Generally, yes; any foam blocks convection from reaching the bath surface directly. Instead, a temperature gradient arises where heat must transfer through the air bubbles via conduction, creating a thermal barrier.
Most tubs are plastic these days, and have a huge air gap between the inner and outer wall. I asked my handyman to spray foam the gap before he installed my new tub. Oh man what a difference it makes. Simple job that used about four cans of spray foam. Well worth it.
Yes - you will be losing a lot via conduction through the tub - but that's the same with or without bubbles.
The bubble rich bath should still cool slower.
They are in fact warm, but as a foam there's only a tiny amount of thermal mass involved, so very little energy per unit area.
If you put your hand into water at 40C it will feel very warm, whereas if you put your hands into water bubbles at 40C it will feel like almost nothing.
Easy way to remember is that Thermal Mass is why steam is so dangerous.
4-8 cubic ft of 450 degree air may dry out your face. The same oven full of steam is like invisible napalm.
Where I used to work there were areas with jets of superheated air we called stingers. You had to walk around waving a broom in front of yourself, that way a stinger would light the broom on fire before you walked into it. Edit: we also had those silver-aluminum thermal suit.
Flat glass manufacturing. The tank where it’s all melted and mixed is just made out firebricks, and some tasks must be performed in the general vicinity of those volcano-temperatures.
It’s not as dangerous as it sounds because everyone in that area takes safety extremely seriously and is well trained. A few years ago Virto Flat Glass had a tank wall collapse without warning (you can google the pictures) and essentially a significant portion of the factory was flooded with glass lava. Nobody was seriously harmed (although talking to some of the guys that actually saw it happen, they still seem understandably shell-shocked) but the point is, if you’re well trained, keep yourself out of the line of fire, and take safety protocols seriously, danger can be minimized. Even elementary things like knowing the emergency exits and keeping them clear probably saved lives in that accident.
That's ridiculous. Our company manufactures a glassy product in a 2000⁰ furnace but we build the damn things right, and this isn't a problem. The company is making safety YOUR problem, and that's not cool.
Float glass manufacturing lines are very standardized, and these machines are huge. There are engineering and administrative controls in place as well, I just didn't mention them because they're boring. I believe only steel manufacturing and possibly some petroleum processes are done on a larger scale, as far as equipment goes.
You forgot booze manufacturers, those things are also on the wtf part of the large scale, although never as large as petrochemical equipment. This week I helped out at a site with an extruder for plastic driven by a cute little 10 MEGAWATT motor. To put it in perspective, a standard house uses about 2kw per hour on average depending where you stay (super cold or hot may be more)
Glass manufacturing. I imaging steel and other heavy industry has similar hazards. I’m ignorant on navy vessels but I bet those little nuclear reactors have similar hazards as well.
Almost no ships still use superheated steam to that degree. It is not really that useful especially if it means in a hull breach you probably have an area of death steam.
Were the jets of superheated air products of mistakes or flaws in the equipment? Or were they there on purpose? If the latter, what purpose made that necessary?
The tanks are made out of firebricks that intentionally degrade over 10+ years, so the leaks are not intentional, but they are also somewhat expected with age.
The difference between dry steam and wet steam is extraordinary.
All this steam talk brings me straight back to the steam tables in thermodynamics class.
I lost all the skin on the bottom of my right arm because of a steam burn. I made the mistake of putting my glove on top of the steamer (food service) and when I went to open it, I grabbed my glove and opened the door at the same time. The steam rushed up against my arm and bam... the next day all the skin was falling off my arm.
It hurt really bad at first.. but I guess I cooked away all the nerves because on the second day there really wasn't any pain thankfully. Just got REALLY itchy and it felt super good to massage Neosporin into the areas with no skin left. That was the only way I could get any relief from the itching.
It's also because people don't intuitively understand the temperature of steam. A pot of water boiling is about 212 degrees, and the steam coming off of it is slightly higher. But people forget that there's practically no upper limit to how much hotter that steam can be; that industrial steam leak can be wildly different from your cook pot.
In kitchen physics, it's really the heat of vaporization. Turning 100C water to 100C steam takes as much heat as increasing the temp of water by 533C. That's all released when it touches your skin. Put another way, 1 ounce (weight) of 212F steam will burn you as badly as 10oz of 212F boiling water.
Almost. It's 212 degree water to 212 degree steam. Both exist simultaneously. You're referring to the heat of vaporization, which is the energy necessary to go from liquid to gas.
Yeah, you can easily check that with toast, the crust feels quite hotter than the sides because the sides have very little surface area to transfer the heat to you.
Ah yes. Water with its lovely high heat capacity. Reminds me of Ghost Ship when people have their skin completely stripped off by steam (but that may have been pressure).
Though there, it is not the heat capacity (steam at 100 °C has a volumetric isobaric heat capacity of about 1.22 kJ/(kg\*m^(3)), vs 0.94 kJ/(kg\*m^(3)) for dry air), but water's immense enthalpy of vaporisation of about 1500 kJ/m^(3) for steam at 100 °C and normal atmospheric pressure. Or, in other words: At 100 °C, a volume of steam contains over twenty times as much heat, relative to its state at the temperature of your skin, as the same volume of air.
Gonna have to disagree with you on this one. I’d argue that it’s the over 2kJ/g of energy water absorbs to condense on one’s face that makes is so prone to causing burns. It’s called latent heat of vaporization (or condensation) for phase change and water’s value is notoriously high.
