Applying　a　three-dimensional　two-fluid　model　coupled　with　homogeneous　multiple　size　group　(MUSIG)　approach,　numerical　simulations　of　upward　subcooled　boiling　flow　of　water　at　low　pressure　were　performed　on　the　computational　fluid　dynamics　(CFD)　code　CFX-10　with　user　defined　FORTRAN　program.　A　modified　bubble　departure　diameter　correlation　based　on　the　Unal＇s　semi-mechanistic　model　and　the　empirical　correlation　of　Tolubinski　and　Kostanchuk　was　developed.　The　water　boiling　flow　experiments　at　low　pressure　in　a　vertical　concentric　annulus　from　reference　were　used　to　validate　the　models.　Moreover,　the　influences　of　the　non-drag　force　on　the　radial　void　fraction　distribution　were　investigated,　including　lift　force,　turbulent　dispersion　force　and　wall　lubrication　force.　Good　quantitative　agreement　with　the　experimental　data　is　obtained,　including　the　local　distribution　of　bubble　diameter,　void　fraction,　and　axial　liquid　velocity.　The　results　indicate　that　the　local　bubble　diameter　first　increases　and　then　decreases　due　to　the　effect　of　bubble　breakup　and　coalescence,　and　has　the　maximum　bubble　diameter　along　the　radial　direction.　Especially,　the　peak　void　fraction　phenomenon　in　the　vicinity　of　the　heated　wall　is　predicted　at　low　pressure,　which　is　developed　from　the　wall　repulsive　force　between　vapor　bubbles　and　heated　wall.　Nevertheless,　there　is　a　high　discrepancy　for　the　prediction　of　the　local　axial　vapor　velocity.　(C)　2009　Elsevier　B.V.　All　rights　reserved.