Experimental Investigation Of The Onset Of Nucleate Boiling And Pressure Drop In Horizontal Annular Narrow Channels

There are many application of heat transfer in annular narrow channels in engineering. Two-phase flow boiling heat transfer in narrow channels is an economical and effective forced heat transfer method for its compact structure. Therefore, study on flow boiling heat transfer in narrow channels is significant in order to reduce the size of heat exchanger and to meet the increasing economic, security and reliability need. The law of heat transfer in narrow channels is markedly differs from the one in conventional measurement. So far, there isn't a research which is universal enough to describe the relationship of all parameter in the system. So, more research about heat transfer in narrow channels is indispensable.A removable and multifunctional experimental device is designed and installed. Heating way is big electric current and low voltage. Using water as working fluid, the experimental research was performed with visualization method to investigate the onset of nucleate boiling and the frictional pressure drop trait in low pressure in horizontal annular narrow channels. Various factors which affect ONB and pressure drop are analyzed.The range of experimental parameter are as follows: system pressureP =0.1~0.2MPa; mass flux G =55.4~515.6kg/(m2·s); heat flux q =2.84~344.06kW/ m2; inlet subcooled temperature:Δt sub=30~60℃; channel size s =2~3mm.The experimental results are as follows:1. The heat flux of the onset of nucleate boiling increases with a rise of wall superheat degree, and increases with a rise of system pressure and increases with an increase of mass flux, but decreases with the reduction of channel size. The influence of wall superheat and system pressure is small. The influence of mass flux and channel size are bigger.2. The pressure drop of subcooled flow boiling increases with an increase of mass flux, and increases with a rise of heat flux but decreases with a temperature of inlet water and decreases with a reduction of channel size. The influence of system pressure is small.Based on the experimental and analytic results, applied multiple non-linear regressions to the experimental data, the empirical correlations for predicting the boiling incipience and pressure drop. The calculative value is agreed well with experimental data.