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ABSTRACT
The rotary desiccant wheel dehumidification system has been extensively applied to achieve deep dehumidification in the modern environment with low humidity ratio. The effect of mixing destruction caused by the temperature and humidity inhomogeneity on the thermodynamic performance of the desiccant wheel deep dehumidification (DWDD) system has not been thoroughly illustrated. This research aims to reduce the mixing destruction and improve the overall energy efficiency of the DWDD system. Numerical analyses were carried out to investigate the mixing destruction characteristics of the deep dehumidification process. The results revealed that the mixing exergy destruction gradually becomes a prominent factor as regeneration temperature and humidity ratio increase under deep dehumidification, and there is a significant temperature and humidity ratio gradient in the transition angles from the regeneration side to the process side. The purge angle is regulated to reduce the average temperature and humidity ratio on the process side and lower the air inhomogeneity. The exergy efficiency of the desiccant wheel can be improved from 44.8% to 73.9% at the regeneration humidity ratio of 20 g/kg under the effective purge angle of 30°, indicating a considerable enhancement of exergy efficiency under the effective purge angle at a high regeneration humidity ratio.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Nomenclature
Variables
| cd | = | specific heat capacity of solid desiccant [kJ/(kg·K)] |
| cp,a | = | specific heat capacity of air [kJ/(kg·K)] |
| cp,m | = | specific heat capacity of moist air [kJ/(kg·K)] |
| cp,w | = | specific heat capacity of water [kJ/(kg·K)] |
| COP | = | coefficient of performance (dimensionless) |
| ex | = | exergy per air flowrate (kJ/kg) |
| Ex | = | exergy (kW) |
| f | = | ratio of the solid area to the channel area (dimensionless) |
| HVAC | = | heating, ventilation, and air-conditioning |
| m | = | mass air flowrate (kg/m3) |
| NTU | = | number of transfer units (dimensionless) |
| P | = | pressure (kPa) |
| Q | = | cooling or heating capacity (kW) |
| t | = | temperature in Celsius (°C) |
| T | = | temperature in Kelvin (K) |
| W | = | water content [kg/kg] |
Greek symbols
| = | volume ratio of desiccant material in the solid (dimensionless) | |
| ηex | = | exergy efficiency (dimensionless) |
| ηω | = | dehumidification efficiency (dimensionless) |
| λd | = | heat conductivity of desiccant wheel [W/(m·K)] |
| ρd | = | density of solid desiccant [kg/m3] |
| ρad | = | adsorbent density [kg/m3] |
| = | porosity (dimensionless) | |
| χ | = | air inhomogeneity coefficient (dimensionless) |
| ω | = | humidity ratio (g/kg or kg/kg) |
Subscripts
| a | = | air |
| amb | = | ambient |
| ch | = | chemical |
| dest | = | destruction |
| h | = | heating |
| in | = | inlet |
| m | = | mechanical |
| max | = | maximum |
| mix | = | mixing |
| out | = | outlet |
| p | = | process air |
| purge | = | purge angle |
| r | = | regeneration air |
| R | = | reference state |
| t | = | thermal |
| tr | = | transfer |