This article investigates the in-tube, superheated, saturated, and subcooled condensation of zeotropic refrigerant mixture R454C. R454C is proposed to replace R404A for commercial refrigeration applications. Quasi-local heat transfer coefficients were measured in a 4.7 mm horizontal tube at mass fluxes ranging from 100 to 500 kg m−2 s−1 at three different saturation...
The objective of this paper was to measure and compare the heat transfer coefficient and pressure drop of R404A and two potential replacement candidate refrigerants with a lower global warming potential, R448A and R452A. Experiments were conducted inside a 4.7 mm horizontal tube at mass fluxes ranging from 100 to...
There is growing interest to use supercritical carbon dioxide (sCO2) as a working fluid in thermal management applications. This study investigates the thermal-hydraulic performance of microchannel heat sinks as a function of flow channel geometry and orientation at operating conditions representative of electronics cooling applications. Three different experimental test sections,...
Heat transfer coefficients and frictional pressure drop values are experimentally measured during condensation of R134a and its proposed low global warming potential (GWP) replacement, R450A. R450A is a non-flammable zeotropic mixture of R134a and R1234ze (42/58% by mass). Experiments were conducted in a horizontal tube (ID = 4.7 mm) for...
Membrane based heat pumps systems have attracted the attention of many research groups as a potentially more environmentally friendly alternative to vapor compression systems for space cooling. Several prototype systems have been developed, with reported claims of Energy Efficiency Ratios (EER) approaching 26. At present, no detailed analysis is publicly...
In climate regions with large seasonal variations in solar radiation, such as the Pacific Northwest of the United States, a solar thermal energy collector might not economically satisfy year-round domestic water heating demands, requiring an auxiliary unit, such as a natural gas-fired water heater. Previous studies have shown that the...
Supercritical carbon dioxide (sCO2) experiences a drastic change in its thermophysical properties near the thermodynamic critical point. A non-linear thermophysical property variation can influence the heat transfer behavior of sCO2 which is not predicted well by conventional single phase heat transfer theory. This can become a major hindrance in the...
The advancement of additive manufacturing enables significantly greater freedom of design compared to conventional techniques. Of significant interest is the potential improvements in the design of cold plates and heat sinks for electronics cooling. Greater design freedom could enable new designs that reduce thermal resistance and hydraulic resistance, enabling the...
Concentrated solar power (CSP) plants have the potential to provide 24 h, renewable electricity. Current CSP systems have high capital and operational costs which makes the levelized cost of electricity uncompetitive with conventional techniques. Recent experimental research has shown the potential of small unit cells (up to 2 × 2 cm) containing micropin arrays...
Qualitative two-phase flow regime data are obtained from high-speed visualization of condensing flows of R-134a at mass fluxes from 75 to 150 kg m−2 s−1 and quality from 0.1 to 0.8 in square microchannels (DH = 0.84 mm) cooled from a single side. Superheated R-134a is distributed into multiple parallel microchannels and then partially condensed, using...