Dome HeatQuote from: lamontagne on 11/01/2016 03:12 pmI put a bit of structure inside the dome.Mostly platforms wit a lot of greenery. Could be sports areas instead. Possibly a floor of high intensity agriculture, but that might better be done in closed rooms with controlled atmosphere and lighting. Plants are happy in conditions that people sometimes find not all that pleasant...Again, most of the living area is actually underground, these are just entry points to the city.The exterior wall is a form of curtain wall, in a way. It's self supporting, mostly, and pressure driven, except for the gravity loads that are transmitted by columns to the ground.Nice-looking structure. btw, on winter nights your heat flux will be quite high. For example, if panes are simple 6 cm glass, the flux would be ~100 MW. Might give that some thought.
I put a bit of structure inside the dome.Mostly platforms wit a lot of greenery. Could be sports areas instead. Possibly a floor of high intensity agriculture, but that might better be done in closed rooms with controlled atmosphere and lighting. Plants are happy in conditions that people sometimes find not all that pleasant...Again, most of the living area is actually underground, these are just entry points to the city.The exterior wall is a form of curtain wall, in a way. It's self supporting, mostly, and pressure driven, except for the gravity loads that are transmitted by columns to the ground.
LaMontage.Can you give me the sketchup link? I might put my vizualisation skills to use and make some renderings. Finally a chance to contribute to this forum.Best wishes,M.
Quote from: lamontagne on 11/01/2016 03:12 pmI put a bit of structure inside the dome.Hi lamontagne,I don't think flattened spheres are robust pressure containers. For example in the extreme, upper and lower sides approach flat and would be worse than cubes. I think you can elongate, but not flatten. Cigars and conical points are ok.. I think?Why not just go the full sphere? I posted a picture of a hydrogen tank in the other thread but just noticed there is a picture of it in a NSF article right now:https://www.nasaspaceflight.com/2016/10/ksc-groundwork-sls-block-1b-upgrades/These were the links I posted in the other thread:these gas tanks or this big liquid hydrogen tankEDIT:Ok I did a search on pressure tanks and did find lots of examples that look flattened at the ends. Can anyone explain that to me? (none of them where wider than they were tall though, and when I searched for high pressure tanks, more had spherical ends.)
I put a bit of structure inside the dome.
KelvinZero, and posters, do you think it would be a good idea to merge this thread and the geodesic glass domes thread?
Quote from: wstewart on 11/01/2016 10:48 pmDome HeatQuote from: lamontagne on 11/01/2016 03:12 pmI put a bit of structure inside the dome.Mostly platforms wit a lot of greenery. Could be sports areas instead. Possibly a floor of high intensity agriculture, but that might better be done in closed rooms with controlled atmosphere and lighting. Plants are happy in conditions that people sometimes find not all that pleasant...Again, most of the living area is actually underground, these are just entry points to the city.The exterior wall is a form of curtain wall, in a way. It's self supporting, mostly, and pressure driven, except for the gravity loads that are transmitted by columns to the ground.Nice-looking structure. btw, on winter nights your heat flux will be quite high. For example, if panes are simple 6 cm glass, the flux would be ~100 MW. Might give that some thought.Youre making the same false assumption that you made earlier when you said the polycarbonate would be brittle. You're saying the surface of the dome will be the same temperature as the incredibly thin outside air. That's simply not true.There's not perfect thermal conductivity between the thin Martian air and the dome's surface.
Quote from: LMT on 11/01/2016 10:48 pmDome HeatQuote from: lamontagne on 11/01/2016 03:12 pmI put a bit of structure inside the dome.Mostly platforms wit a lot of greenery. Could be sports areas instead. Possibly a floor of high intensity agriculture, but that might better be done in closed rooms with controlled atmosphere and lighting. Plants are happy in conditions that people sometimes find not all that pleasant...Again, most of the living area is actually underground, these are just entry points to the city.The exterior wall is a form of curtain wall, in a way. It's self supporting, mostly, and pressure driven, except for the gravity loads that are transmitted by columns to the ground.Nice-looking structure. btw, on winter nights your heat flux will be quite high. For example, if panes are simple 6 cm glass, the flux would be ~100 MW. Might give that some thought.Why so high? I was hoping that using a low emissivity on the glass surface would allow for the radiation to be fairly low. I just calculated something like 100 kW. I expected no convection or conduction. Do you have some numbers for this?
