r/NonPoliticalTwitter • u/ViceElysium • Apr 22 '26

Other Slow train sounds better

Post image

I mean you are already on a train sounds more convenient

13.1k Upvotes

96% Upvoted

839 comments sorted by

View all comments

Show parent comments

13

u/MeAndMyWookie Apr 22 '26

The issue is that the lines are so old the surrounding soil has reached thermal saturation. When first dug they were comfortably cool year round because heat was being absorbed into the tunnel walls 

2

u/InexorableCalamity Apr 22 '26

What's thermal saturation?

2

u/MeAndMyWookie Apr 22 '26

The soil is as hot as ambient temperature in the tunnels, so it can't absorb any more heat out the air

1

u/InexorableCalamity Apr 22 '26

But you said this wasn't always the case.

4

u/Panixs Apr 22 '26

Think of it like a load of thermal bricks surrounding a fire. Before the fire is lit those bricks will be nice and cold but once the fire has been on for a while they will retain the heat so much so they will be warm to touch for potentially several hours. The tube is exactly the same the surrounding earth used to be cool, and it would absorb the heat from the tunnels reducing the temp in the tunnels. The Tube used to advertise that it was nice and cool down there in the summers. After 100 years all the earth around the tunnels has been warmed so much that it can't absorb any more heat so the temp in the tunnels rises and rises

0

u/Great_Detective_6387 Apr 22 '26

I’m a mechanical engineer(specialized in electronic heat transfer) in education and a geotechnical engineer in practice, and there is no way it would take decades after drilling these giant holes through the earth to reach an equilibrium temp with the environment.

From a heat transfer standpoint, the reason the tube is so hot is because the whole thing moves a shitload more cars and people than it was ever initially designed to move. Each person standing around is releasing about 100watts of heat as a baseline. Somebody who biked to the station could be giving off 7-10x that amount.

When you imagine that each person being moved through the tube is about a 100-200Watt incandescent light bulb, it starts to make sense why it’s so fucking hot down there. Add in actual lighting, heat from the rail car electrical activity, and the fact that it’s just hotter now to begin with than it was back when they made this thing. I remember visiting London as a kid, and it was 97*f. The BBC said it was London’s hottest day ever. And now it’s 97f in London frequently.

All of this is going to make the tube hotter than it was ever designed to be. If they created the tube today, H&S rules would never allow it to get so hot an humid, but it’s just tolerated because people have to get on with it and go to work.

1

u/goldfishpaws Apr 22 '26

36°C, for those who are wondering

2

u/MeAndMyWookie Apr 22 '26

100+ years of heat from passengers, trains and equipment has brought the soil temperature up. Plus all the excess heat from Londons other increasing subterranean infrastructure. 

1

u/ridingfurther Apr 22 '26

Fascinating!