Refrigerant R-123 at a pressure of 4 bars flows in an adiabatic and helicoidally coiled circular copper tube that has 10.0 mm inner diameter. The temperature of the refrigerant at inlet is −21°C....

Refrigerant R-123 at a pressure of 4 bars flows in an adiabatic and helicoidally coiled circular copper tube that has 10.0 mm inner diameter. The temperature of the refrigerant at inlet is −21°C. Assume that the axis of the coil is vertical, and the total length of the tube is 7 m. Also, for the helically coiled tube R_cl
= 35 cm and l_pch
= 3 cm.

Assume that a test with a mass flux of 125.0 kg/m²
·s is under way.

 a. Calculate the frictional and total pressure drops for the coil assuming that the coil is adiabatic.

b. How long would a straight tube with the same inner diameter have to be to cause the same frictional pressure drop as case a?

 c. For Part a, assume that the coil is subject to a uniform heat flux at its inner surface. What heat flux is needed to cause the refrigerant to reach saturation at exit?

d. In Part c, calculate the inner surface temperature of the tube at its exit. For simplicity, you can use heat transfer correlation(s) that are for UWT boundary conditions