mass_transfer_evaporation_method_1_c7a9d7c0

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. . Mass Transfer Mass transfer is the net movement of mass from one location, usually meaning stream, phase, fraction or component, to another. Mass transfer occurs in many processes, such as absorption, evaporation, drying, precipitation, membrane filtration, and distillation. Mass transfer is used by different scientific disciplines for different processes and mechanisms. Some common examples of mass transfer processes are the evaporation of water from a pond to the atmosphere, the purification of blood in the kidneys and liver, and the distillation of alcohol..

. . Mass Transfer Evaporation Method Formula (eo—ea), where ; uz= Viindspeed at some height z above the water surface, eo= saturation vapor pressure calculated from the temperature of the water surface, and e a=vapor pressure ofthe air. Various forms of the equation use different multiplier constants and different functions of speed based upon area, season, lake size, temperature and other factors..

. . Sample Study #1 Comparison of Evaporation Computation Methods, Pretty Lake, Lagrange County, Northeastern Indiana GEOLOGICAL SURVEY PROFESSIONAL PAPER.

. . Sample Study #1 The study of Pretty Lake assumed the mass-transfer relationship to be in the form developed in the Lake Hefner study (Marciano and Harbeck, 1952) as (11) which is the same equation used with equations 4 and 5 to estimate Q. in the previous section. Here, N is a constant for a specific lake, and is the average wind speed measured 2 meters (6.56 it) above the water surface. Harbeck, realizing that the mass-transfer co• efficient, N, summarizes many variables such as wind and vapor profiles and wave heights, has made an empirical relationship' NE 0.00859/.•1LC0 between the constant and the surface area, A, of the body of water to which it applies (Harbeck, 1962, fig. 31). The eon- stant N can be only roughly related to lake size, for it also is affected by local peculiarities, topography, and point of wind measurement. One purpose of the Pretty Lake study was to determine the mass-transfer co- efficient and to compare the Pretty Lake coefficient with those Of Other lakes or with a coefficient of 0.00661 predicted by Harbeck's surface-area method. Visual inspection of figure IS, especially of the rate plot, may give reason to suspect the validity of an assumed straight-line function. A curved line, logarith- mic, parabolic, or second degree, might seem to be better, especially if it is restricted to pas through the origin. However, in consideration of the origin of the data and the errors contained in the low-rate budget computation, a curved line is not believed to be a better representation of the mass-transfer function than is the straight line. Further discussion of this problem is in a later section of this report. Considering the various coemcients computed by different methods, the relation Eut=o.00560 (14) was selected to compute mass-transfer evaporation.' The mass-transfer coefficient in equation 14 is 15 percent less than the coefficient of 0.00661 preducted by Harbeck's (1962, fig. 31 )method..

. . COMPUTATION OF EVAPORATION TRANSFER Evaporation rates and quantities were computed for the energv•budget by use of equation 14. Table 5 lists thc terms of the computation. Evwation rates and amounts computed by the meth(Ål are shown graphically and further summaü'(l in figures 30 and 31 and in tables 20 and 21 in later u•ction of this report. Accuracy of the mms.transfer data is difficult to estimate there is no absolutely accurate control. Often the judgment of the investigator vides the most tangible estimate Of accuracy..

. . Sample Study #2 EVAPORATION COMPUTED BY ENERGY' BUDGET AND MASS-TRANSFER METHODS AND WATER-BALANCE ESTIMATES FOR DEVILS NORTH DAKOTA, 1986-88 Gregg J, Wiche geotog•c'l Survey.

. . Sample Study #2 EVAPORATION COMPUTED BY kASS-TUNSFER METHOD Yass-Transfer Coefficient In this study, energy-budget evaporation was used as the Independent reasure of evaporation used to determine the russ-transfer coefflclent (N). The relation of mass-transfer product to energy-budget evaporation Is shown fn figure 7. The linear regression equation developed and used to determine N, which is the slope of the line of best fit, is Emt • 0.019+W2(eo-ea). where N • 0.0020 (14).

. . N generally is cmvuted as the slope of a straight Ifne (fig. 7) passing through the origin; In this study, however, a constant (y-fntercept) of 0.019 provides the best fit. The physical basis for having the straight line pass through the origin Is that when the wind is calm there is no vapor pressure gradient (eo-ea 0), and the turbulent exchange of vapor between the lake surface and the air is negligible. The assurption is made that the independ- ent variable used to detemine N is without error. However, error undoubtedly occurs in V2(eo-ea); thus, adding a constant to equation 9 provides the best estimate of mass-transfer evaporation from Devils Lake. Equation 14 has a coefficient of determination of 0.73 and a standard error of estimate of 0.03 inch per day..

. . Source: https://en.\Nikipedia.org/\\iki/Mass transfer https://MMW.sciencedirect.com/science/article/pii/S00170_31010_341701 https://pubs.usgs.gov/pp/0686a/report.pdf https://MMM'.swc.nd.gov/info edu/reports and publications/pdfs/MT investigat ions/\iT11 report.pdf.