Monster Media 1996 #14/Monster Media No. 14 (April 1996) (Monster Media, Inc.).ISO/business/mixing10.zip/MIXER.TXT

Text File | 1992-01-03 | 25KB | 557 lines

                        MIXER DESIGN

            LIQUID BLENDING PROGRAM INSTRUCTIONS




The program disks contain the Liquid Blending program, the Gas
Mixing program, 6 example problems for the blending program, and 3
example problem for the gas mixing program.  You should review the
example problems to examine the various features of this program.

The disk is not copy protected and you can install it easily on
your hard disk by following the normal DOS procedures.  It is
important to copy all of the programs on the disk that is
compatible with your monitor to your hard disk's subdirectory or to
use the original disk since the MIXER program is designed to use
screens that have been saved on the disk.

The purchaser of the commercial version of the mixer program is
entitled to use it on one Computer.   Additional --Legal -- copies
of this program can be obtained from Alchemy Systems for an
additional $200 dollars if you wish to expand your companies use of
this program.

                        HOW TO START

After the programs have been transferred to an appropriate
subdirectory on your hard disk the  mixer program is activated by
going to this subdirectory and giving the command MIXER.

The Mixer program features a Main Menu that addresses the
Subprograms that permit the entry of data and calculate the
requirements of the Vessel, Agitator, and Shaft design.  The
Subprograms feature a command line that allows you to alter the
data and perform alternate case analyses.

Data entry is simplified by the use of pop up windows that prompt
for data and present default values for the design.

These default values can be accepted by pressing the return key and
enable the user to select industrial standards in their design
comparisons.








                          MAIN MENU


The Main Menu of the blending program offers choice of several
subprograms.  These subprograms are addressed by entering the first
key of the command word on the menu.  For example, to call up the
Vessel input routine just press the letter V followed by a the
return key.

The disk functions Load, Save, and Index allow you to save and
retrieve problems to the disk.  These disk functions permit the use
of Path instructions so that you can use other drives or
subdirectories to store the problems.
The Function called New case will wipe out an existing problem set
from memory and allow the input of a new problem from scratch.

The Function Quit will quit the program and return to DOS.

The Subprogram Vessel allows the input of the mixer vessel data and
does sizing calculations.

The Subprogram Fluids permits the properties of the bulk and
disperse fluids to be entered and the mixture properties are
calculated.

The Subprogram Agitator calculates the power requirements and
flow properties of seven different types of agitators and
calculates heat transfer coefficients.

The subprogram Diameter shaft will estimate the required diameter
of the mixer shaft with and without a bottom steady bearing.  It
performs this by calculating the critical speed of the shaft and
agitators.

                       DISK  FUNCTIONS

DIRECTORY   This command allows you to change the directory or disk
that is used to save the mixer design problem files. When this
command is activated, a window pops up that gives the present
subdirectory you are working in.  If no changes are desired then
press the return key to cancel the command.
You can use change the default directory to save or load your files
from a floppy disk by giving the command A: or B: and then pressing
the enter key.  You can also switch to a new sub directory by
entering the DOS path name of the directory.  The sub directory
must however exist before you call it otherwise and error will
occur.

LOAD   will retrieve a previously saved mixing problem from the
disk.  When you select this command, A directory of all the saved
files on the default drive with the extension MIX is given to help
you select the correct file.  You select the file to load by using
the arrow key to move the colored cursor to the file and then press
the enter key.

SAVE   will save the program input data to disk.  A window will pop
up that requests the name of the file to be saved.  Enter up to 8
letters for the name.  Do NOT add the period or the extension MIX
to the file name.  This is done automatically by the program.
Saving two program with the same name to a disk will replace the
old program with the new one.

NEW CASE   The NEW command will erase any existing data from memory
and allow you to start from scratch with new input.
It is used if you were previously working with a problem that had
been loaded in from the disk and wish to start over with a new
problem.  You should save the previous problem before you press
this key since it will wipe out all data in memory.

