Question 397Steam Plants - Assistant Engineer

The correct answer is B) gas film. The gas film on the fireside of the boiler acts as the greatest deterrent to heat transfer from the fireside to the waterside. This is because the gas film has a much lower thermal conductivity compared to the water film on the waterside. The gas film, typically composed of combustion products, creates an insulating layer that slows down the rate of heat transfer across the boiler's walls. The other options are incorrect because water film, water eddies, and gas eddies do not have as significant an impact on heat transfer as the gas film. The water film, while important, does not provide as much resistance to heat transfer as the gas film. Water and gas eddies can affect heat transfer, but their impact is not as significant as the insulating effect of the gas film.