Transcript Heat Transfer To A Fluid In A Stirred Tank

Group 5
Alex Guerrero
Andrew Duffy
Bernard Hsu
Daniyal Qamar
Jeff Tyska
Ryan Kosak
Tomi Damo
March 10, 2011
Introduction

The stirred tank is an important experiment
concerning the heat transfer (HT) to a fluid
 Due to the great variety of types of stirred tanks
there are only a few reliable correlations.

A steam jacket allows HT to the internal
liquid and an internal cooling coil uses cold
water to remove heat.
 Liquid exits into a HX that is also fed with cold
water. Cooled liquid is returned to the tank.
Purpose

The purpose of this laboratory
experiment is to measure the heat
transfer coefficient (HTC) between the
fluid and the inside tank wall.

These measurements will be taken
during three HT processes involving the
stirred tank unit.
Purpose

These three processes include:
 Steady State Unbaffled Tank
 Steady State Baffled Tank
○ Baffles deter vortexes, improving fluid mixing 
increases heat transfer rate.
 Unsteady State Unbaffled Tank

Can then determine the dependence of the
HTC on the impeller speed, fluid
properties, and the use of baffles.
Theory

The HT terms consist of:
 HT across the internal fluid to the wall of the stirred tank
 HT across the tank wall
 HT from the condensing steam to the tank wall
Theory

For Steady State:
Q13 = U(t1-t3)A
 Use this equation to solve for overall HTC.
 t1 is the temp in the tank,t2 is the temp of the
steam trap outlet, and A is the tank area
Theory
Q13 = U(t1-t3)A
 Q13, HT from steam to fluid in vessel, is the
difference between heat removed in cooling
coils and the heat removed by the HX:
Q13 = Qc – Qhx
*Qc and Qhx can each be solved using
Q=mCpΔt
Theory

ho, the HTC at outer wall surface, can be
solved using:
ho = 2960 (DT,o/mst)1/3
 where DT,o is the tank diameter and mst is
the mass flow rate of steam
○ mst can be found be calculating the volume of
steam condensate collected per time interval
Theory

To solve for hi, HTC at inner wall, use the
relation:
hi = (1/U + 1/ho)-1

For unsteady state use the relation:
AU(t1-t3) = mCp[dt3/dΘ]
 In this case, [dt3/dΘ] is the slope of the graph of
unsteady state heating vs. time
Apparatus
1
#
1
Equipment
Strobotac
2
Impeller Motor
3
Variable Transformer
4
5
Cooling Coil Inlet Flowrator
Tube
Cooling Water Inlet Valve
6
Recycle Water Flowrator Tube
7
9
Tank Water Out of Heat
Exchanger Thermometer
Water Inlet To Cooling Coil
Thermometer
Tank Thermometer
10
Pump Power Switch
11
Water Out of Cooling Coil
Thermometer
3
2
10
6
8
11
4
8
9
7
5
Apparatus
12
#
Equipment
12
Tank
13
Cooling Water Outlet of
Condenser Thermometer
14
Condenser
15
Pump
16
Cooling Water Inlet To
Condenser Thermometer
17
Tank Water To Inlet of Heat
Exchanger Thermometer
18
Heat Exchanger
18
17
14
15
13
16
Materials
Equipment
Water
Graduated Cylinder
Baffles
Stop Watch
Measuring Ruler
Heat Gloves
Mop
Procedure
Steady State Stirred Tank (Unbaffled):
1. Fill tank with water to about 2 inches from top.
Measure height of liquid level.
2. Turn on impeller motor and set to ~ 100 RPM.
3. Turn on cooling water to cooling coils.
4. Turn on cooling water to HX.
5. Close pump discharge and pump suction valves.
Open pump bypass valve.
Procedure
Steady State Stirred Tank (Unbaffled):
6. Turn on pump.
7. Open cooling water valve to steam condenser.
8. Open steam inlet valve.
9. After reaching steady state record flow rates, temperatures, and impeller
speed.
10. Repeat for different impeller speeds.
*Note: Adjust HX flow rate to a higher temperature to obtain
data for two different temperatures at constant impeller speeds.
Procedure Continued
 Steady State Stirred Tank (Baffled):
1. Repeat steps 1-10 of previous procedure using the mechanical baffles.
Unsteady State:
1. Open water inlet valve, fill tank.
2. Close all the valves for the cooling coil and recirculation water lines.
3. Turn on cooling water to condenser.
4. Open the condenser water valve, slightly open steam valve.
5. Turn on the impeller.
6. Adjust impeller speed to speeds used in SS trials.
7. Open the steam valve.
8. Measure the temp and time intervals and record data (until reach 85 oC).
Safety

Take note of equipment exposed to high
heat steam and use heat gloves when
necessary.

Avoid the impeller when in use.

Be cautious of water spills to prevent
slipping.
References

Bird, R. B., Warren E. Stewart, and Edwin N. Lightfoot.
Transport Phenomena. 2nd ed. New York, NY: Jonh Wiley &
Sons, Inc., 2002

Perry, Robert H., and Don W. Green. Perry's Chemical
Engineers' Handbook. New York: McGraw-Hill Professional,
2007.

University of Illinois at Chicago - UIC. Web. 13 Sept. 2010.
<http://www.uic.edu/depts/chme/UnitOps/entry.html>.

McCabe, Warren L., Julian C. Smith, and Peter Harriott. Unit
Operations of Chemical Engineering. New York: McGraw-Hill,
1993. (pp: 1058-1065) Print.

Wankat, Phillip C. Separation Process Engineering. (2nd
Edition). Boston, MA: Pearson Education, Inc., 2007. (pp: 573 –
579) Print.