This paper introduces a new parameter to design the $2{ imes}2$ microfluidic centrifuge with single flow rotation positioned at the center of microchamber. The dimensional centrifugal acceleration momentum flux which is defined as the interfacial momentum flux divided by distance from the center of the chamber explains the flow rotation and its threshold provides a reference to expect single flow rotation. Through the numerical and experimental visualization of the flow rotation, the number and position of flow rotation in the $2{ imes}2$ microfluidic centrifuge were examined. At a channel width of $50{mu}m$ and chamber width of $250{mu}m$, single flow rotation was obtained over at a Reynolds number of 300, while at a channel width of $100{mu}m$ and chamber width of $500{mu}m$, single flow rotation did not appear. The numerical analysis showed that the threshold centrifugal acceleration momentum flux to obtain single flow rotation was $3500kg/m{cdot}s^2$.