Conjugate forced convection in a semi-cylindrical cavity with entropy generation Oktay Çiçek and A. Cihat Baytas  Faculty of Aeronautics and Astronautics, Istanbul Technical University, Istanbul, Turkey Abstract Purpose – The aim of this paper is to investigate the conjugate forced convection in a semi-cylindrical cavity with air flow. Isotherms, streamlines, Bejan number and local entropy generation number are obtained for the semi-cylindrical cavity. Local Nusselt number, the temperature and the skin friction along the interface wall are calculated with different Reynolds numbers and geometric configurations. Design/methodology/approach – The governing differential equations discretized by finite volume method are solved using SIMPLE algorithm. In this study, collocated grid, where all flow variables are stored at the same location, is used. Alternating direction implicit method and tri-diagonal matrix algorithm are used to solve linear algebraic equation systems. Findings – The effects of Reynolds numbers,inlet and exit cross-section, the locations of exit section on fluid flow are also numerically investigated. It has been observed that since the secondary vortices developed near the exit cross-section negatively affect heat transfer, the temperature value is higher at this region. Better cooling inside cavity is provided in the cases of higher Re number, larger inlet and exit cross-section. The minimum average Nu numbers are computed for the location of L = 0.40 and the minimum total entropy generation numbers are founded in the case of L = 0.20. Originality/value – This study provides insight into proper cooling and entropy generation inside the semi-cylindrical cavity for different conditions. Keywords Finite volume method, Forced convection, Entropy generation, Conjugate heat transfer, Semi-cylindrical cavity Paper type Research paper Nomenclature A = the ratio of thermal diffusivity; 2b = size of inlet cross-section (m); 2B = dimensionless size of inlet cross-section, equation (10); Be = Bejan number, equation (24); C f = skin friction coeffcient, equation (25); d = size of exit cross-section (m); D = dimensionless size of exit cross-section, equation (10); FFI = local entropy generation due to fluid friction, equation (18); g = acceleration due to gravity (ms 2 ); HTI = local entropy generation due to heat transfer, equation (18); k = thermal conductivity (Wm 1 K 1 ); K = the ratio of thermal conductivity, equation (10); l = location of exit cross-section (m); L = dimensionless location of exit cross-section, equation (10); N = local entropy generation number, equation (18); Forced convection in a semi-cylindrical cavity 3879 Received 2 September 2019 Revised 21 October 2019 Accepted 24 October 2019 International Journal of Numerical Methods for Heat & Fluid Flow Vol. 30 No. 8, 2020 pp. 3879-3902 © Emerald Publishing Limited 0961-5539 DOI 10.1108/HFF-09-2019-0670 The current issue and full text archive of this journal is available on Emerald Insight at: https://www.emerald.com/insight/0961-5539.htm