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Heat Transfer in a Fluidized Bed with Immersed Tubes Using Moist Coal Particles

  • Research Article - Chemical Engineering
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Abstract

The moisture content of coal (MCC) has an important effect on the thermophysical properties and the granular flowability. However, it brings both active and negative influence to the heat transfer between the fluidizing moist coal and the immersed tubes in the fluidized bed. Four groups of bituminous coal with same size distribution (0.25–2.8 mm) but different MCC (7.86–15.18%) have been examined to study the variation of the heat transfer in an experimental setup. The average heat transfer coefficients \((h_{\mathrm{avg}})\) for the four groups of test samples have the same changing trend by increasing the superficial velocity \((U_{\mathrm{g}})\). However, the maximum heat transfer coefficients \((h_{\mathrm{max}})\) display different peak values. With the increase in MCC, the \(h_{\mathrm{max}}\) rises at first and begins to fall when reaching a critical value. To predict the \(h_{\mathrm{avg}}\) accurately with different MCC, the angle of repose has been imported to measure the variation of the granular flowability. A novel semiempirical correlation has been thereupon proposed by the dimensional analysis, and it accords well to the experimental data from this study and the previous research.

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Abbreviations

Ar:

Archimedes number

\(A_{\mathrm{t}}\) :

Surface area of heat transfer tube \(\left( \hbox {m}^{2}\right) \)

\(\hbox {Cp}_{\mathrm{g}}\) :

Specific heat of gas phase \(\left( \hbox {J}\,\hbox {kg}^{-1}\,\hbox {K}^{-1}\right) \)

\(\hbox {Cp}_{\mathrm{em}}\) :

Specific heat of emulsion phase \(\left( \hbox {J}\,\hbox {kg}^{-1}\,\hbox {K}^{-1}\right) \)

\(D_{\mathrm{t}}\) :

Diameter of heat transfer tube (mm)

\(d_{{i}}\) :

Mean diameter of particle between the screen mesh (mm)

\(d_{\mathrm{p}}\) :

Sauter mean diameter of particle (mm)

h :

Heat transfer coefficient \(\left( \hbox {W}\, \hbox {m}^{-2}\,\hbox {K}^{-1}\right) \)

\(h_{\mathrm{avg}}\) :

Average heat transfer coefficient \(\left( \hbox {W}\,\hbox {m}^{-2}\,\hbox {K}^{-1}\right) \)

\(h_{\mathrm{b}}\) :

Average heat transfer coefficient of bubble phase \(\left( \hbox {W}\,\hbox {m}^{-2}\,\hbox {K}^{-1}\right) \)

\(h_{\mathrm{em}}\) :

Average heat transfer coefficient of emulsion phase \(\left( \hbox {W}\,\hbox {m}^{-2}\,\hbox {K}^{-1}\right) \)

\(h_{{i}}\) :

Local heat transfer coefficient \(\left( \hbox {W}\, \hbox {m}^{-2}\,\hbox {K}^{-1}\right) \)

\(h_{{i},-90^{\circ }}\) :

Local heat transfer coefficient at \({-}90{^{\circ }}\,\left( \hbox {W}\,\hbox {m}^{-2}\,\hbox {K}^{-1}\right) \)

\(h_{{i},0^{\circ }}\) :

Local heat transfer coefficient at \(0{^{\circ }}\, \left( \hbox {W}\,\hbox {m}^{-2}\,\hbox {K}^{-1}\right) \)

\(h_{{i},+90^{\circ }}\) :

Local heat transfer coefficient at \({+}90{^{\circ }}\, \left( \hbox {W}\,\hbox {m}^{-2}\,\hbox {K}^{-1}\right) \)

I :

Electric current (A)

\({ Nu}_{\mathrm{em}}\) :

Nusselt number of emulsion phase

\({ Pr}_{\mathrm{em}}\) :

Prandtl number of emulsion phase

\({ Pr}_{\mathrm{g}}\) :

Prandtl number of gas phase

\({R}^{2}\) :

Square coefficient of association

Re :

Reynolds number

\(Re_{\mathrm{pmf}}\) :

Reynolds number at minimum fluidization

\(T_{\mathrm{b}}\) :

Bed temperature (K)

\(T_{\mathrm{t}}\) :

Tube surface temperature of heat transfer tube (K)

\(U_{\mathrm{g}}\) :

Superficial velocity \(\left( \hbox {m}\,\hbox {s}^{-1}\right) \)

\(U_{\mathrm{q}}\) :

Circumstance of the cross-sectional for the heat transfer tube (m)

V :

Electric voltage of heating rod (V)

w :

External moisture of coal (%)

\(x_{{i}}\) :

mass fraction (%)

\(\Delta {p}_{\mathrm{b}}\) :

Bed pressure drops (Pa)

\(\alpha _{\mathrm{b}}\) :

Bubble fraction

\(\beta \) :

The growth rate for angles of repose

\(\lambda _{\mathrm{em}}\) :

Thermal conductivity of emulsion phase \(\left( \hbox {W}\,\hbox {m}^{-1}\,\hbox {K}^{-1}\right) \)

\(\lambda _{\mathrm{p}}\) :

Particle thermal conductivity \(\left( \hbox {W}\,\hbox {m}^{-1}\,\hbox {K}^{-1}\right) \)

\(\lambda _{\mathrm{g}}\) :

Gas thermal conductivity \(\left( \hbox {W}\, \hbox {m}^{-1}\,\hbox {K}^{-1}\right) \)

\(\lambda _{\mathrm{HI}}\) :

Thermal conductivity of heat insulation material \(\left( \hbox {W}\,\hbox {m}^{-1}\,\hbox {K}^{-1}\right) \)

\(\mu _{\mathrm{g}}\) :

Dynamic viscosity \(\left( \hbox {Pa}\,\hbox {s}\right) \)

\(\varepsilon _{\mathrm{e}}\) :

Voidage of emulsion

\(\varepsilon _{\mathrm{mf}}\) :

Voidage at minimum fluidization

\(\rho _{\mathrm{g}}\) :

Gas density \(\left( \hbox {kg}\,\hbox {m}^{-3}\right) \)

\(\rho _{\mathrm{s}}\) :

Particle density \(\left( \hbox {kg}\,\hbox {m}^{-3}\right) \)

\(\varphi \) :

Shaper factor

\(\varphi _{0}\) :

Angle of repose for dry state (\({^{\circ }})\)

\(\varphi _{\mathrm{w}}\) :

Angle of repose for moist coal (\({^{\circ }})\)

CMC:

Coal moisture control

FBIT:

The fluidized bed with immersed tubes

MCC:

The moisture content of coal

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Authors and Affiliations

  1. Thermal Engineering Department, School of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai, 200093, China

    Dongwei Yang, Hongling Yu & Ruiyang Li

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  1. Dongwei Yang
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  2. Hongling Yu
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Correspondence to Ruiyang Li.

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Yang, D., Yu, H. & Li, R. Heat Transfer in a Fluidized Bed with Immersed Tubes Using Moist Coal Particles. Arab J Sci Eng 43, 2263–2272 (2018). https://doi.org/10.1007/s13369-017-2680-2

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  • DOI: https://doi.org/10.1007/s13369-017-2680-2

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