                   INPUT NEW PROBLEM DATA

Either the Vessel or Fluid command should be used first when
inputting data on a new problem.  If the Fluid program is used
first then the total volume of the combined mixture fluids will be
printed on the vessel program screen.  If the Vessel program is
used first then the volume of the vessel will be given on the Fluid
data entry screen to aid in selecting the correct values.


                        FLUID PROGRAM

FLUID   will call up a screen to enter the volume and physical
properties of the two fluids to be mixed.  You will be asked to
enter the volume, density, viscosity, heat capacity, and thermal
conductivity of the Bulk and the Disperse Fluids.  Enter the data
in English units as requested by the program.  The density can
however be entered in either Lb/Ft3 or as Specific gravity.

If you just press return, when adding the Disperse Fluid the data
will default to zero volume with the same properties as the Bulk
Fluid.

The Mixture properties of the Bulk and Disperse Fluids are
automatically calculated, after the Bulk and Disperse Fluid
properties have been added.  After data entry, you may go back and
correct the data or print the data by using the Command line.
Press B or D to change the Bulk or Disperse fluid properties, press
P to print the fluid data.  Pressing A for Accept will return you
to the Main menu.

The viscosity of the blend mixture is calculated by a computer
algorithm based upon the ASTM liquid viscosity blending charts.
The other properties are calculated by simple weight averages.

                    VESSEL SIZING PROGRAM

VESSEL   will permit you to rate or design the Mixer vessel. For
new problem input, It first prompts you for a Title to describe the
problem.  A description name can be entered of up to 80 characters.

The total volume of the liquid to be mixed will be displayed if the
Fluid program has been previously run.
After you have given the Case name, you are directed by the program
to select the values to Design the vessel.
First you are requested for the Design pressure in Psig.  Next the
total gallons and the vessel length/diameter ratio is requested.
A Window will pop up to help you select the vessel head.  Your
Choices are Flat bottom, ASME F&D, 2/1 Elliptical, and
Hemispherical.  Finally you are requested to confirm or input the
values to use for Stress , Weld efficiency, and corrosion allowance
for calculating the thickness and weight of the vessel.
The Default values can be chosen by pressing the return key.

You have now inputted all the values and the program will calculate
the vessels diameter and length. as well as  The surface area of
the vessel, The vessels volume in Cu.Ft and gallons.
The liquid height in the vessel is given in inches on the straight
side.  If the vessel is too small or the liquid height exceeds the
vessel straight side for the liquid given previously a value of
10000 is given.
The program also calculates the vessel shell thickness and the
vessel weights, and the width and offset of the recommended
baffles.  Note the program assumes the use of 4 baffles in all
cases.

The command line on the bottom of the screen  will allow you to run
case studies on this vessel.  The options are Accept, Rating,
Design, Weight, CaseName and Print.  Press the first key of the
command word to select the appropriate alternative.

RATING   The program will allow you to rate the vessel by pressing
the key R for Rate.  You then supply the Diameter, Length
(straight-side).  and the type of vessel head. The program then
calculates the volumes, CSA, and surface area of the mixer vessel.
The recommended baffle size and offset from the wall is also
calculated as well as the straight side liquid height.
Three types of head can be specified, Flat, ASTM dished, and 2-1
Elliptical.  The use of Elliptical heads is recommend for high
pressures.


DESIGN   If you press the key D for Design  you will repeat the
procedure for initial input of vessel data.

WEIGHT   If you press the key W for weight; you can change the
default values used for Stress, welding efficiency and corrosion
allowance.

The weight of the vessel is only  approximate since the weight of
Nozzles Flanges etc. can affect the weight.  The shell and head
thicknesses are also approximate and the final values selected must
be determined by a qualified vessel engineer.  They are provided
only for estimating purposes.

PRINT   The key P will print the Vessel screen to your printer.

ACCEPT  The key A will return you to the main menu.  If you return
to the vessel screen from the main menu,  it will display your
previously inputted data and default to the Command line on the
bottom of the screen.  If you had loaded in a previously saved
problem from the disk, all the screens will be active and display
the data loaded when you call up the subprogram.

                     AGITATOR DESIGN PROGRAM

The Agitator program can only be run after the vessel and fluid
data have been inputted or if an existing program has been loaded
from the disk.

