Chemical Engineering Community Forum - Recent Posts

For the GATE 2027, Can you share me the formula sheets or cheat sheets

nitishg — Fri, 17 Jul 2026 09:37:05 +0000

I am looking for the Chemical Engineering GATE cheat sheets for the preparation of GATE 2027. Can you people share me?

RE: Fouling Factor for Cooling Tower range

nitishg — Fri, 17 Jul 2026 09:34:27 +0000

This depends heavily on your cooling water quality, but as a starting point, TEMA gives fouling resistances in the range of 0.0002 to 0.0005 m²·K/W (0.001 to 0.003 hr·ft²·°F/BTU) for treated cooling tower water, going up toward 0.0005-0.001 for untreated or brackish water, and higher still for seawater or water with high suspended solids.

If you're doing a new design, don't just grab a number from a table blindly, you should ask your water treatment vendor for actual fouling data from similar service, because the TEMA values are conservative defaults from decades ago and can lead to serious over-design (bigger exchanger, higher pressure drop, higher cost) if applied everywhere without thought.

On cleaning frequency that should be less about a fixed calendar and more about tracking actual performance. Trend your exchanger's overall U value (back-calculated from operating data) over time. Once it drops to somewhere around 75-80% of clean/design U, or once your approach temperature starts creeping up and you can't hit your outlet target even with full water flow, that's your signal to clean. Typical intervals for cooling water service run anywhere from 6 months to 2 years depending on water treatment quality, but let the data decide, not the calendar.

RE: How do I estimate the number of theoretical stages using the McCabe-Thiele method for a non-ideal system?

nitishg — Fri, 17 Jul 2026 09:32:14 +0000

The classic McCabe-Thiele method (operating lines plus equilibrium curve, stepping off stages between them) technically assumes constant molar overflow, which strictly only holds for near-ideal systems with similar molar heats of vaporization. For a genuinely non-ideal system, you have a couple of options depending on how far off ideal you are.

If the non-ideality is moderate, you can often still use McCabe-Thiele but generate the equilibrium curve (x-y diagram) from actual VLE data or an activity coefficient model (NRTL, UNIQUAC, Wilson) rather than assuming Raoult's law that alone captures a lot of the real behavior, including azeotropes, which will show up clearly as the equilibrium curve crossing the 45° line. The graphical stepping-off procedure itself still works fine as long as your equilibrium curve is accurate.

If the system also has significantly different heats of vaporization between components (so constant molar overflow genuinely fails), you need to move to an energy-balance-based method - either the Ponchon-Savarit method (which uses an enthalpy-composition diagram and accounts for varying liquid and vapor flows tray to tray), or more practically today, just build it in Aspen Plus or HYSYS with a rigorous tray-by-tray simulation (RadFrac or the equivalent) using a proper activity coefficient or equation-of-state model. Honestly, for anything beyond a classroom problem or first-pass estimate, rigorous simulation has mostly replaced hand methods for non-ideal systems - use McCabe-Thiele for intuition and quick checks, but verify with simulation before you commit to a design.

You can learn the Mccabe-Thiele diagram here - https://youtu.be/gw2rtssRyvo?si=1AZ5S2MWQm0f5jIY

How do I estimate the number of theoretical stages using the McCabe-Thiele method for a non-ideal system?

James Smith — Wed, 15 Jul 2026 09:55:59 +0000

How do I estimate the number of theoretical stages using the McCabe-Thiele method for a non-ideal system?

Fouling Factor for Cooling Tower range

James Smith — Wed, 15 Jul 2026 09:53:47 +0000

What is a typical fouling factor for cooling water service, and how often should exchangers be cleaned?

Hi, I am James Smith

James Smith — Wed, 15 Jul 2026 09:40:12 +0000

Hi everyone, my name is James! I'm based in the US and currently studying Chemical Engineering

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Hi, I am Nitish

nitishg — Tue, 30 Jun 2026 06:25:41 +0000

Hi, I am nitish, I am a Chemcial Engineer, i have completed my M.Tech and a working professional today, having more than 7 years of experience in chemical engineering.