Correct Answer: the flames and hot gases pass through the tubes which are surrounded by water
3. A device used to empty the boiler whenever required and to discharge the mud, scale or sediments which are accumulated at the bottom of the boiler, is called blow off cock.
7. The boiler efficiency is given by (where m = Total mass of water evaporated into steam in kg/h, mf = Mass of fuel in kg/h, C = Calorific valve of fuel in kJ/kg of fuel, h = Total heat of steam in kJ/kg, and hf1 = Sensible heat of feed water in kJ /kg)