Gang Chen

Although ubiquitous in nature and industrial processes, transport processes at the interface during evaporation and condensation are still poorly understood. Experiments have shown temperature discontinuities at the interface during evaporation and condensation but the experimentally reported interface temperature jump varies by two orders of magnitude. Even the direction of such temperature jump is still being debated. Using kinetic-theory based expressions for the interfacial mass flux and heat flux, we solve the coupled problem between the liquid and the vapor phase during evaporation and condensation. Our model shows that when evaporation or condensation happens, an intrinsic temperature difference develops across the interface, due to the mismatch of the enthalpy carried by vapor at the interface and the bulk region. The vapor temperature near the interface cools below the saturation temperature …

Although water is almost transparent to visible light, we demonstrate that the air–water interface interacts strongly with visible light via what we hypothesize as the photomolecular effect. In this effect, transverse-magnetic polarized photons cleave off water clusters from the air–water interface. We use 14 different experiments to demonstrate the existence of this effect and its dependence on the wavelength, incident angle, and polarization of visible light. We further demonstrate that visible light heats up thin fogs, suggesting that this process can impact weather, climate, and the earth’s water cycle and that it provides a mechanism to resolve the long-standing puzzle of larger measured clouds absorption to solar radiation than theory could predict based on bulk water optical constants. Our study suggests that the photomolecular effect should happen widely in nature, from clouds to fogs, ocean to soil surfaces, and plant …

Salt solutions have attracted significant interest as water sorbents for a wide range of applications due to their large hygroscopicity and low cost. However, despite their promise, no existing model fully describes the experimentally observed absorption and desorption behavior of salts. Here, we develop a model that accurately captures absorption and desorption of water vapor into salt solutions. Our results show that the nonlinear driving force due to the chemical activity of water leads to previously unexplained behaviors such as faster desorption than absorption and absorption-rate dependence on humidity. We leverage our model to demonstrate the trade-off of uptake and sorption time as the humidity and salt type are changed and show the dependence of the timescale on the system's parameters. This model represents a fundamental advancement in the understanding of salt solution absorption-desorption and …

The present disclosure generally relates to textiles that are optimized to maximize moisture wicking and evaporative performance thereof. In some embodiments, raw polyethylene (PE) powder can be extruded into fibers that can be modified by oxidation along a surface thereof to increase hydrophilicity of the surface. Once sufficiently oxidized, the fibers can be bundled to form multi-filament yarns that can then be spun, weaved, knitted, and/or otherwise associated with one another to form a polyethylene fabric. The PE fibers can be further modified to increase a capillary force of the bundle, thereby further increasing hydrophilicity of the resulting fabric. Engineering of the capillary force can be performed by optimizing one or more of a fiber size, a density, or a cross-section of the fibers and/or the bundles. The resultant fabric can exhibit a strong weight reduction, stain resistance, and drying capabilities, among other …

D64. 00008: Cloud Absorption and Fog Heating by Visible Light due to Photomolecular Effect

Exergy represents the maximum useful work possible when a system at a specific state reaches equilibrium with the environmental dead state at temperature To. Correspondingly, the exergy difference between two states is the maximum work output when the system changes from one state to the other, assuming that during the processes, the system exchanges heat reversibly with the environment. If the process involves irreversibility, the Guoy-Stodola theorem states that the exergy destruction equals the entropy generated during the process multiplied by To. The exergy concept and the Gouy-Stodola theorem are widely used to optimize processes or systems, even when they are not directly connected to the environment. In the past, questions have been raised on if To is the proper temperature to use in calculating the exergy destruction. Here, we start from the first and the second laws of thermodynamics to unambiguously show that the useful energy loss (UEL) of a system or process should equal to the entropy generation multiplied by an equivalent temperature associated with the entropy rejected out of the entire system. For many engineering systems and processes, this entropy rejection temperature can be easily calculated as the ratio of the changes of the enthalpy and entropy of the fluid stream carrying the entropy out, which we call the state-change temperature. The UEL is unambiguous and independent of the environmental dead state, and it should be used for system optimization rather than the exergy destruction.

Kinetic theory has long predicted that temperature inversion may happen in the vapor-phase for evaporation and condensation between two parallel plates, ie, the vapor temperature at the condensation interface is higher than that at the evaporation interface. However, past studies have neglected transport in the liquid phases, which usually determine the evaporation and condensation rates. This disconnect has limited the acceptance of the kinetic theory in practical heat transfer models. In this paper, we combine interfacial conditions for mass and heat fluxes with continuum descriptions in the bulk regions of the vapor and the liquid phases to obtain a complete picture for the classical problem of evaporation and condensation between two parallel plates. The criterion for temperature inversion is rederived analytically. We also prove that the temperature jump at each interface is in the same direction as externally …

One central challenge in understanding phonon thermal transport is a lack of experimental tools to investigate frequency‐resolved phonon transport. Although recent advances in computation lead to frequency‐resolved information, it is hindered by unknown defects in bulk regions and at interfaces. Here, a framework that can uncover microscopic phonon transport information in heterostructures is presented, integrating state‐of‐the‐art ultrafast electron diffraction (UED) with advanced scientific machine learning (SciML). Taking advantage of the dual temporal and reciprocal‐space resolution in UED, and the ability of SciML to solve inverse problems involving O(103)$\mathcal{O}({10^3})$ coupled Boltzmann transport equations, the frequency‐dependent interfacial transmittance and frequency‐dependent relaxation times of the heterostructure from the diffraction patterns are reliably recovered. The framework is …