Dynamic response characteristics of microchannel evaporator in a mechanically pumped two-phase loop under hypergravity environment

The unique hypergravity environment and severe heat-dissipation requirements of modern fighter aircrafts pose serious challenges to the potential utilization of mechanically pumped two-phase loops (MPTLs), which are an efficient cooling technology. The microchannel evaporator is a key component of the MPTL system, and understanding its startup and operation characteristics is of great significance for design and optimization. In this context, an experimental MPTL system is built and fixed on a rotating platform, which is designed to generate hypergravity ranging from 0 g0 0 to 15.0 g0 0 (g0 0 = 9.8 m & sdot;s-2). & sdot; s- 2 ). The dynamic-response characteristics of the temperature, pressure, and flow rates during the startup and operation of the microchannel evaporator under various hypergravity conditions are investigated. The results indicate that different startup modes, namely gradual startup under low hypergravity and overshoot startup under high hypergravity, are achieved on the micro- channel evaporator, even if the flow rate and heat flux are not changed, which is completely different from that under normal gravity. These two startup modes can be quantitatively recognized by two dimensionless numbers: the boiling number (Bo) Bo ) and Froude number (Fr). Fr ). A larger Bo or 1/Fr, , which corresponds to a larger heat flux or hypergravity; both conditions contribute to the startup mode of the microchannel evaporator shifting from gradual to overshoot startup. During the operation of a microchannel evaporator, the competition between the elevated saturation temperature of the fluid and the induced Coriolis and centrifugal forces caused by hyper- gravity determines the wall-temperature variation of the evaporator. The dynamic wall temperature decreases under hypergravity below 2.5 g0, 0 , is stable with small fluctuations under hypergravity from 4.7 g0 0 to 7.5 g0, 0 , and increases for hypergravity larger than 11.0 g0. 0 .