Airflow Temperature Research Articles

Static and Dynamic Characteristics of Nonmetallic Labyrinth Seals Based on Fluid–Solid–Thermal Coupling

In this paper, static and dynamic characteristics of a labyrinth seal were studied by fluid–solid–thermal coupling analysis (FSTCA). Deformation and stress distribution of nonmetallic labyrinth seals (i.e., PEEK and PEEK-CA30) were further analyzed to investigate the effects on leakage and rotor stability compared to that of metallic material (i.e., AL alloy). The results show that a higher pressure drop of airflow at the last tooth along the airflow direction suggested a more remarkable energy conversion to kinetic energy. Airflow velocity at the tooth root was obviously lower than that at the tooth tip because of vortex in tooth cavity. Maximum deformation of the seal occurred at tip of the first tooth, while equivalent stress mainly distributed at the root. Both axial and radial deformations led to deformations of seal cavities and upward movements of the teeth, resulting in greater radial clearances. PEEK-CA30 had the lower radial and axial maximum deformations compared to PEEK and AL alloy, which in turns caused a lower leakage with increasing inlet temperature and inlet/outlet pressure ratio and a higher effective damping coefficient under different vortex frequencies, indicating a better seal performance and a better stability of rotor system. The equivalent stress for AL alloy deeply depended on inlet temperature of airflow due to higher elasticity modulus, higher thermal conductivity and higher thermal expansion coefficient, which made the seal more likely to fail under higher inlet temperature.

A comparative study of property-constant and property-variable icing models

ABSTRACT Icing on cold surfaces is ubiquitous in many natural and engineering processes, and various icing models have been proposed with little advice given on model selection. Here, we calculate the ice accretion characteristics using property-constant and property-variable icing models under different airflow parameters. The ice thickness, water film thickness, temperature profile, critical ice thickness, and critical time are compared. The property-variable icing model yields a larger ice thickness at the early icing stage but a smaller one at the later stage. The water film appears earlier, and the water film thickness is larger in the property-variable model. The temperature profiles are a logarithmic curve and a straight line in the property-variable and property-constant models. The property-variable model yields a shorter critical time and a smaller critical ice thickness. A smaller liquid water content, airflow velocity, and collection efficiency or a lower airflow temperature enlarges the difference in the ice accretion characteristics between the property-variable and property-constant models. The property-variable icing model is recommended when the airflow coefficient is smaller than 50. The findings in this work provide guidance for the model selection in icing prediction.

Energy Efficiency and Optimization Strategies in a Building to Minimize Airborne Infection Risks

Heating, ventilation, and air conditioning (HVAC) systems play a crucial role in either increasing or decreasing the risk of airborne disease transmission. High ventilation, for instance, is a common method used to control and reduce the infection risk of airborne diseases such as COVID-19. On the other hand, high ventilation will increase energy consumption and cost. This paper proposes an optimal HVAC controller to assess the trade-off between energy consumption and indoor infection risk of COVID-19. To achieve this goal, a nonlinear model predictive controller (NMPC) is designed to control the HVAC systems of a university building to minimize the risk of COVID-19 transmission while reducing building energy consumption. The NMPC controller uses dynamic models to predict future outputs while meeting system constraints. To this end, a set of dynamic physics-based models are created to capture heat transfer and conservation of mass, which are used in the NMPC controller. Then, the developed models are experimentally validated by conducting experiments in the ETLC building at the University of Alberta, Canada. A classroom in the building is equipped with a number of sensors to measure indoor and outdoor environmental parameters such as temperature, relative humidity, and CO2 concentration. The validation results show that the model can predict room temperature and CO2 concentration by 0.8%, and 2.4% mean absolute average errors, respectively. Based on the validated models, the NMPC controller is designed to calculate the optimal airflow and supply air temperature for every 15 min. The results for real case studies show that the NMPC controller can reduce the infection risk of COVID-19 transmission below 1% while reducing energy consumption by 55% when compared to the existing building controller.

