Determining the Recoverable Geothermal Resources Using a Numerical Thermo-Hydraulic Coupled Modeling in Geothermal Reservoirs

Recoverable geothermal resources are very important for geothermal development and utilization. Generally, the recovery factor is a measure of available geothermal resources in a geothermal field. However, it has been a pre-determined ratio in practice and sustainable utilization of geothermal resources was not considered in the previous calculation of recoverable resources. In this work, we have attempted to develop a method to calculate recoverable geothermal resources based on a numerical thermo-hydraulic coupled modeling of a geothermal reservoir under exploitation, with an assumption of sustainability. Taking a geothermal reservoir as an example, we demonstrate the effectiveness of the method. The recoverable geothermal resources are 6.85 × 1018 J assuming a lifetime of 100 years in a well doublet pattern for geothermal heating. We further discuss the influence of well spacing on the recoverable resources. It is found that 600 m is the optimal well spacing with maximum extracted energy that conforms to the limit of the pressure drop and no temperature drop in the production well. Under the uniform well distribution pattern for sustainable exploitation, the recovery factor is 26.2%, which is higher than the previous value of 15% when depending only on lithology. The proposed method for calculating the recoverable geothermal resources is instructive for making decisions for sustainable exploitation.

The Phenomena and Criteria Determining the Cracking Susceptibility of Repair Padding Welds of the Inconel 713C Nickel Alloy

The creep-resistant casting nickel alloys (e.g., Inconel 713C) belong to the group of difficult-to-weld materials that are using for precise element production; e.g., aircraft engines. In precision castings composed of these alloys, some surface defects can be observed, especially in the form of surface discontinuities. These defects disqualify the castings for use. In this paper, the results of technological tests of remelting and surfacing by the Tungsten Inert Gas method (TIG) in an argon shield and TecLine 8910 gas mixture are presented for stationary parts of aircraft engines cast from Inconel 713C alloy. Based on the results of metallographic studies, it was found that the main problem during remelting and pad welding of Inconel 713C castings was the appearance of hot microcracks. This type of defect was initiated in the partial melting zone, and propagated to the heat affected zone (HAZ) subsequently. The transvarestraint test was performed to determine the hot-cracking criteria. The results of these tests indicated that under the conditions of variable deformation during the remelting and pad welding process, the high-temperature brittleness range (HTBR) was equal 246 °C, and it was between 1053 °C and 1299 °C. In this range, the Inconel 713C was prone to hot cracking. The maximum deformation for which the material was resistant to hot cracking was equal to 0.3%. The critical strain speed (CSS) of 1.71 1/s, and the critical strain rate for temperature drop (CST), which in this case was 0.0055 1/°C, should be used as a criteria for assessing the tendency for hot cracking of the Inconel 713C alloy in the HTBR. The developed technological guidelines and hot-cracking criteria can be used to repair Inconel 713C precision castings or modify their surfaces using welding processes.

Biocompatible and Thermoresistant Hydrogels Based on Collagen and Chitosan

Hydrogels are considered good biomaterials for soft tissue regeneration. In this sense, collagen is the most used raw material to develop hydrogels, due to its high biocompatibility. However, its low mechanical resistance, thermal stability and pH instability have generated the need to look for alternatives to its use. In this sense, the combination of collagen with another raw material (i.e., polysaccharides) can improve the final properties of hydrogels. For this reason, the main objective of this work was the development of hydrogels based on collagen and chitosan. The mechanical, thermal and microstructural properties of the hydrogels formed with different ratios of collagen/chitosan (100/0, 75/25, 50/50, 25/75 and 0/100) were evaluated after being processed by two variants of a protocol consisting in two stages: a pH change towards pH 7 and a temperature drop towards 4 °C. The main results showed that depending on the protocol, the physicochemical and microstructural properties of the hybrid hydrogels were similar to the unitary system depending on the stage carried out in first place, obtaining FTIR peaks with similar intensity or a more porous structure when chitosan was first gelled, instead of collagen. As a conclusion, the synergy between collagen and chitosan improved the properties of the hydrogels, showing good thermomechanical properties and cell viability to be used as potential biomaterials for Tissue Engineering.

