Increase In Temperature Difference Research Articles

Ventilation performance study of a high-speed train cabin based on displacement ventilation and mixed ventilation

Indoor ventilation systems play an important role in controlling energy consumption, thermal comfort, and airborne pollutants. This work is concerned with whether the combination of displacement and mixed ventilation can overcome these systems' respective shortcomings to improve the ventilation performance of high-speed train cabins. This work is based on computational fluid dynamics. The results show that when more fresh airflow enters the compartment from the top vents, the flow field is mainly driven by mechanical forces, and two vortices are formed. When more fresh airflow enters the compartment from the bottom vents, the flow field is mainly driven by thermal buoyancy. Meanwhile, the airflow mainly spreads upward, with lower cooling energy consumption, lower wind speed, higher ventilation efficiency, and smaller longitudinal diffusion of pollutants, but increased temperature difference. When the ratio of top and bottom supply air flow is 75%/25%, thermal comfort can be improved, while balancing energy consumption and air quality. If there was a disease outbreak, the flow rate of the bottom air supply could be increased appropriately. To further improve the ventilation performance, on the one hand, it is necessary to appropriately increase the temperature of the bottom air supply, and on the other hand, it is necessary to avoid short-circuiting of the airflow, due to the lack of synergy between thermal buoyancy and mechanical force. The results of the study can provide a reference for safeguarding passengers and improving the ventilation design of high-speed trains.

Thermodynamic analysis of a novel gas separator based on molecular exchange flow

An energy analysis model and several evaluation indexes are established for a novel gas separator employing molecular exchange flow as working principle. The influences of several important factors on energy consumption and thermal efficiency are investigated. As temperature difference increases, both energy consumption and thermal efficiency rise linearly. As Knudsen number increases, total work decreases while minimum separation work and thermal efficiency initially increase and subsequently decrease. When inlet velocity increases, total work increases but minimum separation work and thermal efficiency go down. Furthermore, both energy consumption and thermal efficiency initially rise and then decline with an increasing mole fraction of the lighter molecular weight component. The results indicate that energy consumption and separation performance should be taken into consideration when selecting temperature differences. In addition, it is preferable to choose the Knudsen number corresponding to optimal separation performance and the intermediate value for component mole fraction. Moreover, it had better employ a lower inlet velocity as long as the separation requirements are satisfied. This study presents a method to optimize the performance of the novel separator based on molecular exchange flow from the perspective of energy conversion and utilization.

Identifying enhancement of double slope solar still performance by adding water cooling to walls

The object of this research is a double-slope solar still with the addition of water cooling on the wall (DSSS.WCW). The issue with solar stills is that the temperature of the cover glass is quite high, which consequently reduces the rate of evaporation. Methods to reduce the cover glass temperature involve water cooling, by flowing water and spraying it onto the cover glass. Both of these methods have been shown to reduce the temperature of the cover glass, but they still require additional energy and can decrease the solar radiation energy received by the absorber plate. This research proposes using a water cooling method on the wall that does not require additional energy and can prevent a reduction in the solar radiation energy received by the absorber plate. Experimental and theoretical research was conducted to study the effect of using DSSS.WCW. The results showed a 13.48 % reduction in the cover glass temperature, consequently increasing the temperature difference between the fins and the cover glass by 9.82 °C. The increase in temperature difference resulted in a 13.82 % increase in freshwater productivity theoretically by 2.80 kg/hour and a 13.10 % increase experimentally for the DSSS.WCW by 2.58 kg/hour. In addition, there was a theoretical increase in energy efficiency of 22.29 % and an experimental increase of 22.82 %, along with an increase in exergy efficiency of 15.71 %. The implementation of water cooling on the wall has been shown to enhance the efficiency of the double-slope solar still. In addition, the water cooling method on the wall does not reduce the solar radiation energy that can be received by the absorber plate and does not require additional energy. The results of this research can be applied in remote islands in Indonesia, particularly during the dry season

Enhanced performance of thermoelectric generation system by increasing temperature difference using spray cooling

