Air Tunnel Research Articles

Passive design for green buildings by using green glass space and earth air tunnel

In recent years, an increasing number of buildings have adopted passive technologies to meet the needs of energy saving and urban sustainable development. A conflicting relationship exists between energy saving and improving thermal comfort in buildings. Green glass space (GGS), as one of the passive technologies, is a transitional space consisting of glass facades that have the potential to balance thermal comfort and energy savings. Nevertheless, the heat transfer through the glass facades at times of high solar irradiation in summer can lead to overheating, further affecting the balance. In this work, ‘green glass space’-‘earth air tunnel’ coupled system (GGS-EATS) is proposed to improve thermal comfort in a passive way, which can reduce cooling loads. The parameters of GGS-EATS (e.g., supply air temperature (Tsu) and air changes per hour (ACH)) are optimized based on a comprehensive evaluation. A comprehensive evaluation index (CEI) is proposed, which is considered as thermal comfort, sensible cooling capacity and cost of investment. Results indicate that GGS-EATS is effective in solving overheating problems. The maximum sensible cooling capacity and investment cost reduction can reach 11.5 times and 35.6% respectively with Tsu of 25 °C and ACH of 14. The findings can provide the reference for green building design, further to promote sustainable urban development.

Research on the movement law and traffic safety zoning of spalled blocks in the linings of high-speed railway tunnels

Recent years have brought to notice the spalling and falling off problem of the lining of high-speed rail tunnels, which is dangerous for traffic safety. In this study, a three-dimensional spalled block–train–tunnel–air gas–solid coupling calculation model was built using FLUENT numerical simulation software. This model was used to simulate the trajectory characteristics of the spalled blocks under the operating condition of a high-speed rail at a speed of 300 km/h. The spatial movement characteristics of the block falling from the lining under four influencing factors, namely, block's geometric size, density and positions and train's speeds were analyzed. During the operation of the train, the lateral displacement of the spalled block decreases with the increase of the density of the spalled block, increases with the increase of the vehicle speed, and first increases and then decreases with the increase of the geometric size of the spalled block. Considering the above influencing factors comprehensively, the safe area and dangerous area in the tunnel are divided depending on whether the traffic safety was threatened by the falling of the spalled blocks from tne tunnel lining. The results show that the area 4.5 m away from the ground is a dangerous area where the tunnel operation and maintenance need to be paid attention to. Meanwhile, it is recommended to install the auxiliary equipment in a safe area to avoid the peeling off of the surrounding lining and thereby threatening train-driving safety.

