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ABSTRACT
Evaporation and steam generation are two of the most vital processes in industry. A new method to advance the efficiency of evaporation involves localizing heat at the water surface where the vapor escapes into the air to minimize energy loss. In this research, we numerically investigate the improvement of a novel evaporation process via solar heat localization in a porous medium. A layer of carbon foam with a combination of interconnected and dead-end pores with a high hydrophilicity surface adjacent to a layer of expanded graphite with known porosity and properties were modeled numerically using a finite volume method. The hydrophilic porous media facilitates the capillary forces for better transportation of the bulk water through the porous media to the top surface of the porous media where the absorbed solar energy is delivered to the water inside the pores for evaporation. Continuity, momentum, heat and mass transfer equations were solved in this modeling effort. The modeling results were validated with the experimental data available in the literature. The findings in this numerical study can shed light on the complex interplay between the fluid dynamics and heat and mass transfer across the porous medium, which are important for efficient evaporation processes.
Acknowledgments
Authors thank the Industrial Assessment Center, Center for Manufacturing Research, and Center for Energy Research at Tennessee Technological University for their financial and technical support.
Nomenclature
| A | = | Interfacial area density, kg·m−2 |
| AA | = | Middle line of graphite region along the x-axis |
| BB | = | Middle line of carbon foam along the x-axis |
| C | = | Inertial resistance factor, dimensionless |
| CC | = | Middle line of water along the x-axis |
| d | = | Diameter, m |
| D | = | Chamber diameter, m |
| DD | = | Center line of the chamber along the y-axis |
| E | = | Energy, J |
| F | = | Evaporation-Condensation Flux, kg·s−1·m−2 |
| = | Body force, N | |
| = | Gravitational constant, m·s−2 | |
| h | = | Sensible enthalpy, J·kg−1 |
| K | = | Permeability, m2 |
| L | = | Latent heat, J·kg−1 |
| L1 | = | Graphite layer height, m |
| L2 | = | Carbon foam layer height, m |
| L3 | = | Bulk water height, m |
| M | = | Coefficient matrices, dimensionless |
| = | Mass flux, kg.s−1 | |
| n | = | Number of phases, dimensionless |
| N | = | Coefficient matrices, dimensionless |
| P | = | Pressure, Pa |
| P* | = | Vapor partial pressure, Pa |
| q | = | Solar irradiation, J·s−1 |
| R | = | Universal gas constant, J·K−1·mol−1 |
| S | = | Volumetric heat sources, J·m−3 |
| SE | = | Other volumetric heat sources, J |
| T | = | Temperature, °C |
| T* | = | Vapor partial temperature, °C |
| t | = | Time, s |
Greek symbols
| α | = | Volume fraction, dimensionless |
| β | = | Vapor molecules going into the liquid surface, dimensionless |
| f | = | Inverse of the relaxation time, s−1 |
| ρ | = | Vapor Density, kg·m−3 |
| v | = | Specific volume, m3kg−1 |
| = | Velocity, m·s−1 | |
| μ | = | Viscosity, m·Pa·s |
| η | = | Efficiency, dimensionless |
Subscripts
| b | = | Bubble |
| dr | = | Drift |
| eff | = | Effective |
| i | = | Vector component of x, y, or z |
| k | = | Phase k |
| l | = | Liquid |
| lv | = | Liquid–vapor phase change |
| m | = | Mass |
| sat | = | Saturation |
| th | = | Thermal |
| v | = | Vapor, dimensionless |
Additional information
Notes on contributors
Hamidreza Ghasemi Bahraseman
Hamidreza Ghasemi Bahraseman is a Ph.D. student at Tennessee Technological University in Cookeville, TN, USA, working under supervision of Dr. Languri. He received his Biomedical Engineering M.Sc. Degree in 2012 from the Science and Research Branch of Azad University in Tehran, Iran. His current research is on solar heat harvesting for enhanced energy storage and evaporation systems.
Ehsan Mohseni Languri
Ehsan Mohseni Languri received his Mechanical Engineering Ph.D. in 2011 from the University of Wisconsin-Milwaukee, followed by two Postdoctoral Fellow appointments at the University of Wisconsin-Milwaukee and Texas A&M University. Later, he worked as a Senior Mechanical Engineer at Applied Research Associates. He is currently an Assistant Professor in the Mechanical Engineering Department and also Associate Director of the U.S. Department of Energy-funded Industrial Assessment Center, both at Tennessee Tech University. His current research include thermal energy storage and conversion systems and efficiency enhancement in energy systems.