Thermoelectric generation system (TEGS) can directly convert the waste heat to electricity in practice. The power generation is highly impacted by the temperature difference between the hot and cold ends. To significantly improve the temperature difference, various cooling technologies have been applied to TEGS. However, there is still room to further increase the power generation efficiency of TEGS by enhancing the cooling performance. Herein, spray cooling was introduced to the TEGS and influencing factors were investigated. The experimental study demonstrates that, upon the spray cooling, the cold-end temperature can be dramatically reduced up to 27 °C. Further, the output performance of the TEGS was substantially increased by optimizing spray heights, flow rates and heat source temperatures, etc. For example, for the spray height of 3 cm, the TEGS achieves a maximum output voltage because the thermoelectric generation module (TGM) is completely covered by the spray area in this study. Moreover, the temperature difference between cold/hot ends and voltage of the TEGS are further increased to 55 °C and 1.39 V at a flow rate of 100 L/min. On the other hand, increasing the heat source temperature (hot end temperature) can also strongly improve the output performance of the TEGS. Particularly, compared to passive air cooling, spray cooling can enable the TEGS to significantly increase its output voltage and current by 17 and 27 times, respectively. Finally, this study would potentially provide a new cooling strategy to strongly enhance the output performance of TEGS.

Background-oriented schlieren experimental and simulation study of the effect of sidewalls on optical turbulence anisotropy in a thermal convection turbulence simulator

The anisotropic optical structure characteristics within the Rayleigh-Bénard (RB) turbulence simulator have been investigated through experiment and simulation. We collected data using background-oriented schlieren technology and extracted displacements using optical flow algorithms. The wavefront phase can be recovered using the conjugate gradient iterative algorithm. We analyzed the optical structural characteristics within the turbulence simulator under different temperature differences. It is observed that with an increased temperature difference, the spatial correlation of the refractive index field decreases at an accelerated rate as the separation distance increases, and the degree of anisotropy characterized by the phase structure function increases. Large eddy simulation and split-step beam propagation method complement experimental results. Numerical simulations demonstrate consistency with experimental data. The results show that the von Karman power spectral density fits the simulation and experimental phase structure function very well relative to the Kolmogorov power spectral density, which demonstrates that the simulation system combining dynamics simulation and optical simulation can achieve power spectral characteristics that are consistent with reality. The experimental and simulation results are crucial for understanding the flow field's optical structural properties inside the turbulence simulator. They will help to construct a suitable turbulence simulator for optical engineering applications and establish a rational scheme for analyzing its internal optical structural properties.

Applying isovolumic steam capsule as new thermal energy storage unit

In order to make up the inefficiencies of liquid–solid phase change material (PCM) such as low latent heat and low heat transfer rate, the possibility of adopting water steam as the phase change material is explored. Although great volume change occurs during the gas–liquid phase-changing, the specific latent heat is at least one order of magnitude larger than that of liquid–solid phase-changing. To minimize the adverse effect of the great volume change during vaporization or condensation, the steam can be accommodated inside sealed vessel with sturdy shell. In this study, an isovolumic steam capsule (ISC) was made by filling a cylinder with a small amount of liquid water and then heated and boiled to extinguish the non-condensable gas (NCG) before sealing it. Thermodynamic analysis shows the thermal energy contained in the isovolumic steam capsule per unit volume increases in approximately an exponential manner with the increase of temperature due to the evaporation of liquid, and can reach several times that of liquid–solid phase change material, demonstrating great potential as energy storage material. The heat transfer experiments show that the energy charging and discharging rates increase with the temperature difference. There exists thermodynamic non-equilibrium during heat transfer and the deviation from saturation enlarges with increasing temperature difference and non-condensable gas concentration. For both charging (vaporization) and discharging (condensation), a higher non-condensable gas concentration in the steam exhibits larger heat transfer rate in the beginning, but smaller heat transfer rate in the later stage. The mechanism of vaporization and condensation in the isovolumic steam capsule awaits to be further clarified.

