mass transfer equation, Lecture notes of Heat and Mass Transfer

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RADIATON

RADIATON EXAMPLE 12-7 Radiation Heat Transfer between Parallel Plates Two very large parallel plates are maintained at uniform temperatures T, = 800 K and Tp = 500 K and have emissivities e, = 0.2 and e, = 0.7, respec- tively, as shown in Figure 12-25. Determine the net rate of radiation heat trans- fer between the two surfaces per unit surface area of the plates. SOLUTION Two large parallel plates are maintained at uniform temperatures. The net rate of radiation heat transfer between the plates is to be determined. Assumptions Both surfaces are opaque, diffuse, and gray. Analysis The net rate of radiation heat transfer between the two plates per unit area is readily determined from Eq. 12-38 to be FIGURE 12-25 The two parallel plates considered in Example 12-7. . — On o(T$-TH _ 6.67 x 10-8 Wim? - K*)[(800 K)4 — (500 Ky] 92> ml I —_ Baw = 3625 Wim? 12-26 Two very large parallel plates are maintained at uni- es 12-26 Two very large parallel plates are maintained at uniform temperatures. The net rate of radiation heat transfer between the two plates is to be determined. Assumptions 1 Steady operating conditions exist 2 The surfaces 2, =05 are opaque, diffuse. and gray. 3 Convection heat transfer is not considered. Properties The emissivities ¢ of the plates are given to be 0.5 and T,=400K 0.9. Analysis The net rate of radiation heat transfer between the two surfaces per unit area of the plates is determined directly from On _ (74-74) _ (667x107 Wim? -K*)[(600K)* -(400K)*] 4, 11, ji 1. £, £2 os 09 = 2795 Wim?