Coupled heat-fluid-solid numerical study on heat extraction potential of hot dry rocks based on discrete fracture network model

Fracture networks within hot dry rock(HDR)geothermal reservoirs are complex,and heat extraction via water injection is thus a coupled process of heat-fluid-solid multifield.In this paper,utilizing the theory of normally distributed random functions,we develop a corresponding pre-processing subprogram to establish a discrete network model of complex fracture distribution in HDR reservoirs;then construct a heat-fluid-solid finite element model for heat extraction via water injection and compare the numerical solution with the analytical solution of the one-dimensional non-isothermal consolidation problem for verification.The numerical simulation results show that the main factors affecting the heat extraction efficiency of HDR reservoirs include fracture width,fracture density,fracture permeability,and matrix permeability.When a HDR reservoir is injected with water for heat extraction,there is a certain threshold value of these influential parameters,beyond which the outlet temperature drops significantly,resulting in an obvious thermal breakthrough.When injecting water for heat extraction,the values of these parameters should be controlled and kept at a reasonable level,otherwise,the HDR reservoir may enter a thermal breakthrough stage in advance,which is not conducive for long-period heat extraction.Influenced by the random distribution of complex fractures,the leading edge of the cold front may present an irregular distribution.During the process of heat extraction,the stress gradually changes from a compressional state to a tensile state,which induces further damage to the HDR reservoir.

The mechanical measuring method of welding heat source efficiency

Based on the principle of residual deformation induced by superposition of the welding residual stress and working stress, the welding heat source efficiency has been determined by measuring displacement changes of specimens under loading and unloading in tensile tests, and combining with calculating welding parameters. Meanwhile, the welding heat source eficiencies obtained are compared with those of the measuring-calculating method. The research results show that the welding heat source efficiencies are almost the same as those obtained by the measuring-calculating method. Therefore, the welding heat source efficiency can be determined accurately by this method, and a new determining method of the heat source efficiency for the welding heat process calculating has been provided.

Performance and Optimization for a Ground-Coupled Liquid Loop Heat Recovery Ventilation System

Ground-coupled heat pumps(GCHP)are commonly used in residential heating system.To mitigate the boreholes temperature dropping with operating time,a new exhaust-air recharging system is developed.The new recharging system can be used in three operational modes.In this paper,a ground-coupled heat recovery ventilation(HRV)model is discussed.A thermal model is set up to find the optimal brine flow rate and heat transfer allocation ratio between exhaust and supply coils for maximum heat recovery efficiency.Contrary to the conventional liquid-loop HRV systems,the brine temperature entering the exhaust coil never goes blow zero(0℃),and hence defrosting is needless in the ground-coupled HRV system.This can make the ground-coupled HRV system over 20% more efficient than a conventional HRV system at low outdoor temperatures.

Experimental investigation of effect of refrigerant gases,compressor lubricant and operating conditions on performance of a heat pump

In the field of heat pumps,there are a number of parameters that affect the performance and efficiency of the apparatus,which have been the subject of studies by individual researchers in the literature.This study describes an experimental method in order to investigate the effects of some significant parameters on heat pump performance.In this regard,a laboratory heat pump setup has been utilized to operate in different working conditions for achieving an appropriate estimation to find out effects of mentioned parameters such as refrigerant type and charge amount,compressor oil viscosity,compressor cooling fan,secondary fluids temperature and flow rate.Different refrigerants have been selected and used as circulating fluid in the installed heat pump.Although this work has been devoted to a detailed attempt to recognize the effects of various parameters on the coefficient of performance(COP) value,an appropriate method has been carried out to survey the obtained results by using economic analysis.It was revealed that one of the main parameters is refrigerant charge amount which has a notable effect on COP.The temperature of the heat source was also tested and the performance of the system increased by more than 11% by employing mentioned modifications and various operating conditions.In addition,by selecting a low viscosity compressor oil,the system performance increased by 18%.This improvement is more than 6% for the case that cooling fan is installed to cool the compressor element.

