ABSTRACT

The thermohydraulic effect of microstructuring of the heat transfer surfaces of plate heat exchanger was studied experimentally. The aim of this enhancement strategy is to raise the heat transfer coefficient for the evaporation and condensation of the refrigerant in a vapor compression cycle up to the same level as typical single-phase heat transfer coefficients, when water is used as a secondary fluid. This would result in a better overall heat transfer performance. Titanium herringbone corrugated plates with no microstructure, micro-bump structures created by press rolling and femtosecond-laser-produced microstructures were studied. At first studies of the microstructured plates were performed in a visualization setup using 380 × 380 mm corrugated plate segments. Heat transfer and pressure drop were measured for liquid single-phase flow and evaporation with low vapor quality (x < 0.1). For the single-phase situation, the heat transfer coefficient of the microstructured plates dropped up to 5%, depending on the mass flux, while the pressure drop is not affected. For the evaporation situation, the heat transfer coefficient increased by about 25%, while the pressure drop stayed unchanged within the measurement uncertainty range. A second set of experiments was performed in an industrial-sized vapor compression cycle using R134a with a 100 kW plate evaporator and a 150 kW plate condenser. The microstructured plates gave a very moderate increase of less than 10% in heat transfer within the condenser, but a strong increase of about 40% in the evaporator as compared to the smooth plates.

摘要

对板式换热器传热面微结构的热工水力效应进行了实验研究。这种增强策略的目的是将水用作二次流体时，将蒸汽压缩循环中制冷剂蒸发和冷凝的传热系数提高到与典型单相传热系数相同的水平。这将导致更好的整体传热性能。研究了无微结构的钛人字形波纹板、压延产生的微凸块结构和飞秒激光产生的微结构。起初，使用 380 × 380 mm 波纹板段在可视化装置中对微结构化板进行研究。测量了液体单相流和蒸汽质量低 (x < 0.1) 的蒸发的传热和压降。对于单相情况，微结构板的传热系数最多下降 5%，具体取决于质量通量，而压降不受影响。对于蒸发情况，传热系数增加了约 25%，而压降在测量不确定度范围内保持不变。第二组实验是在工业规模的蒸汽压缩循环中使用 R134a 和 100 kW 板式蒸发器和 150 kW 板式冷凝器进行的。与光滑板相比，微结构板在冷凝器内的传热增加了不到 10% 的非常温和的增加，但在蒸发器中增加了约 40%。