Korean Journal of Air-Conditioning and Refrigeration Engineering (설비공학논문집)

The Society of Air-Conditioning and Refrigerating Engineers of Korea (대한설비공학회)
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Effect of Oil on Pool Boiling of Refrigerant on Enhanced Tubes having Different Pore Sizes

다공도가 다른 전열촉진관의 냉매 풀비등에 미치는 오일의 영향

  • Published : 2006.03.01
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Abstract

The effect of enhanced geometry (pore diameter, gap width) is investigated on the pool boiling of R-123/oil mixture for the enhanced tubes having pores with connecting gaps. Tubes with different pore diameters (and corresponding gap widths) are specially made. Significant heat transfer degradation by oil is observed for the present enhanced tubes. At 5% oil concentration, the degradation is 26 to 49% for $T_{sat}=4.4^{\circ}C$. The degradation increases 50 to 67% for $T_{sat}=26.7^{\circ}C$. The heat transfer degradation is significant even with small amount of oil (20 to 38% degradation at 1% oil concentration for $T_{sat}=4.4^{\circ}C$), probably due to the accumulation of oil in sub-tunnels. The pore size (or gap width) has a significant effect on the heat transfer degradation. The maximum degradation is observed for $d_p$ = 0.20 mm tube at $T_{sat}=4.4^{\circ}C$, and for $d_p$=0.23 mm tube at $T_{sat}=26.7^{\circ}C$. The minimum degradation is observed for $d_p$=0.27 mm tube for both saturation temperatures. It appears that the oil removal is facilitated for the larger pore diameter (along with larger gap) tube. The highest heat transfer coefficient with oil is obtained for $d_p$ =0.23 mm tube, which yielded the highest heat transfer coefficient for pure R-123. The heat transfer degradation increases as the heat flux decreases.

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References

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