The purpose of this work is to describe nucleate and transition boiling occurring in an inclined narrow space (0° ≤ φ ≤ 35°) between a heated upward-facing copper disk and an unheated surface for saturated n-pentane. The distance between the heated surface and the confinement plate is enclosed between 200 μm ≤ s ≤ 90 mm. The heat flux and the wall temperature are determined by mean of an inverse heat conduction method. The instantaneous volume fraction of the vapour phase within the confined space is measured using capacitive sensors. The influence of the confinement and the inclination angle on the boiling curves and the flow patterns are analysed. The evolution of void fraction with the heat flux increase, the reduction of the gap size and the inclination of the heated surface are determined. Boiling becomes unsteady for given heat flux and inclination angle ranges. The boiling cycles are characterized by periodic liquid feeding and two-phase structure expulsion from the confined space. The cycle’s frequency increase with the heat flux and the inclination angle increase is analyzed. The conditions of unsteady boiling apparition are summarized in unsteady boiling pattern maps.

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