High viscosity fluids

Commonly used heat-transfer surfaces are internal coils and external jackets. Coils are particularly suitable for low viscosity Hquids in combination with turbine impellers, but are unsuitable with process Hquids that foul. Jackets are more effective when using close-clearance impellers for high viscosity fluids. For jacketed vessels, wall baffles should be used with turbines if the fluid viscosity is less than 5 Pa-s (50 P). For vessels equipped with cods, wall baffles should be used if the clear space between turns is at least twice the outside diameter of the cod tubing and the fluid viscosity is less than 1 Pa-s (10... 

Bismaleimide Resins via EI E Reaction. The copolymerization of a BMI with o,o -diallylbisphenol A [1745-89-7] (DABA) is a resia coacept that has beea widely accepted by the iadustry because BMI—DABA bleads are tacky soHds at room temperature and therefore provide all the desired properties ia prepregs, such as drape and tack, similar to epoxies. Crystalline BMI can easily be blended with DABA, which is a high viscosity fluid at room temperature. Upon heating BMI—DABA blends copolymerize via complex ENE and Diels-Alder reactions as outlined ia Eigure 8. 

In the case of particulate fouling, one of the more common types, insuring a sufficient flow velocity and minimizing areas of lower velocities and stagnant flows to help keep particles in suspension is the most common means of deahng with the problem. For water, the recommended tubeside minimum velocity is about 0.9 to 1.0 m/s. This may not always be possible for moderate to high-viscosity fluids where the resulting pressure drop can be prohibitive. 

Scraped-surface exchangers are particularly suitable for heat transfer with crystalhzation, heat transfer with severe folding of surfaces, heat transfer with solvent extraction, and heat transfer of high-viscosity fluids. They are extensively used in paraffin-wax plants and in petrochemical plants for ciystallization. 

In the deaeration of high-viscosity fluids such as polymers, the material is flowed in thin sheets along solid surfaces. Vacuum is apphed to increase bubble size and hasten separation. The Versator (Cornell Machine Co.) degasses viscous liquids by spreading them... 

For an incompressible fluid, the density variation with temperature is negligible compared to the viscosity variation. Hence, the viscosity variation is a function of temperature only and can be a cause of radical transformation of flow and transition from stable flow to the oscillatory regime. The critical Reynolds number also depends significantly on the specific heat, Prandtl number and micro-channel radius. For flow of high-viscosity fluids in micro-channels of tq < 10 m the critical Reynolds number is less than 2,300. In this case the oscillatory regime occurs at values of Re < 2,300. 

W. M. Harms. Catalyst for breaker system for high viscosity fluids. Patent US 5143157,1992. 

Thermosyphon reboilers are the most economical type for most applications, but are not suitable for high viscosity fluids or high vacuum operation. They would not normally be specified for pressures below 0.3 bar. A disadvantage of this type is that the column base must be elevated to provide the hydrostatic head required for the thermosyphon effect. This will increase the cost of the column supporting-structure. Horizontal reboilers require less headroom than vertical, but have more complex pipework. Horizontal exchangers are more easily maintained than vertical, as tube bundle can be more easily withdrawn. 

Diaphragm pumps are used for metering small amounts of additive into a fuel or fuel oil. The cost of these pumps is low compared to other positive displacement pumps. These pumps are excellent metering pumps and are primarily designed for low-pressure, low-flow applications. Also, they are not recommended for pumping high-viscosity fluids. 

However, the viscosity at which this transition takes place cannot easily be calculated because many high jyiscosity fluids are non-Newtonian. This means that the viscosity varies according to the rate at which the fluid is flowing. It is therefore best to carry out a small-scale test in order to determine whether or not flow will be laminar. A possible test method is given in A2.3.3. Chapter 10 gives more information on high viscosity fluids. 

Bell, S D Morris R Oster, "Vent Line Void Fractions And Mass Flow Rates During Top Venting Of High Viscosity Fluids , J Loss Prev Process Ind, Vol 6, No1,31-35,1993... 

S D Morris, Bell R Oster, "Top-Venting Of Flashing High-Viscosity Fluids", Chemical Engineering Processing, 31, 297-305, 1992... 

High viscosity fluids may behave in a number of different ways ... 

The characterisation of the viscosity is difficult for non-Newtonian fluids because the viscosity changes as a result of the flow process, which increases the shear rate. This is further complicated for two-phase fluids because the presence of bubbles will also affect the viscosity. The simpler methods to obtain G for high viscosity fluids make the simplifying assumptions that the fluid viscosity is equal to the liquid viscosity and that the fluid is Newtonian. 

Considerable work has been. done at JRC Ispra to visualise level swell for viscous fluids17,8,91. This indicates that t moderate viscosity (around. 100 cP) foaming behaviour of the. fluid (if it occurs) dominates viscous effects. Many high viscosity fluids are foamy because they are not pure fluids. At higher viscosities, approaching 1000 cP, there appears to be much less foaming and the flow characteristics are dominated by. viscous effects. 

For low-speed flow of gases viscous dissipation is rarely important. However, in highspeed flows, where the velocities increase toward the sound speed, and in supersonic flows, viscous dissipation is important. Also for the flow of high viscosity fluids, like oils in a journal bearing, viscous dissipation must be considered. 

For high-viscosity fluids (e.g., oils), high rod velocities, or small gaps, the thermal energy generation by viscous dissipation may be important. In this case the steady-state, incompressible, thermal energy equation reduces to... 

LAMINAR FLOW. A condition of fluid flow in a closed conduit in which the fluid panicles or "streams tend to move parallel to the flow axis and not mix. This behavior is characteristic of low flow rates and high viscosity fluid flows. As the flow rate increases (or viscosity significantly decreasesi. the streams continue to flow parallel until a velocity is reached where the streams waver and suddenly break into a diffused pattern. This point is called the critical velocity. See also Turbulent Flow. 

Positive displacement Liquids only 20 (See Volume 1, Section 6.3.9) Hydrocarbon liquids, glues, food products (jams, chocolate, etc.) Suitable for high viscosity fluids. High accuracy and wide range... 

These are low-speed stirrers and generally have diameters in the range dr/dt — 1.5-2. For low-viscosity fluids, stirrers are used with baffles, and for high-viscosity fluids, they can be used without baffles. These stirrers are especially suited for liquid homogenization. 

The volumetric gas-liquid mass transfer coefficient, khaL, largely depends on power per unit volume, gas velocity (for a gassed system), and the physical properties of the fluids. For high-viscosity fluids, kLaL is a strong function of liquid viscosity, and for low-viscosity fluids (fi < 50 mPa s), kLaL depends on the coalescence nature of the bubbles. In the aeration of low-viscosity, pure liquids such as water, methanol, or acetone, a stable bubble diameter of 3-5 mm results, irrespective of the type of the gas distributor. This state is reached immediately after the tiny primary bubbles leave the area of high shear forces. The generation of fine primary gas bubbles in pure liquids is therefore uneconomical. 

Estimate viscous power number for the helix impeller. A helical-ribbon impeller, also called a helix impeller, is used primarily when high-viscosity fluids are being processed. Most of the power data on such impellers have been obtained in the laminar and transitional flow ranges. The effect on power of common geometry factors, i.e., impeller diameter D, tank diameter T, helix pitch P, impeller height H, and helix (blade) width W, can be incorporated into a correlation for a (dimensionless) viscous power number ... 

Thus, a properly instrumented reactor may be used as a viscometer for high-viscosity fluids. 

For high-viscosity fluids, the critical Weber nvunber [3] is corrected as foUows ... 

---