Thank you so much for this! I have now obtained the answerharuspex said:
Heat flux is the rate at which thermal energy is transferred through a surface per unit area. It is measured in units of energy per unit time per unit area, such as watts per square meter.
Heat flux from hot gas in a pipe to water outside occurs through a process called convection. This is when heat is transferred through a fluid, such as air or water, by the movement of that fluid.
The rate of heat flux is affected by several factors, including the temperature difference between the hot gas and the water, the surface area of contact between the two substances, and the properties of the materials involved.
The rate of heat flux can be calculated using the equation Q = hAΔT, where Q is the heat flux, h is the convective heat transfer coefficient, A is the surface area of contact, and ΔT is the temperature difference between the hot gas and the water.
The rate of heat flux can be increased by increasing the temperature difference between the hot gas and the water, increasing the surface area of contact, or increasing the convective heat transfer coefficient. This can be achieved through methods such as increasing the flow rate of the fluid or using materials with higher thermal conductivity.