Dynamic analysis of heat extraction rate by supercritical carbon dioxide in fractured rock mass based on a thermal-hydraulic-mechanics coupled model

Heat production from geothermal reservoirs is a typical heat transfer process involving a cold working fluid contacting a hot rock formation.Compared to the thermal-physical characteristics of water,supercritical CO_(2)(scCO_(2))has a higher heat storage capacity over a wide temperature-pressure range and may be favored as a heat transfer fluid.Singularly characteristic of scCO_(2)-based heat extraction is that the hydraulic-thermal properties of the scCO_(2) vary dramatically and dynamically with the spatial pressure gradient during unsteady-state flow along fracture.This highly nonlinear behavior presents a challenge in the accurate estimation of heat extraction efficiency in scCO_(2)-based EGS.In this paper,a thermal-h ydraulic-mechanical(THM)coupled model is developed by considering deformation of the fractured reservoir,non-Darcy flow and the varying thermal-physical properties of scCO_(2).The proposed model is validated by matching the modeling temperature distribution with published data.The results show that during continuous injection of scCO_(2),the fracture first widens and then narrows,ultimately reopening over the long term.The sequential fracture deformation behaviors are in response to the combined impacts of mechanical compression and thermally-induced deformation.By controlling the injection parameters of the scCO_(2),it is found that the heat extraction rate is positively correlated to its pore pressure or mass flow rate.The heat extraction rate can be significantly enhanced,when the inlet temperature of scCO_(2) is below its critical temperature.As a result,the heat increment recovered per unit mass of scCO_(2) decreases as the hot rock is gradually cooled.Meanwhile,the heat increment recovered per unit mass of scCO_(2) decreases by increasing the inlet temperature of scCO_(2) or its mass flow rate,but increases as the outlet pressure rises.Furthermore,multi-linear regression indicates that controlling the inlet temperature of the scCO_(2) can significantly improve the thermodynamic efficiency of heat extraction.

Discriminative Features of Abnormities in a Spiral Groove Gas Face Seal Based on Dynamic Model Considering Contact

It is a difficult task to root the cause of the failure of a gas face seal because different causes may result in similar observations.In the work being presented,the discrimination of multiple types of abnormities in a spiral groove gas face seal is studied.A dynamic model is employed to analyze groups of cases in order to uncover the dynamic behaviors when the face contact is induced by different mixtures of abnormities,whose discriminative features when motion and contact are monitored are studied and uncovered.A circumferential-pattern-related oscillation phenomenon is discovered,which is extracted from contact information and implies the relative magnitude of the moment on stator and the rotor tilt.The experimental observation shows consistent results.It means that the grooves(or other circumferential patterns)generate useful informative features for monitoring.These results provide guidance for designing a monitored gas face seal system.

Numerical modeling of contaminant advection impact on hydrodynamic diffusion in a deformable medium

The self-weight of solid waste or machine-rolled compaction can induce or trigger contaminant migration in the landfill.Although the consolidation-induced hydraulic gradient driving solution transport has been extensively investigated,little attention has been paid to ion migration caused by its concentration gradient variation.It is necessary to more precisely predict the multi-stage contaminant transports in deforming porous material.Based on the modified Cam-clay model,the proposed fluid-solid coupled model can simulate the elastoplastic deformation behavior of layered kaolinite and KBr solution transport/sorption,and its modeling results were validated by published laboratory data.The solid-fluid interactions were analyzed by comparing various transport manners of K^(+)and Br^(−)from excess pore pressure generation to dissipation.Results reveal that the consolidation process can accelerate KBr solute advection from the contaminated layer into the uncontaminated layer,and then affects the subsequent diffusion,mechanical dispersion and sorption for K^(+)and Br^(−).The simulations also indicate that consolidation-induced solute transport is time-dependent,and therefore the ion diffusion and mechanical dispersion should receive more attention.

