College of Engineering Technical Reports
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2540 Dole Street, Holmes 240
Honolulu, Hawaii 96822
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ItemCorrosion tests in Hawaiian geothermal fluids(National Research Council of Canada, 1984)Exposure tests were conducted in binary geothermal brine on the island of Hawaii. The steam which flashes from the high pressure, high temperature water as it is brought to ambient pressure contains substantial amounts of H2S. In the absence of oxygen this steam is only moderately aggressive but in the aerated state it is highly aggressive to carbon steels and copper alloys. The liquid after flashing is intermediately aggressive. The Hawaiian fluid is unique in chemistry and corrosion behavior; its corrosiveness is relatively mild for a geothermal fluid falling close to the Iceland-type resources.
ItemHawaii Geothermal Project : the effect of steady withdrawal of fluid in geothermal reservoirs(Hawaii Geothermal Project, University of Hawaii at Manoa, 1975)The problem of combined free and forced convection in geothermal reservoirs resulting from steady withdrawal of fluid is investigated numerically. The aquifer is confined by caprock on the top, heated by an impermeable surface at the bottom, and is recharged continuously from the ocean. The governing quasilinear partial differential equations in terms of pressure and temperature are approximated by finite difference equations which are solved numerically by iteration. Computations were carried out for both cylindrical and rectangular reservoirs for a selected set of parameters. It is found that the withdrawal rates and the location of the withdrawal site have a significant effect on heat transfer and fluid flow characteristics in a geothermal reservoir.
ItemHawaii Geothermal Project : the effect of dike intrusion on free convection in geothermal reservoirs(Hawaii Geothermal Project, University of Hawaii at Manoa, 1974)A perturbation analysis is made for the simultaneous heat and mass transfer in unconfined geothermal reservoirs with dike intrusion. The perturbation equations are of elliptic type that can be solved numerically by the finite difference method. Up to the second-order approximations are retained in the numerical computation. The effects of dike intrusion on streamlines, temperature distribution, and the shape of water table in two-dimensional aquifers with low permeability are shown.
ItemHawaii Geothermal Project : buoyancy induced flows in a saturated porous medium adjacent to impermeable horizontal surfaces(Hawaii Geothermal Project, University of Hawaii at Manoa, 1975)Boundary-layer analysis is performed for the buoyancy-induced flows in a saturated porous medium adjacent to horizontal impermeable surfaces. Similarity solutions are obtained for the convective flow above a heated surface or below a cooled surface, where wall temperature is a power function of distance from the origin. Analytical expressions for boundary layer thickness, local and overall surface heat flux are obtained. Applications to convective flow in a liquid-dominated geothermal reservoir are discussed.
ItemHawaii Geothermal Project : free convection about a vertical cylinder embedded in a porous medium(Hawaii Geothermal Project, University of Hawaii at Manoa, 1975)An analysis is made for free convective flow about a vertical cylinder embedded in a saturated porous medium, where surface temperature of the cylinder varies as xλ, a power function of distance from the leading edge. Within the framework of boundary layer approximations, exact solution is obtained for the special case where surface temperature varies linearly with x, i.e., λ = 1. For other values of λ, approximate solutions based on local similarity and local non-similarity models are obtained. It is found that the local similarity solutions are sufficiently accurate for all practical purposes. Analytical expressions for local surface heat flux and overall surface heat flux are obtained.
ItemHawaii Geothermal Project : similarity solutions for free convection about a dike(Hawaii Geothermal Project, University of Hawaii at Manoa, 1975)An analysis is made for steady free convection of groundwater about a hot dike trapped in an aquifer of infinite extent. Within the framework of boundary layer approximations, similarity solutions are obtained for a class of problems where wall temperature varies as xλ, i.e., a power function of distance from the origin where wall temperature begins to deviate from that of the surrounding groundwater. The uniform heat flux solution emerged as a special case with λ = 1/3. It is found that vertical velocity and the temperature profiles are of the same shape, and that the boundary layer thickness is proportional to the square root of the distance from the leading edge. Analytical expressions are obtained for boundary layer thickness, local and overall surface heat flux, as well as the local and average heat transfer coefficients. Some representative velocity and temperature profiles around a dike are also presented.
ItemHawaii Geothermal Project : numerical solutions for steady free convection in island geothermal reservoirs(Hawaii Geothermal Project, University of Hawaii at Manoa, 1975)The problem of steady free convection in an island aquifer, confined by caprock at the top and heated by an impermeable surface from below is considered. The governing non-linear partial differential equations are approximated by a set of finite difference equations, which are solved numerically by the iteration method. To guarantee convergence of the iteration process, the non-linear convective terms in the energy equation are approximated by the upwind difference scheme. The effects of thermal conditions at the caprock, the geometry of the reservoir, the variation of Rayleigh number, the length of the heating surface, and the magmatic intrusion, on fluid flow and heat transfer characteristics in island geothermal reservoirs are discussed.
ItemHawaii Geothermal Project : characteristics of vapor flashing geothermal plants(Hawaii Geothermal Project, University of Hawaii at Manoa, 1974)A study of the important parameters of a vapor flashing plant and characteristics of its major components is presented. The investigations by others showed that a steam and water mixture can be transported in a single pipe without the problems of water hammer, cavitation, and vibration, and that the pressure drop of a two-phase fluid can be determined using Lockhart and Martinelli correlation. The optimum flashing temperature has been calculated by numerical method, and the effects of wellhead pressure and number of stages on power output were analyzed. The design and operating features of a bottom outlet cyclone separator are given. The steam rates of a mixed pressure turbine for geothermal application were estimated in terms of the size, loading, throttle pressure and temperature, and condensing pressure. A procedure is described to determine the performance and size of an induced-draft, cross-flow cooling tower. By performing a simple heat balance calculation, effects of non-condensable gas content and condensing pressure on the net power output were determined. Finally, the possible arrangements of the heat rejection equipment and the factors involved in the selection of a plant site are discussed.
ItemHawaii Geothermal Project : a parametric study of a vertical heat exchanger designed for geothermal power plant application(Hawaii Geothermal Project, University of Hawaii at Manoa, 1974)The preliminary design of a vertical, counterflow, shell and tube heat exchanger for use in a binary fluid power cycle is presented. The heat exchanger is to be part of a representative geothermal power plant generating 10 MW utilizing geothermal brine at 350°F with isobutane as the working fluid. The computational procedure for determining heat transfer coefficients, tube lengths, number of tubes, and pressure drops is outlined. Detailed in graphical form are results of a parametric study showing how these four parameters are affected by changes in turbine inlet temperature, tube diameter, tube pitch, isobutane velocity, scale thickness, pinch point temperature difference, and system pressure.
ItemHawaii Geothermal Project :regenerative vapor cycle with isobutane as working fluid(University of Hawaii, 1974)Theoretical discussion of regenerative vapor cycle - binary - geothermal applications.