Determination of Evaporative Fluxes Using a Bench-Scale Atmosphere Simulator

Abstract

An accurate determination of evaporative fluxes is critical for efficient water management in semi-arid climates such as in the Canadian Prairies. The main achievements of this research are the design and operation of a bench-scale atmosphere simulator, performance evaluation using selected weather scenarios pertaining to regional atmospheric conditions, validation using established empirical correlations, and estimation of evaporation rates and the amount for a typical local water body. Results indicate that the measured data achieved the target values for the various parameters and the data were found to be stable during the 3-h test duration. The vapour flux was found to have large variation during summer (0.120 g∙s−1∙m−2 during the day and 0.047 g∙s−1∙m−2 at night), low variation during spring (0.116 g∙s−1∙m−2 during the day and 0.062 g∙s−1∙m−2 at night), and negligible change during fall (0.100 g∙s−1∙m−2 during the day and 0.076 g∙s−1∙m−2 at night). The measured vapour flux was generally within one standard deviation of the equality line when compared with that predicted by both the mass-transfer equations and the combination equations. The average evaporation ranged from 4 mm∙d−1 to 8 mm∙d−1 during the day and decreased to 1 mm∙d−1 to 3 mm∙d−1 at night. The 24-h evaporation was found to be 8 ± 1 mm∙d−1 from late April through late October. Likewise, the cumulative annual evaporation was found to be 1781 mm, of which 82% occurs during the day and 18% at night.

Effect of Salinity on Evaporation from Water Surface in Bench-Scale Testing

“…The vapor pressure deficits (atmospheric and surface) were nearly the same for water and brine surfaces because the analyzed values are based on the controlled parameters of humidity, air temperature, and surface temperature. The atmospheric vapor pressure deficit followed the air temperature trends with high diurnal variation in summer ( 989 The determination of energy fluxes was based on an infinitely thin surface with no heat storage [30], such that inputs and outputs were categorized as either radiant, evaporative, sensible, or ground flux, with details provided by Suchan and Azam [24]. The available energy (difference between net radiant flux and ground flux) at the water surface was generally twice that at the brine surface because the presence of salt decreases fluid chemical potential, thereby reducing the latent heat energy of the brines [5].…”

“…The atmospheric parameters (hourly land-based measurements) were obtained from the Canadian Weather Energy and Engineering Datasets (CWEEDS), based on data from 1998 to 2014. Details on the selection of surface-atmosphere parameters and standard deviations are given in Suchan and Azam [24]. The tests were conducted using 15 mL of sample (distilled water and saturated brine) in a clean and air-dried container mounted on an analytical scale balance.…”

“…Summary of empirical equations for estimation of evaporative flux, modified after Suchan and Azam[24].…”

Determination of Soil Behavior during Evaporation Using Geotechnical Datasets

“…The high-demand evaporation experiments were performed under Canadian Prairie summer day conditions [24], continuously capturing water loss from the soil. Located in "3.…”

Development of BAS2 for determination of evaporative fluxes

“…Therefore, there was a need to develop an atmospheric simulator that can adequately fulfill the following criteria: (i) capture a wide range of each relevant field parameter; (ii) maintain controlled conditions over the required testing time; (iii) utilize readily available components for modular fabrication; and (iv) facilitate operational efficiency between individual modules. Suchan and Azam [27] recently developed a bench-scale atmosphere simulator (BAS) that can effectively control the four meteorological variables related to evaporation, namely: air velocity, temperature, humidity, and solar irradiation, and can monitor surface-atmosphere variables such as air pressure and surface temperature. This paper presents the detailed design and the operational procedure of a thoroughly improved second version of the bench-scale atmosphere simulator (BAS2).…”