Low Air Velocity Research Articles

Drying and color in punamuña leaves (Satureja boliviana)

Drying allows water to be removed and food to be preserved, however, this operation can degrade color. Punamuña leaves are aromatic and used for medicinal purposes in the Peruvian Andes. This research aimed to determine and model the drying kinetics, the diffusivity coefficient (Def), the activation energy (Ea), and the color of punamuña leaves. A horizontal dryer was used at 40, 50, and 60 °C and airspeed of 1.0 and 0.5 m / s; drying kinetics was modeled with 10 models. Def was determined with the Fick equation, Ea with the Arrhenius equation; the color was determined in the L* a* b* space. It was found that the triple exponential model with six parameters better represented the drying kinetics (R2> 99.73 and E <3.04%); Def increased with temperature and air velocity. Ea was found between 43.62 to 44.52 kJ/mol for speeds of 1.0 to 0.5 m/s respectively; L* and a*/b* decreased, the color difference ΔE * increased with increasing temperature and lower air velocity

Air and H2 feed systems optimization for open-cathode proton exchange membrane fuel cells

In this study, air and H2 feed systems optimization for open-cathode proton exchange membrane fuel cells (PEMFCs) has been evaluated. For air feed system, a spoiler was introduced. The air velocity distribution, polarization curve, single-cell voltage distribution, and temperature distribution of the 11-cell open-cathode fuel cell stack with blowing, blowing-spoiler, and drawing air feed system were assessed. On this basis, the influences of the distance between the fan and stack with different air feed systems were investigated. The results show that the application of the spoiler could solve the problem of low air velocity in the middle of the stack and increase stack performance by 7.3%. And drawing air feed system could enhance the heat dissipation capacity of the stack and the uniformity of temperature distribution, resulting in the 7.9% stack performance increase. Optimization of the distance between the fan and stack enhances the full development of turbulence and the rate of heat transfer. In addition, the effects of four different H2 feed systems and the flow direction between air and hydrogen on the fuel cell performance were also investigated. It is beneficial for open-cathode PEMFC to be operated with the location of the H2 inlet and outlet staggered in two different endplates for better stack performance and single-cell voltage uniformity. Evidence also shows that the higher performance also could be obtained when the flow direction of air and hydrogen is vertical with lower ohmic resistance, charge and mass transfer resistance. The study contributes to the design of the open-cathode fuel cell stack to get better performance and reliability.

Investigation on the thermal insulation regulating performance of a newly developed air inflatable garment

It is important to keep body thermal comfort experiencing transient thermal environments, and adjusting clothing thermal insulation is expected to be a feasible strategy. In this study, to realize the thermal insulation regulating performance, a novel air inflatable garment (AirIG) using natural air as the thermal insulator was developed, and the thickness of the air layer entrapped in AirIG was determined through computer simulation. The thermal insulation regulating performance of AirIG was investigated using ‘Newton’ thermal manikin. Thermal insulation values of the AirIG were measured under four air inflation volumes [i.e., CON (no air inflation), 1/3FULL, 2/3FULL and FULL (the maximum air inflation)]. Besides, the effects of garment pattern and air velocity (i.e., 0.15 m/s, 1.55 m/s and 3.04 m/s) on the thermal insulation regulating performance of the AirIG were also studied. Results showed that with the increasing air inflation volumes, thermal insulation in the upper of the AirIG firstly significantly increased and then remained stable (i.e., CON<1/3FULL<2/3FULL, FULL, p < 0.01). Adding sleeves remarkably increased the thermal insulation when the air inflation volume increased from CON to FULL (p = 0.056). Increasing air velocity significantly decreased the thermal insulation in the upper and local body regions of the AirIG. The thermal insulation regulating performance of the AirIG disappeared when the air velocity increased to 1.55 m/s, evidenced by the insignificant thermal insulation difference among the four air inflation volumes (p > 0.1). Therefore, the AirIG can be recommended as an effective thermal insulation regulating strategy for human body in low air velocities.

