Joe Blake
27th February 2007, 01:41
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
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