Viscosity correction

The equations presented herein do not include any viscosity correction to reflect the difference between the viscosity at the wall temperature and the bulk fluid temperature. This effect is generally negligible, except at low temperatures for organic fluids having viscosities that are strongly temperature dependent. For such conditions, the values tabulated in Table 2 should be appropriately modified. 

The chart given in Figure 16 can be used in the following manner in order to size a relief valve for liquid service. First, determine the area required, A, without any viscosity correction (i.e., for K = 1). Then select the next larger standard orifice size from manufacturer s literature. Determine the Reynolds number, based on the following definition ... 

Nolo that a preliminary orifice size must be determined in order to calculate Reynolds number. If the viscosity correction is significant, it may be necessary to iterate to get a final size. 

Viscosity correction for head, to convert to water performance... 

Correlating factor for viscous flow power, Table 5-1 Mixing factors, turbulent flow power. Table 5-1 Viscosity correction factor for turbulent How (static mixer)... 

To apply the viscosity correction K, a preliminary or trial calculation should be made for the areas required using the equation of paragraph (e) above or the modified equation (still ASME conformance [33] but not... 

Since the viscosity correction factor is dependent upon the actual orifice area, direct solution is not possible and a trial orifice size must be found before Ihe Ku can be determined accurately. 

Select Ihe next larger orifice size, or an M" orifice with 360 sq in. orifice area. (This should be about 20% greater than the calculated area to allow lor reduction of capacity due to Ihe viscosity correction factor "Ku")... 

Figure 7-23. Liquids viscosity correction using chart method for Kp. By permission, Teledyne Farris Engineering Co.

Viscosity Correction Using Reynold s Number Method of API RP520... 

Ky = liquid viscosity correction factor (see Figures 7-23 or Figure 7-24). 

A viscosity correction should be made if hl > 10.0 cp by multiplying the % flood obtained from Equations 9-72 through 9-73A by the term in cp. 

Note This has the viscosity correction included. A correction multiplier must he used to correct the results of Figure 10-62 for tubes different than /g-in. O.D. 

Figure32.26 Viscosity correction curves (adapted from Hydraulic Institute Standards, 12th edition, Flydraulic Institute, Cleveland, Ohio, 1969)...

Unless specifically identified otherwise, the BHP values read from a manufacturers performance curve represent the power only for handling a fluid of viscosity about the same as water and a specific gravity the same as water, i.e., SpGr = LG. To obtain actual horsepower for liquids of specific gravity other than 1.0, the curve values must be multiplied by the gravity referenced to water. Viscosity corrections are discussed in another section. Good design must allow for variations in these physical properties. 

Turbine type performance, 178 Vertical in-line, 165, 175 Vertical multistage, 168 Vertical propeller, 169 Viscosity correction, 203-207 Pumps classes, 161... 

Effects of performance changes, 201-203 Head curve for single pump, 198 Relations between head, horsepower, capacity and speed, 200 Temperature rise 207-209 Viscosity corrections, 203-207 Purging, flare stack systems, 535 Reciprocating pumps, 215—219 Flow patterns, 219 Specification form, 219 Relief areas, 437 External fires, 451, 453 Sizing, 434, 436... 

External fires, 450 Unwetted gas only vessels, fire, 454 Viscosity correction, centrifugal pumps, 203-207... 

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