Two-phase flow behaviour in a smooth hairpin

Fin-and-tube heat exchangers are often used as evaporators in HVAC&R systems. To increase the compactness, the tubes of these heat exchangers are folded up in a sequence of hairpin tubes. These hairpins consist of two straight tubes interconnected by a sharp U-bend. The working fluid will pass through one or multiple hairpin tubes while evaporating. The geometry of the bends and how the sequence of bends is built up influences the two-phase flow behaviour. In this work the evolution of the two-phase flow behaviour downstream of a sharp return bend is studied. This is done by measuring the capacitance of the flow on several locations downstream of the return bend. Due to the difference in dielectric constant between the phases, the measured capacitance will vary depending on the amount of each phase present between the electrodes. Previous work has already shown that the flow behaviour can be characterized based on the capacitance signal of the flow. The refrigerant used in this study is R134a, the mass flux was varied between 150 and 450 kg/m²s and the vapour quality varied between 0 and 1. It was observed that downstream of the return bend a significant effect on the flow regime was induced up to 10 tube diameters downstream of the bend

Two phase flow behaviour in a smooth hairpin tube

Fin-and-tube heat exchangers are often used as evaporators in HVAC&R systems. To increase the compactness, the tubes of these heat exchangers are folded up in a sequence of hairpin tubes. These hairpins consist of two straight tubes interconnected by a sharp U-bend. The working fluid will pass through several hairpin tubes while evaporating. The two-phase flow behaviour in the tubes will be influenced by the geometry of the bends and how the sequence of bends is built up. In this work the evolution of the two-phase flow behaviour downstream of a sharp return bend is studied. This is done by measuring the capacitance of the flow on several locations downstream of the return bend. Due to the difference in dielectric constant between the phases, the measured capacitance will vary depending on the amount of each phase present between the electrodes. Previous work has already shown that the flow behaviour can be characterized based on the capacitance signal of the flow. The refrigerant used in this study is R134a, the mass flux was varied between 150 and 450 kg/m²s and the vapour fraction varied between 0 and 1. It was observed that downstream of the return bend a significant effect on the flow regime was induced up to 10 tube diameters downstream of the bend

Development of quality indicators for type 2 diabetes, extractable from the electronic health record of the general physician. A rand-modified Delphi method

AIMS: Type 2 diabetes mellitus is a worldwide cause of significant morbidity and mortality. The general physician (GP) plays an important role in managing this disease and the use of the electronic health record (EHR) can improve quality for type 2 diabetes care. We aimed to develop a set of evidence-based and EHR extractable quality indicators for type 2 diabetes, enabling an automated quality assessment. METHODS: We used a Rand-modified Delphi method. Recommendations were selected from (inter)national guidelines using the 'SMART' principle and scored by a multidisciplinary expert panel. After analysis of the median score, prioritization and consensus, recommendations were discussed during a consensus meeting. A final validation round resulted in a core set of recommendations, which were transformed into quality indicators. RESULTS: A total of 101 recommendations originating from 10 (inter)national guidelines were presented to the expert panel, which resulted in a core set of 50 recommendations that were merged and modified into 36 recommendations after the consensus meeting. The panel added 3 recommendations. This resulted in a final set of 39 quality indicators. CONCLUSIONS: Our study presents a set of 39 quality indicators for type 2 diabetes in primary care that are EHR extractable, enabling automated quality assessment.status: publishe