Oil in vacuum tubes

[Mart Hale]

The big problem I have seen with oil that is heated is keeping it hot.... I have considered using zeolite instead which store the heat in water chemically, to extract the heat you just add water ->

 

[Hedges]

It wasn't the wheel they reinvented. It was the availability of inexpensive rubber and the additional speed from the technology of the automobile that made the steel rimmed wheels obsolete.

And so now we can drive easily to our favorite fishing stream.
Unfortunately, there weren't any salmon there.

University Research Links Salmon Death to Tire Dust Chemical

Salmon are as important to West Coast ecosystems as they are delicious. So what do tires have to do with it? A tire dust constituent called 6PPD is key.

www.motortrend.com

 

[bengelha]

Yes, but most of those are not exactly practical at this time. You could use paraffin, but you have the disadvantage that it has a low thermal conductivity so getting energy into it is harder. For other reasons, molten salt would be excellent - but again, not exactly practical on the scale we're talking her

Is there any reason why you could NOT use molten salts in a solar vacuum tube?

 

[Hedges]

Is there any reason why you could NOT use molten salts in a solar vacuum tube?

Yes, if you mean common salts like NaCl

Evacuated tubes stagnate around 250 to 350 degrees F.
NaCl melts at 1470 degrees F.

You need a salt (or other crystalline material) with melting point above the temperature you can produce.
There are some exotic ($$$) materials that melt at lower temperatures in the right range.

With concentrators you could melt materials of high temperature. They will require active tracking to keep the sun focused.
Also need materials that can contain the melted substance. Likely melted salt will be quite corrosive.

 

[bengelha]

Yes, if you mean common salts like NaCl

Evacuated tubes stagnate around 250 to 350 degrees F.
NaCl melts at 1470 degrees F.

You need a salt (or other crystalline material) with melting point above the temperature you can produce.
There are some exotic ($$$) materials that melt at lower temperatures in the right range.

With concentrators you could melt materials of high temperature. They will require active tracking to keep the sun focused.
Also need materials that can contain the melted substance. Likely melted salt will be quite corrosive.

I was thinking 60% sodium nitrate and 40% potassium nitrate with a melting temperature nearer to 300 C. Also, as you suggest, it will need concentrated solar.

I think the key question is the maximum temperature of the selective surface in the vacuum tube. Do you know what the over the counter max temps are? I've seen 300/350C, which is maybe the binding constraint.

 

[Hedges]

May I suggest you don't also order fuel oil?
You might hear a knock on the door ...

My knowledge of chemistry is limited to blowing up the junior high school chem lab, and managing to get a passing grade in JC Chem 1A.
I've absorbed some published literature on solar-thermal and evacuated tube collectors, don't know the particular temperature limits except I saw a stagnation temperature for the heat pipe.
As for materials, got to watch the TCE because higher temperatures would cause more expansion and stress on glass. Mostly I saw double-wall glass thermos tubes. Alternate construction could have an inner metal tube and an accordion fold metal seal for more compliance. might need a radiating surface (heat sink) to limit what temperature ends of the glass reaches.

You could probably fabricate a horizontal trough reflector, glass tube, inner metal tube, some thermally insulating seal (like silicone or teflon gasket between two discs.) A vacuum pump could restore vacuum as air leaks in.

By the way, amorphous glass block UV but quartz passes it, so you might want quartz to capture that end of the spectrum.

 

[WillyP]

I was thinking 60% sodium nitrate and 40% potassium nitrate with a melting temperature nearer to 300 C. Also, as you suggest, it will need concentrated solar.

I think the key question is the maximum temperature of the selective surface in the vacuum tube. Do you know what the over the counter max temps are? I've seen 300/350C, which is maybe the binding constraint.

everything I have read say 185°F

 

[renewablejohn]

Yes it can quite easily be done using themal oil. I would not recommend unless you are used to dealing with liquids at high temperatures in excess of 200C. Commercial systems using thermal oil are well developed with the bakery industry using thermal oil ovens. For storage of hot thermal oil insulated shipping containers used in the Asphalt industry are widely available. From a domestic point of view hot thermal oil at 200C and water in excess of 100C do not mix it is a recipe for a steam bomb and I would not recommend. Again commercially thermal oil steam evaporators are available to do the heat exchange safely but the systems are not cheap.

