Abstract: In this paper,visualization of bubble behavior and two-phase flow in inclined confined spaces are performed for near-saturated demineralized water at atmospheric pressure with gap sizes of 3mm to 8mm,and inclination angles of 0° to 30°.Based on the results,three boiling regimes are observed:isolated deformed bubbles,coalesced deformed bubbles and partial dry-out.A flow pattern map for confined pool boiling,based on the Bond number and a dimensionless number of heat flux,has been developed in order to determine the regimes.Objective criteria are proposed for the transitions between various regimes.It is shown that the transition criteria between isolated deformed bubbles and coalesced deformed bubbles is Q=0.16 and Q=0.55 between coalesced deformed bubbles and partial dry-out.It has to be pointed out that the gap structures and downward facing heating surfaces may be responsible for the special flow patterns