Membrane muscles tension bat wings for faster flight

Watching a bat flit through the night sky, you might think that the delicate membrane stretched between the animal's elbow, long splayed digit bones and down its side to the hind limbs is no more than an inert flexible surface that catches air passively like fabric covering the struts of a kite. Yet, the elegant wing membrane is spanned by thin thread-like muscles. Could the muscles, known as plagiopatagiales proprii, tense and relax the membrane to fine-tune how the structure bows and catches the air as the animals swoop and flutter? Jorn Cheney, Jeremy Rehm, Sharon Swartz and Kenny Breuer from Brown University, USA, decided to find out.But first, the team need to know how Jamaican fruit bats (Artibeus jamaicensis) fly when they had full use of the wing membrane muscles. Cheney and Rehm tempted the animals with guava juice to fly through still air in a wind tunnel and into a 5 m s−1 head wind, filming the animals with six high-speed cameras to reconstruct the wing shape during their distinctive wingbeats to find out how much the membrane bowed as the animals propelled themselves forward. Then the pair painstakingly paralysed all 25 of the fine muscles in each wing by individually injecting botulism toxin into each, inactivating them temporarily. ‘We use tiny, microliter amounts of dilute Botox, much less than would be used in a cosmetic procedure to minimize a single forehead wrinkle’, says Swartz. Once the animals had recovered, Cheney and Rehm then encouraged the bats to fly again in the still air and headwind, to find out how loss of muscle control affected the animals. The animals with the paralysed wing membrane muscles struggled to remain aloft in the motionless air. Even though they could still fly at 6.2 m s−1 into the head wind – which was 1 m s−1 slower than they had managed with full use of the wing membrane muscles – the animals struggled when there was no headwind, descending rapidly to the ground as they tried to remain aloft. And, when the team compared the bats’ wing membranes as they flew into the head wind, it was clear that the membranes of the paralysed bats were slacker, bowing 12% more than the wing membranes of the bats that still had the use of their plagiopatagiales proprii, also increasing the amount of air drag on the wing to slow the animals by 16%. However, the bats with the immobilised wing membrane muscles managed to compensate for the increased drag by increasing their wing beat amplitude from ∼60 to ∼75 deg and tipping the wing more to sweep it through a less vertical angle.‘Reduced forward speed, reduced ability for low-speed flight and changes in kinematics [when the plagiopatagiales were inactive] are consistent with the plagiopatagiales playing a crucial role in reducing drag through active control over membrane tension indirectly controlling camber’, says Cheney, explaining that using the muscles to tension the wing membrane helps bats to fly at higher speeds. However, the team points out that the bats with the paralysed muscles could have taken advantage of their slacker wing membranes to select slower preferred speeds; so why didn't they? They suspect that the animals may not be able to provide the additional flight power required to remain aloft at the lower speeds caused by bowed wing membranes. The researchers conclude, ‘Jamaican fruit bats likely always employ their wing membrane muscles during sustained flight to control camber [bowing] and to enhance flight efficiency’. And, happily, the bats soon recovered full use of their plagiopatagiales muscles after their wing slackening experience to regain full bat mobility.

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/m2 and 38.33 W/m2, respectively. The effect of capillary inlet water temperature was more remarkable than that of the tunnel air temperature on the capillary heat exchange process.

Field Measurement and Evaluation of Effective Ventilation and Particulate Matter Discharge Efficiency of Air Shafts in Subway Tunnels

The ventilation performance of air shafts is important to the air quality of subway tunnels, but there is no unified evaluation index of ventilation performance. In this paper, the air shafts at different locations in subway tunnels were taken as research objects, and the wind speed as well as the particulate matter concentration of each air shaft was tested. The effective ventilation volume and PM2.5 discharge efficiency of the air shafts were defined to evaluate the ventilation performance. It was found that on average, during the subway train service, the station air shaft on the train-arriving side can discharge 2050 m3 of dirty air in the tunnels and inhale 218 m3 of fresh air from the outside environment, while the station air shaft on the train-leaving side can absorb 2430 m3 of fresh air but can hardly effectively discharge dirty air; meanwhile, the middle air shaft can not only effectively exhaust 1519 m3 of dirty air but can also absorb 7572 m3 of fresh air. In addition, the middle air shaft has better ventilation performance if its inner opening is set on the top rather than on the side of the tunnel. The PM2.5 discharge efficiency of the station air shaft on the train-arriving side is 52.0~62.8%, higher than that of the middle air shaft of which the value is 26.8~40.7%. This research can provide guidance for ventilation performance evaluation of subway air shafts and provide a reference for subway tunnel air shaft location design.

Pollutants Concentration during the Construction and Operation Stages of a Long Tunnel: A Case Study of Lowari Tunnel, (Dir–Chitral), Khyber Pakhtunkhwa, Pakistan

Long tunnels with significant overburden, changeable geological conditions, a steep gradient, water infiltration, and heavy traffic flow are susceptible to environmental concerns during both construction and operation. The availability of fresh air and visibility is the most important necessity in excavation for tunnel workers inside the tunnel during the construction phase, as well as those crossing the tunnel during operation. Lowari Tunnel’s tunnel air pollutants were researched. Carbon monoxide (CO), carbon dioxide (CO2), oxygen (O2), hydrogen sulfide (H2S), sulfur dioxide (SO2), nitrogen oxide (NO), ammonia (NH3), nitrogen dioxide (NO2), PM1, PM2.5, PM10, air velocity, dust morphological and particle size distribution analysis are among the parameters under consideration. The findings provide evidence for the development of tunnel air quality.

