Lifecycle cost analysis of an insulated duct with an air gap.

The insulation materials are used to reduce heat loss to/from the ducts with additional investment. This study introduces an air gap between insulation and duct surface to reduce the quantity of insulation. It uses lifecycle cost (LCC) analysis to determine the economic benefits of the air gap, considering four insulation materials for insulating the duct and natural gas as an energy source for chiller operation. The preliminary data regarding design and operating parameters were obtained from a renowned pharmaceutical company. The duct's annual energy loss was estimated for given operation hours in a year using the preliminary data and ambient conditions. The estimated energy loss through the duct was fed in LCC analysis to determine the impact of the air gap on optimum insulation thickness (OIT) corresponding to the minimum LCC and payback period. Results revealed that OIT thickness for a duct with an air gap was lower than insulated duct without an air gap, resulting in maximum cost savings within a shorter payback period. Among different insulation materials, insulated duct with expanded polystyrene was investigated as cost-effective insulation material with maximum cost savings of USD (508.8-766.8)/m/year and a payback period of 1.15-1.17 years. On the contrary, the air gap was the most effective in terms of cost savings for the ducts insulated with rock wool. In conclusion, an air gap is a cost-effective design approach for duct applications.

Thermochemical Nitriding and Oxynitriding of Ti Alloys.

Nitrided and oxynitrided coatings that formed on α alloy (c.p.-Ti), near-α alloy (Ti-2.1Al-2.5Zr), (α + ß) alloy (Ti-6Al-4V), and ß alloy (Ti-6Al-2Zr-1Mo-1V) were microstructurally characterized. The nitriding at 950 °C and PN2 ═ 105 Pa for 5 h formed TiN, Ti2N, and α-Ti(N) layers from the surface. The nitriding tendency increased in the order of ß alloy, (α + ß) alloy, near-α alloy, and α alloy. The Ti-N coatings transformed to Ti-N-O coatings when the nitrided alloys were exposed to PO2 ═ 10-2 Pa during cooling at the final stage of the nitriding. This oxynitriding process led to the formation of TiNxO1-x, Ti2N, and α-Ti(N,O) layers from the surface where a small amount of rutile-TiO2 coexisted. Oxynitriding was more effective than nitriding in increasing the surface microhardness, with the former accumulating more compressive residual stress than the latter.