The surface of a steel gear of 1022 steel (0.22 wt % C ) is to be gas-carburized at 927°C. Calculate the time necessary to increase the carbon content to 0.3 wt% at 0.081 in. below the surface of the gear. Assume the carbon content of the surface to be 1.20wt%. D (C in iron ) at 927°C = 1.28 x 10^-11 m^2/s. The answer should have one decimal of accuracy and be in minutes.

To save energy, the air supply to a 2000 ft office has been shut off overnight and the room temperature has dropped to 40°f. in the morning, the thermostat is reset to 70°f and warm air at 120 f begins to flov in at 200ft'/min. the air is well mixed within the room, and an equal mass flow of air at room temperature (changing with time) is withdrawn through a return duct. the air pressure is nearly 1 atm everywhere. ignoring heat transfer with the surroundings and kinetic and potential energy effects, estimate how long it takes for the room temperature to reach 70°f. plot the room temperature as a function of time.

In the winter, in order to keep the classroom steadily at 68 f before 10 pm, heating with an average rate of 42,000 btu/hr is provided. assume the outdoor temperature maintains at 32°f, determine the electrical power (kw) required to (a) operate a reversible heat pump (b) operate a real heat pump with a cop (7) of 4.5 and (c) operate an electrical-resistance heater.

Write a technical essay (maximum two pages) about stress concentration. and paste from the textbook. instead, read updated material about this phenomenon and provide a technical evaluation of the different techniques to avoid/reduce such phenomenon. consider in your analysis cutting-edge computational techniques such as fea to study and analyze stress concentrations.