What is the heat source to a tray?

• A. Vapors from Below
• B. Liquid from Above
• C. Electric Heater Above the Tray
• D. Ambient Air

Answer: (A)

Heat for a tray comes from the vapors rising from below. The bottom portion is heated, boiling the liquid there and sending vapors upward. As these vapors pass through each tray, they transfer heat to the liquid on the tray, causing it to vaporize and continue the process. This energy flow from below is what drives the tray’s heating. The other options don’t fit this setup: liquid from above isn’t a heat source for the tray, ambient air isn’t used as a heat source in this arrangement, and an electric heater above the tray would alter the normal heat transfer path and isn’t how heat is supplied to the tray in a typical distillation column.