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The interaction between electromagnetic waves and heat transfer phenomena due to microwave treatment is of utmost importance for an energy-efficient microwave-integrated grinding circuit. In this study, the effect of microwave irradiations on the heat absorptions of crushed particles is carried out by developing a numerical model. Crushed particles are simulated as diced-shaped geometries with different sitting arrangements but similar size distributions. The energy efficiency of the microwave treatment process is studied by introducing temperature-dependent dielectric properties and accounting for the convective heat loss from the particle boundaries to the surrounding environment. The simulations are quantitatively validated with the experimental results for heat over microwave efficiency. Heat absorption of larger particles is found to be significantly higher, and the arrangement of particles exerts a negligible effect on overall energy absorption. It is also found that ores with a larger average diameter can yield higher energy efficiencies, and the maximum absorption can be achieved by placing the particles at certain distances from the waveguide of the microwave. [ABSTRACT FROM AUTHOR]

One method to accelerate carbon sequestration within mine tailings from remote mines involves the injection of diesel generator exhaust into dry stack tailings. The techno-economic feasibility of this approach heavily depends on understanding the flow characteristics inside the perforated injection pipes embedded within the tailings. Two distinctive yet dynamically coupled transport phenomena were identified and evaluated: (i) gas transport inside the pipe and (ii) gas injection into the porous body of the tailings. This paper presents two models to investigate these transport phenomena, a three-dimensional (3D) and a one-plus-one-dimensional (1 + 1)D model. An experimental investigation of the pressure profile through the injection pipe was carried out to validate the models at the experimental scale. To apply the (1 + 1)D model to larger scales, the results were compared with those of the 3D model, as the (1 + 1)D model required significantly less computational resources and time. To include the effect of the perforations in the pipe on the pressure profile of the (1 + 1)D model, an analytical fluid velocity profile was developed in relation to geometric and physical parameters. The performance of the (1 + 1)D model with an impact factor was then evaluated against the 3D model results for the inlet pressure, pressure profile and gas outflow distribution under various conditions than those investigated experimentally. The developed (1 + 1)D model can be used to design an energy-efficient approach for large-scale implementation with a wide range of desired operating parameters. [ABSTRACT FROM AUTHOR]

Contemporary off-grid mining operations rely on diesel fuel for the provision of their total energy including electricity, heat, and haulage. Given the high cost of diesel and its imposed greenhouse gas emissions, mining companies are looking for more affordable and cleaner sources of energy for their operations. Although renewable energy systems, such as solar photovoltaic and wind provide efficient solutions to address this challenge, full decarbonization has shown to be very challenging, mainly due to the high cost of battery storage along with the inability to meet total site energy demand. Integrating hydrogen and thermal storage with battery banks can facilitate a full transitioning off diesel. In this sense, the present study intends to offer an innovative decarbonized solution by integrating wind turbines with a multi-storage system (battery, hydrogen, and thermal storage) to supply the total energy (electricity, heat, and haulage) for remote open-pit mines. Among the different proposed fully decarbonized configurations in this study, it is shown that a renewable system with a hydrogen-powered fleet and hybridized battery/hydrogen storage configuration can present the most economically viable case for open-pit mines with a considerably less life-of-mine cost. [ABSTRACT FROM AUTHOR]

