Fixed bed tubular reactors are widely used in the chemical processing industry to carry out solid- catalyzed reactions. Such tubes have many hundreds of particle diameters long, but only a few across, facilitating radial heat loss to the tube wall. A knowledge of the effective radial heat transfer mechanisms through the wall and packing of fluid flowing through a single tube forms an important aspect of the design of catalytic reactors. Whereas, in these systems both reactor selectivity and velocity of reactions depend largely on bed temperature. Knowledge of temperature profile within the bed and heat removal rate or which has been added is essential to achieve reactor productivity and product homogeneity. In this book mathematical model is developed for predicted the radial temperature profiles within nonisothermal fixed bed gas reactor at high pressure and estimate the characteristic parameters of heat transport at these conditions. Also investigate of the parameters influenced on the wall heat transfer coefficient in a fixed bed reactor at high pressure including Reynolds number, pellet sizes and orientation of the particles ..etc.