Heat pumps and shape-memory alloys motor

In summary, the conversation discusses the possibility of using a heat pump and shape-memory alloys motor to generate electricity. It is suggested that this would not be efficient as it would involve converting electricity to heat and then back to electricity. The efficiency of a shape-memory alloys motor is also questioned, with comparisons made to the efficiency of a Stirling engine and an electric solar panel. It is concluded that the efficiency of a shape-memory alloys motor would depend on the temperature differential between the thermal energy source and the thermal energy sink, and that achieving perpetual motion in this way would not be possible.
  • #1
magi
53
0
Heat pumps and shape-memory alloys motor...

Hi.

Would it be possible to get some electricity from a heat pump and shape-memory alloys motor/engins with a generator?

A heat pump use 1 kW and give you 3-5 kW heat.

Would it be possible to use shape-memory alloys motor and a generator to generate some electricity.

Or is the efficiency too low?

http://www.smaterial.com/SMA/engine/engine.html

Or what about a solar parabol.

The efficiency of electric solar panels is at the most 20%.

Can you get more efficiency when using a shape-memory alloys motor?

Regards Magi
 
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  • #2
The proposed motor seems to be a variation on a Sterling engine, or a K-cycle with NiTiNOL replacing the pistons. It's certainly workable, but I don't know what the efficiency would be compared to a regular Sterling.
 
  • #3
magi said:
Hi. Would it be possible to get some electricity from a heat pump and shape-memory alloys motor/engins with a generator? A heat pump use 1 kW and give you 3-5 kW heat.

Are you talking about a perpetual motion device? Getting electricity out with no electricity input? Are you saying you would have a heat pump driven by a shape memory engine in a closed loop, but in which case the shape memory engine produces more mechanical energy than is required by the heat pump?
 
  • #4
I hope that's not what he meant! It's possible, I guess, but I assumed that he meant that the thing produced 3-5kW from an input of 4-6kW (1kW wastage).
 
  • #5
Ben Wiens said:
Are you talking about a perpetual motion device? Getting electricity out with no electricity input? Are you saying you would have a heat pump driven by a shape memory engine in a closed loop, but in which case the shape memory engine produces more mechanical energy than is required by the heat pump?

Not a perpetual motion device.

I were just asked if shape-memory alloys could be used in any way.
 
  • #6
I'm just wondering why you are considering using the thermal energy from a heat pump? What's the point of using electricity to generate some thermal energy? That's the part that had me confused. Some shape memory engines could run off the small temerpature differential of a heat pump, but what's the point of doing so?
 
  • #7
Ben Wiens said:
I'm just wondering why you are considering using the thermal energy from a heat pump? What's the point of using electricity to generate some thermal energy? ?

Agreed. There is no point and it is not engineerably sensible to convert electricity into heat and then electricity again. The conversion of heat into any form of mechanical energy (and electricity is an energy with an extraordinary internal available amount of mechanical energy) is very inefficient.
 
  • #8
Ben Wiens said:
I'm just wondering why you are considering using the thermal energy from a heat pump? What's the point of using electricity to generate some thermal energy? That's the part that had me confused. Some shape memory engines could run off the small temerpature differential of a heat pump, but what's the point of doing so?

A guy just asked me a simpel question once.

-I take 1 kW and feed it into a heat engine and get heat out of it around 3-4 kW. Why can't I transform the heat to energy to get a perpetual motion device.

I know about the carnot cycle.

Then a guy asked what is possible to do with shape-memory alloys.

A sterling engine has a efficiency around 30 % and a electric solar panel have 20- 30 % so what efficiency have a shape-memory alloys engine.

And I just wanted to see what people said about this... :)
 
  • #9
magi said:
A sterling engine has a efficiency around 30 % and a electric solar panel have 20- 30 % so what efficiency have a shape-memory alloys engine.

It sounds like you're still fuzzy about the issue. A Stirling or any other engine does not have a definite efficiency such as 30%. It totally depends on the temperature differential between thermal energy source and thermal energy sink. So if the Stirling engine is receiving thermal energy from a heat pump with a coefficient of performance of 5, then the heat engine will have an efficiency of no greater than 20% or 1/5th. If the Stirling engine is receiving thermal energy from a heat pump with a coefficient of performance of 10, then the heat engine will have an efficiency of no greater than 10% or 1/10th.
 
  • #10
Heat Pump COP and perpetual motion machine

Ben Wiens said:
It sounds like you're still fuzzy about the issue. A Stirling or any other engine does not have a definite efficiency such as 30%. It totally depends on the temperature differential between thermal energy source and thermal energy sink. So if the Stirling engine is receiving thermal energy from a heat pump with a coefficient of performance of 5, then the heat engine will have an efficiency of no greater than 20% or 1/5th. If the Stirling engine is receiving thermal energy from a heat pump with a coefficient of performance of 10, then the heat engine will have an efficiency of no greater than 10% or 1/10th.

I'm a little fuzzy on the efficiency calculations. Wouldn't a heat pump with a COP of 5 put out five times the energy it requires to run? In that case it could be coupled to a Sterling engine with, say 25% efficiency for a net efficiency of 125% (enough for "perpetual motion"). The heat pump could be run by the shaft output of the Sterling, avoiding electircal conversion losses.
 
  • #11
Ben is correct.

Real heat pumps don't have efficiencies anywhere near that high, but the reall killer is that while the Stirling engine's efficiency is directly proportional to temperature difference, the heat pump's efficiency is inversely proportional to temperature difference. So the higher you get the heat pump in efficiency, the lower the Stirling engine gets. And vice versa.

Just look at the equations for http://en.wikipedia.org/wiki/Carnot_heat_engine" (Equation 3 - same as Stirling Engine
and
http://en.wikipedia.org/wiki/Coefficient_of_performance"

Notice the terms are the same (Tc, Th).

You can always get your heat from another source (ie, the sun), but then that isn't perpetual motion either.
 
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1. What is a heat pump?

A heat pump is a device that transfers heat from one location to another, usually from a colder area to a warmer one. It uses a small amount of energy to accomplish this, making it an efficient way to heat or cool a space.

2. How do heat pumps work?

Heat pumps work by using a refrigerant to absorb heat from one location and then releasing it in another location. This process is accomplished through the use of a compressor, condenser, expansion valve, and evaporator. The refrigerant is constantly cycled through these components, allowing it to transfer heat from one place to another.

3. What are shape-memory alloys?

Shape-memory alloys are metals that have the unique property of being able to "remember" their original shape after being deformed. This is due to their ability to undergo a reversible phase transformation when exposed to heat or a change in temperature.

4. How are shape-memory alloys used in motors?

Shape-memory alloys can be used in motors as actuators, which are components that convert energy into motion. When an electric current is passed through a shape-memory alloy, it heats up and can change shape, causing the motor to move. This makes them useful for applications where precise and controlled movements are necessary.

5. What are the advantages of using shape-memory alloy motors in heat pumps?

Shape-memory alloy motors have several advantages in heat pumps, including their ability to operate quietly, efficiently, and with precise control. They also have a long lifespan and are resistant to wear and tear, making them a durable option for use in heat pumps. Additionally, their compact size allows for more efficient use of space in the heat pump system.

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