 

[acdoctor]

This is the biggest problem. There are so many variables, it is almost impossible to simply plug in a mathematical formula and just calculate the needs. One of the biggest unknowns is; what is the normal discharge temperature of the water in a slab with pex pipes. Of course computing that requires knowing all sorts of other unknowns, like the slab temperature, the length of the pipes,

Depending upon the floor coverings 80 to 85 degF entering the slab. Most use a mixing valve at the zone manifold. Or course wood is the most sensitive.

 

[Zil]

We last heard from WillyP near the end of May 2021.
Wondering how they did with solar heat storage.

 

[renewablejohn]

We last heard from WillyP near the end of May 2021.
Wondering how they did with solar heat storage.

Maybe the warning of the construction of a potential bomb came to late.

 

[rin67630]

Oil will be much harder to pump when it gets cold.

Why would you want to pump it when it is cold?
Arent't you supposed to transport heat?

 

[Insolation]

I read all of this, and I wonder, what about a closed loop of heat transfer liquid? (I do realize that some oils have a lower specific heat but much higher boiling and flashpoint). SO--how about just a solar collector and a 375F tank of oil in the basement and a radiator (if necessary) next to the tank? Seems like a single pump would suffice, and once that tank was heated up, it would be an enormous heatsink for a lot of cloudy or dark hours, supplemented by a backup source, if needed. I imagine a large tank of 375F oil in the corner of the basement and a pile of stone would be a great source of warmth up through the house.

 

[upnorthandpersonal]

I read all of this, and I wonder, what about a closed loop of heat transfer liquid? (I do realize that some oils have a lower specific heat but much higher boiling and flashpoint). SO--how about just a solar collector and a 375F tank of oil in the basement and a radiator (if necessary) next to the tank? Seems like a single pump would suffice, and once that tank was heated up, it would be an enormous heatsink for a lot of cloudy or dark hours, supplemented by a backup source, if needed. I imagine a large tank of 375F oil in the corner of the basement and a pile of stone would be a great source of warmth up through the house.

You could build a sand battery, and use a heat exchanger with water to extract the heat.

Thermal energy storage - Wikipedia

en.wikipedia.org

Cheaper and safer than hot oil, no leaking.

 

[Mart Hale]

I suggest you watch this guys videos ->

he has out of the box thinking and the comment section is gold.

 

[Mart Hale]

You could build a sand battery, and use a heat exchanger with water to extract the heat.

Thermal energy storage - Wikipedia

en.wikipedia.org

Cheaper and safer than hot oil, no leaking.

This guy heats it up with a fire outside and brings it inside.

 

[Warpspeed]

Pumped solar thermal systems used to be the big thing a few decades ago, and we all know the problems of boiling and freezing, constant maintenance, leaks and so on.

Technology has come a long way since the old days, heat pumps are now vastly more efficient, and solar panels and batteries have improved as well, and come down in cost.
Water is pretty difficult to beat as a cheap non toxic bulk thermal storage medium.

These days, a solar/air sourced heat pump working into a large water thermal storage, powered from solar panels, might be worth investigating.

 

[WillyP]

Maybe the warning of the construction of a potential bomb came to late.

LOL! I'm still here. Don't be sendin' DHS to the house yet. I did get delayed due to a car crash. I won't be building anything for at least another year. But I am healing and growing stronger.

 

[WillyP]

I read all of this, and I wonder, what about a closed loop of heat transfer liquid? (I do realize that some oils have a lower specific heat but much higher boiling and flashpoint). SO--how about just a solar collector and a 375F tank of oil in the basement and a radiator (if necessary) next to the tank? Seems like a single pump would suffice, and once that tank was heated up, it would be an enormous heatsink for a lot of cloudy or dark hours, supplemented by a backup source, if needed. I imagine a large tank of 375F oil in the corner of the basement and a pile of stone would be a great source of warmth up through the house.

that would work. But I am designing a system tht will actually heat the house all winter. I'm not looking to supplement a different system.

As to heat transfer fluid, it is formulated to cool quickly. Usually it is used in large machines that need to be cooled.

 

[WillyP]

Pumped solar thermal systems used to be the big thing a few decades ago, and we all know the problems of boiling and freezing, constant maintenance, leaks and so on.

