Suspended micro channel resonators (SMCs) consist of hollow resonant structures containing an embedded u-shaped micro fluidic channel. The confinement of the fluid inside the resonator allows real time detection of liquid compounds in air or in vacuum, while the device quality factor remains almost unaffected. Quality factor of conventional cantilevers immersed in fluid monotonically decreases as the fluid viscosity increases. On the other hand SMCs exhibit a non-monotonic energy dissipation as the fluid viscosity is increased or decreased. In this work we present a fully three dimensional modal analysis of the fluid structure interaction (FSI) problem to predict the quality factor dependence on fluid properties. The reliability of our model is demonstrated through literature comparison of analytical model and experimental results.