Journal of Energy Engineering

In 1987, the Tennessee Valley Authority (TVA) authorized a comprehensive review of reservoir operating priorities that had been followed since 1933. The purpose was to ensure optimum operation of the reservoir system, recognizing that needs, demands, and values change over time. The review resulted in a five-year, $50 million program to improve the quantity and quality of releases from 20 dams in the Tennessee Valley. TVA worked with state and federal resource agencies to define minimum flow and dissolved oxygen targets for each tailwater. Facilities and operating procedures were designed and installed to meet the target conditions. This paper describes the facilities, operating procedures, and performance of the reservoir release improvements. Alternative approaches, monitoring requirements, operational problems, and costs are discussed. Results from four years of operation are presented.

This paper investigates the susceptibility of soil to liquefaction using a probabilistic approach. In order to determine the factor of safety against the potential for liquefaction, a Monte Carlo approach to the probabilistic determination of liquefaction is used instead of the traditional deterministic approach. In the proposed approach, variability is considered in the properties of the soil and in the control motion. Final results are given in terms of probability of occurrence. The approach described in this paper is applied to a homogeneous sand profile and to an actual site with a soil profile that includes both sand and clay. Parameters that may be significant for the occurrence of liquefaction are investigated for these particular examples.

The improvement in performance of a double pipe heat exchanger fitted with twisted tape as a turbulence promoter with twist ratios of 15.649, 8.54, 5.882, 4.95, and 4.149 was experimentally studied. A maximum percentage gain of 44.7% in energy transfer rate was obtained for the twisted tape of twist ratio 4.149. For all twist ratios, the gain decreases with the Reynolds number and becomes constant for Reynolds numbers greater than 3,000. The smaller the twist ratio is, the larger the gain in energy for a specific Reynolds number.