Linear flow rate

Capacity factor, 2 Separation factor Length Flow rate Linear velocity Cycle time Number of plates Yield Packing... 

As noted above, the mean retention volumes determined from the mean elution times measured at three different flow rates and were invariant with flow rate. Linearity in the logarithm of Vo-versus-1/T plot is present above and below the glass transition temperature with a change of slope at the glass transition temperature. Using this... 

These are compounds that can be added to the electrolyte to alter the direction and rate of the electro-osmotic flow. Flow rate varies inversely with ionic strength and is independent of column diameter. The effect of pH between 2 and 12 and applied potential increase the electro-osmotic flow rate linearly. The flow can be reversed by adding quaternary amines, such as cetyltrimethylammonium bromide or tetradecyl-trimethylammonium bromide. Zero flow occurs when 5-benzyIthiouronium chloride is added to the buffer. Organic molecules such as methanol and putrescine reduce the flow, whereas acetonitrile increases the flow. Covalently bonded polyethylene glycol reduces the flow. 

However, it is possiUe to maximize the parameter NQ at constant analyas time by varying the flow rate ( linear velocity). In tifis case, one neously changes the plate count N and the gradient steepness fr,. Because of the influence of the factor one obtains an optimum at lin velodties higher than those that correspond to the maximum plate count in isocratic chromatography (see also the section on gradient optimization). 

E. Check. We can check with a different form of the Kremser equation or by solving the results graphically both give the same result. We should also check that the major assunptions of the Kremser equation (constant flow rates, linear equilibrium, and isothermal) are satisfied. In this dilute system they are. 

The flow rate through a capillary column whose inner diameter is less than 0.53 mm is difficult to measure accurately and reproducibly by a conventional soap-bubble meter. Instead, the flow of carrier gas through a capillary column is usually expressed as a linear velocity rather than as a volumetric flow rate. Linear velocity may be calculated by injecting a volatile nonretained solute and noting its retention time, tM (seconds). For a capillary column of length L in centimeters. 

The final part of a gas chromatograph is the detector. The ideal detector has several desirable features, including low detection limits, a linear response over a wide range of solute concentrations (which makes quantitative work easier), responsiveness to all solutes or selectivity for a specific class of solutes, and an insensitivity to changes in flow rate or temperature. 

La.mina.r Flow Elements. Each of the previously discussed differential-pressure meters exhibits a square root relationship between differential pressure and flow there is one type that does not. Laminar flow meters use a series of capillary tubes, roUed metal, or sintered elements to divide the flow conduit into innumerable small passages. These passages are made small enough that the Reynolds number in each is kept below 2000 for all operating conditions. Under these conditions, the pressure drop is a measure of the viscous drag and is linear with flow rate as shown by the PoiseuiHe equation for capilary flow ... 

Vortex-shedding flow meters typically provide 1% of flow rate accuracy over wide ranges on Hquid, gas, and steam service. Sizes are available from 25 to 200 mm. The advantages of no moving parts and linear digital output have resulted in wide usage in the measurement of steam, water, and other low viscosity Hquids. 

Volumetric heat generation increases with temperature as a single or multiple S-shaped curves, whereas surface heat removal increases linearly. The shapes of these heat-generation curves and the slopes of the heat-removal lines depend on reaction kinetics, activation energies, reactant concentrations, flow rates, and the initial temperatures of reactants and coolants (70). The intersections of the heat-generation curves and heat-removal lines represent possible steady-state operations called stationary states (Fig. 15). Multiple stationary states are possible. Control is introduced to estabHsh the desired steady-state operation, produce products at targeted rates, and provide safe start-up and shutdown. Control methods can affect overall performance by their way of adjusting temperature and concentration variations and upsets, and by the closeness to which critical variables are operated near their limits. 

In any gas burner some mechanism or device (flame holder or pilot) must be provided to stabilize the flame against the flow of the unbumed mixture. This device should fix the position of the flame at the burner port. Although gas burners vary greatly in form and complexity, the distribution mechanisms in most cases are fundamentally the same. By keeping the linear velocity of a small fraction of the mixture flow equal to or less than the burning velocity, a steady flame is formed. From this pilot flame, the main flame spreads to consume the main gas flow at a much higher velocity. The area of the steady flame is related to the volumetric flow rate of the mixture by equation 18 (81,82)... 

Expressions for the a. derivatives are of the same form r = rate of reaction, a fi motion of s and T G = mass flow rate, mass/(time)(siiperficial cross section) u = linear velocity D = diffiisivity k = thermal conductivity... 

Rotameter A rotameter consists of a vertical tube with a tapered bore in which a float changes position with the flow rate through the tube. For a given flow rate the float remains stationary since the vertical forces of differential pressure, gravity, viscosity, and buoyancy are balanced. The float position is the output of the meter and can be made essentially linear with flow rate by makiug the tube areavaiy hn-early with the vertical distance. 

Kinds oi Inputs Since a tracer material balance is represented by a linear differential equation, the response to anv one kind of input is derivable from some other known input, either analytically or numerically. Although in practice some arbitrary variation of input concentration with time may be employed, five mathematically simple input signals supply most needs. Impulse and step are defined in the Glossaiy (Table 23-3). Square pulse is changed at time a, kept constant for an interval, then reduced to the original value. Ramp is changed at a constant rate for a period of interest. A sinusoid is a signal that varies sinusoidally with time. Sinusoidal concentrations are not easy to achieve, but such variations of flow rate and temperature are treated in the vast literature of automatic control and may have potential in tracer studies. 

Variables sueh as eoneentration of reaetants, reaetion eoil length, injeetion volume, flow rate. ete. are studied and optimized. Reprodueibility, linearity, deteetion limit and statistieal evaluation are shown. The methods results are in good agreement to other standard methods. 

Liquid chromatography was performed on symmetry 5 p.m (100 X 4.6 mm i.d) column at 40°C. The mobile phase consisted of acetronitrile 0.043 M H PO (36 63, v/v) adjusted to pH 6.7 with 5 M NaOH and pumped at a flow rate of 1.2 ml/min. Detection of clarithromycin and azithromycin as an internal standard (I.S) was monitored on an electrochemical detector operated at a potential of 0.85 Volt. Each analysis required no longer than 14 min. Quantitation over the range of 0.05 - 5.0 p.g/ml was made by correlating peak area ratio of the dmg to that of the I.S versus concentration. A linear relationship was verified as indicated by a correlation coefficient, r, better than 0.999. 

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