Question

In flashing of jams, the temperature of concentrated jam _____ on flashing. Also, the vapor pressure of the concentrated jam _____

(a) Decreases, sustains combustion

(b) Increases, sustains combustion

(c) Decreases, does NOT sustain combustion

(d) Increases, does NOT sustain combustion

This question was addressed to me in an interview for job.

My doubt stems from Unit Operations topic in chapter Heat Transfer Equipment, Microwave Heating, Evaporation, Diffusion and Mass Transfer and Dehydration of Food Engineering

Answer 1

Right choice is (a) Decreases, sustains combustion

The explanation is: In flashing of jams, the temperature of concentrated jam decreases on flashing as the source of ignition is the solvent itself.  Also, the vapor pressure of the concentrated jam sustains combustion as the temperature is brought down to the flash point which is the lowest temperature at which the vapor pressure is just sufficient to sustain combustion.