{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

hw3 - ME 114 Homework Set 3 Fall 2008 Due'September 18 A...

This preview shows pages 1–2. Sign up to view the full content.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ME 114 Homework Set 3 Fall 2008 Due'September 18 A thermopane window consists of two pieces of . glass 7 mm thick that enclose an air space 7 mm ;/ . p ‘ thick. The window separates room air at 20°C from f} V15 j 61) 6Q? : 94 CI _ {E ‘14) outside ambient air at -lO°C. The convection co- efficient associated with the inner (room-side) sur- face is 10 W/m2 ' K. (a) If the convection coefficient associated with the outer (ambient) air is 710 = 80 W/m2 - K, what is the heat loss through a Window that is 0.8 m long by 0.5 rn wide? Neglect radiation, and assume the air enclosed between the panes to be stagnant. E3] Compute and plot the effect of ha on the heat loss for 10 S 11,, S 100 W/rn2 - K. Repeat this calculation for a triple-pane construction in which a third pane and a second air space of equivalent thickness are added. Consider a composite wall that includes an 8-min- thiclc hardwood sidinc, 40—min by 130-mm hard- 5 {5 p . _ . . _ ° JAMS» g+a+zalig§4LZW wood studs on 0.65-ni centers with glass fiber in- sulation (paper faced, 28 leg/m3), and a 12-min layer of gypsum (vermiculite) wall board. Wood siding ' Stud Insulation Wall board 4O mm—vi i+— What is the thermal resistance associated with a wall that is 2.5 m high by 6.5 m wide (having 10 studs, each 2.5 in high)? ’1 lirethgine (1/; = 0.026 W/In - K) is used to insulate t e si ewa and the mp and bottom of a 0* lindrical ’1 ' ' ‘ ’ ‘ " ’ hot water tank. The insulation is 40 mm {hick and V15 " (99? Li q: / d 6U» is sandwiched between sheet metal of thin-wall J construction. The height and inside diameter of the tank are 2 In and 0.80 m, respectively, and the tank is in ambient air for which Tn =, 10°C and h = 10 W/m: ' K. If the hot water maintains the inner sur- face at 55°C and energy costs amount to \$0.15/ltWh, what is the daily cost to maintain the water in stor- age? l . it? A .1 —Six identical power transistors with aluminum casing are attached on one side of a 1.2-cm—thick ZO-cm >< 30-c1n copper plate (it = 386 W/rn - ”C) by screws that exert an aver- age pressure of 10 MPa. The base area of each transistor is 9 cm2, and each transistor is placed at the center of a .lO-cm >< 10-cm section of the plate. The interface roughness is estimated to be about 1.4 ,um. All transistors are covered by a thick Plex- iglas layer, which is a poor conductor of heat, and thus all the heat generated at the junction of the transistor must be dissi- pated to the ambient at 23°C through the back surface of the Plexiglas .. = ‘ cover Lappu \ Transistor plate [.2 cm copper plate. The combined convection/radiation heat transfer coefﬁcient at the back surface can be taken to be 30 W/rn2 . °C. If the case temperature of the transistor is not to exceed 75°C, determine the maximum power each transistor can dissipate safely, and the temperature jump at the case-plate interface. ’4 Mg: ATMCr’face : 0 J 35—3/le a? A 4-n1m-diameter and 10—crn-long aluminum (l: = 237 W/ni - °C) is attached to a surface. If the heat transfe coefficient is 12 W/m2 - “C, determine the percent error in rate of heat transfer from the fin when the infinitely long ﬁn sumption is used. instead of the adiabatic fin tip assumptl i , Ma A alO-W power transistor is to be cooled by attaching it» to one of the commercially available heat sinks shown in la 3—6. Select a heat sink that will allow the case temnerature he tran51stor not to exceed 90°C in the ambient air at "30°C ...
View Full Document

{[ snackBarMessage ]}

What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern