Lateral Thinking: Heat Exchange

[Joe Blake]

Having just suffered a fairly intense "hot spell" it occurred to me that one of the "blind spots" designers seem to suffer from is the idea that an engine can only work by generating heat, usually by burning fuel. But really, what seems to be important is the temperature differential.

In places with a high ambient temperature (such as Perth, particularly in summer) why not take the reverse? Use the ambient energy (solar, photo etc) to REMOVE heat from a storage medium (eg a tank of water) at a "home base", then when the engine is required to perform work, the ice (how cool could it go I wonder? My little 12 volt Engel car freezer can take it down to -20 deg Centigrade) is loaded into the "fuel cell", and away you go.

How would it work? Two ways spring to mind. The Peltier/Seeberg effect, thermocouple generation of electricity, or even the Stirling heat engine, except instead of injecting heated air into the cylinder, an injection of super-cooled air, and draw ambient heat into the cylinder (perhaps by use of radiant fins or heat transferring liquid circulation). This heat then causes the air in the cylinder to heat up, which moves the piston/turbine.

A couple of possible advantages. There would be nothing pressurised, since it would only be storage of (negative) heat and not fuel as such (as in hydrogen), so there would no need to have strong containment cells. Any exhaust would only be cool air (or cooler than ambient).

Would it work? Probably not sufficiently to be useful, but it's a starting point. I've used a vaguely similar effect in "gar-bag ballooning". Get a black plastic garbage bag, a bucket of ice with a small fan and some fishing line. Find a cool, shady spot, partially inflate the garbage bag with cooled air, using the fan etc. Tie up the neck of the bag tightly, put the fishing line around the neck, and move the bag into the sun. The black plastic absorbs the heat, which then causes the cooled air to expand, further inflating the gar-bag. Since the function of a "hot-air" balloon is actually the relative density of the internal air compared to the ambient air and not properly speaking a function of absolute temperature (eg if the external air was 50 degrees C and the internal air is 65 deg, it is harder to obtain flotation than if the ambient air was 10 deg and the internal air was 50 degrees) pre-cooling the air before sealing the bag increases the efficiency of lift. So if the air is pumped in at say 4 degrees C, and the ambient temperature is 35 degrees, then the internal air is going to quickly reach ambient temperature, and achieve floatation.

Okay, it struggles to pick up more than few grams of mass, but it's flight on sunshine (especially if the ice water comes from a solar powered freezer).

Anyway, a lateral thought for the brain pond.

Joe

[Mark Parsons]

About 6 months ago I stumbled across a company website about a developer of a free piston Stirling engine that worked bi-directional i.e. insert electricity get cooling at 70% efficiency, or with temperature differential get electricity at 70% efficiency. Can't find it now with a quick search. However, the idea seems to have been picked up by a Japanese company.

http://fpsc.twinbird.jp/en/home_e.html

Further googling will likely re-find the bi-directional product. A large market exists for this efficient technology to replace many applications of the traditional heat pump.

The main maintenance requirement of the technology was periodic recharging of the helium gas. I wonder if Twinbird has resolved this issue?

Mark

[Joe Blake]

I wonder whether the "swing motor" used in my 12 v freezer could be scaled up to be used in a transportation setting?

http://www.i-m-d.com/engel/Tech.htm

It seems remarkably simple, having only one moving part.

Joe

[Mark Parsons]

Hi Joe,

When you first posted that swing motor link it reminded me very much of a free piston stirling motor.

Your freezer swing motor seems designed best doing a compression or pumping job. Drive a vehicle with compressed air?

Certainly some of your Aussie compatriots are working very hard on promoting compressed air engines for vehicle transport.

http://www.engineair.com.au/airmotor.htm

How efficient do you think the swing motor really is? I didn't see any efficiency specs on your link.

Mark

[Joe Blake]

Taking the Stirling engine thought a bit further, I wonder whether it would be possible to have two separate "heat banks", one containing "ice" and the other containing "steam"? The injection of cold air into the cylinder would be followed by an injection of heat (not the steam itself, just heat) to cause the cold air to expand. Then have the same set up as in a compound condensing steam engine where the steam, having been used initially to drive the piston/turbine, is then sent to a second set of pistons/turbine that operate at lower pressure, to scavenge the energy not consumed in the primary set.

