Shandong Zhilin Environmental Protection Technology Co., Ltd.

Three major countercurrent heat transfer advantages of plate fin heat exchangers

Release time:

2021-04-26 15:36

Source:

Finned tube heat exchangers have radial or axial fins attached to the surface of the heat exchange tubes. Commonly used finned tubes can be integrally rolled or cast, or they can be welded or inlaid.

Finned tube heat exchangers have radial or axial fins installed on the surface of the heat transfer tubes. Commonly used finned tubes can be integrally rolled or cast, or they can be welded or inlaid. Finned tube heat exchangers are suitable for occasions where the convective heat transfer coefficients of the two-side fluids differ significantly, such as heating air with saturated steam and cooling materials with air. Air flows outside the tube, and its convective heat transfer coefficient is very small. When fins are installed outside the tube, it increases the turbulence of the external air and increases the external surface area of the heat transfer tube, thereby improving the heat transfer effect.

In recent years, air coolers made of finned tubes have been widely used in chemical production. Using air cooling instead of water cooling is very suitable for water-scarce areas. Fins can also be installed inside the heat transfer tubes, but the fin height is smaller, called low fins, such as threaded tubes, used in cases where the internal heat transfer coefficient is smaller.

Three major counter-current heat transfer advantages of finned tube heat exchangers

Large logarithmic mean temperature difference: Calculations show that, under the same inlet and outlet temperatures, the logarithmic mean temperature difference in counter-current flow is always larger than that in co-current flow of the two fluids. A larger T means that the heat transfer area can be saved. Therefore, in heat exchanger design, designers always try to make the hot and cold fluids flow in opposite directions.

When the hot and cold fluids flow countercurrently, the local heat transfer temperature difference on both sides at any position on the heat transfer surface is relatively uniform, and there will be no situation where the heat transfer temperature difference is too large at one end and too small at the other. A relatively uniform heat transfer temperature difference means that the heat transfer per unit area is also relatively uniform, and there will be no situation where the heat transfer is too large at a certain point, even exceeding its heat transfer capacity, while the heat transfer is too small at the other end, resulting in insufficient utilization of the heat transfer area.

Another advantage of counter-current heat transfer of hot and cold fluids is that the outlet temperature T2 of the cold fluid can even exceed the outlet temperature T1 of the hot fluid. As can be seen from the example above, the outlet temperature of the cold fluid is 40℃, which is higher than the heat transfer of the hot fluid, which allows for a greater increase in the temperature of the cold fluid. This is not possible in co-current flow.

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