Why is it necessary for the double top plate of the exterior wall that is assembled first to be held short at each end by the thickness of the adjoining wall?
Select one:
a. to eliminate the possibility of error
b. because the double top plate of the adjoining wall ties the two walls together
c. to save material
d. to save time when assembling the walls

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?