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.
An Experimental Investigation of R134a Flow Distribution in Horizontal Microchannel Manifolds
This project aims to find correlations between various flow parameters and liquid refrigerant flow distribution within a horizontal manifold supplying two-phase R134a downward into fifteen aluminum microchannels. Liquid flow rates, system pressures, and refrigerant temperatures are recorded. Prior to this project, similar experiments were conducted using an identical manifold setup with water/air as the working fluid. Similarities and differences between the two working fluids are discussed. During refrigerant testing, inlet flow rates are varied between 15 g/s and 35 g/s. Inlet qualities vary between 0% and 35%. Manifold flow path geometry is varied by using three spacer plates of different thickness. Increasing mass flux at the entrance of the manifold improves liquid distribution through the microchannels. At sufficiently high mass fluxes, increasing quality at the entrance also improves liquid distribution. The distance between the manifold inlet and the array of microchannel tubes also has a large effect on liquid distribution.
Techno-economic analysis of chemical looping combustion with humid air turbine power cycle
Abstract Power generation from fossil fuel-fired power plant is the largest single source of CO2 emission. CO2 emission contributes to climate change. On the other hand, renewable energy is hindered by complex constraints in dealing with large scale application and high price. Power generation from fossil fuels with CO2 capture is therefore necessary to meet the increasing energy demand, and reduce the emission of CO2. This paper presents a process simulation and economic analysis of the chemical looping combustion (CLC) integrated with humid air turbine (HAT) cycle for natural gas-fired power plant with CO2 capture. The study shows that the CLC–HAT including CO2 capture has a thermal efficiency of 57% at oxidizing temperature of 1200 °C and reducer inlet temperature of 530 °C. The economic evaluation shows that the 50 MWth plant with a projected lifetime of 30 years will have a payback period of 7 years and 6 years for conventional HAT and CLC–HAT cycles respectively. The analysis indicates that CLC–HAT process has a high potential to be commercialised.