The liquid (gas) fuel is burned in the radiation chamber of the heater, which produces high temperature flue gas, and it flows into the convection chamber as a heat carrier and is discharged from the chimney.
The crude oil to be heated first enters the convection chamber tube of the heater, and the temperature of the crude oil is generally 35 to 50 degrees, and the heat of the flue gas is mainly transferred to the outer surface of the tube by convection, and then to the inner surface of the tube by conduction, and then to the heat is transferred to the crude oil flowing inside the tube by convection.
The crude oil from the convection chamber stove pipe into the radiation chamber stove pipe, where the burner emits the flame mainly in the radiation mode to radiate part of the heat to the outer surface of the stove pipe, and another part to the furnace wall where the stove pipe is laid, and the furnace wall again in the radiation mode to radiate the heat to the outer surface of the stove pipe on the back side of the fire.
These two parts of radiant heat work together to make the outer surface of the furnace tube warm up and form a temperature difference with the inner surface of the tube, which is transferred to the inner wall of the tube by heat conduction, and the crude oil flowing inside the tube continuously gets heat from the inner wall of the tube by convection to realize the process of heating crude oil.
The crude oil is heated directly through the furnace tube, called direct heating; using another medium - heat medium to raise the temperature through the furnace tube and then transfer the heat to the crude oil through the heat exchanger is called indirect heating.