Structures exposed to the sun can store the rmal energy. It is proposed to use t
ID: 1856668 • Letter: S
Question
Structures exposed to the sun can store the rmal energy. It is proposed to use the structure below for complementary heating of a southward facing room. the structure behaves as a flat plate solar collector where the concrete wall is the absorber. Within the gap spacing is air that is heated from the concrete wall. the air flows upward due to the chimney effect. the room temperature T R is 45 C. the outside air temperature T amb is 0 C. the solar incident flux G is 900 W / m 2 the air gap spacing is 5 cm, the height of the glass sheet is 2. 4 m, and the depth is 5 m. Estimate the air mass flowrate [kg / min], the hot air exit temperature, and the net heat transfer rate to the room. To estimate the se values make the following assumptions. To determine the air velocity assume that the air within the gap equilibrates quickly to the concrete wall temperature. Assume the glass and wall act as a flat plate collector as described in class. the air flow does not affect the flat plate collector performance. Assume that the hot air exit temperature is equal to the concrete wall temperature. All pressure are at atmospheric.Explanation / Answer
Conservation of Mechanical energy states that the whole mechanical power (sum of kinetic energy+ potential energy) of a structure remains stable provided the forces acting on the body are conservative. Thus we have K.E + P.E = Constant. W = ?x2x1 Fext dx. W = 12 mv22 - 12 mv12 W = K2 - K1. if V1 and V2 are the Potential energies at position x1 and x2, we have W = ?x2x1 Fext dx W = + ?x2x1 (-12) dX = ?[V]x1x2 W = -[V(x2)?V(x1)] W = -[V2 - V1] W = V1 - V2. K2 - K1 = V1 - V2. K2 + V2 = K1 + V1K + V = constant If effort done by a conservative force is positive, the kinetic energy of body increases and potential energy of body decrease to stay total mechanical energy conserved.