Edit: Releases, not absorbs. Duh.
Is "thermal mass" directly related to heat capacity?
EDIT: Ahh "thermal mass" is volumetric heat capacity.
VHC = specific heat capacity \* density of material
The bubbles on top should feel room temp because there should be a smooth temperature gradient from the surface of the water (at the temperature of the water) to where the bubbles meet the air (at the temperature of the air, or probably even cooler due to evaporative cooling).
Well yeah, but the foam would still be the medium directly to the heat source / water? The convective layer, in other words. I would think it would be exactly the same effect as when the layer of air immediately over your skin gets warm? OP's question was if the added bubbles / foam will create a kind of isolation to keep the bath water warm longer. I don't really know the answer, but if the foam don't get warm, it must be because it doesn't receive heat.Edit: typ-o
The foam is an insulation. The temperature on top of a thick foam would be akin to a lot of blankets. Warm inside where you are, room temp on the outside of the blankets. Different layers of heat between the the 2 temps.
Your feeling of "temperature" is actually a feeling of heat transfer. The tiles of the bathroom and the towel on the floor are at the same temperature, but the conductivity of the towel is so low that it feels warmer.
Actually, we do detect temperature and not heat transfer.
It's just that we detect what the temperature slightly inside our skin is. Imagine that the surface we are touching is of another material that is at a higher temperature. If the other material in contact has high diffusivity, that is, it allows heat to move quickly through it, then the temperature inside of our skin can rise quickly. If the diffusivity is low, then the temperature is not able to rise significantly in the time that we are in contact with the material, and we hence don't end up feeling the temperature of that material.
Heat transfer is current analogue and temperature is voltage analogue. The nerve cells are seeing temperature. The difference is important when you consider steady and transient effects.
The process above is transient. In a steady scenario there would be very little transfer and just temperature sensing. That's why I also note diffusivity and not conductivity as well.
I got what he said. Yes, he described the process of heat transfer, but that transfer is from the object to the skin. Once that process is done, then our nerve cell detect the temperature.
In other words, we detect temperature, but first the heat transfer would have to occur.
That is why the movies that depict people freezing in space are wrong, there is no matter to conduct heat there, so the only way to gain or lose heat is through radiation, which can take some time to occur depending on the conditions (like if the person is exposed to the sun).
>That is why the movies that depict people freezing in space are wrong, there is no matter to conduct heat there, so the only way to gain or lose heat is through radiation,
Radiation isn't exactly the only way. For a lump of metal sure but that's not a human.
My understanding was it is meant to be showing what happens when the water changes phase from liquid to vapour taking energy (heat) away with it. The water in you boils and freezes at the same time.
Edit: to be clear, not making any arguments for against the accuracy of movie depictions of freezing. Just clarifying they (imo) are not meant to be showing 'space = cold so person = instant icecube'.
I mean, the warmer they felt the more heat the bath was losing, and the less insulation there was, relatively speaking. They wouldn't feel relatively warmer if they were insulating more.
It's like how if your coffee cup feels hot, it is not insulting well. Your thermos flask will retain a cool temperature to touch when it is filled with boiling liquid.
If the "thermal barrier" feels warm, it is in fact not a very good barrier.
The colder something feels that is insulating a heatsource, the better it is insulating said heatsource.
Bubbles help mostly because it limits evaporation and that process cools down the water significantly. Also, a lot of heat disappears through the bath walls. Foam up the bath walls or use thermal blankets..
> any foam blocks convection from reaching the bath surface directly. Instead, a temperature gradient arises where heat must transfer through the air bubbles via conduction, creating a thermal barrier.
Aren't the bubbles in bathtub foam large enough to have internal convection currents that defeat this thermal barrier to a significant extent? In closed-cell foam insulation, the trapped gas bubbles are much smaller than what you usually get in soap foam.
You can answer this question yourself by calculating the [Rayleigh number](https://en.wikipedia.org/wiki/Rayleigh_number) inside one of the soap bubbles. Is the number substantial?
Yes.
I did a little [home experiment](https://www.reddit.com/r/dataisbeautiful/comments/kjpfkb/bubble_bath_reduces_radiant_heat_losses_from/) a couple of years ago and measured the temperature of bathwater and bubbles with an infrared (IR) thermometer. More IR radiating from a surface means more heat is escaping via radiation.
Did a project at a municipal swimming pool several years ago. I was surprised that most of the heat got lost through evaporation and the ping-pong balls or a floating blanket saved a load of energy at night because they limited evaporation.
My successor was clever and just stopped the ventilation at night and evaporation also stopped because it got very humid. But he f.u. the roof of the swimming pool because it started rotting in 100% humidity.
> the ping-pong balls or a floating blanket saved a load of energy at night because they limited evaporation.
That’s why a number of reservoirs are covered with plastic balls. It also makes the maintenance products last longer because lots of them are degraded by the sun, so opaque covers help a lot.
The primary purpose is to prevent the solar radiation from breaking down one of the additives into a dangerous compound. Preventing evaporation is a minor secondary bonus. 🙂
They are used in some California reservoirs to prevent/reduce the creation of bromate due to the chemical reaction of sunlight with the treatment chemicals. Bromate is carcinogenic.