Domo DomoQuote from: Lumina on 11/02/2016 01:47 amKelvinZero, and posters, do you think it would be a good idea to merge this thread and the geodesic glass domes thread? Thanks. Could we merge, but consider keeping this thread open for non-dome structures? There are a lot of ideas here; wouldn't want to discourage the other ideas, just because Musk tweeted "dome".
Youre making the same false assumption that you made earlier when you said the polycarbonate would be brittle. You're saying the surface of the dome will be the same temperature as the incredibly thin outside air. That's simply not true.There's not perfect thermal conductivity between the thin Martian air and the dome's surface.
I would prefer them kept separate.. The domes one is about some very specific issues with domes. It is specific enough that it might actually feel answered shortly (..snip..)The thing about that dome thread was specifically issues like anchoring and leaking that made the Dome statement strange to me. Someone did some math about anchoring i havent got around to yet. My expectation is that it is more time, effort and resources for a less trusty and less general result, restricting you to only certain types of ground that may or may not be near the resources you want.
Heat LossQuote from: lamontagne on 11/01/2016 11:29 pmQuote from: wstewart on 11/01/2016 10:48 pmDome HeatQuote from: lamontagne on 11/01/2016 03:12 pmI put a bit of structure inside the dome.Mostly platforms wit a lot of greenery. Could be sports areas instead. Possibly a floor of high intensity agriculture, but that might better be done in closed rooms with controlled atmosphere and lighting. Plants are happy in conditions that people sometimes find not all that pleasant...Again, most of the living area is actually underground, these are just entry points to the city.The exterior wall is a form of curtain wall, in a way. It's self supporting, mostly, and pressure driven, except for the gravity loads that are transmitted by columns to the ground.Nice-looking structure. btw, on winter nights your heat flux will be quite high. For example, if panes are simple 6 cm glass, the flux would be ~100 MW. Might give that some thought.Why so high? I was hoping that using a low emissivity on the glass surface would allow for the radiation to be fairly low. I just calculated something like 100 kW. I expected no convection or conduction. Do you have some numbers for this?It would be good if I've calculated too high there, because lower heat loss would be a win for many hab schemes.I was thinking of heat loss as it's calculated in a typical construction. R-value (thermal resistance) for 6 cm glass works out at ~0.06 m2K/W. Winter night temperature difference is 160 C. That gives a heat flux of 2667 W/m2. For dome surface area I used your previous scaling number of 150 m diameter, eyeballing a 75 m height, and allowing for 25% dome burial with no heat loss there. That leaves 36,620 m2 exposed for heat loss. Multiply area by flux, and total heat loss is ~100 MW.The glass panes insulate very poorly, so convection off panes should be low; but if there's a correction factor for atmospheric pressure I don't know it. Also the dome radiates efficiently because there's no reflector outside the glass surface.In your spreadsheet you have a smaller dome (100 m diameter), and you're using low-e film. I think I'd seen that these films, in practice, reduce heat flux by at most 1/3. Any thought on that? And you're using the T4 Stefan-Boltzmann law, which is fine. Just coming at heat loss from a different direction.
Quote from: wstewart on 11/01/2016 10:48 pmDome HeatQuote from: lamontagne on 11/01/2016 03:12 pmI put a bit of structure inside the dome.Mostly platforms wit a lot of greenery. Could be sports areas instead. Possibly a floor of high intensity agriculture, but that might better be done in closed rooms with controlled atmosphere and lighting. Plants are happy in conditions that people sometimes find not all that pleasant...Again, most of the living area is actually underground, these are just entry points to the city.The exterior wall is a form of curtain wall, in a way. It's self supporting, mostly, and pressure driven, except for the gravity loads that are transmitted by columns to the ground.Nice-looking structure. btw, on winter nights your heat flux will be quite high. For example, if panes are simple 6 cm glass, the flux would be ~100 MW. Might give that some thought.Why so high? I was hoping that using a low emissivity on the glass surface would allow for the radiation to be fairly low. I just calculated something like 100 kW. I expected no convection or conduction. Do you have some numbers for this?
