Unformatted text preview: s. One is a convect ive effect because the change of the amount of total flow coming in into the heat exchanger and the other is a thermal effect since the temperature if the inco ming feed has changed. The convect ive effect is immediate (incompressible fluid) and acts in the first instance and the thermal effect take some t ime to have an impact on the system (the t ime for the change to travel through the heat exchanger). For example, if we introduce a posit ive step change in the disturbance, that is we increase the warm liquid flow, we have and increase on the amount to total flow co ming in, but also a decrease on the temperature of the inco ming stream. Because the increase on the feed stream flow (convective effect) and since the amount of heat taken by the cooling water is constant, then init ially the outlet temperature will go up. After so me t ime, because the feed stream temperature decreased (thermal effect) the outlet temperature will go down. 4. A process is modeled by the fo llowing equat ions: dx
2 1 = -2 x + exp( - x ) - 3u1 x 2
d t dx 2 x 2
= - x +
+ 4u 2 2
d t 1 + x 2 The control objectives dictate the fo llowing output equations: y1 = x 1
y 2 = x 2 a. Find the four transfer functions relat ing the outputs ( y1 , y 2 ) to the inputs ( u1 , u 2 ). b. Solve the equations with the condit ions, u1 ( ) = 1 u 2 (t ) = 1 y (0 = 0 y ( ) = 0 . t , , 1 )
, 2 0 c....
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This note was uploaded on 01/12/2014 for the course CHE 4198 taught by Professor Hjortso,m during the Fall '08 term at LSU.
- Fall '08