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

Den hidtil usete etterspørselen etter klimaanlegg og kjøling utløses av ekstraordinære teknologiske utfordringer, der vår begrensede kunnskap om hvordan varmen overføres spiller en viktig rolle. Design og optimalisering av varmeoverføringsutstyr er avhengig av slik kunnskap og nøyaktige modeller. Dette faktum har motivert betydelig forskning de siste 80 årene for å forutsi og forstå den fysiske mekanismen som overfører varme mellom overflaten og væsken. Å oppdatere disse problemene, forblir uløste. Mens enfasestrømmen er godt forstått, har kompleksiteten til tofasestrømmer begrenset muligheten for å oppnå nøyaktige modeller som til og med nærmer seg nøyaktigheten av enkeltfasestrømningsmodeller. Hovedresultatet fra dette prosjektet har vært å foreslå at denne varmeoverføringen i tofasestrømmer uten dampgenerering på veggen kan tilsvare enkeltfasen. Dette resultatet forenkler modelleringen av varmeoverføringsprosessen uten dampgenerering som reduserer nivået av usikkerhet ved utforming og dimensjonering av varmeoverføringsutstyr og dermed potensiell kostnadsreduksjon.

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.