The study found that the porous medium sintered in the heat transfer tube can reduce the thermal resistance and increase the area available for heat exchange

Image: Left: Conventional Right: Multi-hole tube see more 

Image source: University of Electronic Communication

Although their function of transferring heat from one medium to another may seem simple, they are essential in machines. The heat exchange between the two fluids depends on the material of the heat exchanger, the contact area of ​​the heat exchange, and the properties of the fluid. In order to conduct effective heat exchange between fluids with poor heat transfer performance (such as gases), a larger surface is required.

Porous materials such as granular porous media, foam porous media and fibrous porous media are emerging alternatives. These materials are not attached to the heat transfer tube but are filled inside the heat transfer tube. Therefore, this method does not require modification or modification of the tube to fix the fins, and can be used in existing heat transfer tubes. However, it has recently been discovered that sintering heat transfer tubes and porous media can improve the contact between the fibers and the tube wall, reduce thermal resistance and enhance heat exchange. But how big is the improvement in heat transfer performance?

Now, in a study published in "Applied Thermal Engineering", researchers from the Japan Electric and Communication University and Tokyo University of Agriculture and Technology have compared the heat transfer performance of tubes filled with sintered porous materials with those of ordinary traditional heat transfer tubes. The performance was compared. The paper was published online on July 2, 2021, and published in volume 196 of the print edition on September 1, 2021.

The heat transfer performance of the device is evaluated by measuring the temperature of the discharged air after the heat exchange. One of the authors of the study, Dr. Koji Enoki, associate professor of the University of Electronic Communications, briefly explained the setting: "The inner diameter of the tube is about 10-20 mm, and the length of the tube is 150 mm. Dry air at 200°C flows through the tube, and the outside of the tube Cool with isobutane with a saturation temperature of 2°C." Then, the researchers evaluated the heat transfer performance of the device by measuring the temperature of the exhaust air after the heat exchange.

For traditional heat transfer tubes (without aluminum fibers), the temperature of the air at the outlet was observed to be approximately 130 °C. However, when the tube is filled and sintered with porous aluminum fibers, the temperature of the outlet air is significantly reduced. In addition, for a fill length of 50 mm, the air temperature was found to drop further, approaching the saturation temperature of isobutane (2 °C). Based on the temperature difference between the incoming and outgoing air, the researchers calculated the heat transfer in a tube sintered with a porous medium and found that it was five times that of a traditional heat transfer tube.

Dr. Enoki is optimistic that improvements in heat transfer can pave the way for energy recovery from traditional heat transfer tubes that are currently considered impractical or uneconomical. For economic reasons, the heat from the factory below 200°C has been discharged into the atmosphere. However, the heat transfer tube introduced here successfully increases the heat transfer of the gas by about 20 times compared with the traditional tube, so that waste can be recycled Heat from the factory."

"Considering the energy that can be recovered in the future, it is no exaggeration to say that we have been able to turn a rough diamond into a diamond," he added.

Experimental Research on Heat Transfer and Pressure Drop Performance of Sintered High Porosity Medium

The authors declare that they have no known competing economic interests or personal relationships that may affect the work reported in this article

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UEMURA Takashi University of Electronic Communication uemura@office.uec.ac.jp Office: 81-42--443-5000

ENOKI Koji University of Electronic Communication enoki.koji@uec.ac.jp Office: 81-42-443-5337

Copyright © 2021 American Association for the Advancement of Science (AAAS)

Copyright © 2021 American Association for the Advancement of Science (AAAS)