Refrigerant-134a enters the expansion valve of a refrigeration system at 120 psia as a saturated liquid and leaves at 20 psia. Determine the temperature and internal energy changes across the valve. Use data from the steam tables.

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?

An open feedwater heater operates at steady state with liquid entering at inlet 1 with t? = 40°c and pl = 1 .2 mpa. water vapor att2-200°c and p2 = 1.2 mpa enters at inlet 2. saturated liquid water exits with a pressure of pa 1.2 mpa. neglect heat transfer with the surroundings and all kinetic and potential energy effects, determine the mass flow rate of steam at inlet 2 if the mass flow rate of liquid water at inlet 1 is given as 2 kg/s.

The short distance from the objective lens to the object causes problems at high magnification. which of the following is the most serious? a. cleaning the object surface b. positioning the object c. reflection from the object surface. d. illumination of the object