Hierarchical lichee-like Fe_(3)O_(4) assemblies and their high heating efficiency in magnetic hyperthermia

A nontoxic and biocompatible thermoseed is developed for the magnetic hyperthermia.Two kinds of thermoseed materials:hierarchical hollow and solid lichee-like Fe_(3)O_(4) assemblies,are synthesized by a facile hydrothermal method.The crystal structure of Fe_(3)O_(4) assemblies are characterized by x-ray diffraction,scanning electron microscopy,and transmission electron microscopy.Moreover,the prepared Fe_(3)O_(4) assemblies are used as a magnetic heat treatment agent,and their heating efficiency is investigated.Compared to solid assembly,hollow lichee-like Fe_(3)O_(4) assembly exhibits a higher specific absorption rate of 116.53 W/g and a shorter heating time,which is ascribed to its higher saturation magnetization,larger initial particle size,and the unique hierarchical hollow structure.Furthermore,the magnetothermal effect is primarily attributed to Neel relaxation.Overall,we propose a facile and convenient approach to enhance the heating efficiency of magnetic nanoparticles by forming hollow hierarchical assemblies.

R&D on Resistive Heat Exchangers for HTS High Rated Current Leads

The HTS current leads of superconducting magnets for large scale fusion devices and high energy particle colliders can reduce the power consumption for cooling by 2/3 compared with conventional leads. The resistive sections of high-rated current leads are usually made of a heat exchanger cooled by gas flow. The supply of the cooling mass flow incurs more than 90% of the cooling cost for the HTS leads. The mass flow rate requirement depends not only on the length and material of the resistive heat exchanger, but also on the heat transfer coefficient and HEX surface, the joint resistance at the cold end of a sheet-stack HEX with a larger specific presented in the paper. The test results of efficiency can be achieved. and its cooling approach. The design and operation surface and a much smaller hydraulic diameter are an HTS lead optimized for 8 kA show that a 98.4%

Excess Heat Power Registration in High Voltage Electrolysis Cell Experiments

Experimental research of the heat and high-energy processes occurring in the cathode solid medium in the high voltage electric discharge system （electrolysis cell and glow discharge device） is presented. The experiments were carried out： Electrolysis in heavy water with a Pd cathode, electrolysis in light water with Ni and Pd cathodes, the glow discharge in deuterium with a Pd cathode. Excess heat was observed in experiments with high-voltage electrolysis （1,000 V or more）. The experiments showed that the maximum excess heat power values of 5-8 W for glow discharge and 180-280 W for high-voltage electrolysis and heat efficiency up to 170% for glow discharge, and 800% for high-voltage electrolysis. The production of impurity nuclide yield showing a shift of up to a few per cent from natural isotopic abundances was detected by spark mass spectrometry and by secondary ionic mass spectrometry. The authors propose based on these experimental results a phenomenological model for low energy nuclear reaction.

Mathematical model of absorption and hybrid heat pump

Recovering waste heat from industrial processes is bene ficial in order to reduce the primary energy demands and heat pumps can be used to this purpose.Absorption heat pumps are energy-saving and environment-friendly because use working fluids that do not cause ozone depletion and can reduce the global warming emissions.The hybrid heat pump processes combine the conventional vapor-compression and the absorption heat pump cycles.Studies about the simulations and modeling of hybrid heat pumps are few in literature.In this research a mathematical model for single effect absorption and hybrid heat pump is carried out with Chem Cad? 6.0.1.LiBr–H_2O is used as working fluid while electrolytic NRTL and electrolytes latent heat are used as thermodynamic model due to the better results.Binary parameters of activity coef ficients are regressed from experimental vapor pressure data while default constants are used for the solubility expressions.A design of heat pumps is developed and a new modeling of generator is analyzed.The coef ficient of performance of absorption heat pump and hybrid heat pump is equal to 0.7 and 0.83 respectively.For absorption heat pump a sensitivity analysis is carried out to evaluate the effect of temperature and pressure generator,the concentration of Li–Br solution on coef ficient of performance,cooling capacity and working fluid temperature.For hybrid heat pump,the different coef ficients of performance,the primary energy ratio,the generator heat,and the compressor power are analyzed for different values of compressor proportion.Results show that comparing the two systems the hybrid pump allows to save more primary energy,costs and carbon dioxide emissions with respect to absorption heat pump with the increasing of compressor proportion parameter.Future researches should focus on the construction of this heat pumps integrated in chemical processes as a biogas plant or trigeneration systems.

