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Jet Impingement and Infrared Heating of Cylindrical Foods. Flow and Heat Transfer Studies

Olsson, Eva LU (2005)
Abstract (Swedish)
Popular Abstract in Swedish

Jet impingement och infraröd strålning är metoder för snabb värmeöverföring som kan användas för att snabba upp värmeprocesser i livsmedelsindustrin. Värmningshastigheten påverkar viktiga egenskaper hos livsmedlet, t.ex. brunfärgning. Jet impingement består av riktade strålar av luft med hög hastighet som träffar ytan på livsmedlet och minskar gränsskiktet mellan luften och produktytan, vilket ger en snabb värmeöverföring. Infraröd värmning är termisk strålning som värmer produkten direkt och effektivt utan att värma upp den omgivande luften.



Flöde och värmetransport från en och flera strålar som är riktade mot en eller flera cylindrar placerade på en plan platta har studerats... (More)
Popular Abstract in Swedish

Jet impingement och infraröd strålning är metoder för snabb värmeöverföring som kan användas för att snabba upp värmeprocesser i livsmedelsindustrin. Värmningshastigheten påverkar viktiga egenskaper hos livsmedlet, t.ex. brunfärgning. Jet impingement består av riktade strålar av luft med hög hastighet som träffar ytan på livsmedlet och minskar gränsskiktet mellan luften och produktytan, vilket ger en snabb värmeöverföring. Infraröd värmning är termisk strålning som värmer produkten direkt och effektivt utan att värma upp den omgivande luften.



Flöde och värmetransport från en och flera strålar som är riktade mot en eller flera cylindrar placerade på en plan platta har studerats numeriskt med simuleringar i ett CFD-program (CFD=computational fluid dynamics) och turbulensmodellerna k-? SST och RSM. I allmänhet var hastigheten beräknad med CFD i bra överensstämmelse med experimentella mätningar, gjorda med particle image velocimetry (PIV). Värmetransporten, utryckt i lokala vämeövergångstal var inte jämn runt cylindern p.g.a. att gränsskiktets tjocklek varierade runt cylindern. Värmeövergångstalen var störst, högst upp på cylindern i stagnationspunkten och mindre nära separationspunkten och på baksidan av cylindern. Som komplettering till CFD-simuleringarna beräknades de lokala värmeövergångstalen runt cylindern från uppmätta temperaturprofiler i olika positioner runt cylindern. En känslighetsanalys gjordes också. Värmeövergångstalen var i allmänhet större än de beräknade med CFD. Växelverkan mellan flera luftstrålar påverkade värmeöverföringen runt cylindern. Avståndet och öppningen mellan luftstrålarna var betydelsefulla för att få en hög och jämn värmetransport vid användning av flera luftstrålar.



Värmning med impingement och infraröd strålning samtidigt studerades också med CFD, vilket visade att det finns en synergistisk effekt när man kombinerar de två värmningsmetoderna. Genom att kombinera de båda metoderna kunde man få en högre värmetransport än med var och en av metoderna separat. Hur jet impingement och infraröd värmning påverkade färg och skorpbildning på baguetter studerades experimentellt. Impingement och infraröd värmning gav olika temperaturprofiler i skorpan vilket i sin tur resulterade i olika färg- och skorpbildning. Snabb värmning ökade färgbildningen och förkortade den totala värmningstiden, vilket gav en tunn skorpa och reducerade den totala vattenförlusten. Kombinationen av jet impingement och infraröd värmning gjorde det möjligt att skapa produktegenskaper som inte kunde fås med värmningsmetoderna för sig. En tjockare skorpa och bättre centrumvärmning kunde bara fås genom kombination av infraröd strålning och impingement.



Beräkning av flöde och värmetransport med CFD kan användas till att designa utrustning och processbetingelser som ger optimal värmeöverföring till produkten och därmed en hög och jämn produktkvalitet. (Less)
Abstract
Rapid heat transfer methods such as jet impingement and infrared radiation can be used to speed up thermal processing in the food industry. The heating rate affects important food characteristics, such as colour. Jet impingement consists of directed jets of air with a high velocity that impinge on the food surface, which reduces the velocity boundary layer between the air and surface and gives a fast heat transfer. Infrared heating is a radiative heat transfer method with instant and effective heating of the food product, without heating the surrounding air.



Flow and heat transfer from single and multiple jets impinging on a circular cylinder placed on a flat surface were studied numerically by computational fluid... (More)
Rapid heat transfer methods such as jet impingement and infrared radiation can be used to speed up thermal processing in the food industry. The heating rate affects important food characteristics, such as colour. Jet impingement consists of directed jets of air with a high velocity that impinge on the food surface, which reduces the velocity boundary layer between the air and surface and gives a fast heat transfer. Infrared heating is a radiative heat transfer method with instant and effective heating of the food product, without heating the surrounding air.



Flow and heat transfer from single and multiple jets impinging on a circular cylinder placed on a flat surface were studied numerically by computational fluid dynamics (CFD) simulations using the k-? SST and RSM models. The results concerning velocity obtained by CFD were generally in good agreement with experimental measurements using particle image velocimetry (PIV). The heat transfer distribution on the cylinder surface, expressed as local heat transfer coefficients, was non-uniform due to air flow characteristics that influenced the boundary layer thickness. The heat transfer was highest on the top of the cylinder, and lower close to the separation point and on the back of the cylinder. In addition to making CFD simulations, the local heat transfer coefficients were determined by an inverse heat transfer method, including a sensitivity analysis, using temperature profiles in the cylinder at different positions. The heat transfer coefficients were generally higher than what was predicted by CFD. The interaction between multiple jets strongly affected the heat transfer around the cylinder. The distance and opening between the jets were found to be important to achieving a high and even heat transfer rate using multiple jets.