Effect of window-glass type on solar heat gain and velocity and temperature distributions inside air-conditioned rooms – A conjugate numerical analysis

Conjugate mixed-convection numerical analysis is conducted in order to investigate effect of employing different types of window glass on solar heat gain in air-conditioned rooms using mixing air-distribution system. ANSYS Fluent and RNG k-ε turbulence model are utilized. Single- and double-pane clear and tinted window glass are considered with window-to-wall ratio of 0.33. The rate of air change per hour (ACH) is varied in range 5–20. Part of solar radiation absorbed by glass is conducted indoor while solar radiation transmitted through glass heats portion of floor and is released as a heat source to inner space. The numerical model is validated against measurements available under simpler conditions. Results of model application show that airflow pattern and temperature distribution are sensitive to the solar heat gain and, hence, to the type of glass used. It is found that air-conditioning load due to window glass heat gain is reduced by 55% by using double-pane tinted glass compared to using single-pane clear glass. A criterion to distinguish between forced and mixed convection situations in terms of ACH is also developed. In addition, further calculations are made using standard k-ω turbulence model and satisfactory agreement with RNG k-ε model results is obtained.

Study of energy-efficient heat resistance and cooling technology for high temperature working face with multiple heat sources in deep mine

In the present research, we proposed a scheme to address the issues of severe heat damage, high energy consumption, low cooling system efficiency, and wastage of cold capacity in mines. To elucidate the seasonal variations of environmental temperature through field measurements, we selected a high-temperature working face in a deep mine as our engineering background. To enhance the heat damage control cability of the working face and minimize unnecessary cooling capacity loss, we introduced the multi-dimensional heat hazard prevention and control method called "Heat source barrier and cooling equipment". First, we utilize shotcrete and liquid nitrogen injection to eliminate the heat source and implemented pressure equalization ventilation to disrupt the heat transfer path, thereby creating a heat barrier. Second, we establish divisional prediction models for airflow temperature based on the variation patterns obtained through numerical simulation. Third, we devise the location and dynamic control strategy for the cooling equipment based on the prediction models. The results of field application show that the heat resistance and cooling linkage method comply with the safety requirement throughout the entire mining cycle while effectively reducing energy consumption. The ambient temperature is maintained below 30 °C, resulting in the energy saving of 10% during the high-temperature period and over 50% during the low-temperature period. These findings serve as a valuable reference for managing heat damage in high-temperature working faces.

Experimental study on buoyance-aided mixed convective heat transfer in an asymmetrically heated vertical channel

This paper studied the buoyance-aided mixed convective heat transfer of air-cooling flow in a 5 m long and 1.2mX0.3 m cross-section vertical channel. One of the channel walls was uniformly heated and the rest three walls were unheated and insulated. Heat was transferred from the heated wall by convection and radiation, and heat was also transferred from unheated walls to the air flow by convection originated from their net radiation gain from the heated wall. The air flow rate, the inlet and outlet air flow temperatures, and local surface heat fluxes and temperatures on the heated wall were measured. The Reynolds number of air flow was from 2900 to 221,000 and Richardson number was changed from 0.006 to 90.6. The results showed that for walls with larger emissivity the total convection heat transfer was not deteriorated in mixed convection zone. Therefor a modified heat transfer correlation was developed for the aiding mixed convection in the asymmetrically heated channel considering both mixed convection and radiation. It predicted the experiment results with a deviation less than 18%.

