Thermodynamics HW Solutions 259

Thermodynamics HW Solutions 259 - Chapter 3 Steady Heat...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 3 Steady Heat Conduction 3-147 The U -value of a wall is given. A layer of face brick is added to the outside of a wall, leaving a 20- mm air space between the wall and the bricks. The new U -value of the wall and the rate of heat transfer through the wall is to be determined. Assumptions 1 Steady operating conditions exist. 2 Heat transfer through the wall is one-dimensional. 3 Thermal properties of the wall and the heat transfer coefficients are constant. Properties The U -value of a wall is given to be U = 2.25 W/m 2 . ° C. The R - values of 100-mm face brick and a 20-mm air space between the wall and the bricks various layers are 0.075 and 0.170 m 2 . ° C/W, respectively. Analysis The R -value of the existing wall for the winter conditions is RU existing wall existing wall 2 mC / W == = ° 11 2 2 5 0 4 4 4 // . . Noting that the added thermal resistances are in series, the overall R- value of the wall becomes C/W m 689 . 0 170 . 0 075 . 0
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 01/19/2012 for the course PHY 4803 taught by Professor Dr.danielarenas during the Fall '10 term at UNF.

Ask a homework question - tutors are online