About 90% of the star's total life is spent on the main sequence
Indicate whether the statement is true or false
TRUE
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A heat sink made of an array of fins that have a straight, rectangular cross section is used to cool an electronic micro-chip module, as schematically shown in the figure. The heat sink (base and fins) is made of copper, and each fin is 3 mm thick and 30 mm long. If the fin-base temperature is 85°C and the cooling air is at 25°C with an average convective heat transfer coefficient of ch =100 W/(m2 K), determine the temperature distribution in one fin and the rate of heat transferred per unit width of the fin. If the fins are made of aluminum instead, what is the change in the rate of heat dissipated by the aluminum fin of same thickness? For the numerical analysis, in both the cases, consider a minimum of 11 nodes from the base to tip and convective heat transfer from the fin tip.
Compare the results with the one- dimensional fin analysis
GIVEN
• Heat sink made of an arry of straight rectangular cross section fins.
• Fin base temperature (T0)= 850C
• Surrounding air temperature (T?)= 250C
• Convection heat transfer coefficient ( ch )= 100 W/(m2 K)
• Fin thickness(t)= 3 mm = 0.003 m
• Fin length (L)= 30 mm =0.03 m
• Number of nodes (N)=11
FIND
(a) Temperature distribution in one fin considering convection from fin tip
(b) Heat transfer rate per unit width of fin
(c) Rate of change in heat dissipated if Aluminum of same thickness is used.
PROPERTIES
• Thermal conductivity of copper(kCu)= 396 W/(m K)
• Thermal conductivity of Aluminum (kAl)=238 W/(m K)
SKETCH
A car is traveling counterclockwise along a circular bend in the road whose effective radius is 100 m. At a certain instant of time, the car is traveling due north, has a speed of 10 m/s, and is in the process of increasing that speed at a rate of 1 m/s2. The direction of the car’s acceleration at that instant is most nearly
A. North B. Northeast C. East D. Northwest E. West F. Southwest T. Zero
Electrons in the presence of a magnetic field transition from 4p energy states to 3d states. How many different spectral lines could be observed from these transitions?
A) one B) two C) three D) five
The short lifetime of muons created in the upper atmosphere of the Earth would not allow them to reach the surface of the Earth unless their lifetime increased by time dilation. From the reference system of the muons, the muons can reach the surface of the Earth because:
a. time dilation increases their energy. b. time dilation increases their velocity. c. the relativistic speed of the Earth toward them is added to their velocity. d. length contraction decreases the distance to the Earth.