TWO-PHASE FLOW THERMAL INSTABILITIES IN A HORIZONTAL IN-TUBE BOILING SYSTEM WITH ENHANCED SURFACES

摘要

This study is aimed at presenting the experimental results on two-phase flow thermal instabilities in a horizontal pipe with enhanced surfaces. Five different heat transfer surface configurations including one bare tube and four tubes with different enhancement inserts were used. Two types of thermal oscillations were observed: independent thermal oscillations and compound thermal oscillations. Independent thermal oscillations occurred due to the oscillatory behavior of the mixture-vapor transition point. Compound thermal oscillations are system-induced fluctuations and occur in a region of pressure drop oscillations where film boiling is occurring. The results reveal that the tubes with no enhanced surface give the smallest amplitudes and periods on the basis of the thermal oscillations in comparison to the all enhanced surfaces. Both the period and the amplitude of the independent thermal oscillations decrease with increasing inlet mass flow rate and with increasing inlet temperature. Heat transfer enhancement devices affected the thermal oscillation characteristics.