**2.2. Boundary conditions**

This chapter gives an excellent example for this type of approaches. To identify the reasons for the rupture of a heavy-duty, high-pressure natural gas heat exchanger, as shown in **Figure 1**, the flow field of the heat exchanger was numerically examined. Based on the findings, a new configuration was suggested and the corresponding flow field was studied. The installed modified heat exchanger has been trouble-free used to date. In the following sections, the computational domain, mesh, numerical methods, flow features of the two designs, and the

**Figure 1.** The natural gas heat exchanger: (a) the damaged heat exchanger; and (b) a close view of the cracks on the top

The natural gas heat exchanger has a nominal power of 390 KW, and the effective length of its heavy-duty vessel is 3785 mm with an outside diameter of 457.2 mm. As a sketch shown in **Figure 2**, it accommodates 138 (276 rods) heating elements. The diameter of these elements is 10.9 mm, and the length is 3277 mm for 64 long elements and 3252 mm for 74 short elements.

cause of the heat exchanger damage are presented and discussed.

**2.1. Computational domain and mesh of the original design**

**Figure 2.** The computational domain of the original design.

**2. Numerical simulations**

256 Numerical Simulations in Engineering and Science

surface of the vessel.

The inlet boundary conditions for the numerical simulations are listed in **Table 1**.

The heavy-duty vessel was wrapped with insulation material, and so it was reasonable to assume adiabatic boundary condition for its external wall boundaries. A heat flux of 4.48 KW/m2 was specified at the heating-element surfaces starting from the middle cross section of the inlet pipe to the end of the heater elements. An increase in natural gas temperature by ~200 K, from the room temperature, was expected. In the investigation, the natural gas was considered as pure methane.
