Packing & demister pressure drop (fluids.packed_tower)

This module contains correlations and functions for calculating pressure drop from packings and demisters; separation efficiency of demisters; demister pressure drop; and demister geometry.

For reporting bugs, adding feature requests, or submitting pull requests, please use the GitHub issue tracker or contact the author at Caleb.Andrew.Bell@gmail.com.

Packing Pressure Drop

fluids.packed_tower.Robbins(L, G, rhol, rhog, mul, H=1.0, Fpd=24.0)

Calculates pressure drop across a packed column, using the Robbins equation.

Pressure drop is given by:

$$\Delta P = C_3 G_f^2 10^{C_4L_f}+0.4[L_f/20000]^{0.1}[C_3G_f^210^{C_4L_f}]^4$$

$$G_f=G[0.075/\rho_g]^{0.5}[F_{pd}/20]^{0.5}=986F_s[F_{pd}/20]^{0.5}$$

$$L_f=L[62.4/\rho_L][F_{pd}/20]^{0.5}\mu^{0.1}$$

$$F_s=V_s\rho_g^{0.5}$$

Parameters

Lfloat

Specific liquid mass flow rate [kg/s/m^2]

Gfloat

Specific gas mass flow rate [kg/s/m^2]

rholfloat

Density of liquid [kg/m^3]

rhogfloat

Density of gas [kg/m^3]

mulfloat

Viscosity of liquid [Pa*s]

Hfloat

Height of packing [m]

Fpdfloat

Robbins packing factor (tabulated for packings) [1/ft]

Returns

dPfloat

Pressure drop across packing [Pa]

Notes

Perry’s displayed equation has a typo in a superscript. This model is based on the example in Perry’s.

References

1

Robbins [Chem. Eng. Progr., p. 87 (May 1991) Improved Pressure Drop Prediction with a New Correlation.

Examples

>>> Robbins(L=12.2, G=2.03, rhol=1000., rhog=1.1853, mul=0.001, H=2.0, Fpd=24.0)
619.6624593438102

fluids.packed_tower.Stichlmair_dry(Vg, rhog, mug, voidage, specific_area, C1, C2, C3, H=1.0)

Calculates dry pressure drop across a packed column, using the Stichlmair [1] correlation. Uses three regressed constants for each type of packing, and voidage and specific area.

Pressure drop is given by:

$$\Delta P_{dry} = \frac{3}{4} f_0 \frac{1-\epsilon}{\epsilon^{4.65}} \rho_G \frac{H}{d_p}V_g^2$$

$$f_0 = \frac{C_1}{Re_g} + \frac{C_2}{Re_g^{0.5}} + C_3$$

$$d_p = \frac{6(1-\epsilon)}{a}$$

Parameters

Vgfloat

Superficial velocity of gas, Q/A [m/s]

rhogfloat

Density of gas [kg/m^3]

mugfloat

Viscosity of gas [Pa*s]

voidagefloat

Voidage of bed of packing material []

specific_areafloat

Specific area of the packing material [m^2/m^3]

C1float

Packing-specific constant []

C2float

Packing-specific constant []

C3float

Packing-specific constant []

Hfloat, optional

Height of packing [m]

Returns

dP_dryfloat

Pressure drop across dry packing [Pa]

Notes

This model is used by most process simulation tools. If H is not provided, it defaults to 1. If Z is not provided, it defaults to 1.

References

1

Stichlmair, J., J. L. Bravo, and J. R. Fair. “General Model for Prediction of Pressure Drop and Capacity of Countercurrent Gas/liquid Packed Columns.” Gas Separation & Purification 3, no. 1 (March 1989): 19-28. doi:10.1016/0950-4214(89)80016-7.

Examples

>>> Stichlmair_dry(Vg=0.4, rhog=5., mug=5E-5, voidage=0.68,
... specific_area=260., C1=32., C2=7.0, C3=1.0)
236.80904286559885

fluids.packed_tower.Stichlmair_wet(Vg, Vl, rhog, rhol, mug, voidage, specific_area, C1, C2, C3, H=1.0)

Calculates dry pressure drop across a packed column, using the Stichlmair [1] correlation. Uses three regressed constants for each type of packing, and voidage and specific area. This model is for irrigated columns only.

