Jeffrey M. Gordon

Thermodynamic modeling of reciprocating chillers

A simple model for predicting the performance of reciprocating chillers is developed. The basic irreversibilities that mitigate against fast and slow cooling rates are accounted for. The model proposed here is consistent with real performance data for 30 chillers that span a range of cooling rates from 30 to 1300 kW and, with adjustable parameters that characterize a particular chiller, is shown to be capable of reproducing actual performance data to within better than experimental uncertainty.

Predictive and diagnostic aspects of a universal thermodynamic model for chillers

Abstract There are fundamental aspects of chiller behavior—characterized by the chiller coefficient of performance as a function of cooling rate and coolant temperatures—that pertain to all refrigeration devices. We review, further develop, and validate against extensive experimental measurements a simple thermodynamic model that captures the universal aspects of chiller behavior. The model provides a procedure for predicting chiller performance over a broad range of operating conditions from a small number of selected measurements, as well as a diagnostic tool. The accuracy of the model is illustrated for reciprocating, centrifugal and absorption chillers. Universal aspects of chiller behavior are further illustrated with less conventional small-scale cooling devices such as thermoacoustic and thermoelectric chillers.

Centrifugal chillers: Thermodynamic modelling and a diagnostic case study

Abstract The diagnostic capability of a simple thermodynamic model for chiller performance is illustrated by a case study for a commercial, installed centrifugal chiller. Performance data were measured both prior to, and subsequent to, chiller maintenance that improved chiller efficiency. Using these experimental measurements, we show that the simple thermodynamic model, originally developed for reciprocating and absorption chillers, (1) succeeds in predicting the fundamental relation between coefficient of performance and cooling rate for the centrifugal chiller, and (2) permits a clear diagnostic analysis of heat exchanger fouling on chiller performance.

A general thermodynamic model for absorption chillers: Theory and experiment

Abstract A general thermodynamic model for cooling devices is derived and applied to absorption chillers. Observing that finite-rate mass transfer dominates irreversibilities in absorption chillers, we derive how chiller coefficient of performance should depend on cooling rate and key system variables. Model predictions are compared against performance data from journal articles, manufacturer catalogue data, and our own experimental measurements, with favourable results.

Experimental study of the fundamental properties of reciprocating chillers and their relation to thermodynamic modeling and chiller design

From detailed experimental measurements on commercial reciprocating chillers, the loss mechanisms that dominate chiller performance can be identified, quantified and incorporated into a general irreversible thermodynamic model for predicting chiller behavior. The data can also be used to demonstrate the weaknesses and inaccuracies of a host of endoreversible chiller models that have been presented, where the primary sources of internal dissipation have been ignored. We quantitatively establish the dominant contributions to chiller performance of internal irreversibilities, such as fluid friction in the compressor and evaporator, and of finite-rate heat transfer at the heat exchangers. Heat leaks are measured experimentally and shown to be close to negligible. The empirical wisdom that has evolved in the commercial production of reciprocating chillers, namely, that rated capacity operation corresponds to near maximum efficiency, is explained in terms of a general thermodynamic model. Taking account of constraints of heat exchanger size and cost, we use experimental data to show that simple thermodynamic modeling can account for the optimal designs that are produced by the chiller industry.

Achieving uniform efficient illumination with multiple asymmetric compound parabolic luminaires

Luminaire designs based on multiple asymmetric nonimaging compound parabolic reflectors are proposed for 2-D illumination applications that require highly uniform far-field illuminance, while ensuring maximal lighting efficiency and sharp angular cutoffs. The new designs derive from recent advances in nonimaging secondary concentrators for line-focus solar collectors. The light source is not treated as a single entity, but rather is divided into two or more separate adjoining sources. An asymmetric compound parabolic luminaire is then designed around each half-source. Attaining sharp cutoffs requires relatively large reflectors. However, severe truncation of the reflectors renders these devices as compact as many conventional luminaires, at the penalty of a small fraction of the radiation being emitted outside the nominal cutoff. The configurations that maximize the uniformity of far-field illuminance offer significant improvements in flux homogeneity relative to alternative designs to date.

Recent discoveries in the rich landscape of aplanatic optics

Aplanatic optics were invented over a century ago, motivated principally to achieve high-fidelity imaging in telescopes, microscopes and cameras. Aplanats are designed to completely eliminate the two leading orders of geometric aberration - spherical and comatic - and the simplest designs comprise two contours that can be reflective and/or refractive. Aplanats of high radiative efficiency can also approach the thermodynamic limit to flux concentration and light collimation - of particular value in nonimaging applications such as solar energy collection, light-emitting-diode collimation, and infrared technology. Recently, it was discovered that the original aplanatic mirrors and lenses cover only a small spot in a rich landscape of fundamental categories of optical devices, which opened a broad spectrum of powerful new designs. In this presentation we review these advances, and summarize the complete classification schemes that have now been elucidated for aplanats. They include examples of practical designs for achieving radiative transfer near the thermodynamic limit in flux concentration and irradiation applications, based on dual-mirror, dual-contour lens and lens-mirror combinations. The representative designs that are illustrated also include the most recent progress in Fresnel (faceted) aplanats, motivated by the quest for progressively more compact optical systems, as well as examples of hybrid designs – combining aplanats of different classifications for enhanced performance.