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Electrohydrodynamic drying
- 2. Drying is a mass transfer process comprising the removal of water by evaporation. Applications β β’ Restrain microbial development β’ Inhibit quality decay β’ Aid in processing β’ Confer desirable texture β’ Cost reduction Drying is an energy-intensive process and accounts for about 10-20 % the total energy required in food processing industries.
- 3. Afterdeals of conventional drying β’ Loss of quality β’ Loss of energy β’ Longer time β’ Prohibitively expensive at commercial scale Major Concerns β β’ Reduction of energy usage in drying in terms of reducing greenhouse gas (GHG) emissions β’ consumer demand for superior quality
- 4. there is a need for novel and promising alternative drying processes. One such promising technique is Electrohydrodynamics (EHD) drying. EHD is a method of inducing Electric wind (corona wind) that is generated by gaseous ions under the influence of a high-voltage electric field. Fig. 1. corona discharge
- 5. Literature Review Product comparison Inference Reference Tomato Air and oven dry Increased drying rate No difference in shrinkage Ali et al., 2011 Spinach Oven drying Higher Retention of color and ascorbic acid Bajgai et al., 2001 Shrimps Oven air drying Better color and rehydration Less shrinkage Bai et al., 2011 Scallop muscle Oven and air drying 72 % energy saving Better quality retention Bai et al., 2012 Japanese radish Oven and air drying Higher moisture removal Better quality retention Bajgai et al., 2001 Sea cucumber Oven drying Better quality 78 % energy saving Bai et al., 2013 Table 1: studies of EHD dryimg on food products
- 6. Product Comparison Inference Reference Grape pomace Thermal drying at 80 0 c Better color retention Superior energy efficiency Martynenko et al., 2015 Rice Batch (45 0c ) drying Incresed breakage susceptibility Ali et al., 2012 Chinese wolfberr y Hot air drying Higher moisture removal and vitamin c retention Yang et al., 2001 carrot Oven , air EHD (+,-) Better color Less shrinkage Lesser energy consumption Alemrajabi et al., 2011 banana Microwave drying Lesser energy Better quality Longer time Ali et al., 2013 apple Ambient air drying Increased drying rate Hashinaga et al., 2013 tofu Ambient air drying Increased drying rate Bai et al., 2010
- 7. Mechanism β’ Production of electrical wind by corona discharge. β’ A corona discharge is brought on by the ionization of a fluid such as air surrounding a conductor that is electrically charged. β’ On sharp points in air corona can start at potentials of 2 - 6 kV Fig. 2. Schematic diagram emitter-collector plate interaction
- 8. Ions under the effect of strong electric field experiences the coulomb force and propagates towards opposite charge electrode F = E π π Where E is electric field And π π is charge density Along the way they collide with neutral gas molecule. β’ Chain effect β’ Electrical wind Fig. 3. wind by corona discharge
- 9. Negative corona have more no. of free Electrons and higher electon density Compared to positive corona. Fig. 4. negative and positive discharge
- 10. β’ Corona wind disturbs the boundary layer developed from the grounded surface on which the biological material is placed β’ Under the electric field molecules orient themselves in the direction of an electric field. During this process, a lowering of entropy occurs, which in turn lowers the temperature of the material being dried. β’ Vortex effect due to internal diffusion.
- 11. Wind velocity ( v ) v = (π π/π π) π/π E where π π is the dielectric permittivity of air (8.85 Γ10β12 F/m); π π is the air density E is electric field Assumption - β’ ionic wind flow is laminar β’ the turbulence caused due to viscosity of the medium is negligible
- 12. Warburg Current density distribution π = π0 πππ 5 ΞΈ Where ΞΈ<60 And π0 is current density at ΞΈ=0 Fig. 5. Warburg Current density distribution
- 13. EHD Drying system set up Fig. 6. EHD Drying system set up
- 14. FOOD VOLTAGE (KV) FOOD VOLTAGE (KV) potato 5 Banana 6, 8, 10 carrot 5.2 Wheat 10, 12.5, 15 Rough rice 10 Rapeseed 8,9,10 Radish 4.3 Chinese wolfberry 20, 24, 28, 32 Apple 5 Scallop 5-50 spinach 4.3 Tomato 3,4,5 ELECTRIC FIELD β’ moisture removal rate and energy consumption is proportional to applied voltage . β’ High voltage transformer are connected to corresponding configuration Table 2: voltage applied in EHD drying
- 15. Electrode configuration 1. Single point needle β’ Energy efficient β’ round jet Fig. 7. single needle round jet
- 16. 2. Multi-needle Configuration β’ Higher drying rates β’ Multiple round jet Multiple needles Food sample Collector electrode Fig. 8. multiple needle configuration Fig. 9. Top view multiple needle configuration
- 17. Fig. 10.Multiple round jetβ top view Multiple needle impinging flow
- 18. 3. Wire type configuration β’ Forms slot type jet β’ More drying rate than needle type Fig. 12. Wire to mesh configurationFig. 11. Wire to plate configuration
- 19. Wire type impinging flow Wire Wind flow Food sample Collector plate Fig. 13.top view of slot jet Fig. 14. Front view of slot jet
- 20. Electrode spacing 1. Larger than optimum - spacing β’ Less cover up of surface β’ Lower drying rates 2. Lesser than optimum - spacing β’ Interference β’ Lower drying rate β’ Loss of energy due to inter collision
- 21. Optimum inter- spacing β’ highest drying rates β’ no interference β’ Maximum exposing area Fig. 15. Optimum spacing between neighbouring electrodes
- 22. effect of spacing between two neighbouring wires on Tofu β’ 80 % moisture content β’ 45 kV Fig. 16. effect of spacing between two neighbouring wires on Tofu Source : Bai et al., 2010
- 23. Emitter β Collector gap β’ If E-C gap is more than optimum then electric field and corona current and hence velocity of ionic wind will be lesser causing reduced drying rate. β’ If E-C gap is lesser than optimum then due to difference in corona wind will be higher causing reduced drying rates. Electrode gap in cm Fig : effect of E-C gap on tofu
- 24. Energy consumption and efficiency β’ 85-99 % of ππ‘ππ‘ is required for high voltage conversion. β’ power required for corona discharge is given by π· π¬π―π« = π½ π π° π β’ Total energy by corona discharge πΈ πΈπ»π· = ππΈπ»π· Ξt. β’ The energy use of the entire EHD process (ππ‘ππ‘ = ππ‘ππ‘ Ξt) Where Ξt is operational time. β’ The specific energy consumption (SEC, kJ/kg) is mostly used to characterize the efficiency of EHD drying .