Simulation of solar PV surface temperature with dimpled fin cooling

A significant number of cooling technologies have been developed to maintain the PV module temperature within subscribed limits. This paper represents the simulation study of active cooling forced air convection with fins attached to the back of the solar panel using CFD SimScale software. It has been first carefully validated against experimental and numerical results available in the literature. The number of fins and the shape of perforated and dimpled in each fin were varied to compare cooling performance. Three types of fins were adapted into this simulation: traditional fins, circular, and triangle perforated/dimpled fins. The effect of solar irradiation and velocity inlet was also reviewed by applying the nominal operating condition from the experimental works. Results indicated that fin channels are a very effective cooling technique, which significantly reduces the average temperature of the PV cell, especially when increasing the number of fins from 20 to 26 fins. Also, the results show that the dimpled triangle fin had the highest average temperature drop with a percentage difference of 6% compared with the solar panel cooling with traditional fins.

Cooling Cyclic Air of Marine Engine with Water-Fuel Emulsion Combustion by Exhaust Heat Recovery Chiller

The fuel efficiency of marine diesel engine as any combustion engine falls with raising the temperature of air at the suction of its turbocharger. Therefore, cooling the engine turbocharger intake air by recovering exhaust gas heat to refrigeration capacity is a very perspective trend in enhancing the fuel efficiency of marine diesel engines. The application of water-fuel emulsion (WFE) combustion enables the reduction of a low-temperature corrosion, and, as a result, provides deeper exhaust gas heat utilization in the exhaust gas boiler (EGB) to the much lower temperature of 90–110 °C during WFE instead of 150–170 °C when combusting conventional fuel oil. This leads to the increment of the heat extracted from exhaust gas that is converted to refrigeration capacity by exhaust heat recovery chiller for cooling engine turbocharger sucked air accordingly. We experimentally investigated the corrosion processes on the condensation surfaces of EGB during WFE combustion to approve their intensity suppression and the possibility of deeper exhaust gas heat utilization. The fuel efficiency of cooling intake air at the suction of engine turbocharger with WFE combustion by exhaust heat recovery chiller was estimated along the voyage line Mariupol–Amsterdam–Mariupol. The values of available refrigeration capacity of exhaust heat recovery chiller, engine turbocharger sacked air temperature drop, and corresponding reduction in specific fuel consumption of the main low-speed diesel engine at varying actual climatic conditions on the voyage line were evaluated.

Hybrid Nanofluid-Based Thermal Fluid–Structure Interaction (FSI) Investigations for the Thermal Management System of a Computer Microprocessor

The heat extraction from and cooling of computer microprocessors are challenging tasks in the modern era. Previously, the microprocessors were usually cooled by air, but now industry is shifting towards using nanofluids, as their properties are more thermo-physically stable. The experimental and numerical studies have revealed that the rate of heat transfer depends both on the thermal characteristics of the coolant and the geometry of the heat sink. For optimized results, it is recommended to analyze the combined effect of nanofluids and the geometry of the heat sink. Mini-channel heat sinks in combination with a nanofluid offered an excellent rate of heat transfer. However, passing nanofluids continuously through the system causes various problems over time; for example, the thermal stresses on the components are increased, which may lead to wear and tear of the system. In this study, a numerical investigation of mini-channel heat sinks was conducted through thermal-FSI. A numerical model was established with airfoil and Savonius pin-fin mini channel heat sinks, and they were analyzed at different flow rates from 0.25 LPM to 0.75 LPM with an increment of 0.25 LPM with different fluids, i.e., water, Al2O3–H2O, and Fe2O3–H2O nanofluids, varying their volumetric concentration. The minimum stresses were obtained while increasing the temperature drop and decreasing the pressure drop. The thermal stresses were calculated using the thermal-FSI technique and were found to be in the threshold range, and hence the material was within the yield limit at 0.75 LPM when using the Fe2O3-H2O Nanofluid at a 0° angle using the Savonius heat sink.

