Chapter 9: Free Convection

where Pr is the Prandtl number.

“Your problem,” she explained to Kai, pointing to a dimensionless number, “is the Grashof number.”

): This is the most common pitfall. For a vertical plate, it’s the height ( ); for a horizontal cylinder, it’s the diameter ( Calculate the Film Temperature ( Tfcap T sub f ):

Natural convection, or free convection, occurs when a fluid (like air or water) contacts a surface at a different temperature. The resulting temperature gradient causes density variations; for example, air near a hot radiator becomes less dense and rises, while cooler, denser air sinks to take its place. This motion, known as a natural convection current, significantly enhances heat transfer compared to pure conduction. Key Concepts and Mathematical Foundations

Warning: Many free PDFs claiming to be the "Cengel 5th Edition solution manual Chapter 9" are actually for the 3rd or 4th edition. Correlations changed between editions—especially the Churchill and Chu constants. Always cross-check equation numbers.

Chapter 9 of Cengel's Heat and Mass Transfer (5th Edition) focuses on Natural Convection, a mechanism where fluid motion is driven by buoyancy forces rather than external means like fans or pumps. The solution manual provides a systematic approach to determining heat transfer rates for various geometries by first calculating dimensionless numbers to find the convection heat transfer coefficient ( Key Learning Objectives

Ra = Gr * Pr

Solution: