Efficiency with which a power source transforms the potential heat of its fuel into work or output, expressed as a ratio of the useful work done by the power source in a given time interval to the total heat energy contained in the fuel burned during the same time interval, both work and heat being expressed in the same units.
1. Same as thermodynamic efficiency. 2. In climatology, an expression of the effectiveness of temperature in determining the rate of growth, assuming sufficient moisture. The idea was introduced by B. E. and G. J. Livingston (1913). It was applied by C. W. Thornthwaite (1948) in his system of climatic classification. The recognition of this general concept led to one of the first uses of the degree-day, that is, application to plant growth and relationship to the phenological effective temperature of about 42Â°F. Compare precipitation effectiveness. Livingston, B. E., and G. J. Livingston, 1913: Temperature coefficients in plant geography and climatology. Botanical Gazette, 56, 349â€“375. Thornthwaite, C. W., 1948: An approach toward a rational classification of climate. Geogr. Review, 38, 55â€“ 94.