## 2 Experimental Platforms and Devices Materials and Methods  
### Composition of Equipment Experimental Rig  
The experimental platform and devices mentioned in this paper primarily consist of the following: (1) a thermally-stratified water tank, (2) a thermal jet generator, (3) a PIV and PLIF measurement system [28; 29; 30], and (4) a thermal imaging camera. These are illustrated in Figure 1.  
Temperature stratification tanks utilize an insulating membrane to achieve stable temperature stratification, allowing for the connection of jets with different depths of entry. The flowmeter utilizes a double-ring glass rotor flowmeter to accurately measure the outlet flow rate and stabilize the temperature of the thermal jet within a range of 0.1-1 L/min, with a flow rate change range of 0.05-0.5 m/s. The outlet diameter of the jet pipe is 6 mm, and the size of the tank is 0.8 m \(\times\) 0.35 m \(\times\) 0.55 m. The water temperature in the tank is consistent with the indoor environment temperature, and relevant measures are not taken to ensure that the water temperature in the tank is constant at a specific temperature, only to ensure that the difference between the jet discharge temperature and the water temperature in the tank is a certain value. By standing for a period of time, the water temperature inside the tank tends to be consistent and evenly distributed.  
Temperature control switches with thermocouples are used to maintain a constant temperature within the tank, automatically disconnecting when the set temperature is reached and reconnecting when it falls below the set value. The type of thermocouple is a type K, the temperature sensing end is placed in the jet heating pool, and the jet heating pool is independently placed on the right side of the thermally-stratified water tank. Additionally, a tee design at the jet outlet allows for precise discharge of cold water before filling with preset hot water, ensuring accurate experimenting within the temperature stratification tank.  
The fundamental principle of the PIV technique is to disperse tracer particles within the flow field, utilizing a pulsed laser sheet as the light source to illuminate the area of interest in the flow field to capture images of the particles through two or more consecutive exposures using a negative or CCD camera, and then employing image processing technology to divide the resulting image into numerous small areas. Subsequently, utilizing optical Young's stripes, autocorrelation or cross-correlation methods, process the size and direction of the recorded image on the PIV negative or CCD to calculate various motion parameters, including velocity vector map, velocity component map, and streamline map. In essence, PIV measures particle velocities in fluid flows by employing tracer particles with good followability to represent fluid velocities at their respective locations. The high-speed camera used is an I-SPEEDTR type capable of full frame shooting speed up to 2000 FPS  
Figure 1: Experimental platform and device. (**a**) Schematic diagram; (**b**) Physical image.  
with a resolution of 2048 \(\times\) 1024 pixels and maximum shooting speed of 10,000 FPS. It features a large sampling frequency and high-resolution characteristics. The solid-state laser employed is an MGL-W-532 model with an output power of 15 W (Chinese Science Dean Chunguang Machinery Institute, Chunguang, China).  
The PLIF temperature measurement technology utilizes laser excitation to induce fluorescence in a specific fluorescent substance (Rhodamine B) added to the fluid. The molecules of Rhodamine B absorb the laser radiation of a specific frequency and then undergo radiative excursion, resulting in molecular fluorescence. The intensity of Rhodamine B fluorescence is highly sensitive to changes in temperature, exhibiting a strong correlation with temperature variations. High-speed cameras are employed to record the fluorescence intensity, allowing for the inverse deduction of temperature.