Cold Ocean Water Research Articles

Potential environmental impact of open-cycle thermal energy conversion

Ocean Thermal Energy Conversion (OTEC) is a power-generating system that uses the temperature difference between warm surface water in the tropical ocean and the cooler water at depth to run a Rankine-cycle heat engine. For the temperature difference typically available in the upper 1000 meters in tropical and subtropical waters, 20-25C, energy extraction efficiencies are low, two to four percent (Dugger et al. 1981), compared to conventional steam generation plants. Because of the low efficiencies involved, large flows of ocean water (the fuel in an OTEC system) are required: about 10 m3/sec per megawatt (DOE 1979a). Two OTEC operating cycles are currently under development in the United States at Argonne National Laboratory, Argonne, Illinois and at the Solar Energy Research Institute at Golden, Colorado: closedand open-cycle. Because the technology is highly experimental, most of the technical details have not yet appeared in the literature. In closed-cycle systems a low-boiling point working fluid (ammonia or Freon) is evaporated by warm surface waters. The vapor is expanded to drive a turbine. The expanded vapor is then condensed by cooler deep ocean water and returned to the warm side. In open-cycle operations warm surface water is used as the working fluid. Surface sea water is introduced into a evaporator under partial vacuum separating the sea water into steam and brine. The steam, after passing through a turbine, is condensed using cold ocean water. Several configurations for OTEC plants have been considered to date: freefloating plants (grazing and moored), bottom-resting facilities (at various distances from shore), and shore-based plants. The floating and far-offshore con-

Dolomitization by Ground-Water Flow Systems in Carbonate Platforms: ABSTRACT

Dolomite occurs throughout the subsurface of modern carbonate platforms such as the Bahamas. Groundwater flow systems must be responsible for delivery of reactants needed for dolomitization. Reflux, freshwater lens flows, and thermal convection are large-scale flow systems that may be widespread in active platforms. I have evaluated some End_Page 1219------------------------------ aspects of the dynamics and characteristics of these processes with ground-water flow theory and by scaled sandbox experiments. Reflux is not restricted to hypersaline brines, but can occur with bankwaters of only slightly elevated salinity such as those found on the Bahama Banks today (42 ^pmil). The lack of evaporites in a stratigraphic section, therefore, does not rule out the possibility that reflux may have operated. Flows associated with freshwater lenses include flow in the lens, in the mixing zone, and in the seawater beneath and offshore of the lens. Upward transfer of seawater through the platform margins occurs when surrounding cold ocean water migrates into the platform and is heated. This type of thermal convection (Kohout convection) has been studied by Francis Kohout n south Florida. The ranges of mass flux of magnesium in these processes are all comparable and are all sufficient to account for young dolomites beneath modern platforms. Each process yields dolomitized zones of characteristic shape and location and perhaps may be distinguishable in ancient rocks. The concepts presented here may have application to exploration for dolomite reservoirs in the Gulf Coast and elsewhere. End_of_Article - Last_Page 1220------------

The exergy of the ocean thermal resource and analysis of second-law efficiencies of idealized ocean thermal energy conversion power cycles

We develop a fomula here to compute the maximum amount of work which can be extracted from a given combined mass of warm and cold ocean water (a quantity called the exergy of the ocean thermal resource). We then compare the second-law efficiencies of various proposed ocean thermal energy conversion power cycles to determine which best utilizes the exergy of the ocean thermal resource. The second-law efficiencies of the multicomponent working fluid cycle, the Beck cycle, and the open and closed single- and multiple-stage Rankine cycles are compared. These types of OTEC power plants are analyzed in a consistent manner, which assumes that all deviations from a plant making use of all the exergy (one with a second-law efficiency of 100%) occur because of irreversible transfer of heat across a finite temperature difference. Conversion of thermal energy to other forms is assumed to occur reversibly. The comparison of second-law efficiencies of various OTEC power cycles shows that the multistage Rankine open cycle with just three stages has the potential of best using the exergy of the ocean thermal resource.

Geothermal regimes of the Costa Rica Rift, east Pacific, investigated by drilling, DSDP-IPOD Legs 68, 69, and 70

