The effect of pressure on the performance of bubble column dehumidifier

Many experimental and theoretical studies have been conducted on bubble columns to improve its performance. Most of these studies assumed operating under atmospheric pressure condition and neglected the gas-side resistance. In this work, the effect of the pressure on the dehumidification process in bubble column dehumidifier is investigated experimentally under varying operating conditions. The measurements were conducted at absolute pressures in the range of 1–2 bars, superficial velocity range of 2–18 cm/s, and column height range of 3–7 cm. A model is developed for the relationship between the bubble column effectiveness and the number of transfer units which combines the influence of the heat and mass transfer processes. In addition, a semi-empirical model is adopted and modified for the gas-side mass transfer coefficient to capture the effect of the pressure. The model correlates Sherwood number with Reynolds number, Schmidt number, and the density ratio of air and water vapor. It is found that the total heat transfer rate and the effectiveness of the bubble column dehumidifier both increase with the superficial velocity. However, the heat transfer rises and the effectiveness decreases with the pressure. The column height is found to insignificantly affect the heat transfer and the effectiveness. The developed models predict the total heat transfer rate and the bubble column effectiveness with a maximum deviation of 2% from the experimental measurements. The results suggest that operating a bubble column dehumidifier under higher pressure will result in a larger size to compensate for the decrease occurs in the effectiveness.