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. This allows the new correlation to account for the varying fluid properties (including surface tension) that are found in the different refrigerants. The new correlation takes flow regime into account by means of a Weber number based flow transition criteria, following the flow map of Akbar et al. (2003).

Visualizations of adiabatic two-phase refrigerant flow in a glass channel of diameter 0.5 mm have been made for three refrigerants: R134a, Propane (R290), and Ammonia (R717), representing a wide span of fluid properties, which covers most of the refrigerants commercially in use. In these visualizations four flow regimes were observed: bubble-slug, slug, slug-annular, and annular. These flow regimes were compared to various flow maps, including some developed for small channels. Flow visualizations were also made with mixtures of R134a and 68-weight POE oil at oil circulation rates of approximately 0.5, 1.5 and 3 percent. This is of interest when considering refrigeration systems, which have a small percentage of oil in circulation that travels through system and through the heat exchangers. When the refrigerant is in a liquid state, this presents little variation in fluid properties, because the concentration is so small. However, when the refrigerant is partly vapor, the oil concentration in the remaining liquid can have significant effect on the fluid properties. In addition, the saturation temperature and pressure of the oil-refrigerant mixture changes with concentration, where a single-phase vapor is never observed in flows of oil-refrigerant mixtures, even at temperatures exceeding the saturation temperature of the pure mixture. This effect is known as “apparent superheat”.

A downward blowing isothermal wall jet at moderate Reynolds numbers (1,500 to 8,500) with significant inflow turbulence (ca. 6%) was investigated. The flow configuration is an idealization of the air curtains of refrigerated display cases. Flow visualization using particle seeding was employed to identify the flow field eddy dynamics. Particle Image Velocimetry was used to examine the velocity fields in terms of mean and fluctuating values. These diagnostics showed that the air curtain entrainment was dominated by a large variety of eddies that engulfed ambient air into the air curtain. The velocity fields generally showed linear spreading, significant deceleration and high turbulence levels (ca. 25%). It was observed that the air curtain dynamics, velocity fields and growth were not significantly sensitive to Reynolds number variation between Re=3,800 and Re=8,500. However, at low air velocities (Re=1,500), the curtain was found to detach, leading to a large air curtain thickness and high curtain entrainment.

This paper describes guided inquiry investigations of thermodynamic properties and cycles that was used in a sophomore thermodynamics class. A partially-complete computer model of a Carnot cycle was provided to students that was written in Engineering Equation Solver (EES). The students were led through a investigation in pairs or groups using the model designed to familiarize the students with the software as well as the cycle. As part of the investigation, the students were required to modify the model to add features. Following the in-class exercise with the Carnot cycle, students were required to model a Stirling cycle and later a Brayton cycle using the same EES software for a take-home project. In previous classes, the same (and similar) take-home projects were assigned, but this was the first time that these computer projects were preceded by a guided inquiry investigation. The advantages of using such a guided inquiry investigation to introduce the software were primarily evident from the questions that were avoided on the take-home projects, but also evident from the student performance on the projects themselves. A discussion of the investigation is included, as well as critique of what will be changed for the next time the class is taught.