Refrigerant distribution effects on the performance of microchannel evaporators.
The performance of air to refrigerant heat exchangers can be affected greatly by both refrigerant and air flow distribution. Maldistribution of either fluid stream can lead to reduced heat transfer effectiveness of the heat exchanger and thus lower system efficiency and capacity. Microchannel evaporators are especially susceptible to refrigerant maldistribution as they typically have many parallel channels fed by a common header or manifold. This paper outlines general trends in refrigerant flow distribution in such evaporators taking into account various heat exchanger orientations. In addition, links between heat exchanger performance and refrigerant flow distribution characteristics in microchannel evaporators are made using both analytical and experimental methods. These results show that unification of the liquid refrigerant flow distribution in the evaporator can lead to quantifiable improvements in evaporator performance.
Distribution of air–water annular flow in a header of a parallel flow heat exchanger
The air and water flow distribution are experimentally studied for a heat exchanger composed of round headers and 10 flat tubes. The effects of tube protrusion depth as well as header mass flux, and quality are investigated, and the results are compared with previous 30 channel data. The flow at the header inlet is annular. For the downward flow configuration, water flow distribution is significantly affected by tube protrusion depth. For flush-mounted geometry, significant portion of water flows through frontal part of the header. As the protrusion depth increases, more water is forced to rear part of the header. The effect of header mass flux or quality is qualitatively the same as that of the protrusion depth. For the upward flow configuration, however, significant portion of water flows through rear part of the header. The effect of protrusion depth is the same as that of the downward flow. However, the effect of header mass flux or quality is opposite to the downward flow case. Compared with the previous 30 channel configuration, the present 10 channel configuration yields better flow distribution. Possible explanation is provided from flow visualization results.
First Along the River: A Brief History of the U.S. Environmental Movement
Chapter 1: Philosophical Foundations Chapter 2: The 1400s through the 1700s: Inhabiting a New Land Chapter 3: The Early 1800s: Destroying the Frontier Chapter 4: The Late 1880s: Building an Industrial Nation Chapter 5: The 1900s through the 1930s: Beginnings of the Conservation Movement Chapter 6: The 1940s through the 1960s: Prelude to the Green Decade Chapter 7: The 1970s: The Conservation Movement Matures Chapter 8: The 1980s: A Conservative Backlash Chapter 9: The Early 1990s: Government Retrenchment and Public Apathy Chapter 10: The Environmental Movement in the Post-9/11 World Conclusion