Boiling Heat Transfer in an Open Thermosyphon : Report 1, An Experiment with Water

Abstract

An experiment on boiling heat transfer in a vertical open thermosyphon is performed. Tubes and annuli are used as the open thermosyphon. The latter consists of an unheated core and an externally heated tube. Data are taken using pure water by changing the diameter and the length of the heated tube, the diameter of the unheated core and the entrance temprature of the liquid. The heat transfer coefficient α is correlated with q⁰.4(Δt_s/Δt)⁰.9, where q is heat flux, Δt_s is excess wall temperature above saturation of the liquid, Δt is wall temperature minus entrance temperature of the liquid. It is also shown that the heat transfer coefficient is hardly affected by the length and the diameter of the heated tube. For the extremely small gap of the annulus, however, the heat transfer coefficient increases with a decreasing gap. The heat transfer coefficient in the thermosyphon is larger than that of pool boiling, but the critical heat flux is considerably smaller. Flow patterns in the open thermosyphon are observed and their relation with the heat transfer coefficient is discussed.