Experimental investigations are reported for air-water two-phase flow through a 2.1-mm horizontal circular minichannel. Influence of inlet premixing on two-phase flow is established by constructing various T-junction geometries with cross-flow arrangement of air and water. Six different flow patterns are observed and flow pattern maps are developed. The developed flow pattern maps are then compared for different inlet designs. It is observed that the degree of premixing of the two fluids has significant effect on flow patterns, particularly for surface-tension-dominated regime. The results obtained from these experiments can provide guidelines for selection, design, and control of wide-ranging microfluidic applications. The flow pattern map established in the present study may facilitate prediction of flow regimes in pulsating heat pipes based on the inlet flow rates of the gas and liquid.