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HEAT PROCESSES

HEAT PROCESSES. HP12. Electroheat. Electroheat. Direct ohmic heating, radiofrequency heating and microwave heating. Rudolf Žitný, Ústav procesní a zpracovatelské techniky ČVUT FS 2010. Direct Ohmic Heating. HP12.

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HEAT PROCESSES

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  1. HEAT PROCESSES HP12 Electroheat Electroheat. Direct ohmic heating, radiofrequency heating and microwave heating. Rudolf Žitný, Ústav procesní a zpracovatelské techniky ČVUT FS 2010

  2. Direct Ohmic Heating HP12 Ohmic heating is one of these new technologies,which consists of the direct passage of electric currentthrough the product. The permanent motion of electricalcharges creates heat in the product in agreement with Joule's law Gradient of electric potential [V/m] Specific electrical conductivity [S/m] Volumetric heat source[W/m3] Wagner L.M.

  3. Direct Ohmic Heating Holding tube Cooler Electrical insulation Transformer Electrode Aseptic tank Waste Product Pump Filling line Aseptic cooler HP12 APV Baker Ltd. power 75 kW up to 300 kW, mass flowrates 750 kg/h up to 3000 kg/h. Pasterization of acidic products from 20°C to 90°C and sterilization of less acidic products from 65°C to 140°C (the whole line operates at overpressure 4 bars so that the boiling point temperature will be increased) Continuous ohmic heater APV

  4. Direct Ohmic Heating Example HP12 Continuous direct ohmic heater for liquids in our laboratories Direct ohmic heating of foods. Examples Aseptic processing line for apricots and plums Tomatoes

  5. Direct Ohmic Heating Example HP12 applications: space (Mars), earth-based in-package sterilization of foods, or for reheating of military rations Simulations suggestthe presence of significant hot and cold zones,suggesting the need to further optimize pouch design formore uniform heating. In particular, the zones within theV-formed by metal foil electrodes, and the edge of thepouch, where current densities are lowered, are identifiedas points of concern S. Jun, S. Sastry: Reusable pouch development for long term space missions: A 3Dohmic model for verification of sterilization efficacy. Journal of Food Engineering 80 (2007) 1199–1205

  6. Direct Ohmic Heating-Milk HP12 Experimental setup of milk heater in our laboratory

  7. Ohmic Heating-corrosion HP12 Electrode corrosion Metal that is migrating into the medium can be oxidized and can start newsecondary reactions. For example Fe2+ or Fe3+ can be responsible as catalyzers. The corrosion effects can be suppressed either by using a noble materiallike gold or platinum for the electrodes, or by using an increased frequencyabove 50 Hz. Samaranayake, C.P., Sastry, S.K., & Zhang, Q.H. (2005). Pulsed ohmicheating A novel technique for minimization of electrochemical reactionsduring processing. Journal of Food Science, 70(8), 460-465.

  8. Ohmic Heating-corrosion HP12 TiN coating electrodes V=43,5 ml/s Sel=30x40 mm H=10 mm Istart=3 A Tvsádky=70 °C Stainless steel electrodes V=45,5 ml/s Sel=30x40 mm H=10 mm Istart=3 A Tvsádky=70 °C See also: M., Ayadi et al. , Innovative l'ood Science and Emerying Technologies 5 (2004) 465-473

  9. Ohmic Heating-Milk fouling HP12 Model of thermal milk fouling in continuous ohmic heater Jong (1996), Toyoda et al. (1994) Rate of the denaturation and agglomeration of milk proteins Denaturation of native protein -lactoglobulin Agglomeration of denatured -lactoglobulin

  10. Ohmic Heating-Milk fouling HP12 Model of fouling in continuous ohmic heater using Finite Element Program FEMINA Mesh of finite elements T temperature distribution CNativní CDenat. CAgglom

  11. Ohmic Heating-Solid HP12

  12. Ohmic Heating-Solid in Liquid HP12 F.K equation heat transfer with ohmic heating source density of generated heat [W/m3] Laplace equation for electric potential distribution

  13. Ohmic Heating-Solid in Liquid HP12 What is heated faster: liquid (conductivity l) or solid (S)? Laplace equation for voltage in spherical coordinate system f=l,s Continuity of voltage at the sphere surface Remarkable result: Intensity of heat production (Q) is constant (independent of r,)!!! Conclusion: spherical particle will be heated faster than liquid if

  14. Model FEMINA-Solid in Liquid kappa L=0.04kappa S=0.1 potato heats faster than liquid L S kappa L=0.04kappa S=0.01 potato heats slower than liquid +100V -100V 30oC 30oC HP12 The solution is more complicated for solid particles having form of cubes or platelets. Heat generated inside the particles is not uniform and depends upon particle orientation. Numerical solution using FEM is shown as an example

  15. Ohmic Heating-Minced meat 3 4 7 8 5 6 1 2 HP12 Minced meat sample between electrodes with adjustable contact pressure Description: 1 Moving electrode 2 Fixed elecrode 3 Carrier 4 Frame 5 Roller 6 Weight 7 Silon fibre 8 Stop

  16. Ohmic Heating-Minced meat H T1 T2 T3 ½H ¼ H HP12 Temperature measurement by optical fibres

  17. Ohmic Heating-Minced meat k = k + k + k n T p k k 0 k 1 k 2 HP12 Contact layer Contact pressure Meat sample Thickness of sample Electrode

  18. Ohmic Heating-Minced meat HP12 Contact surface and contact pressure F z H B

  19. Ohmic Heating-Minced meat T1 T3 T2 HP12 Results Comparison of temperatures T1 -T2 -T3for pressurep5=8,175kPa.

  20. Modular Heating system HP12

  21. Modular Heating system HP12 Power source + control • Kettle • Boiling pot • Toaster

  22. Modular Heating system HP12 Applicators Control unit Control unit Boiling pot Kettle Power control Filter Rectifier Pulsegenerator Pulse control Microprocessor Power measurement Connector Direct ohmic heating Toaster combined heating Indirect ohmic heating Temperature/power control

  23. Modular Heating system HP12 power control (triacs) Contact heating MOSFET pulse control rectifier Direct ohmic heating

  24. Modular Heating system HP12 Toaster design (combined heating)

  25. Microwave HP12 Microwave heating operates at higher frequencies of electromagnetic waves 900 MHz or 2500 MHz. Polar molecules are heated due to excitation of vibrational mode and viscous friction Intensity of electric field [V/m] Frequency f , Permeability Volumetric heat source[W/m3] Veneziano

  26. Microwave HP12 Waveguide Magnetron K – cathode A – anode M - electromagnet

  27. Microwave HP12 Maxwell equation for distribution of electromagnetic field results to Helmholtz equation for intensity of electric field. Example: One dimensional Helmholt equation describing E in a plate of meat in microwave oven Nonuniform distribution of absorbed energy inside the plate of meat (6 cm thick) at microwave oven with different frequencies

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