單顆液滴對二氧化硫氣體之吸收模式建立

Abstract

本研究主要是為了改進傳統的質傳理論需使用經驗式或半經驗式求得質傳係數，因此另外推導了新的質傳通量式來模擬液滴濃度與時間的關係。 首先假設液滴內部均勻混合無濃度差，結果發現這個模式的模擬值遠大於文獻上之實驗值，誤差約4倍，故該模式並不適用於預估液滴濃度。接著針對污染物進入液滴內部無反應，只有擴散這個質傳機制，加上內部環流修正倍數後，模擬值與實驗值仍有25%∼40%的誤差。最後考慮汙染物在液滴內部有水解反應，加上內部環流修正倍數後，模擬值與實驗值大約符合，誤差約17％。 本研究另外模擬了液滴初始pH值與液滴粒徑大小對於液滴濃度的影響，結果發現，液滴初始pH值愈低，液滴平衡濃度愈低；液滴粒徑愈大，液滴平衡濃度愈高，且達到平衡濃度所需時間愈長。此外亦以模式計算攝入係數γ值，發現γ會隨時間變化，並非文獻上學者所使用的固定值。

A new model is developed in this study to simulate the relationship between the droplet concentration and contact time of a droplet and gas to improve the traditional mass transfer theory in which the liquid-phase mass transfer coefficient is calculated by empirical or semiemperical equation. First, assumed that there is no concentration gradient inside a droplet and the simulated concentration of a droplet is four times the earlier experimental data. In the second condition it is assumed that there is mass diffusion only and no hydrolysis or reaction exists inside a droplet. After the internal circulation revision, the simulated concentration of a droplet is 25%∼40% smaller then the earlier experimental data. Finally, assumed that there is hydrolysis only inside a droplet with internal circulation revision, the simulated concentration of a droplet is comparable with earlier experimental data and the error between simulated result and experimental data is 17%. The effect of droplet initial pH value and of drop diameter on droplet concentration is studied in this new model. We find that the droplet initial pH value is increased from 4 to 7, the droplet equilibrium concentration increases. Moreover when the droplet diameter is increased from 100 μm to 0.576 cm, the droplet equilibrium concentration shows increase and the time required to achieve droplet equilibrium concentration is longer. The contact time between the droplet and gas is increased from 0 to 5 S, the uptake coefficient increases and attains constant value after 5 S.