Experimental investigations were conducted on condensation of R134a in annular helicoidal pipes with three orientations, 0°, 45° and 90°. The experimental results indicated that the refrigerant heat transfer coefficients increased with the increase of cooling water temperature, mass flow rates of refrigerant and cooling water, and decreased with the increase of saturation temperature of R134a. When the orientation increased from 0° to 90°, the refrigerant Nusselt number increased around 11% at refrigerant Reynolds number of 80, and around 16% at 200, the percentage increase of refrigerant Nusselt number from 0° to 45° accounted for more than two times of that from 45° to 90°. The performance of annular helicoidal pipe was evaluated by comparing with equivalent smooth straight pipe and identical helicoidal pipe.

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