Measurement and analysis of airtightness safeguard measures for typical ultra-low energy buildings

Zero-energy buildings constitute an effective means of reducing urban carbon emissions.High airtightness,a typical characteristic of zero-energy building,is closely related to the building’s air infiltration and has a signifi-cant impact on the performance of the building envelope,indoor air quality,building energy consumption,and efficient operation of air-conditioning systems.However,thus far,systematic developments in high-airtightness assurance technologies remain scarce.Most existing studies have tested the airtightness of buildings and typical building components;however,in-depth analyses into the formation of infiltration have not been reported.There-fore,for realizing zero-energy buildings,ensuring airtightness is an urgent problem that needs to be addressed.Accordingly,in this study,based on several building airtightness measurement studies,the typical air leakage paths in buildings were summarized,and the causes of typical air leakage components in buildings were further analysed by tracing construction processes.Moreover,targeted measures for airtightness in buildings were estab-lished and applied to practical cases.Lastly,the resulting improved building airtightness was measured and the results show that the airtightness of the measured ultra-low energy consumption buildings ranges from 0.13 h^(−1)to 0.57 h^(−1),with a mean value of 0.32 h^(−1).The effectiveness of the airtightness safeguard measures was verified.This study serves as a basis for the assumption of the air leakage path distribution when simulating building air infiltration and also provides a design reference for improving the construction technologies and airtightness of buildings.

Resistance-capacitance model of the capillary heat exchanger in subway tunnels

The subway operation generates a large amount of waste heat,which will lead to a disruption of the underground thermal balance.To remove the heat,a ground source heat pump system adopting capillary net as the front-end heat exchanger can be built in the tunnels to recycle the waste heat and use it for building heating.Different simulation method was used to analyze the heat transfer process in the tunnel and the surrounding rock.The existing simulation method usually takes a long time for calculation and can not be used for a real-time regulation of the system.Based on the concept of thermoelectric analogy,a resistance-capacitance(RC)model was proposed for rapid prediction and analysis on the heat transfer of the capillary net in subway tunnel.The annual thermal response in the tunnel was analyzed,and the influence of the tunnel air temperature and the capillary inlet water temperature was examined using this model.The maximum heat transfer flux of the capillary in summer(release heat)and in winter(extract heat)was 55.27 W/m 2 and 38.33 W/m 2,respectively.The effect of capillary inlet water temperature was more remarkable than that of the tunnel air temperature on the capillary heat exchange process.

Rigid–flexible hybrid surfaces for water-repelling and abrasionresisting

Droplets impacting solid superhydrophobic surfaces is appealing not only because of scientific interests but also for technological applications such as water-repelling.Recent studies have designed artificial surfaces in a rigid–flexible hybrid mode to combine asymmetric redistribution and structural oscillation water-repelling principles,resolving strict impacting positioning;however,this is limited by weak mechanical durability.Here we propose a rigid–flexible hybrid surface(RFS)design as a matrix of concave flexible trampolines barred by convex rigid stripes.Such a surface exhibits a 20.1%contact time reduction via the structural oscillation of flexible trampolines,and even to break through the theoretical inertial-capillary limit via the asymmetric redistribution induced by rigid stripes.Moreover,the surface is shown to retain the above water-repelling after 1,000 abrasion cycles against oilstones under a normal load as high as 0.2 N·mm−1.This is the first demonstration of RFSs for synchronous waterproof and wearproof,approaching real-world applications of liquid-repelling.

Impacts of corridor design:An investigation on occupant perception of corridor forms in elderly facilities

The study addresses the issue of monotonous and lengthy corridors with a single spatial form commonly found in Chinese elderly facilities.We aim to assess the influence of the built spatial environment on the emotions of the elderly quantitatively.To do this,Virtual Reality(VR)technology was employed to construct a digital twin model featuring three corridor forms:straight,arc,and folded,respectively.Forty participants experienced walking in each corridor form for 144 s,while electroencephalogram(EEG)data and subjective questionnaires were collected to explore the psychological and physiological effects caused by different corridors.The results of the questionnaire indicate that arc corridor yielded the highest satisfaction,followed by straight corridor,and the satisfaction for folded corridor is the lowest.EEG results show that folded corridor has 26.0%higher average power than arc corridor and 6.6%higher than straight corridor.The participants consume less energy and are more satisfied in arc corridor,compared to straight and folded corridors.The results establish a correlation between spatial form and occupant perception,suggesting that moderate spatial variations contribute to a better experience of the elderly.Moreover,this study provides quantitative cross-referencing information to optimize the design methods of public space in elderly facilities.

