Problem No.6 Coruna, Michael A Flores, Juan Paolo T. Madridejo, Jerome B. Punzalan, Mark Emile H.
Determine the optimum economic thickness of insulation that should be used under the following conditions: saturated steam is being passed continuously in a horizontal 1” Sch 40 steel pipe. The temperature of the steam is 180 o C, and the steam is valued at $0.0035/kg. The pipe is to be insulated with a material that has a thermal conductivity of 0.06 W/mK. The cost of the installed insulation per m of pipe length is $ 200x, where x is the thickness of the insulation in meters. Life of the installation is 10 years with time value of money equal to 15%. The total length of the pipe is 250 m, and the average temperature of the surroundings is 27 o C. Heat transfer resistances due to steam film, scale, pipe wall are negligible. The air film coefficient at the outside of the insulation may be assumed constant for all insulation thicknesses and given by the equation:
Solution Emissivity is assumed to be 0.9 because the type of material used for insulation is not given
Problem 15 <ul><li>An air cooler consisting of a bundle of 1.5” Sch 40 steel pipes enclosed in a well baffled shell is being built to cool 200 kg/hr of air from 80oC to 28oC. The air flows under pressure through the tubes of a 1-shell 2-tube pass heat exchanger. Cooling water at 18oC is under sufficient pressure to force it through at any desired rate, flows through the shell. The heat transfer coefficient based on the inside fluid is 50 W/m2K and for the outside fluid, 2100 W/m2K. Cooling water costs PhP 0.57/m3 and the annual fixed charges is 22% with cooler cost at PhP 24,000/m2. Calculate the Optimum exit temperature of cooling water and optimum length of tubes. </li></ul>