Design of Flat-Plate Dehumidifiers for Humidification–Dehumidification Desalination Systems

Abstract

Flat-plate heat exchangers are examined for use as dehumidifiers in humidification-dehumidification (HDH) desalination systems. The temperature and humidity ratio differences that drive mass transfer are considerably higher than in airconditioning systems, making current air-conditioning dehumidifier designs and design software ill-suited to HDH desalination applications. In this work a numerical dehumidifier model is developed and validated against experimental data. The model uses a logarithmic mass transfer driving force and an accurate Lewis number. The heat exchanger is subdivided into many cells for high accuracy. The Ackermann correction takes into account the effect of non-condensable gases on heat transfer during condensation. The influence of various heat exchanger design parameters is thoroughly investigated and suitable geometries are identified. Amongst others, the relationship between heat flow, pressure drop and heat transfer area is shown. The thermal resistance of the condensate layer is negligible for the investigated geometries and operating point.A particle embedded polymer as a flat-plate heat exchanger material for seawater operation substantially improves the heat flux relative to pure polymers and approaches the performance of titanium alloys. Thus, the use of particle embedded polymers is recommended. The dehumidifier model can be applied in design and optimization of HDH desalination systems.

Experiments and modeling of bubble column dehumidifier performance

“…In its most basic form, a HDH system consists of a heater, a humidifier, a dehumidifier, and the pumps and piping necessary to move fluid between components. Dehumidification technology warrants further study because of the high condenser area required [2,3] to overcome the resistance to diffusion of a dilute vapor through air, and because the effectiveness of the dehumidifier dominates the performance of the entire HDH system [4].…”

Experimental Study of a Humidification-Dehumidification Seawater Desalination System Combined with the Chimney

“…Recent studies on the SHDHSDSs mainly focus on the heat transfer enhancement in the evaporators and condensers [4][5][6][7], the configuration and operation parameters analyses [8][9][10][11], and the experimental studies on demonstration systems [12][13][14][15][16][17][18][19]. Sievers and Lienhard analyzed the heat transfer and fluid flow inside the flatplate and finned-pipe condensers using numerical simulations [4,5]. Moumouh et al fulfilled the heat transfer enhancement of flat-plate collectors with siphon water tanks and packed beds through reviewing the SHDHSDSs in the literature [6].…”

“…The experimental demonstration devices validate the feasibility of the SHDHSDS [12][13][14][15][16][17][18][19]. And the literature review indicates that the methods of increasing the freshwater productivity mainly include reasonably increasing the system energy recovery stages [7,14], increasing the temperatures of the air side and the water side [4-7, 10, 11, 13, 16], increasing the fluid mass flow rate [10,11,16], increasing the compactness of the evaporation and condensation devices [4][5][6][7], and increasing the heat exchange area [4][5][6][7]. However, there is no limit to the total energy input to the systems in the previous study.…”

Thermodynamic balancing of a fixed-size two-stage humidification dehumidification desalination system

“…A major issue that made early HDH systems difficult to commercialize was their need for very large dehumidifiers [4,5] (up to 30 m 2 for a 1 m 3 /day system [6]), which increased their cost of water production greatly. Dehumidifiers contain a very large concentration of air, a noncondensable gas, which leads to very low mass transfer coefficients and increases the surface area needed in conventional dehumidifiers.…”