Visualization Experiment And Numerical Simulation On Subcooled Boiling In A Single Minichannel

Microchannel heat sink cooling technology is an efficient cooling method,has a relatively wide application prospects.In order to improve the micro-channel heat sink cooling effect,working fluid within the micro-channel will generally have phase change occured.The phase change of the working fluid can be divided into subcooled and saturated boiling.Compared with the saturated boiling,the subcooled boiling operation is generally stable and safe,which can achieve accurate temperature controlling and monitoring,and the CHF is higher.The subcooled boiling has been extensively studied,among which the heat transfer and bubble growth mechanism is an important sdudying direction.A microchannel visualization bench was established and a copper-based microchannel with a hydraulic diameter of 0.5 mm was designed and fabricated.High-speed camera and stereomicroscope were used to capture the bubbles in the subcooled boiling process.The bubble periods,and the information on the influence of working parameters on bubble growth and detachment were also analysed.The results show that a bubble period is composed of the waiting time and the time of bubble growth and detachment(ie,the time occupied by the bubble),and the waiting time is generally more than the occupied time.The bubble period decreases with the increase of inlet temperature and flow rate.The waiting time and its proportion are affected by the flow rate,which increases with the increase of flow rate,but the relationship with the degree of subcooling is not significant.With the decrease of flow rate,the flow tends to saturation and the instability of the bubble period increases,and the average departure diameter of the bubble is also increased.It has also been observed that there is a certain correlation between the adjacent bubbles and that the bubbles generated at different position have different characteristics.In the other part,the RPI wall boiling model was used to study the numerical simulation of single microchannel subcooled boiling model.The parameters such as fluid temperature,steam velocity,wall temperature and heat flux were studied.The results show that the quenching heat flux proportion increases rapidly with the increase of the heat load and the generation of the bubbles.With the decrease of the degree of subcooling,the bubble content increases,and the quenching heat flux in the total heat flux gradually replaces the convective heat flux.Changing the cross-sectional shape of the flow path reveals that the flow path with a positive trapezoidal cross section has the best endothermic capacity,due to the fluid gravity center is down and the fluid-solid interface near the heat source is lager.