Drilling durin Deep Sea Drilling Project Legs 68, 69, and 70 on the southern limb of the Costa Rica Rift was used to study geothermal processes in the ocean crust. Two areas were drilled. One was a geothermally hot site on 6.2-m.y.-old crust, where topography is smooth, heat flow is close to that predicted by conductive cooling of the lithosphere (200 mWm −2 ), and hydrothermal circulation may be sealed within the crust. The other was on 3.9-m.y.-old crust, where rough topography is associated with low heat flow (15 to 50 mWm −2 ) and possible open convection of sea water. At both sites, about 250 m of siliceous-calcareous sediments overlies igneous basement. In the hot area, it blankets the topography, whereas in the cold area, basement outcrops still occur. Operations included numerous down-hole experiments in both areas and hydraulic piston coring of a 230-m sediment section in the hot area. Diagenesis of the sediments appears closely related to temperature. At the hot site, chert was found near basement, and the chemistry of pore fluids, sampled from both sediments and basement, is strongly influenced by reactions within the basement. Strong lateral gradients in the composition of pore fluids occur in the sediments. At the cold site, no chert was found, and bacterial processes within the sediment dominated the chemistry of the pore fluids. Basaltic basement in both areas consists mainly of pillow lavas and thin flows, with occasional more massive units. The basalt is relatively magnesian. The degree of alteration is very small in the cold area, but much more extensive in the hot area. Ease of drilling also shows a strong contrast. Basement penetration reached 562 m in the hot area and was halted because of lack of time; at the cold site, 43 m of basement was cored only with difficulty. The most intensive in-hole experiments were conducted in the hot area. Successful runs with the borehole televiewer allowed basement lithology to be determined and showed the presence of more and less fractured zones. Pulse tests using a single borehole packer gave values of basement permeability of about 2 to 40 millidarcies. Numerous temperature logs established a broadly conductive in situ temperature gradient, with temperatures reaching 120 °C at 562 m into the basement. However, anomalously low temperatures in the upper part of the hole, which persisted after drilling disturbance had decayed away, showed that cold ocean water was flowing down the hole and into the basement at about 90 m below the base of the sediments, at rates of about 80 to 100 m/hr. The packer records indicate a pressure at this depth of ∼ 10 bars below hydrostatic. Costa Rica Rift United Scientific Team, made up of shipboard participants on Legs 68/501, 69 and 70, who were, in reverse alphabetical order:

Hydrothermal convection at slow-spreading mid-ocean ridges

The discrepancy observed between measured heat flow data and the heat flow predicted by thermal models of mid-ocean ridges is commonly explained by the presence of hydrothermal convection in young oceanic crust. Numerical modelling of fluid flow through porous media has been used to investigate what permeability, depth of penetration and mass fluxes are necessary to produce conductive heat flow distributions compatible with observed heat flow data at spreading centers. The results presented here were calculated for oceanic crust between 0 and 2 m.y. old at a mid-ocean ridge with a half-spreading rate of 1 cm/yr. The calculations show that theoretical and observed heat flow near mid-ocean ridges can be brought into better agreement if non-uniform rather than uniform permeability is assumed in the oceanic crust. If the crustal permeability is uniform, the percentage of heat flow values (⩾25%) which are increased by upwelling flow above the predicted values is significantly higher than that observed at mid-ocean ridges (<10%). If — due to faulting, for example — zones of high permeability exist in crust of low permeability, upwelling flow can be concentrated and the area of increased heat flow can be greatly reduced. In the latter case, the percentage of sea floor near mid-ocean ridges (⩾90%) where heat flow is depressed below the predicted values corresponds well with observed heat flow distributions near active spreading centers. Average temperatures in crust with hydrothermal convection are considerably lower than those in purely conductive crust. This difference in average temperatures should result in crestal offsets at mid-ocean ridges. The observation that crestal offsets attributable to convective cooling are not larger than 50 m suggests that the depth of penetration of convection strong enough to produce conductive heat flow compatible with observed heat flow distributions is less than 5 km in crust younger than 2 m.y. The downward flow of cold ocean water into the sea floor greatly reduces conductive heat flow. The magnitude of this inflow and hence the degree of heat flow reduction depends on the average permeability of the oceanic crust. Comparison of heat flow measurements from the FAMOUS area and from the Galapagos Spreading Center to heat flow over downwelling areas in our models indicates that the average permeability (including faults or high permeability zones) in young oceanic crust is not larger than 2.5 millidarcy. Finally, the integrated mass flux through sea floor between 0 and 2 m.y. old was found to be approximately 4 · 10 6 g yr −1 (cm of ridge). If this mass flux is considered representative for spreading centers and if older crust is included into the calculations, a total mass of ~1 · 10 17 g yr −1 is convected through the worldwide system of mid-ocean ridges.

Ear canal hyperostosis--surfer's ear. An improved surgical technique.

The increased populatiry of surfing has produced a marked augmentation in the incidence of ear canal exostosis. However, when it becomes moderately severe, I prefer to call it "hyperostosis." Exposure to cold ocean water for many years can be an important etiologic factor in hyperostosis. There is a serious risk, and a high incidence of tympanic membrane perforations during the removal of large external canal hyperostosis. This injury can be prevented by placing a sheet of Silastic against the tympanic membrane beforehand. I describe the method. Serious degrees of hyperostosis, causing transient hearing loss and otitis externa, are increasingly common in coastal towns, where cold-water surfing is a popular year-around sport.

Effect of behavioral variables on cooling rate of man in cold water.

Five different behaviors of man while in cold ocean water (9-10 degrees C) were assessed for their effect on rate of progress into hypothermia. With subjects wearing lifejackets, two thermally protective behaviors were studied which reduce exposure to the water of areas of body surface with high relative heat loss potential. One was huddling of three persons and the other a self-huddle behavior (HELP or Heat Escape Lessening Posture). These two behaviors resulted in significant reductions of rectal temperature cooling rate of 66 per cent and 69 per cent, respectively, of that of a control behavior. With no flotation available, two survival swimming behaviors (treading water and drownproofing) were shown to result in significant increases in cooling rate to 134 per cent and 182 per cent, respectively, of the control behavior. Potential swimming distance of subjects wearing a life-jacket was 0.85 miles in water near 12 degrees C before predicted incapacitation by hypothermia. It was concluded that behavioral variables can be of major importance in determining survival time in cold water through modulation of cooling rate associated with other variables such as fatness, body size, and clothing.