Application of Technology of Additive Manufacturing in Radiators and Heat Exchangers

Radiators and heat exchangers play a key role in the long-term and stable operation of the equipment. The emergence of additive manufacturing technology has released the freedom of design, enabling many innovative structures of radiators and heat exchangers to be manufactured. The paper reviews the application of additive manufacturing in new radiators and heat exchangers. The technology of additive manufacturing boosts the development of new radiators and heat exchangers, which improves heat dissipation performance and heat exchange efficiency. This paper will provide a new idea and method for the development of radiators and heat exchangers via the application of additive manufacturing.

Air flow patterns and noise analysis inside high speed angular contact ball bearings

The vortex formed around the rolling ball and the high pressure region formed around the ball-raceway contact zone are the principle factors that barricades the lubricant entering the bearing cavity, and further causes improper lubrication. The investigation of the air phase flow inside the bearing cavity is essential for the optimization of the oil-air two-phase lubrication method. With the revolutionary reference frame describing the bearing motion, a highly precise air phase flow model inside the angular contact ball bearing cavity was build up. Comprehensive factors such as bearing revolution, ball rotation, and cage structure were considered to investigate the influences on the air phase flow and heat transfer efficiency. The aerodynamic noise was also analyzed. The result shows that the ball spinning leads to the pressure rise and uneven pressure distribution. The air phase velocity, pressure and cage heat transfer efficiency increase as the revolving speed increases. The operating noise is largely due to the impact of the high speed external flow on the bearing. When the center of the oil-air outlet fixes near the inner ring, the aerodynamic noise is reduced. The position near the inner ring on the bigger axial side is the ideal position to fix the lubricating device for the angular contact ball bearing.

Urea Preparation by Oxidative Carbonylation of Ammonia

Effective one-stage method of urea preparation by catalytic oxidative carbonylation of ammonia in liquid phase is developed. The method allows to prepare urea with productivity of-530 g/（L·h） in sufficiently mild conditions （total pressure -30 bar, 45 ℃）. The process is characterized by high selectivity （near 100%） i.e. byproducts separation is not needed. Almost all CO is consumed during the process, this substantially diminishes the waste-gas purification costs and raises the process environmental characteristics; the only byproduct is water.

Development Features of Supercritical (Ultra-Supercritical) Technology in the World and Experiences We Can Learn

The development and technical characteristics in different stages of supercritical (ultra-Supercritical) technology abroad are introduced in this paper. At the same time, according to the development trend of supercritical (ultra-supercritical) technology, the corresponding revelations are given in this paper. That is: It is an inevitable choice to develop supercritical (ultra-supercritical) technology if we want to improve the thermal efficiency and heat efficiency.

