Human mass flow

[ar81]

In my efforts to understand human mass flow for Space Orbinomics II I came to this equation
H2O + Food + O2 = CO2 + Solid waste + Wet waste + Other waste
I came to think that
Other waste = 0
since sweating should not represent a problem of loss of mass.
Wet waste = H2O + Non water waste
H2O + Food + O2 = CO2 + Solid waste + H2O + Non water waste
Since human body dissolutions remain at a certain concentration, then
H2O in = H2O out
and since a human use to keep the same mass with a balanced diet, I could remove H2O to see what changes.
Food + O2 = CO2 + Solid waste + Non water waste
You could think that food contains carbon that is used to create CO2.
Food = Non carbon food + C
So it means I have
C + O2 = CO2
and
Non carbon food + C + O2 = Solid waste + Non water waste + CO2
With stechiometry I could calculate materials needed to produce CO2
Daily food is about 2 Kg per day (Non carbon food + C) and I know that non water waste is about 15% of the 1.5 Kg/day of wet waste.
So I can calculate solid waste.
Is this approach correct?

 

[Urwumpe]

Sweating can cause serious loss of mass, it is actually not really minimal, especially if you do an EVA.

 

[ar81]

How do I calculate that loss of mass?

 

[Urwumpe]

How do I calculate that loss of mass?

Did you already look into the NASA Tech report server for this?

I don't know the hard numbers, but you can sure find them there, as these standards define how space suits are designed.

 

[ar81]

It seems that it is about 5% in the experiment.
It means that you need to eat more and drink more to compensate.

 

[Urwumpe]

It seems that it is about 5% in the experiment.
It means that you need to eat more and drink more to compensate.

Yes, the energy content of food is really critical, especially for EVA astronauts.

 

[perseus]

Perhaps These data will serve as aid

http://axxon.com.ar/not/167/c-1670090.htm
http://www.projectrho.com/rocket/rocket3g.html

 

[spcefrk]

I'd suggest going with H20_in = Eff*H20_out. If you're doing an EVA or something else strenuous then you switch to a lower Efficiency to simulate the fact that not all water can be collected. You might have two or three efficiency factors, one for EVA, one for Sleep, one for Awake, etc...

I also wouldn't necessarily look at CO2 as a byproduct of food and O2. CO2 is a rather constant buildup whether we eat or not (of course it's a different rate if we're sleeping, awake, or doing strenuous work).

If you want to get deep into this stuff, I recommend one of the SMAD books -- there's one on human spaceflight that details all this stuff pretty well. ISBN 0-07-236811-X It's a pretty handy reference. It lists the following:

Human water needs (Table 17-5):
Req. in kg per person per day (potable,hygiene)
Drinking (1.6,--)
Preparing Food (0.75,--)
Water in Food (1.15,--)
Shower (--,2.7)
Hand Wash (--,4.1)
Laundry (--,12.5)
Dishwashing (--,5.5)
Urinal Flushing (--,0.5)
Medical (5 per event)
EVA - Cooling (7.3)

Section 5.4 lists (for a lunar base example) per person per day
0.62 kg of food solids
3.52 kg of potable water
25.4 kg of nonpotable water
0.84 kg of Oxygen
0.11 kg of solid waste (all sources)
3.87 kg of liquid waste (all sources)
25.4 kg of water, nonpotable, for recycling
1.0 kg of CO2

Table 14-5 on Planetary Surface Vehicles notes:
1.6-3.6 kg of Potable Water
5-25 kg of Hygiene Water
0.6-1 kg of Oxygen
0.5-2 kg of Buffer leakage
0.7-3 kg of CO2 production
3.5-5.5 kg per person per hour of cooling water for EVA
1.5-2 kg of food (containing 2/3 chemically bound water)

Anyway, if you're big on getting environmentals and such worked out, you should really pick up a copy of the book. There are lots of subtleties to the various numbers.

 

[ar81]

Perseus, great links. Those links led me to discover Sabatier reaction...
It looks like a great addition to the vessel equations.

I have learned about stechiometry, which seems very useful.
As things go on like this, I could also release a stechiometric calculator.

Another idea came to my mind... reactions may not be complete, so upgrades could improve the efficiency of equipment.

spcefrk, amazing set of data.
I will compare it with current data.

I must tell you that what you have done is great!!
I used to hate chemistry, as I never understood a bit.
I had a chemistry teacher in high school who was very old and her explanations were less than poor, but her exams were tough.
When I reached university I had a professor who was a great researcher but bad for teaching.
So I always disliked chemistry... until now...

 

[joeybigO]

Interesting food for thought here.

Why would you have to make calculation of weight based on mass of the personnel?

I know I haven't done this in awhile, but it should be only if a burn were to have to happen... Or if you were calculating orbital degradation.

Is there any other use for this?

 

[ar81]

I see all components of waste treatment as an input vs output formula.
I do not care about human mass, only what gets in or out.
However if there is more input than output, it means that there is an increase of mass, and if some substance increases its amount, concentration will change inside human body system.

So I am working on the assumption of constant weight of person and constant concentration of substances inside human body. Even if I do not care about person-s mass, I play with constraints because of these conditions. And that allows me to create guesstimates.

 

[spcefrk]

ar81, I was thinking about this again and about how I would code such a process. I'm no good at coding in C but I suspect the following would be helpful:

For Object 1
G_in = Gas In
L_in = Liquids In
S_in = Solids In
G_out = Gas Out
L_out = Liquid Out
S_out = Solid Out
Dur = Percent of Duration left

I would have each of those six variables actually be arrays sized to the number of variables involved. For people, any outputs are considered waste.

For instance. For Gases (assuming Object 1 is a person):
G_in(1)= O2 ingested this time step
G_in(2)= N2 ingested this time step
G_out(1)= O2 expelled this time step (we don't exhale pure CO2)
G_out(3)= CO2 expelled this time step

For something like a LiOH canister:
G_in(3)= CO2 ingested this time step
G_out(1)= O2 expelled this time step
Dur = Subtract percent of life used this time step

So you could have a set number of arrays -- one each for every object that reacts with the environment, plus one for the environment itself (to keep track of the amount of each gas, liquid, and solid in the cabin).

 

[ar81]

Indeed I will use a different approach.
I recalled a course of simulation of production processes some time ago when I was a student. Simulating a process was something I always wanted to do.

I have substances and I have reactions.
I will create an array of substances (inventory).

The concept of "environment" does not exist.
You may think that all CO2 that goes to environment is indeed stored in a tank (inventory).
That way you simplify the simulation.

Reactions are processes that work based on stoichiometry.
So if you know how much of a certain substance is consumed, you have a limiting substance, so you apply stoichiometry to know the result.

I will not deal with incomplete reactions or reactions containing pollution that produce secondary byproducts. It will be a simplified model.

A real production process have a certain complexity because you can't have a "tank" or "inventory" but you need to track changes made on each unit of production and create and delete objects from your production process (like when you jettison fairings of a launcher), except for chemical industry where the way of simulation that we use here is somehow simpler.

The complexity of a real production process is that you have reprocessing, probability of failure, single or batch processing, setup times, process times depending on products, etc. Also you deal with probability distibutions.

Making this was a first step to understand how to simulate a production process in a very simplified manner.

 

[ijuin]

For waste, you might be neglecting the creation of garbage? That food comes in wrappers, after all.