## 1 Introduction
Therefore, the main objectives addressed in the present work are the numerical investigation of the impact of deposit thickness inside tubes on the minimum thickness of the water tube for safe operation under different working loads and the influence the operating conditions, such as heat flux and flow rate, on the minimum thickness of the furnace water tube during the boiler lifetime. Ansys fluent software student version 2021 R2 provides a suite to cover the entire range of physics, which enables virtual access to any field of engineering simulation, thereby permitting designing models to identify problems and functional processes. Conventional gas boilers have been shown to dissipate a high heat loss. Thus, the engineers designed a new type of boiler with thermal efficiency [13; 14]. Regardless, the efficient boiler engineers continued to develop to minimize complete heat loss and designed Ansys software that analyzes the internal water distribution within the heat exchanger [14; 15]. Thus, ref. [14] pointed out that the engineers aim to improve the heat exchange coefficient within the tube to permit higher water flow velocity. Furthermore, ref. [16] added that the system predicts the fluid flow behavior of water in the heat exchanger and throughout its distribution. In addition, ref. [16] showed that the software supported the designing of the simulation model for the boiler with boundary conditions of heat transfer and heat loss in the system. Thus, using the software, several simulations were garnered over many years for a substantial improvement in the flow and heat exchanging behavior of the boiler with the updated shape of the baffle. This study concentrates on the CFD model, which provides easy simulation of different input parameters. The CFD is categorized into three types of systems: Reynolds-averaged Navier-Stokes (RANS) computations, large-eddy simulations (LES), and direct numerical simulations (DNS). The RANS technique applied is used mainly for resolving the mean values of each quantity that uses turbulent models for unclosed terms, whereas DNS solves the full instantaneous Navier-Stokes equations without the inclusion of turbulent motions models [17]. On the other hand, LES measures the turbulent large eddies and models the small-scale eddies that prove to be effective in establishing the mechanism required to stabilize the problem [17]. Ref. [17], integrated LES with Computational Fluid Dynamics to successfully simulate the effectiveness simulate the ultra-supercritical boiler at different operation load conditions, which concurred with the findings of [18]. Nevertheless, ref. [19] presented use of the DNS only to be feasible for calculating academic issues, such as heat flow due to the computational cost. Refs. [20,21] studies have shown its application in terms of superheaters where the thermal efficiency of the furnace is based on the performance of the boiler. CFD analysis is mostly employed at the designed stage, troubleshooting stage, and performance evaluation during the plant operation [22]. Ref. [22], stated that the outcome obtained from the CFD analysis had shown an effective approach to visualize the condition of the tubes and predict the further life of the tube depending upon the condition. Recently, the implementation of the PRO-E design software enabled the authors to evaluate the thermal flow at different velocities in the 3D model simulation that provided a complex identification of the transfer of heat flux along with ANSYS analysis [22]. Moreover, it enabled the engineer to adjust the high-temperature zone to prevent tube erosion and refrain from tube leakage issues [23]. Ref. [23] demonstrated crude oil substitution with oil using the CFD approach. Thus, the advanced property of the system allowed several authors to study the operating parameters responsible for erosion without halting the process [23, 24, 25].