critical heat flux is the heat flux at critical point

Direction of heat flux on an isothermal surface is always normal to the surface.

Heat flux is the primary performance paramater in boiler performance. Heat flux can be affected by many factors espacially by boiler tube fouling ( or exchange surfaces) that will considerably reduce heat exchange.

W. H. Atkinson has written:

'Turbine blade and vane heat flux sensor development phase 2' -- subject(s): Heat transfer coefficients, Cross flow, Turbine blades, Heat flux, Vanes

'Development of advanced high-temperature heat flux sensors' -- subject(s): Heat flux transducers, Transmission, Heat, Aeronautical instruments, Instruments

The term flux, is used to indicate the amount of something crossing a unit area per second. In the case of heat flux, it would be the number of calories or BTU crossing a square meter or foot per second.