Law of Countercurrent Energy Dissipation of Fresh Air by Coal and Gas Outburst Shock Waves

Accidental coal and gas outbursts lead to major disasters in coal-producing countries and are difficult to mitigate. To elucidate the energy dissipation law for coal and gas outburst shock waves in a complex ventilation network of mines, a coal-and-gas-outburst-energy-propagation simulation and parameter determination test device were developed and used to perform physical simulation experiments under different outburst strength conditions. These experiments were combined with numerical simulations to obtain the propagation law of outburst shock waves in a roadway and analyze different outburst intensities according to the gas counterflow criterion, highlighting the hazard characteristics of shock waves in a fresh air tunnel. The results showed that when a shock wave passed through the turning roadway, its intensity and speed were greatly attenuated and that the overpressure value of a shock wave in a straight roadway was greater than that at a corner. Upon encountering a rigid wall, the superposition of the incident and reflected shock waves increased the peak overpressure of the shock wave per unit area. When a fresh air roadway is near the coal uncovering position in rock drift (“Shimen”) a corresponding counter-backflow device should be installed at the location of the connecting road near the fresh air roadway, under the condition that normal ventilation is not affected. These numerical simulation results are consistent with general experimental trends, indicating that the analyses conducted in this study are reliable and can provide a theoretical basis for the prevention of secondary disasters due to coal and gas outbursts in mines.

Simulation of tunnel methane dispersion and airflow using three-dimensional lattice Boltzmann method based large-eddy simulation

ABSTRACT The lattice Boltzmann method (LBM) and large-eddy simulation (LES) were combined with a scalar subgrid-scale model to simulate the tunnel air velocity field and methane dispersion. The presented model was validated by comparing its results with the published experimental results and the results of other numerical models (the OpenFOAM-K-Epsilon model and the OpenFOAM-LES model). Four local ventilation systems of a coal mine tunnel were evaluated based on the presented model. This demonstrated that the time-averaged results of the LBM-LES model agree well with the experimental results. Both the LBM-LES model and the OpenFOAM-LES model can capture the transient velocity fluctuation of the tunnel airflow. In diluting the methane near the heading face, the forced ventilation system performs the best. The exhaust ventilation system can prevent methane from spreading further from the heading face.

Measurement-based investigation of subway station tunnel thermal environment

Compared with the interval tunnel, the subway station tunnel has higher temperature. Therefore, more attention should be paid. In order to study the thermal environment characteristics of station tunnels, this paper selects four typical stations in Guangzhou, China. The station tunnel air temperature, tunnel exhaust duct temperature, and air inlet temperature of train air conditioning condenser were tested. The results show that the subway station tunnel has a temperature rise of about 4 °C from the opening to the operation scale. Temporal variations of temperature are determined by the passenger flow and train density; however, it has nothing to do with the operation year. The TEF (Tunnel Exhaust Fan) plays a clear role in ensuring the normal operation of the train air conditioner; when the fan is turned off, the instantaneous air inlet temperature of the train air conditioning condenser frequently exceeds 45 °C during the evening peak, and fails to work. Once the fan is turned on, the air conditioner can operate normally. The effect of the TEF on reducing the tunnel temperature is limited with a reduction range within 1 °C. In addition, the heat removal effect of TEF was quantitatively analyzed. The research results describe the characteristics of the thermal environment of the station tunnel in the hot summer and warm winter climate area. Moreover, the results also provide a reference for the design and operation of the TEF system.

