Longitudinal vortex generation is a technique for enhancing heat transfer and can be accomplished byplacing small flow manipulators on the fin surface of a heat exchanger. This technique is of particular benefit inplain-fin-and-tube heat exchangers where the fin pitch is large (5-10mm) and the air-side convective coefficient issmall.In this study, a single row of delta-wing vortex generators is applied to a refrigerator evaporator with a finspacing of 8.5 mm both along the leading edge and at a location halfway along the flow length for a total of 108vortex generators. Heat transfer and pressure drop performance are measured before and after to determine theeffectiveness of the vortex generator under frosting conditions. Under lightly frosted conditions, reductions in airsidethermal resistance of 3.5% to 22.8% are achieved for face velocities of 0.45 m/s to 1.1 m/s. This heat transferenhancement monotonically increases with air velocity and results in a small pressure drop penalty that isincommensurate with the achieved enhancement. Maximum frost accumulation in the enhanced heat exchanger isalso examined for a single row of leading edge delta wings. Under these conditions, a reduction in the air-sidethermal resistance is observed that falls within the uncertainty of the experiment.Finally, a second, denser array of 324 vortex generators is examined for the same evaporator where thedelta wings are attached along four rows in an alternating single row, double row arrangement at core depth intervalsof 50.8 mm (2 in). For Reynolds numbers between 500 and 1200, a reduction of 35.0% to 42.1% is observed in theair-side thermal resistance. Correspondingly, the heat transfer coefficient is observed to lie between 26-51 W/m2-Kfor the enhanced evaporator and between 16-26 W/m2-K for the baseline evaporator. Two different performanceevaluation criteria are calculated and both show that the enhanced evaporator outperforms the baseline specimen forReynolds numbers greater than approximately 700-750. Tests conducted under maximum frosting conditions reveala diminished but statistically significant heat transfer enhancement.
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机译：纵向涡流产生是一种增强传热的技术，可以通过在热交换器的翅片表面上放置小流量操纵器来实现。该技术在翅片节距较大（5-10mm）且空气对流系数较小的普通翅片管式换热器中特别有用。在本研究中，使用了单排三角翼式涡流发生器总共有108个涡流发生器，在前缘和流动长度的一半位置处的翅片间距为8.5 mm的冰箱蒸发器。在结霜条件之前和之后测量传热和压降性能，以确定涡旋发生器的有效性。在轻度结霜的条件下，工作面速度在0.45 m / s至1.1 m / s的情况下，可将气室热阻降低3.5％至22.8％。该传热增强随空气速度单调增加，并导致较小的压降损失，这与所实现的增强不相称。对于单排前缘三角翼，还要检查增强型热交换器中的最大霜冻累积量。在这些条件下，观察到了空气侧热阻的降低，这在实验的不确定性之内。最后，对于同一蒸发器，检查了第二个密度更高的324个涡流发生器阵列，其中三角翼沿四行连接。芯深度间隔为50.8毫米（2英寸）的交替单排，双排布置。对于500至1200之间的雷诺数，空气侧热阻降低了35.0％至42.1％。相应地，对于增强型蒸发器，传热系数在26-51 W / m2-K之间，对于基线蒸发器，传热系数在16-26 W / m2-K之间。计算了两个不同的性能评估标准，并且两个标准都表明，对于大于大约700-750的雷诺数，增强型蒸发器的性能优于基线样品。在最大结霜条件下进行的测试表明，传热增强有所降低，但在统计学上显着。
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