17-74 Steam exiting the turbine of a steam power plant at 40°C is to be condensed in a large condenser by cooling water flowing through copper pipes (k = 386 W/m.°C) of inner diam- eter 1 cm and outer diameter 1.5 cm at an average temperature of 20°C. The heat of vaporization of water at 40°C is 2407 kJ/kg. The heat transfer coefficients are 13,000 W/m2-°C on the steam side and 200 W/m2.°C on the water side. Determine the length of the tube required to condense steam at a rate of 115 kg/h. Answer: 622 m

manufacturer plans to use steel wire (ks = 25 Wm-1 K-1 ) in a household appliance. For safetyconsiderations, we would like an estimate of the smallest electric current that is required to melt the wire.The bare wire is exposed to 20°C air with convective heat transfer coefficient of 15 Wm-2 K-1 and hasdiameter of 2.0 mm and electrical resistance of 0.20 W/m (i.e., per meter of wire). Thermal energy isproduced within the wire at the rate I2 Re , where I is the electrical current through the wire and Re is thewire’s electrical resistance. I = 0.643 Solve the microscopic energy balance in the steel wire with a prescribed temperature Ts at the wiresurface, as well as the requirement that temperature be finite at the center of the wire, to find anexpression for the temperature at the center of the wire in terms of the surface temperature Ts . Use yourresult to estimate the electric current at which the wire begins to melt.

The resistance wire of a heater is composed of nichrome (a nickel-chromium alloy), completely surrounded by a 1/8 in (k = 0.15 BTU / h ft ºF) layer of asbestos, and this in turn, surrounded by another layer of 1/8 in.thick stainless steel (k = 10 BTU / h ft ºF). If the core temperature of the wire is kept constant at 1000 F, the convective heat transfer coefficient is 3 BTU / hft ºF, and the ambient temperature is 70 ºF. Calculate: a) The heat flux delivered to the wire in BTU / h ft^2 b) The outside temperature of the wire in ºF

Heat transfer is of critical importance in various industrial applications, including manufacturing. During machining, both the cutting tool and the workpiece will be significantly heated by friction heating. The heating of the cutting tool will reduce the tool hardness and strength, deteriorate the cutting quality, and shorten the tool life. Therefore, it is essential to prevent the overheating of the cutting tool during machining. Coolants are an instrumental part of machining to help cool the tool and the workpiece, provide lubricant, flush away chips, and prevent corrosion. The task of this project is to design the coolant to maintain the maximum machine tool temperature below 100 °C during the side milling process. As shown in the figure below, the machine tool has a diameter of 10 mm (D) and a length of 5 cm. The tool material is M2 high speed tool steel (T11302) and the workpiece is aluminum 6061. The spindle speed (w) is 2000 RPM and the cutting speed (v) is 50 mm/min. The feed…