Energy Extraction Rate Research Articles

The evolution of sociopolitical complexity in prehistoric Hawaii: An assessment of the archaeological evidence

The sociopolitical system of late prehistoric Hawaii was among the most complex of any Oceanic chiefdom, as indexed by such characteristics as scale, rate of energy extraction, degree of functional specialization, and political hierarchy. Various anthropologists and archaeologists have advanced models of how this complex sociopolitical system developed out of an earlier Ancestral Polynesian society. Recent advances in Hawaiian archaeology have now begun to provide a wealth of data on the course of prehistoric change in the archipelago over some 1500 years and, thus, provide evidence which can be used to test alternative models of the evolution of sociopolitical complexity. This paper reviews the major alternative models that have been put forward and provides a synopsis of the archaeological evidence relevant to their testing.

Smith-Purcell free-electron laser.

We analyze the operation of a free-electron laser in an open periodic structure. When operated as an amplifier, it is shown that exponential gain can develop in such a device. An analytic expression for this gain is presented, and it is shown that this gain decays exponentially with the beam height above the grating; the gain dependence on the beam thickness is also analyzed. As the energy extraction rate is much higher in an exponential gain regime, we also investigate the operation of an oscillator based on the same concept. In this case, the Smith-Purcell radiation ``provides the startup'' through a feedback system. The latter consists of several mirrors, which are placed in such a way that (1) only a wave with the desired frequency develops and, at the same time, (2) small deviations in the wave parameters due to the wave-beam interaction do not cause deflection of the wave from the feedback loop. The minimal current needed to sustain oscillations is given in an analytical form. Numerical calculations show that this current is more than three orders of magnitude lower than that necessary for an oscillator which operates in an algebraic gain regime.

A non-convecting solar pond with a constant energy extraction rate

One of the applications in which a solar pond can be utilized is the industrial process heating. In many heating applications, the heat should be supplied at a constant rate and within certain specified temperature limits. In this paper, the possibility of using a solar pond for such a purpose is studied. The mathematical model presented in a previous paper is modified in the present case to meet the new requirements imposed by the nature of the load and is then used to predict the performance of the pond under these conditions. The idea of using a performance chart is presented. This chart can be used to facilitate obtaining the optimum dimensions of a pond intended for a certain heating application. As the numerical values of the results obtained depend on weather data that are location dependent, the chart given in this paper is for Benghazi, Libya (32.1°N). However, the method presented here can be used to construct a performance chart for any other location.

Honeybees maximize efficiency by not filling their crop

Honeybees often abandon non-depleting food sources with a partially filled crop. This behaviour does not maximise the net rate of energy extraction from the food sources, and thus contradicts predictions of some common models for central place foragers. We show that including the metabolic costs of transport of nectar leads to models that predict partial crop-loading. Furthermore, the observed crop loads of honeybees are less consistent with those predicted by maximization of delivery rate to the hive (net energetic gain/ unit time), than with those predicted by maximization of energetic efficiency (net energetic gain/unit energy expenditure). We argue that maximization of energetic efficiency may be an adaptation to a limited flight-cost budget. This constraint is to be expected because a worker's condition seems to deteriorate as a function of the amount of flight performed.

Maximum tolerable reservoir impedances for hot dry rock

The finite hydraulic impedance of the natural and artificial fractures that constitute the water flow paths in hot dry rock reservoirs is shown to influence the cost of generating electricity from such resources in two ways. First, pumps, and hence power, will be required to circulate water through the fracture system. Second, the pressure difference across the reservoir cannot be increased indefinitely to improve the energy extraction rate as too high a pressure at the injection borehole will cause unacceptable losses of the circulating water.

