Heat Extraction Rate Research Articles

Geothermal waste heat utilization from in situ thermal bitumen recovery operations.

In situ thermal methods for bitumen extraction introduce a tremendous amount of energy into the reservoirs raising ambient temperatures of 13 °C to as high as 200 °C at the steam chamber edge and 50 °C along the reservoir edge. In essence these operations have unintentionally acted as underground thermal energy storage systems which can be recovered after completion of bitumen extraction activities. Groundwater flow and heat transport models of the Cold Lake, Alberta, reservoir, coupled with a borehole heat exchanger (BHE) model, allowed for investigating the use of closed-loop geothermal systems for energy recovery. Three types of BHEs (single U-tube, double U-tube, coaxial) were tested and analyzed by comparing outlet temperatures and corresponding heat extraction rates. Initial one year continuous operation simulations show that the double U-tube configuration had the best performance producing an average temperature difference of 5.7 °C, and an average heat extraction of 41 W/m. Given the top of the reservoir is at a depth of 400 m, polyethylene piping provided for larger extraction gains over more thermally conductive steel piping. Thirty year operation simulations illustrate that allowing 6 month cyclic recovery periods only increases the loop temperature gain by a factor of 1.2 over continuous operation. Due to the wide spacing of existing boreholes and reservoir depth, only a small fraction of the energy is efficiently recovered. Drilling additional boreholes between existing wells would increase energy extraction. In areas with shallower bitumen deposits such as the Athabasca region, i.e. 65 to 115 m deep, BHE efficiencies should be larger.

An extension of the Kampmann–Wagner numerical model towards as-cast grain size prediction of multicomponent aluminum alloys

The Kampmann–Wagner numerical (KWN) model, which has been widely adopted as a precipitation modeling framework accounting for concurrent nucleation, growth and coarsening kinetics, was extended to predict the as-cast grain size of inoculated multicomponent aluminum alloys. In the model, the heterogeneous nucleation of grains on inoculant particles was modeled based on the free growth criterion, while the influence of the solute on the nucleation behavior, in terms of the solute suppressed nucleation (SSN) effect, was rigorously defined and integrated. In order to fully address the solidification behavior of multicomponent alloys, a coupling of the KWN model to CALPHAD was carried out. These extensions allow the treatment of two different nucleation-ceasing mechanisms induced by grain growth: recalescence stifling and solute segregation stifling. Given melt composition, inoculation and heat extraction rate, the model is able to predict maximum nucleation undercooling, cooling curve and the final as-cast grain size of multicomponent alloys without invoking the binary equivalence assumption used in the existing models. The proposed model was tested with a variety of binary and multicomponent aluminum alloys, and the predictions were compared with the experimental measurement results and previous grain size prediction models. The simulation results show that the SSN effect has a negligible influence on the nucleation behavior and the final grain size during isothermal melt solidification, but a strong influence on the ceasing of grain nucleation during directional solidification. Reasonable agreement was obtained between the model prediction and measurement results on a direct chill casting experiment of an AA5182 alloy. Our work proves that the application of the precipitation modeling framework for the solidification problem is successful.

Experimental analysis of a direct expansion geothermal heat pump in heating mode

Abstract In this study, we present an experimental analysis of a direct expansion (DX) geothermal heat pump (GHP) installed in the Thermal Technology Center (TTC) of the Ecole de technologie superieure in Montreal. The residential heating system studied consists of three geothermal 30 m deep wells, which use R22 as refrigerant. During the test campaign, which ran over a one-month period in early spring, the coefficient of performance of the heat pump varied between 2.70 and 3.44, with a daily average of 2.87. The heating capacity reached a daily average of 8.04 kW, for a cooling water constant volumetric flow rate of 0.38 L s −1 . The mean the ground heat extraction rate from was 58.2 W m −1 . The tests performed helped to highlight a pressure drop coupled with a relatively large superheating revealing a flow rate mal-distribution in geothermal evaporators. The effects of some factors (condenser cooling water inlet temperature, condensing temperature, pressure drop in the evaporator, thermal properties of soil and grout) that affect DX system performance are also presented. Finally, a comparative study between the use of electricity and the DX heat pump as home heating source shows that the DX heat pump provides savings of approximately 70% over the electricity.