Pressure drop is given by:

$$\frac{\Delta P_{irr}}{H} = \frac{\Delta P_{dry}}{H}\left(\frac {1-\epsilon + h_T}{1-\epsilon}\right)^{(2+c)/3} \left(\frac{\epsilon}{\epsilon-h_T}\right)^{4.65}$$

$$h_T = h_0\left[1 + 20\left(\frac{\Delta Pirr}{H\rho_L g}\right)^2\right]$$

$$Fr_L = \frac{V_L^2 a}{g \epsilon^{4.65}}$$

$$h_0 = 0.555 Fr_L^{1/3}$$

$$c = \frac{-C_1/Re_g - C_2/(2Re_g^{0.5})}{f_0}$$

$$\Delta P_{dry} = \frac{3}{4} f_0 \frac{1-\epsilon}{\epsilon^{4.65}} \rho_G \frac{H}{d_p}V_g^2$$

$$f_0 = \frac{C_1}{Re_g} + \frac{C_2}{Re_g^{0.5}} + C_3$$

$$d_p = \frac{6(1-\epsilon)}{a}$$

Parameters

Vgfloat

Superficial velocity of gas, Q/A [m/s]

Vlfloat

Superficial velocity of liquid, Q/A [m/s]

rhogfloat

Density of gas [kg/m^3]

rholfloat

Density of liquid [kg/m^3]

mugfloat

Viscosity of gas [Pa*s]

voidagefloat

Voidage of bed of packing material []

specific_areafloat

Specific area of the packing material [m^2/m^3]

C1float

Packing-specific constant []

C2float

Packing-specific constant []

C3float

Packing-specific constant []

Hfloat, optional

Height of packing [m]

Returns

dPfloat

Pressure drop across irrigated packing [Pa]

Notes

This model is used by most process simulation tools. If H is not provided, it defaults to 1. If Z is not provided, it defaults to 1. A numerical solver is used and needed by this model. Its initial guess is the dry pressure drop. Convergence problems may occur. The model as described in [1] appears to have a typo, and could not match the example. As described in [2], however, the model works.

References

1(1,2,3)

Stichlmair, J., J. L. Bravo, and J. R. Fair. “General Model for Prediction of Pressure Drop and Capacity of Countercurrent Gas/liquid Packed Columns.” Gas Separation & Purification 3, no. 1 (March 1989): 19-28. doi:10.1016/0950-4214(89)80016-7.

2

Piche, Simon R., Faical Larachi, and Bernard P. A. Grandjean. “Improving the Prediction of Irrigated Pressure Drop in Packed Absorption Towers.” The Canadian Journal of Chemical Engineering 79, no. 4 (August 1, 2001): 584-94. doi:10.1002/cjce.5450790417.

Examples

Example is from [1], matches.

>>> Stichlmair_wet(Vg=0.4, Vl = 5E-3, rhog=5., rhol=1200., mug=5E-5,
... voidage=0.68, specific_area=260., C1=32., C2=7., C3=1.)
539.876823725352

Packing Flooding

fluids.packed_tower.Stichlmair_flood(Vl, rhog, rhol, mug, voidage, specific_area, C1, C2, C3, H=1.0)

Calculates gas rate for flooding of a packed column, using the Stichlmair [1] correlation. Uses three regressed constants for each type of packing, and voidage and specific area.

