Thermal Response Measurement and Performance Evaluation of Borehole Heat Exchangers: A Case Study in Kazakhstan

The purpose of the present work was to determine the thermal performance of borehole heat exchangers, considering the influences of their geometric configurations and the thermophysical properties of the soil, grout and pipe wall material. A three-dimensional model was developed for the heat and mass transfer in soil (a porous medium) and grout, together with one-dimensional conductive heat transfer through the pipe walls and one-dimensional convective heat transfer of the heat transfer fluid circulating in the pipes. An algorithm was developed to solve the mathematical equations of the model. The COMSOL Multiphysics software was used to implement the algorithm and perform the numerical simulations. An apparatus was designed, installed and tested to implement the thermal response test (TRT) method. Two wells of depth 50 m were drilled in the Almaty region in Kazakhstan. Gravel and till/loam were mainly found, which are in accordance with the stratigraphic map of the local geological data. In each well, two borehole heat exchangers were installed, which were an integral part of the ground source heat pump. The TRT measurements were conducted using one borehole heat exchanger in one well and the data were obtained. The present TRT data were found to be in good agreement with those available in literature. The numerical results of the model agreed well with the present TRT data, with the root-mean-square-deviation within 0.184 °C. The TRT data, together with the predictions of the line-source analytical model, were utilized to determine the soil thermal conductivity (λg = 2.35 W/m K) and the thermal resistance of the borehole heat exchanger from the heat transfer fluid to the soil (Rb = 0.20 m K/W). The model was then used to predict the efficiencies of the borehole heat exchangers with various geometric configurations and dimensions. The simulation results show that the spiral borehole heat exchanger extracts the highest amount of heat, followed by the multi-tube, double U-type parallel, double U-type cross and single U-type. It is also found that the spiral configuration can save 34.6% drilling depth compared with the conventional single U-type one, suggesting that the spiral configuration is the best one in terms of the depth and the maximum heat extracted. The simulation results showed that (i) more heat was extracted with a higher thermal conductivity of grout material, in the range of 0.5–3.3 W/m K; (ii) the extracted heat remained unchanged for a thermal conductivity of pipe material higher than 2.0 W/m K (experiments in the range of 0.24–0.42 W/m K); (iii) the extracted heat remained unchanged for a volumetric flow rate of water higher than 1.0 m3/h (experimental flow rate 0.6 m3/h); and (iv) the heat extracted by the borehole heat exchanger increased with an increase in the thermal conductivity of the soil (experiments in the range of 0.4–6.0 W/m K). The numerical tool developed, the TRT data and simulation results obtained from the present work are of great value for design and optimization of borehole heat exchangers as well as studying other important factors such as the heat transfer performance during charging/discharging, freezing factor and thermal interference

Ab initio calculations of pure and Co+2-doped MgF2 crystals

This research was partly supported by the Kazakhstan Science Project № AP05134367«Synthesis of nanocrystals in track templates of SiO2/Si for sensory, nano- and optoelectronic applications», as well as by Latvian Research Council project lzp-2018/1-0214. Calculations were performed on Super Cluster (LASC) in the Institute of Solid State Physics (ISSP) of the University of Latvia. Authors are indebted to S. Piskunov for stimulating discussions.Ab initio calculations of the atomic, electronic and vibrational structure of a pure and Co+2 doped MgF2 crystals were performed and discussed. We demonstrate that Co+2 (3d7) ions substituting for Mg is in the high spin state. In particular, the role of exact non-local exchange is emphasized for a proper reproduction of not only the band gap but also other MgF2 bulk properties. It allows us for reliable estimate of the dopant energy levels position in the band gap, and its comparison with the experimental data. Thus, the present ab initio calculations and experiment data demonstrate that the Co+2 ground state level lies at ≈2 eV above the valence band top.Kazakhstan Science Project № AP05134367; Latvian Council of Science project lzp-2018/1-0214; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Diffusion of Oxygen in Hypostoichiometric Uranium Dioxide Nanocrystals. A Molecular Dynamics Simulation

Received: 04.02.2021. Revised: 30.03.2021. Accepted: 30.03.2021. Available online: 31.03.2021.This article belongs to the PCEE-2020 Special Issue.A molecular dynamic simulation of diffusion of intrinsic oxygen anions in the bulk of hypostoichiometric UO2-x nanocrystals with a free surface was carried out. The main diffusion mechanism turned out to be the migration of oxygen by the anionic vacancies. It is shown that in the range of values of the non-stoichiometry parameter 0.05 ≤x ≥ 0.275 the oxygen diffusion coefficient D is weakly dependent on temperature, despite the uniform distribution of the vacancies over the model crystallite. The reliable D values calculated for the temperature T = 923 K are in the range from 3∙10-9 to 7∙10-8 cm2/s, in quantitative agreement with the experimental data. The corresponding diffusion activation energy is in the range from 0.57 eV to 0.65 eV, depending on the interaction potentials used for the calculations.The work was financially supported by the State Atomic Energy Corporation Rosatom, state contract no. Н.4о.241.19.20.1048 dated 17.04.2020, identifier 17706413348200000540. S.K. Gupta thanks the Department of Science and Technology (India) and the Russian Foundation for Basic Research (Russia) for the financial support (Grant no.: INT/RUS/RFBR/IDIR/P-6/2016)