Study on the Coupled Heat Transfer of Conduction, Convection, and Radiation in Foam Concrete Based on a Microstructure Numerical Model

Foam concrete is a typical cement-based porous material; its special microstructure endows it with excellent properties, such as light weight, energy efficiency, thermal insulation, and fire resistance. Therefore, it is widely used as a thermal insulation material for buildings. The heat transfer modes of foam concrete include conduction, convection, and radiation. However, previous studies considered conduction to be the dominant mode, often neglecting the effects of convection and radiation. In this study, a stochastic numerical model of the foam concrete microstructure is established based on the statistical parameters of the pore structure. With this model, the heat transfer mechanism of foam concrete is analyzed at the mesoscopic level, and the equivalent thermal conductivity is calculated. By comparing four different working conditions, the influence of conduction, convection, and radiation on the heat transfer of foam concrete is analyzed, and the specific contribution rates of conduction, convection, and radiation are calculated. The results show that the convection effect is weak due to the pore size being smaller than 1 ; so, the influence of convection can be neglected in the heat transfer analysis of foam concrete. The contribution of radiation increases with the decrease in foam concrete density and the increase in temperature difference. When the temperature difference is 40 and the density is 300 , the contribution of radiation exceeds 20. Therefore, for low-density and high-temperature difference situations, the influence of radiation cannot be ignored. The heat transfer in foam concrete is mainly through conduction, but with the decrease in density and the increase in temperature difference, the contribution of conduction shows a downward trend. Nevertheless, the contribution of conduction is still much larger than that of radiation and convection.

A semi-analytical strategy for mixed convection non-Newtonian nanofluid flow on a stretching surface using Cattaneo-Christov model

This study investigates flow of non-Newtonian fluid containing nano particles and gyrotactic micro-organisms on stretching surface considering magnetic factor and thermal radiations. Cattaneo-Christov model is employed to analyze flow characteristics. The governing Partial Differential Equations (PDEs) along with associated boundary conditions describing the model are converted into Ordinary Differential Equations (ODEs) by suitable transformations. Homotopy Analysis Method (HAM), a semi-analytic solution technique is employed to obtain the solutions. The inspiration of important embedding variables on velocity, temperature, and concentration profiles are presented in tabular and graphical form to elaborate flow properties. It is deduced that the convective parameter and Weissenberg number, both have positive effect on dimensionless velocity whereas buoyancy ratio factor, bio-convective Rayleigh number, and magnetic force have inverse relationship with velocity profile. The presence of radiations and Brownian motion parameter boost energy transfer while it diminishes for higher Prandtl number values and mixed convection factor. Concentration intensifies for larger Prandtl number, activation energy, and thermophoresis parameters whereas it decreases for increasing temperature difference, Brownian motion, Schmidt number, and mixed convection factor. Bio-convective Peclet number, Lewis number, and microorganism concentration gradient factor, all depreciate microorganism concentration panel.

Experimental Study of Water Vapor Adsorption on Bare Soil and Gravel Surfaces in an Arid Region of Ningxia, China

Water vapor adsorption on soil, a crucial non-rainfall water resource in arid regions, warrants further experimental investigation, particularly on two typical land surfaces: bare soil and gravel. This study examined the formation characteristics and influencing factors of vapor adsorption in an arid region of Northwestern China. Observations and analyses were conducted on adsorption and evaporation measurements taken by two small weighing lysimeters (SLSs); soil temperature at a depth of 5 cm; surface temperature; relative humidity; and air temperature at a height of 30 cm above the ground from 2019 to 2020. The adsorbed water in this area was more abundant at night and less abundant during the day, with a stable nightly adsorption rate of 0.013 mm/h. Adsorption was more frequent in spring and winter (from January to June and November to December), accounting for about 90% of the total annual adsorption. In 2019 and 2020, the ratio values of adsorption to evaporation were 0.16 and 0.10 for bare soil, and 0.10 and 0.12 for gravel, respectively. Adsorption was more likely to occur when the soil moisture content was less than 13%; the highest adsorption frequency was close to 20% when the RH was between 75 and 95%; low soil temperatures were more conducive to the occurrence of adsorption. The effect of temperature differences (Ta−Ts) on adsorption was stronger than that of relative humidity. The adsorption frequency generally showed a bimodal change with increasing temperature difference, but the effect of temperature differences was less effective for gravel than bare soil. When the relative humidity was high and the temperature difference was weakly positive, the maximum adsorption intensity could reach 0.18 mm/h.