Summary: Due to their relatively high thermal effectiveness and ease‐of‐use, direct contact heat exchange units are a favorable choice in heat recovery applications. Today, spray‐based direct heat exchangers are commonly used for a variety of applications, including evaporative cooling and heat recovery. Yet in spite of their versatility, these heat exchangers are not well‐understood, mainly due to their complex liquid/gas interactions, which may deem poorly‐designed systems as undesirable and infeasible. Spray nozzle height and type (hollow and full cone), droplet diameter distribution, inlet air velocity and humidity, and water spray velocity are key parameters required to establish a clear understanding of direct heat exchange performance. To better understand such a multivariable phenomenon, this article offers a comprehensive study of the impact of these key factors. The main purpose of this study is to evaluate the validity of two different methods proposed for evaluating the performance of heat and mass transfer in large‐scale direct contact heat exchangers, namely one‐dimensional and three‐dimensional approaches. The results of the present study show that while the one‐dimensional approach is able to capture the experimental data within 10% of agreement with experiment, the three‐dimensional approach reduces this error to 5%. In addition, this study aims to provide a framework to conduct future parametric studies with the goal of highlighting key performance factors understanding of which are a necessity for improved design of direct contact heat exchangers used in mine waste heat recovery applications. Novelty Statement: To investigate the performance of an industrial‐scale direct (spray) heat exchange system with a vertical configuration for application in mine waste heat recovery, two different models, namely; '1‐D' and '3‐D', are developed.Accuracy of two models in predicting heat transfer is evaluated through comparison with experimental data.A series of parametric studies are conducted to examine the impact of various operating parameters on the performance of heat exchange system. [ABSTRACT FROM AUTHOR]

With the increasing engineering applications of geothermal borehole heat exchangers (BHEs), accurate and reliable mathematical models can help advance their thermal design and operations. In this study, an analytical model with a time-dependent heat flux boundary condition on the borehole wall is developed, capable of predicting the thermal performance of single, double, and multiple closed-loop BHEs, with an emphasis on solar- and waste-heat-assisted geothermal borehole systems (S-GBS and W-GBS) for energy storage. This analytical framework begins with a one-dimensional transient heat conduction problem subjected to a time-dependent heat flux for a single borehole. The single borehole scenario is then extended to multiple boreholes by exploiting lines of symmetry (or thermal superposition). A final expression of the temperature distribution along the center line is attained for single, double, and multiple boreholes, which is verified with a two-dimensional finite-element numerical model (less than 0.7% mean absolute deviation) and uses much lesser computational power and time. The analytical solution is also validated against a field-scale experiment from the literature regarding the borehole and ground temperatures at different time frames, with an absolute error below 6.3%. Further, the thermal performance of S-GBS and W-GBS is compared for a 3-by-3 borehole configuration using the analytical model to ensure its versatility in thermal energy storage. It is concluded that our proposed analytical framework can rapidly evaluate closed-loop geothermal BHEs, regardless of the numbers of boreholes and the type of the heat flux on the borehole wall. [ABSTRACT FROM AUTHOR]

This study seeks to investigate the concept of using large waste rocks from mining operations as waste-heat thermal energy storage for remote arctic communities, both commercial and residential. It holds its novelty in analyzing such systems with an experimentally validated transient three-dimensional computational fluid dynamics and heat transfer model that accounts for interphase energy balance using a local thermal non-equilibrium approach. The system performance is evaluated for a wide range of distinct parameters, such as porosity between 0.2 and 0.5, fluid velocity from 0.01 to 0.07 m/s, and the aspect ratio of the bed between 1 and 1.35. It is demonstrated that the mass flow rate of the heat transfer fluid does not expressively impact the total energy storage capacity of the rock mass, but it does significantly affect the charge/discharge times. Finally, it is shown that porosity has the greatest impact on both fluid flow and heat transfer. The evaluations show that about 540 GJ can be stored on the bed with a porosity of 0.2, and about 350 GJ on the one with 0.35, while the intermediate porosity leads to a total of 450 GJ. Additionally, thermal capacity is deemed to be the most important thermophysical factor in thermal energy storage performance. [ABSTRACT FROM AUTHOR]

