Continuous flow microwave sterilisation focussing on aqueous media

Buchner-Jones, Jordan (2020-03)

Thesis (MEng)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: This thesis contains details regarding the research and development of a continuous flow, temperature controlled, microwave heating sterilisation unit. The microwave hardware design promotes the propagation of the fundamental 𝑇𝐸10 mode for rectangular waveguide structures at 2.45 GHz. The system design incorporates a single mode applicator chamber which considers the microwave heating patterns within the system. The heating patterns were predicted through rigorous electromagnetic thermal coupled simulations. The temperature control system operates by maintaining output magnetron power whilst varying the media flow rate. The system has a controllable temperature range between 60 C and 95 C resulting in a variable system output flow rate between 3.3 l/h and 6 l/h. The constant output power produced by the magnetron can be set to either 700 W, 350 W or 210 W, using a technique called saturable reactor control and this is demonstrated and explained in the project. The magnetron and high voltage supply were obtained from a conventional microwave oven. Calibration techniques for various stages in the system are discussed and implemented to ensure measured data obtained is accurate and repeatable. The materials used to transport the targeted media inside the treatment chamber were selected based on a low dissipation factor ( 𝑡𝑎𝑛 ), effectively making the materials “invisible” to microwave radiation. This allows for selective heating of the media to be treated inside the system. The microwave sterilisation treatments were conducted with a strain of Lactococcus lactis (NZ9000) with an antibiotic marker (chloramphenicol at 10 μg/ml) suspended in sterile saline. The experiments conducted and observations made during development suggest that the designed system is a successful, effective, sterilisation solution.

AFRIKAANSE OPSOMMING: Hierdie tesis bevat besonderhede rakende die navorsing en ontwikkeling van 'n deurlopende vloei, temperatuurbeheerde, mikrogolfverwarmingsterilisasie-eenheid. Die ontwerp van die mikrogolf-hardeware bevorder die voortplanting van die fundamentele 𝑇𝐸10 modus vir reghoekige golfleier strukture by 2,45 GHz. Die stelselontwerp bevat 'n enkel-modus toediener wat die mikrogolfpatroon in die stelsel in ag neem. Die verwarmingspatrone is voorspel deur streng elektromagnetiese termiese gekoppelde simulasies. Die temperatuur beheerstelsel werk deur die magnetron uittree drywing te handhaaf terwyl die media se vloeitempo verander word. Die stelsel het 'n beheerbare temperatuurbereik tussen 60 C en 95 C, wat lei tot 'n veranderlike uittree tussen 3,3 l / h en 6 l / h. Die konstante uittree drywing wat deur die magnetron gelewer word, kan op 700 W, 350 W of 210 W ingestel word met behulp van 'n tegniek genaamd versadigde reactor beheer, en dit word in die projek gedemonstreer en verduidelik. Die magnetron en hoogspanning krag toevoer is verkry uit 'n konvensionele mikrogolfoond. Kalibreringstegnieke vir verskillende fases in die stelsel word bespreek en geïmplementeer om te verseker dat die gemete data akkuraat en herhaalbaar is. Die materiaal wat gebruik word om die geteikende media binne die toediener te vervoer, is gekies op grond van 'n lae verlies faktor (𝑡𝑎𝑛), wat die materiaal effektief 'onsigbaar' maak vir mikrogolf straling. Hierdeur kan selektiewe verhitting van die media binne die stelsel behandel word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107975
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