Pressure drop is given by:

$$\frac{\Delta P_{irr}}{H} = \frac{\Delta P_{dry}}{H}\left(\frac {1-\epsilon + h_T}{1-\epsilon}\right)^{(2+c)/3} \left(\frac{\epsilon}{\epsilon-h_T}\right)^{4.65}$$

$$h_T = h_0\left[1 + 20\left(\frac{\Delta Pirr}{H\rho_L g}\right)^2\right]$$

$$Fr_L = \frac{V_L^2 a}{g \epsilon^{4.65}}$$

$$h_0 = 0.555 Fr_L^{1/3}$$

$$c = \frac{-C_1/Re_g - C_2/(2Re_g^{0.5})}{f_0}$$

$$\Delta P_{dry} = \frac{3}{4} f_0 \frac{1-\epsilon}{\epsilon^{4.65}} \rho_G \frac{H}{d_p}V_g^2$$

$$f_0 = \frac{C_1}{Re_g} + \frac{C_2}{Re_g^{0.5}} + C_3$$

$$d_p = \frac{6(1-\epsilon)}{a}$$

Parameters

Vlfloat

Superficial velocity of liquid, Q/A [m/s]

rhogfloat

Density of gas [kg/m^3]

rholfloat

Density of liquid [kg/m^3]

mugfloat

Viscosity of gas [Pa*s]

voidagefloat

Voidage of bed of packing material []

specific_areafloat

Specific area of the packing material [m^2/m^3]

C1float

Packing-specific constant []

C2float

Packing-specific constant []

C3float

Packing-specific constant []

Hfloat, optional

Height of packing [m]

Returns

Vgfloat

Superficial velocity of gas, Q/A [m/s]

Notes

A numerical solver is used to solve this model.

References

1(1,2)

Stichlmair, J., J. L. Bravo, and J. R. Fair. “General Model for Prediction of Pressure Drop and Capacity of Countercurrent Gas/liquid Packed Columns.” Gas Separation & Purification 3, no. 1 (March 1989): 19-28. doi:10.1016/0950-4214(89)80016-7.

Examples

Example is from [1], matches.

>>> Stichlmair_flood(Vl = 5E-3, rhog=5., rhol=1200., mug=5E-5,
... voidage=0.68, specific_area=260., C1=32., C2=7., C3=1.)
0.6394323542746928

Demister Pressure Drop

fluids.packed_tower.dP_demister_dry_Setekleiv_Svendsen(S, voidage, vs, rho, mu, L=1.0)

Calculates dry pressure drop across a demister, using the correlation in [1]. This model is for dry demisters with no holdup only.

$$\frac{\Delta P \epsilon^2}{\rho_f v^2} = 10.29 - \frac{565} {69.6SL - (SL)^2 - 779} - \frac{74.9}{160.9 - 4.85SL} + 45.33\left( \frac{\mu_f \epsilon S^2 L}{\rho_f v}\right)^{0.75}$$

Parameters

Sfloat

Specific area of the demister, normally ~250-1000 [m^2/m^3]

voidagefloat

Voidage of bed of the demister material, normally ~0.98 []

vsfloat

Superficial velocity of fluid, Q/A [m/s]

rhofloat

Density of fluid [kg/m^3]

mufloat

Viscosity of fluid [Pa*s]

Lfloat, optional

Length of the demister [m]

Returns

dPfloat

Pressure drop across a dry demister [Pa]

Notes

Useful at startup and in modeling. Dry pressure drop is normally negligible compared to wet pressure drop. Coefficients obtained by evolutionary programming and may not fit data outside of the limits of the variables.

References

1

Setekleiv, A. Eddie, and Hallvard F. Svendsen. “Dry Pressure Drop in Spiral Wound Wire Mesh Pads at Low and Elevated Pressures.” Chemical Engineering Research and Design 109 (May 2016): 141-149. doi:10.1016/j.cherd.2016.01.019.