Numerical modeling of conjugate heat and mass transfer with water vaporization in solid materials inside a convective hot air tunnel

A two-dimensional conjugate model describes heat and mass transfer with liquid to vapor phase change of water in solid materials inside a hot air tunnel. Computational modeling allows to assess the evolution of convective fluid mechanics and heat convection in laminar airflow and coupled heat-mass transfer diffusion inside a rectangular solid. A transient finite volume method conjugate model characterizes the fluid mechanics and heat transfer in airflow, and the local convective heat (h(L)) and mass(hm(L)) transfer coefficients. The results indicate that h(L) was found to vary spatially on each surface of the solid between 5.71 and 101.62 W/m2K, while hm(L) varied from 5.05×10−6 to 1.38×10−6 m/s. Heat and mass transfer by unsteady diffusion inside the solid were accounted for by a second transient diffusion model. Experimental findings of apple slice dehydration kinetic reported in the literature allowed to validate the coupled heat and mass transfer model, with deviation lower than 2% for the water mass losses. Finally, the proposed model applied on a thin-layer of murta berry puree inside a hot air tunnel predicted transient non-uniform heat and mass transfer processes, with a difference of 13.5 K between the coldest and front areas.

A new sustainable energy based freeze proof method for drainage system in cold-region tunnels: A case study of Tianshan Shengli Tunnel

In order to solve frost damage problems in cold-region tunnels, a new sustainable energy based freeze proof method for tunnel drainage system is proposed. The method is applied to Tianshan Shengli Tunnel, China as a case study to show the concept and details of tunnel drainage system ground heat exchangers (GHEs) including calculation of active heating length and maximum heating load, design of heat extraction in cross tunnel, the segmented design method. Long-term performance of tunnel drainage system GHEs is also fully discussed. Multi-field simulations are performed to achieve corresponding thermal responses of the tunnel drainage system GHEs. Results show that anti-freezing measures provide an initial heating length 900 m of the drainage system at the entrance of Tianshan Shengli Tunnel during full life cycle. When the tunnel drainage system GHEs are employed, the heating length can be reduced to 600 m. Maximum total heating load of the tunnel drainage system in heating period is 84.40 kW. The calculation method of segmented heating load is suggested for precise prevention and control of frost damage in cold-region tunnels, owing to varying tunnel air temperature with the distance from the tunnel entrance. The use of boiler heating in winter will enhance the compensation between operation and recovery period and provides good long-term performance. This study provides a potential reference for antifreeze design of cold-region tunnels utilizing geothermal energy.

Characterization of reflected shock tunnel air conditions using a simple method

A new method to characterize air test conditions in hypersonic impulse facilities is introduced. It is a hybrid experimental–computational rebuilding method that uses the Fay–Riddell correlation with corrections based on thermochemical nonequilibrium computational fluid dynamic results. Its benefits include simplicity and time-resolution, and using this method, a unique characterization can be made for each individual experimental run. Simplicity is achieved by avoiding the use of any optical techniques and overly expensive numerical computations while still maintaining accuracy. Without making any assumptions to relate the reservoir conditions to the nozzle exit conditions, the work done characterizing four test conditions in a reflected shock tunnel is presented. In this type of facility, shock compression is used to produce an appropriate reservoir, which is then expanded through a nozzle to produce hypersonic flow. Particular focus is given to the nozzle exit total enthalpy where a comparison is made with the reservoir enthalpy obtained using the measured shock speed and pressure in the shock tube. Good agreement is observed in all cases providing validation of the new approach. Additionally, static pressure measurements showed clearly that conditions III and IV have a thermochemical state which likely froze shortly after the nozzle throat. Also, the nozzle flow is shown to be almost isentropic. Due to the simplicity of the current method, it can be easily implemented in existing facilities to provide an additional independent estimate alongside existing results.