Radiant Cooling with Dehumidified Air Ventilation for Thermal Comfort in Buildings in Tropical Climate

Radiant cooling is an alternative air-conditioning that havs been implemented successfully in high latitude regions. In tropical region as Thailand, radiant cooling is quite challenge due to its cooling performance being limited by high-moisture ambient air. This paper reports an investigation of radiant cooling in a tropical building. The study comprises full-scale experiments of a radiant cooling system with cool panels installed in a room of a laboratory building. A separate fan coil unit was installed to remove humidity of the ventilation air before suppluying it into the room. A software namely TRNSYS was used to model the systems in order to determine the heat extraction rate of the cool panels. Thermal comfort level in the room was evaluated by predicted mean vote (PMV) index. The results show that the radiant cooling is able to use for air conditioning for human comfort in tropical buildings. However, a sophistical system to control temperature of the chilled water supplied to the cool panels and the fan coil unit for the ventilation air dehumidification is inevitably required.

A semi-analytical method to generate g-functions for geothermal bore fields

This paper introduces a new methodology for the generation of thermal response factors of geothermal bore fields using the concept of g-functions introduced by Eskilson. Boreholes are divided into segments to consider the variation of the heat extraction rates along the length of the boreholes and the analytical finite line source (FLS) solution is used to calculate the temperature variations at the wall of each borehole segment along the axial direction. The proposed methodology accounts for the time variation of the heat extraction rates among boreholes and along the length of individual boreholes to obtain a uniform borehole wall temperature equal for all boreholes in accordance with the original boundary conditions proposed by Eskilson. In addition, the methodology is generalized to account for boreholes of different lengths and buried depths. g-Functions calculated with the proposed methodology are compared to the numerical technique used by Eskilson to derive the g-functions for fields of 1 to 12×12 boreholes. The difference between the two models is within 5% for all studied bore fields, except for fields of boreholes located on a single row. The variation of the heat extraction rates of individual boreholes along their length as well as in time also showed good agreement with the numerical model. It is shown that using 12 borehole segments is adequate to calculate the g-functions in most practical cases. For instance, the error on the g-function of a 10×10 bore field calculated using 12 borehole segments is 2.2% after 20years and 4.7% at steady-state.

Numerical Simulation and Experimental Validation of a Vertical U-Tube Ground Heat Exchanger

Vertical U-tube ground heat exchanger (GHE) is a key component in geothermal energy utilization systems like ground source heat pump (GSHP). This paper used a two-dimensional transient mathematical model for predicting the heat extraction rate of a vertical U-tube GHE, which also took into account the temperature distribution under the ground. Furthermore the modelling predictions were validated using experimental data. The experimental validation on the model was performed in a GSHP system with a double U-tube GHE, which was of 55m depth. For temperature distribution under the ground, the absolute error and relative error between experiment and simulation are within 0.62°C and 3.71 %. Simulation results agreed well with the experimental results that validate the feasibility of the mathematical model.

Optimizing the design of a geothermal district heating and cooling system located at a flooded mine in Canada

Flooded underground mines are attractive for groundwater heat pump systems, as the voids created during mining operations enhance the subsurface permeability and storage capacity, which allows the extraction of significant volumes of groundwater without requiring extensive drilling. Heat exchange at a flooded mine is, however, difficult to predict because of the complex geometry of the underground network of tunnels. A case study is presented here to demonstrate that numerical simulations of groundwater flow and heat transfer can help assess production temperatures required to optimize the design of a heat pump system that uses mine water. A 3D numerical model was developed for the Gaspe Mines located in Murdochville, Canada, where a district heating and cooling system is being studied. The underground mining tunnels and shafts are represented in the model with 1D elements whose flow and heat transfer contributions are superimposed to those of the 3D porous medium. The numerical model is calibrated to simultaneously reproduce the groundwater rebound that occurred when the mine closed and the drawdown measured during a pumping test conducted in a former mining shaft. Predictive simulations over a period of 50 years are subsequently performed to minimize pumping rate and determine maximum heat extraction rate.

