Thermal dispersion and wall heat transfer in packed beds

Gunn, Dixon; Khalid, M.

doi:10.1016/0009-2509(75)80014-5

Cited by 75 publications

(39 citation statements)

References 3 publications

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“…In the following discussion, the average Nusselt number for a packed tube at constant wall temperature is defined as (30) where while that for a packed channel heate asymmetrically at T h and Tc is defined as (31) It must be pointed out, however, a comparison of theoretical and existing experimental results on Nusselt number is difficult because of the following reasons: (I) the heat flux was not measured in most of the early experiments, and (2) the reported Nusselt number was dermed as Eq. (4) but the value of To was usually not reported.…”

Section: ~T--------------------------'mentioning

confidence: 99%

Forced Convection in Packed Tubes and Channels with Variable Porosity and Thermal Dispersion Effects

Cheng

Chowdhury

Hsu³

1991

Convective Heat and Mass Transfer in Porous Media

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ABSTRACT. Previous work in chemical engineering literature on the determination of the effective transverse thermal conductivity and Nusselt number for forced convection in packed tubes and channels are reviewed. Discrepancies in existing Nusselt number correlation equations are discussed. Some of the existing experimental data are reanalyzed based on the recent thermal dispersion theory developed by Hsu and Cheng with variable porosity effects Iaken into considmltion in an approximate manner. Numerical results are obtained for forced convection of air and water in packed tubes and channels. For forced convection in a packed column, it is found that the avemge Nusselt number depends not only on the Reynolds number, but also on the dimensionless particle diameter, the dimensionless length of the tube, the thermal conductivity ratio of the fluid phase to the solid phase, and the Prandd number of the fluid. IN1RODUcnONForced convection in packed tubes and channels have been the subject of intensive study in chemical engineering literature during the past six decades [I]. As early u 1931, Colbmn [2] found that the heat transfer rate for forced convection of air through a packed tube is about eight times higher than that of an empty tube. The substantial increase in the heat transfer rate hu been attributed to the mixing of fluid owing to the presence of the solid matrix known u the thermal dispersion process. During the ensuring years, more than thirty experiments have been performed on forced convection through cylindrical , annular [33][34][35]

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Section: ~T--------------------------'mentioning

confidence: 99%

Forced Convection in Packed Tubes and Channels with Variable Porosity and Thermal Dispersion Effects

Cheng

Chowdhury

Hsu³

1991

Convective Heat and Mass Transfer in Porous Media

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“…Table 2 shows that the aim of the most studies was to determine the radial effective thermal conductivity, and the axial thermal conductivity was neglected or calculated from a reported correlation in the literature. Bunnell et al [28], Borkink and Westerterp [34], Metzger et al [51], Testu et al [52,53], Gunn and Khalid [41], Clement and Jorgensen [44], and Levec and Carbonell [45] determined both the axial and transverse effective thermal conductivity ratios, experimentally. Elsari and Hughes [46], Yagi et al [47], Vortuba et al [48], Gunn and de [49] performed the experimental study to determine only the axial effective thermal conductivity.…”

Section: Discussionmentioning

confidence: 99%

“…It was also mentioned that the effective thermal conductivity ratio is proportional to the square root of the Peclet number for the Reynolds numbers below 100. Gunn and Khalid [41] studied air flowing cylindrical packed beds with glass and metallic particles. The investigated Reynolds number range was between 1 and 400.…”

Section: Heatmentioning

confidence: 99%

“…Calculated Neglected A reported correlation was used Smirnov et al [23][24][25] X X Thomeo and Freire [26] X X Demirel et al [27] X X Bunnell et al [28] X X Wen and Ding [29] X X Dixon and van Dongeren [30] X X Borkink and Westerterp [32,33] X X Borkink and Westerterp [34] X X Kwong and Smith [35] X X Bey and Eigenberger [36] X X Jorge et al [38] X X Dekhtyar et al [40] X X Gunn and Khalid [41] X X Gunn and De Souza [43] X X Clement and Jorgensen [44] X X Levec and Carbonell [45] X X Elsari and Hughes [46] X X Yagi et al [47] X X Vortuba et al [48] X X Vortmeyer and Adam [49] X X Metzger et al [51] X X Testu et al [52,53] X X Water, 0 < Re < 18…”

Section: A Reported Correlation Was Usedmentioning

confidence: 99%

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Thermal Dispersion in Porous Media—A Review on the Experimental Studies for Packed Beds

