Exhaust Heat Recovery - Steam Power

[jdgFirefly]

Originally Posted by Dr. Jerryrigger

I don't know how much power you can get off of one of these, but it looks like it might have enough torque if the RPM's were reduced with a gear or pulley. I think this one would melt with steam, but the basic design, and even sizing of this looks like it might work out well.
instructables Tesla-Turbine

I just did some reading about the Tesla turbine. I heard of it before but never looked into what made it different. Vary interesting and elegantly simple. Daox If your set on building a turbine you should definitely check it out. It has no vanes or blades, so the points I made earlier wouldn't have much affect.

The Tesla turbine (in case you don't already know) is only made up of smooth closely spaced discs. Basically the surface area of the discs and fluid friction is what drives the turbine as the high speed fluid flows through the discs to the center where it is exhasuted. Its hard to say what the actual eff of this turbine is, I heard it is only about 40% but Tesla claimed 95%. He tended to exaggerate a lot but it sound like he used a variable nozzle to achieve the high eff so maybe its possible.

This turbine will have to go on the list of things to build when I'm retired with a large workshop.

[Piwoslaw]

From Wikipedia:

Tesla's design sidestepped the key drawbacks of the bladed turbine. It does suffer from other problems such as shear losses and flow restrictions. Some of Tesla turbine's advantages lie in relatively low flow rate applications or when small applications are called for. The disks need to be as thin as possible at the edges so as not to introduce turbulence as the fluid leaves the disks. This translates to needing to grow the number of disks as the flow rate increases. Maximum efficiency comes in this system when the inter-disk spacing approximates the thickness of the boundary layer, and since boundary layer thickness is dependent on viscosity and pressure, the claim that a single design can be used efficiently for a variety of fuels and fluids is incorrect. A Tesla turbine differs from a conventional turbine only in the mechanism used to transfer energy to the shaft. Various analyses show that the flow rate between the disks must be kept relatively low to maintain efficiency. Reportedly, the efficiency of the Tesla turbine goes down with increased load. Under light load, the spiral taken by the fluid moving from the intake to the exhaust is a tight spiral, undergoing many rotations. Under load, the number of rotations drops and the spiral becomes progressively shorter. This increases the shear losses and reduces the efficiency.

Efficiency is a function of power output. A light load makes for high efficiency and a heavy load, which increases the slip in the turbine, lowers the efficiency. This is not exclusive to Tesla turbines.

The turbine efficiency of the gas Tesla turbine is estimated to be above 60, reaching a maximum of 95 percent. Keep in mind that turbine efficiency is different from the cycle efficiency of the engine using the turbine.
[...]
In the 1950s, Warren Rice attempted to re-create Tesla's experiments, but he did not perform these early tests on a pump built strictly in line with the Tesla's patented design (it, among other things, was not a Tesla multiple staged turbine nor did it possess Tesla's nozzle). Rice's experimental single stage system used air as the working fluid. Rice's test turbines, as published in early reports, produced an overall measured efficiency of 36% to 41% for a single stage. Higher percentages would be expected if designed as originally proposed by Tesla.
[...]
Actual modern multiple stage bladed turbines typically reach 60% - 70% efficiency. Actual volute-rotor matched Tesla-type machines of reasonable size with common fluids (steam, gas, and water) would also be expected to be around this range (if not higher).

[user removed]

Animated Engines, CO2 motor

Here is an interesting and simple design. Like the air motor in the Air Hog planes.

Any reciprocting engine is going to give you significant losses due to the laws of inertia.

regards
Mech

[user removed]

I remember a long time ago reading about a VW that was converted to steam power using freon (long before R12 was found to be bad for the ozone layer).

Your main issues.

Insulation to maximize heat retention.

What fluid to use that would provide enough lubrication to ensure longevity.

To be "self starting" you must have 3 cylinders or some means of initiating rotation of the engine.

Using a flywheel to store energy and pulsing the flywheel, then engaging the field on the alternator will probably be necessary, kind of like a pulse and glide strategy that would give you usable power.

An enlarged pipe section immediately behind the catalyst, with a spiral wound stainless steel tubing coil, will be the best source of heat (my opinion).

I once measured the temp of the header on an idling Nissan Z engine and the thermometer only read 175 degrees, so you might consider a fluid with a lower boiling point than water.

Not trying to be negative about your quest.

I think DYI may not be practical, but the wasted energy (67% on average according to DOE figures), certainly is an enticement to trying to find a solution, and it will require great perseverance (like getting a Patent) to succeed.

I still think my previously linked functional prototype is probably the best solution to actually get something working, but building a from scratch working system would be very cost prohibitive.

The Stanley Steamers used a tube boiler because it made boiler explosions a non event.

regards
Mech

[Dr. Jerryrigger]

Low temps on the outside of exhaust pipes is no reason for concern. I know the gas coming out of the block is hotter, and I still have a few square feet for Fiberfrax blanket laying around. Though I don't have enough to rap header to tail pipe, it isn't that hard to come by if you know what your looking for.