Study on the conversion coefficient between ACH_(50)and ACH in typical zones of public buildings

The air infiltration of buildings is closely related to its indoor and outdoor environment and energy consumption.However,measuring air infiltration of a building under natural conditions is time-consuming,easily affected and expensive,so it’s often inferred based on building airtightness in practical engineering.Empirical models can nevertheless make a rapid prediction without building parameters,which are widely applied in practical engineering.At present,most of the existing empirical models take residential buildings as objects,therefore they are difficult to be applied to public buildings.Hence,it is imperative to build an empirical model applicable to public buildings.In this study,the conversion coefficients between the airtightness(air change rate under the pressure difference of 50Pa)and the air infiltration rates under natural conditions of four typical zones of public buildings were analyzed.Firstly,the airtightness of four zones of public buildings in the cold region of China was measured.Secondly,their air infiltration rates under 1800 combined conditions of wind pressure and stack effect pressure were simulated based on the airtightness measured results.Finally,calculation and statistical analysis of the conversion coefficient were carried out based on the measured and simulated results,and the recommended value of conversion coefficient was proposed.Analysis results show that the CC of each zone is significantly affected by outdoor meteorological conditions and varies in a wide range(1#zone:3.21 to 188.44).It is advised to ignore the extreme data and take the mean value of the CC corresponding to 95%of the data volume as the recommended value(22.2).This study can provide theoretical basis for the formulation of standards for the performance evaluation of building airtightness.

Prediction model of air infiltration in single-zone buildings with high airtightness

Air infiltration through building envelopes has a considerable impact on the comprehensive performance of build-ings,especially in terms of their energy demand and indoor air quality.Therefore,it is important to accurately predict building air infiltration rates under various scenarios.High airtightness is one of the typical character-istics of passive ultra-low energy buildings.With the rapid application of passive technology in building energy efficiency,the airtightness of new urban buildings has been significantly improved.The centralized air leakage path distribution assumption of current prediction model for building air infiltration rate is inconsistent with the actual situation of high airtightness buildings,which reduces its prediction accuracy and application range.Therefore,it is of great practical significance and academic value to carry out the research on the prediction model of air infiltration rate of buildings with high airtightness.This paper presents an air infiltration prediction model for single-zone buildings with adventitious openings.The building envelope was broken down into permeable parts and impermeable parts,and the air leakage path-ways were assumed to be uniformly and continuously distributed in the permeable envelope.A linear pressure distribution over the building facade was assumed,and the airflow rate was integrated in the vertical and hori-zontal planes to theoretically predict the air infiltration rate.The feasibility of the proposed model was tested by comparing the air infiltration rates simulated by this model with those determined using the tracer gas attenua-tion method of an airtight building.The initial test results suggest that this model is mathematically robust and is capable of modeling the air infiltration of a building in a wide variety of scenarios.Reasonable agreement was found between the tested and simulated results.This study can provide basic theoretical support for the coupling performance analysis of high airtightness buildings.

Up-conversion fluorescence biosensor for sensitive detection of CA-125 tumor markers

Sensitive and specific bioassays of tumor markers are critical for early cancer detection and treatment.In recent years,lanthanide(Ln3+)doped upconversion nanoparticles(UCNPs)have attracted wide attentions in tumor markers detectio n.Herein,we co mbined NaYF4:Yb,Tm and silver nanoparticles,serving as energy donor and receptor,respectively,to form an up-conversion fluorescence based inhibitory tumor marker biosensor system.The tumor marker CA-125 molecules are labeled with silver NPs,and the energy transfer fluorescent signal can be detected between the UCNPs and the silver NP receptors.The biosensor shows good stability,high sensitivity and selectivity in the tumor marker concentration range from 5 to 100 ng/mL,as well as a detection limit of 120 pg/mL.Due to the advantage of ease of fabrication and operation,low cost and high information capacity,this technology holds great potential for the clinical applications.

Pneumatic programmable superrepellent surfaces

Morphological transformation of surface structures is widely manifested in nature and highly preferred for many applications such as wetting interaction;however,in situ tuning of artificial morphologies independent of smart responsive materials remains elusive.Here,with the aid of microfluidics,we develop a pneumatic programmable superrepellent surface by tailoring conventional wetting materials(e.g.,polydimethylsiloxane)with embedded flexible chambers connecting a microfluidic system,thus realizing a morphological transformation for enhanced liquid repellency based on a nature‐inspired rigid‐flexible hybrid principle(i.e.,triggering symmetry breaking and oscillator coupling mechanisms).The enhancement degree can be in situ tuned within around 300 ms owing to pneumatically controllable chamber morphologies.We also demonstrate that the surface can be freely programmed to achieve elaborated morphological pathways and gradients for preferred droplet manipulation such as directional rolling and bouncing.Our study highlights the potential of an in situ morphological transformation to realize tunable wettability and provides a programmable level of droplet control by intellectualizing conventional wetting materials.