Exergy efficiency and heat transfer from the condenser in heat pump systems

In cooling systems, the thermal energy transfer capability of the condensers used for the condensation of the refrigerant is very important for the efficient operation of the systems. A heat pump assembly was installed and R134a was used as the fluid. During operation, the temperature of the refrigerant compressed in the condenser increases and reaches the superheated vapor phase. Heat is transferred from the surface of the condenser, whose temperature is increasing, to the environment with the help of a fan. The exergy efficiency of the condenser was determined based on the inlet and outlet temperature of the refrigerant to the condenser, the temperature of the air flow to and from the condenser surface, its masses and thermodynamic properties. It was observed that the exergy efficiency (ψ) increased and the irreversibility (İ) decreased with the increase of the air temperature difference (ΔT) passing over the condenser surface. In addition, it was determined that the exergy efficiency (ψ) and surface temperature of the condenser decreased with the increase in the amount of air passing through (ma) the condenser surface.

Effect of Temperature on Photosynthetic Pigment Degradation during Freeze–Thaw Process of Postharvest of Celery Leaves

Celery (Apium graveolens L.) is a kind of green leaf vegetable with a large consumption demand in the food industry. It is a commonly used material in quick-frozen food stuffing such as dumplings and steamed stuffed. Fresh celery leaf blades and petioles are rich in photosynthetic pigments including chlorophyll and carotenoid, their contents are closely related to the quality of celery and its products. In order to explore the effects of freezing and thawing temperature and thawing time on the degradation of photosynthetic pigments in celery leaf blades and petioles, the changes in photosynthetic pigments during thawing storage were measured under different freezing and thawing temperatures. The results showed that lower freezing and thawing temperatures were beneficial to the preservation of photosynthetic pigments in celery leaf blades and petioles, and the loss of photosynthetic pigments enhanced with the increase in thawing temperature and thawing time. Under the cold storage condition of −80 °C, the loss rate of pigment substances can be reduced by nearly 20% compared with that of −18 °C, and −80 °C and 4 °C could be the best temperature combination of freezing and thawing. The content and degradation rate of photosynthetic pigments in celery leaf blades were higher than that in petioles during thawing, with a total chlorophyll loss rate reaching 35% during 6 to 12 h after thawing. The increase in temperature difference between freezing and thawing could aggravate the damage to the cell structure and the degradation of the pigment, as chlorophyll is more sensitive to temperature changes, and the degradation rate is significantly higher than that of carotenoids. From the perspective of delaying the degradation of photosynthetic pigments, the results of this study will provide potential references for the reasonable configuration of freezing and thawing temperatures in the process of storage and transportation of celery products.

Identifying the Risk Factors of Allergic Rhinitis Based on Zhihu Comment Data Using a Topic-Enhanced Word-Embedding Model: Mixed Method Study and Cluster Analysis.

Allergic rhinitis (AR) is a chronic disease, and several risk factors predispose individuals to the condition in their daily lives, including exposure to allergens and inhalation irritants. Analyzing the potential risk factors that can trigger AR can provide reference material for individuals to use to reduce its occurrence in their daily lives. Nowadays, social media is a part of daily life, with an increasing number of people using at least 1 platform regularly. Social media enables users to share experiences among large groups of people who share the same interests and experience the same afflictions. Notably, these channels promote the ability to share health information. This study aims to construct an intelligent method (TopicS-ClusterREV) for identifying the risk factors of AR based on these social media comments. The main questions were as follows: How many comments contained AR risk factor information? How many categories can these risk factors be summarized into? How do these risk factors trigger AR? This study crawled all the data from May 2012 to May 2022 under the topic of allergic rhinitis on Zhihu, obtaining a total of 9628 posts and 33,747 comments. We improved the Skip-gram model to train topic-enhanced word vector representations (TopicS) and then vectorized annotated text items for training the risk factor classifier. Furthermore, cluster analysis enabled a closer look into the opinions expressed in the category, namely gaining insight into how risk factors trigger AR. Our classifier identified more comments containing risk factors than the other classification models, with an accuracy rate of 96.1% and a recall rate of 96.3%. In general, we clustered texts containing risk factors into 28 categories, with season, region, and mites being the most common risk factors. We gained insight into the risk factors expressed in each category; for example, seasonal changes and increased temperature differences between day and night can disrupt the body's immune system and lead to the development of allergies. Our approach can handle the amount of data and extract risk factors effectively. Moreover, the summary of risk factors can serve as a reference for individuals to reduce AR in their daily lives. The experimental data also provide a potential pathway that triggers AR. This finding can guide the development of management plans and interventions for AR.

Numerical simulation of hydraulic fracture propagation after thermal shock in shale reservoir

The scale of propagation of hydraulic fractures in deep shale is closely related to the effect of stimulation. In general, the most common means of revealing hydraulic fracture propagation rules are laboratory hydraulic fracture physical simulation experiments and numerical simulation. However, the former is difficult to meet the real shale reservoir environment, and the latter research focuses mostly on fracturing technology and the interaction mechanism between hydraulic fractures and natural fractures, both of which do not consider the influence of temperature effect on hydraulic fracture propagation. In this paper, the hydraulic fracturing process is divided into two stages (thermal shock and hydraulic fracture propagation). Based on the cohesive zone method, a coupled simulation method for sequential fracturing of deep shale is proposed. The effects of different temperatures, thermal shock rates, and times on the scale of thermal fractures are analyzed. As well as the effects of horizontal stress difference and pumping displacement on the propagation rule of hydraulic fractures. The results show that the temperature difference and the thermal shock times determine the size and density of thermal fractures in the surrounding rock of the borehole, and the number of thermal fractures increases by 96.5% with the increase of temperature difference. Thermal fractures dominate the initiation direction and propagation path of hydraulic fractures. The main hydraulic fracture width can be increased by 150% and the length can be increased by 46.3% by increasing the displacement; the secondary fracture length can be increased by 148.7% by increasing the thermal shock times. This study can provide some inspiration for the development of deep shale by improving the complexity of hydraulic fractures.

Effect of the magnetic field on the thermomechanical flexural wave propagation of embedded sandwich nanobeams

This work examines thermo-mechanical bending wave propagation in a sandwich nanobeam using advanced sandwich nanobeam and nanolocal strain gradient elasticity theories. The sandwich nanobeam is a unique structure with biocompatible ceramic ZrO2 and metal Ti6Al4V on the top and bottom sides. Sandwich nanobeam cores have functionally graded materials. This combination gives the nanobeam distinctive qualities and opens up many uses in diverse industries. The wave propagation equation is computed by applying the Navier method to the medium’s thermal, Lorentz, and viscoelastic equations of motion. The sandwich nanobeam is analyzed using four distinct models, taking into account its composition of ceramic and metal materials. The various factors that affect sandwich nanobeam bending wave propagation have been extensively studied. In the scenario where the magnetic field intensity is Hm = 0, an increase in temperature difference causes the wave frequency of all models (except Model 2) to decrease to zero, resulting in buckling. In Model 2, the sandwich nanobeam exhibits a phase velocity of 0.43 Km/s at ΔT = 0, which subsequently decreases by ∼9% to 0.39 km/s at ΔT = 500. These factors include the strength of the magnetic field, the impact of thermal loads, the nonlocal effect, the dimensions of the sandwich nanobeam, and the foundation’s influence. The findings of this research will help build nanosensor systems that can work in aerospace applications under extreme temperatures. These findings will contribute to the optimization of the design process, ensuring the reliability and functionality of the nanosensors under severe thermal conditions.

Optimization of a thermoelectric cooler-based system for atmospheric water production in terms of temperature of condensing surface

The extraction of water from the atmosphere is considered as a potential solution to alleviate the problem of water shortages. Therefore, it is crucial to improving the efficiency of water production from atmosphere. In this work, the effect of temperature of the condensing surface below 0 °C on the water productivity of thermoelectric water generator (TWG) has been studied for the first time. The experimental results indicate that the average water productivity increases with the decrease of the condensing fin surface temperature and there is a maximum increase of 186 % in the average water productivity of TWG when the temperature of condensing fin surface decreases from 5 °C to −10 °C, which is due to the increased temperature difference and the enhanced thermal conductivity of the ice layer. When the form of condensation on the surface of condensing fins is changed from condensing to frosting, the water productivity is increased by 22.1 % at maximum, which can be attributed to the higher thermal conductivity of ice than water. The effect of the sampling time on average water productivity of TWG has also been studied. With the increase of sampling time (0.5 h–3.5 h), the average water productivity of the device gradually decreases by 30.3 %. And the highest average productivity of TWG has been observed at a sampling time of 0.5 h. In addition, the effects of flow rate of water in water block heat exchanger, air flow rate of the cooling fan, voltage of TEC on water productivity are experimentally investigated as well. This study provides a strong theoretical foundation for enhancing the water productivity from humid air.

