Recuperator - tubular heat exchanger

In a ceramic tubular heat exchanger with a length of 300 mm and a diameter of 180 mm, filled 50% with ceramic material, the process of heating air is virtually impossible due to the limitations of heat transfer physics.

Here's why:

1. Short contact time between air and ceramic At an air velocity of 2 m/s, the airflow passes through the tube in just 0.15 seconds. In such a short time, the ceramic cannot transfer a significant amount of heat to the air, as heat exchange between two mediums (ceramic and air) occurs slowly.

2. Small heat exchange surface area Even with 50% of the tube filled with ceramic material, the surface area of the ceramic in contact with the air is insufficient for effective heating. Heat is transferred only through this surface, and its limited size significantly restricts the efficiency of the process.

3. Low heat transfer coefficient Ceramic has low thermal conductivity, and the heat exchange between ceramic and air is further limited by a low heat transfer coefficient. This means that even with a significant temperature difference between the ceramic (20 °C) and the air (5 °C), the air heating will be minimal.

4. Low heat capacity of air Air has a low heat capacity and mass, so even if the ceramic manages to transfer some heat, it is insufficient to significantly raise the air temperature. For example, calculations show that the air may warm by only fractions of a degree during one cycle.

5. Periodic cooling of the ceramic Each operating cycle of the heat exchanger includes both heating the ceramic (during exhaust) and cooling it (during intake).

Under constant alternation of flows, the ceramic does not have enough time to accumulate sufficient heat to effectively warm the air during the next cycle. Conclusion Technical limitations, such as short contact time, small heat exchange surface area, low heat transfer coefficient, and constant cooling of the ceramic, make heating air in such a heat exchanger impossible. The heat exchange efficiency is so low that this type of heat exchanger is practically useless for transferring heat to the air.