Hot combustion gases of a furnace are flowing througha concrete chimney (k =1.4 w/m · °c) of rectangular cross section. the flow section of the chimney is 20 cm ×40 cm, and the thickness of the wall is 10 cm. the average temperatureof the hot gases in the chimney is ti=280°c, and the averageconvection heat transfer coefficient inside the chimney is hi=75 w/m2· °c. the chimney is losing heat from its outer surfaceto the ambient air at to=15°c by convection with a

Coiled springs ought to be very strong and stiff. si3n4 is a strong, stiff material. would you select this material for a spring? explain.

Ajournal bearing has a journal diameter of 3.250 in with a unilateral tolerance of 20.003 in. the bushing bore has a diameter of 3.256 in and a unilateral tolerance of 0.004 in. the bushing is 2.8 in long and supports a 700-lbf load. the journal speed is 900 rev/min. find the minimum oil film thickness and the maximum film pressure for both sae 20 and sae 20w-30 lubricants, for the tightest assembly if the operating film temperature is 160°f. a computer code is appropriate for solving this problem.

The short distance from the objective lens to the object causes problems at high magnification. which of the following is the most serious? a. cleaning the object surface b. positioning the object c. reflection from the object surface. d. illumination of the object