Re: thoughts on pressure

On 24 A ustos, 23:37, Danny <da...@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
yuvali...@xxxxxxxxx wrote:
It's about pressure, not force. Most old members of this group may not
understand what pressure is, but at least the new members shall have a
chance to get it right, I mean. Anyhow, some progress seems to be
accomplished.

David

With an attitude like that you are sure to impress, old & new.

Pressure = force
-----
area

The unit of pressure is the Pascal - the force of 1 Newton exerted
over 1 square metre.

pressure is directly proportional to force, and inversely proportional
to area.

Espresso machines are designed with the (I assume) optimal area, the
area of a 58mm pf, and the pressure needed to ensure the correct flow
through the cake was calculated in order to arrive at the force needed
from a spring in the early days or a pump in later machines. The
pressure on this area is directly propotional to the force exerted on
this area, and can be calculated.

--
Regards, Danny

http://www.gaggia-espresso.com (a purely hobby site)
(apparently bad grammar but I like it that way...)


No! It's not the area of the P/F and there is not a single relevant
force (force of the spring or else). The calculation of the pressure
in this case is complicate, it involves theoretical models, serious
math., surface area of all coffee partikels etc.. Therefore the
pressure will be not calculated, for the sake of simplicity. It will
be measured, directly or indirectly. Direct measurement: pressure
gauge in circuit. Indirect measurement: measurement of the flow i.E.
mass per unit time. That's what Illy did, he hasn't try to calculate
the performance of coffee machines!

David

.

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