Thermodynamics of energy extraction from fractured hot dry rock

Entropy generation minimization (finite time thermodynamics, or thermodynamic optimization) is the method that combines into simple models the most basic concepts of heat transfer, fluid mechanics, and thermodynamics. These simple models are used in the optimization of real (irreversible) devices and processes, subject to finite-size and finite-time constraints. The review traces the development and adoption of the method in several sectors of mainstream thermal engineering and science: cryogenics, heat transfer, education, storage systems, solar power plants, nuclear and fossil power plants, and refrigerators. Emphasis is placed on the fundamental and technological importance of the optimization method and its results, the pedagogical merits of the method, and the chronological development of the field.

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“…The optimal time-dependent strategy of running such a power plant ͑e.g., the optimal water flow rate͒ was developed in Ref. 196.…”

Section: Solar Power Plantsmentioning

confidence: 99%

Entropy generation minimization: The new thermodynamics of finite-size devices and finite-time processes

Bejan

1996

Journal of Applied Physics

1,702

605

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“…As pointed out by Lim JS et al [17], there exists an optimum geothermal mass flow rate at which heat energy is extracted from a given hot-dry-rock system to produce maximum net power output. In the extreme cases of faster and slower circulation of the geothermal fluid, the resultant exergy is much lower due to no temperature raise of the rapidly flowing geothermal fluid or the lower mass flow rate, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…Among others, Bejan [15] developed alternatives to thermodynamic performance and optimization of system subject to physical constraints such as entropy generation minimization (EGM), Yilmaz et al [16] conducted a second-law based performance evaluation criteria using both entropy and exergy as evaluation parameters to assess the performance of heat exchangers. An elaborated investigation on energy extraction from fractured hot-dry-rock was conducted by Lim JS et al [17] using the energy and exergy analysis. Their study determined under the effect of transient conduction, the optimum geothermal flow rate required to circulate water through the narrow fractures created in the subterranean hot-dry-rock bed to maximize the delivery of exergy over the lifetime of the hot-dry-rock system.…”

Section: Introductionmentioning

confidence: 99%

Design and optimization of a downhole coaxial heat exchanger for an enhanced geothermal system (EGS)

2013

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The present study considers the design, performance analysis and optimization of a downhole coaxial heat exchanger for an enhanced geothermal system (EGS). The optimum mass flow rate of the geothermal fluid for minimum pumping power and maximum extracted heat energy was determined. In addition, the coaxial pipes of the downhole heat exchanger were sized based on the optimum geothermal mass flow rate and steady state operation. Transient effect or timedependent cooling of the Earth underground, and the optimum amount and size of perforations at the inner pipe entrance region to regulate the flow of the geothermal fluid were disregarded to simplify the analysis. The paper consists of an analytical and numerical thermodynamic optimization of a downhole coaxial heat exchanger used to extract the maximum possible energy from the Earth's deep underground (2 km and deeper below the surface) for direct usage, and subject to a nearly linear increase in geothermal gradient with depth. The thermodynamic optimization process and entropy generation minimization (EGM) analysis were performed to minimize heat transfer and fluid friction irreversibilities. An optimum diameter ratio of the coaxial pipes for minimum pressure drop in both limits of the fully turbulent and laminar fullydeveloped flow regime was determined and observed to be nearly the same irrespective of the flow regime. Furthermore, an optimum geothermal mass flow rate and an optimum geometry of the downhole coaxial heat exchanger were determined for maximum net power output.Conducting an energetic and exergetic analysis to evaluate the performance of binary power cycle, higher Earth's temperature gradient and lower geofluid rejection temperatures were observed to yield maximum first-and second-law efficiencies.

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A study in forced convection of water in a single uneven planar rock fracture for geothermal application

Tso

Zhao

1994

Renewable Energy

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Thermodynamics of energy extraction from fractured hot dry rock

Cited by 9 publications

References 7 publications

Entropy generation minimization: The new thermodynamics of finite-size devices and finite-time processes

Entropy generation minimization: The new thermodynamics of finite-size devices and finite-time processes

Design and optimization of a downhole coaxial heat exchanger for an enhanced geothermal system (EGS)

A study in forced convection of water in a single uneven planar rock fracture for geothermal application

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