Heat Extraction Efficiency Research Articles

High temperature heat extraction from counterflow porous burner

Energy extraction from an adiabatic regenerative porous burner is studied numerically. Steady state governing equations are solved to predict the fluid and thermal properties of the system. The temperature of heat extraction is varied from 300 K to 1300 K. The numerical simulation predicts the effect of efficiency of energy extraction on the location and extraction temperature of heat exchangers. Higher extraction temperatures tend to decrease the extracted energy and consequently raise the exhaust temperature of the burner. Two burner configurations are studied comparatively by changing the properties of the wall separating the incoming reactants from the exhaust gases. Out of the two materials used to study the effect of separation wall on energy extraction, the study predicts higher gains for alumina as compared to silicon carbide. The maximum heat extraction efficiency of 35% is reported for extraction at 1300 K when silicon carbide separation wall is used in the burner. Whereas for porous burner with alumina separation wall, 60% of the heat can be extracted at 1300 K.

High efficiency high temperature heat extraction from porous media reciprocal flow burner: Time-averaged model

The high temperature heat extraction from a porous media reciprocal flow burner (RFB) is studied numerically. In RFB, the air/fuel mixture flow direction is switched periodically to contain and sustain combustion. High temperature heat extraction is essential for the efficient operation of small electrical and thermal systems based on thermoelectric generators, Stirling engines and micro-turbines. In this paper, the efficiency of the heat extraction is studied for different extraction locations, temperatures and equivalence ratios. An 1-D time-averaged model is developed and validated to represent a RFB and to further predict the behavior of the burner. Optimization on the burner’s geometry is also performed to increase the heat extraction efficiency.

An Experiment on Heat Recovery Performance Improvements in Well-Water Heat-Pump Systems for a Traditional Japanese House

Concerns about resource depletion have prompted several countries to promote the usage of renewable energy, such as underground heat. In Japan, underground heat-pump technology has begun to be utilized in large-scale office buildings; however, several economic problems are observed to still exist, such as high initial costs that include drilling requirements. Further, most of the traditional dwellings “Kyo-machiya” in Kyoto, Japan have a shallow well. This study intends to propose an effective ground-source heat-pump system using the well water from a “Kyo-machiya” home that does not contain any drilling works. In previous research, it was depicted that the well-water temperature decreases as the heat pump (HP) is operated and that the heat extraction efficiency steadily becomes lower. In this study, an experiment is conducted to improve efficiency using a drainage pump. Based on the experimental results, the effect of efficiency improvement and the increase in the electric power consumption of the drainage pump are examined. It is indicated that short-time drainage could help to improve efficiency without consuming excessive energy. Thus, continuous use of the heat pump becomes possible.

Thermal management of machine compartment in a built-in refrigerator

In general a multi-door refrigerator machine compartment comprises of fan, condenser, compressor, control box, drain tray, and drain tubes. The performance of machine compartment depends upon the efficiency of heat extraction or heat exchange from heat generating components such as condenser and compressor. The efficiency of heat exchange can be improved by addressing two major factors, namely (1) Air bypass and (2) Hot air recirculation. The hot air recirculation in the machine compartment for builtin multi-door refrigerator configuration is the focus of this study. The results from Computational Fluid Dynamics (CFD) simulations show that efficiency of heat exchange for built-in application is lower than that for free-standing configuration. Recirculation of hot air and reduction in airflow are the two major factors which contribute towards the variation in machine compartment performance. The CFD simulations were coupled with Partial Factorial Design of Experiment (DoE) approach to systematically investigate the effect of variables such as (a) side gap and top gap between kitchen cabinetry and the refrigerator, (b) the baffle/flap (i.e. back and bottom of machine compartment) on the performance effectiveness of machine compartment. The results of the simulation provided critical design improvement directions resulting in performance improvement. Furthermore, the CFD simulation results were also compared to test data and the results compared favourably.

Numerical investigation of the efficiency of emission reduction and heat extraction in a sedimentary geothermal reservoir: a case study of the Daming geothermal field in China.