Examples

>>> dP_demister_dry_Setekleiv_Svendsen(S=250, voidage=.983, vs=1.2, rho=10, mu=3E-5, L=1)
320.3280788941329

fluids.packed_tower.dP_demister_dry_Setekleiv_Svendsen_lit(S, voidage, vs, rho, mu, L=1.0)

Calculates dry pressure drop across a demister, using the correlation in [1]. This model is for dry demisters with no holdup only. Developed with literature data included as well as their own experimental data.

$$\frac{\Delta P \epsilon^2}{\rho_f v^2} = 7.3 - \frac{320} {69.6SL - (SL)^2 - 779} - \frac{52.4}{161 - 4.85SL} + 27.2\left( \frac{\mu_f \epsilon S^2 L}{\rho_f v}\right)^{0.75}$$

Parameters

Sfloat

Specific area of the demister, normally ~250-1000 [m^2/m^3]

voidagefloat

Voidage of bed of the demister material, normally ~0.98 []

vsfloat

Superficial velocity of fluid, Q/A [m/s]

rhofloat

Density of fluid [kg/m^3]

mufloat

Viscosity of fluid [Pa*s]

Lfloat, optional

Length of the demister [m]

Returns

dPfloat

Pressure drop across a dry demister [Pa]

Notes

Useful at startup and in modeling. Dry pressure drop is normally negligible compared to wet pressure drop. Coefficients obtained by evolutionary programming and may not fit data outside of the limits of the variables.

References

1

Setekleiv, A. Eddie, and Hallvard F. Svendsen. “Dry Pressure Drop in Spiral Wound Wire Mesh Pads at Low and Elevated Pressures.” Chemical Engineering Research and Design 109 (May 2016): 141-149. doi:10.1016/j.cherd.2016.01.019.

Examples

>>> dP_demister_dry_Setekleiv_Svendsen_lit(S=250, voidage=.983, vs=1.2, rho=10, mu=3E-5, L=1.0)
209.083848658307

fluids.packed_tower.dP_demister_wet_ElDessouky(vs, voidage, d_wire, L=1.0)

Calculates wet pressure drop across a demister, using the correlation in [1]. Uses only their own experimental data.

$$\frac{\Delta P}{L} = 0.002357(1-\epsilon)^{0.375798}(V)^{0.81317} (d_w)^{-1.56114147}$$

Parameters

vsfloat

Superficial velocity of fluid, Q/A [m/s]

voidagefloat

Voidage of bed of the demister material, normally ~0.98 []

d_wirefloat

Diameter of mesh wire,[m]

Lfloat, optional

Length of the demister [m]

Returns

dPfloat

Pressure drop across a dry demister [Pa]

Notes

No dependency on the liquid properties is included here. Because of the exponential nature of the correlation, the limiting pressure drop as V is lowered is 0 Pa. A dry pressure drop correlation should be compared with results from this at low velocities, and the larger of the two pressure drops used.

The correlation in [1] was presented as follows, with wire diameter in units of mm, density in kg/m^3, V in m/s, and dP in Pa/m.

$$\Delta P = 3.88178(\rho_{mesh})^{0.375798}(V)^{0.81317} (d_w)^{-1.56114147}$$

Here, the correlation is converted to base SI units and to use voidage; not all demisters are stainless steel as in [1]. A density of 7999 kg/m^3 was used in the conversion.

In [1], V ranged from 0.98-7.5 m/s, rho from 80.317-208.16 kg/m^3, depth from 100 to 200 mm, wire diameter of 0.2mm to 0.32 mm, and particle diameter from 1 to 5 mm.

References

1(1,2,3,4)

El-Dessouky, Hisham T, Imad M Alatiqi, Hisham M Ettouney, and Noura S Al-Deffeeri. “Performance of Wire Mesh Mist Eliminator.” Chemical Engineering and Processing: Process Intensification 39, no. 2 (March 2000): 129-39. doi:10.1016/S0255-2701(99)00033-1.

