Abnormal temperature evolution

Hi, everyone ! I am simulating the heating process of a fixed bed, which consists of two mutually perpendicular cylinders. The fixed bed has two airflows flowing in, as shown in the picture, but the temperature rise of the particles is too fast, and the temperature rise rate keeps increasing. Normally, the temperature rise should slow down as the particle temperature rises. I can’t figure out what’s wrong with my setup. With the same model settings, but the geometric model is set to a single cylinder. The temperature rise is normal. Can you help me see where the problem is? Thank you.
abnormal.zip (37.8 MB)
normal.zip (41.2 MB)