In order to correct the errors of “periodic full-section calculation model” and “unit flow channel model,” the author proposes a numerical simulation method of a longitudinal flow shell-side heat exchanger based on CAD. The numerical simulation of the fluid flow and heat transfer characteristics of the three-blade orifice plate heat exchanger is carried out by using FLUENT software, and the “periodic full-section calculation model” and “unit flow channel model” are established, as well as the calculation results of comparative analysis. Experimental results show the following: With the increase of the inner diameter
D
of the heat exchanger shell, the calculation results of the two models are gradually reached. When
D
>
800
mm
, the error of the calculation results of the two models has been reduced to about 10%; at this time, the “unit flow channel model” has practicability and applicability. When
D
≤
800
mm
, the correction algorithm of the “unit flow channel model” is proposed, and the correction correlation formula of the pressure gradient and convective heat transfer coefficient is given. The revised results of the simulation can not only meet the engineering needs but also save computer resources and improve the calculation efficiency, which provides a theoretical basis for the development, improvement, and further industrial application of the “unit flow channel model” of the longitudinal shell-side heat exchanger.