Critical heat flux and bubble behaviour study on differently oriented flat plates during pool boiling

Abstract

An experimental study is brought off to analyse the effect of flat plate length, width, orientation, and pool liquid temperature on CHF under atmospheric conditions during pool boiling. The bubble nucleation and departure for the aforementioned parametric and operational conditions are discussed. Based on bubble behavior, various pool boiling regimes under uniform heat flux conditions are investigated. The pool is maintained at 25℃ and saturation temperature corresponding to ambient pressure. The occurrence of burnout on the heater plates is analysed on the basis of bubble behaviour. It is analysed that prior to the occurrence of CHF a liquid film enclosed with vapour leads to initiate the dry patch. It is observed that with an increase in pool temperature, the magnitude of CHF reduces. It has been estimated that there is a decrement of around 62 % in the magnitude of CHF in saturated conditions as compared with subcooled conditions. The vertical orientation of the plates results in a higher CHF magnitude. In the subcooled pool, the CHF in vertical orientation ranges between 6.197 MW/m2 to 2.909 MW/m2. Whereas in the saturated pool the CHF magnitude in vertical orientation ranges between 2.652 MW/m2 to 0.998 MW/m2. As the length of the heater plate increases, the CHF value reduces. The minimum magnitude of CHF is obtained as 0.898 MW/m2 for downward facing heater of 300 mm in length at the saturated pool. Higher the width lesser the CHF. The obtained experimental results are compared with available correlations to access its viability. An empirical correlation is suggested, implicating the effect of heater length, width, orientation, and pool temperature for the pool boiling CHF on flat plates.