Measurement of the turbulent heat fluxes in mixed convection using combined stereoscopic PIV and PIT

The results of simultaneous measurements of velocity and temperature fields in a turbulent mixed convection airflow are analyzed and discussed. To access local temperature and velocity fields in airflows, we present a combination of stereoscopic particle image velocimetry and particle image thermometry. The obtained flow fields make it possible to determine the local convective heat fluxes, thus giving insight into the dynamics of plumes and Taylor–Görtler-like vortices. The evaluated mean local heat fluxes further reveal that the main convection roll transports a substantial amount of heat along the cooling plate and back to the heated bottom plate. Yet, the associated mean turbulent heat fluxes remain positive as they are dominated by the correlation of the temperature and the vertical velocity component. More specifically, a statistical analysis of the local heat flux distribution reveals that Taylor–Görtler-like vortices lead to more skewed distributions of the turbulent convective heat fluxes than plumes.Graphical abstract

Mitigating Coffee Ring Effects for Efficient Upscaling of Flexible Organic Solar Cells

As a roll‐to‐roll compatible technology, slot‐die coating has shown great potential for manufacturing industrial‐level organic solar cells (OSCs). However, in the slot‐die coatings process, coffee rings are often formed due to the slow film‐forming kinetics, leading to a significant loss of power conversion efficiency (PCE) in upscaling device area. Herein, the coffee rings are suppressed by introducing an airflow‐assisted slot‐die technique to obtain a suitable active layer morphology with improved flatness and homogeneity. Synergistically, optimization of airflow and substrate temperature conditions, the PCE of 1 cm2 flexible OSC devices reaches 13.69%. Moreover, large‐area flexible OSC modules with 30 cm2 achieve a PCE of 13.08%, maintaining 95% of 1 cm2 device, which is the minimum PCE loss from 1 cm2 to large‐area devices. Morphology characterization shows that airflow can suppress excessive molecular aggregation and obtain suitable phase separation. Therefore, this work provides an efficient method to fabricate high‐efficiency flexible large‐area OSC modules, which will promote OSC devices from lab to fab.

Heat and species map prediction for the generic MEA using an air node model derived from high level requirements

Current developments to implement the More Electric Aircraft (MEA) result in a fundamental change of the aircraft systems architecture. Components may be resized or new components may be introduced. This results in new challenges for the thermal management and safety assessment of systems and therefore parametric and fast simulations tools will become crucial to explore the entire design space. The effects of component heat dissipation on airflow in the aircraft fuselage can be qualified using a zonal simulation model. Zonal airflow models subdivide the indoor space into typically 102 zones exchanging air. This allows to predict the impact of systems locations, ventilation and cooling strategies on the thermal management and safety considerations in an early design stage. This paper presents the setup of such an aircraft zonal model based on high-level requirements for a MEA of regional airplane size. These requirements cover the number of passengers, the flight profile and system components to be integrated, like e.g. the battery. Additional requirements are derived from standards for example providing information on required airflow rates and temperatures in the cabin. These requirements are translated into a geometry, ventilation pattern and systems layout. The model application is demonstrated on the example of the safety consideration in case of a battery failure leading to exhaust of harmful gas. This is done by comparing the gas dispersion for two different battery positions in the aircraft.

Effects of Airflow Disturbance on the Content of Biochemical Components and Mechanical Properties of Cucumber Seedling Stems

