Experimental study and theoretical model for the effect of air on performance of falling film absorbers

Other Title(s)

دراسة عملية و نظرية لتأثير المواد الغير قابلة للامتصاص على كفاءة أداء أعمدة الامتصاص ذات الطبقة الساقطة

Dissertant

Abd Allah, Arubah Nafi

Thesis advisor

Halabiyah, Isam Khidr

University

University of Technology

Faculty

-

Department

Department of Chemical Engineering

University Country

Iraq

Degree

Ph.D.

Degree Date

2006

English Abstract

A thin falling film is well suited to simultaneous heat and mass transfer due to the small thermal resistance through the film and the large contact surface achievable at low flow rates, the film enters as a smooth laminar flow and quickly transitions into small-amplitude wavy flow.

The flow regime is termed "wavy-laminar flow", and modern heat and mass transfer equipment operate in this complicated transition regime.

The absorption of water-vapor (absorb ate) by lithium-chloride (absorbent) was studied experimentally and theoretically in the presence of non-absorbable (air) in a counter - current falling film absorber (0.0187 m outer diameter 1.25 m height).

An experimental apparatus was installed and series of experimental runs were carried out.

The experiments were designed using factorial method for three operating variables (total column pressure, inlet solution flow rate, and non-absorbable gas concentration).

The minimum and maximum values of the operating conditions used in the experimental work are :- - Inlet solution flow rate as a function of film Reynolds number (Ref) = (40tol20).

-Total column pressure = (200 to 350) Torr.

-Non - absorbable concentration = (0 to 10 %) vol %.

Also the present work has been devoted to formulate a mathematical model within transient state capable of predicting concentration and temperature profiles through the liquid falling-film absorber.

The model includes the effects of hydrodynamics, mass and heat transfer rates.

The mathematical model consisted of mass and heat differential balance equations in both liquid and gas phases with their corresponding boundary conditions.

These equations are solved numerically to obtain concentration and temperature profiles along the absorber.

Using goodness-of-fit test, the comparison between the theoretical and experimental results proved that the model results are statistically significant at a 95 % confidence level.

It has been shown that waves enhance the absorption rates while the presence of non- absorbable depress the absorption rates significantly.

An increase in non-absorbable gas concentration degrades the mass, heat transfer rates.

This effect is most prominent at low solution flow rates, at Ref = 60, increasing the non-absorbable concentration from0 % to 2 % decreased the mass and heat transfer rates approximately 35 % and 25 % respectively.

At Ref = 80, there was decrease in the mass and heat transfer rates, 14% and 16 % respectively.

This suggested that higher solution flow rates would be required to maintain certain absorption rates when the non-absorbable concentration is high.

Increasing the column pressure from (200 to 300) Torr will increase mass transfer rates and heat transfer rates to about 22 %, and 20 % respectively in the absence of non-absorbable.

But increasing the percentage of non-absorbable.

To 2 % for the same increase in column pressure will yield increment in the mass and heat transfer rates to 32 % and 40 % respectively.

This mean that the pressure of the column can be more effective in the presence of non- absorbable in the system.

The results of the mathematical model were compared with that of smooth film absorption as well as the results of wavy film absorption in the absence of non-absorbable.

Main Subjects

Chemistry

Topics

• Chemical industry
• Adsorption

• APA
• MLA
• AMA

Language

English

Data Type

Arab Theses

Record ID

BIM-305972