A single-side heating apparatus is set up to study the flow boiling and heat transfer in vertical narrow rectangular channel together with high speed video camera to get the flow images in the channel. The experiment results show that: the heat transfer coefficient exists a maximum value; Heat transfer coefficient gradually decreases with increasing thermodynamic vapour quality (heat flux increasing)

and flow type turns to liquid film evaporation

at this case it necessarily needs to control heat flux to avoid the occurrence of dry-out.