[jdgFirefly]

Originally Posted by Old Mechanic

Animated Engines, CO2 motor

Here is an interesting and simple design. Like the air motor in the Air Hog planes.

Any reciprocting engine is going to give you significant losses due to the laws of inertia.

regards
Mech

I think this CO2 motor link was posted earlier in this thread. On a positive note it is simple and would be easy to make, but it wouldn't be vary eff. The steam isn't allowed to fully expand, and the remaining pressure is wasted. After the exhaust port is covered the piston wastes energy and a useless compression stroke.

I wouldn't say that a reciprocating motor has significant losses due to the laws of inertia. The energy of accelerating/decelerating the pistons isn't lost it is simply transferred to other cylinders and into the flywheel for example decelerating piston 1 helps accelerate piston 2. The energy is all transferred mechanical through solid parts so the losses are almost nothing. The only losses would be form increased friction on bearing surfaces due to the forces of acceleration (basically only the con rod bearing) and from the vary small amount of flex and dampening in the solid parts.

[jdgFirefly]

Daox your air drill experiment looked like a success why give up on that Idea?

Also the information you linked about hooking up alternators made it sound like you need to add a resister to the field windings to adjust the load and amp output. However it didn't look like you did that in the video. Or is that what the voltage regulator already does?

[Daox]

It was my understanding that once the regulator has taken over it regulates the field control, so a resistor isn't needed.

The drill barely hit 14V which is sufficient, but I think as soon as I load up the battery (and thus the alternator), I'd need more pressure to keep the voltage/rpm high enough. I have no idea what the drill is rated at unfortunately. Perhaps a more heavy duty drill would be able to handle it, but I kinda doubt it. We need this turbine/pump/whatever to easily handle spinning up the alternator at no load conditions.

[user removed]

Originally Posted by jdgFirefly

I think this CO2 motor link was posted earlier in this thread. On a positive note it is simple and would be easy to make, but it wouldn't be vary eff. The steam isn't allowed to fully expand, and the remaining pressure is wasted. After the exhaust port is covered the piston wastes energy and a useless compression stroke.

I wouldn't say that a reciprocating motor has significant losses due to the laws of inertia. The energy of accelerating/decelerating the pistons isn't lost it is simply transferred to other cylinders and into the flywheel for example decelerating piston 1 helps accelerate piston 2. The energy is all transferred mechanical through solid parts so the losses are almost nothing. The only losses would be form increased friction on bearing surfaces due to the forces of acceleration (basically only the con rod bearing) and from the vary small amount of flex and dampening in the solid parts.

The se-saw logic of eliminating the cost of accelerating and decelerating reciprocating masses, is something I would tend to believe would make Newton laugh out loud.

I don't see a single cylinder engine as having your proposed energy transfer benefit that negates Newtons Law, and I find the logic behind such a rationale flawed. Are you saying that only a multi cylinder engine can benefit from the "energy transfer" you propose. I don't see that benefit present in any comparison of the efficiencies of engines based on their number of cylinders. Also consider 5 cylinder engines. One of the piston and rod assemblies has no second component to transfer it's energy to, which also supports my belief that such a phonemon does not exist.


A se-saw is a form of lever, not a rotating crankshaft with oscillating big rod ends converting the rotational energy of the crankshaft to the reciprocating piston.

Each piston accelerates from TDC to 90 degrees, then decelerates to 180 degrees. 4 strokes per combustion event. A mass forced to accelerate by combustion resists such acceleration becuse it contains mass. The fact that it has to rotate a crankshaft as well as other pistons, does not make it more efficient than it would be if there were no other pistons.

By that logic I must respectfully disagree with your post.

I do agree with you on the wasted compression on the CO2 motor, but I also think that the compression may not be as costly as you might believe, since it woul also combine with the pressure of the fluid entering the cylinder to create useful work.

A rotary valve could be utilized to eliminate the wasted compression with a timing that eliminated any pressurization on the up stroke of the piston.

regards
Mech

[user removed]

Here is a small pump out of a pancake air compressor. I has a sealed bearing that might hold up to the heat and fluid blowby from the steam, but it also might get hot enough to casue the sealed bearing to fail.

Not sure if it could produce enough power, but it probably could handle significant RPM.

The problem with steam is efficiency, even large turbines are only about 35% efficient, unless you run the exhaust from one turbine into another turbine.

In the Titanic they used triple or quadruple expansion engines as well as turbines. It was one of one kind and two of the other, I don't remember which. Even with the huge masses involved in some of the quadruple expansion engines at the end of the steam era, the piston engines were more efficient than the turbines. That was one of the reasons Britain used oil fired turbines on their capital ships when they built the Dreadnought. The fuel consumption was astronomical with the turbines, and Britain used oil for fuel even though they relied on imported oil to run their fleet of Dreadnought battleships.

The piston multiple expansion engines continued on and even today the tons per mile energy cost of the last of the steam railroad locomotives rivals the diesel engines of today.

regards
Mech