Thermal Analysis of Solar Air Heater with Ventilator Turbine and Fins

Solar air heater (SAH) is a renewable energy application for the drying process. SAH has a challenge to produce high performance under uncertain weather. The performance of SAH can be enhanced by providing the absorber plate by adding the fins. This study aims to evaluate the thermal performance of SAH with rectangular fins SAH at low air velocity. This study compares the performance of SAH without fins and SAH with rectangular fins. Two variations of a tilt angle of SAH are 0° and 30° which are observed in this study. The SAH uses a ventilator turbine to suck air into the collector box. The air velocity is 0.01 m/s. The method is experimental. The SAH is tested under real condition from 9 a.m. to 4 p.m. The measurement tools consist of a pyranometer, an anemometer, a temperature sensor in the inlet section, 3 sensors in the absorber plate, a sensor in the outlet section, 6 temperature sensors in the drying cabinet. The result showed the thermal efficiency of SAH with rectangular fins is 29.67 % higher than SAH without fins at 0˚ tilt of angle at noon. The thermal efficiency of SAH with rectangular fins is 25.26 % higher than that of without fins at 30˚ tilt of angle at noon.

Evaluation of Carbon Monoxide and Smoke Sensors at a Low Ventilation Velocity

This paper presents the results of large-scale fire experiments on evaluating the performances of carbon monoxide (CO) and smoke sensors at low ventilation velocities. Experiments using three different combustibles—conveyor belt, coal, and diesel fuel—were conducted in the Experimental Mine at the National Institute for Occupational Safety and Health (NIOSH) Bruceton Research Facility. A total of eight sensor stations were located downstream of the fire with each station containing CO, smoke, carbon dioxide, oxygen, humidity, barometric pressure, temperature sensors, and two airflow sensors. The airflow velocity ranged from 0.22 to 0.26 m/s (44 to 51 fpm) in the tests. The response times were recorded for the CO and smoke sensors at each sensor station when smoke and gaseous products of combustion of each burning combustible reached the station. The response times of the CO sensors were used to determine the appropriate sensor spacing in the belt entry with a low air velocity. The performance of the smoke sensor was found to be affected by the high humidity in the experiments. The results on proper selection of sensors and the determination of sensor spacing at a low ventilation velocity can be helpful for ensuring sufficient early fire warning for underground workers, thereby improving the health and safety of miners.

Response surface methodology to model the electrostatic precipitation of nanoparticles at low air velocities

Baixas velocidades de ar não são totalmente exploradas no campo de precipitação eletrostática devido às limitações de escala em equipamentos industriais, embora tenham fornecido altas eficiências de coleta de nanopartículas em estudos realizados em escala laboratorial. Visando contribuir com a ciência de precipitação eletrostática, um planejamento fatorial 3² completo foi realizado para avaliar o efeito de condições operacionais (voltagens de -8.0 a -8.2 kV e velocidades do ar de 1.67 a 19.9 cm s-1) sobre a eficiência mássica global de precipitação eletrostática de nanopartículas de KCl (5.94–224.7 nm). Metodologia de Superfície de Resposta foi usada para obter a faixa de condições operacionais que forneciam as maiores eficiências. A maior eficiência percentual (99.870 ± 0.008) foi obtida para -8.2 kV e 6.67 cm s-1. Um modelo polinomial ajustou bem os dados experimentais (R² = 0.99217).

Air Temperature Analysis of a Residential House Using Soliworks Flow Simulation

The model house under study is a typical house with a G.I. roofing but it was retrofitted by adding a green-material (bamboo) into, thereby forming a parallel plate air passage. The air, in passing this channel (airgap), undergoes a natural or free convection process of cooling. Buoyant forces cause this downward flow of cooled air through the airgap. The roofing airgap designed to direct this cooled air to the room to be ventilated. The flow through the airgap is laminar because of the low air velocity caused by the free-convection process of cooling. This study evaluated the performance of a house with roofing that was retrofitted with a type of green-material called bamboo. An evaluation applied to 88 square meters of space through air-temperature analysis. The tool used in this analysis was the FloEFD simulation software. The inputs required in setting up the FloEFD model are initial boundary conditions, ambient pressure and temperature, the estimated space heat load (assumed to be constant), and the roof module. Based on the results obtained, the indoor temperature depends on the boundary conditions or the outside environmental temperature. The indoor air temperature decreased an average of 2 ℃ from outdoor temperature with the initial conditions of 31 ℃ and room heat flux of 300 Watts/m2 with a resultant air movement inside the room ranging from 0.217 m/s to 0.651 m/s. The insulating property of green-material utilized in the roofing system was instrumental in lowering the airgap exit temperature by an average of 4 ℃.

