Gases pressure drop calculations

In pipe distributors, the pressure drop requited for good gas distribution is 30% of the bed pressure drop for upward facing holes, but only 10% for downward facing ones. The pressure drop calculation and the recommended hole density are the same as for a perforated plate. To maintain good gas distribution within the header system, it is recommended the relation... 

The pressure drop due to condensing is usually negligible in a unit of this type. As a maximum, it may be taken as one half of the gas flow drop calculated for one baffle. This would be 1.16/8 = 0.145 psi for the condensing portion. Note that this does not recognize tube supports at 50% cut area, but for pressure units, this pressure drop will be nil. 

Pressure driven membrane process, 78 507 Pressure-driven membranes, in water treatment, 26 111 Pressure drop, 77 804 from area change, 73 261-262 in cake filtration, 77 330-332, 333-335 flow maldistribution and, 73 270 from flow turning, 73 262 frictional, 73 260-261 in gas adsorption, 7 657-658 in hyperbar vacuum filtration, 77 377 shellside tube bundle, 73 262-263 in vacuum filtration, 77 349-350 Pressure drop calculations, in heat exchanger design, 73 259-260 Pressure drop information, for resins, 74 399... 

It is important to appreciate that different flow regimes occur at different gas and liquid flow rates and differences also occur for different materials. In order to have any confidence when calculating pressure losses in two-phase flow it is necessary to be able to predict the flow regime and then to use an appropriate pressure drop calculation procedure. 

Motionless Mixers. Major mixer manufacturers agree that the Lockhart and Martinelli parameters for two-phase flow in pipes (9) can also be applied to motionless mixers. To estimate the pressure drop, the single-phase liquid and gas pressure drops are first calculated. The Lockhart and Martinelli para-meter X is found from... 

Acceleration pressure drop. When the gas density or the vapor mass fraction changes, there is an acceleration pressure drop calculated from... 

Gas pressure drop across the spout, APv, and gas flow rate through the spout, Ggv, are the more important variables for the design and operation of the V-valve. From Eqs. (6) and (7), we can see that in order to calculate APv and Ggv, the gas-solids relative velocity (uro - up0) must be known. The value of (Wf0 - uPo) can be calculated by solving the simultaneous differential Eqs. (2) to (5) for the trapezoidal spout, with the boundary conditions of simultaneous equations consists of a trial-and-error process for the numerical method. 

Calculate head loss due to surface tension From Example 4.6, the surface tension is 70 dyne/cm = 0.07 N/m. Substituting in equation (4-42), ha = 0.0087 m = 0.87 cm. Calculate the total head loss/tray Substituting in equation (4-37) gives us hf = 8.45 cm of clear liquid/tray. For a liquid density of 986 kg/m3, this is equivalent to a gas-pressure drop of APG = 0.0845 x986 x9.8 = 817 Pa/tray. 

A wastewater stream of 0.038 m3/s, containing 10 ppm (by weight) of benzene, is to be stripped with air in a packed column operating at 298 K and 2 atm to reduce the benzene concentration to 0.005 ppm. The packing specified is 50-mm plastic Pall rings. The airflow rate to be used is five times the minimum. Henry s law constant for benzene in water at this temperature is 0.6 kPa-m3/mol (Davis and Cornwell, 1998). Calculate the tower diameter if the gas-pressure drop is not to exceed 500 Pa/m of packed height. Estimate the corresponding mass-transfer coefficients. The diffusivity of benzene vapor in air at 298 K and 1 atm is 0.096 cm2/s the diffusivity of liquid benzene in water at infinite dilution at 298 K is 1.02 x 10 5 cm2/s (Cussler, 1997). 

Design a tower packed with 50-mm ceramic Hiflow rings for the carbon disulfide scrubber of Problem 5.11. Assume isothermal operation and use a liquid rate of 1.5 times the minimum and a gas-pressure drop not exceeding 175 Pa/m of packing. Calculate the tower diameter, packed height, and total gas-pressure drop. Assume that Ch for the packing is 1.0. 

The absorption tower will be filled with 50-mm ceramic Pall rings. Design for a gas-pressure drop not to exceed 400 Pa/m of packed depth. Assume that cooling coils will allow isothermal operation at 300 K. The gas will enter the column at the rate of 1.0 m3/s at 300 K and 1 atm. The partial pressure of methanol in the inlet gas is 200 mmHg (ScG = 0.783). The partial pressure of methanol in the outlet gas should not exceed 15 mm Hg. Pure water enters the tower at the rate of 0.50 kg/s at 300 K. Neglecting evaporation of water, calculate the diameter and packed depth of the absorber. 

