Temp: 4418.98 K | Mass: 4762.46 kg
Time: 0.45s | Gas Temp: 59793.28 K | Pipe Temp: 4511.28 K | Mass: 4868.29 kg
Time: 0.46s | Gas Temp: 59793.61 K | Pipe Temp: 4603.44 K | Mass: 4974.12 kg
Time: 0.47s | Gas Temp: 59793.95 K | Pipe Temp: 4695.43 K | Mass: 5079.96 kg
Time: 0.48s | Gas Temp: 59794.29 K | Pipe Temp: 4787.28 K | Mass: 5185.79 kg
Time: 0.49s | Gas Temp: 59794.62 K | Pipe Temp: 4878.97 K | Mass: 5291.62 kg
Time: 0.50s | Gas Temp: 59794.96 K | Pipe Temp: 4970.51 K | Mass: 5397.45 kg
Time: 0.51s | Gas Temp: 59795.29 K | Pipe Temp: 5061.90 K | Mass: 5503.28 kg
Time: 0.52s | Gas Temp: 59795.63 K | Pipe Temp: 5153.13 K | Mass: 5609.12 kg
Time: 0.53s | Gas Temp: 59795.96 K | Pipe Temp: 5244.21 K | Mass: 5714.95 kg
Time: 0.54s | Gas Temp: 59796.29 K | Pipe Temp: 5335.15 K | Mass: 5820.78 kg
Time: 0.55s | Gas Temp: 59796.63 K | Pipe Temp: 5425.93 K | Mass: 5926.61 kg
Time: 0.56s | Gas Temp: 59796.96 K | Pipe Temp: 5516.56 K | Mass: 6032.45 kg
Time: 0.57s | Gas Temp: 59797.29 K | Pipe Temp: 5607.04 K | Mass: 6138.28 kg
Time: 0.58s | Gas Temp: 59797.62 K | Pipe Temp: 5697.36 K | Mass: 6244.11 kg
Time: 0.59s | Gas Temp: 59797.95 K | Pipe Temp: 5787.54 K | Mass: 6349.94 kg
Time: 0.60s | Gas Temp: 59798.28 K | Pipe Temp: 5877.57 K | Mass: 6455.78 kg
Time: 0.61s | Gas Temp: 59798.61 K | Pipe Temp: 5967.45 K | Mass: 6561.61 kg
Time: 0.62s | Gas Temp: 59798.94 K | Pipe Temp: 6057.18 K | Mass: 6667.44 kg
Time: 0.63s | Gas Temp: 59799.27 K | Pipe Temp: 6146.76 K | Mass: 6773.27 kg
Time: 0.64s | Gas Temp: 59799.60 K | Pipe Temp: 6236.19 K | Mass: 6879.11 kg
Time: 0.65s | Gas Temp: 59799.93 K | Pipe Temp: 6325.47 K | Mass: 6984.94 kg
Time: 0.66s | Gas Temp: 59800.26 K | Pipe Temp: 6414.61 K | Mass: 7090.77 kg
Time: 0.67s | Gas Temp: 59800.58 K | Pipe Temp: 6503.59 K | Mass: 7196.60 kg
Time: 0.68s | Gas Temp: 59800.91 K | Pipe Temp: 6592.43 K | Mass: 7302.44 kg
Time: 0.69s | Gas Temp: 59801.24 K | Pipe Temp: 6681.12 K | Mass: 7408.27 kg
Time: 0.70s | Gas Temp: 59801.56 K | Pipe Temp: 6769.66 K | Mass: 7514.10 kg
Time: 0.71s | Gas Temp: 59801.89 K | Pipe Temp: 6858.06 K | Mass: 7619.93 kg
Time: 0.72s | Gas Temp: 59802.21 K | Pipe Temp: 6946.31 K | Mass: 7725.77 kg
Time: 0.73s | Gas Temp: 59802.54 K | Pipe Temp: 7034.41 K | Mass: 7831.60 kg
Time: 0.74s | Gas Temp: 59802.86 K | Pipe Temp: 7122.37 K | Mass: 7937.43 kg
Time: 0.75s | Gas Temp: 59803.19 K | Pipe Temp: 7210.17 K | Mass: 8043.26 kg
Time: 0.76s | Gas Temp: 59803.51 K | Pipe Temp: 7297.84 K | Mass: 8149.09 kg
Time: 0.77s | Gas Temp: 59803.83 K | Pipe Temp: 7385.36 K | Mass: 8254.93 kg
Time: 0.78s | Gas Temp: 59804.16 K | Pipe Temp: 7472.73 K | Mass: 8360.76 kg
Time: 0.79s | Gas Temp: 59804.48 K | Pipe Temp: 7559.96 K | Mass: 8466.59 kg
Time: 0.80s | Gas Temp: 59804.80 K | Pipe Temp: 7647.04 K | Mass: 8572.42 kg
Time: 0.81s | Gas Temp: 59805.12 K | Pipe Temp: 7733.98 K | Mass: 8678.26 kg
Time: 0.82s | Gas Temp: 59805.45 K | Pipe Temp: 7820.77 K | Mass: 8784.09 kg
Time: 0.83s | Gas Temp: 59805.77 K | Pipe Temp: 7907.42 K | Mass: 8889.92 kg
Time: 0.84s | Gas Temp: 59806.09 K | Pipe Temp: 7993.92 K | Mass: 8995.75 kg
Time: 0.85s | Gas Temp: 59806.41 K | Pipe Temp: 8080.28 K | Mass: 9101.59 kg
Time: 0.86s | Gas Temp: 59806.73 K | Pipe Temp: 8166.50 K | Mass: 9207.42 kg
Time: 0.87s | Gas Temp: 59807.05 K | Pipe Temp: 8252.58 K | Mass: 9313.25 kg
Time: 0.88s | Gas Temp: 59807.37 K | Pipe Temp: 8338.51 K | Mass: 9419.08 kg
Time: 0.89s | Gas Temp: 59807.68 K | Pipe Temp: 8424.30 K | Mass: 9524.92 kg
Time: 0.90s | Gas Temp: 59808.00 K | Pipe Temp: 8509.94 K | Mass: 9630.75 kg
