Fundamental study of hydrodynamics and mass transfer in annular-mist flow

The unprecedented demand for air conditioning and refrigeration is unleashing extraordinary technological challenges where our limited knowledge about how heat is transferred plays a major role. The design and optimization of heat transfer equipment depend on such knowledge and accurate models. This fact has motivated substantial research in the last 80 years to predict and understand the physical mechanism transferring heat between the surface and fluid. To date these issues, remain unresolved. While single-phase flow is well understood, the complexity attributed to two-phase flows has limited the possibility of achieving accurate models which even approach the accuracy of single- phase flow models. On the main result from this project has been to suggest that that heat transfer in two-phase flows without vapor generation at the wall can be equivalent to the single-phase. This result simplifies the modeling of heat transfer process without vapor generation reducing the level of uncertainties in the design and sizing of heat transfer equipment and thus potential reduction of costs.

The achievement of the project are related to identifying the dominant heat transfer and pressure drop mechanism during flow boiling. This results have the possibility of reducing the uncertainties in the design of heat transfer equipment which will result in lower equipment costs and energy consumption.

Flow boiling is an efficient heat transfer mechanism and it is the main choice when dealing with high heat fluxes encountered in the miniaturized process equipment such as micro- and mini-heat exchangers, micro-reactors and fuel cells. In this sense, annu lar-mist flow regime is particularly relevant since it is one of the most common two-phase flow regimes found in several industrial applications. During the past decades, extensive research has been carried out in predicting models for pressure drop, heat and mass transfer in multiphase systems in general and in annular flow in particular. Nevertheless, current models are restricted to geometry, working fluids, and operating conditions. The project will address two main topics within the area of annular- mist flow, namely the mathematical modeling and the experimental investigation of annular-mist flow in order to get a better insight into the underlying physical phenomena controlling heat and mass transfer during this flow regime. The main goal of the pr oject is to gain fundamental understanding of the hydrodynamics, heat and mass transfer processes in annular-mist flow. The project will be carried out over a period of 4 years (Jan 2014-Dec2017) with 1 PhD and 1 postdoc projects included in the proposed research activities. The problem will be investigated experimentally and by modeling the underlying processes. In the experimental study the main features of annular-mist flow will be studied with focus on the characterization of the liquid film, the drop let phase, and the droplet-film interaction. In the modeling task, a Boltzmann-type equation (Population Balance Equation) for the droplet phase and for the film and the corresponding interactions such as droplet entrainment and deposition, hold-up and wa ll and interfacial shear will be implemented for investigating the dominant mechanisms.