Studie Primárního Rozpadu Kapaliny ve Vztahu k Interakci Kapek

Study of the Primary Breakup in Twin-Fluid Atomizers with regard to the Droplet Interaction

abstract

en

Several types of twin-fluid atomizers have been developed in the last decades. The mechanism of the liquid primary breakup has been studied in several publications for many types of these atomizers. However, a compar-ison of the performance of different atomizers is very rare. This study focuses on the examination of four different twin-fluid atomizers. These atomizers are such where fluids are mixed inside the body, i.e. internal-mixing type. The mixing principle differs amongst the examined atomizers. The aim of this paper is to examine the effect of an internal atomizer design to the primary breakup, droplet-air interaction and droplet-droplet interaction in the spray. The phase Doppler analyser (PDA) was used to obtain time-dependent data of the droplet motion. Liquid structures presented in the area near to the atomizer were captured by the high-speed camera. The results point to the differ-ences of the primary breakup even though atomizers were examined under the same operating conditions. Mech-anisms of the primary breakup differs for each atomizer. An analysis of droplet velocity were performed for five drop size classes. The velocity profiles confirms the importance of the primary breakup. Two examined atomizers have expected velocity profiles. Other two atomizers differ demonstrably. These profiles were then correlated with droplet collision rate profiles and good agreement was found. Results give an insight into a link between the mixing principle of the atomizer, the primary breakup of liquid and the resulting droplet dynamics.

Mnoho typů dvoumédiových trysek bylo zkoumáno v průběhu posledních desetiletí. Mechanismus primárního rozpadu kapaliny byl studován v mnoha publikacích pro různé trysky. Nicméně, porovnání jednotlivých funkce trysek mezi sebou je pouze ojedinělé. Tato studie se soustředí na čtyři různé dvoumédiové trysky. V těchto tryskách dochází ke směšování kapalné a plyné fáze uvnitř těla trysky, tzv. trysky s vnitřním směšováním. Princip směšování se lišší pro každou zkoumanou trysku. Cílem tohoto článku je vyzkoumat vliv návrhu trysky na primární rozpad kapaliny a interakci kapek ve spreji. Fázový Dopplerovský analyzátor (PDA) byl použit k získání časově závislých dat o pohybu kapek. Kapalina vystupující z trysky byla zachycena pomocí vysokorychlostní kamery. Výsledky poukazují na rozdíly v mechanismu rozpadu kapaliny i za předpokladu, že trysky byly provozovány za stejných podmínek. Analýza rychlosti byla provedena roztříděním dat do pěti rychlostních tříd. Rychlostní profily potvrzují vliv primárního rozpadu. Dvě ze zkoumaných trysek mají předpokládané profily. Další dvě trysky se rapidně lišší. Tyto profily byly poté porovnány s mírou kolizí kapek, primárního rozpadu kapaliny a výsledné dynamiky kapek ve sprejích.

Several types of twin-fluid atomizers have been developed in the last decades. The mechanism of the liquid primary breakup has been studied in several publications for many types of these atomizers. However, a compar-ison of the performance of different atomizers is very rare. This study focuses on the examination of four different twin-fluid atomizers. These atomizers are such where fluids are mixed inside the body, i.e. internal-mixing type. The mixing principle differs amongst the examined atomizers. The aim of this paper is to examine the effect of an internal atomizer design to the primary breakup, droplet-air interaction and droplet-droplet interaction in the spray. The phase Doppler analyser (PDA) was used to obtain time-dependent data of the droplet motion. Liquid structures presented in the area near to the atomizer were captured by the high-speed camera. The results point to the differ-ences of the primary breakup even though atomizers were examined under the same operating conditions. Mech-anisms of the primary breakup differs for each atomizer. An analysis of droplet velocity were performed for five drop size classes. The velocity profiles confirms the importance of the primary breakup. Two examined atomizers have expected velocity profiles. Other two atomizers differ demonstrably. These profiles were then correlated with droplet collision rate profiles and good agreement was found. Results give an insight into a link between the mixing principle of the atomizer, the primary breakup of liquid and the resulting droplet dynamics.

Primary breakup; twin-fluid; droplet interaction

23.08.2015

ICLASS 2015

107–107

261