Reynolds Number For One Dimensional Oscillating Flow Through Pipe

Hello friends,

Though this question seems very easy but I am still confused about 'Reynolds Number for one dimensional oscillating flow through pipe'. I am considering the characteristics length scale as 'delta x', width of a cell when domain is discretized in 'n' equal parts. Where 'delta x'= Total length/'n'

Is it correct to take delta x as characteristics length? If not what should it be?

Second thing, I am having mass flow rate instead of velocity,

Will my Reynolds number be (Mass flow rate)x(Characteristics length)/(Dynamic Viscosity x Area of cross-section) ??