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.