Technology has come a long way since the old days, heat pumps are now vastly more efficient, and solar panels and batteries have improved as well, and come down in cost.
Water is pretty difficult to beat as a cheap non toxic bulk thermal storage medium.

These days, a solar/air sourced heat pump working into a large water thermal storage, powered from solar panels, might be worth investigating.

you do make some great points about the cost of PV solar. But I really really want radiant floor heat. I will get my electricity from PV solar. It will run the AC.

 

[WillyP]

As an update. I have been convinced oil is a bad idea. It has many good points, but the bad outweighs the potential.

I will be using water in the vacuum tubes to heat underground storage tanks. The main reason I am doing it that way, is so I will have a constant supply of water heated to a specific temperature (95°F).

As for building this system and more importantly my new home. I had a pretty severe car crash in September of 2021. I will be needing another year (or two) before I can start a project this huge. For now I am living in my house in Dale City VA.

 

[Warpspeed]

I have some practical experience with a fairly large (25,000 gallons) solar powered hydronic heating system that was installed in a school.
Your hope of maintaining a constant water temperature is hopelessly impractical.

Any heat added or removed from the storage will greatly change the water temperature, and its that temperature change that represents the useful energy. The greater the temperature swing, the more energy is stored/released per unit volume.
You quickly reach the point of either of boiling, or the water cools so much its not hot enough to do anything useful with.

Its all very well to say increase the volume of water, we had a tank about twenty five feet high and about fifteen feet in diameter (from memory).
It was HUGE.
But it really needed to be about five times that volume to work the way it was supposed to work.
I was not involved in the original planning, that was before my time, but I was the poor bugger that had to monitor the project and maintain it.
It simply did not work, and was ripped out and replaced with heat pumps a few years later.

I suggest you do all the thermal calculations before you spend a single dollar.

 

[WillyP]

I have some practical experience with a fairly large (25,000 gallons) solar powered hydronic heating system that was installed in a school.
Your hope of maintaining a constant water temperature is hopelessly impractical.

Any heat added or removed from the storage will greatly change the water temperature, and its that temperature change that represents the useful energy. The greater the temperature swing, the more energy is stored/released per unit volume.
You quickly reach the point of either of boiling, or the water cools so much its not hot enough to do anything useful with.

Its all very well to say increase the volume of water, we had a tank about twenty five feet high and about fifteen feet in diameter (from memory).
It was HUGE.
But it really needed to be about five times that volume to work the way it was supposed to work.
I was not involved in the original planning, that was before my time, but I was the poor bugger that had to monitor the project and maintain it.
It simply did not work, and was ripped out and replaced with heat pumps a few years later.

I suggest you do all the thermal calculations before you spend a single dollar.

It sounds like a really poorly designed system. I really don't think keeping water at a certain temperature is all that hard. Especially if I use heat exchangers and a discharge tank. My system is designed to be under ground, inside a greenhouse with an insulated bottom. I could see some over heating as a problem. But not enough to render the system unusable.

 

[Hedges]

Sure, you can keep water at a certain temperature. All you have to do is put in exactly the amount of energy lost.

That is like keeping decoupling capacitors at a specific voltage. Easy enough, but they provide absolutely zero energy storage. Only by cycling in voltage (temperature in the case of water) do you get to store/extract energy. With the exception of phase-change materials, but many of those work over a temperature range. Ice in water is one with a set temperature.

You could use a hot water tank plus tempering valve to deliver constant-temperature water.

 

[WillyP]

Sure, you can keep water at a certain temperature. All you have to do is put in exactly the amount of energy lost.

That is like keeping decoupling capacitors at a specific voltage. Easy enough, but they provide absolutely zero energy storage. Only by cycling in voltage (temperature in the case of water) do you get to store/extract energy. With the exception of phase-change materials, but many of those work over a temperature range. Ice in water is one with a set temperature.

You could use a hot water tank plus tempering valve to deliver constant-temperature water.

The tempering valves are usually used in gas fired systems. Or at least that is how I understand it. In a closed system, the water doesn't cool when some of it is removed. The only way that would happen is, if the cold water was returned to the storage tank. I plan to have a discharge tank that will store the cold water, then heat it before returning it to storage. Of course the storage could cool if it wasn't kept at a constant temperature. But being buried in an insulated vault should keep it warm.