Comparative study on the thermal performance and economic efficiency of vertical and horizontal ground heat exchangers

The ground-coupled heat pump is a shallow geothermal exploitation method taking soil as the thermal energy source. The ground heat exchanger is an important component of this system, which includes vertical or horizontal configurations. However, to the best of our knowledge, few studies exist involving the comparison of thermal performances and installation costs of two heat exchanger types considering the influence of ground climate, which makes the selection of heat exchanger configuration challenging for a specific field application. Hence, a 3-dimensional numerical model considering the variations of atmospheric conditions and soil water content is constructed in this paper. Based on this model, the thermal performances and economical efficiencies of vertical and horizontal ground heat exchangers are compared. The results indicate that the thermal performance difference between the two heat exchangers is greater in winter than in summer. The thermal performance is hardly influenced by the injection mass flow rate, while it is considerably affected by the length of heat exchanger. The thermal power rises linearly with the increase in heat exchanger length, and the increment of the vertical ground heat exchanger is higher. In addition, when the heat exchanger length is shorter than 40 m, the installation cost and thereby the total cost of the horizontal ground heat exchanger is considerably higher. With regard to both the thermal performance and economic efficiency, a vertical ground heat exchanger is only recommended when installing a single shallow ground heat exchanger.Cited as: Cui, Q., Shi, Y., Zhang, Y., Wu, R., Jiao, Y. Comparative study on the thermal performance and economic efficiency of vertical and horizontal ground heat exchangers. Advances in Geo-Energy Research, 2023, 7(1): 7-19. https://doi.org/10.46690/ager.2023.01.0

AlN nanostructures : tunable architectures and optical properties

Novel AlN nanostructures with tunable building units of the architectures have been successfully synthesized without any catalyst or template; the subsequent photoluminescence (PL) indicates that the optical properties of the AlN nanostructures can be adjusted by tuning the architectures.<br /

Three-dimensional AlN microroses and their enhanced photoluminescence properties

Novel three-dimensional AlN microroses, for the first time, have been synthesized via direct reaction between Al and N2 in arc plasma without any catalyst and template.<br /

One-step synthesis of AlN branched nanostructures by an improved DC arc discharge plasma method

Aluminium nitride (AlN) branched nanostructures with tree shapes and sea urchin shapes are synthesized via a one-step improved DC arc discharge plasma method without any catalyst and template. The branched nanostructures with tree shapes and sea urchin shapes can be easily controlled by the location of collection. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies show that the branches of tree shaped nanostructures grow in a sequence of nanowires, nanomultipeds and nanocombs. The growth mechanisms of these branched nanostructures are discussed in detail. The optical properties of AlN branched nanostructures with tree shapes and sea urchin shapes are investigated

China’s Language Services Industry: Status Quo and Suggestions for Sustainable Development

The language services industry merits investigation, given its increasingly significant role and rapid development in China and even around the world. This paper gives a brief look at the global picture and a close look at the status quo in China. While in the global market, language services tend to be diversified and technology will be the common denominator to success, in China, despite the rapid growth in recent years, the market leaves much to be desired when it comes to technology, language diversity, high-end talent development, and overall competitiveness. To tackle these problems, this paper proposes some measures for China’s language services providers to catch up with their international counterparts and for China’s language services industry to achieve sustainable development

Design of mine-used wearable folded half-mode substrate-integrated cavity antenna

Based on half-mode substrate-integrated cavity antenna, a mine-used wearable folded half-mode substrate-integrated cavity antenna was designed considering requirements for underground wearable antenna. Width of antenna is reduced by use of folded geometry, and planar antenna is realized with horizontal feeding probe structure. The simulation results show that the antenna resonates at 5 GHz, -10 dB bandwidth is 254 MHz, the maximum gain is 5.4 dBi, radiation efficiency is 70%, and the antenna has radiation direction with wide beamwidth and low back radiation. Besides, -10 dB bandwidth of the antenna can be increased with thicker upper substrate

The injection-production performance of an enhanced geothermal system considering fracture network complexity and thermo-hydro-mechanical coupling in numerical simulations

Abstract The effect of fracture networks on EGS performance remains worth further investigation to guide the formulation of geothermal extraction strategy. We established models that account for thermo-hydraulic-mechanical (THM) coupling and that are based on the framework of discrete fracture network (DFN) to evaluate the heat extraction performance in deep-seated fractured reservoir. Our numerical results reveal that the zones of temperature, pressure, and stress perturbation diffuse asynchronously during the circulation of injection-production, and the stress perturbation always lags behind the other two. Furthermore, the effects of the fracture network characteristics including randomness, geometry, length, aperture, and injection parameters on the heat production are quantitatively investigated. Under the same number of fractures, different network geometry leads to different EGS production performance, the network with horizontal fracture set shows better thermal extraction performance but poor injection performance, which is because the fracture dip affects the thermal evolution on the horizontal plane. The effect of fracture length on EGS performance highly depends on its orientation, the excessive increase of fracture length towards injection-production wells is detrimental to heat extraction. The fracture aperture affects the working fluid transport and thus the EGS performance, the fractured reservoir with smaller fracture aperture shows the worse fluid flow performance but the better geothermal extraction performance, thus we believe that the optimal fracture aperture should be kept at a level of 0.5–1.0 mm in a self-propping fractured granitic system. The main influence of injection parameters on thermal extraction from the fractured reservoirs is the injection mass rate, because a high injection rate results in significant solid responses, including failure stress concentration, decreased safety factor, and increased permeability, which occur in those fractures that are originally connected to the injection well. These results of our research and the insights obtained have important implications for deep geothermal geoengineering activities