Optimal energy extraction from a hot water geothermal reservoir

An analytical decision model is presented for determining optimal energy extraction rates from hot water geothermal reservoirs when cooled brine is reinjected into the hot water aquifer. This applied economic management model computes the optimal fluid pumping rate and reinjection temperature and the project (reservoir) life consistent with maximum present worth of the net revenues from sales of energy for space heating. The real value of product energy is assumed to increase with time, as is the cost of energy used in pumping the aquifer. The economic model is implemented by using a hydrothermal model that relates hydraulic pumping rate to the quality (temperature) of remaining heat energy in the aquifer. The results of a numerical application to space heating show that profit‐maximizing extraction rate increases with interest (discount) rate and decreases as the rate of rise of real energy value increases. The economic life of the reservoir generally varies inversely with extraction rate. Results were shown to be sensitive to permeability, initial equilibrium temperature, well cost, and well life.

High-power MHD system combustor development testing

This paper describes some of the technical accomplishments of the most recently completed phase of a multiphase program to design, construct, and test a lightweight, high-power prototype portable MHD generator system. The main objective of this phase was to demonstrate the feasibility of hot-gas flow train components of high-performance, lightweight design. Significant advances in terms of such parameters as combustor heat release density, combustion efficiency, channel power density, and energy extraction rates were made. The combustion system has a high-performance, 160-element injector, and the channel was constructed using lightweight electrode frames and a high-strength, lightweight glass-fiber-wound composite outer wall structure. The test results are compared to the theoretical predictions and are evaluated in terms of their impact on the overall goals of the High-Power MHD Systems program. The evaluation indicated that the initial program goals are achievable performance levels.

Heat transfer measurements in the 1977 Kilauea Lava Flow, Hawaii

The September‐October 1977 eruption of Kilauea volcano, Hawaii, produced a river of basaltic lava which flowed for several days. A heat transfer probe containing two heat flux gauges measured the conduction‐dominant heat transfer rates from molten lava into a cold probe inserted in an eddy in the lava river. During a 5‐min test period the primary heat flux gauge indicated transient‐decaying conductiondominant heat fluxes ranging from 200 kW/m2 down to 50 kW/m2. A secondary heat flux gauge verified that convective heat flux rates, due to either natural or forced convection in the eddy, were of the order of 10 kW/m2 or less. Theoretical calculations of the expected conduction‐dominant heat transfer rates between the lava and the probe agree with the experimental data from the primary gauge to within an error of 20% or less. The type of information gained from this field experiment is useful in predicting such diverse things as potential energy extraction rates for heat exchangers in lava or magma as well as the thickness of the solid wall of the natural levee containing a lava flow. Future heat transfer experiments should investigate the low convection heat flux range (below 10 kW/m2) in eddys and the much higher forced‐convection heat flux range in the main channel of lava rivers.

Cretan windmills

A resurgence of interest in this type of windmill has occurred recently because of its design simplicity and low cost. With it a relatively high rate of energy extraction may be achieved from low-speed winds.

Theoretical study of hydraulically fractured penny‐shaped cracks in hot, dry rocks

AbstractA simple and analytical method of solving the problem of heat extraction from a penny‐shaped crack having both inlet and outlet holes is developed by using a two‐dimensional flow model when fluid is injected at a constant flow rate. Temperature distributions in both rock and fluid are obtained by taking into account the hydraulic and thermal growth of the crack. The outlet fluid temperature and energy extraction rate versus time are shown by some illustrative examples. Although the effect of thermal, contraction of rock upon the crack width is large, its influence upon flow rate and crack tip stress intensity factor is sufficiently small within the first several years so that the crack radius can be determined mainly by the mechanical deformation of, the rock.

Thermosyphon Models for Downhole Heat Exchanger Applications in Shallow Geothermal Systems

The analysis of downhole heat exchangers used to extract energy from relatively shallow geothermal wells leads to the consideration of several interesting problems of buoyancy-driven heat transfer in enclosures. This paper considers thermosyphoning through and around the wellbore casing which is perforated at two or more depths. Analytical models are developed for thermosyphoning in the cased well both with and without a heat exchanger installed. Theoretical results are compared with experimental values. These comparisons show that the observed energy extraction rates and flow rates through the well casing are possible with thermosyphoning as the only circulation mechanism within the well bore. The model with a heat exchanger installed is parametrically evaluated to illustrate the sensitivity of the model to estimated parameters and the effect of changes in design variables or constraints.