The exhaust air from the primary cylinder of the Stirling engine would, hopefully, be at a different temperature to the ambient air. Perhaps a set of sensors would determine the further actions. If the exhaust from the primary Stirling cylinder is at a higher temperature than ambient air, then ambient air is injected into the secondary piston/turbine, to be warmed by the exhaust. If the exhaust is COOLER than the ambient, then the reverse would occur.

I must see if I can find a small Stirling engine I can play with.

Joe

[Ralph Day]

I look forward to Mark's pictures of his prototype based on Joe's description in what, 3 months? ;) Imagine if you two guys lived on the same continent or even closer to each other? Think of the things you could build!!

ralph

[Mark Parsons]

Ralph,

Are you making fun of Joe and I?:p

I'm thinking that Joe lives a little further out of the box than I do....:D

Mark

[Joe Blake]

Sometimes living outside the box is a very good place to live.

After all, isn't a coffin a type of box?

;)

I'm not ready to live in a box just yet.

Joe

[Joe Blake]

A couple of "fun" things.

A Stirling engine coffee cooler. If your coffee's too hot, just put this wee beastie on top and the fan starts up, cooling the coffee. As the coffee cools, the engine slows.

http://jlnlabs.ifrance.com/jlnlabs/html/stirling.htm

The Stirling Engine Sunflower.

http://www.energyinnovations.com/sunflower.html

The whole idea of a "sunflower" layout I find intriguing. Either for generating heat to run a Stirling or light to generate a PV cell array.

Why? Well, it seems too good an idea not to use, a sunflower reflector made up of recycled CDs/DVDs, stuck onto pieces of PVC pipe.

MUST think of that one a bit more.

Side thought: One of the "down" sides of intensifying light on PV arrays is heat. Too much sunlight could melt the panels.

Solution? Shine the light through a pane of glass. Will that trap the infra red? Or would you need TWO panes of glass, like a double glazed window, but open top and bottom to allow air to circulate and remove heat?

Damn it all. On one of the few days I have an idea I can test, and I've now got the tool(s) (ie a non-contact infra-red thermometer, a whole bunch of old CDs and plenty of PVC pipe and self-tapping screws.) the sun isn't shining. We've got rain forecast for today and tomorrow.

Anyway, I'll put that idea on the back burner for today and let it simmer away.

Joe

[Joe Blake]

"Google" is your friend.

http://www.physics.sfasu.edu/astro/courses/egr112/StirlingEngine/stirling.html

Almost exactly what I had in mind, except the heat is being supplied by the small candle. I suppose it would work by circulating hot water, maybe not as efficiently perhaps ...

Even mentions using ice to cool the incoming air.

Love the video. Looks just like something I'd build.

Fascinating.

Joe

[Peter Mckinlay]

Having just suffered a fairly intense "hot spell" it occurred to me that one of the "blind spots" designers seem to suffer from is the idea that an engine can only work by generating heat, usually by burning fuel. But really, what seems to be important is the temperature differential.

In places with a high ambient temperature (such as Perth, particularly in summer) why not take the reverse? Use the ambient energy (solar, photo etc) to REMOVE heat from a storage medium (eg a tank of water) at a "home base", then when the engine is required to perform work, the ice (how cool could it go I wonder? My little 12 volt Engel car freezer can take it down to -20 deg Centigrade) is loaded into the "fuel cell", and away you go.

How would it work? Two ways spring to mind. The Peltier/Seeberg effect, thermocouple generation of electricity, or even the Stirling heat engine, except instead of injecting heated air into the cylinder, an injection of super-cooled air, and draw ambient heat into the cylinder (perhaps by use of radiant fins or heat transferring liquid circulation). This heat then causes the air in the cylinder to heat up, which moves the piston/turbine.

A couple of possible advantages. There would be nothing pressurised, since it would only be storage of (negative) heat and not fuel as such (as in hydrogen), so there would no need to have strong containment cells. Any exhaust would only be cool air (or cooler than ambient).

