Episode: 3883
Title: HPR3883: Emergency Show: How to demonstrate the power of condensing steam
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr3883/hpr3883.mp3
Transcribed: 2025-10-25 07:14:40

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This is Hacker Public Radio Episode 3883 for Wednesday, the 21st of June 2023.
Today's show is entitled Emergency Show How to Demonstrate the Power of Condensing
Steam.
It is hosted by Mike Ray and is about 8 minutes long.
It carries a clean flag.
The summary is a kitchen experiment to demonstrate the power of condensing steam.
Hello and welcome to Hacker Public Radio.
My name is Mike Ray.
Uh oh, you're hearing that sound because this is an emergency show.
Each PR is running low on scheduled podcasts.
If you would like to submit a show, email admin at hackerpublicradio.org for more information.
Today we're going to do a kitchen experiment which very impressively demonstrates the
awesome power of condensing steam to create a partial vacuum.
What are we going to need?
The first thing you need is an empty drinks can, like a 330 millilitre coke soda can.
Perhaps a bigger 400 millilitre can might work, but I've only ever tried it with a
330 millilitre can.
Wash it out thoroughly so there's no sugary residue in it.
We're also going to need a source of heat and the best thing is the kitchen cooker top.
And we're going to need a wide shallow container like a baking tray or something similar, something
which can contain a small amount of cold water, which presents a large target.
And we're going to need a pair of barbecue tongs or something, some kind of kitchen
tongs that you can use to grab hold of the hot can when it's very hot without your hand
being close enough to the heat to be in any danger of burning itself.
So what do we do?
After we've washed out the can, put about half an inch or a centimeter of water in the
bottom of the can.
Perhaps a centimeter and a half, something that will cover the sort of concave end of the
can.
And not too much.
And put a similar depth of cold water, it doesn't have to be very cold, just as cold as
it comes out of the cold water tap in the baking tray and stand the baking tray on the
kitchen worktop next to the cooker.
Now place the can on the heat or on the burner, turn on the burner or turn up the electricity
whatever.
And the can will very quickly start to come to the boil.
The water is only a very small amount of water in the bottom of it, so it will boil quite
quickly.
And you can observe the steam begin to appear through the hole in the top of the can.
Leave it to steam for several seconds to make sure that the can is nice and full of steam.
And without actually removing or jogging can from the heat, grab a hold of it with the
tongs.
Now you need to do this with a sort of underhand grip so that you can very quickly and
in one swift and smooth motion, pick up the can, flip it through 180 degrees onto its head
and splash it down in the shallow water in the baking tray.
Now when you do this, do it as quickly and as smoothly as you can possibly do it.
So pick the can up, rotate your wrist so that the can is now upside down and slam it
down in the cold water and you need to slam it down but as quickly as possible place
it top down in the cold water.
What happens is the steam inside the can will instantly condense producing a partial
vacuum inside the can and the can will bam, be crushed by the atmospheric pressure outside
the can because there's a partial vacuum inside it.
And that is really all there is to it and that's a brilliant demonstration for onlookers,
for kids to demonstrate the awesome power of condensing steam.
Have a look at the show notes because they contain a few sentences about how the condensation
of steam is used in a steam engine.
Most people think of a steam engine, they think of steam being injected into a cylinder
to push a piston out of the cylinder or along the cylinder connected to piston rods and
cranks and things to convert the linear motion into rotary motion but that's only really
half the story.
Most of the efficiency comes from using an injection of cold water into a cylinder containing
pressurized superheated steam to instantly condense the steam and produce a partial vacuum
which will effectively suck the piston back along the cylinder and produce as much usable
energy on the return stroke as in fact more stronger energy on the return stroke than
was produced by injecting superheated steam into the cylinder to push the piston up and
out of the cylinder and the same effect condensing steam to produce a partial vacuum is used
to draw hot gases from the furnace, from the coal fire at the back end of the steam engine
through pipes that run through the boiler, the superheated the pressurized boiler into
the smokebox at the front of the steam engine to heat and those gases passing through the
pipes helps to heat the water and the same partial vacuum created at the smokebox end
as well as drawing the products of combustion through the boiler produce a draft of very
stronger aft of fresh air into the furnace at the driving end which you can actually hear
if you listen to a big powerful steam engine trying to pull a heavy train from a standing
start to motion there will be very deep-throated chugs or chuffs or puffs of noise and gases
shooting out the chimney rhythmically in synchronization with the effect of injecting cold
water into the steam at the end of the locom to produce the partial vacuum which draws
the gases and draws the draft across the furnace and the sound that you hear the impressive
sound that you hear is the explosive power of the partial vacuum producing that draft
and drawing those gases through the boiler.
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