## 5 Analysis of Experimental and Simulation Results
### Thermally-Stratified Water Body Conditions
#### 5.2.1 Case 5 Working Conditions  
In Case 5 conditions, the initial velocity of the jet is 0.1 m/s, the water depth is 0.26 m, the temperature difference with the ambient water body is 10 \({}^{\circ}\)C, and the temperature difference of the ambient water body background stratification is 4 \({}^{\circ}\)C. The planar laser-induced fluorescence (PLIF) technique is utilized to measure variations in the temperature field distribution of the thermal jet at time intervals of 5 s, 10 s, 15 s, 20 s, 25 s, and 30 s in a uniform water body environment. The experimental findings are presented in Figure 13.  
The figure illustrates the trend of the jet temperature diffusion. It can be observed that, when the jet ascends to the stratified interface, its temperature diffusion state is similar to Case 1 conditions. At 5 s, the horizontal temperature diffusion distance of the thermal jet is approximately 10 cm, with a vertical floating height of less than 5 cm. After discharging for 5 s, both the horizontal and vertical jet temperature diffusion distances double, resulting in a temperature difference of 2-4 \({}^{\circ}\)C between the core area and the ambient water body. By 15 s, as the jet temperature floats upwards to the stratified interface, it ceases to diffuse vertically and instead transitions to rightward horizontal diffusion from its core temperature region. The temperature difference between this core region and the ambient water is now less than 4 \({}^{\circ}\)C--less than background ambient stratified temperatures. At 20 s, the temperature of the jet continues to diffuse to the right in the horizontal direction. The area of horizontal temperature diffusion is approximately 70%, with a diffusion distance exceeding 30 cm. The temperature difference between the jet and the ambient water body in this region is less than 2 \({}^{\circ}\)C, and there is an apparent dissipation of the jet temperature at that time. At 25 s, there is no significant change in the area of the jet temperature diffusion. The increment in horizontal temperature diffusion distance is minimal. A noticeable dissipation of the jet temperature occurs within a horizontal distance of 15 cm from the discharge port. By contrast, within a range of horizontal distances from 15 cm to 35 cm, the area for horizontal temperature diffusion extends up to 20 cm with a vertical height of about 7.5 cm, and the overall temperature diffusion area of the jet is limited below the stratified interface. Compared to Case 1, where the initial jet velocity, temperature difference, and jet depth are the same, the only difference in Case 5 is the temperature stratification of the background environmental water body. Prior to the diffusion of the jet temperature to the stratified interface, the trend of jet temperature diffusion is essentially identical, with minimal \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Case** & **Velocity (m/s)** & **Depth (cm)** & **TD (\({}^{\circ}\)C)** \\ \hline
5 & 0.1 & 26 & 10 \\
6 & 0.2 & 26 & 10 \\
7 & 0.1 & 26 & 25 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Hydrostatic-thermally-stratified Water Experiment Conditions. differences in diffusion distance and floating height. However, once the jet temperature diffuses to the stratified interface, it encounters a stratified temperature difference within the environmental water body. This results in a density difference between the upper and lower layers of 0.33 kg/m\({}^{3}\). As a result, when the jet's temperature decreases to that of the lower layer by 4 \({}^{\circ}\)C and matches that of the upper layer in terms of density, it can no longer continue floating. Influenced by the stratified interface effect, there is an observable cessation in the upward movement of the jet after discharging for a period of time. Instead, it begins diffusing horizontally towards its right side. This horizontal diffusion covers a larger area with reduced dissipation, resulting in a 27% increase in horizontal temperature diffusion distance compared to before reaching this interface.