This work performs a fundamental study of a Dual Compensation Chamber Loop Heat Pipe (DCCLHP) through partial visualization of the flow phenomenon inside its compensation chambers and the condenser. Both startup and steady-state performance of the DCCLHP and the influence of initial vapor-liquid distribution, startup heat load, heat sink temperature and relative orientations on the performance of the DCCLHP are studied. The result shows a typical 'V' curve operation temperature at heat loads over 50W at the steady-state, and reveals some unique phenomena during the startup of the DCCLHP such as bubble generation in the liquid core, reverse flow, fluctuated flow and liquid re-distribution between the compensation chambers and the external loop, which are caused mainly by the radial heat leak from the evaporator. Some unstable phenomena during the startup, steady-state operation and unloading period of the DCCLHP are also revealed in this study including temperature fluctuations, temperature hysteresis and transient penetration of vapor. (C) 2010 Elsevier Ltd. All rights reserved.