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Journal ArticleDOI

Thermal transport in two-phase gas—solid suspension flow through packed beds

01 Jul 1990-Powder Technology (Elsevier)-Vol. 62, Iss: 1, pp 51-57
Abstract: A method to evaluate the overall Nusselt numbers for heat transfer rates in a packed bed with gas—solid suspension flow through it is presented. The model based on earlier work of the authors on heat transfer in single-phase fluid flow through packed beds, includes separation of the overall heat transfer coefficient into conduction, convection and radiation contributions and their interactions. Numerical results indicate that the heat transfer rates increase with loading ratios and Reynolds number, as expected, but the increase varies with different bed materials. This dependence on the properties of the bed material is discussed and predictions using the present model are compared with a correlation available in the literature. For the special case where the bed materials are the same, the literature correlation prediction and the present model agree and the differences obtained where other bed materials are used further illustrates the importance of considering the properties of the bed materials in evaluating the total heat transfer rates.

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Topics: Heat transfer coefficient (64%), Kozeny–Carman equation (62%), Heat transfer (61%) ...read more
Citations
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Journal ArticleDOI
Thang Ngoc Cong1, Yurong He1, Haisheng Chen1, Yulong Ding1  +1 moreInstitutions (2)
Abstract: An experimental study has been carried out on both the transient and steady state heat transfer of a gas–solid two-phase mixture flowing through a cylindrical packed bed reactor under the constant wall heat flux conditions. A logarithmic mean temperature difference (LMTD) method is used to process the steady state data to obtain the overall heat transfer coefficient. The effects of solids loading, particle size and flow Reynolds number are investigated. The results show that the introduction of suspended particles greatly enhances the heat transfer and the enhancement increases approximately linearly with solids loading and the effect of particle size is relatively weak under the conditions of this work. A correlation is proposed based on the experimental data, which relates well the Nusselt number to the Reynolds number, the Archimedes number and the suspended solids loading. Given other conditions, the Nusselt number at the constant wall heat flux conditions is much higher than that under the constant wall temperature conditions. It is shown that the Reynolds number and particle loading have a greater influence on the Nusselt number under the constant heat flux conditions than that under the constant wall temperature conditions investigated by the authors in a previous study.

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23 citations



Journal ArticleDOI
Dongsheng Wen1, Thang Ngoc Cong1, Yurong He1, Haisheng Chen1  +1 moreInstitutions (1)
Abstract: This paper reports an experimental study on both transient and steady-state heat transfer behavior of a gas–solid two-phase mixture flowing through a packed bed under constant wall temperature conditions. A logarithmic mean temperature difference (LMTD) method is used to process the temperature data to obtain the overall heat transfer coefficient. The influences of particle loading and gas flow Reynolds number are investigated. The results show that the introduction of suspended particles greatly enhances heat transfer between the flowing gas–solid two-phase mixture and the packed bed, and the enhancement increases approximately linearly with increasing particle loading. The heat transfer coefficient data are processed to give the Nusselt number, which is found to correlate well to the Reynolds number, the Archimedes number and the suspended particle loading ratio. A comparison of the data of this work with the published data reveals large discrepancy. Possible reasons for the discrepancy are discussed.

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16 citations


Journal ArticleDOI
Abstract: The use of pneumatic conveying duct as gas–solid heat exchanger is in vogue in the form of preheater and dryer in cement and pharmaceutical industries, among several other industries. Experiments were conducted to study the effect of solids feed rate, particle size and air velocity on thermal conductance of a vertical pneumatic conveying heat exchanger for preheating of dry solids. Sand and gypsum were used as cold medium while air was used as hot medium. Thermal conductance (defined as the ratio of heat transfer rate to driving force) was found to increase with solids feed rate and air velocity. A dimensionless correlation has been proposed for thermal conductance that predicts the present experimental data for air–sand and air–gypsum heat transfer within an error of ±18%. The relevant properties of solids are incorporated in the form of a dimensionless number, Fedorov number (Fe). The proposed correlation may be used to analyze pneumatic conveying heat exchanger of similar geometry.

