Hydrogen is an increasingly attractive low-carbon energy carrier for a variety of stationary and mobile applications. Currently, the vast majority of hydrogen in the United States is produced via the energy intensive steam reforming of natural gas. The cost and carbon emissions associated with hydrogen production can be reduced by...
Large amounts of energy are wasted when conditioned air in buildings is exhausted to meet ventilation requirements. There are several technologies to recover some of this energy, including the recent development of membrane based energy recovery ventilators (ERVs). ERVs exchange sensible heat and moisture between incoming fresh and outgoing exhaust...
With the continued decrease in size and subsequent increase in power of computer processors, thermal management in electronics is becoming more important than ever before. The chip heat densities are reaching new peaks (> 100 W cm-2) that current cooling methods are not able to keep up with. However, some...
This work investigates the in-tube condensation of low global warming potential (GWP) zeotropic refrigerant mixtures R448A, R450A, R452A, R454B and R454C. These refrigerants have been proposed for a wide range of commercial heating, ventilation, air-conditioning applications, but their heat and momentum transport phenomenon were not well understood. Thus, in this...
Predicting condensation flow regimes and the associated heat transfer and pressure drop in microchannels is critical for designing terrestrial and space systems for heating, cooling, power generation, and advanced manufacturing. It is well established that in flows approaching the microscale (Dh < 1 mm) gravity-dominated flow regimes become less relevant,...
Seven decades of supercritical heat transfer research have not seen an attempt to characterize turbulent thermal transport in internal flows subject to asymmetric heating. Existing heat transfer models therefore do not account for phenomena that dictates thermal transport, in the proximity of the pseudo-critical point, for non-uniform heating. Additionally, past...
In the vicinity of the pseudocritical point, supercritical carbon dioxide (sCO₂) undergoes a steep change in properties from “liquid-like” to “gas-like” as it is heated at a constant pressure. At the same time, there is a large spike in specific heat which can yield high heat transfer coefficients and heat...
This work compares the condensation heat transfer and pressure drop for zeotropic refrigerant R-454C and its individual components, R-32 and R-1234yf, in horizontal microfin tubes. One microfin tube has a 4 mm outer diameter, 0.18 mm wall thickness, and a surface area ratio of 1.56. The second tube has a...
Waste-heat-recovery Organic Rankine Cycle (ORC) systems use excess heat from industrial processes to produce electrical power. In many cases, the temperatures and mass flow rates of these excess-heat streams vary significantly over time, causing the ORC to often operate far from its design point. In this study, a control strategy...
Membrane based heat pumps systems have attracted the attention of many research groups as a potentially more environmentally friendly alternative to vapor compression systems that are being used for space cooling in 90\% of the buildings in the United States. Several prototypes systems have been developed, with reported claims of...