Modeling of Residential Attics with Radiant Barriers

This paper gives a summary of the efforts at ORNL in modeling residential attics with radiant barriers. Analytical models based on a system of macroscopic heat balances have been developed. Separate models have been developed for horizontal radiant barriers laid on top of the insulation, and for radiant barriers attached to the bottom of the top chords of the attic trusses. The models include features such as a radiation interchange analysis within the attic space, convective coupling with the ventilation air, and sorption/desorption of moisture at surfaces facing the attic enclosure. The paper gives details of the models and the engineering assumptions that were made in their development. The paper also reports on the status of efforts that are underway to verify the models by comparing their predictions with the results of laboratory and field tests on residential attics and test cells, both with and without radiant barriers. Comparisons are given for a number of selected sets of experimental data. Suggestions are given for needed model refinements and additional experimental data. Plans for utilization of the models for extrapolation to seasonal and annual performance in a variety of climatic conditions are also described

Excitation Energy Dependence of the Exciton Inner Ring

We report on the excitation energy dependence of the inner ring in the exciton emission pattern. The contrast of the inner ring is found to decrease with lowering excitation energy. Excitation by light tuned to the direct exciton resonance is found to effectively suppress excitation-induced heating of indirect excitons and facilitate the realization of a cold and dense exciton gas. The excitation energy dependence of the inner ring is explained in terms of exciton transport and cooling.Comment: 5 pages, 4 figure

Measurement techniques and instruments suitable for life-prediction testing of photovoltaic arrays

Array failure modes, relevant materials property changes, and primary degradation mechanisms are discussed as a prerequisite to identifying suitable measurement techniques and instruments. Candidate techniques and instruments are identified on the basis of extensive reviews of published and unpublished information. These methods are organized in six measurement categories - chemical, electrical, optical, thermal, mechanical, and other physicals. Using specified evaluation criteria, the most promising techniques and instruments for use in life prediction tests of arrays were selected

Mechanical properties of wood-derived silicon carbide aluminum-alloy composites as a function of temperature

The mechanical behavior [i.e., stiffness, strength, and toughness (K_(IC))] of SiC Al–Si–Mg metal–ceramic composites (50:50 by volume) was studied at temperatures ranging from 25 to 500 °C. The SiC phase was derived from wood precursors, which resulted in an interconnected anisotropic ceramic that constrained the pressure melt-infiltrated aluminum alloy. The composites were made using SiC derived from two woods (sapele and beech) and were studied in three orthogonal orientations. The mechanical properties and corresponding deformation micromechanisms were different in the longitudinal (LO) and transverse directions, but the influence of the precursor wood was small. The LO behavior was controlled by the rigid SiC preform and the load transfer from the metal to the ceramic. Moduli in this orientation were lower than the Halpin–Tsai predictions due to the nonlinear and nonparallel nature of the Al-filled pores. The LO K_(IC) agreed with the Ashby model for the K_(IC) contribution of ductile inclusions in a brittle ceramic

Transplant Thought-Experiments: Two costly mistakes in discounting them

‘Transplant’ thought-experiments, in which the cerebrum is moved from one body to another, have featured in a number of recent discussions in the personal identity literature. Once taken as offering confirmation of some form of psychological continuity theory of identity, arguments from Marya Schechtman and Kathleen Wilkes have contended that this is not the case. Any such apparent support is due to a lack of detail in their description or a reliance on predictions that we are in no position to make. I argue that the case against them rests on two serious misunderstandings of the operation of thought-experiments, and that even if they do not ultimately support a psychological continuity theory, they do major damage to that theory’s opponents

Evaluation of Foamseal ceiling panels in the large scale climate simulator under winder conditions. Phase I

This report serves to document Phase I of tests on ceiling panels fabricated by Foamseal Urethane Technology, Inc. in the Large Scale Climate Simulator (LSCS). The work reported here was accomplished during August, 1991

Superinsulation in refrigerators and freezers

The results presented here were obtained during Phase 4 of the first CRADA, which had the specific objective of determining the lifetime of superinsulations when installed in simulated refrigerator doors. The second CRADA was established to evaluate and test design concepts proposed to significantly reduce energy consumption in a refrigerator-freezer that is representative of approximately 60% of the US market. The stated goal of this CRADA is to demonstrate advanced technologies which reduce, by 50%, the 1993 National Appliance Energy Conservation Act (NAECA) standard energy consumption for a 20 ft{sup 3} (570 L) top-mount, automatic-defrost, refrigerator-freezer. For a unit this size, the goal translates to an energy consumption of 1.003 kWh/d. The general objective of the research is to facilitate the introduction of efficient appliances by demonstrating design changes that can be effectively incorporated into new products. In previous work on this project, a Phase 1 prototype refrigerator-freezer achieved an energy consumption of 1.413 kWh/d [Vineyard, et al., 1995]. Following discussions with an advisory group comprised of all the major refrigerator-freezer manufacturers, several options were considered for the Phase 2 effort, one of which was cabinet heat load reductions