Wind and seed: a conceptual model of shape-formation in the cushion plant Azorella Selago

AimsThe sub-Antarctic cushion plant, Azorella selago, is usually hemispherical when small but frequently crescent-shaped when larger. Spatial variation in wind speed and in air-borne seed and sediment deposition is examined to determine if wind scouring and deposition patterns could contribute to the development of non-hemispherical shapes in cushion plants.MethodsComputational fluid dynamic analyses were conducted for hemispherical and crescent-shaped cushion plants parameterizing models with data from A. selago habitats on Marion Island. Numerical data were contextualized with field observations to arrive at a conceptual model for shape development.ResultsAirflow modelling showed that both wind scouring and seed deposition of the commonly co-occurring grass Agrostis magellanica are greater on the windward side of the plant. By contrast, heavier sediment particles are predominantly deposited on the leeward side of plants, leading to burial of lee-side A. selago stems. This sediment accumulation may initiate the development of the crescent-shape in hemispherical plants by increasing stem mortality on the plant’s leeward edge. Once developed, the crescent-shape is probably self-reinforcing because it generates greater air recirculation (and lower air velocities) which enhances further deposition and establishment of A. magellanica grasses in the lee of the crescent. The conceptual model consists therefore of three stages namely, (1) negligible air recirculation, (2) sediment deposition and grass establishment, and (3) differential cushion growth.ConclusionThis conceptual model of plant shape development may explain the occurrence and orientation of crescent-shaped cushion plants and highlights how predicted changes in wind patterns may affect vegetation patterns.

Turbulent transport mechanisms on the heat confinement in tunnels by using low-velocity air curtains

Simulations with the Fire Dynamics Simulator (FDS) were performed to study the ability of Double Stream–Twin Jets (DS-TJ) air curtains to confine heat. Numerical simulations aimed to model a 1:34 scale tunnel, equipped with a heat source and two DS-TJ air curtains emerging from the tunnel ceiling. The novelty of this work was the imposition of low jet velocities to reduce fans power as much as possible, while ensuring confinement. Streamwise velocity and temperature were contrasted with experimental data.We observed a systematic deviation towards the faster jet, thus providing a better confinement than perfectly vertical curtains. Kelvin-Helmholtz instabilities related to turbulent transport were identified in the mixing layer, which induced leakage at the impingement on the tunnel ground. These instabilities were observed to amplify Reynolds stresses, playing a role on the flow regimes, the mass and heat balance and the confinement achieved.Temperature reached plateau values at both sides of the DS-TJ air curtain, thus heat diffusion was attenuated. Temperature drop in the protected zone occurred and the confinement effect was increased. Turbulent heat flux direction depended on the velocity difference between both jets, which defined the confinement characteristics.

Cardiovascular risk assessment of the population under adverse weather conditions

Introduction. Climate change around the world determines the relevance of the study of its effects on the human health. Nowadays, due to the development of modern medical science, the methods of evidence-based analysis of negative impact of the environmental factors on the public health are being widely implemented into preventive medicine. Their use should make it possible to quantify the various risks with high confidence and to manage them effectively. Material and methods. The weather conditions of the territory of Vladikavkaz for a 15-years period (2001-2015) have been studied. On the basis of the data from the primary medical documentation of emergency medical care (EMC) for the same period, the health status of the adult population in the city has been studied. The impact of the meteorological elements under the study on the frequency of seeking EMC was estimated using the relative (RR) and population risks (Rpop) values. Results. For the city of Vladikavkaz (according to the medical classification of weather conditions), high air humidity is typical for 65% of the days in a year, low air velocity (less than 3 m/s) - 77% of the days in a year. Inter-day fluctuations in temperature and atmospheric air pressure, exceeding the optimal levels for the human body, are recorded more than in 30% of the days in a year. Discussion. The city of Vladikavkaz is characterized by windless, wet weather, with frequent inter-day fluctuations in temperature and atmospheric air pressure, which corresponds to the clinically irritating and acute types of weather. Conclusion. The calculations of the relative and the population risks of impact of meteorological changes on the developing of urgent cardiovascular conditions in the population of Vladikavkaz showed RR of combining two unfavourable weather factors to be of 1.081 (p &lt;0.0001), and the Rpop increases by more than 3600 additional EMC calls due to cardiovascular pathology.

