In cooling of high energy density miniaturized electronic devices, PCBs, data centers etc. pulsating heat pipe (PHP) has received substantial attention in last few years. A unit cell pulsating heat pipe (PHP) has been studied experimentally to understand the thermo-hydrodynamic behavior at various orientations. Experimental setup consists of transparent evaporator at bottom followed by adiabatic and condenser section with a reservoir at the top. Hot and cold circulating water is used to maintain evaporator and condenser temperature constant and n-pentane is used as working fluid. When the working fluid is heated in the evaporator section, beyond a threshold self-sustained oscillating flow is in capillary tube with train of vapor bubbles and liquid plugs. A parametric study has been carried out by varying the evaporator and condenser temperature and the angle of inclination. Transparent set up facilitates the easy visualization of the development of the film and oscillation of the meniscus with time using a high speed camera. By tracking the interface of liquid film and vapor, different regimes for film-flow and flooding phenomenon in the condenser section are observed and characterized using terminologies consistent with the ones used for reflux and flow condensers. Film-vapor interfacial instabilities interfere with the meniscus oscillations. The optimum inclination angle, evaporator and condenser temperatures are found to exist for the PHP unit cell which maximize the oscillation amplitude. Three different flooding mechanisms are recognized, viz., wave transport with film drainage delay, wave transport with slug formation, and droplet entrainment. The approximate liquid deficit in the evaporator caused by flooding is also estimated for one of the mechanisms, viz. wave transport with slug formation. The superficial velocity of vapor at the onset of flooding and film-vapor interfacial wavelength are determined and compared to the respective predictions based on some of the most widely accepted correlations. The study would help to achieve a better elementary understanding of the two-phase flow in real PHPs, which in turn would assist piloting their thermal performance as per the operational constraints.