Quote from: LMT on 11/28/2016 12:38 pmQuote from: guckyfan on 11/28/2016 12:04 pmQuote from: LMT on 11/28/2016 11:54 amQuote from: Robotbeat on 11/28/2016 04:05 amSabatier waste heat (which is optimally 300-400C)Sabatier reaction is exothermic, but it can't run at a scale to heat Hew Thermopylae in winter because the energy input required to maintain the reaction is far too high, as I think you know. It's more efficient to heat electrically, from PV, and skip intermediary processes. But in winter the PV for tunnel heating just isn't there.As you stated the Sabatier reaction is exothermic. It does not need any energy input to run except the initial energy to get it to operating temperature.Needeed is hydrogen from water electrolysis, this indeed needs a lot of energy. You can produce the hydrogen during the day and keep the Sabatier reaction going all night.The reaction needs hydrogen, heat and pressure, yes, and exothermy doesn't get us there, unfortunately. As example, Zubrin's unit is predicted to output 1 kg/hr, while requiring 700 W electrical, continuous.And his hydrogen comes from a bottle, gratis.You are ignoring scale which is why Zubrin needed input power for a very exothermic reaction. If you're doing megawatts of Sabatier youll need to dump heat to keep your reactor from melting
Quote from: guckyfan on 11/28/2016 12:04 pmQuote from: LMT on 11/28/2016 11:54 amQuote from: Robotbeat on 11/28/2016 04:05 amSabatier waste heat (which is optimally 300-400C)Sabatier reaction is exothermic, but it can't run at a scale to heat Hew Thermopylae in winter because the energy input required to maintain the reaction is far too high, as I think you know. It's more efficient to heat electrically, from PV, and skip intermediary processes. But in winter the PV for tunnel heating just isn't there.As you stated the Sabatier reaction is exothermic. It does not need any energy input to run except the initial energy to get it to operating temperature.Needeed is hydrogen from water electrolysis, this indeed needs a lot of energy. You can produce the hydrogen during the day and keep the Sabatier reaction going all night.The reaction needs hydrogen, heat and pressure, yes, and exothermy doesn't get us there, unfortunately. As example, Zubrin's unit is predicted to output 1 kg/hr, while requiring 700 W electrical, continuous.And his hydrogen comes from a bottle, gratis.
Quote from: LMT on 11/28/2016 11:54 amQuote from: Robotbeat on 11/28/2016 04:05 amSabatier waste heat (which is optimally 300-400C)Sabatier reaction is exothermic, but it can't run at a scale to heat Hew Thermopylae in winter because the energy input required to maintain the reaction is far too high, as I think you know. It's more efficient to heat electrically, from PV, and skip intermediary processes. But in winter the PV for tunnel heating just isn't there.As you stated the Sabatier reaction is exothermic. It does not need any energy input to run except the initial energy to get it to operating temperature.Needeed is hydrogen from water electrolysis, this indeed needs a lot of energy. You can produce the hydrogen during the day and keep the Sabatier reaction going all night.
Quote from: Robotbeat on 11/28/2016 04:05 amSabatier waste heat (which is optimally 300-400C)Sabatier reaction is exothermic, but it can't run at a scale to heat Hew Thermopylae in winter because the energy input required to maintain the reaction is far too high, as I think you know. It's more efficient to heat electrically, from PV, and skip intermediary processes. But in winter the PV for tunnel heating just isn't there.
