Choose all of the two-phase material systems from the list below. (a) Solid ductile cast iron (ferrite solid solution + embedded graphite spheres)
(b) Solid sodium chloride (salt, NaCl)
(c) Liquid bronze (Cu + Sn liquid solution)
(d) Solid gray cast iron (ferrite solid solution + embedded graphite flakes)
(e) Solid aluminum featuring dissolved silicon
(f) Solid lead-tin solder (a mixture of Pb-rich and Sn-rich solid solutions)
(g) Partially melted aluminum
(h) Frozen water with trapped air bubbles
(i) Epoxy embedded with carbon fibers

Fluids at rest possess no flow energy. a)- true b)- false

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?

Coiled springs ought to be very strong and stiff. si3n4 is a strong, stiff material. would you select this material for a spring? explain.