More Like this

1. EVAPORATION OF WATER FROM OTTAWA SAND USING AIR FLOWS ABOVE AND BELOW THE SAND LAYER

   https://doi.org/10.1615/TFEC2023.esy.045917  

   Paap, Dylan; Weinhold, Benjamin; Chakraborty, Partha Pratim; VandenBos, Will; Derby, Melanie M. (March 2023, 8th Thermal and Fluids Engineering Conference (TFEC))

   The primary source of water for crops and livestock in the United States Central High Plains is irrigation from the Ogallala Aquifer. Due to the semi-arid climate of this region, little rainfall contributes to watering crops, thereby resulting in water scarcity. Reducing the evaporation from soil is one approach to conserve the water. In this study, a soil evaporation chamber was designed and constructed to study the impacts of environmental conditions on evaporation from Ottawa sand. Prior to entering the sand test section, compressed air flow was dried in a desiccator then split in two flows before entering the 57mmx228mmx838mm test section, with one airflow flowing above the 57mm thick sand layer and the other below and, subsequently, flowing through the moist sand layer. The percent relative humidity (RH) was measured at the entrance and exit to record the change in relative humidity and, therefore, water content removed from the sand. Using inlet air mass flow rates of air of approximately 1E-4kg/s–2E-4kg/s, temperatures of 28–31oC, and dry air (i.e. 0–1%RH), exit flows of 19–20oC and 80–85%RH were measured. Measured evaporation rates ranging from 3.0E-6kg/s to 5.0E-6kg/s for soil saturation levels of 55–80.5%. 

   more » « less
2. Evaporation Mechanisms and Heat Transfer in Porous Media of Mixed Wettabilities With a Simulated Solar Flux and Forced Convection Through the Media

   https://doi.org/10.1115/1.4065608  

   Paap, Dylan; Weinhold, Benjamin; Chakraborty, Partha Pratim; VandenBos, Will; Derby, Melanie M (October 2024, ASME Journal of Heat and Mass Transfer)

   Abstract An experimental apparatus was designed to study the impacts of wettability on evaporation of water from Ottawa sand. Evaporation rates were measured for: (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 sand–water mixtures experienced forced convection above and through the sand layer, while a simulated solar flux (i.e., 112±20 W/m2) was applied. Evaporation from homogeneous porous media is classified into the 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 all hydrophilic sand, hydrophobic layer, and hydrophobic mixture, respectively. Wettability affected the duration of the experiments, as the all hydrophilic sand, hydrophobic layer, and hydrophobic mixture lasted 17, 20, and 26 trials, respectively. Both experiments with hydrophobic particles lasted longer than the all hydrophilic experiment and had shorter constant-rate evaporation periods, suggesting hydrophobic material interrupts capillary action of water to the soil surface and reduces evaporation. Sand temperatures suggest more evaporation occurred near the test section inlet for higher saturations and the hydrophobic layer experienced more evaporation occur near the outlet. Evaporation fluxes were up to 12× higher than the vapor diffusion flux due to enhanced vapor diffusion and forced convection. 

   more » « less
3. EVAPORATION FROM A SIMULATED SOIL PORE: EFFECTS OF RELATIVE HUMIDITY

   Chakraborty, Partha P.; Derby, Melanie M. (June 2018, Proceedings of the ... International Conference on Nanochannels, Microchannels and Minichannels)

   Reduction of irrigation is a pressing issue in the food-water-energy nexus. Around two-third of global water withdrawals are used for irrigation in the areas with insufficient rainfall. In the U.S. Central High Plains, the Ogallala Aquifer is responsible for providing water for the production of corn, wheat, soybeans, andreducing the evaporation of water from soil provides an excellent opportunity to decrease the need for irrigation. In this paper, evaporation of sessile 4-μl water droplets from a single simulated soil pore was observed. Soil pores were created using three 2.35-mm hydrophilic glass or hydrophobic Teflon beads of the same size. The experiments were conducted at the same temperature (20° C) and two relative humidity levels, 45% and 60% RH. Evaporation times were recorded and the transport phenomena were captured using a high-speed camera. Relative humidity directly affected evaporation; evaporation times were lower at the lower RH. The glass surface had higher wettability and therefore the droplets were more stretched on the glass beads, more droplet-air areas were created and evaporation times were approximately 30 minutes at 60% RH. The Teflon surface was hydrophobic, for which air-water contact areas were lower, and evaporation times were longer – approximately 40 minutes at 60% RH. As evaporation progressed, a liquid island formed between two beads at both 45% and 60% RH in for glass and Teflon pores. The rate of decrease of the radius of the liquid island was shorter in Teflon than glass beads, which corresponded to lower evaporation rates from Teflon. 

