Heat transfer and pressure drop characteristics of condensation for R134a at saturation temperature of 320 K inside horizontal circular and square minichannels were investigated numerically. The results indicated that the heat transfer coefficients and frictional pressure drop gradients increased with mass flux and vapor quality

while the pressure drops decreased with increasing vapor quality at x>0.85. Compared with the circular tube

the square channel with the same perimeter as the corresponding circular tubes can enhance heat transfer coefficients and increase the pressure losses. The numerical results agreed well with the well-known empirical correlations for condensation. A thicker liquid film was obtained at the bottom of the round tube

while the liquid film for the square channel accumulated at the bottom and the middle top of the channels at lower vapor quality. The proportion of the thinner liquid film region

which corresponded to a higher heat transfer coefficient

increased with increasing vapor quality

leading to a higher heat transfer coefficient at higher vapor quality. The liquid film thicknesses in square channels were lower than that in circular channels

thus enhancing the heat transfer.