Cold SkinQuote from: Robotbeat on 11/02/2016 02:28 amYoure making the same false assumption that you made earlier when you said the polycarbonate would be brittle. You're saying the surface of the dome will be the same temperature as the incredibly thin outside air. That's simply not true.There's not perfect thermal conductivity between the thin Martian air and the dome's surface.? The polycarbonate only needs to reach -60 C at one point on its surface, to become brittle there, and put the dome at risk. On a typical night with -90 C air and ground, a -60 C cold spot on the exterior surface seems very likely to me. Especially along the ground, where conduction produces even faster heat loss. And heaven forbid the dome heating system should fail even briefly, when a polycarbonate dome's integrity is so fragile at martian temperatures. (Come to think of it, how would you ensure that the polycarbonate never reached -60 C during construction, when a dome heating system was not yet available? Logistically, that seems a challenge in itself.)If you wanted to make an opposite case, and give reassurance that the polycarbonate would never approach -60 C, I suppose you'd need to model 1-D polycarbonate thermal profiles, with thermal front skin depth evolution over 1 sol, both in air and on the ground. Or is there some model already available, for polycarbonate, polyethylene or some similar sheet material?
Quote from: LMT on 11/02/2016 04:33 amHeat LossQuote from: lamontagne on 11/01/2016 11:29 pmQuote from: LMT on 11/01/2016 10:48 pmDome HeatQuote from: lamontagne on 11/01/2016 03:12 pmI put a bit of structure inside the dome.Mostly platforms wit a lot of greenery. Could be sports areas instead. Possibly a floor of high intensity agriculture, but that might better be done in closed rooms with controlled atmosphere and lighting. Plants are happy in conditions that people sometimes find not all that pleasant...Again, most of the living area is actually underground, these are just entry points to the city.The exterior wall is a form of curtain wall, in a way. It's self supporting, mostly, and pressure driven, except for the gravity loads that are transmitted by columns to the ground.Nice-looking structure. btw, on winter nights your heat flux will be quite high. For example, if panes are simple 6 cm glass, the flux would be ~100 MW. Might give that some thought.Why so high? I was hoping that using a low emissivity on the glass surface would allow for the radiation to be fairly low. I just calculated something like 100 kW. I expected no convection or conduction. Do you have some numbers for this?It would be good if I've calculated too high there, because lower heat loss would be a win for many hab schemes.I was thinking of heat loss as it's calculated in a typical construction. R-value (thermal resistance) for 6 cm glass works out at ~0.06 m2K/W. Winter night temperature difference is 160 C. That gives a heat flux of 2667 W/m2. For dome surface area I used your previous scaling number of 150 m diameter, eyeballing a 75 m height, and allowing for 25% dome burial with no heat loss there. That leaves 36,620 m2 exposed for heat loss. Multiply area by flux, and total heat loss is ~100 MW.The glass panes insulate very poorly, so convection off panes should be low; but if there's a correction factor for atmospheric pressure I don't know it. Also the dome radiates efficiently because there's no reflector outside the glass surface.In your spreadsheet you have a smaller dome (100 m diameter), and you're using low-e film. I think I'd seen that these films, in practice, reduce heat flux by at most 1/3. Any thought on that? And you're using the T4 Stefan-Boltzmann law, which is fine. Just coming at heat loss from a different direction.You're missing the convective term on the outer surface of your glass. In a typical building insulation calculation, you will have the internal film coefficient, the insulation of the building wall composition, then the outside film coefficient, usually equivalent to R 0.1. However, if you analyse this film coefficient in detail, you will find that it is an expression of the convective conduction from the mass flow of the air on the surface of the building. Q=hAdT where h is a factor of the mass flow. Using a slightly different equation, Q=mf*Cp*dT, power=mass flow x specific heat x temperature difference, on Mars with the atmosphere 100 times less dense than on Earth, the mass flow will be 100 times less, so the heat transfer film coefficient will be 100 times higher, or about R10 (imperial units) or 2 inches of styrofoam equivalent. Now if you have double pane glass, you will have 2 more film coefficient, one on the inside and another on the outside of the second pane. So the overall R will be practically 30. Therefore the surface temperature of the outer glass pane will be near to the environment temperature, and the radiation will be very low.And to further reduce heat low you can put the low emissivity film of the