Arab J Sci Eng (2014) 39:9025–9038 DOI 10.1007/s13369-014-1418-7 RESEARCH ARTICLE - MECHANICAL ENGINEERING Laminar Natural Convection for Thermally Active Partial Side Walls in a Right-Angled Triangular Cavity Manoj K. Triveni · Dipak Sen · Rajsekhar Panua Received: 30 January 2014 / Accepted: 31 August 2014 / Published online: 5 November 2014 © King Fahd University of Petroleum and Minerals 2014 Abstract The effect of partial heating and cooling on lam- inar natural convective heat transfer in right-angle triangular cavity ﬁlled with water has been investigated numerically. The triangular cavity is presented in nine different conﬁgu- rations namely Left-Bottom, Left-Middle, Left-Top, Middle- Bottom, Middle-Middle, Middle-Top, Right-Bottom, Right- Middle and Right-Top and the length of the thermally active wall is b = L /3. The base wall is considered as partially hot while the side wall as partially cold. Two-dimensional steady- state continuity, Navier–Stokes and energy equations along with the Boussinesq approximation are solved using the ﬁnite volume method. The Rayleigh number is varied from 10 5 to 10 7 . Results revealed that the heat transfer rate is high for LB walls whereas low for RT location. Also, the heat trans- fer rate enhancement is observed for all values of Rayleigh number. Keywords Natural convection · Partially active walls · Triangular enclosure · Rayleigh number M. K. Triveni (B ) · D. Sen · R. Panua Mechanical Engineering Department, National Institute of Technology, Agartala, India e-mail: triveni_mikky@yahoo.com List of symbols g Acceleration due to gravity (m s -2 ) H Height of the cavity (m) L Width of the cavity (m) b Length of the thermally active wall (m) p Pressure (KPa) P Dimensionless pressure u ,v Velocity components (ms -1 ) U, V Dimensionless velocity component x , y Co-ordinates X , Y Dimensionless co-ordinates T Temperature (K) T h Hot wall temperature (K) T c Cold wall temperature (K) Pr Prandtl number Ra Rayleigh number Nu x Local Nusselt number Nu Average Nusselt number 123