空氣－水二相柱狀流於平滑及內設扭旋片直立管之流場及壓損特性比較研究

COMPARATIVE STUDY OF FLOW CHARACTERISTIC AND PRESSURE DROP FOR AIR-WATER TWO-PHASE FLOW CONDITION IN VERTICAL PLAIN AND SWIRL TUBES AT SLUG FLOW

Two-phase interfacial structure, void fraction, Taylor-bubble velocity as well as the lengths of Taylor-bubble andliquid-slug in a vertical tube with and without the twisted tape insert at the concurrent air-water slug flow condition wereexperimentally studied using the flow images detected by the computerized high frame-rate videography. Thepressure-drop data obtained from the plain and swirl tubes at the turbulent slug flow regime were accordingly interpretedby the flow physics revealed from the flow visualization results. With the presence of a spiky twisted tape insert, theseparated shear layers tripped by the spiral spikes and the swirling flow induced by the centrifugal force interact with theintermittent Taylor bubble and liquid slug to modify the interfacial structure from the plain-tube scenario. A set ofpressure-drop data obtained from the plain and swirl tubes at the single- and two-phase flow conditions is comparativelyexamined. At the slug flow condition, the pressure-drop ratio between the plain and swirl tubes is considerably reducedfrom the single-phase level as the additional drag attributed to the two-phase phenomena has neutralized the dominant roleof drag production by the spiky twisted tape at the single-phase condition. Empirical correlations for void fraction, Taylorbubble velocity, lengths of Taylor bubble and liquid slug and pressure drop coefficient for plain and swirl tube at the slugflow regime are derived for engineering applications. 本實驗分析電腦化高速攝影之流場影像，研究空氣－－水同向柱狀流（slug flow）於平滑及內設扭旋片直立管之二相流結構、空洞比（void fraction）、泰勒氣泡（Taylor-bubble）流速以及泰勒氣泡與水柱（liquidslug）之長度；並以流場觀測結果詮釋此平滑及內設扭旋片直立管於紊態柱狀流域（turbulent slug flowregime）之壓損數據。於管中裝設柱狀扭旋片，流體流經各螺旋排列柱鰭激發之分離剪力層以及離心力所導引之渦流，與間歇流動之泰勒氣泡及水柱交互作用，改變平滑直立管中之二相流結構。實驗數據並比較自平滑及內設扭旋片直立管於單相及二相流狀態所檢測之壓損（pressure drop）數據。於柱狀二相流域檢測之內設扭旋片管壓損係數與平滑管壓損係數之比值，顯著低於單相流狀態所檢測之壓損係數比值。此壓損係數比值降低之結果，歸因於二相流之流場現象弱化扭旋片對單相流壓損係數之主導性影響。本研究並推導出平滑及內設扭旋片直立管於同向紊態柱狀流域，其空洞比、泰勒氣泡流速、泰勒氣泡與水柱（liquid-slug）長度以及壓損係數之實驗公式，提供工程應用。