Sabatier waste heat (which is optimally 300-400C)
Quote from: Robotbeat on 11/28/2016 03:31 pmQuote from: wstewart on 11/28/2016 12:38 pmQuote from: guckyfan on 11/28/2016 12:04 pmQuote from: wstewart on 11/28/2016 11:54 amQuote from: Robotbeat on 11/28/2016 04:05 amSabatier waste heat (which is optimally 300-400C)Sabatier reaction is exothermic, but it can't run at a scale to heat Hew Thermopylae in winter because the energy input required to maintain the reaction is far too high, as I think you know. It's more efficient to heat electrically, from PV, and skip intermediary processes. But in winter the PV for tunnel heating just isn't there.As you stated the Sabatier reaction is exothermic. It does not need any energy input to run except the initial energy to get it to operating temperature.Needeed is hydrogen from water electrolysis, this indeed needs a lot of energy. You can produce the hydrogen during the day and keep the Sabatier reaction going all night.The reaction needs hydrogen, heat and pressure, yes, and exothermy doesn't get us there, unfortunately. As example, Zubrin's unit is predicted to output 1 kg/hr, while requiring 700 W electrical, continuous.And his hydrogen comes from a bottle, gratis.You are ignoring scale which is why Zubrin needed input power for a very exothermic reaction. If you're doing megawatts of Sabatier youll need to dump heat to keep your reactor from meltingA Sabatier reactor is not a nuclear reactor. It's chemistry: net useful energy output < electrical energy input. Losses occur at each step, and no practical design catches all the waste heat at each step. So we minimize steps, ideally down to just one: convert PV electrical power directly to heat, for example in a tunnel heating wire. But of course PV itself is a problem in winter, because there doesn't seem to be nearly enough. Disagree? Well, you can sum the energy inputs and outputs in a Sabatier/electrolysis system, and just see.
Quote from: wstewart on 11/28/2016 12:38 pmQuote from: guckyfan on 11/28/2016 12:04 pmQuote from: wstewart on 11/28/2016 11:54 amQuote from: Robotbeat on 11/28/2016 04:05 amSabatier waste heat (which is optimally 300-400C)Sabatier reaction is exothermic, but it can't run at a scale to heat Hew Thermopylae in winter because the energy input required to maintain the reaction is far too high, as I think you know. It's more efficient to heat electrically, from PV, and skip intermediary processes. But in winter the PV for tunnel heating just isn't there.As you stated the Sabatier reaction is exothermic. It does not need any energy input to run except the initial energy to get it to operating temperature.Needeed is hydrogen from water electrolysis, this indeed needs a lot of energy. You can produce the hydrogen during the day and keep the Sabatier reaction going all night.The reaction needs hydrogen, heat and pressure, yes, and exothermy doesn't get us there, unfortunately. As example, Zubrin's unit is predicted to output 1 kg/hr, while requiring 700 W electrical, continuous.And his hydrogen comes from a bottle, gratis.You are ignoring scale which is why Zubrin needed input power for a very exothermic reaction. If you're doing megawatts of Sabatier youll need to dump heat to keep your reactor from melting
Quote from: guckyfan on 11/28/2016 12:04 pmQuote from: wstewart on 11/28/2016 11:54 amQuote from: Robotbeat on 11/28/2016 04:05 amSabatier waste heat (which is optimally 300-400C)Sabatier reaction is exothermic, but it can't run at a scale to heat Hew Thermopylae in winter because the energy input required to maintain the reaction is far too high, as I think you know. It's more efficient to heat electrically, from PV, and skip intermediary processes. But in winter the PV for tunnel heating just isn't there.As you stated the Sabatier reaction is exothermic. It does not need any energy input to run except the initial energy to get it to operating temperature.Needeed is hydrogen from water electrolysis, this indeed needs a lot of energy. You can produce the hydrogen during the day and keep the Sabatier reaction going all night.The reaction needs hydrogen, heat and pressure, yes, and exothermy doesn't get us there, unfortunately. As example, Zubrin's unit is predicted to output 1 kg/hr, while requiring 700 W electrical, continuous.And his hydrogen comes from a bottle, gratis.
Quote from: wstewart on 11/28/2016 11:54 amQuote from: Robotbeat on 11/28/2016 04:05 amSabatier waste heat (which is optimally 300-400C)Sabatier reaction is exothermic, but it can't run at a scale to heat Hew Thermopylae in winter because the energy input required to maintain the reaction is far too high, as I think you know. It's more efficient to heat electrically, from PV, and skip intermediary processes. But in winter the PV for tunnel heating just isn't there.As you stated the Sabatier reaction is exothermic. It does not need any energy input to run except the initial energy to get it to operating temperature.Needeed is hydrogen from water electrolysis, this indeed needs a lot of energy. You can produce the hydrogen during the day and keep the Sabatier reaction going all night.
