CBE 465 4/19/2017 Heuristics 19 Oct 12

Agitators and Mixing Equipment CBE 465 Agitators and Mixing Equipment 4/19/2017 Suspend solids Disperse gases and liquids Emulsify one liquid in another Promote heat transfer Blending two or more materials together Overmixing maybe undesirable in biological application, high shear may damage organisms polymer molecules may be damaged by long mixing or high shear For design or consideration of mixing process should understand: mechanism of mixing scale-up criteria power consumption flow patterns mixing time/rates types of equipment available Coulson and Richardson’s Chemical Engineering Volume 1, 6th ed.

Agitators and Mixing Equipment CBE 465 Agitators and Mixing Equipment 4/19/2017 Fluid mixing Coulson and Richardson’s Chemical Engineering Volume 1, 6th ed.

Agitators and Mixing Equipment CBE 465 Agitators and Mixing Equipment 4/19/2017 Fluid mixing: Baffles Unbaffled mixing tanks often used: in transition region for sticky materials where perfect cleaning is required in large tanks where baffle effects are small processes where it is not clear baffles have an effect on mixing performance http://www.youtube.com/watch?v=H4JQUBnCeHk&list=PL92460BA36337C5A4&index=5&feature=plpp_video 3 min G.B. Tatterson., Fluid Mixing and Gas Dispersion in Agitated Tanks, McGraw-Hill, 1991 Coulson and Richardson’s Chemical Engineering Volume 1, 6th ed.

Agitators and Mixing Equipment CBE 465 Agitators and Mixing Equipment 4/19/2017 Fluid mixing: Baffles Fluid mixing: off-center http://www.youtube.com/watch?v=0N1z_kbhtFs&list=PL92460BA36337C5A4&index=3&feature=plpp_video 4:10 min Coulson and Richardson’s Chemical Engineering Volume 1, 6th ed.

Agitators and Mixing Equipment CBE 465 Agitators and Mixing Equipment 4/19/2017 Side mounted mixers. Flow patterns for side-entering propeller Coulson and Richardson’s Chemical Engineering Volume 1, 6th ed. Paul, et.al., Handbook of Industrial Mixing, Wiley, 2004

Agitators and Mixing Equipment CBE 465 Agitators and Mixing Equipment 4/19/2017 Common Impellers Figure 7.20 Commonly used impellers (a) Three-bladed propeller (b) Six-bladed disc turbine (Rushton turbine) (c) Simple paddle (d) Anchor impeller (e) Helical ribbon. http://www.youtube.com/watch?v=swnIBdiyhNg&list=PL92460BA36337C5A4&index=7&feature=plpp_video 2 min Coulson and Richardson’s Chemical Engineering Volume 1, 6th ed.

Agitators and Mixing Equipment CBE 465 Agitators and Mixing Equipment 4/19/2017 Various Turbine Impellers Coulson and Richardson’s Chemical Engineering Volume 1, 6th ed.

Various Impeller Types CBE 465 Various Impeller Types 4/19/2017 Axial Flow Impellers Hydrofoil Impellers High-Shear Impellers Radial Flow Impellers Paul, et.al., Handbook of Industrial Mixing, Wiley, 2004

Various Impeller Types CBE 465 Various Impeller Types 4/19/2017 R. Hesketh, mixing notes

Various Impeller Types CBE 465 Various Impeller Types 4/19/2017

Agitators and Mixing Equipment CBE 465 4/19/2017 Agitators and Mixing Equipment Selecting Agitator Type Used to make preliminary agitator selection based on tank volume and liquid viscosity. Turbines, Pitched Blade Turbines, and Propellers are typically used at high Re and low viscosity. Anchor, Helical Ribbon, and Paddle agitators are used for higher viscosity (more laminar-like Re) fluids. 1 cP = 0.001 Pa*s = 1 mPa*s 1 Pa*s = 1 N*s/m2 = 1 kg/(m*s) Coulson and Richardson’s Chemical Engineering Volume 1, 6th ed.

Flow Patterns for Various Impellers CBE 465 Flow Patterns for Various Impellers 4/19/2017 Flat Blade Turbine = FBT Pitched Blade Turbine = PBT Paul, et.al., Handbook of Industrial Mixing, Wiley, 2004

Typical Dimensions for Mixing Equipment CBE 465 Typical Dimensions for Mixing Equipment 4/19/2017 G.B. Tatterson., Fluid Mixing and Gas Dispersion in Agitated Tanks, McGraw-Hill, 1991

Typical Dimensions for Mixing Equipment CBE 465 Typical Dimensions for Mixing Equipment 4/19/2017 G.B. Tatterson., Fluid Mixing and Gas Dispersion in Agitated Tanks, McGraw-Hill, 1991

Power Consumption and Scale-up in Mixing CBE 465 Power Consumption and Scale-up in Mixing 4/19/2017 Consider geometry, fluid properties, flow patterns, power, and so on. Has been considered through dimensional analysis. With: For geometrically similar vessels, ratios of all terms to right of the Froude number are negligible. The Froude number is only important when significant vortex develops (in unbaffled tanks); for baffled tanks the NP does not depend on the Froude number. P = power dissipation to the fluid. W=J/s = N-m/s = kg-m^2/s^3 Power rating of the driver must exceed P, i.e. has to overcome losses of driver, seals, bearing, etc. As R.O.T., estimate losses as 25 % of calculated P Therefore: Pdriver = 1.25 * P Use 1.75 factor when solids might settle on propeller before it is started. (info from Cheremisinoff) Tatterson & Colson and Richardson.

Power Consumption and Scale-up in Mixing CBE 465 Power Consumption and Scale-up in Mixing 4/19/2017 Consider low viscosity, unbaffled systems. Colson and Richardson.