Özgümüş¹,

Mobedi²,

Özkol

et al. 2013

Applied Mechanics Reviews

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Thermal dispersion is an important topic in the convective heat transfer in porous media. In order to determine the heat transfer in a packed bed, the effective thermal conductivity including both stagnant and dispersion thermal conductivities should be known. Several theoretical and experimental studies have been performed on the determination of the effective thermal conductivity. The aim of this study is to review the experimental studies done on the determination of the effective thermal conductivity of the packed beds. In this study, firstly brief information on the definition of the thermal dispersion is presented and then the reported experimental studies on the determination of the effective thermal conductivity are summarized and compared. The reported experimental methods are classified into three groups: (1) heat addition/removal at the lateral boundaries, (2) heat addition at the inlet/ outlet boundary, (3) heat addition inside the bed. For each performed study, the experimental details, methods, obtained results, and suggested correlations for the determination of the effective thermal conductivity are presented. The similarities and differences between experimental methods and reported studies are shown by tables. Comparison of the correlations for the effective thermal conductivity is made by using figures and the results of the studies are discussed.

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“…A solução analítica deste modelo, em termos de séries infinitas de funções de Bessel, corresponde às Equações 6 e 7, e pode ser encontrada em GUNN & KHALID [10] e DIXON & PATERSON [7]. onde e b i são as raízes da equação (7).…”

Section: -Modelo Matemáticounclassified

Estimativa das propriedades térmicas efetivas de grãos em um secador de leito fixo

Fregolente¹,

Santos²,

Jorge³

2004

Ciênc. Tecnol. Aliment.

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-INTRODUÇÃOO conhecimento das propriedades térmicas efetivas é de grande importância para o projeto, simulação, análise, otimização e controle de processos não-isotérmicos em leito fixo. Por sua vez, estes processos podem ocorrer na ausência ou na presença de transferência de massa.Regeneradores de calor de leito fixo são um exemplo de equipamento industrial no qual ocorre apenas a transferência de calor, enquanto reatores químicos não-isotérmicos e secadores de leito fixo exemplificam equipamentos onde ocorre simultaneamente a transferên-cia de calor e de massa na presença e na ausência de reação química, respectivamente.A estimativa de propriedades térmicas efetivas em leito fixo tem sido extensivamente estudada nas últi-mas décadas, especialmente nas situações de ausên-cia de transferência de massa e na presença de reações químicas. Entretanto, a estimativa de propriedades térmicas efetivas em secadores de leito fixo tem sido pouco explorada. Especialmente quando o leito é composto por grãos. RESUMOA secagem de grãos em leito fixo é um processo complexo, ocorrendo simultaneamente a transferência de calor e de massa, dificultando a estimativa dos parâmetros térmicos efetivos, pois estes podem sofrer variações significativas no decorrer da secagem em função de alterações no teor de umidade. Neste trabalho, este problema foi contornado estimando-se os parâmetros térmicos efetivos no final da secagem, quando o teor de umidade dos grãos que compõem o leito alcança valores de equilíbrio, deixando de existir a transferência de massa, persistindo apenas a transferência de calor em regime permanente. Nestas condições, o leito possui um teor de umidade constante e a estimativa dos parâmetros térmicos efetivos pode ser efetuada a partir do ajuste de um modelo pseudo-homogêneo bidimensional estático à várias medidas de temperatura no leito de grãos no final da secagem. Os resultados indicam que a estratégia utilizada para estimativa da condutividade térmica efetiva radial e do coeficiente efetivo de transferência de calor parede-leito foi adequada. Além do que, constatou-se que dentre os grãos estudados -soja, feijão, milho e trigo -a soja apresenta os menores valores de condutividade efetiva radial, enquanto o trigo apresenta o maior valor do coeficiente de transferência de calor parede-leito. Palavras-chave: secagem de grãos; propriedades térmicas efetivas; leito fixo. SUMMARY ESTIMATION OF EFFECTIVE GRAIN THERMAL PROPERTIES IN A FIXED BED DRYER.Fixed bed grain drying is a complex process, where mass and heat transfer occur simultaneously, complicating the estimation of the effective thermal parameters, because they can go through significant variations along the drying process, due to moisture content variations. In this work, this problem was avoided by estimating the effective thermal parameters at the end of the drying process, when the grain moisture content reaches equilibrium, and mass transfer stops, persisting only the steady state heat transfer. In these conditions, the bed has a constant moisture content an...

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Thermal dispersion and wall heat transfer in packed beds

Cited by 75 publications

References 3 publications

Forced Convection in Packed Tubes and Channels with Variable Porosity and Thermal Dispersion Effects

Forced Convection in Packed Tubes and Channels with Variable Porosity and Thermal Dispersion Effects

Thermal Dispersion in Porous Media—A Review on the Experimental Studies for Packed Beds

Estimativa das propriedades térmicas efetivas de grãos em um secador de leito fixo

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