- 25. Convective Cross-Flow β’ Suppression of ionic wind. β’ To quantify interaction between convective air flow and ionic wind, the dimensionless EHD number (π πΈπ»π·) is introduced. π΅ π¬π―π« = π π π Where π’ π πππ u are ionic wind velocity and cross-flow air velocity, respectively. The effect of EHD was significant only at low air velocity (π΅ π¬π―π« > 1). negligible effect of low air velocity in the range 0 to 0.4 m /s on EHD efficiency.
- 26. Product Specific energy consumption [kJ/kg] πΈ πΈπ»π· πΈπ‘ππ‘ Grape pomace 611-641 45000 Sea cucumber - 4386 Chinese Wolfberry 882 3920 Tomato 4400-16500 - Banana - 350 carrot - 700-2500 mushroom - 48-745 Specific energy consumption of EHD drying Table 3:Specific energy consumption by EHD drying on food
- 27. Food Shrinkage Color change Rehydrati on Vitamin c retention Banana less Insignificant more - Radish less Insignificant more - Carrot Less less - - Tomato Less Less - - Spinach - Less - higher Wolfberry Insignificant - more higher Table 5: Effect of EHD drying quality parameters of food products Effect of EHD drying quality parameters of food products
- 28. Food Shrinkage Color change Rehydratio n Texture Scallop muscle Less less More - Sea cucumber Less Less More Less hardnes Shrimps Less Less More softer Okara cake - - - Lesser crannies
- 29. REFERENCES Bajgai, T., Raghavan, G., Hashinaga, F.,Ngadi, M. (2006), Electrohydrodynamic dryingβA concise overview. Drying Technology, 24(7), 905β910. Li, F., Li, L., Sun, J., Tatsumi, E. (2006). Effect of electrohydrodynamic (EHD) technique on drying process and appearance of okara cake. Journal of Food Engineering, 77(2), 275β280. Chen, Y.,Barthakur, N., Arnold, N. (1994). ( Electrohydrodynamic (EHD) drying of potato slabs. Journal of Food Engineering, 23(1), 107β119. Lai, F., Wong, D. (2003). EHD-enhanced drying with needle electrode. Drying Technology, 21(7), 1291β1306. Hashinaga, F., Bajgai, T., Isobe, S., Barthakur, N. (1999). Electrohydrodynamic (EHD) drying of apple slices. Drying Technology, 17(3),479β495. Basiry, M., Esehaghbeygi, A. (2010). Electrohydrodynamic (EHD) drying of rapeseed (Brassica napus L.). Journal of Electrostatics, 68(4), 360β363. Goodenough, T., Goodenough, P., Goodenough, S. (2007). The efficiency of corona wind drying and its application to the food industry. Journal of Food Engineering, 80(4), 1233β 1238. Li, F., Li, L., Sun, F., Tatsumi, E. (2005). Electrohydrodynamic (EHD) drying characteristic of okara cake. Drying Technology, 23(3), 565β580.
- 30. Esehaghbeygi, A.,Basiry, M. (2011). Electrohydrodynamic (EHD) drying of tomato slices (Lycopersicon esculentum). Journal of Food Engineering, 104(4), 628β631. Cao, W., Nishiyama, Y., Koide, S. (2004). Electrohydrodynamic drying characteristics of wheat using high voltage electrostatic field. Journal of Food Engineering, 62(3), 209β213. Yaxiang, B., Hu, Y., Li, X., Li, J. (2009). Experiment study of electrohydrodynamic (EHD) drying scallop. Power and Energy Engineering Conference, 2803β2806. Xue, G., Uchino, T., Matsuo, M. (1994). Drying promotion of radish using corona discharge. Journal of the Japanese Society of Agricultural Machinery, 56(5), 35β42. Bajgai, T., Hashinaga, F. (2001). High electric field drying of Japanese radish. Drying Technology, 19(9), 2291β2302. Bajgai, T.R.; Hashinaga, F. (2001). Drying of spinach with a high electric field. Drying Technology, 19(9), 2331β2341. Bai, X., Sun, B. (2011). Study of electrohydrodynamic (EHD) drying technique for shrimps. Journal of Food Processing and Preservation, 35(6), 891β897. Yaxiang, B.; Yucai, H.; Xinjun, L. (2010). The tofuβs characteristics of electrohydrodynamic drying with wire electrode. Presented at Power and Energy Engineering Conference (APPEEC), 1β4.