Example

Using the conductance heat transfer equation, calculate the amount of heat lost through 2 m2 (21.528 ft2) of a cold storage wall that is composed of three layers of material. The wall consists of 4-in. (0.1016-m) thick concrete block (xc) on the outside, 6-in. (0.1524-m) thick polystyrene insulation (xp), and 2-in. (0.0508-m) thick fir wood (xf ) on the inside. The inside wall of the cold room is - 40°F (- 40°C) and the outside wall is 68°F 20°C). From Table

2, the thermal conductivities are kc = 0.76 W • m/m2 • K = 5.27 (BtuXin.)/ft2Xhj(°F) kp = 0.038 W • m/m2 • K = 0.263 (BtuXin.MftiXhJCF) kf = 0.11 W ■ m/m2 • K = 0.76 (Btu)(in.)/(ft?)(h)(°F)

Using equation 12 where the area is constant (Fig. 1), t, - t„

In SI units:

Table 2. Thermal Conductivity of Selected Foods and Processing Facility Materials

Thermal conductivity, ka

Table 2. Thermal Conductivity of Selected Foods and Processing Facility Materials

Thermal conductivity, ka

°C

(W)(m) (m4)(K)

(BtuXin.) (ft2)(h)(°F)

Apple

Sleeping Sanctuary

Sleeping Sanctuary

Salvation For The Sleep Deprived The Ultimate Guide To Sleeping, Napping, Resting And  Restoring Your Energy. Of the many things that we do just instinctively and do not give much  of a thought to, sleep is probably the most prominent one. Most of us sleep only because we have to. We sleep because we cannot stay awake all 24 hours in the day.

Get My Free Ebook


Post a comment