Thermal Science 2023 Volume 27, Issue 1 Part A, Pages: 71-87
https://doi.org/10.2298/TSCI2301071N
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Experimental and CFD analysis of wire coil turbulators in biomass boilers
Novčić Đorđe A. 
(Faculty of Mechanical and Civil Engineering in Kraljevo, University of Kragujevac, Kragujevac, Serbia)
Nikolić Miloš V. (Faculty of Mechanical and Civil Engineering in Kraljevo, University of Kragujevac, Kragujevac, Serbia)
Todorović Dušan M. (Faculty of Mechanical Engineering, University of Belgrade, Belgrade, Serbia)
Karamarković Rade M. (Faculty of Mechanical and Civil Engineering in Kraljevo, University of Kragujevac, Kragujevac, Serbia), karamarkovic.r@mfkv.kg.ac.rs
Obradović Marko O. (Faculty of Mechanical Engineering, University of Belgrade, Belgrade, Serbia)
To achieve as complete fuel burnout with as little excess air as possible,
small wood log boilers (< 50 kW) use stage combustion. The first stage is
often a process similar to downdraft gasification that consequently
produces a flue gas laden with particulates. To prevent the build-up of
solids and promote heat transfer in pipes of the convective part of these
boilers, wire coils are used. The paper presents their in-situ examination
together with CFD analysis. The analysis is carried out in a 460 mm long
pipe, with a diameter of 82.5 mm, equipped with different wire coils for
flue gas temperatures in the range between 300°C and 150°C. The analyzed
coils are with and without a conical spring at their free end. The addition
of this conical top is economical and should influence the rotation of the
core flow. Proper pipe surface cleaning limited the analyzed wire coil
designs to the dimensionless pitch, p/d, in the range between 0.36-0.61,
dimensionless wire diameter e/d = 0.04-0.1, and pitch to wire diameter
ratios p/e = 3.75-14.3, and three different angles (60⁰, 90⁰, and 120⁰) of
the conical top. The goals are to find the optimal flue gas velocity for the
given operating conditions, pipe, and wire coil dimensions, and to
investigate the addition of the conical top on heat transfer enhancement.
Several evaluation criteria are used to achieve the goals.
Keywords: wire coils, heat transfer enhancement, turbulators, CFD model, biomass boiler
Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. 451-03-68/2022-14/200108 and Grant no. 451-03-68/2022-14/200105
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