How is heat transfer handled in tubular reactors?

Heat transfer options: external heat exchange (shell-side heating/cooling fluid, jackets), direct heating (fired heaters for endothermic like steam reforming), autothermal operation (exothermic reaction provides heat for endothermic), and adiabatic beds with interstage heat exchange. Design parameters: tube diameter (smaller improves radial heat transfer but increases pressure drop), tube length, number of tubes, and coolant flow pattern. Heat transfer coefficient depends on Reynolds number, packing, and fluid properties. Radial temperature gradients must be considered.