The program will start out by prompting you for the type of
agitator to be used.  There are seven choices.  You may choose
between Pitched Blade or Axial turbines, Propeller, Flat Blade,
Disk, Retreat Blade { Pfaudler Type } Anchor and Double Helix
agitators.

The Axial turbine option refers to conventional pitch blade turbine
with 45 degree angle blades.  Four blades are normally used.

The new Hydrodynamic axial turbines can be approximated by
selecting the propeller option with a pitch of 1.25.  The flow and
BHP obtained will be sufficiently close for estimation purposes.
However the final design of these turbines must be left to the
agitator vendor since they are a very specialized design.

The propeller design option allows the specification of different
degrees of pitch.

Flat Blade and Disk turbines refer to conventional Radial flow
turbines.  The Disk type has a center disk to aid in dispersing gas
or immiscible fluids to the blades.

The Retreat Blade selection is based upon a 3 blade impeller.  This
selection should closely approximated the performance of the
Pfaudler type impeller with two finger Baffles.

The Anchor Agitator assumes that the diameter of the agitator is
0.90 the vessel diameter.  You will be asked to specify the height
/ diameter ratio of the agitator.

The Helix agitator is based upon the double ribbon type design as
described in Nagata'.  There are two ribbon blades with a standard
diameter of 0.95 of the vessel diameter.  The Blade width is 0.1
the diameter.  The program will prompt for the Screw pitch to use
in the Helix agitator design.
The selection of the Axial, or Radial type of impellers will result
in the program requesting additional information to describe the
impeller.
The Number of blades on the impeller is requested in a pop up
screen.  The standard number for an axial turbine is 4 blades.  The
standard number for a Radial ie. Flat or Disk type  is 6 blades.
You will also be requested for the width to diameter ratio of the
turbine blades.  The default value provided is 0.2.  You can change
this if desired.  Width to diameter ratio down to 0.125 are used
for high shear applications.  This only pertains to radial flow
type impellers.  High Shear is intensified by the use of narrow
blade widths. There is no value in selecting blade widths greater
than 0.2.  The user should generally accept the default values
unless you wish to develop a non-standard design for special
purposes.

Default values are supplied for all values requested.  Just press
the return key to accept these default values.  The Default values
are the most commonly used dimensions for the type of agitator
selected, and I suggest you accept them for your initial design
calculations.

After the type of agitator is selected, the program will prompt for
information on the number of impellers,and the diameter of the
impeller.

A window will then pop up that will help you to specify the
agitators location in the vessel.  The screen will give the liquid
height, the depth of the heads and will suggest agitator spacing
from the bottom of the vessel.  The spacing for one agitator will
be approximately 1/3 of the liquid depth from the bottom.
You can override these suggestions by inputting new data or accept
them by pressing the return key.
The location of the agitators is use to make a fine correction on
the impellers BHP called the Proximity factor in OldShues Mixing
Technology Book.  Radial turbine will have a reduction in their Bhp
consumption if they are located close to the vessel bottom since
the impeller is starved for liquid flow.  Axial turbines have a
small increase in Bhp due to Back pressure.

The location of the agitators is also used later in the program to
calculate the diameter of the shaft.

After the impeller location data is inputted. the program will
prompt for the RPM to use in the calculations.  A window will pop
up that lists the standard RPM's used by the AGMA (American Gear
Manufactures Association.)  These standard RPM's should generally
be chosen to insure a standard and lower cost design.  Other RPM's
will require special gearing or hydraulic variable speed drives.

Selection of the correct RPM for Helix agitators depends upon the
application.  Generally the Rpm is less that 30 and higher than 5
Rpm.  Helix agitator due to the high viscosities tend to be high
torque devices that operate a low RPM,s.