The utilization of geothermal energy is clean and has great potential worldwide, and it is important to utilize geothermal energy in a sustainable manner. Mathematical modeling studies of geothermal reservoirs are important as they evaluate and quantify the complex multi-physical effects in geothermal reservoirs. However, previous modeling efforts lack the study focusing on the emission reduction efficiency and the deformation at geothermal wellbores caused by geothermal water extraction/circulation. Emission efficiency is rather relevant in geothermal projects introduced in areas characterized by elevated air pollution where the utilization of geothermal energy is as an alternative to burning fossil fuels. Deformation at geothermal wellbores is also relevant as significant deformation caused by water extraction can lead to geothermal wellbore instability and can consequently decrease the effectiveness of the heat extraction process in geothermal wells. In this study, the efficiency of emission reduction and heat extraction in a sedimentary geothermal reservoir in Daming County, China, are numerically investigated based on a coupled multi-physical model. Relationships between the efficiency of emission reduction and heat extraction, deformation at geothermal well locations, and geothermal field parameters including well spacing, heat production rate, re-injection temperature, rock stiffness, and geothermal well placement patterns are analyzed. Results show that, although large heat production rates and low re-injection temperatures can lead to decreased heat production in the last 8years of heat extraction, they still improve the overall heat production capacity and emission reduction capacity. Also, the emission reduction capacity is positively correlated with the heat production capacity. Deformation at geothermal wellbore locations is alleviated by smaller well spacing, lower heat production rates, and smaller numbers of injectors in the well pattern, and by placing wells at locations with higher rock stiffness. Compared with the reference case with coal burning for heating purposes, the yearly emission reduction capacity can reach 1 × 107kg by switching to the direct utilization of geothermal energy in Daming field.

Highly efficient heat extraction by double diamond heat-spreaders applied to a vertical external cavity surface-emitting laser

We compare the heat extraction efficiency for a standard Vertical External Cavity Surface-Emitting Laser and the distributed Bragg reflector (DBR)-free structure employing a single and double diamond heat-spreaders, respectively. Both heterostructures grown by Molecular Beam Epitaxy employ two identical active regions designed for emission at 980 nm. We show that the thermal resistance has been decreased 15 times when there is no DBR and heat is extracted from both side of active region. For DBR-free laser no thermal rollover of power conversion characteristic was observed in the range of considered input powers.

Geochemical implications of production and storage control by coupling a direct-use geothermal system with heat networks

This paper outlines a method in which the heat production of a geothermal system is controlled in relation to the demand from a district-heating network. A model predictive control strategy is designed, which uses volume measurements in the storage tank, and predictions of the demand, to regulate the production of the geothermal system in real time. The implications of such time-varying production for the reservoir are investigated using a 2D reactive transport reservoir model. As a case study, the Groningen geothermal project is considered. The numerical data generated by the controller, in closed loop with a modelled district-heating network, are used as inputs for the reservoir simulations. The latter make use of discrete parameter analyses to evaluate the effect of pressure depletion, reservoir permeability, flow rate, re-injection temperature and injection pH on the geothermal reservoir, and also mitigate possible risks during development. Using a model predictive control does not create adverse geochemical effects in the reservoir; instead, the controller is able to improve the efficiency of the geothermal heat extraction. The findings pave the way for stronger integration between elements of heat networks and a more sustainable development of geothermal resources.

Proactive Thermal-Aware Resource Management in Virtualized HPC Cloud Datacenters

Clouds provide the abstraction of nearly-unlimited computing resources through the elastic use of federated resource pools (virtualized datacenters). They are being increasingly considered for HPC applications, which have traditionally targeted grids and supercomputing clusters. However, maximizing energy efficiency and utilization of cloud datacenter resources, avoiding undesired thermal hotspots (due to overheating of over-utilized computing equipment), and ensuring quality of service guarantees for HPC applications are all conflicting objectives, which require joint consideration of multiple pairwise tradeoffs. An innovative proactive thermal-aware virtual machine consolidation (involving allocations as well as migrations) technique is proposed to maximize computing resource utilization, to minimize data center energy consumption for computing, and to improve the efficiency of heat extraction. The capability to migrate virtual machines away from lightly-loaded servers in a thermal-aware manner opens up opportunity to improve resource consolidation over time and, hence, achieve the aforementioned goals. The effectiveness of the proposed technique is verified through experimental evaluations with HPC workload traces under single- as well as federated-datacenter scenarios.

