To reduce heat losses, a horizontal rectangular duct that is W = 0.80 m wide and H = 0.3 m high is encased in a metal radiation shield. The duct wall and shield are separated by an air gap of thickness t = 0.06 m. For a duct wall temperature of T_d = 40°C and a shield temperature of T_sh = 20°C, determine the convection heat loss per unit length from the duct.

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Duct T₁ = 40°C Shield Tsh = 20°C W = 0.80 m t = 0.06 m Air H = 0.30 m 8