Evaluating the performance of a large borehole ground source heat pump for greenhouses in northern Japan

Abstract The objective of this study was to use both field data and a numerical simulation to examine the long-term performance and environmental effects of a large GSHP (ground source heat pump) system that heats and cools industrial greenhouses in a cold region. A large vertical GSHP system was installed in the city of Akabira in the north of Hokkaido, Japan to provide heating and cooling for 12 greenhouses. The system has a maximum capacity of 640 and 648 kW for heating and cooling, respectively. The system was monitored and analyzed from Oct. 2010 through May 2011. The system had a COP (coefficient of performance) of 3.0 and SCOP (system coefficient of performance) of 2.7. The average heat extraction rate of the system was approximately 27.7 W/m. In addition, the ground temperature at a depth of 40 m decreased from approximately 7.8 °C to 0 °C after 8 months of operation. A numerical model of the system was developed in FEFLOW to predict its future behavior under conditions where the demand for heating surpasses the demand for cooling. The simulation results suggest that the system could maintain the heat exchange rate for several years without significantly compromising its performance. The risk of operating the system under unbalanced heating and cooling loads was addressed via case studies. Groundwater flow decreases the risk of operating the system when the heat extraction was much higher or lower than the heat injection.

Numerical modelling of macrosegregation and shrinkage in large diameter steel roll castings: a mould study

Minimising macrosegregation and shrinkage defects during uphill teeming of medium carbon roll ingots has always presented a major technical challenge. Process improvements have been achieved by balancing the total heat input of a cast roll and the rate of heat extraction from the roll surface. Injecting dilute alloy through a submerged entry nozzle (SEN) into the net shaped roll ingot further mitigated the undesirable consequences of solute enrichment especially at the ingot centreline. Both the centreline segregation problems and midradius channel segregates can be significantly minimised, by combining these techniques. The objectives of this study are to determine the effect of mould thickness and material type (steel versus cast iron) on the centreline and especially on the midradius segregation, the solidification behavior in the transition region between the outer shell and the diluted interior region, as well as the mould durability. To accomplish these objectives, a multiphase multicomponent computational fluid dynamics (CFD) code was developed for studying the macrosegregation and shrinkage under various casting conditions for a 65 tonne, 1·6 m diameter steel roll processed via SEN. The developed CFD framework consists of solving for the volume fraction of phases (air and steel mixture), temperature, flow and solute balance in multicomponent alloy systems.

Heat extraction from Non-Convective and Lower Convective Zones of the solar pond: A transient study

Heat extraction from the Non-Convective Zone (NCZ) or gradient layer and Lower Convective Zone (LCZ) of the solar pond has been investigated through one-dimensional finite difference transient model. Instantaneous efficiency of the solar pond is introduced and defined in this paper. The solar pond considered in the present study is assumed to have an in-pond heat exchanger for heat extraction. The rate of heat transfer is controlled by the mass flux of heat transfer fluid in this model. As in reality mass flux of heat transfer fluid is the simplest and most practical way to control the rate of heat extraction. In this model for an ideal situation it is assumed that the heat transfer fluid is initially at the local daily average ambient temperature and the in-pond heat exchanger has heat transfer effectiveness equal to unity. With these assumptions the model can predict the thermal performance of the solar pond with maximum heat extraction for a desired mass flux of the heat transfer fluid. This paper presents the comparison of the transient thermal performance of solar pond with heat extraction from LCZ alone and that with combined heat extraction from LCZ and NCZ. It is shown how the efficiency of the solar pond increases when heat is extracted from both NCZ and LCZ. The main objective of this study is to offer a simple method to predict transient thermal performance of a solar pond with heat extraction from NCZ and to estimate the mass flux of heat transfer fluid used in an in-pond heat exchanger for heat extraction from different layers of solar pond.

