A1/10th scale model of an airplane is to be tested in a wind tunnel that operates with air at a pressure of 20 atmospheres. the plane is expected to fly at a speed of 500 [km/hr]. (a) what speed should the wind tunnel be run? (b) if the drag measured on the model is 337.5 [n], what is the corresponding drag on the full size airplane? recall that the viscosity is effectively independent upon pressure changes.

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?