Emission characteristics and removal of heavy metals in flue gas: a case study in waste incineration and coal-fired power plants.

Heavy metal pollutants such as Hg, As, Pb, Cr, and Cd emitted from coal and waste combustion have received widespread attention. In this study, we systematically investigated the emission characteristics of heavy metals in waste incineration and coal-fired flue gases, focused on testing the removal effect of self-made cold electrode electrostatic precipitator (CE-ESP) on heavy metals in flue gas, and made a comparative analysis with the existing air pollution control devices (APCDs). Test results from waste incineration power plant showed that each APCD showed a certain effect on the removal of heavy metals in condensable particulate matter (CPM), with an average removal efficiency of bag filter was 86%, but its effect on Hg removal was slightly worse. Under the coupled field with electrified cold electrode plate operation mode, the average removal efficiency of CE-ESP on heavy metals in CPM was as high as 93%, including 76% for Hg. The removal efficiency of heavy metals (especially Hg) in CPM increased with the increase of flue gas temperature difference between inlet and outlet of CE-ESP. Test results from this coal-fired power plant showed that heavy metals were enriched in fly ash to a higher degree than in slag, the synergistic control of heavy metals in submicron particulate matter by the dust remover was not obvious, and there was a significant correlation between each heavy metal emission factor and its content in coal. Under the temperature field with non-electric cold electrode plate operation mode, the overall effect of CE-ESP on the removal of gaseous heavy metals was better than that of particulate heavy metals. Under the conventional electric field operation mode, CE-ESP was less effective in removing particulate Cr and gaseous Hg0. Under the coupled field with electrified cold electrode plate operation mode, the average removal efficiencies of CE-ESP for particulate and gaseous heavy metals were 82.37% and 76.16%, respectively.

Feasibility study on radioisotope-powered thermophotovoltaic/thermoelectric hybrid power generation system used in deep-sea: From design to experiment

This study aims to comprehensively examine the feasibility of a hybrid power generation system that integrates solar and thermoelectric technologies, with a focus on utilizing a radioisotope heat source (RHU) for deep-sea applications. The investigation encompasses the whole design process as well as rigorous testing procedures. The self-designed coupling device establishes a connection between the silicon photovoltaic (PV) cell and the bismuth telluride (Bi2Te3) thermoelectric modules (TEMs), therefore creating a photovoltaic-thermoelectric (PV-TE) hybrid system. The measuring platform incorporates the system to investigate the influence of varying light intensity (ranging from 400 to 1600 W/m2) on the electrical properties of the system, specifically focusing on three subgroups of PV cell temperature (20 °C, 25 °C, and 30 °C). The findings suggest that the enhanced performance of the photovoltaic (PV) cell and thermoelectric modules (TEMs) under identical PV cell temperatures may lead to an improvement in the electrical performance of the system due to variations in light intensity. Nevertheless, when the temperature of the photovoltaic (PV) cell increases, there is a gradual decline in the growth rate of the output power. The subsequent research provide evidence that there exist discrete mechanisms responsible for the reduction in intensity between thermoelectric modules (TEMs) and photovoltaic (PV) cells. The processes arise due to the impact of thermal effect on the photovoltaic materials and the increased temperature difference between hot and cold junctions of the thermoelectric modules (TEMs), respectively. Furthermore, a control group is incorporated by calculating the performance of the hybrid system under the same operating conditions as the single thermoelectric (S-TE) system. According to a comparative analysis comparing the Radioisotope Thermal-Photovoltaic-Thermoelectric (RTPV-TE) hybrid power production systems and the S-TE system, it has been shown that the former exhibits a potential increase in output power of up to 271% while operating under identical conditions. This work offers insights and methodologies for the design and measurement of RTPV-TE hybrid power generating systems in engineering application situations.

