Journal
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
Volume 149, Issue -, Pages -Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.ijheatmasstransfer.2019.119231
Keywords
Exergy efficiency; Energy efficiency; Numerical simulation; Carrot drying; Heat and mass transfer; Relative humidity
Categories
Funding
- National Key Research and Development Program of China [2017YFD0400905]
- National Natural Science Foundation of China [31772026, 31760471, 31360399]
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Industrial drying is one of the most energy intensive unit operations encountered in most industrial sectors. Therefore, much effort has been devoted to energy savings in drying. Most methods applied to convective drying are based on heat recovery from dryer exhaust. However, there are major limitations on how much of the energy can be recovered cost-effectively. Here a new concept based on the relative humidity (RH) control of convective drying of carrot cubes was evaluated with the purpose of enhancing the energy and exergy efficiency of drying. Numerical simulations of heat and mass transfer were performed to investigate hot air drying behavior of carrot cubes. The model fitted well the moisture ratio and the material temperature data with average relative errors of 6.5% and 0.8%, respectively. Results show that both the energy loss caused by exhaust air and the irreversibility loss of thermodynamic process decreased with increase in RH of the drying medium from 4% to 40%. Multistage relative humidity control strategy improved both the drying rate and exergy efficiency. Among the tested schemes, the three-stage RH control strategy, i.e. (1) RH of 40% for 2 h, (2) RH of 20% for 2 h and (3) RH of 4% for 3.5 h was found to be the strategy with the highest exergy efficiency (53.3%). It was almost three times higher than that for constant 4% RH values. (C) 2019 Elsevier Ltd. All rights reserved.
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