Studies of local heat transfer in a gas–liquid system agitated by double disc turbines in a slender vessel

Karcz, J.

doi:10.1016/s1385-8947(99)00005-4

Cited by 18 publications

(17 citation statements)

References 10 publications

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“…Esse cálculo aproximado é efetuado através da equação 1, utilizando-se as temperaturas médias da amostra, calculadas pela equação 2, ou seja: (2) onde e são as temperaturas da amostra na superfície interna e no centro geométrico da embalagem, respectivamente. Os calores específicos das amostras de pasta de tomate e de doce de leite foram calculados utilizando a equação 3, proposta por SIEBEL [6].…”

Section: -Resultados E Discussãounclassified

Uso de transdutores de fluxo de calor no estudo da transferência de calor em alimentos embalados

Carciofi¹,

Güths²,

Laurindo³

2002

Ciênc. Tecnol. Aliment.

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A densidade de fluxo de calor que atravessa uma superfície é classicamente determinada mediante a medição das temperaturas apropriadas e da aplicação da Lei de Fourier. Uma alternativa a esse procedimento é a utilização de transdutores de fluxo de calor, os quais geram um sinal elétrico proporcional ao fluxo térmico que os atravessa. Neste trabalho, processos de aquecimento e de resfriamento de alimentos foram estudados em laboratório, utilizando-se um recipiente de vidro cilíndrico para simular uma embalagem. Dois transdutores de fluxo de calor a gradiente tangencial foram previamente instalados no recipiente, revestindo completamente a superfície lateral do mesmo. O recipiente contendo a amostra foi inserido em banho de água circulante à temperatura constante. Os sinais fornecidos pelos transdutores e por termopares inseridos no interior do recipiente foram registrados por um sistema de aquisição de dados computadorizado. Os resultados obtidos com o uso dos transdutores foram comparados com aqueles obtidos através de balanços de energia realizados a partir dos dados experimentais de evolução temporal das temperaturas da amostra junto à superfície interna da embalagem e no centro da mesma. A comparação mostrou que os transdutores de fluxo de calor a gradiente tangencial puderam determinar os fluxos de calor, com tempo de resposta característico dos termopares. Os resultados apresentados mostraram a viabilidade de utilização desses fluxímetros no estudo não destrutivo e não invasivo dos processos de aquecimento e de resfriamento de alimentos, fornecendo informações complementares àquelas obtidas pelo uso de termopares instalados no interior da embalagem.Palavras-chave: tratamento térmico; alimentos; fluxímetros de calor. SUMMARY THE USE OF HEAT FLUX TRANSDUCERS TO STUDY HEAT TRANSFER IN CANNED FOODS. Heat flux determination in thermalprocesses is classically carried out by appropriate temperature measurements and the application of the Fourier Law. An alternative to this procedure is to determine the heat flux that crosses a surface using heat flux transducers, thus producing heat flux dependent signals. In this work, heating and cooling processes of foods were studied in the laboratory using a cylindrical glass container with the external surface covered by two heat flux meters. Water, maintained at a constant temperature by a thermostatically controlled bath, was circulated within an external jacket to promote heating or cooling of the sample-container system. The signals provided by the transducers and thermocouples placed inside the container were registered by an on-line data acquisition system. Comparison of the results from the heat flux meters with those calculated by using the sample temperature histories and energy balances in the containersample system showed to be in good agreement with each other. The time-response of the heat flux meters had the same magnitude as those obtained by the thermocouples. The results showed that heat transducers could be used to carry out non-destructive heat flux measur...

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Section: -Resultados E Discussãounclassified

Uso de transdutores de fluxo de calor no estudo da transferência de calor em alimentos embalados

Carciofi¹,

Güths²,

Laurindo³

2002

Ciênc. Tecnol. Aliment.

