Viscosity Profile: it is important to understand the viscosity profile, specifically the maximum, as viscosity may change during the mixing cycle. This additional engineering effort exacerbates upfront development costs and time to the mixer selection and fabrication process, increasing costs for users. Manufacturers must ensure the drive components and agitators are properly designed to ensure safe and continuous operations. These mixers endure a great deal of mechanical stress during operation, and must be engineered to withstand these forces. Scalability: scale-up from the lab to production is more difficult with high viscosity materials. To achieve the requisite homogeneity, some manufacturers add viscous ingredients more slowly or stop the mixing operation to manually mix the material within the tank– both of which significantly lengthen cycle times and risk low quality results. This is a big problem for some manufacturers, specifically within the pharmaceutical industry, that relies on uniform dispersion of the Active Pharmaceutical Ingredients (API) throughout the product. Due to their resistance to flow, viscous mixes are at risk of localized mixing near and around the impeller, causing “dead spots” within the tank where minimal mixing occurs. Cycle Times: as previously noted, it is challenging to achieve uniformity with viscous materials. To manage this issue, some companies utilize additional heat exchange equipment and temperature controls. Additionally, the large amount of energy created by the impeller does not dissipate well in viscous materials and can result in heat build-up. Larger horsepower motors may be used in these cases but the energy efficiency declines significantly, driving up operating costs. Unfortunately, the viscosity sometimes reaches a point where the mixing motor starts to overload. Energy Consumption and Heat Generation: it is no surprise that more energy is required to mix viscous ingredients that tend to be thick and heavy. Many manufacturers have to slow down the mixing cycle to avoid high shear stresses and preserve particle integrity (and protect equipment) – resulting in longer cycle times. In general, the more rapidly the blade moves through the vessel, the more shear. Shear is exacerbated by the movement of any agitator through the materials. Particle structures may be torn, broken, or severed and the overall particle size in the mix may decrease. These are called shear forces and can result in damage to individual particles. High Shear: when high viscosity fluids are mixed, stress and friction are created among the particles as they move. Below are some principles of mixing high viscosity materials that should be considered when working with viscous ingredients. For this reason, high viscosity materials are some of the most difficult ingredients to mix effectively and present unique challenges during mixing, particularly byproducts of high shear such as heat and material damage, higher power consumption, and equipment stress and wear. Turbulent flow is directly dependent on the fluid viscosity: the higher the viscosity, the more challenging it is to achieve turbulent flow. 
When it comes to mixing, turbulent flow is desired within the mixing vessel to create ideal mixing conditions. Some highly viscous materials have a viscosity of hundreds of millions centipoise. For comparison, water has a viscosity of 1 cP while honey has a viscosity ranging from 2,000 to 10,000 cP. Low viscosity materials, such as water, have a lower resistance and flow more rapidly whereas high viscosity materials, such as honey or tar, resist deformation and flow more slowly. Viscosity is a measure of how resistant a fluid is to flow and is measured in centipoise (cP).
Viscosity is one of the properties that influences how easily a mixture can achieve homogeneity. The time it takes for the liquid to travel from Mark 2 to Mark 1 is used to compute the viscosity.Homogeneity of the final blend is a critical aspect of mixing as uniformity impacts the final product in many ways such as stability and durability. The liquid is then drawn up through the opposite side of the tube. \) The capillary, submerged in an isothermal bath, is filled until the liquid lies at Mark 3.
0 kommentar(er)
