Data set of evaporation from Ottawa sand with mixed wettabilities under simulated solar flux and forced convection

This data set contains data collected during multiple evaporation experiments of Ottawa sand. In this study, a soil-water evaporation experimental apparatus was designed and constructed to study evaporation of water from Ottawa sand, with a forced air flow convection above and through the sand layer. A simulated solar flux i.e. (112 ± 20 W/m2) was applied to the sand, while varying soil wettability. Evaporation rates were measured for three cases: 1) a 5.7-cm-thick layer of hydrophilic Ottawa sand; 2) a 5.7-cm-thick layer with 12% hydrophobic content, consisting of a 0.7-cm-layer of n-Octyltriethoxysilane coated hydrophobic sand buried 1.8 cm below the surface of hydrophilic sand; and 3) a 5.7-cm-thick layer with mixed wettabilities consisting of 12% n-Octyltriethoxysilane coated hydrophobic sand mixed into hydrophilic sand.
The evaporation rate for each trial of the three experiments was calculated using the air flow temperature, pressure, and relative humidity recorded at the inlets and outlet to the test section. These values were used to calculate the mass flow rate of the air and the humidity ratio which were used to calculate the evaporation rate. The saturation ratio was calculated using a scale that measured the change in mass of the test section throughout experimentation. The steady-state value of these trials was determined when the temperature of the outlet air flow remained constant. This data set displays the average values recorded when the steady state air temperature was reached for each trial of each experiment. The uncertainty of each trial was calculated using the uncertainties of the instrumentation used for measurements and the uncertainty in the preparation of the sand-water mixture. The calculated uncertainties for each trial are also presented in this data set.
Evaporation from homogeneous porous media is frequently classified into three, distinct periods: constant-rate, falling-rate, and slow-rate periods. Wettability affected the observed evaporation mechanisms, including the transition from constant-rate to falling-rate periods. Evaporation entered the falling-rate period at 12%, 20%, and 24% saturations for the hydrophilic, hydrophobic layer, and hydrophobic mixture, respectively. The duration of the experiments was affected by the wettability, as the hydrophilic, hydrophobic layer, and hydrophobic mixture lasted 17, 20, and 26 trials, respectively. The temperatures measured in the sand suggest more evaporation occurring in the sand near the inlet to the test section for higher saturations. The evaporation flux was found to be 0.1-12 times higher than the vapor diffusion flux calculated, due to enhanced vapor diffusion and forced convection above and through the sand.