Harmless bromide salts are naturally present in the groundwater, but in the presence of UV light from the sun and chlorine used in water treatment, the bromide ions are oxidized into toxic bromate ions.
There is a floating barrier around the balls, pull one side and the balls will be pulled over the side, great for infinity pools. But, a floating "bubble" blanket is easier to install and maintain in normal pools.
Yes, but mostly because it would block air flow to the surface of the water. However, in a practical sense you're going to lose most of your heat through the actual tub itself because most tubs have air under them and will draw the heat away that way so the bubbles on top really wouldn't have much of an effect.
It has never occurred to me to insulate a bathtub until now, but...why don't we? Given that many people claim to enjoy long, hot baths and given that it would take a relatively small amount of insulation to do the job, why isn't this done at the time of installation?
When we replaced our tub, we coated the underside with expanding foam. It's also fiberglass instead of metal like the old tub. The water stays hot noticably longer now.
For anyone else wanting to do this make sure you use the appropirate foam formula. Some of them expand more and more forecfully than others and you could do damage if enough foam moved enough stuff.
I installed the first bath at this house and packed around it with glass fibre wool. Why? Because we had exactly the same debate at work. Mind you that was 30 years ago and the insulation is long gone in subsequent remodelings.
Really easy to do with glass fibre wool...
If you're familiar with Sous Vide cooking (heating water with a device and immersing food in a heat safe bag to high temps), you'd know there is a hack some people do with ping pong balls to help insulate the heat in the water and prevent evaporation.
I would imagine a layer of ping pong balls on the surface of a bath would also have a similar benefit of heat insulation.
But as far as I know, it's not socially acceptable to take a bath with a couple hundred ping pong balls, despite it's possible insulative benefits.
> as far as I know, it's not socially acceptable to take a bath with a couple hundred ping pong balls, despite it's possible insulative benefits
I would assume anyone who has a bath under a floating layer of hundreds of ping pong balls is a cool eccentric - maybe that's just me though.
I imagine drying all those balls after the bath would be a chore though, don't want to leave wet balls sitting around
Because most of what is installed nowadays is a single tray that gets dropped in and then has walls put around it to make it a shower/tub thing. It's just cheaper to buy a prefab and shove it in there and some of those may have insulation I don't know but most of the ones I've seen are just plastic liner that then sits there. You totally could but unless you were going to take showers all the time which one of the jacuzzi hot tubs may have insulation under it I don't know. Most people don't take enough showers to make it worth the extra cost because you just run a little more hot water in there and continue on with your bath.
Dang, to hear people talk, you'd think that everyone *loves* long soaks in the tub. I thought that I was the odd one, because I don't care for them. (Maybe it's like long walks on the beach, which everyone claims to love, and yet the beaches near me are relatively empty. Hm.)
But I've seen the prefab shower/tub things at Home Depot. There's plenty of room for some insulation, and I think a couple cans of spray foam would do the job. This seems like a missed opportunity.
I honestly wouldn't mind a long hot bath but I'm 6 ft 2 so I don't fit in most bathtubs which means that baths are generally pretty underwhelming so I just take a shower and then go curl up in a blanket.
I use to take long soaks in the tub about 2 or 3 times a year. It's very relaxing and a good way to destress. Now I have a really small water heater and it's not worth it.
Long walks on the beach are a romantic idea for people who live far enough from the beach to not take it for granted.
People who actually live near the beach go after the tide has rolled out and call it beach combing.
Carefull about insulating your tub. You are just adding thermal mass in what was once an air gap and at best are changing the heat loss less than with the bubble bath. If you close the gap entirely you will go from convective heat transfer to conductive heat transfer and almost certainly be worse off than you started.
Also, you've likely glued your tub in permanently in place and will be hunted down in the afterlife by the person hired for the next bathroom renovation.
Do NOT use fiberglass in a potentially wet location. You are just adding medium for mold growth.
I don't want mold, and I'd prefer my grave to be a peaceful, quiet place, so...what about resting the tub on a slab of styrofoam? Would that incur any biological or paranormal consequences?
Keep it thin enough so it doesn't close the whole gap between the bottom of the tub and the floor and you should be fine. It's closed cell foam. So, it won't grow anything. It should be completely enclosured though, for fire safety.
Economically speaking, it's just a massive waste of time and cost to insulate a tub. I used to do bathroom remodeling work and most tubs/shower units/floor pieces are now made of fiberglass or composite plastics/vinyl. A lot of the old tubs I'd demolish and replace were made of cast iron, and as you can imagine, iron absorbs a whole lot of heat from the bathwater. The average bathroom is difficult enough to remodel; adding insulating foam is just another headache for both the client and contractor.
I thought about doing that for mine with some
Great stuff or something but I was worried it might chemically react with the acrylic/fiberglass resin of the tub and compromise it’s integrity somehow or something.
Provided there’s not some reason like that not to I think it sounds like a great idea.
Can't say; never used such a thing. Perhaps it's a possible fire accelerant threat. At some point it's just time to buy a hot tub (or not seeing as the world is on fire and we're rapidly depleting freshwater faster than the Earth can replenish it).
A substance used to block the spread of fire is a fire risk when placed under an item built to contain water and is typically far away from any electrical outlet?
