Concurrent heating modes

Fig. 2.15 Combining of concurrent heating modes in a refractory-lined furnace, kiln, incinerator, or opi heater, with suggested formulas and electrical analogy.

Radiation differs from the other two heat transfer mechanisms in that it does not require the presence of a material medium to take place. In fact, energy transfer by radiation is fastest (at the speed of light) and it suffers no attenuation in a vacuum. Also, radiation tran.sfer occurs in solids as well as liquids and gases. In most practical applications, all three modes of heat transfer occur concurrently at varying degrees. But heat transfer through an evacuated space can occur only by radiation. For example, the energy of the sun reaches the earth by radiation. 

Rg. 2.21 The many concurrent modes of heat transfer within a fuel-fired furnace. Some refractory surfaces, r, and charged loads, c, are convection-heated by hot poc flowing over them. Triatomic molecules of the combustion gases, g, and soot particles, p, radiate in all directions to refractories, r and loads, c. The surfaces of r and c in turn radiate in all possible directions, such as r to r, r to c, c to c, and c to r. 

Table 4 is a simple listing of the modes of heat input to the drying material. Note that these modes may be applied individually (e.g., only convection) or in combination (e.g., convection with microwave). They may be applied concurrently or sequentially (e.g., convection followed by radiation followed by convection). Further, the energy supply may be... 

---