STABILITY ANALYSIS IN SINGLE VERTICAL TUBE THERMOSYPHON REBOILER

Abstract

The present study has been undertaken to identify and analyze the static instability ( boiling crisis ) from the available experimental data on a single vertical tube thermosyphon reboiler. Static instabilities - Boiling crisis is manifested in sudden increase in wall temperature are due to occurrence of dryout condition leading to reduced heat transfer coefficient vis- a -vis accumulation of heat depicted through increase in wall temperature. This identification have been observed in the experimental data collected for all five test liquids studied [1]. The obtained experimental data on it has been analyzed parametrically both dimensionally (in terms of q, ATsub, and S) and non-dimensionally (in terms of PeB, Ksub, and S). This analysis deals with effect of these parameters on observed ATmax and AT•maX for nearly all the test liquids. The trend so obtained have been discussed and interpreted. In an effort to predict these instabilities in terms ofp,T max in terms of_ imposed operating_parameters in their dimensionless form, an empirical correlation of the following form has been obtained using experimental data on all systems except Acetone: AT max = C . (PeB • (Ksub)n2 • (S)"3 iii Where constant C and exponents n1, n2, and n3 have been found to be strong parameters of Ksub, and S. These values are shown in the following table I -r'r 4" NS1 CII W I 1 , • KSUb < 200 0.75 <S < 1 0.576 0.65 0 2.088 . KSUb < 200 14.72 -- do -- 0 11.85 0.5 < S <0.75 KSUb < 200 -- do -- 1.439 0 -- do -- S < 0.5 KSUb› 200 0.576 0,65 - 0.0103 2,088 0.75 < S < 1 KSUb > 200 373.825 -- do -- - 0.596 11.85 0.5 <S <0.75 Ksub > 200 -- do -- 1.439 -- do -- -- do -- S <0.5 The predictions made by this correlation were compared against corresponding experimental observed values. This comparison reveals that the obtained results through above equation may be taken within the acceptable range and fruitful predictions of stabilities in terms of AT*ms, may be made.