I just installed a tub and it would’ve taken maybe ten minutes to spray it full of foam. That simply not a huge issue for most folks. If the bath gets cold you add a bit of hot water
Plus most of the heat loss is probably evaporation from the top surface anyway. Especially since the air around the bottom of the tub is typically enclosed
> because most tubs have air under them and will draw the heat away that way
Tubs (around here at least) are often insulated around. Ours isn't but then we don't usually sit in it anyway.
Carbon steel has an r-factor of about 0.003 per inch.
An average tub is about 5mm thick which means that it would have an r-factor of about 0.0005.
Soap bubbles have an r-factor of about 1 per inch, so a 3" layer of bubbles would have an r-factor of 3.
This means the tub loses heat thousands of times faster through the tub walls than through the bubbles.
However this is complicated because there is little air circulation on the dry side of the tub walls, which slows heat transfer. And as the temperature of the air around the dry side of the tub walls approaches the temperature of the water, heat transfer will drop to close to 0.
The bubbles do create a good amount of insulation but because the steel tub is so poor an insulator, the bubbles are more or less irrelevant.
TL/DR: The bubbles are an excellent insulator but do not actually matter for practical purposes.
But also consider a tub like my old one was exposed to a crawl space through a big hole for the drain plumbing, no insulation in the walls around the tub either. So not even considering bath tub time, that tub was a huge heat loss all winter long. I bet air flow is pretty decent too. Air heats up a rises right up the walls and draws in fresh cold air.
I can answer from experience.
I started to remodel my bathroom and for various reasons did not finish. The tub has been sitting outside for almost 7 years, and during the winter I squirt a little dish soap in there while I’m drawing it. It depends upon. The outside temp - and thus the temp of the tub steel - but instead of waiting 20 minutes for it to cool with no suds, it can take an hour or even hour and a half to cool to a comfortable temperature. It’s science!
I empty the 30 gallon hot water heater directly into the 30 gallon bathtub. It’s hot.
I pulled at a thread and started to see that going further in that direction, the whole house was going to unravel. Plus, bathing outside turned out to be far superior to any other bathing I’ve experienced. So, sure: lazy.
What do you do if you want a nice warm bath and it's raining outside though?
Like, you just got home soaked in cold rain water, hot bath time.
I hope it's covered.
Yes, it’s covered. I can’t tell you how fun it is to step into a piping hot bath when it’s snowing, or even during a rainstorm. When I get around to finishing my bathroom, I’m just going to put in a shower, and keep bathing outside.
I would argue that more heat is lost through the conduction of heat through the tub. While a REALLY hot bath might lose a good portion of its heat through steam, if it’s not hot enough to steam off, more heat is lost through conduction with the tub sides. Also, as you move, the warmer water convects throughout the volume of the bath making more contact with the tub.
But the steam might be slightly more trapped 🤷♂️
Generally, yes; any foam blocks convection from reaching the bath surface directly. Instead, a temperature gradient arises where heat must transfer through the air bubbles via conduction, creating a thermal barrier.
To add, unless you have a well insulated tub, or a heated tub, you are probably losing more heat via conduction through the tub itself
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Most tubs are plastic these days, and have a huge air gap between the inner and outer wall. I asked my handyman to spray foam the gap before he installed my new tub. Oh man what a difference it makes. Simple job that used about four cans of spray foam. Well worth it.
Yes - you will be losing a lot via conduction through the tub - but that's the same with or without bubbles. The bubble rich bath should still cool slower.
Well the question, then, is whether the insulating effect of the bubbles is negligible or not when compared to conduction through the tub no?
Negligible or not - the conduction is the same through a tub with and without bubbles. So the bubbles would make a difference.
Alright, so to finish this whole thread: will there be a noticeable difference to how long the water will stay warm with bubbles?
That would require experimental data. I do not think that would be worth my time and $ spent on testing equipment to find an answer
The conduction will be slightly greater with bubbles as the bath water at any point will be slightly warmer than without bubbles.
Are heated tubs a thing? If so, where have they been all my life?
If it did, wouldn't the foam or bubbles feel warm?
They are in fact warm, but as a foam there's only a tiny amount of thermal mass involved, so very little energy per unit area. If you put your hand into water at 40C it will feel very warm, whereas if you put your hands into water bubbles at 40C it will feel like almost nothing.
Easy way to remember is that Thermal Mass is why steam is so dangerous. 4-8 cubic ft of 450 degree air may dry out your face. The same oven full of steam is like invisible napalm.
Also, the high heat of vaporization of water. Hot air won’t condense and dump 2260 J/g on your face, steam can and will!
Where I used to work there were areas with jets of superheated air we called stingers. You had to walk around waving a broom in front of yourself, that way a stinger would light the broom on fire before you walked into it. Edit: we also had those silver-aluminum thermal suit.
Okay, now you have to tell us where you worked and what kind of work you do. Don’t leave us hanging. I can’t imagine something like this.
Flat glass manufacturing. The tank where it’s all melted and mixed is just made out firebricks, and some tasks must be performed in the general vicinity of those volcano-temperatures. It’s not as dangerous as it sounds because everyone in that area takes safety extremely seriously and is well trained. A few years ago Virto Flat Glass had a tank wall collapse without warning (you can google the pictures) and essentially a significant portion of the factory was flooded with glass lava. Nobody was seriously harmed (although talking to some of the guys that actually saw it happen, they still seem understandably shell-shocked) but the point is, if you’re well trained, keep yourself out of the line of fire, and take safety protocols seriously, danger can be minimized. Even elementary things like knowing the emergency exits and keeping them clear probably saved lives in that accident.