Enhancing the efficiency of solar pond heat extraction by using both lateral and bottom heat exchangers

In this study, heat extraction from both the gradient and heat storage zones of a salinity-gradient solar pond (SGSP) has been evaluated. For this purpose, an experimental solar pond pilot plant was constructed in 2009 in Barcelona (Spain). The structure of the pond is a cylindrical tank of 3-m height and 8m diameter with a total area of 50m2. The main objective was to evaluate a heat-extraction system from the SGSP designed to enhance the system efficiency under different conditions. Thus, an in-pond heat exchanger covering all of the lateral wall area of the pond was installed, and its performance was compared with the traditional in-pond heat exchanger situated on the bottom of the pond. Heat extraction experiments were performed using both heat exchangers individually or both at the same time. The study covers the experiments performed at three different seasonal temperature conditions: winter (December), summer (July) and autumn (October and November). The variations of the temperature inside the pond during the heat extraction were measured and analyzed. The results demonstrated that the efficiency of the pond increases when the heat is removed from the lateral heat exchanger alone compared to either using the bottom heat exchanger or using both heat exchangers simultaneously.

Numerical Modeling of a Soil‐Borehole Thermal Energy Storage System

Core IdeasBorehole thermal energy storage is studied with a 3D transient fluid flow and heat transfer model.BTES heat extraction efficiency increases with decreasing soil thermal conductivity.BTES efficiency decreases with convective heat losses associated with high soil permeability.Borehole thermal energy storage (BTES) in soils combined with solar thermal energy harvesting is a renewable energy system for the heating of buildings. The first community‐scale BTES system in North America was installed in 2007 at the Drake Landing Solar Community (DLSC) in Okotoks, AB, Canada, and has since supplied >90% of the thermal energy for heating 52 homes. A challenge facing BTES system technology is the relatively low efficiency of heat extraction. To better understand the fluid flow and heat transport processes in soils and to improve BTES efficiency of heat extraction for future applications, a three‐dimensional transient coupled fluid flow and heat transfer model was established using TOUGH2. Measured time‐dependent injection temperatures and fluid circulation rates at DLSC were used as model inputs. The simulations were calibrated using measured soil temperature time series. The simulated and measured temperatures agreed well with a subsurface having an intrinsic permeability of 1.5 × 10−14m2, thermal conductivity of 2.0 W m−1°C−1, and a volumetric heat capacity of 2.3 MJ m−3°C−1. The calibrated model served as the basis for a sensitivity analysis of soil thermal and hydrological parameters on BTES system heat extraction efficiency. Sensitivity analysis results suggest that: (i) BTES heat extraction efficiency increases with decreasing soil thermal conductivity; (ii) BTES efficiency decreases with background groundwater flow; (iii) BTES heat extraction efficiency decreases with convective heat losses associated with high soil permeability values; and (iv) unsaturated soils show higher overall heat extraction efficiency due to convection onset at higher intrinsic permeability values.

Impact of coupled heat transfer and water flow on soil borehole thermal energy storage (SBTES) systems: Experimental and modeling investigation

A promising energy storage option is to inject and store heat generated from renewable energy sources in geothermal borehole arrays to form soil-borehole thermal energy storage (SBTES) systems. Although it is widely recognized that the movement of water in liquid and vapor forms through unsaturated soils is closely coupled to heat transfer, these coupled processes have not been considered in modeling of SBTES systems located in the vadose zone. Instead, previous analyses have assumed that the soil is a purely conductive medium with constant hydraulic and thermal properties. Numerical modeling tools that are available to consider these coupled processes have not been applied to SBTES systems partly due to the scarcity of field or laboratory data needed for validation. The goal of this work is to test different conceptual and mathematical formulations that are used in heat and mass transfer theories and determine their importance in modeling SBTES systems. First, a non-isothermal numerical model that simulates coupled heat, water vapor and liquid water flux through soil and considers non-equilibrium liquid/gas phase change was adopted to simulate SBTES systems. Next, this model was used to investigate different coupled heat transfer and water flow using nonisothermal hydraulic and thermal constitutive models. Data collected from laboratory-scale tank tests involving heating of an unsaturated sand layer were used to validate the numerical simulations. Results demonstrate the need to include thermally induced water flow in modeling efforts as well as convective heat transfer, especially when modeling unsaturated flow systems. For the boundary conditions and soil types considered, convective heat flux arising from thermally induced water flow was greater than heat transfer due to conductive heat flux alone. Although this analysis needs to be applied to the geometry and site conditions for SBTES systems in the vadose zone, this observation indicates that thermally induced water flow can have significant effects on the efficiency of heat injection and extraction.

