A computational study on nanofluid impingement jets in thermal management of photovoltaic panel

Effects of surface active agents on DNAPL migration and distribution in saturated porous media.

The presence of multicomponent nonaqueous phase liquid (NAPL) source zones in the subsurface can significantly complicate remediation efforts, transport predictions, and the development of accurate risk assessments. A series of flow-cell experiments was conducted to investigate the effectiveness of two different enhanced-solubilization agents for the removal of a multicomponent dense nonaqueous phase liquid (DNAPL) source zone from homogeneous porous media. The source zone consisted of an equal 1:1:1 mole mixture of cis-1,2-dichloroethene (DCE), trichloroethene (TCE), and tetrachloroethene (PCE) with NAPL saturation (Sn) targeted between 8 and 14 %. Solutions (5 wt%) of hydroxypropyl-β-cyclodextrin (HPCD) and sodium dodecyl sulfate (SDS) were flushed through the flow-cell system until nearly complete contaminant removal was achieved. Analysis of elution curves indicate that SDS was approximately 10 times more efficient at removing all three components from the system compared to HPCD. Although enhancement factor magnitudes vary for each specific contaminant component and enhanced-solubilization agent, the lowest-solubility contaminant component (i.e., PCE) consistently experienced the greatest relative solubility enhancement during flushing. SDS was generally superior when evaluated on a recovery basis; however, HPCD outperformed SDS for all contaminant components when compared based on moles-contaminant to moles-reagent removal efficiency analysis. Contaminant mass flux reduction analysis showed that enhanced-solubilization flushing (HPCD and SDS) resulted in general inefficient contaminant removal behavior. Raoult’s Law could be used to successfully predict aqueous contaminant concentrations from the multicomponent DNAPL source zone, indicating that dissolution processes were relatively ideal during both HPCD and SDS enhanced-solubilization flushing. These findings suggest that multicomponent NAPL source dissolution and removal depend upon the flushing agent itself and of the solubility and properties of the individual components of the NAPL mixture. The selection of a particular enhanced-flushing agent should be evaluated carefully prior to remediation as the dissolution, removal, and mass flux behavior of each component can vary significantly.

Intermediate-Scale Investigation of Enhanced-Solubilization Agents on the Dissolution and Removal of a Multicomponent Dense Nonaqueous Phase Liquid (DNAPL) Source

A pore-scale investigation of heavy crude oil trapping and removal during surfactant-enhanced remediation.

Experiments and sensitivity coefficients analysis for multiphase flow model calibration of enhanced DNAPL dissolution.

Machine learning regression-CFD models for the nanofluid heat transfer of a microchannel heat sink with double synthetic jets

A series of column and flow cell experiments were conducted to investigate the impact of nonuniform organic liquid distribution on the relationship between reductions in contaminant mass discharge and reductions in source zone mass under conditions of enhanced-solubilization flushing. Trichloroethene was used as the model organic liquid, and sodium dodecyl sulfate and ethanol were used as representative enhanced-flushing reagents. The results were compared to those of waterflood control experiments. Concentrations of trichloroethene in the effluent exhibited a multi-step behavior with time, wherein multiple secondary periods of quasi steady state were observed. This nonideal behavior was observed for both the waterflood and enhanced-flushing experiments. For all flow cell experiments, the later stage of mass removal was controlled by the more poorly accessible mass associated with higher-saturation zones. The profiles relating reductions in contaminant mass discharge and reductions in mass exhibited a generally similar behavior for both the waterflood and enhanced-flushing experiments. This indicates that while the rates and magnitudes of mass removal are altered by the presence of a solubilization reagent solution, the fundamental mass removal process is not. The profiles obtained for the flow cell systems differed from those obtained for the column systems, highlighting the impact of source zone heterogeneity on mass removal behavior.

/pdf/impact-of-enhanced-flushing-reagents-and-organic-liquid-2uoa6l667k.pdf

Impact of Enhanced-Flushing Reagents and Organic Liquid Distribution on Mass Removal and Mass Discharge Reduction

Nanofluid heat transfer in a microchannel heat sink with multiple synthetic jets and protrusions

Phase change materials (PCMs) can isothermally absorb heat in electronic devices, and optimizing PCM heat sink designs to improve heat dissipation is therefore important to improve the performance of a system, including its ability to withstand cyclic thermal shocks. In this study, a low melting point alloy (LMPA)-based heat sink with crossed copper fins is developed and optimized to cope with cyclic ultra-high thermal shocks (100 W/cm²). Gallium is selected as an LMPA candidate due to its high thermal conductivity. The numerical model is validated against available experimental results where the transient temperature is predicted with a maximum discrepancy of 4.9%. The main goal of the study is to determine the design configurations that minimize the heat sink peak temperature after thermal shock and with minimal cooling time. An approach that couples the Response Surface Methodology (RSM) with numerical simulations is applied for this purpose. The height and thickness of fins and the PCM thickness, are treated as design variables in the two-objective optimization. Two correlations are presented to estimate the peak temperature and cooling period of the system in presence of thermal shock. The effect of the three parameters is thoroughly analysed following the optimization process. The optimum values for fin height, fin thickness and PCM thickness are found to be 8.77 mm, 0.55 mm, and 1.51 mm, respectively, where the PCM volumetric percentage is found to be 53.73%. Single-objective optimizations are also conducted to design a system satisfying a minimum peak temperature or minimum cooling period separately. Overall, the cyclic evaluation shows that the two-objective optimized heat sink delivers peak temperature up to 8.63% and 36.26% lower than that of single-objective optimized systems after five cycles of thermal shocks within periods of 30–60 s. This study shows how LMPA-based heat sink may be optimized and demonstrates a potential approach in the design of novel thermal management systems to prevent overheating from thermal shocks. 

Ann Russo Lee

Papers

Machine learning regression-CFD models for the nanofluid heat transfer of a microchannel heat sink with double synthetic jets

A computational study on nanofluid impingement jets in thermal management of photovoltaic panel

Impact of Enhanced-Flushing Reagents and Organic Liquid Distribution on Mass Removal and Mass Discharge Reduction

Nanofluid heat transfer in a microchannel heat sink with multiple synthetic jets and protrusions

Improvement on the cyclic thermal shock resistance of the electronics heat sinks using two-objective optimization