Study On Electrohydrodynamic Energy-saving Drying Technology And Its Applications

With the continuous improvement of living standards, traditional drying techniques for aquatic products are becoming increasingly inadequate and no longer even meet certain requirements, such as high product quality and low energy consumption. Electrohydrodynamic (EHD) drying technology, as a novel drying method, is a prospective alternative for heat-sensitive materials due to its pronounced advantages, including low equipment expense, low energy consumption, and non-thermal processing. To improve the drying rate and reduce the energy consumption of EHD drying technology when used on aquatic products, five parts are addressed in the present thesis:A contrast experiment of drying rate on tofu using a needle electrode, a wire electrode and a plate electrode under different voltages have been evaluated respectively. At the same time, the contrast experiments of drying rate on tofu using needle electrode with glass enclosure and counterpart without it, as well as high electric field pretreatment. According to the experiment results, the mechanism of EHD drying was confirmed, the impact of ion wind on the drying material played a major role to increase drying rate.The factors related to the drying rate and energy consumption were quantitatively studied by changing the voltage, the voltage polarity, the electrode spacing and the distance between the two neighboring needles (wires). The results indicate that when the electrode spacing is 9 cm and the distance between the two neighboring needles is 8 cm, the drying rate is the highest while the energy consumption is relative least,45 kV is the optimum value for drying voltage.Sea cucumber, shrimp, and scallop muscle samples, as representatives of aquatic products, were dried using ambient air, an EHD system, and an oven. The energy consumption of EHD and oven drying, the shrinkage rate, water absorption, and rehydration ratio, and sensory properties, such as color and trimness, of the dried products were measured. Results showed that the drying rate of the aquatic products significantly improved using the EHD drying system. Compared with oven drying, EHD drying was more efficient in terms of energy savings. It also only costs less than 30% of the electric energy required for oven drying. The dried products obtained by EHD had less shrinkage, better rehydration, and better sensory qualities, such as better color, lower distortion, and so on. The dried sea cucumber obtained by EHD had higher protein and acid mucopolysaccharide contents and lower hardness.With Spanish mackerel as materials, dried investigated voltage, sample thickness, moisture content and environmental temperature on the drying rate of EHD have been experimentally evaluated. The experimental data were analysed by mathematical analysis and SPSS software and has established the mathematical model about the voltage, environmental temperature, the thickness and moisture content of the Spanish mackerel and the drying rate.Combination of EHD drying and vacuum freeze drying was examined as a potential mean for drying sea cucumber. The energy consumption of combination and vacuum freeze drying; the shrinkage rate, rehydration ratio; the protein content, the acid mucopolysaccharide content and sensory properties such as color and hardness of the dried product were measured. Compared with vacuum freeze drying, the combined process take less drying time and energy comsuption, Compared with EHD drying, the combined process had lower shrinkage rate, higher rehydration rate, higher protein content, lower hardness and better sensory qualities.