In no more than two typed pages, describe the role, either for good or for bad, of the following in achieving energy sustainability: wind, solar, hydro, and wave-powered electricity,
cars that run on hydrogen fuel,
electric cars,
improvements in residential energy efficiency, and
government policies that mandate new technologies to improve motor fuel efficiency

The y form of iron is known as: a) ferrite b) cementite c) perlite d) austenite

Air is to be cooled in the evaporator section of a refrigerator by passing it over a bank of 0.8-cm-outer-diameter and 0.4-m-long tubes inside which the refrigerant is evaporating at -20°c. air approaches the tube bank in the normal direction at 0°c and 1 atm with a mean velocity of 4 m/s. the tubes are arranged in-line with longitudinal and transverse pitches of sl- st 1.5 cm. there are 30 rows in the flow direction with 15 tubes in each row. determine (a) the refrigeration capacity of this system and (b) pressure drop across the tube bank. evaluate the air properties at an assumed mean temperature of -5°c and 1 atm. is this a good assumption?

Different types of steels contain different elements that alter the characteristics of the steel. for each of the following elements, explain what the element does when alloyed with steel.