Geothermal Energy System for Passive Design in Buildings: Applications and Comparative Analysis

The use of renewable energy is essential for sustainable development, and buildings are responsible for a significant part of energy consumption. Therefore, this study is focused on geothermal energy and its application to buildings and its potential significance for energy savings and minimizing the carbon footprint. In this study, geothermal systems like earth air tunnel systems, geothermal exchange systems, earth sheltering systems have been studied and classified, based on their efficiency in different building typologies and climate, and factors affecting these systems are discussed, and systems selection for different needs and method of installation have been analyzed. Four case studies based on different geothermal systems in different regions and of different building typologies have also been compared to assess the performance and evolution in the field. Sustainable development is not the idea but the need for the future and minimizing the carbon footprint of the building is a step towards it, the use of renewable energy supports that step. Geothermal energy alone can be used for different purposes like electricity generation, passive and active heating, and cooling, also other renewable energies like solar for lighting load, use of biofuels for consumption purposes, will lead to an environment where the carbon footprint of the building can be minimized to zero.

Aerodynamic Behavior and Impact on Driving Safety of Spalling Blocks Comprising High-Speed-Railway Tunnel Lining

The lining of operating high-speed-railway tunnels suffers from cracks, the peeling of material, and other deteriorations and defects, all of which seriously affect driving safety. However, the trajectory of a falling block from the tunnel lining in a tunnel train wind environment and its impact on driving safety are unknown. To study the movement of falling blocks under a coupling effect of tunnel train wind and the local flow field of the falling blocks, a three-dimensional gas–solid-coupling numerical calculation model of spalling blocks–train–tunnel–air was established using FLUENT software The aerodynamic evolution mechanism governing the spalling blocks of the lining was analyzed, and we found that the falling process of a spalling block is affected by the coupling of its own characteristics and transient train wind. Train wind directly induced the horizontal motion of falling blocks, generated curves and eddy currents, and changed the motion state of spalled blocks. Furthermore, by comprehensively considering the motion trajectories of flaky and blocky blocks at different positions, the impact of spalling blocks on driving safety was obtained. The dangerous area of spalling blocks was approximately 5.5 m above the ground, which must be paid attention to. Our results provide guidance for the operation and maintenance of high-speed-railway tunnels.

Felswärmeeintrag belüfteter Tunnelbauwerke

AbstractPredicting the heat input from rock is particularly important for climatic conditions in long tunnels during the construction phase because, although other heat sources are present, this often has the greatest impact on the amount of heat transferred to the air in tunnels with a high rock overburden. Correctly predicting the time‐dependent rate at which the excavated tunnel tube cools is of fundamental importance, as this determines the amount of cooling power required to maintain the working climate. Two different rock heat calculation methods will be presented here: an analytical method based on a series development and a method based on solving the heat conduction equation using a numerical method.

PRE-COOLING / PRE-HEATING CHARACTERISTICS OF THE EARTH-TO-AIR HEAT EXCHANGER SYSTEM IN LONG-TERM OPERATION (PART 2): INVESTIGATION OF ACTUAL CONDITION OF AIR ENVIRONMENT IN UNDERGROUND AIR TUNNEL THROUGH FIELD MEASUREMENT AND CFD ANALYSIS IN SUMMER

In this study, we aim to propose the optimal operation method of an earth-to-air heat exchanger (EAHE). As a first step, in this paper, we investigated the relationship between the occurrence of condensation and air pollution by fungi in the underground air tunnel of an actual building. Firstly, we evaluated of condensation in the underground air tunnel based on actual measurement and unsteady CFD analysis. Secondly, exhaustive investigation of fungal flora in the underground air tunnel was conducted by DNA analysis.

Design and application of a dust suppression technology of the forcing air curtain in fully mechanized rock tunnelling faces.

