Showing papers by "Anthony M. Jacobi published in 1997"

An Entropy-Based, Air-Side Heat Exchanger Performance Evaluation Method: Application to a Condenser

Abstract: This paper describes the development of a straightforward, entropy-based method for evaluating air-side heat exchanger performance. Using energy conservation, the appropriate rate equations, and the second law of thermodynamics, all energy interactions were cast into their available- work equivalents with heat transfer rate limitations. The proposed method improved on previous techniques in two ways. First, it placed value explicitly on heat duty, recognizing system design constraints and external entropy generation. Second, it accounted for marginal entropy generation due to coupling between the system and the heat exchanger. The effects of the heat exchanger design on the system can cause significant exergy destruction and must be considered by any good performance measure. The proposed methods were applied to the evaluation of a condenser in a vapor-compression system. The condenser example is discussed here in detail, to explore design tradeoffs.

An Experimental Study of Flow and Heat Transfer in Wavy Passages

Abstract: Wavy passages are one of the many devices being considered by manufacturers in the HV ACIR industry to increase the air-side heat transfer coefficient for a variety of heat exchanger applications. The purpose of this research is to obtain a better understanding of the flow instabilities and heat transfer in wavy passages so that design guidelines may be developed. Flow visualization experiments on twelve different geometries revealed the flow patterns and behavior in laminar wavy-channel flow. At low Reynolds numbers, there is evidence of macroscopic mixing between the core flow and the near-wall fluid. The onset location of this macroscopic mixing moves closer to the entrance of the channel with increasing Reynolds number. The instabilities in the cp=180° geometry appear to be fundamentally different from the instabilities in the cp=O° and the cp=90° geometries. A parametric study revealed that for a given Reynolds number, instabilities in the cp=00 and the cp=90° geometries occur at a farther upstream location than in the cp=180° geometries. Relative wavelength did not affect channel performance in the experimental range. An increase in the relative amplitude of the channel delayed the intial onset of instability in the wavy passage, but had little effect as the location of the onset of instabiltiy moved closer to the entrance of the channel. Heat transfer experiments confirmed that the instabilities observed in the flow visualization experiments enhance heat transfer. The results of this research may help in determining wavy channel geometries with high heat transfer rates for a particular application.

Fundamental study of refrigerant-line transients: Part 1 - description of the problem and survey of relevant literature

Abstract: Dangerous pressure excursion incidents in industrial refrigeration systems have been caused by condensation-induced shock and vapor-propelled liquid slugging; however, some of the mechanisms responsible for initiating these hydraulic transients remain unclear. In this paper, simple descriptions of these shock-initiating conditions are given, and a thorough survey of the related technical literature is provided. The main contribution of this work is a literature database for practitioners and researchers interested in condensation-induced shock and vapor-propelled liquid slugging in refrigeration systems.

A fundamental study of refrigerant-line transients. Part 2: Pressure excursion estimates and initiation mechanisms

Abstract: Dangerous pressure excursion incidents have been associated with condensation-induced shock and vapor-propelled liquid slugging; however, some of the mechanisms responsible for initiating these hydraulic transients in industrial refrigerating systems are unclear. In a companion paper (part 1), an exhaustive compendium of the relevant literature was presented. In this paper, specific shock initiation mechanisms are described, an analysis for estimating the pressure excursion of a shock is presented, and a method for avoiding one possible path to hydraulic shock in refrigerating systems is presented.