Thermal balance and survival time prediction of man in cold water.

Metabolic rates and rectal temperatures were continuously monitored for humans immersed in cold ocean water (4.6--18.2 degrees C) under stimulated accident conditions. The subjects wore only light clothing and a kapok lifejacket while either holding-still or swimming. While holding-still, metabolic heat production (Hm,kcal-min--1) was inversely related to water temperature (Tw, degrees C) according to the equation Hm equals 4.19 minus-0.117 Tw. This temperature response pattern is shown to be similar to that for exposure to air of the same temperature when air velocity is just over 5 m.p.h. (2.24 m/s). The thermogenic response was one-third efficient in balancing the calculated heat loss in cold water, resulting in hypothermia at a rectal temperature cooling rate (C, degrees C-min--1) dependent on water temperature (Tw, degrees C) according to the relation C equal 0.0785 - 0.0034Tw. Although swimming increased heat production to 2.5 times that of holding-still at 10.5 degrees C water temperature, cooling rate was 35% greater while swimming. A prediction equation for survival time (ts, min) of persons accidentally immersed in cold water (Tw, degrees C) has the form ts equal 15 + 7.2/(0.0785-0.0034Tw), based on the findings of this study, and it is compared to pre-existing models.

Sea Grant: Four Years Later

After four full years of operation of Sea Grant Program, an oceanic imitation of century-old Land Grant Program, four universities have been named Sea Grant Colleges: Rhode Island, Oregon State, Washington and Texas AM enjoyment and use of our marine resources; new sources of food; and new means for development of marine through programs for research, education and training of skilled manpower and advisory services. There is no question that program is an active one. More than 400 scientific reports have been issued to date, encompassing every conceivable aspect of lake and marine conservation and exploitation. Since 1968, $40 million has been invested in projects in 27 states, Virgin Islands and District of Columbia. Currently, Sea Grants finance some 547 projects, 457 of them under institutional grants to 13 colleges and universities. These projects cover areas of fisheries and aquaculture, ocean engineering, coastal zone resources management, marine pharmacology and pharmaceuticals, pollution, ecological studies, mineral resources, marine and coastal zone law and economics, biological oceanography, seafood science and technology, management and preservation of environment, man in sea, and physical and chemical oceanography. Published reports cover such subjects as acoustic techniques of estimating fish populations, wave forces on submerged structures, sand mining on continental shelf, extending shipping season on St. Lawrence Seaway. Among its more spectacular accomplishments are discovery and identification of mineral deposits in Great Lakes valued at over $300 million, first commercial harvest of cultured shrimp, and a system to use deep, cold ocean water as an aquacultural nutrient source. The program also has solid Federal support. Robert White, head of National Oceanic and Atmospheric Administration, which manages program, says that NOAA attaches the highest priority to Sea Grant Program, pointing out that, once having been allocated $15 million (a $2 million increase over its base in President's budget), Sea Grant Pro-. gram has never been considered for any cut-the only program in all of NOAA SO favored. In fact, Congress tacked on an additional $2.5 million. In spite of all this, Madison conferees seemed unelated. In sessions on coastal zone programs, ocean engineering, aquaculture, legal-economic aspects of fisheries, and advisory services, most of time was devoted to discussion of problem or subject in general; question of Sea Grant's potential contribution was answered in only very general terms. In legal-problems area, for example, it was decided to continue support of scientific research, develop new programs to send results to users, study institutional barriers to effective national fisheries policy (such as archaic state laws), analyze fishing industry interests from point of view of individual fisherman, and provide inputs to national policy and to

Groundwater Flow and Geothermal Regime of Florida Plateau: ABSTRACT

Temperature surveys in oil-exploratory wells indicate that the geothermal profile underlying the Floridan Plateau is modified anomalously to a negative geothermal gradient (i.e., the ground water becomes colder) to a depth of about 3,000 ft below sea level. The anomaly is related to cold ocean water below the thermocline in the Gulf of Mexico and the Florida Straits. At 3,000 ft below sea level the ground water has a temperature of about 70°F near the edge of the deep sea water bodies, and warms to more than 108°F toward the central axis of the Floridan Plateau. The horizontal and vertical temperature distributions suggest the possibility that cold, dense sea water flows inland through the cavernous dolomite in the deep part of the aquifer where it progressively becomes heated by upward geothermal heat flow. The reduction in density produces an upward convective circulation which brings the sea water into contact with fresh water recharged through sinkholes in the karst region of central Florida. The mixing with fresh water further reduces the density and the diluted salt water then flows seaward and discharges by upward leakage through confining beds into shallow aquifers and thence back to the sea or by discharge through submarine springs on the continental shelf and slope. End_of_Article - Last_Page 2165------------