發(fā)布時(shí)間：2018-11-22 07:38

【摘要】：噴霧冷凍干燥(SFD)過程中存在霧化液滴在設(shè)備壁面的冷凍沉積問題,不僅造成產(chǎn)品收集率的下降,且會(huì)對(duì)產(chǎn)品造成二次污染,影響設(shè)備的傳熱傳質(zhì)速率,而對(duì)單液滴撞擊冷板面的研究有助于解決這一問題。本文在前期單液滴撞擊冷板面的實(shí)驗(yàn)基礎(chǔ)上,以單個(gè)蒸餾水及普魯蘭多糖液滴為研究對(duì)象,使用數(shù)值模擬的方法研究了直徑為3.2 mm的單液滴與冷板面(小于0℃)撞擊鋪展和固化過程,分析了撞擊高度(H=100mm、250 mm、500 mm)和板面溫度(T=253 K和268 K)以及板面傾角(α=0。、30。、45。和60。)對(duì)撞擊過程的影響以及液滴在冷板面上凍結(jié)過程。對(duì)液滴在冷板面上的鋪展和凍結(jié)過程進(jìn)行了理論分析,建立了描述液滴鋪展過程及在冷板面上固化的數(shù)學(xué)模型,建立了液滴鋪展的二維與三維物理模型,將水平集方法和固化模型相結(jié)合,使用基于溫度的熱傳導(dǎo)方程代替原有的焓值方程,并且在熱容源項(xiàng)中加入熔化潛熱,利用COMSOL Multiphysics 4.2(?)軟件,耦合“兩相流水平集”與“流體傳熱”兩個(gè)物理場(chǎng),求解了存在相變的傳熱問題。結(jié)果表明,撞擊高度與板面溫度對(duì)液滴在水平冷板面的鋪展過程起到重要作用,撞擊傾斜板面時(shí),板面的傾角也會(huì)影響液滴在冷板面上冷凍沉積的發(fā)生,隨著撞擊速度和傾斜角度的增加,板面溫度對(duì)液滴撞擊動(dòng)力學(xué)行為的影響逐漸變小,減小了液滴沉積的可能。物料的性質(zhì),如黏度等也會(huì)對(duì)液滴的冷凍沉積發(fā)生重大影響,對(duì)于較高黏度物料,溫度并不起決定作用,黏度會(huì)影響液滴的鋪展速率及鋪展直徑,且影響趨勢(shì)較為明顯。本文采用的模擬模型和實(shí)驗(yàn)的結(jié)果吻合較好,反映了液滴鋪展凍結(jié)過程中的溫度變化與固化情況,有利于對(duì)液滴發(fā)生凍結(jié)的狀況進(jìn)行直觀解釋。
[Abstract]:In the process of spray freeze-drying (SFD), there exists the problem of freezing deposition of atomized droplets on the wall of the equipment, which not only leads to the decrease of product collection rate, but also causes secondary pollution to the product and affects the heat and mass transfer rate of the equipment. The research of single droplet impingement on the surface of cold plate is helpful to solve this problem. On the basis of the previous experiments of single droplet impinging on the surface of cold plate, single distilled water and pullulan polysaccharide droplet were taken as the object of study. Numerical simulation was used to study the impact spread and solidification process of a single droplet with a diameter of 3.2 mm with a cold plate surface (less than 0 鈩，

本文編號(hào)：2348533