inside of the outer glass pane. This film is an infrared mirror, so the radiation from the inner glass plane gets reflected, and the radiative heat gain on the outer glass pane is almost nil. Summing up the very low convection and the very low radiation, you get very low heat transfer, about 1000 times less than your first order estimate, or about 100 kW. For 12 hours of night then about 1200 kWh of heat loss. As the heat gain is higher, the domes will tend to overheat, if the solar heat gain is not reduced. So curtains during the day, and not during the night!The reason low-e windows are not that effective is that they have an atmospheric pressure gas in the void. If you had a Mars pressure gas in the void, they would insulate as well as, or better, than the walls. Of course, they would implode first ;-)
Heat LossQuote from: lamontagne on 11/01/2016 11:29 pmQuote from: LMT on 11/01/2016 10:48 pmDome HeatQuote from: lamontagne on 11/01/2016 03:12 pmI put a bit of structure inside the dome.Mostly platforms wit a lot of greenery. Could be sports areas instead. Possibly a floor of high intensity agriculture, but that might better be done in closed rooms with controlled atmosphere and lighting. Plants are happy in conditions that people sometimes find not all that pleasant...Again, most of the living area is actually underground, these are just entry points to the city.The exterior wall is a form of curtain wall, in a way. It's self supporting, mostly, and pressure driven, except for the gravity loads that are transmitted by columns to the ground.Nice-looking structure. btw, on winter nights your heat flux will be quite high. For example, if panes are simple 6 cm glass, the flux would be ~100 MW. Might give that some thought.Why so high? I was hoping that using a low emissivity on the glass surface would allow for the radiation to be fairly low. I just calculated something like 100 kW. I expected no convection or conduction. Do you have some numbers for this?It would be good if I've calculated too high there, because lower heat loss would be a win for many hab schemes.I was thinking of heat loss as it's calculated in a typical construction. R-value (thermal resistance) for 6 cm glass works out at ~0.06 m2K/W. Winter night temperature difference is 160 C. That gives a heat flux of 2667 W/m2. For dome surface area I used your previous scaling number of 150 m diameter, eyeballing a 75 m height, and allowing for 25% dome burial with no heat loss there. That leaves 36,620 m2 exposed for heat loss. Multiply area by flux, and total heat loss is ~100 MW.The glass panes insulate very poorly, so convection off panes should be low; but if there's a correction factor for atmospheric pressure I don't know it. Also the dome radiates efficiently because there's no reflector outside the glass surface.In your spreadsheet you have a smaller dome (100 m diameter), and you're using low-e film. I think I'd seen that these films, in practice, reduce heat flux by at most 1/3. Any thought on that? And you're using the T4 Stefan-Boltzmann law, which is fine. Just coming at heat loss from a different direction.
Quote from: LMT on 11/02/2016 05:02 amCold SkinQuote from: Robotbeat on 11/02/2016 02:28 amYoure making the same false assumption that you made earlier when you said the polycarbonate would be brittle. You're saying the surface of the dome will be the same temperature as the incredibly thin outside air. That's simply not true.There's not perfect thermal conductivity between the thin Martian air and the dome's surface.? The polycarbonate only needs to reach -60 C at one point on its surface, to become brittle there, and put the dome at risk. On a typical night with -90 C air and ground, a -60 C cold spot on the exterior surface seems very likely to me. Especially along the ground, where conduction produces even faster heat loss. And heaven forbid the dome heating system should fail even briefly, when a polycarbonate dome's integrity is so fragile at martian temperatures. (Come to think of it, how would you ensure that the polycarbonate never reached -60 C during construction, when a dome heating system was not yet available? Logistically, that seems a challenge in itself.)If you wanted to make an opposite case, and give reassurance that the polycarbonate would never approach -60 C, I suppose you'd need to model 1-D polycarbonate thermal profiles, with thermal front skin depth evolution over 1 sol, both in air and on the ground. Or is there some model already available, for polycarbonate, polyethylene or some similar sheet material?Perhaps LDPE would do the trick? It has a glass transition temperature of -125C. I was hopping to use it for plastic algae grow tubes on the surface of Mars. However, plain glass is a good building material, I don't quite see why it needs to be replaced by plastic, in particular if it is produced in situ. Shouldn't there be some obsidian flows available on Mars? Good source of glass, that, since it's already glass.