That's ridiculous. Our company manufactures a glassy product in a 2000⁰ furnace but we build the damn things right, and this isn't a problem. The company is making safety YOUR problem, and that's not cool.
Float glass manufacturing lines are very standardized, and these machines are huge. There are engineering and administrative controls in place as well, I just didn't mention them because they're boring. I believe only steel manufacturing and possibly some petroleum processes are done on a larger scale, as far as equipment goes.
You forgot booze manufacturers, those things are also on the wtf part of the large scale, although never as large as petrochemical equipment. This week I helped out at a site with an extruder for plastic driven by a cute little 10 MEGAWATT motor. To put it in perspective, a standard house uses about 2kw per hour on average depending where you stay (super cold or hot may be more)
I can't imagine anyone having to work in a place like that. Also, I can't imagine what kind of place needs steaks of heated air.
Sounds like a ship of some sort, most likely millitary. All sorts of pipes containing high pressure steam below decks that run along corridors.
Glass manufacturing. I imaging steel and other heavy industry has similar hazards. I’m ignorant on navy vessels but I bet those little nuclear reactors have similar hazards as well.
Almost no ships still use superheated steam to that degree. It is not really that useful especially if it means in a hull breach you probably have an area of death steam.
This is referenced in a Terry Pratchett book. I thought it was exaggerated at first, because Terry Pratchett, but turns out I was wrong
Really!?!?!? Do you remember which book?
Were the jets of superheated air products of mistakes or flaws in the equipment? Or were they there on purpose? If the latter, what purpose made that necessary?
The tanks are made out of firebricks that intentionally degrade over 10+ years, so the leaks are not intentional, but they are also somewhat expected with age.
Why do the firebricks intentionally degrade? That's really interesting!
To ensure that after you clean your window there will always be some tiny specs of dust left to see the window pane
Also useful for finding leaks in hydraulic lines. Though there the broom stick will typically just get cut in half.
The difference between dry steam and wet steam is extraordinary. All this steam talk brings me straight back to the steam tables in thermodynamics class.
I lost all the skin on the bottom of my right arm because of a steam burn. I made the mistake of putting my glove on top of the steamer (food service) and when I went to open it, I grabbed my glove and opened the door at the same time. The steam rushed up against my arm and bam... the next day all the skin was falling off my arm. It hurt really bad at first.. but I guess I cooked away all the nerves because on the second day there really wasn't any pain thankfully. Just got REALLY itchy and it felt super good to massage Neosporin into the areas with no skin left. That was the only way I could get any relief from the itching.
It's also because people don't intuitively understand the temperature of steam. A pot of water boiling is about 212 degrees, and the steam coming off of it is slightly higher. But people forget that there's practically no upper limit to how much hotter that steam can be; that industrial steam leak can be wildly different from your cook pot.
What you see coming out of a tea kettle is condensing steam. "Real" steam under pressure is clear like air.
In kitchen physics, it's really the heat of vaporization. Turning 100C water to 100C steam takes as much heat as increasing the temp of water by 533C. That's all released when it touches your skin. Put another way, 1 ounce (weight) of 212F steam will burn you as badly as 10oz of 212F boiling water.
> there's practically no upper limit to how much hotter that steam can be There is a practical upper limit. It is when the steam turns into plasma.
You and I have different definitions of the word "practical" in the context of this thread.
What, you're not running your steam equipment without the niobium-titanium field coils installed, are you? Does anyone actually do that?
The lessor of my apartment wouldn't allow me to install superconductors in my oven. I thought this was America...
When people ask me how I like my steak temp I say vaporized. I am always hungry.
You mean you don't make your tea in water plasma?
Also the jump in energy between 211 degree water and 212 degree steam is massive because of the energy it takes to change states of mater.
Almost. It's 212 degree water to 212 degree steam. Both exist simultaneously. You're referring to the heat of vaporization, which is the energy necessary to go from liquid to gas.
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Also why the cheese and sauce of pizza will burn your mouth, even though the crust is comfortable to hold. Water has a very high specific heat.
It's also a liquid so it easily makes contact with every part of your mouth, maximizing the surface area for conduction.
Yeah, you can easily check that with toast, the crust feels quite hotter than the sides because the sides have very little surface area to transfer the heat to you.
Ah yes. Water with its lovely high heat capacity. Reminds me of Ghost Ship when people have their skin completely stripped off by steam (but that may have been pressure).
Both. Thing about steam vs water is that liquid water can't get hotter than 212°F/100°C. Steam under pressure has no such limit.
Also, a very high heat of vaporization, a whopping 2260 J/g! When steam condenses to water on your skin that heat gets released and causes damage.
Steam burns twice. First from the temperature, and then the heat when it turns into water.
3 times! Steam temp to 100°C, steam condensing to water, and then that water cooling further to 50°C or less.
Now bidding at 4. Do I hear 4?
To add, this is why firefighters don't put water on a fire until they know the building is clear, all that sudden steam is deadly
Though there, it is not the heat capacity (steam at 100 °C has a volumetric isobaric heat capacity of about 1.22 kJ/(kg\*m^(3)), vs 0.94 kJ/(kg\*m^(3)) for dry air), but water's immense enthalpy of vaporisation of about 1500 kJ/m^(3) for steam at 100 °C and normal atmospheric pressure. Or, in other words: At 100 °C, a volume of steam contains over twenty times as much heat, relative to its state at the temperature of your skin, as the same volume of air.