Wellbore–reservoir coupled simulation to study thermal and fluid processes in a CO2-based geothermal system: identifying favorable and unfavorable conditions in comparison with water

Using CO2 as a heat transmission fluid to extract geothermal energy is currently considered as a way to achieve CO2 resource utilization and geological sequestration. As a novel heat transmission fluid, the thermophysical properties of CO2 are quite different from those of water. CO2 has many advantages, such as larger mobility and buoyancy resulted from the lower density and viscosity. This will reduce the consumption of pressure driving the circulation, and save the energy of external equipment. The cycle even can be achieved by siphon phenomenon under a negative circulating pressure difference. However, there are still some disadvantages for CO2 as the heat transmission fluid, such as small heat capacity, leading to a less heat at the same mass flow rate. At the same time, because of the lager expansion and compression coefficient for CO2, changes in temperature and pressure may cause a more complex flow and thermodynamic processes. The lager compressibility makes it possible to get high temperature at the bottom of the injection well, whereas the lager expansion coefficient makes the temperature drop rapidly along the production well. Therefore, how to scientifically control the production pressure to guarantee sufficient high temperatures at the head of production well and, thereby, improve the efficiency of heat extraction are the key issues needed to be further addressed. The geological and geothermal conditions correspond to the central depression of the Songliao Basin located in the Northest of China. This depression has a high geothermal gradient and heat flow. In this article, a classic idealized “five-spot” reservoir model coupled with wellbores is used for simulations and analyses. The objectives of the present work are: (1) to investigate the fluid flow and thermal processes of supercritical CO2 along the wellbore and in the reservoir, (2) to understand the heat-extracting mechanism, (3) to identify advantages and disadvantages of using CO2 as the heat transmission fluid, and (4) to provide a theoretical basis for the selection of heat transmission fluid.

Numerical studies on CO2 injection–brine extraction process in a low-medium temperature reservoir system

CO2 sequestration in deep saline formations has been proved to be an effective method for reducing greenhouse emissions into the atmosphere. However, pure sequestration of CO2 will add to the costs incurred by both industries and governments. A win–win method of CO2 injection and hot brine (water) extraction can become attractive to the investors, as it will not only increase the storage capacity of the injected CO2, but also offset the costs by selling and using the produced hot water for industrial, agricultural or household purposes. For instance, water from very hot geothermal reservoirs (T ≥ 150 °C) can be used for electricity generation in power plants and water from low-medium temperature reservoirs, the most predominant in natural systems, are more popular for direct use, e.g., in heating systems, household hot water, baths, aquaculture, etc. In this paper, low-medium geothermal reservoirs widely distributed in China, especially those in the Ordos Basin, were selected for the numerical case studies using TOUGH2MP with the ECO2N module for the simulations. Generally, simulation parameters were taken from the Ordos Basin, where the first full-integration CO2 sequestration project had been operated since 2010. The simulations in the base case study lasted 35 years, based on the lifespan of a normal geothermal project. Shallow re-injection systems were also considered to investigate the influence of thermal breakthrough, pressure perturbation, etc. Results show that injection of cold CO2 causes sharp decrease in temperature in the reservoir region near the injection well, which is enlarged with continuous injection. The region near the production well is dominated by different fluid phases during the CO2 driven process, including a single water phase, a two-phase fluid (water and CO2) and a phase of almost pure CO2. Results also show that the CO2 breakthrough lags far behind the pressure response in the geothermal production system. Before breakthrough, the injected CO2 pressurizes the reservoir, improving the overall performance of the geothermal reservoir. Furthermore, the heat extraction efficiency of CO2-based system is obviously higher than H2O-based system.