Time: 0.91s | Gas Temp: 59808.32 K | Pipe Temp: 8595.45 K | Mass: 9736.58 kg
Time: 0.92s | Gas Temp: 59808.64 K | Pipe Temp: 8680.81 K | Mass: 9842.41 kg
Time: 0.93s | Gas Temp: 59808.96 K | Pipe Temp: 8766.03 K | Mass: 9948.25 kg
Time: 0.94s | Gas Temp: 59809.27 K | Pipe Temp: 8851.11 K | Mass: 10054.08 kg
Time: 0.95s | Gas Temp: 59809.59 K | Pipe Temp: 8936.04 K | Mass: 10159.91 kg
Time: 0.96s | Gas Temp: 59809.90 K | Pipe Temp: 9020.84 K | Mass: 10265.74 kg
Time: 0.97s | Gas Temp: 59810.22 K | Pipe Temp: 9105.49 K | Mass: 10371.58 kg
Time: 0.98s | Gas Temp: 59810.54 K | Pipe Temp: 9190.01 K | Mass: 10477.41 kg
Time: 0.99s | Gas Temp: 59810.85 K | Pipe Temp: 9274.38 K | Mass: 10583.24 kg
Per Google:
There is no single "best possible alloy" of steel, as "best" depends on the application, but typical steel alloys have a melting range between approximately 1370°C and 1530°C, which is about 1643 K to 1803 K. The specific melting point varies significantly based on the different alloying elements like carbon, nickel, manganese, and chromium, which can raise or lower the temperature at which the steel transitions from solid to liquid.
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Gas temperature is nearly 60,000K. The gas will be ionised plasma at this temperature. That is a direct result of shock heating. Your tube temperature reaches 9000K in <1s. I don't see how this could work as a method for gathering propellant from the atmosphere.
One thing I find interesting. The specific heat of air between 100K and 60,000K, averages at 1KJ/kg.K. Roughly what it is under standard conditions.
Last edited by Calliban (Yesterday 10:47:51)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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For Calliban re #6
This entire topic is intended as a learning opportunity for NewMars members and for readers who are not members.
I'd like to point out that the SABRE engine (as I understand it) was designed to capture air and cool it using hydrogen gas as the coolant.This had to take place using metal fins for heat exchange. The engine was (apparently) tested with some success on the ground. I don't know much more than that.
One detail of this study should be explained for our readers...
The study is of performance of a gas gun, such as designed and tested by Dr. John Hunter. This forum contains a number of posts about Dr. Hunter, and if anyone is interested it should be easy to find.
Dr. Hunter's design envisioned a launch in the 5-7 km/s range. I am interested in exploring the potential for a more ambitious use of the technology, which is why I've chosen 11 km/s as the exit velocity.
The current study is run at 11 km/s, which is why the problem is so difficult.
Indeed, the end result may well be confirmation that the air capture idea cannot be put into practice in the Real Universe, at this velocity.
That is why the idea of doing the air capture at a lower velocity is interesting.
One more note for our readers.... this study is being done to evaluate the potential of capture of air for sale on orbit. This has nothing to do with propulsion. The value of oxygen and nitrogen on orbit is measured in Falcon 9 rates per kilogram.
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Using a light gas gun to accelerate payloads to Earth escape velocity is an innovative approach. Barrel wear would be a problem at such speeds. I wonder if the barrel can be lined with a sacrificial shell that is discarded after each shot?
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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