Surface-to-bed heat transfer for high-density particles in conical spouted and spout

Yaman, O., Kulah, G., & Koksal, M. (2019). Surface-to-bed heat transfer for high-density particles in conical spouted and spout–fluid beds. Particuology, 42, 35-47. https://doi.org/10.1016/j.partic.2018.03.013

Surface-to-bed heat transfer for high-density particles in conical spouted and spout–fluid beds

Onur Yaman ^a, Gorkem Kulah ^a*, Murat Koksal ^b *

a Department of Chemical Engineering, Middle East Technical University, 06800 Ankara, Turkey
b Department of Mechanical Engineering, Hacettepe University, 06800 Ankara, Turkey

10.1016/j.partic.2018.03.013

Volume 42, February 2019, Pages 35-47

Received 25 November 2017, Revised 16 February 2018, Accepted 11 March 2018, Available online 14 September 2018, Version of Record 21 January 2019.

E-mail: gorkemk@metu.edu.tr; koksalm@hacettepe.edu.tr

Highlights

• Bed-to-surface heat transfer experiments were conducted in conical spouted and spout–fluid beds.

• Glass beads, alumina and zirconia particles were used in heat-transfer experiments.

• The appropriate location of a submerged cylindrical heater was the spout–annulus interface.

• A proposed correlation was applicable for predicting average heat transfer coefficient in annulus.

Abstract

Bed-to-surface heat transfer experiments from a vertically submerged cylindrical surface were conducted in laboratory-scale (D_c = 25 cm) conical spouted and spout–fluid beds at two different conical angles (31° and 66°) in the high particle density range (2500 kg/m³ ≤ ρ_p ≤ 6000 kg/m³). The effects of the bed design parameters (conical angle and inlet diameter of spouting gas entrance) and operating conditions (static bed height, particle size, density, and spouting and fluidization gas flow rates) on the heat transfer characteristics were investigated in detail. The heat transfer coefficients were shown to be dependent on the density and size of the particles. The minimum stable spouting velocities of the denser and larger particles were higher, which led to higher operational spouting velocities and thereby resulted in higher heat transfer coefficients. The positive effect of increasing the particle diameter on heat transfer was more pronounced in the spout and at the spout–annulus interface, whereas this effect was diminished in the annulus region. The heat transfer coefficient increased with increasing spouting gas velocity up to 1.0U_ms–1.1U_ms, beyond which no significant change was observed regardless of the particle type. The heat transfer coefficient in the annulus decreased with increasing conical angle because of reduced particle circulation. The spout–fluid operation increased the heat transfer coefficient by a maximum of 10% at the expense of a significant increase of the total gas flow rate. This result was attributed to the inability of the fluidizing gas to penetrate the annulus. An empirical correlation for the average heat transfer coefficient in the annulus was also proposed based on the data obtained in this work.

Graphical abstract

Keywords

Conical spouted bed; Spout–fluid bed; Bed-to-surface heat transfer; Submerged heat transfer surface

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