Power Extraction from Water Waves

Salter has demonstrated experimentally that a horizontal cylinder in the free surface of water can be a device to extract energy from the incident waves. This paper proposes a design which is based on the idea of a tethered-float breakwater, and gives the theoretical design criteria for maximum power extraction from a general floating cylinder with one or two degrees of freedom. It is shown that the rate of energy extraction must be equal to the rate of radiation damping and that the floating body must be made to resonate then for a body with one degree of freedom, the maximum efficiency at a given frequency can be at leastone half if the body is symmetrical about a vertical axis, and greater for an asymmetrical body. For a body with two degrees of freedom, all the wave power can be extracted. Hydrodynamical aspects of the controlled motion are examined. Viscous effects are ignored.

Foraging Efficiencies and Time Budgets in Nectar-Feeding Birds

We examined the relationship between time budgeting for major activities of nectar—feeding birds and the foraging efficiency (total energy intake divided by total energy spent foraging) required to maintain an energetically balanced, 24—h energy budget. The hyperbolic shape of the curve relating this “required foraging efficiency” to percent time foraging (percent of daylight hours) suggests that at low percent times for foraging a major change in foraging efficiency would be required to decrease substantially the time for feeding, whereas at low foraging efficiency small changes in foraging efficiency would produce major changes in time budgeting for foraging. For hummingbirds, which usually hover while foraging, and for sunbirds, which usually perch while foraging the required foraging efficiency increased at a given percent time for foraging with (1) decreasing body size, (2) decreasing day length, (3) lower average temperatures, and (4) increasing nonfeeding flying time (such as for feeding young and territorial defense). The sunbirds would require a higher foraging efficiency (all other conditions being equal) than hummingbirds because of their lower foraging costs per unit time. However, the generally lower extraction efficiency of hummingbirds, due to their higher costs for feeding, tends to balance their lower required foraging efficiency, resulting in foraging time budgets similar to those for sunbirds. Actual foraging efficiency of these nectar—feeding birds is an increasing function of energy available per flower. The asymptotic relationship of empirical measures of this "achieved foraging efficiency" and nectar volume obtained per flower derives from a combination of coast and benefit terms relating to (1) rate of energy extraction per flower, and (2) time spent not probing flowers on a foraging bout. This relationship suggests that at low initial nectar volumes substantially more foraging efficiency results from slight increases in average nectar volumes per flower, whereas at high initial volumes virtually no change occurs in foraging efficiency with similar nectar availability changes. Thus, slight increases of nectar availability per flower should produce no obvious change in percent—time foraging at high initial volumes, but a marked decrease in percent—time foraging at low initial volumes. Similarly, the benefits achieved from an equivalent increase in average nectar volumes per flower through additional defense costs are proportionately higher and increase faster at low initial volumes than at high initial volumes. The general concept of foraging efficiency, or profitability, seems to be an important component of theories dealing with prey selection, especially in relation to foraging time.

Extraction of Flow Energy by a Wing Oscillating in Waves

This paper attempts to investigate the possibility of extracting energy from surrounding flow by a two-dimensional hydrofoil oscillating through a gravity wave in water, or by an airfoil in gust. The greatest possible rate of energy extraction is obtained by the optimum mode of heaving and pitching of the hydrofoil, which is determined by the method of variational calculation of parameters. It is found that energy extraction is impossible if the incident flow is uniform, and becomes feasible only when the primary flow contains a wave component having a transverse velocity distribution normal to both the mean free stream and the wing span. When such waves of sufficiently large amplitude are present, not only flow energy but also a net mechanical power can be extracted from the surrounding flow.