After all the data is supplied the program calculates the agitators
requirements.   The following data is calculated:

     The impellers diameter to tank diameter ratio.
     The mixing Reynolds Number.
     The Prandel Number used in the heat transfer calculations.
     The agitators Power number. Np
     The impellers Flow number Nq.
     The Proximity correction factor for the Btm Agitator
     The Average Proximity Factor
     The Tip Speed of the turbine.
     The Maximum Shear and average Shear for radial Turbines.
     The Discharge Flow of one impeller.
     The vertical velocity in the tank of the fluid.
     The Blend Time and Turnover Time.
     The Impeller Bhp for the total number of agitator selected is
     calculated with and without the proximity factor correction.
     If 4 agitators were selected then this value  will be the sum
     for all 4 impellers.
     The Torque of the impeller is calculated in Ft-Lbs. Torque is
     based upon the uncorrected impeller BHP.
     The BHP/ 1000 gallons is calculated for convenience.
     The Standard Motor is selected for the impeller BHP
     requirement.  This assumes a value of 0.9 for the motor
     efficiency and gear losses.

                          Heat Transfer

     The Heat transfer coefficients are generated for the Jacket
     and for coils. The heat transfer coefficients are developed
     for a viscosity correction of 1 and for typical heating and
     cooling viscosity corrections.  The coefficients are based
     upon the outside surface area for the coils.  The U values for
     cooling water and for steam are estimates that are based upon
     a water velocity of 6 ft/sec for water and an inside
     coefficient of 1500 for steam.  A fouling factor of 0.003 is
     also applied.


     The jacket heat transfer coefficient is based upon the
     following equation with no viscosity correction:


(HjT/k) = 0.85(Nre)**0.66*(Npr)**0.33(Z/T)**-0.56 X
     (D/T)**0.13  for a viscosity correction of one.




All values calculated assume that the tank is fully baffled with 4
baffles of the size given in the Vessel program. or assumes that
gravitational effects are not significant as in high viscosity
service.

The command line on the bottom of the screen will allow you to
perform case studies to explore the effect of different RPM or
impeller diameters on the mixer results.

Press the first letter of the command line to redo selected data
input.
The letter T will allow you to change the type of agitator.  This
results in a complete data input.
Selecting N for Number will allow you to change the number of
impellers of the same type and to change the location of the
agitators.
D will redo the calculations with a different diameter.
R will allow you to change the RPM of the agitator.
The Letter P will print the screen to your printer.
A for Accept will return you to the main menu.

                    SHAFT DIAMETER SIZING

The Shaft Diameter program selected by pressing D from the main
menu will calculate the diameter of the shaft and the critical
speed for top supported and shafts with bottom steady bearings.
This program is not accurate for double helix or Anchor agitator
but can be used for pitched blade, Flat Blade or Disk turbines.  It
cannot be run unless the Agitator program has been run first.  The
shaft diameter program will generally oversize the diameter for low
power propeller applications since the damping effect of the liquid
is not considered in suppressing vibration.

The shaft diameter sizing program requires input on the location of
the agitators.  This data was inputted during the agitator program.
But the location of the agitators can be changed by typing R from
the command line.  The program gives the distances from the top of
the upper support to the various agitators.  Where Agitator 1 is
the bottom one.

The agitator sizing program must be run first, since the values
required for torque and Bhp are calculated in this step.  The
impeller dimensions and RPM are also determined in this step.

The program calculates the agitator weights including the Hub
weights and the appropriate moments of inertia.






The diameter of a top supported agitator shaft is often determined
by the thickness needed to prevent vibration.
The first critical speed is calculated and the diameter is
increased until the RPM of the agitator is less than 70% of the
critical speed.

The diameter of bottom anchored shafts is usually set by torque
requirements since the critical speed is much higher, however the
critical speed for this case is also calculated and the diameter is
adjusted if required.

The Shaft diameter sizing calculations should be used as a
guideline, but the final selections for shaft sizing should be left
to a qualified vendor since the actual weights of the agitators can
vary as well as the metallurgy used in the shafts.

              GUIDELINES FOR AGITATOR SELECTION

HELIX agitators should only be used for high viscosity applications
with viscosities above 30000 cp.  The program is accurate for
Newtonian Fluids at high viscosity.
It can be used for pseudo plastic fluids through a trial and error
procedure to determine the effect of Shear stress on the Fluid
viscosity.  This procedure is complex but is given in Nagata's book
referenced below.  Visco-Elastic Fluids are nearly impossible to
predict.  Lab data is needed and this program will give optimistic
answers for blend time.  Most polymer systems are pseudo plastic
and are not visco elastic.
If two fluids are to be mixed with greater than three magnitudes of
difference in viscosity a Helix agitator can have major problems.
This typically happens if monomers are added to a polymerization
reactor.  In this case the feed viscosity must be increased by
premixing before adding the feed to the agitator.

