Session: 10-01: Heat and Mass Transfer in Small Scale

Paper Number: 131261

131261 - An Investigation of the Co-Boiling Phenomenon Between Napl and Water Within Porous Media: Implications for In-Situ Thermal Desorption 

Abstract: 

The improper discharge of non-aqueous phase liquids (NAPL) has led to an escalating issue of organic contamination in both soil and groundwater. These contaminants tend to accumulate on strata with low permeability, posing a continuous risk to the quality of soil and groundwater. In situ thermal desorption (ISTD) provides an efficient solution for remediating soil and groundwater contaminated with NAPL. It is crucial to establish the correlation between the increase in subsurface temperature and the removal of NAPL to optimize energy consumption during the ISTD process. The coexistence of NAPL and water, due to their immiscibility, results in a composite system exhibiting a vapor pressure that exceeds that of any individual pure component. This elevation in vapor pressure subsequently induces a decrease in the boiling point at a given environmental pressure. This particular behavior, referred to as “co-boiling” in previous studies, facilitates the removal of NAPL under conditions where the temperature is maintained below its boiling point. The phenomenon of co-boiling involving NAPL and water is frequently observed in the implementation of ISTD. It has been empirically established that this occurrence significantly influences the underground temperature field beneath the surface during the ISTD process. Our prior investigations have revealed that within the two immiscible fluid strata, where water serves as the primary fluid and NAPL functions as the secondary fluid constituent, bubble formation occurs and accumulates proximal to the interface of the two fluids. These vapor bubbles ascend through the alternate immiscible fluid, instigating disturbances, exhibiting distinct temperature fields across different phases, and are influenced by the thermal input. Nevertheless, the implications of the co-boiling phenomenon involving two immiscible liquids transpiring within porous media during ISTD application remain to be elucidated.

In this study, our objective was to delineate the scope of the co-boiling impact on the temperature field, particularly discerning whether this effect is restricted to the proximity of the NAPL-water interface or extends throughout the entire domain where the NAPL and water phases coexist. Additionally, we established a relationship between the temperature field during the co-boiling phase and the subsequent removal of NAPL. We designed a two-dimensional sand box, the interior of which was filled with transparent glass beads with a diameter of 1 mm. The sandbox, measuring 400 mm x 365 mm x 42 mm. The entire experimental apparatus was situated within a dark environmental chamber to mitigate the potential influence of external light variations on the experimental outcomes. The orthogonal distance between the sandbox and the LED panel which operated at a power consumption of 18 W was meticulously adjusted to 0.3 m. We employed a digital camera (EOS 5D Mark IV, Canon, Japan) to continuously capture the co-boiling phenomenon of NAPL and water within the sandbox. To facilitate observation, we utilized Oil Red (0.05g/L, Aladdin) to stain the NAPL phase. The heating rod, with a maximum input power of 500 W, was equipped with a temperature controller and thermal insulation patches on both sides to ensure precise temperature regulation. We employed a temperature heat flow meter (JTNT-A, JT. Technology) to continuously monitor and calculate the heat leakage of the sandbox. Concurrently, we utilized a thermocouple array (WRNK 191, XUNFEI Meter) for real-time surveillance of the temperature field within the sandbox. Leveraging image processing methodologies, we are able to quasi-continuously monitor the entire mass of NAPL without perturbing the inherent flow dynamics and temperature field. After considering the temporal and spatial fluctuations of light, we select an apt the appropriate color model and color channel, transform the monochrome light adjustment image into a binary image for NAPL quantification. Subsequently, we compute the correlation between NAPL saturation and the image, thereby enabling the determination of NAPL saturation. This investigation will augment our comprehension of the subterranean thermal mass transfer mechanism, thereby laying a robust foundation for achieving precise control and optimizing energy conservation during ISTD.

Presenting Author: Xinyu Xu Zhejiang University

Presenting Author Biography: Xinyu Xu is a currently pursuing her Ph.D. in the School of Energy Engineering, Zhejiang University. Her research interests mainly focus on heat and mass transfer during co-boiling process between NAPL and water and its application for in-situ thermal desorption of organic-contaminated sites.

Authors:

Xinyu Xu Zhejiang University
Hu Nan Zhejiang University
Liwu Fan Zhejiang University