Cardiovascular risk assessment of the population under adverse weather conditions

Introduction. Climate change around the world determines the relevance of the study of its effects on the human health. Nowadays, due to the development of modern medical science, the methods of evidence-based analysis of negative impact of the environmental factors on the public health are being widely implemented into preventive medicine. Their use should make it possible to quantify the various risks with high confidence and to manage them effectively. Material and methods. The weather conditions of the territory of Vladikavkaz for a 15-years period (2001-2015) have been studied. On the basis of the data from the primary medical documentation of emergency medical care (EMC) for the same period, the health status of the adult population in the city has been studied. The impact of the meteorological elements under the study on the frequency of seeking EMC was estimated using the relative (RR) and population risks (Rpop) values. Results. For the city of Vladikavkaz (according to the medical classification of weather conditions), high air humidity is typical for 65% of the days in a year, low air velocity (less than 3 m/s) - 77% of the days in a year. Inter-day fluctuations in temperature and atmospheric air pressure, exceeding the optimal levels for the human body, are recorded more than in 30% of the days in a year. Discussion. The city of Vladikavkaz is characterized by windless, wet weather, with frequent inter-day fluctuations in temperature and atmospheric air pressure, which corresponds to the clinically irritating and acute types of weather. Conclusion. The calculations of the relative and the population risks of impact of meteorological changes on the developing of urgent cardiovascular conditions in the population of Vladikavkaz showed RR of combining two unfavourable weather factors to be of 1.081 (p &lt;0.0001), and the Rpop increases by more than 3600 additional EMC calls due to cardiovascular pathology.

Behavioral responses of turkeys subjected to different climatic conditions

I was evaluated the effect of seven different combinations of temperature, air velocity, and relative air humidity on the frequency and duration of eating, drinking, resting, cannibalism, dust bathing, scratching, ground pecking, shivering, and stretching behaviors of turkeys at three different ages. The combinations tested of temperature, relative air humidity, and air velocity were, respectively: 1 (22 °C, 50%, 1 m/s); 2 (26.2 °C, 73.2%, 0.45 m/s); 3 (26.6 °C, 71.2%, 1 m/s); 4 (28.9 °C, 72%, 1.4 m/s); 5 (31.1 °C, 85%, 0.45 m/s); 6 (34.1 °C, 82.1%, 1 m/s); and 7 (34.4 °C, 82.1%, 1.4 m/s) for three ages of birds (61, 96, and 131 days of age). Seven birds were housed per pen, at a density of 3 males/m2, totaling 147 birds in the entire experiment. Each combination was applied for 5 days. The data were analyzed considering the number of times the bird performed the behavior and the time it performed (in seconds). Each pen was considered a repetition. A comparison of the medians was used to compare the treatments by each age. The results showed that young birds were more likely to suffer from the combination of low temperature and high air velocity, reducing their frequency of normal behaviors. Increased humidity at a low temperature raised the frequency of scratching, shivering, and cannibalism behaviors leading to poorer bird welfare. It is recommended that the temperature, relative air humidity, and air velocity combination of 26.6 °C; 71.2%; and 1 m/s, respectively, for young birds, and 22 °C; 50%; and 1 m/s, respectively, for older birds should be used.

Mathematical model and energy utilization evaluation of a coaxial impinging stream drying system for parboiled paddy

The impinging stream drying technique has a high capability for removing water in a very short period. Energy consumption is strongly impacted by several of this type of dryer’s operating parameters, i.e., air temperature, air velocity, particle feed rate, and air recycle percentage. A mathematical model would be useful for finding the optimum condition from just a small number of experiments. A mathematical model at a mesoscopic scale that couples heat and mass transfer between gas and solid particles and tracks moisture or temperature distribution inside a single particle was developed in this study; it was used to simulate the effects of air velocity (15–25 m/s), parboiled paddy feed rate (80–250 kgdry solid/h) and exhaust air recycle level (0–80%) on the specific energy consumption (SEC). The developed model was able to predict the average moisture content, average grain temperature, and SEC accurately. The simulated moisture distribution inside a grain kernel showed that this drying technique, which incorporated 4 min tempering between drying cycles, provided a nearly constant rate of drying even though the moisture content decreased to 0.22–0.25 d.b. (dry basis). The use of higher air temperatures noticeably reduced the total specific energy consumption (SECtotal). The air velocity and parboiled paddy feed rate had synergetic effects on the energy consumption. Drying at lower air velocities consumed lower energy when the parboiled paddy feed rate was lower than 170 kgdry solid/h. At higher parboiled paddy feed rates, ranging from 170–250 kgdry solid/h, however, the use of higher air velocities tended to save more total energy. At 80% of recycled exhaust air, the SECtotal was around 4 MJ/kgH2O, which saved 40–45% of SECtotal compared with the case of without exhaust air recycle.