Would it work? Probably not sufficiently to be useful, but it's a starting point. I've used a vaguely similar effect in "gar-bag ballooning". Get a black plastic garbage bag, a bucket of ice with a small fan and some fishing line. Find a cool, shady spot, partially inflate the garbage bag with cooled air, using the fan etc. Tie up the neck of the bag tightly, put the fishing line around the neck, and move the bag into the sun. The black plastic absorbs the heat, which then causes the cooled air to expand, further inflating the gar-bag. Since the function of a "hot-air" balloon is actually the relative density of the internal air compared to the ambient air and not properly speaking a function of absolute temperature (eg if the external air was 50 degrees C and the internal air is 65 deg, it is harder to obtain flotation than if the ambient air was 10 deg and the internal air was 50 degrees) pre-cooling the air before sealing the bag increases the efficiency of lift. So if the air is pumped in at say 4 degrees C, and the ambient temperature is 35 degrees, then the internal air is going to quickly reach ambient temperature, and achieve floatation.

Okay, it struggles to pick up more than few grams of mass, but it's flight on sunshine (especially if the ice water comes from a solar powered freezer).

Anyway, a lateral thought for the brain pond.

Joe

Hello Joe,

Your idea is on track. Similar has been done. Attached

[Peter Mckinlay]

Having just suffered a fairly intense "hot spell" it occurred to me that one of the "blind spots" designers seem to suffer from is the idea that an engine can only work by generating heat, usually by burning fuel. But really, what seems to be important is the temperature differential.

In places with a high ambient temperature (such as Perth, particularly in summer) why not take the reverse? Use the ambient energy (solar, photo etc) to REMOVE heat from a storage medium (eg a tank of water) at a "home base", then when the engine is required to perform work, the ice (how cool could it go I wonder? My little 12 volt Engel car freezer can take it down to -20 deg Centigrade) is loaded into the "fuel cell", and away you go.

How would it work? Two ways spring to mind. The Peltier/Seeberg effect, thermocouple generation of electricity, or even the Stirling heat engine, except instead of injecting heated air into the cylinder, an injection of super-cooled air, and draw ambient heat into the cylinder (perhaps by use of radiant fins or heat transferring liquid circulation). This heat then causes the air in the cylinder to heat up, which moves the piston/turbine.

A couple of possible advantages. There would be nothing pressurised, since it would only be storage of (negative) heat and not fuel as such (as in hydrogen), so there would no need to have strong containment cells. Any exhaust would only be cool air (or cooler than ambient).

Would it work? Probably not sufficiently to be useful, but it's a starting point. I've used a vaguely similar effect in "gar-bag ballooning". Get a black plastic garbage bag, a bucket of ice with a small fan and some fishing line. Find a cool, shady spot, partially inflate the garbage bag with cooled air, using the fan etc. Tie up the neck of the bag tightly, put the fishing line around the neck, and move the bag into the sun. The black plastic absorbs the heat, which then causes the cooled air to expand, further inflating the gar-bag. Since the function of a "hot-air" balloon is actually the relative density of the internal air compared to the ambient air and not properly speaking a function of absolute temperature (eg if the external air was 50 degrees C and the internal air is 65 deg, it is harder to obtain flotation than if the ambient air was 10 deg and the internal air was 50 degrees) pre-cooling the air before sealing the bag increases the efficiency of lift. So if the air is pumped in at say 4 degrees C, and the ambient temperature is 35 degrees, then the internal air is going to quickly reach ambient temperature, and achieve floatation.

Okay, it struggles to pick up more than few grams of mass, but it's flight on sunshine (especially if the ice water comes from a solar powered freezer).

Anyway, a lateral thought for the brain pond.

Joe

hello Joe, Peter from Qld.

Ambient heat above -40*C will set a CO2 turbine in motion. The workings follow fridge physics. Hot high pressure CO2 drives a turbine which takes away the CO2 energy causing it to phase change into cold liquid. Which may be gravity fed back into the heat cell or pumped there by the turbine shaft acting as screw pump.