Because a sailboat cannot sail directly into the wind, and traveling straight downwind is usually slow, the shortest sailing
distance is rarely a straight line. thus sailboats tack upwind—the familiar zigzag course—and jibe downwind. a tactician's
decision of when to tack and where to go can determine the outcome of a race. describe the process of tacking a sailboat
as the wind shifts direction. sketch a block diagram depicting tills process.

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?