In order to explore the changes in biochemical components and mechanical properties of cucumber seedlings with dwarfing characteristics under airflow disturbance treatment, ‘Jinyou No. 1’ cucumber seedlings were used as experimental materials and the split-plot design was used. The cucumber seedlings were treated with airflow disturbance with two airflow temperatures of 25 ± 5 °C and 35 ± 5 °C as the main factors and four airflow velocities of 1, 3, 6 and 9 m/s as the secondary factors. At the same time, cucumber seedlings without airflow disturbance were used as controls to study the effects of airflow temperature and velocity on the biochemical components and mechanical properties of cucumber seedling stems. The results showed that with the increase in airflow velocity, the content of the stems’ biochemical components increased to varying degrees, and the bending load, shear load, elastic modulus, bending strength and shear strength of the seedling stems also increased. Under the same airflow velocity, the biochemical component content and the accepted load of seedlings under the 25 ± 5 °C airflow temperature treatment were larger than those under the 35 ± 5 °C airflow greenhouse treatment, but the elastic modulus, bending strength and shear strength of seedlings under the 25 ± 5 °C airflow temperature treatment were lesser than those under the 35 ± 5 °C airflow temperature treatment. Using the grey relational analysis method, the correlation degree between the biochemical components of the stem and the mechanical properties of the stem was different. The correlation degree between the biochemical components of the seedling stem and the mechanical properties under different airflow temperature treatments was significant. The correlation degree between the biochemical components of the seedling stem and the mechanical properties under different airflow velocity treatments was greater than 0.60, indicating that the biochemical components of the seedling stem under airflow velocity treatments had a greater influence on the mechanical properties. In summary, airflow disturbance significantly affected the biochemical components and mechanical properties of cucumber seedlings. The biochemical components and mechanical properties of seedlings were negatively correlated with airflow temperature and positively correlated with airflow velocity. With a decrease in airflow temperature and an increase in airflow velocity, the biochemical components and mechanical properties of seedlings increased.

Optimizing and simulating cooling of electric transformer room utilizing genetic algorithm to reduce electricity/water demand by incorporating borehole ground heat exchangers

BackgroundIn this study, the optimization of the transformer room cooling systems was discussed and investigated. According to the cooling requirements of the transformer room (airflow and maximum temperature), a water-cooled chiller and air conditioner were used. MethodsBy using numerical analysis, the mass/energy of the cooling tower was studied. To improve the effectiveness of the cooling strategy, the cooling tower was removed and the ground heat exchanger was incorporated into the cooling system. ResultsBased on the numerical analysis, if the ground heat exchanger is added, the electricity and water demand was reduced by 12.65 kWh and 1.94 m3 per square meter. The performance of the geothermal heat exchanger depends on the number of pipes, but the amount of dependence decreases with the increase in the number of pipes. To find the best number of tubes, the genetic algorithm was used and it was observed that if the number of tubes reaches sixteen, for every one percent increase in costs, the heat transfer in the geothermal exchanger increases by 2.54 percent.

Cold sprayed AlNiCoFeCr–TiB2 metal matrix composite coatings

In this work, the mechanically alloyed AlNiCoFeCr high entropy alloy (HEA) was used as matrix to develop metal matrix composite (MMC) coatings. Dense and thick AlNiCoFeCr – 30 wt % TiB2 MMC coatings were firstly fabricated by solid-state cold spraying (CS) technique at the low pressure of 0.9 MPa, and temperature of 300 and 450 °C. The effect of compressed air flow temperature and pressure parameters on structure and mechanical properties of coatings were established. As a low-temperature deposition process, CS completely retained the phase composition and nanostructure in the coatings without any phase transformation. With an increase in pressure up to 0.9 MPa a refinement of the coating structure and a double increase in the fraction of TiB2 particles in the coating were detected. An increase in temperature at least to 300 °C breaks down the oxide layers of the particles, multiplying the deposition efficiency and the properties of the coatings. The coatings fabricated at a spraying temperature of 450 °C and a compressed air flow pressure of 0.9 MPa exhibit the average thickness of 1110 μm, as well as a good combination of high microhardness (6.9 GPa) and sufficient indentation fracture toughness (3.8 MPa∙m1/2).

