MT-Peer Discussion - Session-3

Karthikeyan led a session focused on mass transfer, emphasizing its importance for placements and chemical engineering design-based jobs. He planned to cover GATE questions from 2024, 2023, and potentially 2022, depending on time. Before diving into the questions, Kartikeyan invited participants to share any doubts or unclear concepts about mass transfer, offering to clarify them during the session.

Karthikeyan explained the concept of drying rates and moisture content, discussing how the rate remains constant initially and then decreases linearly due to a shift from surface phenomena to diffusion control. He used a formula to find the critical moisture content and total drying time, substituting given values to solve the problem. Karthikeyan emphasized understanding these concepts for the GATE examination and invited discussion on why the drying rate decreases after the critical moisture content. Studen-1 contributed by explaining the transition from surface phenomena to diffusion control, which affects the drying rate.

Karthikeyan explained the process of finding the reflux ratio in a binary distillation column using the McCabe-Thiele method. He outlined the steps to derive the operating lines, equilibrium line, and calculate the reflux ratio using the given data on vapor compositions. Karthikeyan emphasized the importance of understanding the equilibrium relationship and the use of ideal trays. He also highlighted common mistakes to avoid when solving such problems.

Karthikeyan explained two problems related to distillation. In the first problem, he demonstrated how to find the slope and intercept of an equilibrium line using three known points, which led to finding the reflux ratio. In the second problem, he discussed an absorption column where ethanol concentration needed to be reduced from 5 to 0.3 mole percentage using pure water as the solvent, explaining how to calculate the minimum and actual \(L/G\) ratios and find the mole fraction of ethanol in the spent water.

Karthikeyan explained the concepts of loading, flooding, weeping, foaming, and channeling in gas-liquid contactors. He clarified that loading occurs when gas flow rate increases, causing liquid accumulation, while flooding happens when gas flow exceeds a limit, stopping downward liquid movement. Smrti and Jeevitha participated in the discussion, with Smrti correctly defining foaming and channeling. Karthikeyan also addressed common misconceptions about tray towers and packed towers, emphasizing that tray towers are preferred for systems requiring frequent cleaning due to their ease and cost-effectiveness of cleaning.

Karthikeyan explained a batch distillation problem involving a binary mixture where the initial mole fraction of component \(B\) was 0.9, and the final mole fraction was 0.1, with a constant relative volatility of 4.5. He emphasized the importance of determining which component is more volatile before solving such problems and outlined the steps to find the mole fraction of \(B\) remaining in the vessel using the Rayleigh equation. Karthikeyan also noted that the final answer should be rounded to three decimal places to avoid incorrect marks.

Karthikeyan explained the concept of humid eater and its unit, kilojoule per kilogram Kelvin, in the context of an Adiabatic saturator where no heat is supplied. He emphasized the importance of understanding the derivation of the equation to grasp why each term is placed as it is. Karthikeyan discussed the process of air being initially at 50°C and not saturated, being sent into the Adiabatic saturator to achieve full humidification, resulting in an exit temperature of 25°C. He highlighted the need to use the specific heat of the water vapor and the importance of memorizing the specific heat of water vapor, which is 1.87 or 1.88 kJ/(kg.^oC).

Karthikeyan explained the concept of evaporative cooling and how it relates to the wet bulb temperature, which is always less than the dry bulb temperature due to the evaporation of water from the wet wick into the air. He described how the wet bulb temperature can be measured and used alongside the dry bulb temperature to determine humidity levels using a psychometric chart. Student-1 contributed by explaining that the difference in moisture content between dry air and air with a wet wick causes the lower reading on a wet bulb thermometer.

Karthikeyan explained a problem involving wet bulb temperature and humidity calculations, emphasizing the importance of understanding concepts like wet bulb depression and Antoine's equation. He demonstrated how to find the wet bulb temperature, saturation pressure, and humidity using given data and equations. Karthikeyan stressed the relevance of these concepts in cooling tower design and encouraged the group to ask questions for further clarification.