Experimental and Theoretical Investigations of a Ground Source Heat Pump System for Water and Space Heating Applications in Kazakhstan

The ground source heat pump heating system is considered as one of the best solutions for the transition towards green heating under the continental climate conditions like Kazakhstan. In this paper, experimental and theoretical investigations were carried out to develop a ground source heat pump-based heating system under the weather conditions in Kazakhstan and to evaluate its thermodynamic performance. The water-to-water heat pump heating system, integrated with a ground source heat exchanger and used refrigerant R134a, was designed to provide hot water to meet the requirements for space heating. The predicted values of the coefficient of performance and the experimental results were found to be in good agreement within 6.2%. The thermodynamic performance of the system was also assessed using various environment-friendly refrigerants, such as R152a, R450A, R513A, R1234yf and R1234ze, as potential replacements for R134a. Although R152a is found to be a good alternative for R134a in terms of coefficient of performance and total equivalent warming impact, its flammability hinders its application. The heating system using refrigerants R450A, R513A, R1234yf and R1234ze shows 2–3% lower coefficient of performance than that of R134a. The highest exergy destruction is found to be attributed to the compressor, followed by the expansion valve, evaporator, and condenser. Considering their low flammability and low environmental impact, R450A, R513A, R1234yf and R1234ze are identified as valuable replacements for R134a

Ab-initio calculations of CO2 adsorption on nonpolar (100) ZnO surface

In this paper, the ab-initio calculations of the CO2 molecule adsorption on the nonpolar ZnO surface were carried out in order to find the equilibrium configuration of the adsorbed molecule, as well as we studied the effect of impurity concentration and the presence of native point defects onto binding energy of molecule. Also, the potential for-mation of a new molecular complex is considered. All results were compared with known experimental data

HIGH-PERFORMANCE COMPUTATIONAL MODELING OF CATION DIFFUSION IN DEFECT-FREE MIXED URANIUM, PLUTONIUM AND THORIUM DIOXIDES

Molecular dynamics (MD) modeling of the diffusion of intrinsic cations of thorium, plutonium and uranium in the volume of nanocrystals of mixed composition (U,Pu,Th)O2, containing from 5460 to 27600 particles, was carried out at temperatures correspond to the superionic state.Д.Д, Сеитов и К.А. Некрасов благодарят Комитет науки Министерства науки и высшего образования Республики Казахстан Республики Казахстан, проект AP19174919

Variable-Charge Molecular Dynamics Model of UC, U2C3 и UC2 Crystals

A potential model describing metallic, covalent and ionic bonding using dynamically varying charges is proposed. Parameters are restored by minimizing the total energy of UxCy crystals defined by charge states. A linear expansion model coefficients vs experimental data numerical consent is obtained.Исследование выполнено при финансовой поддержке Министерства науки и высшего образования Российской Федерации в рамках проекта № FEUZ-2020-0060

Assessment of adherence to treatment in patients with refractory arterial hypertension

Currently of resistant arterial hypertension considers as a frequent cause of high mortality from cardiovascular diseases in Russia, despite the fact that there are not conclusive data about the prevalence of true resistant hypertension. In this fashion, the study of treatment adherence in this group of patients gives the opportunity to improve the quality of life and optimally stabilize the numbers arteriotony.В настоящее время резистентная артериальная гипертензия рассматривается как частая причина высокой смертности от сердечно-сосудистых заболеваний в России, несмотря на то, что убедительных данных о распространенности истинно резистентной артериальной гипертензии нет. Таким образом, изучение приверженности к лечению у данной категории пациентов дает возможность улучшить качество жизни и оптимально стабилизировать цифры АД

Use of endovascular radio- frequency denervation of renal arteries in the rational combined therapy of patients with resistant arterial hypertension

The aim of the study was to study the safety and efficacy of endovascular radiofrequency denervation of the renal arteries in the combined therapy of patients with resistant arterial hypertension. Endovascular radiofrequency denervation of renal arteries was performed in 27 patients. The observation period was 1,3,6,12 months after the procedure, with the assessment of adverse events and daily measurement of blood pressure. As a result, the clinical significance of the method to reduce systolic and diastolic blood pressure was determined according to the results of a year's observation, which in turn reduces the risk of cardiovascular complications, as well as the risk of death.Целью исследования было изучение безопасности и эффективности эндоваскулярной радиочастотной денервации почечных артерий в комбинированной терапии пациентов с резистентной артериальной гипертензией. Процедура эндоваскулярной радиочастотной денервации почечных артерии проведена 27 пациентам. Период наблюдения составил 1,3,6,12 месяцев после проведения процедуры, с оценкой нежелательных явлений и суточным измерением артериального давления. В результате определена клиническая значимость метода по снижению систолического и диастолического артериального давления по результатам годичного наблюдения, что в свою очередь снижает риск развития сердечно-сосудистых осложнений, а также риск смерти