Performance prediction results of a 500 square metres Pondicherry salt gradient solar pond

Solar pond modelling studies (SGSP) have been made to predict the heat collecting pattern of the present 500 sq.m. solar pond with a pond perimeter of 90 m, on its annual storage zone temperature development. Periodically measured temperature and specific gravity dataset of the brine solution is observed at various depths of SGSP has been utilised to study the performance of the solar pond. The recorded temperature profiles of the SGSP have been utilised in the estimation of the solar thermal conversion efficiency of the SGSP. Transmission function, heat loss of the solar pond is estimated numerically during heat extraction period. Various heat extraction efficiency of the pond at steady state was presented. Experimental studies have been made on the SGSP to find its suitability for delivering a daily thermal load of 500 kWh.

Along‐axis hydrothermal flow at the axis of slow spreading Mid‐Ocean Ridges: Insights from numerical models of the Lucky Strike vent field (MAR)

AbstractThe processes and efficiency of hydrothermal heat extraction along the axis of mid‐ocean ridges are controlled by lithospheric thermal and permeability structures. Hydrothermal circulation models based on the structure of fast and intermediate spreading ridges predict that hydrothermal cell organization and vent site distribution are primarily controlled by the thermodynamics of high‐temperature mid‐ocean ridge hydrothermal fluids. Using recent constraints on shallow structure at the slow spreading Lucky Strike segment along the Mid‐Atlantic Ridge, we present a physical model of hydrothermal cooling that incorporates the specificities of a magma‐rich slow spreading environment. Using three‐dimensional numerical models, we show that, in contrast to the aforementioned models, the subsurface flow at Lucky Strike is primarily controlled by across‐axis permeability variations. Models with across‐axis permeability gradients produce along‐axis oriented hydrothermal cells and an alternating pattern of heat extraction highs and lows that match the distribution of microseismic clusters recorded at the Lucky Strike axial volcano. The flow is also influenced by temperature gradients at the base of the permeable hydrothermal domain. Although our models are based on the structure and seismicity of the Lucky Strike segment, across‐axis permeability gradients are also likely to occur at faster spreading ridges and these results may also have important implications for the cooling of young crust at fast and intermediate spreading centers.

A three-dimensional transient model for EGS subsurface thermo-hydraulic process

Understanding the subsurface thermo-hydraulic process in enhanced or engineered geothermal systems (EGS) is crucial to the efficiency of heat extraction and the sustainable utilization of geothermal reservoir. We present in detail a three-dimensional transient model for the study of subsurface thermo-hydraulic process during EGS heat extraction and demonstrate its capability through test simulations. Since this model considers the actual existence of local thermal non-equilibrium between rock matrix and fluid flowing in the porous heat reservoir during EGS heat extraction, the model results shed light on the local heat exchange in the reservoir. One other salient feature of this model is its capability of simulating the complete subsurface thermo-hydraulic process during EGS heat extraction, not only the thermo-flow in the reservoir and well boreholes, but also the heat conduction or transport in rocks enclosing the reservoir. The results obtained from the test simulations, though the considered reservoir is imaginary and homogeneously fractured, corroborate the capability and validity of the present model. Moreover, the model results from the specially designed triplet well EGS case indicate its superior heat extraction performance.

Integration of Carbon Geological Storage and Geothermal Energy Development in Low-Permeability Reservoirs

Carbon dioxide (CO2) has recently been considered as an alternative geothermal working fluid because of some favourable fluid dynamics and heat transfer properties compared to water. The concept, however, was initially proposed in the context of engineered geothermal systems (EGS). EGS has encountered considerable unfavourable conditions and socio-political issues. Consequently, use of the CO2sequestration site to recovery geothermal energy may be practical, so called CO2-plume geothermal (CPG) system. We have performed numerical simulations to study non-isothermal multiphase flow processes of CO2displacing water and behaviour of a CPG system in a low-permeability reservoir. A number of numerical simulations under various geological and pressure/temperature conditions are performed. The objective of this research is to (1) investigate the heat extraction efficiency using supercritical CO2in comparison with water, (2) evaluate favourable and unfavourable conditions for heat extraction.