Investigating the performance of a solid oxide electrolyzer multi-stack module with a multiphysics homogenized model

Limited by the lower power of a solid oxide electrolyzer (SOE) stack, the scaling-up of the SOE technology requires multiple stacks to be integrated into a hotbox to form a multi-stack module (MSM). It is critical to guarantee the uniformity of stacks in an MSM, which has a prominent impact on its performance and durability. However, the thermo-fluid-electrical couplings between different stacks in an MSM are highly dependent on its structure and stack arrangement, which flowsheet models with lumped parameters cannot describe. This study proposes a three-dimensional (3D) multiphysics MSM model accelerated by the homogenization approach to investigate the MSM performances. By simplifying the stack structure using the homogenization method, the number of mesh elements is remarkably reduced, making it possible to complete the simulation of a four-stack MSM model within 3min. Simulation shows that a 33% drop in maximum power and a 30°C increase in temperature difference are induced by uneven gas distribution and unequal stack resistances for an MSM with serial electrical arrangement. It is also shown that the parallel arrangement is less susceptible to non-ideal factors than the serial arrangement, which enlightened the possibility of optimizing the stack arrangement to improve the MSM’s performance.

Cryogenic fracturing using liquid nitrogen on granite at elevated temperatures: a case study for enhanced geothermal systems in Kazakhstan

Cryogenic fracturing using liquid nitrogen (LN2) is a novel stimulation technology that enhances porosity, permeability, and rock-fluid contact area in subsurface formations targetted for geothermal energy extraction. In our experimental study, granite cores collected from the Zhylgyz region in South Kazakhstan were equilibrated at various elevated temperatures before treatments involving LN2 exposure time. Compression, Brazilian, and fracture toughness tests were performed on granite with starting temperatures ranging from 100 to 500 °C to quantify the impact of initial temperature on cryogenic fracturing and to compare with baseline geomechanical tests at 50 °C without LN2 exposure. The results show that LN2 cooling of hot granite induces mechanical rock failure and permeability enhancement. Moreover, the degree of thermo-fracturing augments with initial granite temperature, total freezing time, and number of freezing–thawing cycles. The peak load before failure of granite specimens, both in compression and Brazilian tests, reduces with the increased sample temperature difference and length of LN2 treatment. The fracture toughness of our semi-circular bend (SCB) LN2-treated specimens diminished with increasing temperature difference between granite and boiling point. In both experimental LN2 treatment processes, the specimens with an initial temperature of 500 °C before LN2 treatment formed many new fissures and extensions of pre-existing ones, showing that the plastic behavior is augmented. While cryo-fracturing experimental confirmation is recommended with site-specific samples in planning geothermal operations, these results in our work indicate a threshold downhole temperature, e.g., > 300 °C, for enhanced stimulation outcomes.

Performance Analysis of Stirling Engine Type Alpha Using Thermodynamic Approach Based on Schmidt Theory

Environmental concern and the impact on climate change have spawned various technological innovations for high efficiency engines that save fuel and produce less carbon emissions. Technological innovations that operate on a closed cycle can use variety of heat sources, produce no emissions and very high efficiency was Stirling engine. This research aims to design a Stirling engine type Alpha with a capacity of 228 cc with a phase angle of 90 degrees, then analyze its performance in the form of power indicators and thermal efficiency indicators and determine the effect of the increase in temperature difference between the compression chamber temperature and the expansion chamber temperature towards engine rotation speed. The method used to analyze engine performance is the Schmidt method, which is a Stirling engine performance analysis method based on isothermal expansion and ideal gas compression. The result of this research is that the Stirling engine which is designed starts working when the compression chamber temperature is 31.9 degrees Celsius and the expansion chamber temperature is 482.2 degrees Celsius. The highest engine speed is 598 rpm which is obtained at a compression chamber temperature of 45.5 degrees Celsius and an expansion chamber temperature of 662.4 degrees Celsius. The engine power indicator is 194.6 watt at 598 rpm, while the thermal efficiency indicator is 65.94 percent. Based on the experimental data, it is also known that the increase in temperature difference between the compression chamber temperature and the expansion chamber temperature causes an increase in engine rotation speed.