What is the most efficient small-scale low-temperature heat engine?

In summary, the conversation discusses the most efficient way to convert the thermal energy from a lightbulb into rotational mechanical work to turn a generator. The speaker first considers using a Rankine cycle turbine, but then mentions the possibility of using a Stirling cycle engine. They also mention the Carnot cycle as the most efficient option, but acknowledge that it may not be practical. Another suggestion is to use a thermocouple to create electricity from low level heat. Finally, the idea of using an LED light instead of a traditional incandescent bulb is brought up as a more effective measure for energy efficiency.
  • #1
cxaxnxexs
10
0
I’ve recently become fascinated by high power density energy conversion devices… I was looking at the 100W incandescent light bulb lamp on my desk as 90% of its energy was being wasted as heat and started thinking… I know it is only a rather small amount of energy, but what would be the most efficient way to convert the thermal energy from the lightbulb (surface temp of 136C) into rotational mechanical work to turn a generator?

My intuition at first leads me to think that a Rankine cycle (likely some kind of organic Rankine cycle given the relatively low temperature) turbine would be the answer since it should not experience the kinetic energy losses that appears with the rapid accelerations and decelerations that occur in steam piston engines. Plus, there must be a reason steam turbines are so popular. However, I’ve just started learning about Stirling cycle engines & they are very interesting. Some reports claim them to be more efficient that steam engines --> http://www.bekkoame.ne.jp/~khirata/academic/kiriki/begin/general.html

Any ideas/comments? :uhh:
 
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  • #2
The most efficient engine would be one using the Carnot cycle. (Note: I didn't say it was the most practical - no engine would be practical).

AM
 
  • #3
Haha you are definitely right there. Actually doesn't the 2nd law of thermo show isentropic processes to be impossible? Although I'm sure those crazy quantum theory guys would argue differently.
 
  • #4
cxaxnxexs said:
Haha you are definitely right there. Actually doesn't the 2nd law of thermo show isentropic processes to be impossible? Although I'm sure those crazy quantum theory guys would argue differently.
The Carnot engine cycle is an ideal limit that can be approached but never reached. But generally isentropic processes are not impossible - slow adiabatic processes are isentropic.

Instead of using a heat engine, you could use a thermocouple to create electricity from low level heat. It is not that efficient but no heat engine is going to be very efficient for converting lightbulb heat to useful work.

AM
 
  • #5
The more effective measure would be to trade the glow-bulb for an equally bright led light, consuming a fraction of the 100 watts (apprx. 10 watts). Carnot-efficiency exceeded, by trading heat for electricity, not making heat in the first place. Your approach towards energy-efficiency is common though.
 

1. What is a heat engine?

A heat engine is a device that converts thermal energy into mechanical work. It works by using a heated source to create pressure and drive a piston or turbine, which in turn produces movement.

2. What is a low-temperature heat engine?

A low-temperature heat engine is a type of heat engine that operates at temperatures below 100 degrees Celsius. This is in contrast to high-temperature heat engines, which operate at temperatures above 100 degrees Celsius.

3. What makes a small-scale low-temperature heat engine efficient?

A small-scale low-temperature heat engine is considered efficient if it can convert a high percentage of the available heat energy into mechanical work. This can be achieved through design optimizations such as using efficient materials and minimizing energy losses.

4. What are some examples of small-scale low-temperature heat engines?

Some examples of small-scale low-temperature heat engines include Stirling engines, thermoelectric generators, and organic Rankine cycle engines. These engines can be used for various applications such as power generation, heating and cooling, and waste heat recovery.

5. How does the efficiency of a small-scale low-temperature heat engine compare to a large-scale one?

In general, small-scale low-temperature heat engines have lower efficiency compared to large-scale ones. This is because smaller engines have a larger surface-to-volume ratio, which leads to higher energy losses. However, with advancements in technology and design, the efficiency of small-scale low-temperature heat engines is continuously improving.

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