Contents lists available at ScienceDirect International Journal of Thermal Sciences journal homepage: www.elsevier.com/locate/ijts Characteristics of single wood particle pyrolysis using particle image velocimetry Jacek Kluska, Karol Ronewicz * , Dariusz Kardaś Institute of Fluid Flow Machinery, Polish Academy of Sciences, Fiszera 14, 80-231, Gdańsk, Poland ARTICLE INFO Keywords: Pyrolysis Particle image velocimetry Gas cushion ABSTRACT This study examines the pyrolysis of a single cylindrical wood particle using Particle Image Velocimetry (PIV). The pyrolysis was carried out in the ATR 01/600 pyrolysis reactor designed for this purpose. The experimental setup presented in this study is capable of effectively characterizing the intensity of pyrolysis based on velocity distribution in the vicinity of wood particles. The results of the gas velocity distribution indicate the formation of a gas cushion caused by the evaporation of moisture and devolatilization. Higher heating rates increase the intensity of degassing and the thickness of the gas cushion around the particle and may temporarily slow down the intensity of convective heat transfer to the interior of the particle. 1. Introduction Particle image velocimetry (PIV) is a widely used method in fluid mechanics [1,2]. Fu et al. [3] presented a numerical and experimental investigation of indoor airflow. This article compared PIV and 3D as a function of the tacking density index. Experiments were carried out using an experimental low-turbulence indoor airflow generated by a low-speed tailpipe. Ertür et al. [4] used PIV as a method to model the characteristics and turbulent statistics of the flow in an external gear pump. Nevertheless, there are also many applications of solid elements where the vectors are adopted to measure the displacement of bodies. This issue was presented by Baba and Peth [5] who analyzed the geo- technical testing of soil creep movements. In the paper, the authors demonstrated the large potential of PIV to examine the effect of hy- draulic stresses on creep deformations due to gravity forces. Another example of PIV application in order to define the material properties was presented by Magalhaes et al. [6]. PIV coupled with particle swarm optimization (PSO) and FEM inverse analysis can be used to analyze Young's Modulus of the ASTM A36 steel. PIV has also been used in thermochemistry. Vali et al. [7] analyzed the liquid velocity field in order to understand the transport phenomena in the liquid phase of a laboratory-scale methanol pool fire. The authors showed that PIV can effectively analyze the fluid dynamics of the fluid phase of the pool fire. Di Sarli et al. [8] used the PIV method to analyze the transient interactions that occur between hydrogen-enriched me- thane/air premixed flame fronts and toroidal vortex structures. This work presents the results of applying PIV during pyrolysis of a single cylindrical wood particle. Pyrolysis is the thermochemical con- version of solid fuel to solid, liquid, and gaseous fractions in the absence of air [9,10], which for the lignocellulosic materials occurs between 300 and 500 °C [11–14]. Pyrolysis is extremely complex and includes many different processes, which can occurs simultaneously, like dehy- dration, deploymerization, fragmentation, condensation and carboni- zation. The proportion and composition of pyrolysis products depend on many factors such as feedstock type, heating rate, final temperature, pressure, resident time of fuel particles and pyrolysis gases in the re- actor [12,13,15–17]. Gable and Brown [18] showed that bio-oil yields increased with biomass heating time. Experiments were carried out in a free fall pyrolysis reactor with the nitrogen as a sweep gas. Effects of heat treatment temperature on the products yields during pyrolysis of the paper sludge was presented by Li et al. [19]. The results showed that catalytic effect, caused by a high content of metals in the paper sludge, led to an increase in gas yield and decrease in bio-oils yield with increasing pyrolysis temperature. During the experiment sample was loaded on at the plate in the heated reactor. The nitrogen was used as inert gas. Açıkalın and Kacar [20] showed that temperature was the most significantly parameter during pyrolysis of walnut shell. The in- crease in temperature resulted in a decrease in solid yields and increase in gas yields. The samples were pyrolyzed in the tubular reactor with the nitrogen as a sweep gas. There are also many studies reported in the literature different techniques and construction of reactors to carry out the pyrolysis. One of the common solutions is a fixed bed reactor. Pham et al. [21] pre- sented experimental investigation of oxidative pyrolysis of wheat straw, https://doi.org/10.1016/j.ijthermalsci.2018.09.020 Received 14 June 2017; Received in revised form 10 August 2018; Accepted 12 September 2018 * Corresponding author. E-mail addresses: jkluska@imp.gda.pl (J. Kluska), k.ronewicz@gmail.com (K. Ronewicz), dk@imp.gda.pl (D. Kardaś). International Journal of Thermal Sciences 135 (2019) 276–284 1290-0729/ © 2018 Elsevier Masson SAS. All rights reserved. T