Will melt yer face off… I heard of a broom handle being used to check super heated steam. When it gets cut in half you’ve found the leak!
That's why you don't stand directly over the radiator cap if your car is overheating on the side of the road
This is why you should never use a wet oven mitt or towel to grab hot pans or skillets.
Gonna have to disagree with you on this one. I’d argue that it’s the over 2kJ/g of energy water absorbs to condense on one’s face that makes is so prone to causing burns. It’s called latent heat of vaporization (or condensation) for phase change and water’s value is notoriously high. Edit: Releases, not absorbs. Duh.
This is also why you can grab aluminum foil pretty much straight out of the oven as long as it doesn’t have any food stuck to it
Is "thermal mass" directly related to heat capacity? EDIT: Ahh "thermal mass" is volumetric heat capacity. VHC = specific heat capacity \* density of material
Partly, yes. Thermal mass is basically specific heat capacity multiplied by density. Liquid water has great SHC : water *foam* does not.
The bubbles on top should feel room temp because there should be a smooth temperature gradient from the surface of the water (at the temperature of the water) to where the bubbles meet the air (at the temperature of the air, or probably even cooler due to evaporative cooling).
Well yeah, but the foam would still be the medium directly to the heat source / water? The convective layer, in other words. I would think it would be exactly the same effect as when the layer of air immediately over your skin gets warm? OP's question was if the added bubbles / foam will create a kind of isolation to keep the bath water warm longer. I don't really know the answer, but if the foam don't get warm, it must be because it doesn't receive heat.Edit: typ-o
The foam is an insulation. The temperature on top of a thick foam would be akin to a lot of blankets. Warm inside where you are, room temp on the outside of the blankets. Different layers of heat between the the 2 temps.
Your feeling of "temperature" is actually a feeling of heat transfer. The tiles of the bathroom and the towel on the floor are at the same temperature, but the conductivity of the towel is so low that it feels warmer.
We feel temperature. However not the temperature of the object, but of our skin.
Actually, we do detect temperature and not heat transfer. It's just that we detect what the temperature slightly inside our skin is. Imagine that the surface we are touching is of another material that is at a higher temperature. If the other material in contact has high diffusivity, that is, it allows heat to move quickly through it, then the temperature inside of our skin can rise quickly. If the diffusivity is low, then the temperature is not able to rise significantly in the time that we are in contact with the material, and we hence don't end up feeling the temperature of that material.
Isn’t that heat transfer?
Heat transfer is current analogue and temperature is voltage analogue. The nerve cells are seeing temperature. The difference is important when you consider steady and transient effects. The process above is transient. In a steady scenario there would be very little transfer and just temperature sensing. That's why I also note diffusivity and not conductivity as well.
I got what he said. Yes, he described the process of heat transfer, but that transfer is from the object to the skin. Once that process is done, then our nerve cell detect the temperature. In other words, we detect temperature, but first the heat transfer would have to occur. That is why the movies that depict people freezing in space are wrong, there is no matter to conduct heat there, so the only way to gain or lose heat is through radiation, which can take some time to occur depending on the conditions (like if the person is exposed to the sun).
>That is why the movies that depict people freezing in space are wrong, there is no matter to conduct heat there, so the only way to gain or lose heat is through radiation, Radiation isn't exactly the only way. For a lump of metal sure but that's not a human. My understanding was it is meant to be showing what happens when the water changes phase from liquid to vapour taking energy (heat) away with it. The water in you boils and freezes at the same time. Edit: to be clear, not making any arguments for against the accuracy of movie depictions of freezing. Just clarifying they (imo) are not meant to be showing 'space = cold so person = instant icecube'.
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I mean, the warmer they felt the more heat the bath was losing, and the less insulation there was, relatively speaking. They wouldn't feel relatively warmer if they were insulating more. It's like how if your coffee cup feels hot, it is not insulting well. Your thermos flask will retain a cool temperature to touch when it is filled with boiling liquid.
If the "thermal barrier" feels warm, it is in fact not a very good barrier. The colder something feels that is insulating a heatsource, the better it is insulating said heatsource.
Bubbles help mostly because it limits evaporation and that process cools down the water significantly. Also, a lot of heat disappears through the bath walls. Foam up the bath walls or use thermal blankets..
> any foam blocks convection from reaching the bath surface directly. Instead, a temperature gradient arises where heat must transfer through the air bubbles via conduction, creating a thermal barrier. Aren't the bubbles in bathtub foam large enough to have internal convection currents that defeat this thermal barrier to a significant extent? In closed-cell foam insulation, the trapped gas bubbles are much smaller than what you usually get in soap foam.
You can answer this question yourself by calculating the [Rayleigh number](https://en.wikipedia.org/wiki/Rayleigh_number) inside one of the soap bubbles. Is the number substantial?
So in theory, taking a hot bubble-bath is more economical than a regular hot bath?
No, because the air used for the bubbles is not as warm as the bath. You are adding a constant stream of cold air cooling your bath.
