Abstract:
A concentrated slurry comprises a high molecular weight polymer, a carrier, a wetting agent, and dispersant. The slurry is characterized by its ability to reduce turbulent flow and skin friction thereby reducing drag of a vessel when the slurry is mixed with water and dispersed in a thin sheet along the surface of a vessel.

Description:
The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
    
    
     This is a continuation-in-part of application Ser. No. 184,995 filed 30 Sep. 1971 for a &#34;High Concentration Slurry-Formulation and Application.&#34; (pending) 
    
    
     BACKGROUND OF THE INVENTION 
     The efficiency of a vessel through a fluid medium, such as a boat through water, is inversely related to the rate of fluid flow. Highest efficiencies are attained where the boundary layer is laminar, efficiency and speed being known to deteriorate when the boundary layer ceases to be laminar and becomes turbulent. 
     A great many attempts to solve this problem have utilized specialized shaping of the vehicle structure such as slots and circulation control jets. In addition, various attempts have been made to reduce drag by the addition of a high molecular weight polymer. However, no polymer has been developed which is capable of attainin the drag reduction efficiencies of this invention. 
     SUMMARY 
     The slurry mix comprises a high molecular weight polymer such as polyacrylamide, vegetable gums or polyethylene oxide, of a high molecular weight ranging from one to fifteen million, a surfactant or wetting agent, a carrier such as polyhydric alcohol and a dispersing agent such as polarized montmorillonite clay. 
     This resulting mixture possesses a high polymer to carrier weight ratio with a viscosity such that the mixture which can be moved readily through piping and fittings without plugging. The mixture is maintained in a vessel in a concentration of 30% -54% and is dispersed by admitting seawater under low pressure. The concentrated slurry is then moved along piping under metered flow conditions to a mixing vessel and there is hydrated with seawater to a lower concentration. The lower concentration is then passed to ejector rings located on the skin surface in areas of potential turbulent flow. Expulsion of the slurry through the rings and along the surface of the vessel maintains the boundary layer flow laminar and prevents flow transition from laminar to turbulent. The vessel can thereby maintain speed and efficiency in its movement through the fluid. 
     Among the advantages of the slurry is its storage capability. It can be stored for a period of time in conventional storage tanks aboard a surface or under-sea craft and dispersed as needed. Tanks can then be refilled by pumping new material into the storage tanks. 
    
    
     DESCRIPTION OF THE DRAWING 
     The FIGURE shows the percent drag reduction attained with the slurry. 
    
    
     DESCRIPTION OF THE INVENTION 
     The slurry is comprised of four basic groups of materials in the ranges as listed below. 
     
         ______________________________________Group A)   high molecular weight polymer                         30-54%Group B)   carrier            48-64%Group C)   wetting agent      0.2-2.7%Group D)   dispersant         1.3-5%______________________________________ 
    
     A. High molecular weight polymer. 
     Any high molecular weight polymer having a weight in the range of one to fifteen million and water soluble may be used in the range of 30 to 54%. Polymers such as vegetable gums, polyethylene oxide and polyacrylamide may be used. Examples of vegetable gums are carrageenin, gar gum and gum ocra. 
     The polymers used in accordance with this invention can be selected by evaluating the drag reducing performance of an aqueous resin solution of both the resin (dissolved in water) and of the slurry formulation containing the candidate polymer. Drag reduction takes place when the polymer reduces turbulent flow and induces laminar flow. The phenomenon may be caused by the elasticity of the polymer molecule. 
     Two laboratory methods of determining drag reducing performance have been used. They are: the use of a rheometer, and the use of a piping system equipped with pressure gages along the pipe. Each method measures drag reduction by observing the pressure drop in a fluid flowing through the tube or pipe. The more turbulent the flow, the greater the pressure drop. There is a correlation between fluid flow in pipes and fluid flow around the boundary layer of an object. Therefore, the polymer candidates that cause desirable levels of laminar (non-turbulent) flow will be selected for use in operational slurry formulations to enhance laminar flow of fluids in the boundary layer of sea going vessels. Of course, further testing does take place by field use of the slurry. 
     This experimental technique is necessary for polymer selection since the reasons a polymer acts as a drag reducing agent are not clearly understood at this time. 
     B. Carrier. 
     Carrier liquids which may be used together with the high molecular weight polymer are propylene carbonate, tetrahydrofuryl alcohol, methoxy-triglycol, polypropylene glycol with a molecular weight of 425 , butoxy ethoxytriglycol, 1-butoxyethoxy-2-propanol, ethyleneglycol diacetate and triacetin. 
     The following parameters are critical to the selection of a carrier vehicle: 
     (a) does not dissolve the polymer; 
     (b) does not react chemically with the polymer; 
     (c) high flash point; 
     (d) low freezing point; 
     (e) highly soluble in water; 
     (f) storable for a long period of time 
     with the polymer without changing consistency or state, i.e., it does not form gelatinous rubbery masses; and, 
     (g) low toxicity in both concentrated and diluted form. 
     C. Wetting Agent. 
     A surfactant having a high molecular weight may be satisfactorily used within the slurry. Such surfactants are: hydrocarbon oxide, salts of high molecular weight alcohols and alkyl phenyl hydroxy polyoxyethylene. 
     D. A dispersant. 
     Dispersants which are organic derivatives of montmorillonite clay (Bentone 27, 38) or fumed silica such as Cabosil M5 or H5 may be used. 
     A typical 40% slurry system is composed of 40% of a high molecular weight polymer, 55.40% polyhydric alcohol, 2.63% of a 22 carbon fatty amide and 1.97% of polarized montmorillonite clay. 
     The solid material is ballmilled until a particle size of 44.5 microns is attained, equivalent to a rating greater than 4.5 on the Heg man scale. 
     In mixing, the dispersant and surfactant are mixed together with the carrier and mixed at high speed until a gel develops. The polymer is then added in increments and homogenized. 
     The slurry may be stored until ready to use. In the case of storage in a vessel the slurry may be displaced by admitting low pressure seawater to the slurry tank. The slurry subjected to this low pressure is fed through a mixing chamber where it is diluted to a low concentration suitable for its intended use. The slurry may be ejected by a number of different methods, a suitable method being through a series of ports shaped so that the slurry is ejected in a thin sheet along the surface of a vessel. 
     Referring now to the FIGURE, the effectiveness of the slurry in reducing drag is shown with various concentrations of the slurry. The slurry represented in the FIGURE is composed of 39.7% high molecular weight polymer 56.2% polyhydric alcohol, 2.63% 22 carbon fatty amide, and 1.3% of polarized montmorillonite clay. The slurry may be prepared by combining 750 grams of polymer to 732 grams of carrier with 8.0 grams of surfactant and 10 grams of dispersant (7.0 gms of Cabosil and 3.0 gins of Bentone). 
     For a concentration of 10 ppm of slurry to seawater, the percent of drag reduction realized in tests was 30%. The effectiveness of the slurry is most pronounced in the range between 1 and 10 parts per million with ratio of drag reduction to concentration being 3%/ppm, linearly approximated from the curve shown in the FIGURE. 
     Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.