Preparation and Characterization of Super Pure Coal

Industrial washing oil as solvent, super pure coal was extracted and prepared from raw coal using heat extraction technology. The structures of raw coal and super pure coal were characterized by thermogravimetry and Fu Liye infrared spectrum. The results showed that the heat extraction rate of super pure coal was decreased with the increasing of coalification degree. The ash of raw coal which were silicate and alumina can be concentrated by heat extraction technology into coal residue and the mixtures of various structure were mainly composed of aromatic hydrocarbons also can be extracted effectively.

A study into extraction of geothermal energy from tailings ponds

Assessing the performance of ground-coupled heat exchangers (GCHE) of closed-loop geothermal systems installed in tailings ponds is studied. A heat transfer model is constructed, taking into account heat conduction as well as groundwater advection. A three-dimensional finite volume discretisation method over a structured mesh with variable grid size is used to solve the governing equations. The performance of a GCHE system installed in tailings ponds is assessed based on the rate of energy extraction and the outlet fluid temperature. The geothermal capacity of mine tailings ponds and its sustainable rate of heat extraction are estimated. Effects of tube network configuration and horizontal and vertical underground advection on the performance of the system are investigated. It is found that two-dimensional heat transfer models may lead to over-designed systems and the effect of advection cannot be neglected in highly pervious tailings.

A transient natural convection heat transfer model for geothermal borehole heat exchangers

The effect of buoyancy-driven natural convection on the performance of ground-coupled heat exchangers of closed loop geothermal systems is investigated. The governing equations of continuity, momentum, and energy balance are derived, taking into account a porous ground medium fully saturated with liquid water. Boussinesq approximation is used to model the effect of buoyancy forces in water. A three-dimensional finite-volume discretization method over a structured mesh is used to solve the governing equations numerically. The performance of the ground-coupled heat exchanger system is assessed based on the rate of energy extraction and the outlet fluid temperature. The effects of hydraulic conductivity of the heat exchange medium and seasonal variations of heat load on the heat transfer phenomenon are studied. The results are evaluated by comparing them against the results of existing conduction-based heat transfer models. The influence of natural convection on the sustainable rate of heat extraction from a geothermal resource is underlined and interpreted.

English

The rate of heat extraction, hardness, and severity of quenching of both edible and nonedible bioquenchants for industrial heat treatment was investigated using AISI 4137 medium carbon steel. Results showed that both the maximum and minimum cooling rates occurred in the nucleate boiling stage and were strongly dependent on the viscosity and saponification number. The peak cooling rates of Jatropha oil, groundnut oil, melon oil, sheabutter oil, palmkernel oil, and palm oil were greater than that of mineral oil. The quench severities of Jatropha, sheabutter, and groundnut oil are higher with an H-factor of 5.93, 6.00, and 6.14, respectively. High heat transfer coefficient of 1583, 1180, and 1024 W/m 2 K were obtained for Jatropha oil, groundnut oil, and melon oil; whereas sheabutter oil, palmkernel oil, palm oil, and mineral oil have heat transfer coefficient of 1001, 971, 828, and 589 W/m 2 K, respectively. For all the quenchants, the hardness of steel is increased with an increase in the austenite heating temperature.

Ground Thermal Responses during Heat Exchange at EcoFarm

This paper analyzes the ground thermal responses during constant rate of heat injection and extraction. The undisturbed underground temperature is assumed to be uniform. Seven types of earth material are analyzed using mean values of their thermal properties. Simple equation for Zone of Influence, convenient for quick engineering assessment, is derived. The results show that, among seven underground materials studied, dry sand and sand aquifer are the best for storage type application of thermal energy; whereas igneous is the best for dissipative type application of geothermal energy.