Quote from: lamontagne on 11/02/2016 10:34 amQuote from: wstewart on 11/02/2016 05:02 amCold SkinQuote from: Robotbeat on 11/02/2016 02:28 amYoure making the same false assumption that you made earlier when you said the polycarbonate would be brittle. You're saying the surface of the dome will be the same temperature as the incredibly thin outside air. That's simply not true.There's not perfect thermal conductivity between the thin Martian air and the dome's surface.? The polycarbonate only needs to reach -60 C at one point on its surface, to become brittle there, and put the dome at risk. On a typical night with -90 C air and ground, a -60 C cold spot on the exterior surface seems very likely to me. Especially along the ground, where conduction produces even faster heat loss. And heaven forbid the dome heating system should fail even briefly, when a polycarbonate dome's integrity is so fragile at martian temperatures. (Come to think of it, how would you ensure that the polycarbonate never reached -60 C during construction, when a dome heating system was not yet available? Logistically, that seems a challenge in itself.)If you wanted to make an opposite case, and give reassurance that the polycarbonate would never approach -60 C, I suppose you'd need to model 1-D polycarbonate thermal profiles, with thermal front skin depth evolution over 1 sol, both in air and on the ground. Or is there some model already available, for polycarbonate, polyethylene or some similar sheet material?Perhaps LDPE would do the trick? It has a glass transition temperature of -125C. I was hopping to use it for plastic algae grow tubes on the surface of Mars. However, plain glass is a good building material, I don't quite see why it needs to be replaced by plastic, in particular if it is produced in situ. Shouldn't there be some obsidian flows available on Mars? Good source of glass, that, since it's already glass.Isn't the brittle transition temperature more critical? Both low- and high-density polyethylene transition at -70 C.And how might an algae grow tube maintain the ~10 C growth temperature range, while radiating and conducting heat out on the surface?
Quote from: wstewart on 11/02/2016 05:02 amCold SkinQuote from: Robotbeat on 11/02/2016 02:28 amYoure making the same false assumption that you made earlier when you said the polycarbonate would be brittle. You're saying the surface of the dome will be the same temperature as the incredibly thin outside air. That's simply not true.There's not perfect thermal conductivity between the thin Martian air and the dome's surface.? The polycarbonate only needs to reach -60 C at one point on its surface, to become brittle there, and put the dome at risk. On a typical night with -90 C air and ground, a -60 C cold spot on the exterior surface seems very likely to me. Especially along the ground, where conduction produces even faster heat loss. And heaven forbid the dome heating system should fail even briefly, when a polycarbonate dome's integrity is so fragile at martian temperatures. (Come to think of it, how would you ensure that the polycarbonate never reached -60 C during construction, when a dome heating system was not yet available? Logistically, that seems a challenge in itself.)If you wanted to make an opposite case, and give reassurance that the polycarbonate would never approach -60 C, I suppose you'd need to model 1-D polycarbonate thermal profiles, with thermal front skin depth evolution over 1 sol, both in air and on the ground. Or is there some model already available, for polycarbonate, polyethylene or some similar sheet material?Perhaps LDPE would do the trick? It has a glass transition temperature of -125C. I was hopping to use it for plastic algae grow tubes on the surface of Mars. However, plain glass is a good building material, I don't quite see why it needs to be replaced by plastic, in particular if it is produced in situ. Shouldn't there be some obsidian flows available on Mars? Good source of glass, that, since it's already glass.
Isn't the brittle transition temperature more critical?...
I still think it's better to merge them but it's a step forward for our posters to have clarity on the topic of the other thread. It sounds like it's for extended discussions on glass dome issues around anchoring and leaking.