   more » « less
4. Contact Line Pinning and Depinning Prior to Rupture of an Evaporating Droplet in a Simulated Soil Pore

   https://doi.org/10.1115/ICNMM2020-1091  

   Chakraborty, Partha P.; Derby, Melanie M. (July 2020, ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels collocated with the ASME 2020 Heat Transfer Summer Conference and the ASME 2020 Fluids Engineering Division Summer Meeting)

   Altering soil wettability by inclusion of hydrophobicity could be an effective way to restrict evaporation from soil, thereby conserving water resources. In this study, 4-μL sessile water droplets were evaporated from an artificial soil millipore comprised of three glass (i.e. hydrophilic) and Teflon (i.e. hydrophobic) 2.38-mm-diameter beads. The distance between the beads were kept constant (i.e. center-to-center spacing of 3.1 mm). Experiments were conducted in an environmental chamber at an air temperature of 20°C and 30% and 75% relative humidity (RH). Evaporation rates were faster (i.e. ∼19 minutes and ∼49 minutes at 30% and 75% RH) from hydrophilic pores than the Teflon one (i.e. ∼24 minutes and ∼52 minutes at 30% and 75% RH) due in part to greater air-water contact area. Rupture of liquid droplets during evaporation was analyzed and predictions were made on rupture based on contact line pinning and depinning, projected surface area just before rupture, and pressure difference across liquid-vapor interface. It was observed that, in hydrophilic pore, the liquid droplet was pinned on one bead and the contact line on the other beads continuously decreased by deforming the liquid-vapor interface, though all three gas-liquid-solid contact lines decreased at a marginal rate in hydrophobic pore. For hydrophilic and hydrophobic pores, approximately 1.7 mm2 and 1.8–2 mm2 projected area of the droplet was predicted at 30% and 75% RH just before rupture occurs. Associated pressure difference responsible for rupture was estimated based on the deformation of curvature of liquid-vapor interface. 

   more » « less
5. EVAPORATION FROM POROUS MEDIA: SINGLE HYDROPHOBIC AND HYDROPHILIC PORES

   https://doi.org/10.1615/TFEC2018.ewf.020972  

   Huber, Ryan; Chen, Xi; Derby, Melanie M. (March 2018, 3rd Thermal and Fluids Engineering Conference (TFEC))

   Worldwide, agriculture is responsible for two-thirds of water withdrawals because many productive, food-producing areas lack sufficient rainfall to grow crops without irrigation. In much of the Great Plains, the Ogallala Aquifer is the primary water source for food production, and diminishing water levels require improvements in sustainable agriculture. Reductions in soil evaporation rates will reduce irrigation demands and overall water consumption for crop production, thereby conserving water in areas such as the Ogallala Aquifer. In this study, evaporation of water is studied in a single pore comprised of three 2.38-mm diameter beads to simulate a soil pore. Evaporation times and high-speed imaging were recorded for hydrophilic (i.e., glass) and hydrophobic (i.e., Teflon) beads. Experiments were conducted with moist air at approximately 22.5 °C and approximately 60% RH. Water evaporated faster from the hydrophilic beads; contact line and angle dynamics were documented for hydrophobic and hydrophilic cases. The study found that for droplets on hydrophobic beads the evaporation times were on average 55 minutes and contact area decreased with evaporation. In contrast, water droplets on hydrophilic beads averaged evaporation times of 40 minutes and decreasing contact angle occurred during evaporation. 

   more » « less