Your class is using engineering principles to improve the design of football helmets to prevent brain injury. your teacher divides you into groups and gives you various supplies (such as tape, bubble wrap, and foam) to create, design, and build a new helmet. which of these is a benefit of this type of project in stem education?

students become confident in working independently.
students participate and apply engineering principles.
students use household items to create new products.
students learn to follow steps provided by their teacher.

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?