Dynamic thermal modelling of horizontal ground-source heat pumps

A computer program has been developed for numerical simulation of the dynamic thermal performance of horizontally coupled heat exchangers for ground-source heat pumps, taking account of dynamic variations of climatic, load and soil conditions. The program was used to investigate the effects of operating and start times, installation depth and soil freezing on the heat exchanger performance. It is shown that the rate of heat extraction decreases with increasing operating time. Operating a heat pump with an earlier start date in autumn would give rise to a higher amount of cumulative heat extraction. Also, a heat exchanger installed at a shallower depth can provide a larger heat extraction rate at the early stage of heating operation. In addition, soil freezing enhances heat extraction.

Water Cooled Concentrated Photovoltaic System

Concentrated photovoltaic (CPV) system helps in focusing the direct solar radiation on the photovoltaic module. A CPV unit with water cooling system has been developed and manufactured at the School of Energy and Environment, Southeast University, China. It has been used for evaluating the performance of the CPV module with water cooling system for efficiency, power output and temperature. Also the effect of cooling water flow rate has been analyzed for performance evaluation of the CPV module. It has been found that the electrical output of the water cooled CPV is 4.7 to 5.2 times more than the PV module (without concentration and cooling). It has been noticed that the efficiency of the CPV mainly depends on the heat extraction rate and it helps in managing the cell temperature. And also the heat extraction rate from the CPV module mainly depends on the cooling water flow rate.

Effects of Sand–Bentonite Backfill Materials on the Thermal Performance of Borehole Heat Exchangers

This article presents a quantitative analysis of the effects of sand–bentonite backfill materials on the thermal performance of borehole heat exchangers (BHEs). Laboratory thermal probe tests were conducted to measure the thermal conductivity of sand–bentonite mixtures under different mixed ratios. Based on microscopic observations, the mechanism of bentonite affecting heat conduction between the sand grains was analyzed. Then field tests were carried out to compare the thermal performance of two double U-shaped BHEs with different backfill materials. Test results showed that the thermal conductivity of sand–bentonite mixtures first increased with increasing percentage of bentonite by dry mass, then reached a peak at the range from 10% to 12%, beyond which the thermal conductivity decreased quickly. For the BHE with an optimal sand–bentonite backfill material, the heat injection and heat extraction rate were enhanced on average by 31.1% and 22.2%, respectively, compared with the case with a common sand–clay material. These results can provide helpful guide for the design of ground source heat pump systems.

Simulation of CO2-EGS in a Fractured Reservoir with Salt Precipitation

The use of CO2 as a working fluid in place of formation brines in Enhanced Geothermal Systems (EGS) could allow, in addition to CO2 sequestration, a more efficient recovery of reservoir heat for any given pressure gradient between injection and production wells. We simulate an idealized low-salinity brine-filled reservoir in which we inject CO2. We produce heat from the extracted fluid that is at first just brine, later brine + CO2, and finally CO2 only. As the CO2 plume develops the aquifer dries out, precipitating salt and inducing clogging of the fractures in proximity to the production well. To mitigate this effect, we have simulated combined brine and CO2 injection that, at specific mass fractions, doubles the life of the well but limits the rate of heat extraction. The total heat extracted over the life of the well is 40% larger than in the dry CO2 case. Simulation of more realistic geologic settings with involvement of chemical reactions would be necessary to evaluate the feasibility of CO2-EGS in any particular geothermal system.

Effect of Temperature on Hydraulic Parameters of Cable-In-Conduit-Conductor of SST-1

Stable operation of superconducting magnets de- pend critically on the balance of heat deposition rate versus heat extraction rate by the cryo-coolant. Thus, the mass flow rate of the coolant in case of force-flow cooled supercon- ducting magnet with Cable-In-Co-nduit-Conductor (CICC) construction becomes an important factor for optimum sta- bility of magnets. The Toroidal and Poloidal Field mag- nets of Steady-state Superconducting Tokamak-1 (SST-1) is made of superconducting CICC with a void fraction of 40 % ± 2 %. For adequate cooling of magnets, supercritical helium at 4 bar and 4.5 K is forced-flown through the voids. Effect of temperature on mass flow rate and pressure drop in