In-situ phase separation to improve phase change heat transfer performance

Phase change is widely applied in thermal-power conversion, cooling and thermal management, influencing efficiency, safety and cost of energy systems. The complicated mass, momentum and energy exchanges between two-phases causes large pressure drops, critical heat fluxes and flow instabilities. Here, a review on phase separation principle for phase change heat transfer is provided. The phase separation principle is presented in a theoretical form. Design and operation of phase separation for evaporator, condenser and heat pipe are commented. Because phase separation assigns pathways for liquid and vapor, it improves pool boiling performance and eliminates flow instability for micro-evaporator. For micro-condenser, the lined pin fins array creates liquid and vapor passages. The expanded liquid passage adapts increased flow rate to increased flow passage area for liquid. Pin fins are effective for filmwise condensation to increase heat transfer coefficients at low cost of pumping power. Phase separation for macro-condenser was fulfilled by suspending mesh screen membrane tube in condenser tube to confine vapor in annular region, yielding enhanced thin film condensation. Phase separation was commented on smart heat pipe. Superhydrophilic evaporator and superhydrophobic condenser generate nucleate mechanism, achieving increased heat transfer coefficients when heat loads increase. Perspective of phase separation was discussed.