The program is based on Double Helix Ribbons.  The customary double
ribbon design uses a pitch of 1 on the blades.  Single Ribbon Helix
agitators with a center screw are an alternate design, they are
usually designed with a pitch of 0.5 and have a somewhat lower
power requirement and somewhat longer blend times.
The result from the Double Helix Ribbon program can be used for
approximate estimates of this alternate design.

ANCHOR agitators are used for heat transfer application in
viscosities from 5000 to 50000 cp.  The supply very little top to
bottom mixing and are of limited use for most applications.







AXIAL flow ie. Pitched blade agitators should be selected for most
other applications; particularly liquid mixing or solids
suspension.  They provide the best mixing for the lowest power.
They can be used over a wide range of viscosities up to 30000 cp.
Impeller diameters should be approximately one third and up to 50
percent of the tank diameter.  Increasing the diameter will lower
the power required for a given mixing requirement but will increase
the Torque.

The new types of Axial Flow turbines (HydroDynamic) that are vendor
specialized items give excellent flow characteristics at lower
power consumptions.  Generally around 1/3 of the conventional 45
degree turbine.  Since the blade characteristics are variable in
pitch as well as diameter and thickness, it is difficult to
generalize.  Selection of a propeller designs with the same
diameter and rpm gives a reasonable approximation for these new
turbines BHP, Flow and heat transfer characteristics.
The Hydrodynamic designs must be used with caution in high
viscosity service.  Be concerned if the viscosity is over 4000.

FLAT Blade and DISK blade turbines are used for applications that
require a high shear or high power input.  Typical examples are
Neutralizers that mix caustic with organics, or Dispersion of a Gas
into the liquid.  They are usually designed with a high tip speed.
Disk turbines are similar to Flat blades, but have a central thin
solid disk to direct flow to the blades.  Thin agitator blades ie
width/diameter impeller ratios of 0.125 are usually preferred to
maximize shear at lower power.  This type of impeller should not be
used for flow specific applications such as liquid blending or
solid suspensions.  The power consumption for the flow achieved is
too high.
PROPELLERS are used for small mixing applications.  They typically
are used in low viscosity service and at high RPM's

                       SOURCES OF DATA

The correlations used in this program were developed from standard
text's and papers.  The user is referred to the following texts to
develop expertise.

     Mixing Principals and Applications by Nagata
     Halsted Press

     Mixing  Vol 1 and 2 by Uhl and Grey
     Academic Press

     Fluid Mixing Technology by Oldshue
     McGraw Hill

     Liquid Agitation by Chemineer
     Chemical Engineering Magazine articles 1976


              CORRELATIONS USED IN THE PROGRAM

The correlations for agitator power for axial flow and flat blade
turbines were developed by curve fits of the data supplied for
power numbers vs. Impeller Reynold's numbers developed by Bates,
Fondy, and Fenic.  See Uhl and Grey Vol 1 page 133, Figure 7.

The correlations for power for Double Helix agitators were based
upon equations given by Nagata in his book referenced above Page
55.

The power numbers vs Nre for Anchor agitators and Propellers were
base on data given by OldShue in his text.

The Flow numbers vs Nre were based on data given in the Chemineer
series.

Mixing time correlations should be used with a degree of
skepticism.  They are based on lab data presented in the above
standard texts from colored dye experiments etc.  A rule of thumb
is that the mixing time varies from 3 to 8 times the time required
to turnover the reactor by top to bottom mixing.  See Nagata page
202 for Helix agitator's,  See Chemineer Articles for Axial Flow
agitator's.  Use the blend time correlations only in a relative
sense to compare different agitators.  Blend time is very difficult
to predict without Lab data.  It is strongly dependent on the
specific gravity differences and the viscosity differences of the
two fluids and the published literature in this area is not
adequate to make accurate predictions.