what are the convection used in writing a chemical reactions?
Answers
Answer:
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Explanation:
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Answer:
Convection is mass transfer due to the bulk motion of a fluid. For example, the flow of liquid water transports molecules or ions that are dissolved in the water. Similarly, the flow of air transports molecules present in air, including both concentrated species (e.g., oxygen and nitrogen) and dilute species (e.g., carbon dioxide). Note that the term convection in heat transfer usually refers to the combination of heat transfer by conduction and advection, where advection refers to heat transfer due to bulk fluid motion. In the field of transport phenomena, and also in this text, convection is synonymous with advection.
The animation below illustrates the convection of a region of a fluid, where a certain chemical species is concentratedSince chemical species have a nonzero diffusivity in reality, it is normal to solve the convection-diffusion equation, where both the diffusive and convective contributions to the mass transport are included:
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A discussion of the combination of the two modes of mass transport, considering the relevant length and time scales, can be found at Convection-Diffusion Equation.
Natural Convection
Even in the absence of a forced flow, a buoyancy-driven flow may still arise in the presence of temperature gradients because of density variations and the force of gravity. For volumes of fluid larger than a few milliliters under ambient conditions, convection currents normally persist dynamically, without a steady state being attained. This means that convection will, in practice, contribute to mass transport even when no forced convection applies. In the case where density variations are caused by temperature variations, this effect is referred to as natural convection, free convection, or simply buoyant convection.
We encounter this effect when putting sugar into our tea or coffee, where variations in both temperature and composition cause density gradients. Although it is best to induce forced convection by stirring with a spoon, the sugar will still reach a uniform concentration throughout the fluid much more quickly than would be predicted by diffusion theory alone. Another pronounced effect is the convection caused by gradients in salinity in oceans, which is usually referred to as gravitational convection.