Evaporation time, calculation

To calculate an evaporation rate, you would divide the evaporation time by the quantity of liquid used. Explain why it is possible to use the evaporation times from this lab as evaporation rates. 

In order to obtain the solution desired, a value of Ts is assumed, the vapor pressure of A is determined from tables, and mAs is calculated from Eq. (6.98). This value of mAs and the assumed value of Ts are inserted in Eq. (6.97). If this equation is satisfied, the correct Ts is chosen. If not, one must reiterate. When the correct value of Ts and mAs are found, BT or BM are determined for the given initial conditions Tx or mAco. For fuel combustion problems, mAcc is usually zero however, for evaporation, say of water, there is humidity in the atmosphere and this humidity must be represented as mAco. Once BT and BM are determined, the mass evaporation rate is determined from Eq. (6.87) for a fixed droplet size. It is, of course, much preferable to know the evaporation coefficient (5 from which the total evaporation time can be determined. Once B is known, the evaporation coefficient can be determined readily, as will be shown later. 

PREPARATION OF KETONE DERIVATIVE. For additional evidence of the presence of amphetamine, a ketone derivative is prepared by adding 0.5 cm3 of acetone to the urine extract and evaporating at 60° to a volume of about 50 yl. Some unreacted amphetamine remains. A 5-yl aliquot of the mixture is chromatographed and the relative retention times calculated. The retention time of diphenylamine will not change, as it does not form a ketone derivative. 

Compound Measured vapour pressure (Pa) Calculated evaporation time (s) ... 

The calculated phosphorus removal rates as a function of evaporation time at different temperatures are shown in Fig. 1.11. The experimental results of Suzuki et al. [7] are included in the same figure for comparison. 

A mathematical model of solvent blend evaporation was developed by Walsham and Edwards (61). The model accounts for the nonideal behavior of solvent blends in terms of component activity coefficients. The model allows accurate prediction of blend evaporation time by computer calculations. The technique provides a means to follow residual solvent composition (solvent balance) as evaporation proceeds. 

Rocklin and Bonner (65) developed a computer method that predicts solvent balance and evaporation times of water-solvent blends at any humidity with any number of water-soluble organic solvents. The method also can be used for regular water-free solvent blends but Ignores humidity. Key considerations of the method are the following it uses the UNIFAC method for calculating activity coefficients it computes the actual evaporation temperature on the filter paper substrate it calculates evaporation rates at the calculated temperature by using the activity coefficients at that temperature humidity is accommodated by applying a correction factor to the water evaporation rate. Experimental data on several systems verified the computer calculations. 

As the heat-transfer area varies during the evaporation process, the overall heat-transfer coefficient is best defined in relation to the initial drop area. By calculating the overall resistance to heat transfer directly from the temperature driving force, the total evaporation time and the total heat content of the drop, Sideman, Hirsch, and Gat (SI la) obtained a relationship between the average overall heat-transfer coefficient and the initial diameter. For single pentane drops evaporating in sea water,... 

Figure 3.6 Calculated evaporation times of water/BE blends.

Evaporation characteristics Actual evaporation time and solvent balance during evaporation of organic solvent and water based blends can be predicted under different humidity conditions. The most important parameters (see above) can be calculated and water pick-up by blends of oxygenated, polar solvents during evaporation predicted. 

Fig. 2 A Calculated evaporation times r versus initial drop volume Vq for three cases 0 = 90 and RH = 99% (solid line), 0 = 30 and RH = 99% (dashed line), and 0 = 90° and RH = 30% (dashed-dotted line). Corresponding experimental evaporation times (open symbols) of five drops on the fluoropolymer flhn, all with an initial contact angle 0 = 90°. For the calculations a = 2.5 x 10 m s kg and...

This procedure was first described by Bouche and Verzele (95), who initially completely filled the column with a solution of known concentration of stationary phase. In this procedure, one end of the column is sealed and the other is attached to a vacuum source. As the solvent evaporates, a uniform film is deposited on the column wall. The column must be maintained at constant temperature for uniform film deposition. The coating solution should be free of microparticulates and dust, be degassed so no bumping occurs during solvent evaporation, and there should be no bubbles in the column. Pentane is the recommended solvent because of its high volatility and should be used wherever stationary phase solubility permits. Evaporation time is approximately half that required to evaporate methylene chloride. The static coating technique offers the advantage of an accurate determination of the phase ratio (Section 3.10.3) from which the film thickness of the stationary phase can be calculated. 

Density. The density at room temperature of cis/trans PTBA films cast firom toluene and cyclohexane and prepared at different evaporation times, Xev were obtained fi om dilatometric measurements. The specific volume, Vsp, of the polymer as a function of temperature was calculated using die following relationships 16) ... 

At first we tried to explain the phenomenon on the base of the existence of the difference between the saturated vapor pressures above two menisci in dead-end capillary [12]. It results in the evaporation of a liquid from the meniscus of smaller curvature ( classical capillary imbibition) and the condensation of its vapor upon the meniscus of larger curvature originally existed due to capillary condensation. We worked out the mathematical description of both gas-vapor diffusion and evaporation-condensation processes in cone s channel. Solving the system of differential equations for evaporation-condensation processes, we ve derived the formula for the dependence of top s (or inner) liquid column growth on time. But the calculated curves for the kinetics of inner column s length are 1-2 orders of magnitude smaller than the experimental ones [12]. 

The overall requirement is 1.0—2.0 s for low energy waste compared to typical design standards of 2.0 s for RCRA ha2ardous waste units. The most important, ie, rate limiting steps are droplet evaporation and chemical reaction. The calculated time requirements for these steps are only approximations and subject to error. For example, formation of a skin on the evaporating droplet may inhibit evaporation compared to the theory, whereas secondary atomization may accelerate it. Errors in estimates of the activation energy can significantly alter the chemical reaction rate constant, and the pre-exponential factor from equation 36 is only approximate. Also, interactions with free-radical species may accelerate the rate of chemical reaction over that estimated solely as a result of thermal excitation therefore, measurements of the time requirements are desirable. 

Atomization. Droplet heatup and evaporation calculations can be done for any droplet size, but are most often carried out to reflect the behavior of a mean-sized droplet. The finer the droplet, the less time required for the various steps in the destmction of the waste. 

Refrigerating capacity is the product of mass flow rate of refrigerant m and refrigerating effect R which is (for isobaric evaporation) R = hevaporator outlet evaporator mJef Powei P required foi the coiTipressiou, necessary for the motor selection, is the product of mass flow rate m and work of compression W. The latter is, for the isentropic compression, W = hjisehatge suction- Both of thoso chai acteristics could be calculated for the ideal (without losses) and for the ac tual compressor. ideaUy, the mass flow rate is equal to the product of the compressor displacement per unit time and the gas density p m = p. 

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