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“…The thermal method used in this study to measure local heat transfer coefficient was described in detail in papers 18,22,25 . The local heat source was built at the vessel wall at height z (Fig.…”

Section: Methodsmentioning

confidence: 99%

“…The results of the mean heat transfer coefficient have been given in literature for different agitated liquids, for example: viscous fluids 7-10 , non-Newtonian fluids [10][11][12][13][14] and others [15][16] . The measurements of the local heat transfer coefficient have been also carried out for liquid [17][18][19][20][21] , gas-liquid [21][22][23][24][25][26] , solid-liquid 27 and gas-solid-liquid 28 systems.…”

Section: Introductionmentioning

confidence: 99%

“…However, knowledge of the values of heat transfer coefficients, mean for whole wall of the agitated vessel, is insufficient because, in this way, the regions of different intensity of heat transfer cannot be identified on the heat transfer surface area. For this reason, quantitative analysis of the distributions of heat transfer coefficient in a jacketed, baffled, agitated vessel equipped with two impellers on a common shaft was carried out by Karcz 25 and Bielka et al 22 Karcz 25 performed an experimental study of the distributions of heat transfer coefficient along the wall of the tall agitated vessel equipped with a dual Rushton turbine system. The measurements were performed in a vessel of inner diameter T = 0.3 m, filled with a liquid up to height H = 2T.…”

Section: Introductionmentioning

confidence: 99%

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Experimental Modelling of Local Heat Transfer Process for a Gas-liquid System in an Agitated Vessel with the System of A 315 – RT ImpellersExperimental Modelling of Local Heat Transfer Process for a Gas-liquid System in an Agitated Vessel with the System of A 315 – RT Impellers

Bielka¹

2018

Chem.Biochem.Eng.Q.

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The results of the experimental studies of the local heat transfer process for a gas-liquid system in the region of the cylindrical wall of baffled agitated vessel equipped with the system of A 315 (lower) -RT (upper) impellers are presented. Newtonian liquids of different physical properties and air were used as continuous and dispersed phases, respectively. Local heat transfer coefficients were measured using both thermal and electrochemical methods. Distributions of the heat transfer coefficients were described by means of equations (13) - (16) and (17) -(21), separately, for turbulent and transitional ranges of the fluid flow in the agitated vessel. These equations, concerning both coalescing and non-coalescing gas-liquid systems, have no equivalent in the open literature. Moreover, the results for the A 315 -RT impeller system were compared with our previous heat transfer data obtained using CD 6 -RT or RT -RT impeller systems.

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“…This difference can be taken into account by correction factor p, defined as the ratio of real heat transfer coefficient a and heat transfer coefficient a EDD measured by the electrodiffusion method with small electrodes, i. e. p = a / a EDD . Detailed description of the electrodiffusion method and how to resolve issues with measurements on small electrodes can be found in papers 13,14 . Results of numerical simulations of heat transfer on small electrodes of 0.5 mm and 4 mm diameters and graphical dependencies of correction factor p are stated in paper 13 .…”

Section: Methodsmentioning

confidence: 99%

Heat Transfer at the Bottom of a Cylindrical Vessel Impinged by a Swirling Flow from an Impeller in a Draft Tube

Petera¹

2017

Chem.Biochem.Eng.Q.

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Heat transfer at the bottom of a cylindrical vessel impinged by a flow with tangential velocity component generated by an axial-flow impeller in a draft tube was measured using the electrodiffusion experimental method. Local values of the Nusselt numbers along the radial coordinate of the heat transfer surface and corresponding mean values are presented for relatively small distances of the draft tube from the impinged surface (0.25 ≤ h / d ≤ 1). Such small distances are typical for mixing of liquids, which ensures good homogenization and increases the intensity of heat and mass transfer in many industrial operations. Results are compared with literature data for unconfined impinging jets with no tangential velocity components. The additional tangential velocity component generated by the rotating impeller significantly influences the hydrodynamics of the impinging jet and decreases the heat transfer intensity in the case of small distances from the impinged surface. A correlation describing the mean Nusselt number at the vessel bottom is proposed. It can be used in a design of a real industrial piece of equipment with heat transfer situated at the bottom.

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Studies of local heat transfer in a gas–liquid system agitated by double disc turbines in a slender vessel

Cited by 18 publications

References 10 publications

Uso de transdutores de fluxo de calor no estudo da transferência de calor em alimentos embalados

Uso de transdutores de fluxo de calor no estudo da transferência de calor em alimentos embalados

Experimental Modelling of Local Heat Transfer Process for a Gas-liquid System in an Agitated Vessel with the System of A 315 – RT ImpellersExperimental Modelling of Local Heat Transfer Process for a Gas-liquid System in an Agitated Vessel with the System of A 315 – RT Impellers

Heat Transfer at the Bottom of a Cylindrical Vessel Impinged by a Swirling Flow from an Impeller in a Draft Tube

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