REPLY Age of material in a stock (SD6410)

[SDMAIL jhomer]

Posted by  jhomer at comcast.net

>Jean-Jacques Lauble writes:
>"In equilibrium where inflow = outflow the average age of material in stock =
>Average delivery delay / 2.

The above comments are accurate only in the case of a fixed or conveyor-belt delay, 
where the age distribution is uniform, but not in the case of standard bathtub 
structures in which perfect mixing within the stock is implicitly assumed, and the 
age distribution is exponential.  With the perfect mixing assumed in a bathtub, the 
average age of material in an unchanging stock is equal to the average time-to-
outflow (As=To), whereas in a conveyor-belt delay the average age of material in an 
unchanging stock is one-half of the time-to-outflow.

Jack Homer 
Posted by  jhomer at comcast.net
posting date  Wed, 18 Apr 2007 12:24:40 +0000