Harold Stimson And Nathan Osborne - Water Power

Thermodynamic Properties of Water and Steam for Power Generation
In the early 1900s, the electric power generation industry was experiencing rapid growth and change. The steam engines used for power in the previous century had been displaced by turbines which generated electricity as they were rotated by pressurized steam generated in boilers. Turbines and boilers were operating at highertemperatures and pressures (and also in increasingly complex cycles, which required more sophisticated thermal design and analysis) in order to attain greater thermodynamic efficiency. They were also becoming larger as the demand for electricity skyrocketed. A major source of growing pains for the industry was the lack of accurate and standardized values for the properties of water and steam. For thedesign of power plants and the boilers and turbines within them, it is necessary to have accurate values of thermodynamic quantities such as the vapor pressure (pressure at which water boils at a given temperature) and the enthalpy of vaporization or latent heat (amount of heat required to generate steam from liquid water). More important, the evaluation of the performance of purchased equipmentdepends on the calculation of these properties. The efficiency of a turbine is measured as the fraction of the energy available in the steam that is converted to electricity, but that available energy is calculated to be a different number depending on the values used for the thermodynamic properties. A turbine might appear to be 28 % efficient with one set of properties and only 27 % efficient withanother set; because of the large flows involved, these small differences could mean large sums of money. It therefore became imperative to settle on internationally standardized values for the properties of water and steam, so that all parties in the industry could have a “level playing field” on which to compare bids and equipment performance. The paper Calorimetric Determination of theThermodynamic Properties of Saturated Water in both the Liquid and Gaseous States from 100 to 374 C [1] describes the accurate measurements carried out at NBS that were essential in reaching agreement on the needed standards. In the United States, this problem was first addressed in 1921 by a group of scientists and engineers brought together by the American Society of Mechanical Engineers (ASME). The1921 meeting led to the formation of the ASME Research Committee on Thermal Properties of Steam. This committee, recognizing the 49 need for reliable data, collected subscriptions from industry and disbursed the money to support experimental measurement of key properties of water and steam at Harvard, MIT, and the Bureau of Standards. Because the ASME committee was not as successful in theirfundraising as they had hoped, all three institutions ended up subsidizing some of the research themselves in recognition of its importance. The need for standard, reliable data was also recognized in other countries (notably England, Germany, and Czechoslovakia), and research efforts were coordinated internationally. In the late 1920s and early 1930s, three international conferences were held with thepurpose of agreeing on standardized values for the properties of water and steam. This culminated in 1934 with the adoption of a standard set of tables, covering the range of temperatures and pressures of interest to the power industry at that time. These tables gave the vapor pressure as a function of temperature, values of the volume and enthalpy for the equilibrium vapor and liquid phases alongthe vapor-pressure curve, and volumes and enthalpies at points on a coarse grid of temperatures and pressures. Each value had an uncertainty estimate assigned to it. The data those tables were based on also became the basis for a book of “Steam Tables” produced by J. H. Keenan and F. G. Keyes [2]; the Keenan and Keyes tables were the de facto standard for the design and evaluation of steam power...