Toxic compounds, such as heavy metals, carbonyls, flavoring chemicals, and reactive oxygen species (ROS), have been detected in e-cig aerosols in concentrations that can adversely affect oral health (Figure 1). Some of these toxic compounds, such as diacetyl, can be found in some e-liquids, while others such as metals, carbonyls, and ROS, can form during e-cig use. During the vaping process, e-liquid is vaporized by a heating element operating at temperatures ranging between 100 and 300C depending on the e-cig construction and power output. High temperatures facilitate transfer of heavy metals (e.g. nickel, cadmium, chromium, and lead) from the coil into the e-liquid10. E-liquid impurities and break-down of wick material may also lead to the presence of toxic elements such as arsenic and silica in e-liquids11. Aerosolization of e-liquid leads to emissions of these substances during vaping. A higher e-cig power output as well as aging of heating element wires could increase metal emissions12. Exposure to these metals is of concern as it can cause chronic periodontitis, oral cancer, inflammation, and neurodegeneration11.
heat and mass transfer by ds kumar pdf 41
Download File: https://urlcod.com/2vBpKw
A class of problems of natural convection in tilted boxes is studied by analytical and numerical methods. The convection is assumed to be driven by uniform fluxes of heat (or mass) at two opposing walls, the remaining walls being perfect insulators. Disregarding end-region effects, an exact analytical solution is derived for the state which occurs after initial transients have decayed. This state is steady except for a spatially uniform, linear growth in the temperature (or the species concentration) which occurs whenever the fluxes are not equal. It is characterized by a uni-directional flow, a linear stratification and wall-to-wall temperature profiles which, except for the difference in absolute values due to the stratification, are the same at each crosssection. The mathematical problem is in essence nonlinear and multiple solutions are found in some parameter regions. The Bénard limit of horizontal orientation and heating from below is found to give a first bifurcation for which the steady states both before and after the bifurcation are obtained analytically. For a tilted Bénard-type problem, a steady state with top-heavy stratification is found to exist and compete with a more natural solution. The analytical solution is verified using numerical simulations and a known approximate solution for a vertical enclosure at high Rayleigh numbers. The presented solution admits arbitrary Rayleigh numbers, inclination angles and heat fluxes. Some restrictions on its validity are discussed in the paper. 2ff7e9595c
댓글