## 5 Results and Discussion
### Analysis of TTEG Performance under Varying External Loads  
In order to simulate real-life situations more accurately, the study utilizes the identical testing settings employed by [PERSON] et al. [40] for the FTEG. The TTEG utilizes the engine exhaust of a semi-truck as its heat source, which has a temperature of 550 \({}^{\circ}\)C and a mass flow rate of 0.032 kg/s. The coolant employed is ethylene glycol (C\({}_{2}\)H\({}_{6}\)O\({}_{2}\)) at a temperature of 90 \({}^{\circ}\)C, with a mass flow rate of 0.237 kg/s. The cooling water flow path is established by calculating the difference between the height of the TTEG and the spacing between the tube bundles in the shell and tube heat exchanger, as illustrated in  
Figure 8: This diagram presents a comparative analysis between the performance metrics of a Tubular Thermoelectric Module (TTEG) and the research findings published by [PERSON] et al. [41]. Figure 9. Given the specified test conditions, Figure 10 illustrates the correlation between the external load (Load Resistance) and the output power. The data demonstrate that, as the external load is steadily raised, the output power of the TTEG experiences a sharp increase until it reaches its maximum value, gradually decreasing. When the external load is the same as the internal resistance (0.00262 \(\Omega\)), the TTEG generates an open-circuit voltage of 0.19 V and a maximum output power of 3.31 W. As the external load increases, causing the total resistance to rise, the output current drops, decreasing output power. The pressure differential between the engine exhaust inlet and outflow is 25.45 Pa, far below the recommended back-pressure threshold of 812 Pa proposed by [PERSON] et al. [46]  
Significantly, the results suggest that TTEGs can be highly effective in real-world applications when waste heat is recovered from vehicle exhaust systems. The potential to generate significant power outputs with minimal pressure drops encourages the use of TTEGs in automotive and industrial environments. Relationship between Load Resistance Values and Heat Source Inlet Temperatures on Output Power and Thermal Efficiency  
The study's methodical and comprehensive approach involves setting a wide range of engine exhaust temperatures (ranging from 100 to 625 \({}^{\circ}\)C) and coolant temperatures (between 80 and 100 \({}^{\circ}\)C), considering the variability caused by different engine types, output powers, and fuel types. The specified range covers most situations in internal combustion engines, where exhaust temperatures typically range from 150 to 600 degrees Celsius, and coolant temperatures generally vary from 80 to 100 degrees Celsius. To maintain regulated and consistent circumstances in the investigation, the engine exhaust mass flow rate is constant at 0.032 kg/s, while the coolant (ethylene glycol) mass  
Figure 10: This diagram illustrates the relationship between the external load applied to a Tubular Thermoelectric Module and its resultant output power. It graphically represents how changes in the load affect the module’s power output, highlighting the operational efficiency and performance characteristics under varying load conditions. Figure 9: This diagram provides a schematic illustration of fluid flow simulation within a Tubular Thermal Energy Module. flow rate is set at 0.237 kg/s. This configuration is advantageous for efficiently monitoring and evaluating the TTEG operation under different temperature circumstances at both the high and low ends. The study may assess the impact of temperature variations on the external load, output power, and thermal efficiency of the TTEG. The study seeks insights into ideal TTEG operating parameters by modeling diverse situations to maximize efficiency and waste heat recovery application efficacy. This analysis is essential for determining TTEG integration feasibility in various engine systems, which would enhance energy efficiency and minimize the environmental footprint of internal combustion engines.