hw1-011-ts

# hw1-011-ts - whole window b Horriﬁed at the energy you...

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

C HEMICAL E NGINEERING 120B Homework 1, 2010 1. Read section 1 of the 120B notes. 2. Describe some interesting heat transfer activity you did over the winter break. Be creative, and try to say something non-trivial about how this activity worked (involving conduction, convection and/or radiation) that you did not know before this class started. 3. Consider a 1m by 1m window, which consists of window glass (thermal conductivity k = 1 W/m K). The window is 1 cm thick. a. On a cold Santa Barbara night, the outside temperature is 41 F, or about 5 C, whereas you keep your house at 70 F, or about 20C. Assuming the window to behave as a ﬂat, planar slab for heat conduction, calculate the temperature proﬁle T ( x ) and the heat ﬂux ( q , per unit area). What is the total heat loss per unit time (in watts) through the
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: whole window? b. Horriﬁed at the energy you are wasting, you install a double-paned window. It has the same amount of glass, but now there are two 5 mm-thick slabs, with a 1 mm air gap ( k = . 002W/mK) sandwiched between them. Now compute the temperature proﬁle T ( x ), the heat ﬂux q per unit area, and the total heat loss per unit time. c. Sketch the temperature proﬁles for the single-pane and double-pane windows. d. Why, in this case, does the order of the materials matter? In other words, what would happen if you put the air layer ‘outside’ the two panes of glass? If it were a layer of, e.g. plexiglass, could you rearrange the layers? 4. Which is colder – bathroom ﬂoor tiles or the bathmat? Which feels colder, the tiles or the bathmat? Why?...
View Full Document

{[ snackBarMessage ]}

Ask a homework question - tutors are online