Circulation Can Cure Cold Bottoms

A perfect heating situation would have each load piece completely surrounded (360 degrees in all planes) by equally high heat transfer rates to all its surfaces. That is often impossible or impractical because of (a) load shape and size, (b) handling and support problems, and (c) lack of appropriate piers, posts, or kiln furniture. The resultant uneven heating necessitates a long soak time to let the temperatures even out within the load, with possible increased fuel costs. Long soak times may cause excessive surface oxidation, and they surely cause lowered furnace productivity. 

The fact that the jet gas has its temperature moderated by its inspiration of surrounding gases decreases its ability to transfer heat by gas radiation. This is a way that enhanced heating helps temperature uniformity. If the mixture of jet and entrained gas moving under the load cools only 15°, then the load will have only about a 15° side-to-side AT. 

If the jet gas passageway (tunnel) were reduced from a 2 ft (0.61 m) crosswise gas beam to half as wide, figure 2.13 shows that the ability of 2200 F (1204 C) gas 

Anomaly Summary For good product temperature uniformity, the nnderpas-sages on a batch furnace must have minimum temperature difference from end to end. The following suggestions relate to underfiring where gas underpassages are much smaller than those above the loads. 

The heat transfer rate from the poc gases to the loads must be moderate because the load temperature will reflect the poc temperatures. Therefore, 

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