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15 citations


Journal ArticleDOI
Yulong Ding1, Yurong He1, Ngoc T. Cong1, Wei Yang1  +1 moreInstitutions (1)
Abstract: Flow of a gas–solid two-phase mixture through a packed bed is relevant to a number of industrial processes such as heat recovery and filtration of dusty flue gases, iron making in shaft reactors, gas purification, and sorption enhanced reaction processes. In spite of the industrial relevance, little work has been reported in the literature. The limited amount of research work has mainly addressed the macroscopic hydrodynamics in terms of pressure drop and solids hold-ups at the ambient temperature. Very little is done, until fairly recent, on solids motion at the single particle level, hydrodynamics at elevated temperatures and heat transfer. This paper reviews the recent development in the field including both the hydrodynamics and heat transfer of gas–solid two-phase mixtures flowing through packed beds, which is believed to represent the state-of-the-art in the field. The review is not aimed to be exhaustive but rather focused on our own work carried out over the past few years in the Institute of Particle Science & Engineering at the University of Leeds. And some of our results are compared with that of other groups.

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13 citations


Cites background or result from "Thermal transport in two-phase gas—..."

  • ...16 lies in the interpretation of controversies of Royston [26] and Balakrishnan and Pei [27–29]....

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  • ...[23], Balakrishnan and Pei [27–29], and Royston [26] under various conditions....

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  • ...Similar observations have been obtained by Royston [26] and Balakrishnan and Pei [27]....

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References
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Journal ArticleDOI
N. Wakao1, T. Funazkri1Institutions (1)
Abstract: The published heat transfer data obtained from steady and nonsteady measurements are corrected for the axial fluid thermal dispersion coefficient values proposed by Wakao[1]. The corrected data in the range of Reynolds number from 15 to 8500 are correlated by the analogous form of the mass correlation proposed by Wakao and Funazkri[2]: Nu= 2 + 1.1 Pr13 Re0.6

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856 citations


Journal ArticleDOI

114 citations



Book ChapterDOI
Creighton A. Depew1, Ted J. KramerInstitutions (1)
Abstract: Publisher Summary The rate of heat transfer to the suspension depends on the fluid dynamic properties of the flow and the transport processes are governed by complicated interactions between: (1) fluid and particle, (2) particle and particle, and (3) the mixture and the flow boundary. Local mean fluid dynamic properties that control the energy and the momentum transport includes particle velocity, gas velocity, and local particle flux. This chapter presents the results of various experiments on heat transfer. The discussion includes the correlations of heat transfer data and the discussion of correlating parameters that are based on the theoretical models of the energy transfer process. The fluid dynamic properties of the suspension flow system are fundamental to the heat transfer process, and any advances in understanding and analysis of the thermal system must be based on the progress in the description of the isothermal system. Therefore, the chapter also presents information that is based on experiments on the point mean properties of the isothermal flow of a suspension of glass spheres in air. A universal velocity law for the suspension as a continuum is derived from the fundamental equations and the constants for the law are derived from the experimental observations. Values of the eddy diffusivity for momentum are also derived from the data and presented.

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50 citations


Journal ArticleDOI
Abstract: G, = noise generator k = integral value of B/T K , = controller gain K , = process gain n, = noise sequence s = Laplace transform variable s, = coefficients of the polynomial 6(B) (denominator of G,(B)) t = time T = sampling interval X,(B) = transfer function of forward loop controller (Table 111) y = system output ut = controller signal a = relative perturbation in process parameters = relative perturbation in process time delay r ( B ) = polynomial resulting from factorization (Appendix) y, = coefficients of y ( B ) 6(B) = denominator of G,(B)

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50 citations


Performance
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No. of citations received by the Paper in previous years
YearCitations
20192
20181
20143
20101
20081
20072