Convective Heat Transfer Coefficients of Multifaceted Longitudinal and Transversal Bricks of Lattice Setting in Tunnel Kilns

Abstract

This paper reports the local multifaceted and area-averaged convective heat transfer coefficients (CHTCs) of longitudinal and transverse bricks arranged in lattice brick setting in tunnel kilns, using a three-dimensional (3D) computational fluid dynamics (CFD) model. A mesh sensitivity analysis was performed and the model was validated against reported experimental data in tunnel kilns. Three turbulence models were tested: the standard k–ε, re-normalization group (RNG) k–ε, and k–ω. The k–ω model provided the closest results to the experimental data. The CHTCs from the front, back, left, and right faces of the longitudinal and transverse bricks were calculated under various conditions. Area-averaged CHTCs for bricks were determined from the multifaceted CHTCs. Effects of rows, layers, and walls on faces and area-averaged CHTCs were investigated. A sensitivity analysis was performed to explore the effect of flow channels on the CHTCs. The numerical results showed that the CHTCs are enhanced by 17% for the longitudinal bricks and 27% for the transverse bricks when a uniform flow is reached in the tunnel kilns. Also, similar area-averaged CHTCs for the longitudinal and transverse bricks were obtained as a result of the uniform flow. Therefore, the specific energy consumption, quality, and quantity of brick production could be enhanced.

Combined Effect of Brick Surface Roughness and Lattice Setting Density on Brick Firing in Tunnel Kilns

“…The bricks were arranged longitudinally and transversely to the direction of the flow. The wind tunnel used in the CFD simulations was 3.75 m long, 0.35 m wide, and 0.236 m in height, as was the optimized case achieved by Abou-Ziyan [34]. Both brick settings were located at 1.75 m from the entrance to eliminate the entrance effect.…”

“…Among these efforts are the steady-state and transient simulations of tunnel kiln firing [15][16][17] or fast firing [18], improvements of the kiln performance [19][20][21][22][23][24] through the use of modern equipment [25,26], fuel consumption improvements [14,27], the optimization of recovered air [28], flow uniformity improvements [29,30], and flow mixing improvements via air side injection [31]. As the heat transfer in tunnel kilns contains about 80% convection and 20% radiation, extensive efforts have been made to investigate the heat transfer in tunnel kilns [32][33][34][35][36][37][38]. The improvements in the design data have allowed better simulation and modeling of different aspects in tunnel kilns [39][40][41][42], including in kiln control [43][44][45].…”

“…However, those papers did not explicitly investigate the effect of the setting density. A comprehensive project started in 2016 by the same research team as for this paper aimed to enhance the tunnel kiln performance by developing reliable design data for tunnel kilns [29,33,34,51,52]. Accurate three-dimensional CFD models were developed, using the k-ω turbulence model to study the different aspects of the tunnel kilns, including the flow uniformity [29], convection heat transfer [33,34], setting density [51], and surface roughness [52] of the bricks and kiln boundaries.…”

Artisan Brick Kilns: State-of-the-Art and Future Trends

“…Trends in new brick kiln designs aim to improve the tunnel kiln as it is the most efficient kiln type [59,62,63]. They are composed of a collection of attached opposite directed heat exchangers with the solids on the kiln car that move counter-current with the air flow.…”

Thermal Analysis and Energy Efficiency Improvements in Tunnel Kiln for Sustainable Environment

“…The rest of the energy was consumed in the drying process of the ceramics industry [35]. Best available techniques (BAT) for energy efficiency for ceramics production such as installation of superlative burners to reduce the thermal energy of the entire kiln, a large number of well-controlled burners which can optimize the temperature profile in entire tunnel kiln, installation of metallic recuperator heat exchangers to save thermal energy consumption, introduction of high loading rate and reduction in kiln energy consumption, and introduction of environmental management structure to monitor the flu gas regularly were mentioned [36]. The convective heat transfer analysis of tunnel kiln was investigated, and three turbulence models were accounted for in this study: k-e, k-w and RNG k-w.…”