Unit Operations - Basic to Advance

A: Heat transfer by conduction occurs through direct molecular collisions and energy transfer within a material without any movement of the material itself, such as heat flowing through a metal rod. Convection, on the other hand, involves heat transfer through the bulk motion of fluids (liquids or gases), where the fluid carries thermal energy as it moves. Convection can be natural (caused by buoyancy effects due to density differences) or forced (induced by external means like a pump or fan). Understanding these mechanisms helps in designing heat exchangers and thermal systems. More on this topic can be found at https://www.engineeringtoolbox.com/conduction-convection-radiation-d_430.html.

A: The rate of diffusion in gases is influenced by several factors including the concentration gradient, temperature, pressure, and the properties of the gases involved. According to Fick's law, the diffusion flux is proportional to the concentration gradient. Higher temperatures increase molecular motion, thus enhancing diffusion rates. Pressure can affect the gas density, which also impacts diffusion. Additionally, the molecular size and interactions between gas molecules play a significant role. For quantitative analysis, the Chapman-Enskog equation is used to estimate diffusion coefficients. For detailed information, refer to https://www.sciencedirect.com/topics/engineering/mass-transfer.

A: A distillation column separates components based on differences in their volatilities or boiling points. The mixture is heated to vaporize the more volatile component, which rises through the column. As the vapor ascends, it contacts descending liquid, facilitating mass and heat exchange. Components with lower boiling points concentrate in the vapor phase and are collected as the distillate, while those with higher boiling points condense and are removed as bottoms. The column efficiency depends on factors like the number of theoretical stages, reflux ratio, and tray or packing design. An excellent reference to understand distillation is Warren L. McCabe's 'Unit Operations of Chemical Engineering.' More info available at https://en.wikipedia.org/wiki/Distillation.

A: Pressure drop in packed columns refers to the loss of pressure as fluids flow through the packing material inside the column. It is caused by friction between the fluid and packing surfaces and the resistance to flow through the void spaces. Pressure drop is significant as it affects the hydraulic performance, energy consumption (pumping costs), and operational stability of processes like absorption and distillation. Excessive pressure drop can cause flooding or channeling in the column. Engineers use correlations such as the Ergun equation to estimate pressure drop in packed beds. A detailed explanation is available at https://www.cheresources.com/content/articles/pressuredroppackedbed.

A: Absorption is a mass transfer process where a substance (the absorbate) penetrates into the bulk of another phase (the absorbent), like gas dissolving into a liquid. Adsorption involves the accumulation of molecules only on the surface of a solid or liquid, without entering the bulk phase, such as activated carbon capturing impurities on its surface. Both processes are used for separation and purification, but their mechanisms differ. Absorption involves solubility and diffusivity, while adsorption depends on surface area and chemical affinity. For more insights, see https://www.britannica.com/science/adsorption.

A: Drying is the unit operation of removing moisture from solids by evaporation. It typically occurs in three stages: the initial warming period, the constant rate period, and the falling rate period. In the constant rate period, moisture evaporates from the surface at a constant rate while in the falling rate period, moisture removal becomes diffusion-limited as water evaporates from within the solid. Drying is critical in industries like pharmaceuticals, food, and chemicals to increase product shelf-life or prepare materials for further processing. Detailed physical models and drying kinetics can be found in 'Unit Operations in Food Processing' by K. S. Subrahmanyam. More info at https://www.ahrebs.com/blog/drying.

A: The flow of incompressible fluids in pipes is governed primarily by the Navier-Stokes equations, which describe momentum conservation, and the continuity equation for mass conservation. For practical engineering, these reduce to Bernoulli's equation for inviscid flow and the Darcy-Weisbach equation to calculate head loss due to friction. Engineers use these equations to design pipe networks, select pump sizes, and predict pressure drops. Moody charts are also commonly used to determine friction factors. For an in-depth explanation, check https://www.sciencedirect.com/topics/engineering/pipe-flow and https://www.engineeringtoolbox.com/pipe-pressure-loss-d_253.html.

A: Centrifugation is a separation technique that uses centrifugal force to accelerate the sedimentation of particles within a suspension. By spinning a sample at high speeds, denser particles are forced outward to the bottom of the centrifuge tube, separating from the liquid phase. This method is widely applied in chemical engineering to separate solids from liquids, clarify liquids, and in biochemical applications for separating cellular components. The separation efficiency depends on rotor speed, time, and particle size. For further reading, see https://www.britannica.com/science/centrifugation.