To effectively reduce high dust concentrations and keep clean air in fully mechanized rock tunnelling faces in coal mine, this study carried out a research of dust suppression technology of the forcing air curtain. First, the mechanism of dust diffusion controlled by the forcing air curtain was introduced in this study. Then, numerical simulations of the formation of the forcing air curtain as well as the influence for dust diffusion under the different distance between forcing air duct outlet and heading end were carried out. Moreover, a dust suppression technology of the forcing air curtain was designed and tested in a fully mechanized rock tunnelling face of southern return air tunnel which was located in the Tangkou coal mine of China. It shows that the numerical simulation results were in good agreement with the in situ tests. The average removal rate of total and respirable dust could reach up to 95.1% and 96.1%, respectively, at manned working areas in the tunnel. Research results show that the dust suppression technology of the forcing air curtain is an effective method of dust control in fully mechanized rock tunnelling faces.

Rapid thermal inactivation of aerosolized SARS-CoV-2

Airborne transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is one of the leading mechanisms of spread, especially in confined environments. The study aims to assess the thermal inactivation of SARS-CoV-2 at high temperatures in the time scale of seconds. An electric heater with a coiled resistance wire is located perpendicularly to the airflow direction inside an air tunnel. The airflow rate through the tunnel was 0.6 m3/h (10 L/ min). SARS-CoV-2 were suspended in Dulbecco’s modified Eagle’s medium (DMEM) with 10 % fetal bovine serum (FBS), aerosolized by a nebulizer at a rate of 0.2 L/min and introduced to the airflow inside the heater with the use of a compressor and an aspirator. In the control experiment, with the heater off, SARS-CoV-2 passed through the system. In the virus inactivation test experiments, the heater’s outlet air temperature was set to 150 ± 5 °C and 220 ± 5 °C, and the air traveling through the tunnel was exposed to heat for 1.44 s. An inline gelatine filter harvested SARS-CoV-2 that passed through the system. The viral titer obtained from the gelatine filter in the control experiment was about 5.5 log10 TCID50. The virus's loss in viability in test experiments at 150 °C and 220 °C were 99.900 % and 99.999 %, respectively. The results indicate that high-temperature thermal inactivation substantially reduces the concentration of SARS-CoV-2 in the air within seconds.

Effect of hull displacement on hydro- & aerodynamics of a planing trimaran

The tunnel hydrodynamic and aerodynamic forces are the key to improve the overall resistance of planing trimaran. The variation of hull displacement has different effect on the tunnel flow characteristics at diverse sailing states, resulting in various change trend of resistance per displacement (R / △) of trimaran at various hull displacement. Combined with model tests, this paper conducts numerical investigation for the detailed analysis of hull displacement effect on the hydrodynamics and aerodynamics of a planing trimaran in various speed ranges. It is found that tunnel air cushion occurs when this trimaran running at low speed. The critical Froude Number of air cushion appearance is strongly influenced by the wave interaction in tunnel, where it may occur earlier at heavier hull load. At semi-planing speed, the difference of hull trim angle mainly accounts for the obvious discrepancy of R / △ of trimaran with different hull loads. Apart from the dominant effect of main hull, the high-pressure region at front tunnel, caused by bow wave washing, also plays a boosting role on enlarging the difference of bow-up trim angle between various load conditions. The heavier hull load leads to the stronger interaction between bow waves of main hull and tunnel at semi-planing speed. After entering planing speed, the tunnel wave crest moves astern more quickly at light-load where tunnel ventilation thus occurs earlier. The air flows through tunnel more smoothly at light load, which weaken the tunnel ram pressure effect in turn. At planing state, the variations of tunnel aero-lift and hydro-lift dominantly influence the different growth trend of trimaran R / △ at various hull loads. This work is helpful for the design and performance prediction of planing trimaran which designed for multi working conditions.

Optimization of Geometric Parameters for Enhanced Performance Using Geothermal Clean Energy Based Earth to Air Tunnel Heat Exchanger

Optimization of Geometric Parameters for Enhanced Performance Using Geothermal Clean Energy Based Earth to Air Tunnel Heat Exchanger