A novel three-dimensional transient model for subsurface heat exchange in enhanced geothermal systems

Understanding the subsurface heat exchange process in enhanced geothermal systems (EGS) is crucial to the efficiency of heat extraction and the sustainable utilization of geothermal reservoir. In the present work we develop a novel three-dimensional transient model for the study of the subsurface heat exchange process in EGS. The novelty of this model is embodied by a couple of salient features. First, the geometry of interest physically consists of multiple domains: open channels for injection and production wells, the artificial heat reservoir, and the rock enclosing the heat reservoir, while computationally we treat it as a single-domain of multiple sub-regions associated with different sets of characteristic properties (porosity and permeability etc.). This circumvents typical difficulties about matching boundary conditions between sub-domains in traditional multi-domain approaches and facilitates numerical implementation and simulation of the complete subsurface heat exchange process. Second, the heat reservoir is treated as an equivalent porous medium of a single porosity, while we consider thermal non-equilibrium between solid and fluid components and introduce two sets of heat transfer equations to describe the heat advection and conduction for fluid in rock apertures and the heat conduction in rock matrix, respectively, thus enabling the simulation and analysis of convective heat exchange between rock matrix and fluid flowing in the apertures. Case study with respect to an imaginary EGS demonstrates the validity and capability of the developed model.

3D thermo-fluid MHD simulation of single straight channel flow in LLCB TBM

India is developing lead lithium cooled ceramic breeder (LLCB) blanket for its DEMO fusion reactor. The mock-up blanket (TBM), using this concept, will be tested in ITER for its tritium breeding and high-grade heat extraction efficiency. In this TBM, pressurized helium is used to remove the heat from first wall, top and bottom plates of TBM. The Pb–Li is used to extract heat from the breeder zones. The flow of Pb–Li with average velocity 0.1m/s inside the channel can be significantly modified due to MHD effects, which arise because of the presence of strong toroidal magnetic field. A numerical approach is established to capture this flow modification at higher Hartmann numbers (≥20,000). As a validation part of the developed code, MHD phenomenon is studied in 2-D square geometry and numerically obtained velocity profile is compared with available Hunt's analytical results. Thermo-fluid MHD analysis using this code, has been carried out for single rectangular duct of LLCB TBM. The heat transfer has been studied by keeping hot breeders at both sides of the flow channel. The results suggest modification in steady state MHD velocity profile as the liquid flows along the flow length. However, the temperature in various zone remains well within the maximum allowable limit.

Evaluation of the celite secondary concentration procedure and an alternate elution buffer for the recovery of enteric adenoviruses 40 and 41

The effective recovery of adenovirus from water is a critical first step in developing a virus occurrence method able to provide accurate data for risk assessments and other applications. During virus concentration, electropositive filters are typically eluted with beef extract, undergo secondary concentration using either an organic flocculation or polyethylene glycol (PEG) precipitation technique and are ultimately resuspended in sodium phosphate buffer. In this study, an alternative secondary concentration procedure using celite was optimized by identifying the optimal celite and elution buffer to use. Two elution buffers, sodium phosphate and 1× PBS, were evaluated for their impact on real-time PCR. Sodium phosphate produced high levels of PCR inhibition compared to 1× PBS and so 1× PBS was used in subsequent experiments. The two secondary concentration techniques that were tested with adenovirus 40 and 41 gave recoveries of 69% and 65% for the optimized celite method and 75% and 109% for the organic flocculation method, respectively. Fine particle, calcinated celites in combination with 1× PBS elution buffer were shown to be effective at concentrating adenovirus 40 and 41 during secondary concentration and their subsequent detection using PCR. Heat extraction efficiencies were compared to samples processed using a DNA extraction kit to address possible virus aggregation issues. Samples processed through DNA extraction were found to produce realistic adenovirus recoveries compared to exaggerated recoveries using heat extraction.