Flow Induced Noise Emanating from Evaporator Tube Plates

This work examines, objectively and subjectively, refrigerant noise induced by the flow of R134a through seven different plate-type automotive evaporator tubes with two tube heights and airflow depths ranging from about 45 mm to 75 mm. Experiments were conducted with both superheated and two-phase refrigerant without and with heating, and without/with lubricant. Measurements of tube surface acceleration were used to quantify flow induced acoustic phenomena.

Flow velocity is found to be the critical variable influencing the surface acceleration. Only three types of evaporator tubes consistently whistle above certain threshold velocities. Two other types of tubes produce sporadic, inconsistent whistling, while the remaining two types of tubes never whistle.

Half tubes have little influence on acoustic resonance.Adiabatic two-phase flows through a tube never produce resonance. Heat addition to two-phase refrigerant causes only the three resonating tubes to whistle at lower flow velocities, but the amplitude of the surface acceleration is extremely variable. Lubricant generally decreases the magnitude of surface acceleration and completely damps out resonance at oil concentrations exceeding 4% by mass.