Mathematical modelling and simulation of the dehumidifier for the tropical region of Malaysia
In this paper, mathematical model for an adiabatic dehumidifier of liquid desiccant air conditioning system is presented. Regression approach is used to generate the mathematical relation between enthalpy and humidity ratio. Flow-pattern between air & desiccant mainly affects the performance of adiabatic dehumidifier therefore to get proper dehumidification counter-flow configuration is considered as previous studies show that counter-flow direction of air to desiccant has better dehumidification results. For validation, results of present study were compared with those of numerical and analytical results of previous studies, and the agreement was found to be quite satisfactory. The developed mathematical model is then used to study the performance analyses of adiabatic-dehumidifier for the tropical region of Malaysia. Analyses are made for the week having very high range of humidity ratio (18 - 19.5 g/kg). The main concern of the current article is given on moisture removal from the ambient air according to thermal comfort-zone.
Simplified Heat and Mass Transfer Model for Cross-Flow and Countercurrent Flow Packed Bed Tower Dehumidifiers with a Liquid Desiccant System
A mathematical model is developed using the Matlab/Simulink platform to investigate heat and mass transfer performance of cross-flow and counterflow dehumidifiers with Lithium Chloride (LiCl) solution. In the liquid desiccant dehumidifier, the orthogonal polynomial basis is used to simulate the combined processes of heat and mass transfer. The temperature profiles on cross-flow and countercurrent flow dehumidifiers are demonstrated. The resultant counter flow air changes the temperature profile of the LiCl solution in the longitudinal direction because of the drag forces. In addition, when inlet airflow rate reaches 15 kg·s −1 , the temperature effect becomes less obvious and may be reasonably negligible. Under these conditions, the air changes the design factor and determines the interfacial temperature. It is demonstrated that the mathematical model can be of great value in the design and improvement of cross-flow and countercurrent flow dehumidifiers.
Dimensionless mass-transfer correlations for packed-bed liquid-desiccant contactors
Random and structured packings were studied with varying bed depths in the regenerator and the dehumidifier of a solar-assisted liquid-desiccant system. The slopes of the log−log plots of mass-transfer rate vs solution flow rate were found to be close to 0.8, which indicated that the conditions for the liquid phase were turbulent for the operating conditions in both contactors. The small intercepts obtained for the Wilson plots indicated that the gas-phase mass-transfer resistance was negligible compared to the liquid-phase mass-transfer resistance. Liquid-phase mass-transfer coefficients for the packed bed alone were obtained by separating the contributions of the other mass-transfer regions in the contactors. The random packing mass transfer coefficients varied from 0.48 to 2 mol/(s m2), while the double-layer, structured packing mass-transfer coefficients varied from 0.018 to 0.035 mol/(s m2). These mass-transfer coefficients were converted into a dimensionless form, utilizing experimentally obtained d...