Highly anisotropic thermal conductivity of few-layer CrOCl for efficient heat dissipation in graphene device

With the packing density growing continuously in integrated electronic devices,sufficient heat dissipation becomes a serious challenge.Recently,dielectric materials with high thermal conductivity have brought insight into effective dissipation of waste heat in electronic devices to prevent them from overheating and guarantee the performance stability.Layered CrOCl,an antiferromagnetic insulator with low-symmetry crystal structure and atomic level flatness,might be a promising solution to the thermal challenge.Herein,we have systematically studied the thermal transport of suspended few-layer CrOCl flakes by microRaman thermometry.The CrOCl flakes exhibit high thermal conductivities along zigzag direction,from~392±33 to~1,017±46 W·m^(−1)·K^(−1) with flake thickness from 2 to 50 nm.Besides,pronounced thickness-dependent thermal conductivity ratio(/from~2.8±0.24 to~4.3±0.25)has been observed in the CrOCl flakes,attributed to the discrepancy of phonon dispersion and phonon surface scattering.As a demonstration to the heat sink application of layered CrOCl,we then investigate the energy dissipation in graphene devices on CrOCl,SiO_(2) and hexagonal boron nitride(h-BN)substrates,respectively.The graphene device temperature rise on CrOCl is only 15.4%of that on SiO_(2) and 30%on h-BN upon the same electric power density,indicating the efficient heat dissipation of graphene device on CrOCl.Our study provides new insights into two-dimentional(2D)dielectric material with high thermal conductivity and strong anisotropy for the application of thermal management in electronic devices.

Application analysis of efficient heat dissipation of electronic equipment based on flexible nanocomposites

The efficient heat dissipation of electronic equipment is very important,its heat dissipation performance directly determines the life of the equipment itself.A hand-held electronic communications equipment,when used in surface temperature is exorbitant,need to heat dissipation equipment efficiently,to ensure that the use of comfort in the handheld.In accordance with this requirement,this article presents a flexible composite material based on nano-efficient cooling methods that can keep the layout,through the improvement of internal thermal path,it can achieve the effective heat dissipation.The network thermal resistance method is used to analyze the heat transfer in the equipment,and the thermal analysis of the local thermal resistance is carried out.At the same time,through the modeling of electronic equipment and the analysis of finite elements,the temperature drop of the equipment after improvement is accurately judged.Finally,the device experimental performance comparison before and after the optimization of the standby mode and working mode is verified.The results show that the optimized equipment heat source temperature can be reduced by up to 8.5℃,the surface temperature of the equipment can be reduced by about 5℃~7℃,and the final control equipment in the steady standby state of the temperature of about 39±0.5℃,to ensure the comfort of use,and also improved the service life of the equipment.The efficient thermal design of electronic equipment based on flexible nanocomposites can provide a convenient and reliable cooling solution for high-heat flow density devices.

Thermal Performance of Elliptical Fin-and-Tube Heat Exchangers with Vortex Generator under Various Inclination Angles

Elliptical fin-and-tube heat exchangers are commonly used in air conditioning,heating,refrigeration industries,and ventilation.This study numerically investigates the effect of vortex generators on the performance of elliptical fin-and-tube heat exchanger under different inclination angles.In this study,air flow that is in the transitional regime is selected as the working fluid.Reynolds numbers at the inlet are varied in a range of 1300 to 2100,and the shear stress transport k-ωturbulence model is selected to solve the non-closure of basic turbulence equations.The ellipticity ratios of the tubes which are used for the analysis are between 0.6 and 1.0,and the inclination angles are varied from 15°to 75°.The effects of different inclination angles of vortex generators on the Colburn factor j,friction factor f,and efficiency index j/f are analyzed.The friction and Colburn factors are observed to increase with increasing vortex generator inclination angles.It is found that the efficiency factors for a 15°vortex generator inclination angle at 0.6,0.7,0.8,and 0.9 ellipticity ratios improve compared to the corresponding cases with no vortex generator.However,the vortex generator cannot improve the efficiency factor of the circular tube heat exchanger.The 3 D CFD method employed by this study has great potential for use in optimally designing the arrangement of the vortex generators to enhance the performance of heat exchangers.