Summary: The geothermal potential available from deep underground mines has yet to be utilized. However, stope‐coupled heat exchangers (SCHE) are aiming to take advantage of the unused low‐grade geothermal energy. Backfilled stopes provide a unique opportunity to install nonlinear heat exchangers, as the geometry is not limited to the shape of a borehole. Helical pipes deliver superior fluid mixing and heat exchange compared to straight pipes, due to the effect of the secondary flow within the helical pipe. The helical closed‐loop geothermal heat exchanger enables the backfilled stopes of the mine to be repurposed as thermal energy storage units. This article delves into the experimental results from a unique state‐of‐the‐art laboratory scale helical closed‐loop heat exchanger with varying thermophysical parameters. Additionally, a novel conjugate numerical model is developed and its results are validated against the base case of the experimental studies. Additionally, the numerical model is validated in a spatial‐temporal sense with thermocouple data from the experimental rig. The numerical model is also applied to a helical SCHE situated within a backfilled stope for the first time. The results of the numerical model suggest that the pumping rate through the SCHE has a significant effect on the heat exchange rate and the overall energy transfer between the SCHE and the backfill. Additionally, the temperature contours from the numerical model suggest that a decreased pitch/helical diameter will increase the storage capacity of the helical SCHE. Overall, an average of 2.5 MW can be stored over the first 4 days of geothermal charging with the investigated full‐scale SCHE, boasting a pseudo‐steady‐state storage rate of 1.7 MW. [ABSTRACT FROM AUTHOR]

Double-pipe helical heat exchangers are integral to contemporary mechanical refrigeration equipment. Modification of flow geometry has been widely adopted to enhance heat transfer performance of a heat exchanger. The objective of this study is to numerically investigate heat transfer and entropy generation in a double pipe helical heat exchanger with various cross-sections. A computational model for laminar convective heat transfer was developed and validated against the results from previously published literature. To capture entropy generation, the entropy balance equation for open system is adopted. Effect of inner pipe Dean number, inner pipe and annulus inlet mass flow rate ratio, eccentricity, and flow configuration (co-flow and counter-flow) were examined and discussed in light of computational results. To ensure fair comparison, the considered geometries have same inner pipe cross-section area, same annulus cross-section area, and same outer surface area of inner pipe. The results suggest that square cross-section offers best performance in term of heat transfer, pressure drop and entropy generation. In addition, concentric configuration is more appropriate for low flow rate application while eccentric outer configuration is more suitable for high flow rate application. [ABSTRACT FROM AUTHOR]

This paper performs a techno-economic assessment in deploying solar photovoltaics to provide energy to a refrigeration machine for a remote underground mine. As shallow deposits are rapidly depleting, underground mines are growing deeper to reach resources situated at greater depths. This creates an immense challenge in air-conditioning as the heat emissions to mine ambient increases substantially as mines reach to deeper levels. A system-level design analysis is performed to couple PV with a refrigeration plant capable of generating 200 tonne of ice per day to help to mitigate this issue. Generated ice can directly be used in cooling deep underground mines via different types of direct heat exchangers. State-of-the-art technology is used in developing the model which aims to decrease the size and cost of a conventional refrigeration system run on a diesel generator. Costs associated with deploying a solar system are computed as per the recent market value. Energy savings, carbon emissions reduction, and net annual savings in employing the system are quantified and compared to a diesel-only scenario. In addition, two different energy storage strategies: an ice storage system and a battery storage system, are compared. A detailed economic analysis is performed over the life of the project to obtain the net cash flow diagram, payback period, and cumulative savings for both systems. Moreover, a sensitivity analysis is proposed to highlight the effect of solar intensity on solar system size and the area required for installment. The study suggests that the use of solar PV in mine refrigeration applications is technically feasible and economically viable depending on the sun-peak hours of the mine location. Additionally, the economics of deploying an ice storage system compared to the battery storage system has a better payback period and more cumulative savings. [ABSTRACT FROM AUTHOR]

