Heat transfer between a horizontal tube and a gas-solid fluidized bed

Grewal, N.S.; Saxena, S.C.

doi:10.1016/0017-9310(80)90154-4

Cited by 104 publications

(46 citation statements)

References 9 publications

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“…As concluded for the fixed bed case, the heat transfer coefficient increases when the flow rate increases [27, 30,31]. It is also observed that at the same excess air velocity over minimum fluidization conditions, U/U mf , better coefficients are obtained for the sand; however, sand requires a higher air flow and therefore has a higher energy cost.…”

Section: Fluidized Bedmentioning

confidence: 70%

Experimental heat transfer coefficients between a surface and fixed and fluidized beds with PCM

Izquierdo-Barrientos

Sobrino

Almendros-Ibáñez

2015

Applied Thermal Engineering

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This work presents an experimental study to determine the capacity of a phase change material (PCM) in granular form to be used in fixed and bubbling fluidized beds for thermal energy storage. The experimental measurements are focused on determination of the heat transfer coefficient between a heated surface immersed in the bed and the granular PCM. The flow rate is varied to quantify its influence on the heat transfer coefficient. The PCM used is Rubitherm GR50 with a phase change temperature of approximately 50• C. The PCM is available in two different particle sizes, 0.54 mm and 1.64 mm, of which the finer is used in the fluidized bed and the coarser is used in the fixed bed. In addition, the results obtained for the PCM are compared with the heat transfer coefficients measured for sand, a material commonly used for thermal storage. * Corresponding author. NOTICE: this is the author's version of a work that was accepted for publication in Applied Thermal Engineering. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Applied Thermal Engineering 78 (2015) pp. 373-379. doi:10.1016/j.applthermaleng.2014.12.044 In comparing the heat transfer coefficients for fixed and fluidized beds, the heat transfer coefficients in the fluidized bed with PCM are nearly three times higher than those for the fixed bed at the same gas flow rate. This increase in the heat transfer is a result of two main factors: first, the continuous renewal of PCM particles from the heated surface when they are fluidized, and second, the large quantities of energy in latent form absorbed by the PCM. In the fixed bed there is no renovation of particles, consequently only a small percentage of particles are able to change its phase. Hence, there is no increase in the heat transfer coefficient due to this fact.

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Section: Fluidized Bedmentioning

confidence: 70%

Experimental heat transfer coefficients between a surface and fixed and fluidized beds with PCM

Izquierdo-Barrientos

Sobrino

Almendros-Ibáñez

2015

Applied Thermal Engineering

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“…Immersed tube heat transfer (h im ) coefficients are required as an input for the correlation, which is obtained by using a correlation (Grewal and Saxena 1980) developed for room temperature applications, which is given in Eq. (6).…”

Section: Empirical Correlations For Freeboard Heat Transfermentioning

confidence: 99%

Predicting Freeboard Heat Transfer by Using Empirical Correlations in High Temperature Fluidized Beds (23)

Biyikli

2014

International Journal of Green Energy

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This article is suggesting some empirical correlations to calculate the freeboard entrainment heights and the average heat transfer coefficients for a horizontal tube over the freeboard region of high temperature fluidized bed combustors. The correlations are tested against some published experimental measurements for silica sand 465 µm and limestone 1,400 µm diameters in fluidized beds for temperatures up to 750 • C. The height of a fluidized bed over the static bed is defined as the entrainment height; first a correlation is used to calculate the entrainment heights in order to determine the extent of the freeboard region at different bed temperatures and gas velocities. The heat transfer occurs by radiation, gas convection, and particle contact mechanisms in a high temperature fluidized bed combustor. Contribution of these heat transfer mechanisms to the overall heat transfer is described in detail over the freeboard region of fluidized beds by using empirical correlations. These correlations can be used to calculate the heat transfer characteristics in the design of fluidized bed combustors. The relative contribution of radiation increases with increasing freeboard elevation and approaches a constant fraction of the total average heat transfer.

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“…The studies with B and D particles have demonstrated that heat-transfer coefficients are related to the volumetric heat capacity of the particles, the particle diameter, the thermal conductivity of fluidizing gas (Grewal and Saxena, 1980), and bubbling characteristics in the bed (Chen and Tuzla, 1996). Miyamoto et al (1997) found that heat transfer is enhanced by the particle movement.…”

Section: Introductionmentioning

confidence: 97%