An experimental study of turbulent forced convection heat transfer to water flowing in a vertical annular passage is reported in this paper. The study investigates the influence of eccentricity (ranging from 0% to 80%) and diameter ratio (ranging from 1.5 to 4.0) upon the heat transfer phenomena occurring at the inner boundary of the annular passage. Dimensionless heat transfer parameters calculated from measurements made at the two locations corresponding to the maximum and minimum separation of the inner and outer boundaries of the annular passage are correlated in terms of the Reynolds number, the eccentricity and the diameter ratio. Analysis of the correlations indicates that eccentricity affects the heat transfer phenomena occurring at the two locations on the inner boundary of the annular passage in different fashions; increasing eccentricity causes the heat transfer to increase at the location corresponding to the maximum separation of the boundaries and causes the heat transfer to decrease at the location corresponding to the minimum separation of the boundaries. The magnitude of the increase or decrease in heat transfer is dependent upon the diameter ratio; at a particular level of eccentricity, the greater variations in heat transfer occur at the smaller diameter ratios. Ranges in which eccentricity does not influence heat transfer are found in connection with the larger diameter ratios. Moody friction factors calculated from measurements made with concentric annular passages are correlated as a function of Reynolds number. / Thesis / Master of Engineering (ME)