Impact of Environmental Conditions on Frost Crystal Structure

Frost crystal type and distribution were characterized in the initial periods of frost growth on an aluminum surface. Experiments were carried out for a range of wall temperatures from [Formula: see text]C to [Formula: see text]C, air temperatures from [Formula: see text]C to [Formula: see text]C, relative humidities from 15% to 85%, and air velocities from 0.5 to 5.0[Formula: see text]m/s. The results showed that frost crystal type was strongly dependent on the wall temperature and humidity. Changing the air temperature shifted the region of some frost crystal types. Decreasing the air temperature from 22 down to either [Formula: see text]C or [Formula: see text]C led to the decrease of feather crystals but increased the region of scroll crystals. Air velocity had smaller impacts on frost crystal type but had a strong influence on the distance between the crystals, particularly at lower air velocities. The results were compared to prior researchers. The results should provide a better understanding of frost morphology during the early stages of frost growth on metal surfaces.

THERMAL COMFORT INVESTIGATION ON HOLY MOSQUE IN BANDUNG Case Study : Lautze 2 Mosque Bandung

Abstract -Thermal comfort is a state of mind that expresses satisfaction with the thermal environment. There are two main categories in the effort to obtain a comfort index; empirical and analytical. Empirical is based on social surveys, while analysis is based on the physics principle of heat flow.Bandung city is one of the historical cities in Indonesia which has many historical heritage buidings. One of them which is commonly known as colonial buildings in Bandung is Lautze 2 Mosque, located at Tamblong Street in the city center of Bandung. This research was conducted to analyze the thermal comfort in the Lautze 2 Mosque Bandung. The analytical method used in this study is a quantitative research method by measuring the main factors namely air temperature, air humidity and air velocity. The main factors become obstacles to get thermal comfort data at the Lautze 2 Mosque Bandung is the location of buildings located in areas with tropical climate conditions with high air temperatures, high air humidity, and low air velocitys.The research conclude that thermal comfort in the Lautze 2 Mosque Bandung building can be categorized as uncomfortable, it can be seen from the measurement results of related factors, namely the temperature and humidity that exceeds the comfort limit and the low air velocity in the building becomes an obstacle to obtain thermal comfort. Keywords: colonial buildings, mosque, thermal comfort, tropical climate.

The cooling effect of a spray fan in an indoor hot environment

The aim of this study is to evaluate the cooling effect of a spray fan in an indoor hot environment. An experimental workplace with a thermal environment of high temperature and radiation intensity was set up. The hot environment of the experimental workplace could not meet occupational health requirements when the heat source temperature exceeded 150°C. The effects of air velocity and relative humidity on the natural wet bulb temperature, black globe temperature and wet bulb globe temperature (WBGT) were investigated. The maximum reduction of the WBGT was about 1.7°C, with an air velocity increase by 1 m/s. There was a notable cooling effect on the hot environment for low air velocities (e.g. 0–2 m/s), while the cooling effect only increased slightly for high air velocity (e.g. 2–5 m/s). We also found that the indoor WBGT declined by 0.2–0.8°C when the relative humidity was increased by about 10%. These results may provide guidance for reducing heat stress in industrial hot environment.

An experimental study on a horizontal-vertical pneumatic conveying system using oscillatory flow

To reduce the power consumption of a horizontal-vertical pneumatic conveying system, an oscillator is mounted with a 45° oblique plane through the pipe axis in this study. This experimental study focuses on the effect of oscillatory flow using the oscillator on the horizontal-vertical pneumatic conveying system in terms of the overall pressure drop of the system, power consumption, local pressure drop, and particle velocity. Compared with conventional pneumatic conveying (axial-flow), the pressure drop and power consumption can be reduced using the oscillatory flow in a lower air velocity range. Meanwhile, the particle axial velocity of the oscillatory flow is higher than that of the axial-flow near the bottom of pipe. This outcome indicates that the accelerating effect of oscillatory flow is obvious near the bottom of the pipe, and the particle vertical velocity of the oscillatory flow is positive, whereas the particle vertical velocity of the axial-flow is almost negative. This result shows that the particles of the oscillatory flow are suspended sufficiently, but the particles of the axial-flow have a tendency of deposition. Furthermore, the fluctuation intensity of the particle velocity of the oscillatory flow is higher than that of the axial-flow, especially near the bottom of the pipe.

