On Tue, 16 Jun 2009 23:24:42 +0100, "hungerdunger"
wrote:

"Paul Herber" wrote in message
well.net...

100W+ per person, a couple of MW per train. It all ends up as heat.

Yes, but from my (now possibly incorrect) memory of living in London many
years ago, I seem to remember the Tube was OK in cool weather, but very hot
in hot weather. My point was: shouldn't the temperature be relatively
stable all year round?

If there were no trains and no people then maybe.


--
Regards, Paul Herber, Sandrila Ltd. http://www.sandrila.co.uk/

"hungerdunger" wrote in message
...
| "Paul Herber" wrote in message
| ell.net...
|
| 100W+ per person, a couple of MW per train. It all ends up as heat.
|
| Yes, but from my (now possibly incorrect) memory of living in London many
| years ago, I seem to remember the Tube was OK in cool weather, but very
hot
| in hot weather. My point was: shouldn't the temperature be relatively
| stable all year round?
|
| --
| Hungerdunger

No! The movement of the trains continually drags in air from outside. Stand
on any platform, and you can feel the movement of air as the trains approach
and recede. And more to the point, when you are on the escalators, you can
continually feel the air flow, up or down depending which direction the
nearest train is running.. Coupled with Paul's comments above, then you can
see that there is a lot of heat being generated down there, and continual
hot air being dragged into the whole system during the summer.

The constant temperatures only apply when there is little or no movement of
air in the underground spaces, such as caves and mines.

jim, Northampton

On Jun 17, 12:55*am, "jbm" wrote:

The movement of the trains continually drags in air from outside. Stand
on any platform, and you can feel the movement of air as the trains approach
and recede.

I wonder how the air dynamics of trains has been analysed for the
effect it has on acoustics. The sound of an approaching train vss the
sound of a receding one give credence to the theories about red and
blue shift.

I imagine the vortex tunnels that they form in passing at speed in
excess of 60 mph would trap sounds of some frequencies while the
tunnels last.

Might that be why the louder, deeper sounds persist so long after the
passing of a train? That one has always puzzled me.

Weatherlawyer wrote:
On Jun 17, 12:55 am, "jbm" wrote:
The movement of the trains continually drags in air from outside. Stand
on any platform, and you can feel the movement of air as the trains approach
and recede.

I wonder how the air dynamics of trains has been analysed for the
effect it has on acoustics. The sound of an approaching train vss the
sound of a receding one give credence to the theories about red and
blue shift.

I imagine the vortex tunnels that they form in passing at speed in
excess of 60 mph would trap sounds of some frequencies while the
tunnels last.

Might that be why the louder, deeper sounds persist so long after the
passing of a train? That one has always puzzled me.

The maximum speed of undergound trains is 20mph.

--
Joe Egginton
Wolverhampton
175m asl

Joe Egginton wrote:

Weatherlawyer wrote:
On Jun 17, 12:55 am, "jbm" wrote:
The movement of the trains continually drags in air from outside. Stand
on any platform, and you can feel the movement of air as the trains
approach
and recede.

I wonder how the air dynamics of trains has been analysed for the
effect it has on acoustics. The sound of an approaching train vss the
sound of a receding one give credence to the theories about red and
blue shift.

I imagine the vortex tunnels that they form in passing at speed in
excess of 60 mph would trap sounds of some frequencies while the
tunnels last.

Might that be why the louder, deeper sounds persist so long after the
passing of a train? That one has always puzzled me.

The maximum speed of undergound trains is 20mph.


Average train speed

* 33km per hour (20.5mph) including station stops
* In central London, trains cannot reach speeds of more than 30-40mph
because of the short distance between stations
* On the Victoria line, stations are further apart and trains can reach
speeds of up to 50mph
* On the Metropolitan line, trains can reach over 60mph

Source:
http://www.tfl.gov.uk/corporate/mode...ound/1608.aspx

--
Graham P Davis, Bracknell, Berks., UK. E-mail: newsman not newsboy
"I wear the cheese. It does not wear me."

On Wed, 17 Jun 2009 10:12:09 +0100, Joe Egginton
wrote:

Weatherlawyer wrote:
On Jun 17, 12:55 am, "jbm" wrote:
The movement of the trains continually drags in air from outside. Stand
on any platform, and you can feel the movement of air as the trains approach
and recede.

I wonder how the air dynamics of trains has been analysed for the
effect it has on acoustics. The sound of an approaching train vss the
sound of a receding one give credence to the theories about red and
blue shift.

I imagine the vortex tunnels that they form in passing at speed in
excess of 60 mph would trap sounds of some frequencies while the
tunnels last.

Might that be why the louder, deeper sounds persist so long after the
passing of a train? That one has always puzzled me.

The maximum speed of undergound trains is 20mph.

About 40-50MPH in the tube tunnels.


--
Regards, Paul Herber, Sandrila Ltd. http://www.sandrila.co.uk/

jbm wrote:
"Lawrence Jenkins" wrote in message
...
|
| "Joe Egginton" wrote in message
| ...
| I was watching a building program yesterday, and the builder said it was
| 12c constantly 2 metres underground. They was building a house in
| Maidstone, Kent.
|
| I know builders are known for telling porkies, but is it true that just
2
| metres underground the temperature is constant?
| --
| Joe Egginton
| Wolverhampton
| 175m asl
|
| Hmmm I wonder how that squares with heatpumps? May that's the temp they
| bring the mains up to.
|
|
Your builder was right. Sub-soil temperatures in the UK are standard at
about 50F (10C). This applies from 2 feet down to a couple of hundred feet,
but may vary depending on the depth of the water table. This is why
underground caves are always at pretty much the same temperature throughout
the year irrespective of surface weather conditions.

To use geothermal heat pumps, you would have to drill down a couple of miles
before finding any appreciable rise in temperature, and then the deeper you
go, the hotter it gets. Generally, for every kilometre depth, the
temperature rises by about 30C, so at 3km, the rock temperature will be 90C
above the surface temperature, enough to produce boiling water.

The above figures are not necessarily true in areas of volcanic activity,
and especially suspect in places like Iceland!

jim, Northampton



Groundwater in the UK at the watertable is a pretty constant 10C all
year round. If you geophysically log a borehole (as I have done many
times) the geothermal gradient is very easy to measure in even quite
short distances (100m) with instruments that can measure fractions of a
degree.

Inflows or outflows of colder or warmer water (usually seen as steps in
the gently increasing temperature profile) to the borehole give away the
location of fractures. If water is inflowing at one depth and outflowing
at another depth the temperature profile will show as a straight line
(constant temperature) between those depths.

Certain areas of the UK have a steeper geothermal gradient and are ideal
locations for geothermal power schemes. Southampton is the primary
example and geothermal energy is used there to heat a number of public
buildings. The water used is drawn from a depth of 1.8km and is 76C
(I've geophysically logged one of the original test bores there).