Ventilation plays an important role in energy demands of mining industry. Using the immense volume of waste rock as thermal energy storage mass to shave seasonal air temperature oscillations is a genuine and practical solution to save on ventilation energy demands. The extensive size and considerable temperature gradients exhibited in such systems point to the importance of buoyancy-driven natural convection heat transfer mechanism. The present study investigates the effect of natural convection and identifies the order of significance of various heat transfer mechanisms. A Conjugate heat transfer and fluid flow model is proposed which includes both the porous rock mass placed in the rock-pit and the air positioned above it. The results of the model are compared and validated against the existing Non-Conjugate models. Using this novel model, significance of forced convection, driven by ventilation fan, and natural convection, driven by buoyancy, are compared. The model is also used to study how design parameters, such as position of intake air trenches and flow rate of fresh air, will affect energy savings. [ABSTRACT FROM AUTHOR]

Modern data centers are playing a pivotal role in the global economic situation. Unlike high-quality source of waste heat, it is challenging to recover the decentralized and low-quality waste heat sourced from data centers due to numerous technological and economic hurdles. As such, it is of the utmost importance to explore possible pathways to maximize the energy efficiency of the data centers and to utilize their heat recovery. Absorption chiller systems are a promising technology for the recovery of waste heat at ultra-low temperatures. In fact, the low temperature heat discharged from data centers cannot be retrieved with conventional heat recovery systems. Therefore, the present study investigated feasibility of waste heat recovery from data centers using an absorption chiller system, with the ultimate goal of electrical energy production. To fulfill this objective, a techno-economic assessment of heat recovery using absorption chiller (AC) technique for the data centers with power consumption range of 4.5 to 13.5 MW is performed. The proposed AC system enables saving electricity for the value of 4,340,000 kWh/year and 13,025,000 kWh/year leading to an annual reduction of 3068 and 9208 tons CO2 equivalent of greenhouse gas (GHG) emissions, respectively. The results of this study suggest an optimum change in the design of the data center while reducing the payback period for the investors. [ABSTRACT FROM AUTHOR]

Mining operations in remote locations rely heavily on diesel fuel for the electricity, haulage and heating demands. Such significant diesel dependency imposes large carbon footprints to these mines. Consequently, mining companies are looking for better energy strategies to lower their carbon footprints. Renewable energies can relieve this over-reliance on fossil fuels. Yet, in spite of their many advantages, renewable systems deployment on a large scale has been very limited, mainly due to the high battery storage system. Using hydrogen for energy storage purposes due to its relatively cheaper technology can facilitate the application of renewable energies in the mining industry. Such cost-prohibitive issues prevent achieving 100% penetration rate of renewables in mining applications. This paper offers a novel integrated renewable–multi-storage (wind turbine/battery/fuel cell/thermal storage) solution with six different configurations to secure 100% off-grid mining power supply as a stand-alone system. A detailed comparison between the proposed configurations is presented with recommendations for implementation. A parametric study is also performed, identifying the effect of different parameters (i.e., wind speed, battery market price, and fuel cell market price) on economics of the system. The result of the present study reveals that standalone renewable energy deployment in mine settings is technically and economically feasible with the current market prices, depending on the average wind speed at the mine location. [ABSTRACT FROM AUTHOR]

Subsurface mining operations are continuously getting deeper and more complex due to depletion of shallow deposits. This fact inevitably brings more expensive, high-tech oriented and most importantly energy intensive subsurface mining operations to come alive. Accordingly, while big mining companies are developing sensible extraction methods to exploit orebodies located at great depths, they are also seeking to cut down their costs and carbon footprint. A large percentage of the energy needed by a subsurface mine is due to the mine ventilation and air conditioning reasons. In fact, for mines deeper than 2 km, mine air conditioning becomes a must. Yet, as there are not many alternatives developed, most of the modern mines are subjected to deploy tens of megawatts worth of cooling plants using massive refrigeration units. This does not only create a large financial burden during the project stage but also results in heavy energy demands during the operation. This paper aims to investigate a natural, alternative deep-mine lake cooling system by providing a detailed 'front-end-loading' design conducted for a real-life, Canadian example. [ABSTRACT FROM AUTHOR]

