Abstract
Hollow fibres have been studied as the substitute for metallic materials due to the advantages such as light weight, corrosion resistant and low cost in heat and mass transfer applications. A novel polymer hollow fibre liquid desiccant dehumidification system, in which a cross-flow hollow fibre module (fibre inside diameter = 1.4 mm) serves as the dehumidifier, is presented in this paper. This novel hollow fibre integrated liquid desiccant dehumidification system can be used in an air conditioning system to provide a comfortable indoor environment for hot and humid area. Compared with other conventional liquid desiccant dehumidifier, the polymer hollow fibre has a very small diameter which leads to significantly increased surface area. Moreover, the porous feature of the hollow fibre module can help to eliminate any liquid desiccant droplets carryover into the process air. As a less corrosive and more environmental friendly working fluid, aqueous potassium formate (KCOOH) solution has been selected. The dehumidification performance of the proposed system were analysed experimentally under the conditions of incoming air temperature in the range of 30–45 °C. The variations of dehumidification sensible and latent effectiveness, moisture removal rates were studied by varying the incoming air velocity from 0.65 m/s to 4.5 m/s. With the various values of incoming air relative humidity in the range of 55–75% and the solution concentrations between 36% and 62%, the experimental obtained latent effectiveness are in the range of 0.25–0.43 and the sensible effectiveness are in the range of 0.31–0.52, which is in a satisfactory agreement with the empirical correlation of effectiveness-NTU in the literature.
Highlights
W water wb wet bulb v1 saturated water vapour at the entrance of the hollow fibre module v2 saturated water vapour at the exit of the hollow fibre module
This paper presents a novel polymer hollow fibre integrated evaporative cooling system, with 3000 hollow fibers formed into a circular module
1) Frontal air velocity and pad thickness of the module are two key factors for the evaporative cooling system 2) The optimum frontal velocity was 2.5m/s 1) The novel combined parallel and regenerative counter-flow evaporative cooler could achieve lower outlet air temperature and higher cooling capacity; 2) The optimization criteria allow to establish paretooptimal operational condition 1) The saturation point of the working air is influenced by the working air ratio and channel height; 2) Overall heat transfer coefficient could achieve higher than 100W/m2K
Summary
W water wb wet bulb v1 saturated water vapour at the entrance of the hollow fibre module v2 saturated water vapour at the exit of the hollow fibre module. Compared with porous pad media, hollow fibre materials provide several advantages as following: 1) allow selective permeation of moisture: with pore sizes less than 0.1μm, hollow fibre material will allow the water vapour transfer but eliminate the bacteria and fungi penetration23; 2) provide large surface area per unit volume, which is favourable for enhanced heat and mass transfer. The effects of air velocities on the cooling effectiveness, heat and mass transfer coefficients, specific water consumption and pressure drop across the polymer hollow fibre module were analysed. Two sets of experimentally derived non-dimensional heat and mass transfer correlations were summarized and compared with the results obtained from the literature These sets heat and mass transfer correlations could be favourable for the future design of polymer hollow fibre integrated evaporative cooling system
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