Pressure drop characteristics of reverse circulation pneumatic cuttings removal during coal seam drilling.

To solve the problems that the borehole depth is shallow and the drilling efficiency is low during the gas drainage drilling in soft coal seam with current cuttings removal method, a new technology of reverse circulation pneumatic cuttings removal is proposed. The working principle of reverse circulation pneumatic cuttings removal is analyzed, and the kinetic equation of cuttings in the inner hole of the drill pipe is established. Through experiments, the pressure drop in the drill pipe is measured to reveal the effects of air velocity, cuttings mass flow rate, and cuttings particle size on the pressure drop in inner hole of the drill pipe. When the cuttings mass flow rate is constant, the pressure drop increases with the increase in air velocity. When the air velocity is constant, the pressure drop increases with the increase in cuttings mass flow rate. At low air velocity, the pressure drop of cuttings is primary. As the air velocity increases, the pressure drop ratio of cuttings decreases. Under the same conditions, the order of pressure drop with different particle size cuttings is coarse cuttings > medium cuttings > fine cuttings. Empirical equation of pressure drop coefficient of cuttings is established, which is in good agreement with the actual data.

Effect of Lattice Setting Density on Fluid Flow and Convective Heat Transfer Characteristics of Bricks in Tunnel Kilns

Abstract This paper reports the effect of setting density on flow uniformity, pressure drop, pumping power, and convective heat transfer coefficients (CHTCs). High-density setting (HDS) comprises 768 bricks, and low-density setting (LDS) contains 512 bricks are tested for different inlet air velocities using both local and average approaches. The investigation is carried out using a 3D-computational fluid dynamics (CFD) model with k–ω turbulence model. Both settings are validated against experimental data reported in the literature with errors less than 1.9% for pressure drop and −1.0% for brick surface temperature. The reported results indicated that the LDS has distinct benefits over the HDS as it enhances the flow uniformity, particularly in the stack channels. Also, LDS attains lower pressure drop, pumping power, and firing time than HDS by 45.93%, 50%, and 35%, respectively. In addition, LDS produces larger CHTCs, rates of heat transfer for individual bricks, and the ratio of heat transfer to pumping power than HDS by 24.53%, 35%, and 34%, respectively. Moreover, LDS produces more homogenous heating of the setting bricks than HDS as the maximum difference of CHTCs between bricks is about 4.39% for LDS and 19.62% for HDS. The best performance of the firing process is accomplished at low inlet air velocity (3 m/s), whereas the highest productivity is achieved at high inlet air velocity (9 m/s).

Study on a Dynamic Numerical Model of an Underground Air Tunnel System for Cooling Applications—Experimental Validation and Multidimensional Parametrical Analysis

The underground air tunnel system shows promising potentials for reducing energy consumption of buildings and for improving indoor thermal comfort, whereas the existing dynamic models using the computational fluid dynamic (CFD) method show computational complexity and are user-unfriendly for parametrical analysis. In this study, a dynamic numerical model was developed with the on-site experimental calibration. Compared to the traditional CFD method with high computational complexity, the mathematical model on the MATLAB/SIMULINK platform is time-saving in terms of the real-time thermal performance prediction. The experimental validation results indicated that the maximum absolute relative deviation was 3.18% between the model-driven results and the data from the on-site experiments. Parametrical analysis results indicated that, with the increase of the tube length, the outlet temperature decreases with an increase of the cooling capacity whereas the increasing/decreasing magnitude slows down. In addition, the system performance is independent on the tube materials. Furthermore, the outlet air temperature and cooling capacity are dependent on the tube diameter and air velocity, i.e., a larger tube diameter and a higher air velocity are more suitable to improve the system’s cooling capacity, and a smaller tube diameter and a lower air velocity will produce a more stable and lower outlet temperature. Further studies need to be conducted for the trade-off solutions between air velocity and tube diameter for the bi-criteria performance enhancement between outlet temperature and cooling capacity. This study proposed an experimentally validated mathematical model to accurately predict the thermal performance of the underground air tunnel system with high computational efficiency, which can provide technical guidance to multi-combined solutions through geometrical designs and operating parameters for the optimal design and robust operation.