Comparative Analysis of the Cooling Efficiency in Tropical Climate of Three Alternative Materials for Evaporative Cooling Pads

A comparison between commercial cellulose evaporative cooling pad and pads manufactured with three alternative materials was made for environmental conditions typical of tropical countries. Wind tunnel tests were carried out to compute the convective heat and mass transfer coefficients and to measure the pressure drop across each pad, obtaining expressions that can be used as reference for future simulations. Using a mathematical model, a detailed analysis of the efficiency, Temperature–Humidity Index, temperature drop and relative humidity through the pads was performed in terms of different operative and constructive conditions, such as air velocities, dry-bulb temperatures, relative humidity and pad thickness. Significant differences between the pressure drop across the pads were found, which increases with the inlet air velocity and water flow. A weak relation between the analysed variables and the inlet air velocity was found, while a high correlation between the analysed variables, pad thickness and the external environmental conditions was established. Cooling efficiencies above 40% and a Temperature–Humidity Index below the mild zone of thermal stress were obtained for the alternative panels. Although the cellulose cooling pad showed the best behaviour in all aspects, the alternative pads can be used as substituted in specific applications to reduce the Temperature–Humidity Index inside agricultural facilities.

Comparison of Tar Samples from Reaction Zone and Outlet in Ex-Situ Underground Coal Gasification Experiment

Tar remaining in the gasification cavity during underground coal gasification (UCG) is an important pollution source, while the reported studies only focus on the tar behavior at the outlet. The present work aims to compare the tar properties from the reaction zone and the outlet, analyze the tar evolution during gasification, and discuss possible measures to control tar pollution. Tar was sampled with a self-developed equipment from an ex-situ underground coal gasification experimental system and analyzed by GC-MS. The gas composition, temperature, and PM10 were also compared for the reaction zone and the outlet. Compared with the tar from reaction zone, the tar from outlet has a smaller percentage of high boiling point content, PAHs, C, O, N, S, Cl, Si, and a larger percentage of H. The PAHs percentage in tar at the outlet in this work is closer to the field data than the lab data from literature, indicating the experimental system gives a good simulation of tar behavior in underground coal gasification. Condensation due to a fast temperature drop is one of the main reasons for PAHs decreasing. Tar cracking and soot formation also cause the decrease of heavy tar, proven by the light gas and particulate matter results.

Hazards Generated by an LNG Road Tanker Leak: Field Investigation of Vapour Propagation under Class B Conditions of Atmospheric Stability

The publication presents the results of a field test of 2–4 min releases of 96% LNG from a road tanker designed to carry the gas. The release was performed at a pressure of 5.9–6.1 atm at a discharge rate of 1.67–1.78 kg/s from a height of 0.75 m under class B conditions of atmospheric stability. Comparison of the obtained experimental results of the maximum concentrations and the simulation carried out with the EFFECS (11.2.0) software showed that the Gaussian gas model better describes the gas cloud propagation at most control points at this release intensity than the dense gas model. The dense gas model gave only slightly better results along the cloud propagation axis at close distances, not exceeding 25/30 m at ground level. It is shown that concentrations between 71% and 110% LEL are observed at the cloud visibility limit. The maximum value of the temperature drop, in the release axis, at a distance of 4 m amounts to ∆Tmax = 93.3 °C. This indicates that the cloud of the released LNG is almost entirely in the vapour state already in the short distance from the point of release, due to the turbulent outflow of the pressurised gas.

I-mode pedestal relaxation events in the Alcator C-Mod and ASDEX Upgrade tokamaks

In some conditions, I-mode plasmas can feature pedestal relaxation events (PREs) that transiently enhance the energy reaching the divertor target plates. To shed light on their appearance, characteristics and energy reaching the divertor targets, a comparative study between two tokamaks – Alcator C-Mod and ASDEX Upgrade – is carried out. It is found that PREs appear only in a subset of I-mode discharges, mainly when the plasma is close to the H-mode transition. Also, a growing oscillating precursor before the PRE onset is observed in the region close to the separatrix in both devices, and a discussion on a possible triggering mechanism is outlined. The PRE relative energy loss from the confined region is found to increase with decreasing pedestal top collisionality ν* ped. Similarly, also the relative electron temperature drop at the pedestal top, which is related to the conductive energy loss, rises with decreasing ν* ped. Based on these relations, the PRE relative energy loss in future devices such as DEMO and ARC is estimated. Finally, the divertor peak energy fluence due to the PRE is measured on each device. Those values are then compared to the model introduced in [1] for type-I ELMs. The model is shown to provide an upper boundary for PRE energy fluence data, while a lower boundary is found by dividing the model by three. These two boundaries are used to make projections of the PRE divertor energy fluence to DEMO and ARC.