Abstract
In the humidification and dehumidification solar desalination system, the recovery of vapor condensation latent heat is the key problem. Using a cascaded phase change heat storage method to recover vapor condensation latent heat can improve the phase change heat storage rate and the water production performance of dehumidifier. The exergy analysis and experimental methods are used to study the cascaded phase change storage dehumidifier. The results show that the more stages of phase change materials in the cascaded phase change heat storage device, the greater the exergy efficiency will be. The heat transfer performance of phase change materials increases with the increase of hot and wet air temperature and flow at the inlet of the dehumidifier. The exergy efficiency and gain output ratio of three-stage phase change heat storage are higher than that of the single-stage. The three-stage one is recommended. If the heat recovered by the cascaded phase change heat storage device is supplied to the passive humidification dehumidification desalinator for secondary water output, the water output and gain output ratio will increase by 25% and the water production cost will be reduced by 20%. The results can provide a basis for the design and application of a cascaded phase change heat storage dehumidifier.
Highlights
The application of phase change heat storage technology can effectively solve the contradiction of mismatch between time and space in solar thermal energy and has broad application prospects in the utilization of solar energy and industrial waste heat resources [1].Solid–liquid phase change heat storage has the advantages of high heat storage density, little temperature change and stable chemical properties, but most phase change materials (PCMs) have low thermal conductivity and a slow heat storage and release rate, which cannot meet the requirements of engineering application [1]
Majumdar et al [15] analyzed the effects of different diameter spherical capsules with different melting temperature PCMs filled in the storage tank on the thermal storage performance of multilayer packed bed latent heat thermal energy storage (PBLTS); the results showed that, during the heat charging and heat release process of PBLTS, the arrangement of capsules with different diameters had a significant impact on the heat storage performance of PBLTS
Suresh et al [21] studied the effect of different volume fractions of PCM in a storage tank on the thermal storage performance of a thermal energy storage system during charging and discharging, and the results showed that the higher volume fractions of
Summary
The application of phase change heat storage technology can effectively solve the contradiction of mismatch between time and space in solar thermal energy and has broad application prospects in the utilization of solar energy and industrial waste heat resources [1]. Cheng et al [14] proposed a device with cascaded packed bed cold heat energy storage using multiple PCMs. During the charging process, the thermal performance was close to optimal when using 3~5-stage PCMs, and its charging time was reduced by 15.1%. Cheng et al [22] analyzed the heat transfer performance and the cold storage performance of the devices with phase change heat storage, and the results showed that heat transfer had the best performance when three types of PCMs, with phase change temperatures of 285.45 K, 286.15 K and 286.45 K, were combined with a ratio of 1:1:1 Under these conditions, the exergy efficiency was up to 72.2%.
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