HEAT TRANSFER TO A FLUID IN A STIRRED

TANKGroup 5

Alex GuerreroAndrew DuffyBernard HsuDaniyal QamarJeff TyskaRyan KosakTomi 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 TankSteady 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.

The HT terms consist of:HT across the internal fluid to the wall of the stirred tankHT across the tank wallHT from the condensing steam to the tank wall

Theory

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# Equipment 1 Strobotac

2 Impeller Motor

3 Variable Transformer

4 Cooling Coil Inlet Flowrator Tube

5 Cooling Water Inlet Valve

6 Recycle Water Flowrator Tube

7 Tank Water Out of Heat Exchanger Thermometer

8 Water Inlet To Cooling Coil Thermometer

9 Tank Thermometer

10 Pump Power Switch

11 Water Out of Cooling Coil Thermometer

1

23

4

5

6

7

8

9

10

11

Apparatus# 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

12

13

14

15

16

18

17

MaterialsEquipment

WaterGraduated CylinderBaffles

Stop Watch

Measuring RulerHeat GlovesMop

ProcedureSteady 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.

ProcedureSteady 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.