Finally, calculate the flue gas pressure drop through the convection section using the equation for velocity head,, inches of water. Evaluate the flue gas density at the same average temperature used in calculating the transfer coefficients. 

The next problem is the calculation of the flue gas pressure drop as it crosses the selected finned tube convection section. Using the design information for tubes per row, number of rows, tube spacing, fin and tube geometry and fin pitch, compute the net free volume and friction surface of the convection section. 

In [11], a theoretical value of is estimated from column dimensions, gas viscosity, and pressure drop. Calculation is easy, and possible errors in variables related to column geometry (such as column length and diameter) can be... 

The methods for predicting the flow pattern and the pressure drop for fully developed gas/liquid flow are complex and often the accuracy presented in these methods is not required for the pressure drop calculations involved in a chlor-alkali plant. The reader is referred to papers cited in [7—9] for a thorough discussion on two-phase flow. 

A monolith or parallel passage reactor contains a solid construction with parallel channels, usually with a cross sectional area of a few square mm each. They can be manufactured either by drilling parallel holes in a solid block, or by a ceramic process starting with a pile of layers that look like corrugated cardboard, made of clay, which is then baked. The latter type is used as a carrier for catalysts, and applied where a low gas pressure drop is essential, e.g., in automobile exhaust gas purification. The mass transfer rates in such monoliths can be calculated easily from the equations describing mass (and heat-) transfer in straight tubes, see eqs. (4.24), (4.28) and (4.29). 

In this equation, (AP/AL). is the mixed phase pressure drop per unit bed length and 6 and o , are the liquid in gas pressure drop per unit bed length as calculated using the Ergun equation for each of the liquid and gas flowing separately as single phases... 

Liquid and gas pressure drop per unit bed length calculated using Ergun equation, kPa m ... 

In both laminar and turbulent flow it is assumed that the mixture is pseudoho-mogeneous with respect to density that is, a volume average density is used. The viscosity of the continuous phase is used. Note that for very small dispersed phase drops or bubbles (under 10 p,m), the viscosity may even be higher and non-Newtonian, such as in foams and emulsions. In such cases direct measurements are required of a well-dispersed sample. Avoid correlations that average viscosities. For gas-liquid systems, the method of Lockhart and Martinelli (see Govier and Aziz, 1972) for turbulent flow is very successful and more accurate then the pseudohomogeneous method. The pressure drop for each phase flowing alone is calculated. The liquid/gas pressure drop ratio is made. This is used with an empirical correlation to get an enhancement factor for the liquid-alone pressure drop,... 

In this case there is good agreement between the values calculated for total pressure drop. Since gas flow is predominant, the total empty pipe pressure drop calculated from the gas-only pressure drop using eq. (7-41b) should be used. It should be noted that this Lockhart-Martinelli correlation is considered to be conservative when used in vertical downward flow. The original work was all in horizontal flow. 

If a one-dimensional flow through a packed bed of granular material is assumed (e.g., in moving-bed gasifiers), the pressure drop over a certain bed height Hbed complies to Equation (3.77). It uses the representative diameter based on equivalent specific surface ds, the density of the gas p, the superficial velocity in the bed u, and the dimensionless bed void fraction e for pressure drop calculation (see also Section 3.12.3.2). 

A porous bed support strong enough to carry the full weight of the bed plus the calculated gas pressure drop, and designed to retain fine particles of sorbent. 

Pressure drop calculations and mass estimates were performed for several piping arrangements used in the arrangements trade study. Section 8.4. Table 9-25 below summarizes the percentage AP/P and piping mass results for these arrangements. The arrangements are specified with an x y z" nomenclature, where the first value is the number of turbines, the second is the rtumber of recuperators, and the third is the number of gas coolers... 

For direct measurement from core samples, the samples are mounted in a holder and gas is flowed through the core. The pressure drop across the core and the flowrate are measured. Providing the gas viscosity (ji) and sample dimensions are known the permeability can be calculated using the Darcy equation shown below. 

The primary drive mechanism for gas field production is the expansion of the gas contained in the reservoir. Relative to oil reservoirs, the material balance calculations for gas reservoirs is rather simple the recovery factor is linked to the drop in reservoir pressure in an almost linear manner. The non-linearity is due to the changing z-factor (introduced in Section 5.2.4) as the pressure drops. A plot of (P/ z) against the recovery factor is linear if aquifer influx and pore compaction are negligible. The material balance may therefore be represented by the following plot (often called the P over z plot). 

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