Jet impingement and infrared heating simultaneously was studied using CFD, which showed that there is a synergistic effect when the two heating methods are combined. A higher heat transfer was achieved by combining the methods than by using each method separately. The effect of impingement and infrared heating on colour and crust formation on partially baked baguettes was investigated experimentally. Impingement and infrared heating gave different temperature profiles in the crust, which resulted in different colour development and crust formation. A rapid heating increased the rate of colour development and shortened the total heating time, which resulted in a thin crust and reduction in the total moisture loss. The combination of jet impingement and infrared made it possible to create product properties that cannot be achieved by use of the heating methods alone. A thicker crust and better heating in the centre of the bread could only be achieved by combining infrared and impingement.



For industrial thermal processes, prediction of flow and heat transfer with CFD can be used to design equipment and processes that offer optimal heat transfer to the product, thus resulting in high and even product quality. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor Dumoulin, Elisabeth, Ecole Nationale Supérior des Industries Agricole et Alimentaire, Massy, France
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Termisk teknik, fluiddynamik, plasma, Thermal engineering, applied thermodynamics, Gaser, fluid dynamics, plasmas, Gases, RSM, CFD, inverse heat transfer, jet impingement heat transfer, infrared heating, termodynamik, Food and drink technology, Livsmedelsteknik, PIV, SST, food, cylinder
pages
146 pages
publisher
Department of Food Technology, Lund University
defense location
Lecture hall C, at the Centre of Chemistry and Chemical Engineering (Kemicentrum), Getingevägen 60, Lund Institute of Technology
defense date
2005-12-01 10:30
ISBN
91-628-6683-4
language
English
LU publication?
yes
id
7112cf83-142c-4ad9-af6d-d6227f91b75a (old id 545669)
date added to LUP
2007-10-13 12:54:25
date last changed
2016-09-19 08:45:09
@phdthesis{7112cf83-142c-4ad9-af6d-d6227f91b75a,
  abstract     = {Rapid heat transfer methods such as jet impingement and infrared radiation can be used to speed up thermal processing in the food industry. The heating rate affects important food characteristics, such as colour. Jet impingement consists of directed jets of air with a high velocity that impinge on the food surface, which reduces the velocity boundary layer between the air and surface and gives a fast heat transfer. Infrared heating is a radiative heat transfer method with instant and effective heating of the food product, without heating the surrounding air.<br/><br>
<br/><br>
Flow and heat transfer from single and multiple jets impinging on a circular cylinder placed on a flat surface were studied numerically by computational fluid dynamics (CFD) simulations using the k-? SST and RSM models. The results concerning velocity obtained by CFD were generally in good agreement with experimental measurements using particle image velocimetry (PIV). The heat transfer distribution on the cylinder surface, expressed as local heat transfer coefficients, was non-uniform due to air flow characteristics that influenced the boundary layer thickness. The heat transfer was highest on the top of the cylinder, and lower close to the separation point and on the back of the cylinder. In addition to making CFD simulations, the local heat transfer coefficients were determined by an inverse heat transfer method, including a sensitivity analysis, using temperature profiles in the cylinder at different positions. The heat transfer coefficients were generally higher than what was predicted by CFD. The interaction between multiple jets strongly affected the heat transfer around the cylinder. The distance and opening between the jets were found to be important to achieving a high and even heat transfer rate using multiple jets.<br/><br>
<br/><br>
Jet impingement and infrared heating simultaneously was studied using CFD, which showed that there is a synergistic effect when the two heating methods are combined. A higher heat transfer was achieved by combining the methods than by using each method separately. The effect of impingement and infrared heating on colour and crust formation on partially baked baguettes was investigated experimentally. Impingement and infrared heating gave different temperature profiles in the crust, which resulted in different colour development and crust formation. A rapid heating increased the rate of colour development and shortened the total heating time, which resulted in a thin crust and reduction in the total moisture loss. The combination of jet impingement and infrared made it possible to create product properties that cannot be achieved by use of the heating methods alone. A thicker crust and better heating in the centre of the bread could only be achieved by combining infrared and impingement.<br/><br>
<br/><br>
For industrial thermal processes, prediction of flow and heat transfer with CFD can be used to design equipment and processes that offer optimal heat transfer to the product, thus resulting in high and even product quality.},
  author       = {Olsson, Eva},
  isbn         = {91-628-6683-4},
  keyword      = {Termisk teknik,fluiddynamik,plasma,Thermal engineering,applied thermodynamics,Gaser,fluid dynamics,plasmas,Gases,RSM,CFD,inverse heat transfer,jet impingement heat transfer,infrared heating,termodynamik,Food and drink technology,Livsmedelsteknik,PIV,SST,food,cylinder},
  language     = {eng},
  pages        = {146},
  publisher    = {Department of Food Technology, Lund University},
  school       = {Lund University},
  title        = {Jet Impingement and Infrared Heating of Cylindrical Foods. Flow and Heat Transfer Studies},
  year         = {2005},
}