Submarines change their depth by adding or removing air from rigid ballast tanks, thereby displacing seawater in the tanks. Consider a submarine that has a 700-m3 air-ballast tank originally partially filled with 100 m3 of air at 1650 kPa and 15°C. For the submarine to surface, air at 1650 kPa and 20°C is pumped into the ballast tank until it is entirely filled with air. The seawater leaves the tank at 15°C. Presume that air is added to the tank in such a way that the temperature and pressure of the air in the tank remain constant. Determine the final mass of the air in the ballast tank under this condition. Also determine the total heat transfer while the tank is being filled in this manner. The gas constant of air is R = 0.287 kPa·m3/kg·K. The specific heats of air at room temperature are cP = 1.005 kJ/kg·K and cv = 0.718 kJ/kg·K. The specific volume of water is taken 0.001 m3/kg.

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electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

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