Flow Boiling Pressure Drop And Dynamic Response Characteristics In Microchannels With Different Surface Energy

With the wide application of microchannel heat exchanger, more and more research focus on the microchannels, and the pressure drop characteristics is an important research object.In this paper, purerefrigerant R141 b and γ-Al2O3-R141 b with different mass fraction were used as the working fluid respectively in microchannels to carry out boiling flow experiments to explore the effect on flow boiling pressure drop characteristics from surface energy and mass fraction of nano-refrigerant, and analyse the dynamic pressure response characteristics.The fluorine silicone and anhydrous ethanol was used to prepare for surface modified liquid with different concentrations, which used to obtain the microchannel test specimens with different surface energy, and select three groups of microchannels to study the influence on the pressure drop. The result reflects that microchannel tests with different surface energy show the similar law.Friction pressure drop is the main factor of boiling heat transferpressure drop in microchannels and the proportion reached about 75%~60%.While, the microchannels with different surface energy have different two-phase frictional pressure drop value. Compared with the microchannel without modification, friction pressure drop of the microchannel specimens modified by modification fluid increased to 5.1% and 12.7% approximately.Using γ-Al2O3-R141 b nano refrigerant with different mass fraction as the working fluid, in which mass fraction changed from 0.05% increased to 0.4%, two-phase frictional pressure drop are gradually reduced compared with pure refrigerants. With the increasing of mass fraction of the nano refrigerant, the agglomeration and sedimentation of the nano-particles was more obvious, which improve the surface energy of microchannels in degree, and the two-phase frictional pressure drop decline in a certain extent.When the heating power has a step change, the pressure dynamic response is relatively fast in microchannels, and when the cooling water has a step change, the pressure response is relatively slow. The pressure drop shows the different variation at the time that the experiment system has different step signal. The system has the characteristics of controllable and observability when the pressure is in the course of dynamic response.