Remote communities that have limited or no access to the power grid commonly employ diesel generators for communal electricity provision. Nearly 65% of the overall thermal energy input of diesel generators is wasted through exhaust and other mechanical components such as water-jackets, intercoolers, aftercoolers, and friction. If recovered, this waste heat could help address the energy demands of such communities. A viable solution would be to recover this heat and use it for direct heating applications, as conversion to mechanical power comes with significant efficiency losses. Despite a few examples of waste heat recovery from water-jackets during winter, this valuable thermal energy is often discarded into the atmosphere during the summer season. However, seasonal thermal energy storage techniques can mitigate this issue with reliable performance. Storing the recovered heat from diesel generators during low heat demand periods and reusing it when the demand peaks can be a promising alternative. At this point, seasonal thermal storage in shallow geothermal reserves can be an economically feasible method. This paper proposes the novel concept of coupling the heat recovery unit of diesel generators to a borehole seasonal thermal storage system to store discarded heat during summer and provide upgraded heat when required during the winter season on a cold, remote Canadian community. The performance of the proposed ground-coupled thermal storage system is investigated by developing a Computational Fluid Dynamics and Heat Transfer model. [ABSTRACT FROM AUTHOR]

The experimental and computational analyses of a 500 m deep coaxial borehole heat exchanger system for geothermal power generation are studied in this paper. The experiments are carried out on a high temperature resourced well with an average thermal gradient of 0.38 °C/m. The experiment lasts 456 h, and the findings are described in terms of fluid inlet and outlet temperatures, subsurface temperature distribution profiles over time, and flowrate. The in-situ ground temperature distribution profile is measured using Distributed Temperature Sensing System for different hours of the experiment. A detailed, three-dimensional, unsteady-state, finite volume-based computational model has been developed, which solves conjugate fluid-flow and heat transfer phenomena. The simulation outcomes are compared to the results of the experiments. With validated numerical model, to determine the circle of influence, temperature profile of the ground is observed at various radial distances from the borehole. A parametric study is performed by varying inlet temperature of the fluid, mass flow rate, and the thermal conductivity of the ground. The numerical model developed also predicts the temperature recovery behavior of the ground. The results indicate that the average output thermal power for 456 h from the geothermal system ranges from 172 kW to 262 kW based on operating condition chosen and the total thermal energy generated changes between 82 MWh and 194 MWh from a single borehole. After the extraction is terminated, around 86% of the initial ground temperature is restored after 456 h. • Field-test experiment was performed for 456 h in a fresh drilled well. • 3D conjugate numerical model was developed and validated. • Parametric study was performed for different operating conditions. • Sensitivity analysis was conducted to study the degree of influence. • Temperature recovery period was predicted with the developed numerical model. [ABSTRACT FROM AUTHOR]

Abandoned oil well can be a promising alternative to be retrofitted to extract geothermal energy than the conventional geothermal well. This study investigates the potential of converting abandoned oil well into geothermal energy power plant by combining computational fluid dynamics (CFD) simulation, process simulation, and techno-economic analysis. A detailed CFD model was formulated and validated with verified data from published literature. The model was then utilized to study key performance variables on heat extractions coupled with the Organic Rankine Cycle (ORC) to generate power and its subsequent techno-economic analysis. The results indicate that, due to relatively low temperature profile in typical Malaysian wells, the Levelized Cost of Electricity (LCOE) of the ORC system was found to be almost double than that of conventional geothermal technologies. To reduce the LCOE, at least four abandoned wells in a close proximity are required. Alternatively, other renewable energy sources (e.g., solar, biomass) could be used to upgrade the geothermal well. This techno-economic analysis shall serve as a preliminary assessment on the feasibility of utilizing abandoned oil wells in Malaysia for geothermal energy extraction. • Coupling of CFD and ORC process modeling for geothermal extraction from abandoned oil well. • Techno-economic analysis was conducted for case study in Malaysia. • The levelized cost of electricity (LCOE) is found to be around 6 cent USD per kWh. • Geothermal gradient of the well plays important role on the feasibility of the system. [ABSTRACT FROM AUTHOR]