Conjugate Heat Transfer Investigation on the Cooling Performance of Air Cooled Turbine Blade with Thermal Barrier Coating

A hot wind tunnel of annular cascade test rig is established for measuring temperature distribution on a real gas turbine blade surface with infrared camera.Besides,conjugate heat transfer numerical simulation is performed to obtain cooling efficiency distribution on both blade substrate surface and coating surface for comparison.The effect of thermal barrier coating on the overall cooling performance for blades is compared under varied mass flow rate of coolant,and spatial difference is also discussed.Results indicate that the cooling efficiency in the leading edge and trailing edge areas of the blade is the lowest.The cooling performance is not only influenced by the internal cooling structures layout inside the blade but also by the flow condition of the mainstream in the external cascade path.Thermal barrier effects of the coating vary at different regions of the blade surface,where higher internal cooling performance exists,more effective the thermal barrier will be,which means the thermal protection effect of coatings is remarkable in these regions.At the designed mass flow ratio condition,the cooling efficiency on the pressure side varies by 0.13 for the coating surface and substrate surface,while this value is 0.09 on the suction side.

LESSONS LEARNED: GREEN BUILDING DESIGN TECHNIQUES FOR OFF-GRID LOCATIONS

Over 25 percent of the world’s population lives without access to electricity from a utility-supplied grid[1].In under­developed and developing countries,the reason is primarily a lack of government-sponsored utility infrastructure due to the high cost of power line extension.In developed countries,power line extension costs are again the primary fac­tor in lack of a grid connection,as in most cases the end user must foot the bill for such improvements.In the United States,power line extension can cost over$50,000 per kilometer[2],so the cost of an off-grid electrical system that uses renewable sources to charge a large battery bank for energy storage can compare favorably to that of grid exten­sion-but not always.However,both the design and implementation of such off-grid renewable energy systems differ greatly from more common grid-tied applications,where the utility grid is used as“battery”with which the system can buy and sell electrical energy from and to the utility as needed.Energy efficiency and conservation are paramount in all off-grid renewable energy system designs,as these measures extend at low cost the hours or days of autonomous operation time before a backup power source(usually an internal-combustion generator)must be used for battery charging during periods of no input from renewable solar,wind,or hydroelectric sources.The techniques used in designing and operating an off-grid building can seem extreme compared to the norm,and provide a whole set of new challenges if the retrofitting of an existing structure is required.But the lessons learned from these experiences are quite relevant to modern buildings in urban and suburban areas,as the goal is the same-first reduce energy consumption through efficiency and conservation,rather than simply increasing energy production.With off-grid systems,the payback from these measures simply has a more immediate effect.And at the end of the day,non-electrical energy efficiency measures prove to be at least as effective as electrical ones.

Thermal Management of Electrified Propulsion System for Low-Carbon Vehicles

An overview of current thermal challenges in transport electrification is introduced in order to underpin the research developments and trends of recent thermal management techniques.Currently,explorations of intelligent thermal management and control strategies prevail among car manufacturers in the context of climate change and global warming impacts.Therefore,major cutting-edge systematic approaches in electrified powertrain are summarized in the first place.In particular,the important role of heating,ventilation and air-condition system(HVAC)is emphasised.The trends in developing efficient HVAC system for future electrified powertrain are analysed.Then electric machine efficiency is under spotlight which could be improved by introducing new thermal management techniques and strengthening the efforts of driveline integrations.The demanded integration efforts are expected to provide better value per volume,or more power output/torque per unit with smaller form factor.Driven by demands,major thermal issues of high-power density machines are raised including the comprehensive understanding of thermal path,and multiphysics challenges are addressed whilst embedding power electronic semiconductors,non-isotropic electromagnetic materials and thermal insulation materials.Last but not least,the present review has listed several typical cooling techniques such as liquid cooling jacket,impingement/spray cooling and immersion cooling that could be applied to facilitate the development of integrated electric machine,and a mechanic-electric-thermal holistic approach is suggested at early design phase.Conclusively,a brief summary of the emerging new cooling techniques is presented and the keys to a successful integration are concluded.