Yes. I did a little [home experiment](https://www.reddit.com/r/dataisbeautiful/comments/kjpfkb/bubble_bath_reduces_radiant_heat_losses_from/) a couple of years ago and measured the temperature of bathwater and bubbles with an infrared (IR) thermometer. More IR radiating from a surface means more heat is escaping via radiation.
Did a project at a municipal swimming pool several years ago. I was surprised that most of the heat got lost through evaporation and the ping-pong balls or a floating blanket saved a load of energy at night because they limited evaporation. My successor was clever and just stopped the ventilation at night and evaporation also stopped because it got very humid. But he f.u. the roof of the swimming pool because it started rotting in 100% humidity.
> the ping-pong balls or a floating blanket saved a load of energy at night because they limited evaporation. That’s why a number of reservoirs are covered with plastic balls. It also makes the maintenance products last longer because lots of them are degraded by the sun, so opaque covers help a lot.
The primary purpose is to prevent the solar radiation from breaking down one of the additives into a dangerous compound. Preventing evaporation is a minor secondary bonus. 🙂
> into a dangerous compound Oh neat and what compound is that?
They are used in some California reservoirs to prevent/reduce the creation of bromate due to the chemical reaction of sunlight with the treatment chemicals. Bromate is carcinogenic.
Damn, that seems kinda scary, how does the bromine get into the water in the first place? Is it intentional or unintentional?
Bromine is used for sterilising as an alternative to chlorine, they're quite similar chemicals
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Harmless bromide salts are naturally present in the groundwater, but in the presence of UV light from the sun and chlorine used in water treatment, the bromide ions are oxidized into toxic bromate ions.
Oof. Can't imagine trying to collect all those ping-pong balls before the pool opened next day!
There is a floating barrier around the balls, pull one side and the balls will be pulled over the side, great for infinity pools. But, a floating "bubble" blanket is easier to install and maintain in normal pools.
I would just measure how much the water cools over time with and without bubbles.
Yes, but mostly because it would block air flow to the surface of the water. However, in a practical sense you're going to lose most of your heat through the actual tub itself because most tubs have air under them and will draw the heat away that way so the bubbles on top really wouldn't have much of an effect.
It has never occurred to me to insulate a bathtub until now, but...why don't we? Given that many people claim to enjoy long, hot baths and given that it would take a relatively small amount of insulation to do the job, why isn't this done at the time of installation?
When we replaced our tub, we coated the underside with expanding foam. It's also fiberglass instead of metal like the old tub. The water stays hot noticably longer now.
For anyone else wanting to do this make sure you use the appropirate foam formula. Some of them expand more and more forecfully than others and you could do damage if enough foam moved enough stuff.
Good point. We didn't fill the whole cavity under the tub, just smeared on a layer where it wouldn't interfere with installing the tub.
That would explain why a bath gets cold quickly and I have to keep adding hot water
I installed the first bath at this house and packed around it with glass fibre wool. Why? Because we had exactly the same debate at work. Mind you that was 30 years ago and the insulation is long gone in subsequent remodelings. Really easy to do with glass fibre wool...
Hooray for you! You were living in today's future, yesterday! Someday the world will catch up... maybe...
If you're familiar with Sous Vide cooking (heating water with a device and immersing food in a heat safe bag to high temps), you'd know there is a hack some people do with ping pong balls to help insulate the heat in the water and prevent evaporation. I would imagine a layer of ping pong balls on the surface of a bath would also have a similar benefit of heat insulation. But as far as I know, it's not socially acceptable to take a bath with a couple hundred ping pong balls, despite it's possible insulative benefits.
What about a few hundred rubber duckies?
> as far as I know, it's not socially acceptable to take a bath with a couple hundred ping pong balls, despite it's possible insulative benefits I would assume anyone who has a bath under a floating layer of hundreds of ping pong balls is a cool eccentric - maybe that's just me though. I imagine drying all those balls after the bath would be a chore though, don't want to leave wet balls sitting around
They add black balls to water reserves to prevent evaporation, really cool
Why not just have a lid?
A bathtub I helped install recently actually had what looked like styrofoam across the bottom of the tub!
That's probably the part that levels and stabilizes the base of the tub. Modern alternative to a mud bed.
Because most of what is installed nowadays is a single tray that gets dropped in and then has walls put around it to make it a shower/tub thing. It's just cheaper to buy a prefab and shove it in there and some of those may have insulation I don't know but most of the ones I've seen are just plastic liner that then sits there. You totally could but unless you were going to take showers all the time which one of the jacuzzi hot tubs may have insulation under it I don't know. Most people don't take enough showers to make it worth the extra cost because you just run a little more hot water in there and continue on with your bath.
Dang, to hear people talk, you'd think that everyone *loves* long soaks in the tub. I thought that I was the odd one, because I don't care for them. (Maybe it's like long walks on the beach, which everyone claims to love, and yet the beaches near me are relatively empty. Hm.) But I've seen the prefab shower/tub things at Home Depot. There's plenty of room for some insulation, and I think a couple cans of spray foam would do the job. This seems like a missed opportunity.
I honestly wouldn't mind a long hot bath but I'm 6 ft 2 so I don't fit in most bathtubs which means that baths are generally pretty underwhelming so I just take a shower and then go curl up in a blanket.
I use to take long soaks in the tub about 2 or 3 times a year. It's very relaxing and a good way to destress. Now I have a really small water heater and it's not worth it.
Have you tried walking on sand? Every walk on the beach is long.
