Direct contact condensation induced transition from stratified to slug flow

Computational study of subcooled water injection into steam line: effect of Reynolds number on flow transition to study condensation induced water hammers

The direct contact condensation (DCC) of steam in subcooled water encounters in wide range of the industrial applications. On one side, it is an efficient and rapid, mass and heat transfer phenomenon. But, on the other side, it may generate condensation induced water hammers (CIWH) events which may cause high pressure peaks resulting in severe damage to the mechanical systems. This computational study intends to explore the underlying physics of CIWH events while injecting subcooled water into steam filled horizontal pipe section. The Reynolds number is varied from, Re w  = 60,750 to 646,900, to study the flow regimes (stratified and slug), onset of CIWH and local flooding conditions. The results have been compared with the published data and found in good agreement. It has been observed that for Re w  = 182,300, flow remains stratified. However, the flow regime changes from stratified to slug flow at Re w  = 303,850–646,900, possibly due to the onset of CIWH. Extensive steam pockets have been observed at Re w  = 303,850, which may be considered as onset of CIWH. Local flooding condition is also started at Re w  = 303,850 and is observed to be shifted upstream with the increase in Reynolds number. This study is considered to be useful for the safe design and economical operation of the relevant systems in nuclear and other related industry.

Slug modeling with 1D two-fluid model

Simulations of condensation-induced water hammer with one-dimensional two-fluid model requires explicit modeling of slug formation, slug propagation, and in some cases slug decay. Stratified flow correlations that are more or less well known in 1D two-fluid models, are crucial for accurate description of the initial phase of the slug formation and slug propagation. Slug formation means transition to other flow regime that requires different set of correlations. To use such two-fluid model for condensation induced water hammer simulations, a single slug must be explicitly recognized and captured. In the present work two cases of condensation-induced water hammer simulations performed with WAHA code, are described and discussed: injection of cold liquid into horizontal pipe filled with steam and injection of hot steam into horizontal pipe partially filled with cold liquid.

Computational models to dertermine fluiddynamical transients due to condensation induced water hammer (CIWH)

Condensation induced water hammer (“condensation hammer”, CIWH) represent a dangerous phenomenon in pipings, which can endanger the pipe integrity. If they cannot be excluded, they have to be taken into account for the integrity proof of components and pipe structures. Up to now, there exists no substantiated model, which sufficiently determines loads due to CIWH. Within the framework of the research alliance CIWA, a tool for estimating the potential and the amount of pressure loads will be developed based on theoretical work and supported by experimental results. This first study discusses used computational models, results of experimental observations and gives an outlook onto future techniques.