Rate-Based Calculations

Mass-Transfer Coefficients As described in Rate-Based Calculations, the overall mass-transfer coefficient may be written as... 

EXAMPLE 14.2 RATE-BASED CALCULATIONS IN A TRAYED COLUMN... 

The following results were obtained for tray n from a rate-based calculation of a ternary distillation at 1 atm involving acetone (1), methanol (2), and water (3). Vapor and liquid phases are assumed to be completely mixed. 

In the menu on the left side, you will see Tray Rating, Section 1, and below Setup there will be Rate-Based. Click on this. In the Rate-Based tab, click on the box labeled Rate-based calculations ... 

Example 14.2 Rate-Based calculations in a trayed column... 

Example 8 Calculation of Rate-Based Distillation The separation of 655 lb mol/h of a bubble-point mixture of 16 mol % toluene, 9.5 mol % methanol, 53.3 mol % styrene, and 21.2 mol % ethylbenzene is to be earned out in a 9.84-ft diameter sieve-tray column having 40 sieve trays with 2-inch high weirs and on 24-inch tray spacing. The column is equipped with a total condenser and a partial reboiler. The feed wiU enter the column on the 21st tray from the top, where the column pressure will be 93 kPa, The bottom-tray pressure is 101 kPa and the top-tray pressure is 86 kPa. The distillate rate wiU be set at 167 lb mol/h in an attempt to obtain a sharp separation between toluene-methanol, which will tend to accumulate in the distillate, and styrene and ethylbenzene. A reflux ratio of 4.8 wiU be used. Plug flow of vapor and complete mixing of liquid wiU be assumed on each tray. K values will be computed from the UNIFAC activity-coefficient method and the Chan-Fair correlation will be used to estimate mass-transfer coefficients. Predict, with a rate-based model, the separation that will be achieved and back-calciilate from the computed tray compositions, the component vapor-phase Miirphree-tray efficiencies. 

Based on an average tray efficiency of 90 percent for the hydrocarbons, the eqiiilibniim-based model calculations were made with 36 equilibrium stages. The results for the distillate and bottoms compositions, which were very close to those computed by the rate-based method, were a distillate with 0.018 mol % ethylbenzene and less than 0.0006 mol % styrene, and a bottoms product with only a trace of methanol and 0.006 mol % toluene. 

To the basic current requirement is applied the derating faetors for various service conditions, as noted in Section 1.5.4.2. The equipment, devices and components may then be cbosen to be as close (nearest higher) to this rating as possible from the available standard ratings. Based on these ratings, the minimum cross-sectional areas of the other current-carrying parts used in the circuit, such as interconnecting links and the cables-are calculated. 

An important practical question is, what is the representative pipe diameter in loading circuits comprising different sizes of pipe This has a large effect on the values calculated for velocity and velocity-diameter product. As an example, static ignition of ester mist in a rail car (5-1.3.1) involved 1450 gpm through a 6-in. pipe (v = 5 m/s and vd = 0.76 mVs) followed by a short 4-in. dip pipe assembly (y = 11 m/s and vd = 1.15 mVs). Were nonconductive liquid flow rate restrictions applied to the semiconductive ester (time constant —0.01 s) involved in this fire, the flow rate based on the 4-in. pipe would be unacceptably large based either on a 7 m/s maximum velocity or a 0.80 mVs maximum vd product. However, based on the 6-in. pipe upstream the flow velocity is less than 7 m/s and also meets API s vd < 0.80 mVs criterion. 

Numerical simulation of hood performance is complex, and results depend on hood design, flow restriction by surrounding surfaces, source strength, and other boundary conditions. Thus, most currently used method.s of hood design are based on experimental studies and analytical models. According to these models, the exhaust airflow rate is calculated based on the desired capture velocity at a particular location in front of the hood. It is easier... 

The principle of the traversing method is to measure the local velocity at one or several points of the flow cross-section and then calculate the flow rate based on this information. Generally speaking, an integration of the local velocity over the flow cross-section is made. Mathematically, this is expressed as... 

This article presents an overview of the causes and frequency of failures for submarine and cross-country pipelines handling oil and natural gas. It gives several tables and charts which include information on the type of pipeline, the cause of the failure, and the number of failures. Data from failures in the US and the North Sea are included. Failure rates based on the total length of piping are calculated. 

Calculate the tube-side flow rate based upon the assumed number of tubes per pass and the heat balance. 

The oxygen transfer rate is calculated based on oxygen concentration gradient, by determination of the oxygen level in the liquid phase and the equilibrium value. 

For constant power input based on geometric similarity of the vessels, agitation rate is calculated. 

This section is divided into three parts. The first is a comparison between the experimental data reported by Wisseroth (].)for semibatch polymerization and the calculations of the kinetic model GASPP. The comparisons are largely graphical, with data shown as point symbols and model calculations as solid curves. The second part is a comparison between some semibatch reactor results and the calculations of the continuous model C0NGAS. Finally, the third part discusses the effects of certain important process variables on catalyst yields and production rates, based on the models. 

Figure 4, Decomposition of -n-butyU t -nitrosoacetamide by calf liver RNA in phosphate buffer (pH 7) at 25°C, The dashed line is the calculated rate based on coefficients given in Table II,...

H2O2 Production Rate Based on the collection efficiency A at the Pt collecting electrode located downstream from the working electrode, we calculated the ratio of the H2O2 production rate to the overall ORR rate, P(H202) ... 

When determining the permeability of films to water vapor, we seal a desiccant into a small cup with the polymer covering the opening. We weigh the cup before placing it in an oven at controlled temperature and humidity. After a given period of time we remove it and weigh it a second time. We calculate the film s water vapor transmission rate based on the area of the cup s mouth and the time that it was in the oven. 

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