Heat transfer in agitated vessal. Shawala Azhar 06-chem-63 Qudsia Ramzan 06- chem-62 Samina 06-chem-90 Humera 06-chem-100. Agitation of liquids. Purpose of agitation
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Shawala Azhar 06-chem-63
Qudsia Ramzan 06- chem-62
liquids are agitated for number of purposes depending upon the objective of the processing step.
1- Suspending solid particles.
2- Blending miscible liquids.
3- Dispersing a gas through a liquid in the form
4- promoting a heat transfer between the liquid and a
coil or jacket.
In the catalytic hydrogenation of a liquid agitator is used to
1- Disperse gas through the liquid in which the solid particles of catalyst are suspended.
2-Promoting the removal of heat of reaction by a cooling coil and the jacket.
The heating or cooling time can be reduced
by improving the rate of heat transfer to the fluid.
By agitating the fluid.
By reducing the heat losses from the vessal by insulation.
(a) How long does it take to heat the liquid from 293 to 353K and what is the maximum temperature to which the liquid can be heated.
(b)When the liquid temperature has been reached to 353K, the steam supply is turned off for 2 hours(7.2 ks) and the vessal cools. How long will it take to reheat the material to 353K.
The surface area of the coil is 0.5m2 and the overall heat transfer coefficient for the liquid may be taken as 600W/m2 K. The outside area of the vessal is 6m2and the coefficient of heat transfer to the surroundings may be taken as 10 W/m2 K.
If T(K) is the temperature of the liquid at the time t(sec), then a heat balance an the vessal gives
(1000 *4000)dT/dt = (600*0.5)(393-T)-(10*6)(T-293)
4 * 10^6dT/dt = 135,480-360T
11,111dT/dt = 376.3-T
t=11,111 293 ∫353dT/ (376.3-T)
=14,155 sec (or 3.93 hrs)
The steam is turned off for 7200sec and during this time a heat balance gives:
(1000*4000)dT/ dt = -(10*6)(T-293)
66,700dT/dt = 293-T
353 ∫Tdt / (293-T) = (1/66,700) 0∫7200 dt
ln(-60/293-T) = (7200/66,700)
t =11,111 346.9∫353 dt/(376.3-T)
=11,111 ln (29.4/23.3)
t =2584 sec (0.72hrs)