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Nothing will change beyond L3. As you increase the length of the heat exchanger, the hot will reach the cool temperature, and beyond that point there will be no change. So beyond L3, the temperature of the cool flow and the hot flow will be equal to the cool flow inlet temperature $t_{c,i}$.


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You can buy an incense stick, which burns slowly and produces perfumed smoke. you then position the incense stick at different points in the sauna and make a video of the resulting smoke trails.


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This NASA article discusses some of the common wind tunnel flow visualization methods. A fog machine generally uses a heated mixture of polypropylene glycol and water. You can test different mixture concentrations in an electric kettle, and use a plastic tube to plumb the fog stream to the locations you are interested in visualizing the flow. Tufts or pieces ...


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The flux of a quantity is by definition the rate per time per area of a given quantity normal to the area in question. If you use the original direction of the particles and this direction is not normal to the surface in question, then you are not evaluating the flux through the surface. To use the original particle direction, you would need to use a surface ...


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Stand at any center point along the axis of the pipe where the temperature is $T$. Assume that you can obtain $h_i$, the internal convection heat transfer coefficient, $k$ the thermal conductivity of the pipe with thickness $w$, and $h_o$ the external convection heat transfer coefficient. Assume an external temperature of $T_\infty$. The heat transfer rate $\...


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