CBE 465 In-Class PS Exercise 4/19/2017 Consider a solution of sodium hydroxide with the properties listed below. It is agitated by a propeller mixer that is 0.5m in diameter in a 2.28m diameter unbaffled tank. The liquid depth is 2.28m. The impeller is located 0.5m above the bottom of the tank. If the propeller is rotated at 2 Hz, what power is required? Colson and Richardson

CBE 465 4/19/2017 Heuristics 22 Oct 12

Power Consumption and Scale-up in Mixing CBE 465 Power Consumption and Scale-up in Mixing 4/19/2017 Consider low viscosity, baffled systems. Colson and Richardson.

Power Consumption and Scale-up in Mixing CBE 465 Power Consumption and Scale-up in Mixing 4/19/2017 Consider low viscosity, baffled systems (wall baffles). Curve 1 = Rushton impeller Curves 2 & 4, open, flat blade impellers Curve 5 is Backswept open impeller Curve 6 is PBT (pitched blade turbine) Figure 10.59 Power correlations for turbine impellers in a tank with 4 baffles. [w, D, impeller width and diameter, respectively.] Colson and Richardson.

CBE 465 In-Class PS Exercise 4/19/2017 Assume you are mixing a small amount of material into water in a standard configuration baffled tank. The diameter of the pitched blade turbine is 1 m and it is desired to operate at 84 RPM. Estimate the power required.

Power Consumption and Scale-up in Mixing CBE 465 Power Consumption and Scale-up in Mixing 4/19/2017 Consider low viscosity, baffled systems (wall baffles). N.P. Cheremisinoff, Handbook of Chemical Processing Equipment, B-H, 2000

Power Consumption and Scale-up in Mixing CBE 465 Power Consumption and Scale-up in Mixing 4/19/2017 Propeller pitch: Propeller pitch = (distance fluid (or propeller) travels in one full revolution) / (propeller diameter)

CBE 465 Other Terms in Mixing 4/19/2017 Pumping Capacity: discharge flowrate from an impeller: Tip Speed of an impeller: Torque: “twist” force acting on agitator shaft: Power per unit volume: Q = discharge flowrate, or pumping capacity. For “square-pitched” propellers in turbulent region, take NQ = 0.5 W=J/s = N-m/s = kg-m^2/s^3 http://www.em.doe.gov/PDFS/Slurry%20Handling%20Workshop/2-Short%20Course%20Art%20Etchells/2-2%20DOEM4M5%20Slurry%20Handling%20Course_Part%202_Art%20Etchells_Dec31'07.pdf Blend time (estimation to within 5% desired concentration):

Discharge Coefficient CBE 465 Discharge Coefficient 4/19/2017 N.P. Cheremisinoff, Handbook of Chemical Processing Equipment, B-H, 2000

CBE 465 Mixing Time 4/19/2017 Ni tm = dimensionless mixing time or the number of stirrer rotations to mix the solution to homogenization. Blend time (estimation to within 10% desired concentration): P.M. Doran, Bioprocess Engineering Principles, 2nd Ed., Academic Press 2012

CBE 465 Mixing Time 4/19/2017 Doran suggests that for turbulent mixing conditions, irrespective of the impeller type, that (baffled vessel, single impeller, H=T): Verified under aerated conditions also (impeller not flooded) and for: P.M. Doran, Bioprocess Engineering Principles, 2nd Ed., Academic Press 2012

CBE 465 In-Class PS Exercise 4/19/2017 A fermentation broth with properties as given below, is agitated in a 2.7 m3 baffled tank using a Rushton turbine with a diameter of 0.5 m and a stirred speed of 1 Hz. Estimate the mixing time.

Additional Plots for Non-Standard Mixing CBE 465 Additional Plots for Non-Standard Mixing 4/19/2017 N.P. Cheremisinoff, Handbook of Chemical Processing Equipment, B-H, 2000

Additional Plots for Non-Standard Mixing CBE 465 Additional Plots for Non-Standard Mixing 4/19/2017 N.P. Cheremisinoff, Handbook of Chemical Processing Equipment, B-H, 2000

Additional Plots for Non-Standard Mixing CBE 465 Additional Plots for Non-Standard Mixing 4/19/2017 N.P. Cheremisinoff, Handbook of Chemical Processing Equipment, B-H, 2000

Additional Plots for Non-Standard Mixing CBE 465 Additional Plots for Non-Standard Mixing 4/19/2017 N.P. Cheremisinoff, Handbook of Chemical Processing Equipment, B-H, 2000

Heuristics in Mixing CBE 465 4/19/2017 http://www.em.doe.gov/PDFS/Slurry%20Handling%20Workshop/2-Short%20Course%20Art%20Etchells/2-2%20DOEM4M5%20Slurry%20Handling%20Course_Part%202_Art%20Etchells_Dec31'07.pdf

CBE 465 Heuristics in Mixing 4/19/2017 Colson and Richardson.

CBE 465 In-Class PS Exercise 4/19/2017 A pilot-plant vessel that is 0.3 m in diameter is agitated by a six-bladed turbine impeller (Rushton) that is 0.1 m in diameter. With the impeller NRe at 104, the blending time of two miscible liquids is found to be 15 s. The power per unit volume is 0.4 kW/m3. The mixing vessel is to be scaled-up to a vessel diameter of 1.8 m. Assume that the new vessel is geometrically similar to the pilot-plant vessel. You may assume the NRe in the larger vessel is still 104 or larger. For the scaled-up vessel, what is the power/volume required to keep the blending time the same (15 s)? Comment on your results. For the scale-up, assume that the power/volume required is kept the same as the pilot-plant vessel. What will be the new blending time in the larger tank?

CBE 465 4/19/2017 Heuristics Questions?