Examples

>>> dP_demister_wet_ElDessouky(6, 0.978, 0.00032)
688.9216420105029

Demister Separation Efficiency

fluids.packed_tower.separation_demister_ElDessouky(vs, voidage, d_wire, d_drop)

Calculates droplet removal by a demister as a fraction from 0 to 1, using the correlation in [1]. Uses only their own experimental data.

$$\eta = 0.85835(d_w)^{-0.28264}(1-\epsilon)^{0.099625}(V)^{0.106878} (d_p)^{0.383197}$$

Parameters

vsfloat

Superficial velocity of fluid, Q/A [m/s]

voidagefloat

Voidage of bed of the demister material, normally ~0.98 []

d_wirefloat

Diameter of mesh wire,[m]

d_dropfloat

Drop diameter, [m]

Returns

etafloat

Fraction droplets removed by mass [-]

Notes

No dependency on the liquid properties is included here. Because of the exponential nature of the correlation, for smaller diameters separation quickly lowers. This correlation can predict a separation larger than 1 for higher velocities, lower voidages, lower wire diameters, and large droplet sizes. This function truncates these larger values to 1.

The correlation in [1] was presented as follows, with wire diameter in units of mm, density in kg/m^3, V in m/s, separation in %, and particle diameter in mm.

$$\eta = 17.5047(d_w)^{-0.28264}(\rho_{mesh})^{0.099625}(V)^{0.106878} (d_p)^{0.383197}$$

Here, the correlation is converted to base SI units and to use voidage; not all demisters are stainless steel as in [1]. A density of 7999 kg/m^3 was used in the conversion.

In [1], V ranged from 0.98-7.5 m/s, rho from 80.317-208.16 kg/m^3, depth from 100 to 200 mm, wire diameter of 0.2 mm to 0.32 mm, and particle diameter from 1 to 5 mm.

References

1(1,2,3,4)

El-Dessouky, Hisham T, Imad M Alatiqi, Hisham M Ettouney, and Noura S Al-Deffeeri. “Performance of Wire Mesh Mist Eliminator.” Chemical Engineering and Processing: Process Intensification 39, no. 2 (March 2000): 129-39. doi:10.1016/S0255-2701(99)00033-1.

Examples

>>> separation_demister_ElDessouky(1.35, 0.974, 0.0002, 0.005)
0.8982892997640582

Demister Geometry

fluids.packed_tower.voidage_experimental(m, rho, D, H)

Calculates voidage of a bed or mesh given an experimental weight and fixed density, diameter, and height, as shown in [1]. The formula is also self-evident.

$$\epsilon = 1 - \frac{\frac{m_{mesh}}{\frac{\pi}{4}d_{column}^2 L_{mesh}}}{\rho_{material}}$$

Parameters

mfloat

Mass of mesh or bed particles weighted, [kg]

rhofloat

Density of solid particles or mesh [kg/m^3]

Dfloat

Diameter of the cylindrical bed [m]

Hfloat

Height of the demister or bed [m]

Returns

voidagefloat

Voidage of bed of the material []

Notes

Should be trusted over manufacturer data.

References

1

Helsør, T., and H. Svendsen. “Experimental Characterization of Pressure Drop in Dry Demisters at Low and Elevated Pressures.” Chemical Engineering Research and Design 85, no. 3 (2007): 377-85. doi:10.1205/cherd06048.

Examples

>>> voidage_experimental(m=126, rho=8000, D=1, H=1)
0.9799464771704212

fluids.packed_tower.specific_area_mesh(voidage, d)

Calculates the specific area of a wire mesh, as used in demisters or filters. Shown in [1], and also self-evident and non-empirical. Makes the ideal assumption that wires never touch.

$$S = \frac{4(1-\epsilon)}{d_{wire}}$$

Parameters

voidagefloat

Voidage of the mesh []

dfloat

Diameter of the wires making the mesh, [m]

Returns

Sfloat

Specific area of the mesh [m^2/m^3]

Notes

Should be preferred over manufacturer data. Can also be used to show that manufacturer’s data is inconsistent with their claimed voidage and wire diameter.

References

1

Helsør, T., and H. Svendsen. “Experimental Characterization of Pressure Drop in Dry Demisters at Low and Elevated Pressures.” Chemical Engineering Research and Design 85, no. 3 (2007): 377-85. doi:10.1205/cherd06048.

Examples

>>> specific_area_mesh(voidage=.934, d=3e-4)
879.9999999999994