Is it possible to produce a tiny fluid stream at 110 C from a large fluid reservoir at 50 C?
Basically I'm wondering if a thermal analogy to the hydraulic ram exists.
"This device allows some of the energy in the stream of water flowing from point A [downwards] to point B to be diverted to pump a smaller amount of water from point B to point C [which is above point A]."
Egads&!^%$!!! That would mean perpetual motion, you'd be in crank country.
Regardless of the chosen technology you'll never achieve 100% efficiency, the system is not completely closed. It always radiates some energy. The simplest example is the water wheel used to lift water for irrigation,
improvement on the shadoof.
You can drive that with a tidal flow as the Earth turns in the gravitational field of the Sun and Moon, but there is always an external energy input.
A Peltier junction performs the inverse function of a thermocouple. Where the thermocouple produces electricity via its hot and cold junctions the Peltier junction produces hot and cold junctions from the passage of electrical current. Hence theoretically the thermocouple could supply the current for the Peltier junction. In practice, of course, energy is radiated and the closed system soon stops when the temperature difference falls to zero and equilibrium is reached.
"There are many versions of the second law, but they all have the same effect, which is to explain the phenomenon of irreversibility in nature."
I just discovered another facet to the problem I'm trying to solve, and it looks like I won't need a low-grade-heat to high-grade-heat converter after all... although, academically, it is intriguing to find a thermal analog to the hydraulic ram, as the electrical engineers have found for DC voltage conversion...
Electronics, mass-spring systems, and fluid systems have the advantage that they all have inertia (or an analog of inertia -- inductance) that allow the equivalent of water hammers to be constructed.
Thermal systems don't have that luxury as there is no equivalent of inertia for heat. This is one of the things that makes designing accurate temperature controllers so difficult; without the equivalent of inductance you can't build second order or higher feedback controls.
Not sure about that assertion - no 3 term thermal controllers? Yes, there are. Even the bimetal room thermostat had a built-in pilot heater for getting a leading phase term.... Tell me what you had in mind?
How about at a phase change? Or a chemical reaction... One can rely on a moving fluid to carry heat... and acoustic cooling shows that it can deliver heat across an unfavorable gradient. But these are "sweet spots"...
I've not had too many problems implementing them, so you must be doing a good job!
Then you're relying on a mechanical system to provide the inertia thanks to its bulk motion.
If you consider the components of a "thermal circuit" you have thermal capacity (specific heat), thermal resistance (or conductance), and sources (either heat "current" or temperature). These are analogs of the electrical components of capacitance, resistance, and current or voltage sources.
Heat flow depends only upon the temperature difference and the thermal resistance between two points. If you "turn off" the temperature difference, the flow stops immediately -- no inertia.
Without the equivalent of inductance for thermal circuits, there isn't the equivalent of critical damping, harmonic motion or 'poles' for transfer functions.
To achieve fine thermal regulation you can use a knowledege of the thermal components involved (like the known heat capacity and heat source characteristics) to 'sneak up' on the desired steady state conditions, like tapering off the heat source when you are getting close, anticipating cooling rates, etc..
But you can't form a critically damped closed loop from bare-bones thermal components alone.
Minor quibble. If you are heating a space with an electric heater, you turn the power off, you still get some residual heating for a bit. The fact that "accountants" have removed all excess mass from such components, does not prevent you adding them back in at need...
We design the "inertia" out by reducing the system to fundamentals...
Ah, but the residual heating is only due to the thermal capacity of the heating element and the thermal resistance between it and the room allowing a temperature difference to exist. You wouldn't expect, for example, the unpowered heating element to continue sending heat into the room after it had reached the same temperature as the room, and subsequently get colder than the room (then oscillate around the equilibrium).
To get such an inertial effect you have to (as you say) introduce some mechanical component as a heat conveyor, and then rely on mechanical inertia.
However, this still won't let you get the effect of a hydraulic ram by purely thermal means, whereby the temperature could be driven higher than that of the heat source. For that you must also introduce other mechanical factors, like compression (gas law).
Hmmm.. temperature controllers can certainly oscillate at a step change in delta between sensed and demanded values. This undesired behavior can be moderated to a damped correction, even a dead beat correction. I am supposing for the moment that you may be in error on this one.