Delft University of Technology
The effect of particle size distribution on the bulk thermal conductivity of biomass pellets
Gilvari, Hamid; Eijssen, Dirk; IJzermans, Kasper; Stolk, Maarten; Homsma, Thom; de Jong, Wiebren; Schott, Dingena
Publication date 2018
Document Version Final published version
Gilvari, H., Eijssen, D., IJzermans, K., Stolk, M., Homsma, T., de Jong, W., & Schott, D. (2018). The effect of particle size distribution on the bulk thermal conductivity of biomass pellets. Poster session presented at TU Delft Process Technology Institute (DPTI) annual meeting 2018, Rotterdam, Netherlands.
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The effect of particle size distribution on the bulk thermal conductivity
of biomass pellets
H. Gilvari *a
, D.J. Eijssenb
, K.F. Ijzermansb
, M.J. Stolkb
, T.A. Homsmab
, W. de Jongc
, D. L. Schotta
a Section of Transport Engineering & Logistics, Department of Maritime & Transport Technology, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology
b Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology
c Section of Large Scale Energy Storage, Department of Process & Energy, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology
Table 1. Definition of the terms used in the calculations
The thermal conductivity highly depends on the bulk density, however, it does not show a high correlation with the mean particle length Increasing the particle size distribution does not necessarily lead to higher bulk densities
This work was carried out as a part of the BioForce project co-financed by KIC InnoEnergy (Project Agreement Ref 24_2014_IP102_Bioforce).
*Corresponding author: Hamid Gilvari Email: H.Gilvari@tudelft.nl
The large-scale storage of biomass pellets is challenging due to health issues, material loss, and the risk of fire and explosions. The thermal conductivity is a material property which plays a key role in determining the self-heating properties of biomass.
Meanwhile, understanding the thermal conductivity and the affecting factors help to better understand and
reduce the risk of self-heating and fire explosions.
The thermal conductivity was measured based on:
𝑘𝑘𝑠𝑠 = 𝐴𝐴𝐿𝐿𝑆𝑆𝑄𝑄𝑠𝑠 𝑐𝑐𝑠𝑠∆𝑇𝑇𝑠𝑠 Where ∆𝑇𝑇𝑠𝑠= 𝑇𝑇2 − 𝐴𝐴𝐿𝐿𝑜𝑜𝑄𝑄1 𝑐𝑐𝑐𝑐𝑘𝑘𝑎𝑎𝑎𝑎 − (𝑇𝑇3 + 𝐿𝐿𝑜𝑜𝑄𝑄2 𝐴𝐴𝑐𝑐𝑐𝑐𝑘𝑘𝑎𝑎𝑎𝑎), and 𝑄𝑄𝑠𝑠 = 𝑄𝑄1+𝑄𝑄2 2 𝑄𝑄1 = 𝑘𝑘𝑎𝑎𝑎𝑎𝐴𝐴𝑐𝑐𝑠𝑠𝐿𝐿(𝑇𝑇1 − 𝑇𝑇2) 𝑡𝑡𝑐𝑐 − 2𝜋𝜋𝑘𝑘𝑖𝑖𝑖𝑖𝑠𝑠𝐿𝐿𝑡𝑡𝑐𝑐((𝑇𝑇1 + 𝑇𝑇2 2) − 𝑇𝑇𝑎𝑎𝑎𝑎𝑎𝑎) ln(𝑟𝑟𝑟𝑟2 1) 𝑄𝑄2 = 𝑘𝑘𝑎𝑎𝑎𝑎𝐴𝐴𝑐𝑐𝑠𝑠𝐿𝐿(𝑇𝑇3 − 𝑇𝑇4) 𝑡𝑡𝑐𝑐 − 2𝜋𝜋𝑘𝑘𝑖𝑖𝑖𝑖𝑠𝑠𝐿𝐿𝑡𝑡𝑐𝑐((𝑇𝑇3 + 𝑇𝑇2 4) − 𝑇𝑇𝑎𝑎𝑎𝑎𝑎𝑎) ln(𝑟𝑟𝑟𝑟2 1)
Figure 2. Setup configuration
Biomass pellets with 6 mm diameter made of sawdust were
used in this study. Ten batches of pellets with different particle size distributions were selected for the experiments as shown in
Material and Methods
The measurements were conducted based on the steady state split-bar method (SSM) according to the standard method of measuring the thermal conductivity of polymers (figure 2). To verify the measurement of the custom-build apparatus, the thermal conductivity of 6 batches of the sample were also measured using the transient plane source method (TPS)
𝑘𝑘𝑠𝑠 Thermal conductivity of the sample 𝐿𝐿𝑆𝑆 Sample thickness (m)
𝐿𝐿𝑜𝑜 Thermocouples distance from the sample surface (0.005 m) 𝐿𝐿𝑡𝑡𝑐𝑐 Distance between the thermocouples (0.135 m)
𝐴𝐴𝑐𝑐𝑠𝑠 Contact area of the aluminium rod with the sample (0.0044 m2) 𝑘𝑘𝑎𝑎𝑎𝑎 Thermal conductivity of aluminium (188 W/mK)
𝑘𝑘𝑖𝑖𝑖𝑖𝑠𝑠 Thermal conductivity of the insulation (0.03 W/mK) 𝑟𝑟1 Inner radius of the insulation ring (0.0375 m)
𝑟𝑟2 Outer radius of the insulation ring (0.059 m) 𝑇𝑇1, 𝑇𝑇2, 𝑇𝑇3, 𝑇𝑇4 Recorded temperatures by thermocouples
𝑇𝑇𝑎𝑎𝑎𝑎𝑎𝑎 Ambient temperature Particle length (mm) C um ul at ive par ti cl e si ze ( % )
Figure 1. Particle size distribution of different batches of the pellets
400 450 500 550 600 650 700 750 800 0,09 0,1 0,11 0,12 0,13 0,14 0,15 0,16 0 5 10 15 20 25 B ul k D en s it y ( k g /m 3 ) T he rm al C o n du c ti v it y ( W /m K )
Mean particle length (mm)
Thermal Conductivity Bulk Density 0,08 0,09 0,1 0,11 0,12 0,13 0,14 0,15 0,16 0,17 0,18 0 5 10 15 20 25 T he rm al C o n du c ti v it y ( W /m K )
Mean particle length (mm) SSM Method TPS method Correlation Coefficient=0,938 R² = 0,9222 0,08 0,09 0,1 0,11 0,12 0,13 0,14 0,15 0,16 500 550 600 650 700 750 T he rm al C o n du c ti v it y ( W /m K ) Bulk Density (kg/m3)
Thermal conductivity vs pellet mean length
and bulk density SSM method vs TPS method
Thermal conductivity vs pellet mean length Thermal conductivity vs bulk density
R² = 0,83 0,08 0,09 0,1 0,11 0,12 0,13 0,14 0,15 0,16 0 5 10 15 20 25 T he rm al C o n du c ti v it y ( W /m K )
Mean particle length (mm)
The objectives are (1) to characterise the thermal conductivity of batches of bulk biomass pellets with different particle size
distributions and (2), to determine the correlations between the
b bulk thermal conductivity and the mean particle length of
t the pellets.
Variac 230 V Power supply
TC- 1 TC- 2 TC- 3 TC- 4 XPS insulation Heating element 70W Cardboard box Aluminum reference bar Ø 75 mm Sample, Ø 75 mm PVC outer shell Water inlet Watercooled bath Water outlet
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