Boiliers Flashcards
What are the main components of a boiler?
Burner, combustion chamber, heat exchanger, flue,controls & accessories, Enclosure.
What are the accessories on a boiler?
Safety relief valve, thermal insulation, pre-heater(oil only), high temperature limit control, automatic air vent,pressure gauge, blow down valve.
What is the functions of a boilers burner,
To mix the fuel and air in the correct proportions for optimal efficiency. Too little air results in incomplete combustion and CO. Too much dilutes the heat which results in reduced efficiency.
Why are diluted air flues used.
So that the waste gases can be released below roof level without releasing carbon monoxide.
What is the purpose of the pre-heater
It pre heats oil so that it is atomised and burns most efficiently.
What is the purpose of the high temperature limit control
It switches of the gas supply if the water reaches dangerous temperatures.
What is the purpose of the automatic air vent.
To release the air in the system, to prevent cavitation and blockage of the water flow, and air locks.
What is the purpose of the pressure gauge
To display the pressure in the system.
What is the purpose of the blow down valve.
To clean the system of any sludge/ sediment. This is a manual valve.
What are the two types of boiler losses and what are the typical values
Losses through the case, losses through the flue. Casing losses are about 2-3%.
What is the formula for boiler efficiency
(Flow rate x specific heat capacity of water x delta T)/(mass flow x calorific value)
What is calorific value
It is the number of joules of heat produced by burning a kg of a given substance.
What is indirect efficiency
It is efficiency measured via the heat losses.
How do you calculate heat loss through the flue.
Mass flow rate of the flue x specific heat capacity x 9x (flue temp - ambient temperature).
What is the difference between gross and net efficiency.
Gross calorific value is if the products of combustion leave the flue at atmospheric temperature. Net efficiency is measured against a defined temperature that is higher than the atmospheric temperature. Net efficiency will always be higher than gross efficiency.
