Clever Uses Of Thermal Expansion

Clever Uses Of Thermal Expansion

On any given day, we rely on dozens of hidden computers seamlessly integrated into our lives to function. The low cost, flexibility, and ease of rapid product development of embedded microprocessors have fundamentally changed how products and equipment are designed; finding their way into even the most trivial items.

In this series, we explore how engineers accomplished design goals in a time long before the semiconductor revolution by spotlighting ideas that combined brilliant engineering with innovative uses of material properties.

Thermal expansion is one of the more common physical phenomena we experience daily. Most materials expand when heated. When a material is heated, the kinetic energy of that material increases as its atoms and molecules move about more. At the atomic level, the material will take up more space due to its movement so it expands.

THERMOSTATS

Most vehicle engines operate best around the boiling point of water. Keeping the heat generated by combustion in thermal check is a liquid cooling system that flows coolant in a circuit between the engine and a radiator. Typically the cooling system capacity is large enough to cool the engine at all mode of its operation. But when a cold engine is first started, this cooling capacity becomes a hindrance, as it can overwhelm an engines ability to rapidly warm up to operating temperature. Thermostats are used to regulate this temperature.

BIMETALLIC SWITCHES

Mechanical control by thermal expansion is simple and very reliable but what if we need to perform a nonmechanical form of temperature based control, such as electrical switching.
In a manner similar to wax, metals expand when heated, though different metals expand at different rates. This difference in expansion rates allows for some interesting applications. Bimetallic string bend when heated and can be configured into electrical thermal switches.

FLASHERS

We can expand on the functionality of bimetallic switches further by mounting an electrically resistant heating element to the bimetallic strip. As current flows through the heating element, the electrical resistance causes dissipation of heat, raising the temperature of the bimetallic strip. As it heats up, the thermal motion causes the bimetallic element to switch on the flow of electricity. Current is shunted away from the heating element, cooling it. The bimetallic strip then contracts back to its original state. This opens the switch, restoring current back to the heating element. This cycle of opening and closes forms a thermal flasher.

COIL THERMOSTAT

Bimetallic strips are durable, easily formed and can be used in various configurations. If we coil a bimetallic strip, the thermal motion causes the coil to tighten or unwind, creating rotation. If we calibrate the motion to the temperature of the bimetallic coil we create rotational motion relative to temperature. Add graduations and an indicator needle, and we now have a dial thermometer.
This simple, purely mechanical mechanism not only allows for measuring temperature but also the ability to control it in an adjustable manner. This is how residential, non-electronic adjustable thermostats operate.

THERMOCOUPLE

Combining dissimilar metals for the purpose of temperature sensing also comes in other forms. When a junction between two different metals are formed, such as with the alloys chromel and alumel, the thermoelectric effect occurs. An electrical potential difference across the junction develops with the voltage changing in a temperature dependent manner. This is known as a thermocouple.

Thermocouples are simple, rugged, inexpensive, and interchangeable. Though they aren’t precise, they are used as temperature sensors for both simple and digital control systems.

Other industrial configurations of control by heat exist, though these methods are more integrated into systematic designs, that are impractical for direct electronic control, they employ thermodynamic properties of working fluids such as air, combustion gases, steam or molten salt and as are generally used for power generation or transmission.

SUPPORT NEW MIND ON PATREON

[Onewheelordeal]

3:12 I know this is a serious video but I wasn't ready for the lips on Celsius

[phinok.m.]

Thermal switches in blinkers typically have the resistor and bimetallic switch in series, so the light goes on immediately when you turn the blinker on and turns off once the resistor heats up enough. Also thermal switches in blinkers slow down when a light bulb burns out, as the current through the resistor decreases and it takes longer for it to heat. Relay based blinkers usually speed up when a bulb burns out. And the rate change isn't an accident, it is there so the driver notices when a bulb burns out.

[thesteaksaignant]

The thermal switches for turning lights blew my mind ! I had no idea !

[gonun]

Cool video. Was expecting something about manufacturing processes using thermal expansion like mounting bearings, but this was very intresting too.

[Snyper]

I gotta say, you earned my subscription. Your format is direct, factual, and well rounded in general. You answered pretty much every question I had about thermocouples, and bi-metallic switches. Thanks for your hard work!

[TelmoMonteiro]

This is like mechanical logic! I really like the way you approach the subject. Direct, simple, concise and precise

[emanuelmifsud]

As a teacher of Physics, Chemistry and Electronics etc, may I commend you on your explanations. They are clear, simple and well presented.

[suprafill]

Automotive cooling systems are pressurized around 14-16 psi raising the boiling point an extra 45 degrees. I enjoyed the video I just wanted to offer this information to you.

[oliverfeliciano]

hi, im a power plant control room operator. i know alot about what this video is based on and i think it may be the best demonstration of the physics involved that ive ever seen during my schooling. bravo, you got a new subscriber.

[richardcowan]

An interesting use you didn't mention: thermal expansion is used to join gears, wheels and other rotating objects to shafts/axles. The wheel and shaft are made to slightly overlapping diameters, then the wheel is heated and expands and the shaft is cooled so it shrinks a bit. The wheel is then slid onto the shaft and when the parts cool down/heat up to room temperature, the wheel grips tightly onto the shaft.

[flamencoprof]

Regarding failing safe, I couldn't resist quoting John Gall from 1975, "When a fail-safe system fails, it fails by failing to fail safe." : -)

[haxney]

As a software engineer, the thought of replacing analog mechanical controls with sensors and software terrifies me. The question in software engineering is "what happens when we screw something up?" not "what happens if we screw something up?"

[Stone_]

This is incredibly cool! I took some beginner Electrical Engineering classes as part of my computer science degree, and knew a little about this sort of property and applications of it, but most of this content is absolutely brilliant stuff that I've never heard of before!

Just watched a few other videos, and Definitely agree with another comment on here that the quality of this channel's content is up there with Kurzgesagt and Real Engineering. Fantastic!

[CheapSushi]

I noticed the music volume when you show your intro logo has been too high for nearly all your videos; it's always jolting, especially with headphones. For videos so focused on precision, I'd think you'd try to match the levels more. And honestly your intro music doesn't really fit how relaxing the rest of your channel is. But other than that I love the content.

[cunningham.s_law]

all those Minecraft mods are starting to make sense

[jimwednt]

The degree of enjoyment i get from these videos is palpable.

[boastfultoast]

When I was like 13 I a family friend with an HVAC business showed drove me around and I learned a thing or two. One of the coolest things I will never forget is when I learned how the thermostat double metal coil thing worked based on temperature, and it bending into itself to become a switch. Something about it being such a simple concept really made me appreciate the modern world, where everything is so complex.

[CatNolara]

Nice stuff, haven't heard of some of the mechanisms yet. Something that I missed would be shrinking bearings, gears, couplings etc. onto shafts by heating the piece and maybe cooling the shaft. They then slip together nicely and after normalizing in temperature they clamp extremely tight together. In a similar fashion there are also heat shrink collets for holding endmills and other tools, there are even special inductive heating devices for inserting and removing the tools from the collet. They are really compact and stiff while also being very precise.

[Sigouss]

For machinery purposes of very tight component assembly you've forgotten the ''interference fit''.
Cooling the shaft and heating up what ever goes onto the shaft.

[wk]

50+ years on this planet and I never knew exactly how old school car flashers worked 🤔. Great quality content, this was my first video by you and looking forward to more.