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Research Papers

Statistical Investigation of Air Dehumidification Performance by Aqueous Lithium Bromide Desiccant in a Packed Column: A Thermodynamic Approach

[+] Author and Article Information
L. Omidvar Langroudi

Chemical Engineering Faculty,
Tarbiat Modares University,
Tehran 14155-143, Iran

H. Pahlavanzadeh

Chemical Engineering Faculty,
Tarbiat Modares University,
Tehran 14155-143, Iran
e-mail: pahlavzh@modares.ac.ir

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received October 30, 2014; final manuscript received July 3, 2015; published online August 4, 2015. Assoc. Editor: Samuel Sami.

J. Thermal Sci. Eng. Appl 7(4), 041013 (Aug 04, 2015) (9 pages) Paper No: TSEA-14-1254; doi: 10.1115/1.4031082 History: Received October 30, 2014

Lithium bromide solution is used as a desiccant in air dehumidification systems. Liquid desiccant is a solution that facilitates the removal of humidity directly from the air. In this work, effectiveness of a LiBr based air dehumidifier was studied by correlating the vapor–liquid equilibrium data with a proposed thermodynamic model. For this, the nonelectrolyte Wilson nonrandom factor (N-Wilson-NRF) model and the Pitzer–Debye–Huckel formula were used to represent the contribution of the short and the long range ion–ion interactions. In particular, the proposed model assumed that the electrolyte solution is treated as a mixture of undissociated ion pairs and solvent molecules. The proposed equation of this study is valid for the temperature range of 20–35 °C and concentration range of 0.40–0.60 kg/kg. This relation was employed to estimate the equivalent humidity ratio, and then, the humidity ratio from the previous step was used to calculate the effectiveness of a LiBr based dehumidifier. The response surface methodology (RSM) was applied for the design and analysis of the dehumidification experiments. A quadratic model was implemented to predict the dehumidification effectiveness. This model studies the implications of four primary variables on the effectiveness of a dehumidification process. The optimal values to achieve the maximum effectiveness were found to be 32.5 °C for the air temperature, 0.0210 kg/kg for the air humidity ratio, 2.17 for the mass flow rate ratio, and finally, 0.50 kg/kg for the desiccant concentration. These values gave the dehumidification effectiveness of 0.544. The result of the model was in good agreement with the experimental value 0.542, thus verifying the accuracy of the proposed model.

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References

Figures

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Fig. 1

Schematic of the experimental setup [16]

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Fig. 2

Mean activity coefficient of LiBr solution as a function of mass fraction at 25 °C

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Fig. 3

The activity coefficient of H2O as a function of LiBr solution mass fraction at 25 °C

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Fig. 4

A comparison of the predicted and experimental values of equivalent humidity ratio (ωsat, kg/kg)

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Fig. 5

Predicted dehumidification effectiveness versus the actual values for the dehumidification system with LiBr desiccant

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Fig. 6

Dehumidification effectiveness (ε) with respect to the air humidity ratio (ωa, kg/kg) and desiccant concentration (Xs, kg/kg) at Ta = 32.5 °C and R = 1.53. Images showing (a) contour plots and (b) response surface.

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Fig. 7

Dehumidification effectiveness (ε) with respect to the desiccant concentration (Xs, kg/kg) and the mass flow rate ratio (R) at ωa = 0.0185 kg/kg and Ta = 32.5 °C. Images showing (a) contour plots and (b) response surface.

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Fig. 8

Dehumidification effectiveness (ε) with respect to the mass flow rate ratio (R) and the air temperature (Ta, °C) at ωa = 0.0185 kg/kg and Xs = 0.48 kg/kg. Images showing (a) contour plots and (b) response surface.

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