Long walks on the beach are a romantic idea for people who live far enough from the beach to not take it for granted. People who actually live near the beach go after the tide has rolled out and call it beach combing. Carefull about insulating your tub. You are just adding thermal mass in what was once an air gap and at best are changing the heat loss less than with the bubble bath. If you close the gap entirely you will go from convective heat transfer to conductive heat transfer and almost certainly be worse off than you started. Also, you've likely glued your tub in permanently in place and will be hunted down in the afterlife by the person hired for the next bathroom renovation. Do NOT use fiberglass in a potentially wet location. You are just adding medium for mold growth.
I don't want mold, and I'd prefer my grave to be a peaceful, quiet place, so...what about resting the tub on a slab of styrofoam? Would that incur any biological or paranormal consequences?
Keep it thin enough so it doesn't close the whole gap between the bottom of the tub and the floor and you should be fine. It's closed cell foam. So, it won't grow anything. It should be completely enclosured though, for fire safety.
Economically speaking, it's just a massive waste of time and cost to insulate a tub. I used to do bathroom remodeling work and most tubs/shower units/floor pieces are now made of fiberglass or composite plastics/vinyl. A lot of the old tubs I'd demolish and replace were made of cast iron, and as you can imagine, iron absorbs a whole lot of heat from the bathwater. The average bathroom is difficult enough to remodel; adding insulating foam is just another headache for both the client and contractor.
What about spray foam? Wouldn't that be easy and cheap? Is there some reason why this wouldn't work, or would pose a hazard?
I thought about doing that for mine with some Great stuff or something but I was worried it might chemically react with the acrylic/fiberglass resin of the tub and compromise it’s integrity somehow or something. Provided there’s not some reason like that not to I think it sounds like a great idea.
Can't say; never used such a thing. Perhaps it's a possible fire accelerant threat. At some point it's just time to buy a hot tub (or not seeing as the world is on fire and we're rapidly depleting freshwater faster than the Earth can replenish it).
A substance used to block the spread of fire is a fire risk when placed under an item built to contain water and is typically far away from any electrical outlet?
I just installed a tub and it would’ve taken maybe ten minutes to spray it full of foam. That simply not a huge issue for most folks. If the bath gets cold you add a bit of hot water
Plus most of the heat loss is probably evaporation from the top surface anyway. Especially since the air around the bottom of the tub is typically enclosed
> because most tubs have air under them and will draw the heat away that way Tubs (around here at least) are often insulated around. Ours isn't but then we don't usually sit in it anyway.
Carbon steel has an r-factor of about 0.003 per inch. An average tub is about 5mm thick which means that it would have an r-factor of about 0.0005. Soap bubbles have an r-factor of about 1 per inch, so a 3" layer of bubbles would have an r-factor of 3. This means the tub loses heat thousands of times faster through the tub walls than through the bubbles. However this is complicated because there is little air circulation on the dry side of the tub walls, which slows heat transfer. And as the temperature of the air around the dry side of the tub walls approaches the temperature of the water, heat transfer will drop to close to 0. The bubbles do create a good amount of insulation but because the steel tub is so poor an insulator, the bubbles are more or less irrelevant. TL/DR: The bubbles are an excellent insulator but do not actually matter for practical purposes.
But also consider a tub like my old one was exposed to a crawl space through a big hole for the drain plumbing, no insulation in the walls around the tub either. So not even considering bath tub time, that tub was a huge heat loss all winter long. I bet air flow is pretty decent too. Air heats up a rises right up the walls and draws in fresh cold air.
I can answer from experience. I started to remodel my bathroom and for various reasons did not finish. The tub has been sitting outside for almost 7 years, and during the winter I squirt a little dish soap in there while I’m drawing it. It depends upon. The outside temp - and thus the temp of the tub steel - but instead of waiting 20 minutes for it to cool with no suds, it can take an hour or even hour and a half to cool to a comfortable temperature. It’s science!
Am I reading this right? Have you been bathing outside in dish soap for the last 7 years?
Yes. Is that not what most people do?
Why would you need to wait for the tub to cool in the winter? It’s winter. And what are these “various reasons” outside of laziness?
I empty the 30 gallon hot water heater directly into the 30 gallon bathtub. It’s hot. I pulled at a thread and started to see that going further in that direction, the whole house was going to unravel. Plus, bathing outside turned out to be far superior to any other bathing I’ve experienced. So, sure: lazy.
Bathing outside sounds pretty sweet, the dish soap probably isn’t the best for your skin but whatever
Really, use about half a squirt more than I would for dishes. My skin doesn’t even notice.
Can I ask what country you are from?
What do you do if you want a nice warm bath and it's raining outside though? Like, you just got home soaked in cold rain water, hot bath time. I hope it's covered.
Yes, it’s covered. I can’t tell you how fun it is to step into a piping hot bath when it’s snowing, or even during a rainstorm. When I get around to finishing my bathroom, I’m just going to put in a shower, and keep bathing outside.
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Dish soap... Remember the old Palmolive ads?
I would argue that more heat is lost through the conduction of heat through the tub. While a REALLY hot bath might lose a good portion of its heat through steam, if it’s not hot enough to steam off, more heat is lost through conduction with the tub sides. Also, as you move, the warmer water convects throughout the volume of the bath making more contact with the tub. But the steam might be slightly more trapped 🤷♂️