Quote from: LMT on 11/28/2016 05:22 pm...you can sum the energy inputs and outputs in a Sabatier/electrolysis system, and just see [net heat recovered for Hew Thermopylae]. Youre not getting it. You need to make the methane anyway and you get waste heat as a byproduct
...you can sum the energy inputs and outputs in a Sabatier/electrolysis system, and just see [net heat recovered for Hew Thermopylae].
Quote from: Robotbeat on 11/28/2016 06:04 pmQuote from: wstewart on 11/28/2016 05:22 pm...you can sum the energy inputs and outputs in a Sabatier/electrolysis system, and just see [net heat recovered for Hew Thermopylae]. Youre not getting it. You need to make the methane anyway and you get waste heat as a byproductJust try to sum the energies into and out of the Sabatier/electrolysis system (including heat lost and recovered), and then I think you'll ballpark the fraction of tunnel heat you get from Sabatier PV, relative to what direct PV heating can give. Which itself isn't enough, but still.
Quote from: wstewart on 11/28/2016 05:22 pm...you can sum the energy inputs and outputs in a Sabatier/electrolysis system, and just see [net heat recovered for Hew Thermopylae]. Youre not getting it. You need to make the methane anyway and you get waste heat as a byproduct
We've been off-topic for a while. We have a thread for power source discussions.http://forum.nasaspaceflight.com/index.php?topic=34836.420
Quote from: sghill on 11/28/2016 08:11 pmWe've been off-topic for a while. We have a thread for power source discussions.http://forum.nasaspaceflight.com/index.php?topic=34836.420Sabatier isn't a power source. it produces waste heat
Isn't 15 kW x 3600s x 6 hrs = 324 million joules? so 2000 tonnes rather than 40 000 tonnes?
If you had sun tracking solar panels, you could probably do better than these numbers; less mass or more energy.
... the lower grade losses can be used to heat the base...
Quote from: Robotbeat on 11/28/2016 08:32 pmQuote from: sghill on 11/28/2016 08:11 pmWe've been off-topic for a while. We have a thread for power source discussions.http://forum.nasaspaceflight.com/index.php?topic=34836.420Sabatier isn't a power source. it produces waste heatWaste heat is still usable. If it can be redirected as actual heat for the colony, that is. What seems to escape many peoples' notice, Mars is VERY, very cold. Every bit of heat that can be scavenged, from whatever source available, should be scavenged. Obviously, some heat sources are so low in thermal production, or too far or mobile, to be of use, but all fixed sources, putting out significant amounts of waste heat, should be utilized, if at all possible or practical.
Enough about heat and power production. Don't do an offtopic post and link to another thread, just post in the other thread.Thanks.
In reference to the last one, Musk mentioned that the tunnels would be used for industrial equipment. Even though this thread has had a lot of speculation about living in tunnels, it seems like Musk is implying people would live in the glass dome with tunnels for industry.
QuoteIn reference to the last one, Musk mentioned that the tunnels would be used for industrial equipment. Even though this thread has had a lot of speculation about living in tunnels, it seems like Musk is implying people would live in the glass dome with tunnels for industry.I have experienced first hand how just a spring melt can cause an otherwise relatively safe mine to become active and worthy of concern. Even several hundred feet below a mountain, water finds it way into the mine and can cause minor to major cave ins. Granted water will not be the issue on mars, but changes caused by heat may well be. If your plan is to constantly pump heat into tunnels, I hope you aren't planning on making those places habitats.
Don't want to live in holes? Here is Megatower!1 km high. Self supporting through air pressure, megatower has an external pykrete skeleton made up of 3 free standing columns than serves as backup if the internal pressure is lost. Internal arrangement is independent from the outer shell.Megatower is protected from radiation by a minimagnetosphere that cover about 10 km2. The little white smudge besides the tower is an ITS spaceship. The slightly larger shape is a pickle type tower.Each core is 60m in diameter and weighs 25000 tonnes. It is supported by the air pressure exerted on the dome at the top of the tower. The windows are light polycarbonate, the structure composite.The pykrete columns are water and sand, reinforced with basalt fiber rods. Wind loading is negligeable despite the structure's size. As they are exterior to the habitat, they do not melt.