The bubble dynamics and heat transfer associated with nucleate boiling in parallel microchannels is studied numerically by solving the equations governing conservation of mass, momentum and energy in the liquid and vapor phases. The liquid-vapor interface is tracked by a level set method which is modified to include the effects of phase change at the interface and contact angle at the wall. Also, the reversible flow observed during flow boiling in parallel microchannels has been investigated. Based on the numerical results, the effects of contact angle, wall superheat and the number of channels on the bubble growth and reversible flow are quantified.