The coupled cooling effect of ventilation and spray in the deep-buried high-temperature tunnel

The utilization of ventilation and spray cooling technology is becoming increasingly popular in high-temperature workplaces due to its convenience and environmental friendliness. To investigate the coupled cooling effect of ventilation and spray in a construction tunnel, we established a droplet evaporation model under convective heat transfer conditions by combining the convective heat transfer theory and the droplet heat and mass transfer model. Based on this model, the study focused on the energy change of droplet evaporation in a moving medium by using numerical simulation in the context of a railroad construction tunnel. The material of the droplets used in the study was water. According to the simulation and field measurement results, it was obtained that, firstly, increased air volume of the tunnel and reduced airflow temperature could make the convective heat exchange stronger between the airflow and the wall. Secondly, the particle size of droplets formed by spraying was mainly 30–40 μm in the tunnel. A part of the droplets was evaporated in the high-temperature environment, and another part was trapped by the rock wall and ground. Third, adopting the coupled cooling method of ventilation and spray, the temperature and humidity fields in the tunnel changed significantly, and a low-temperature and high-humidity zone appeared near the nozzle. At the same time, the evaporation rate of droplets increased, the heat index of the workplace decreased, and the cooling effect was effective. Therefore, the coupled cooling method of ventilation and spray can effectively improve the thermal environment in high-temperature construction tunnels and enhance the thermal comfort of personnel. This study serves as a reference for the parameters and cooling effect of ventilation and spray cooling systems in construction sites.

Drying behavior of a horizontal vibrated fluidized bed dryer for continuous manufacturing

Twin-screw wet granulation offers the possibility to granulate continuously. A drying step after wet granulation is required to realize a full continuous manufacturing line. Aim of this study was to gain insights into the drying behavior of a continuous vibrated fluidized bed dryer intended for pharmaceutical research and development. A Design of Experiment was conducted to examine the influence of process parameters during drying of granules using drying temperature, air flow and vibration acceleration as factors. The obtained temperature and humidity profiles during drying of lactose-MCC and mannitol granules displayed the first and second drying stage which is spatially resolved. With higher drying temperature or higher air flow the second drying stage was achieved earlier. Increase in vibration acceleration shortened the residence time and by this the second drying stage was reached later at lower granule temperature and thus higher residual moisture of the granules. Formulation dependent impact of the drying parameters was observed as lactose-MCC led to smaller granules when increasing the temperature or air flow.

Thermal Performance Evaluation for Two Designs of Flat-Plate Solar Air Heater: An Experimental and CFD Investigations

The main objective of this research was to create two different configurations of a flat-plate solar air heater, namely, Conventional-Case A and Modified-Case B, and develop a three-dimensional computational fluid dynamics (CFD) model using ANSYS R15.0. The purpose of the CFD model was to simulate the heat transfer behavior of the proposed solar air heaters under unsteady conditions. The RNG k-ε turbulence model was employed for this CFD study. The experiments were conducted on sunny days, under the same conditions as the Egyptian climate. The results of the experiments show that the simulated CFD model and the measured outlet airflow temperatures, relative humidity, and velocities of the two tested solar air heaters were compared. The developed model made very satisfactory predictions. Moreover, the deviations between the average CFD outlet air temperatures and the experimental results were 7% and 7.8% for Case B and Case A, respectively. The CFD-simulated average relative humidity was reduced by 31.6% when using Case B compared with Case A, and it was reduced by 28.8% when comparing the experimental data to Case B. Additionally, the average CFD thermal efficiencies obtained for Case B and Case A were 28.7% and 21.6%, respectively, while the average experimental thermal efficiencies for the cases were 26.4% and 18.2%, respectively. The proposed model can be used to design and simulate other solar air heater designs.

PAXTA TOZALASH KORXONALARIDA HAVO OQIMINI CHANGDAN TOZALOVCHI AGREGAT KONSTRUKTSIYASINI TAKOMILLASHTIRISH

A detailed analysis of cyclones for cleaning dusty air coming out of ginneries has been provided in this article. The composition, temperature and speed of the dusty airflow coming out of ginneries have been studied. Depending on the composition of the dusty air, a new unit has been developed with a number of improvements up to the cyclone separator. With the help of the SOLIDWORKS Flow Simulation program, a new model for the design of a unit for cleaning a dusty air flow in a cyclone was developed, and a unit with the highest cleaning efficiency was selected among the new developed models. The design of an improved new cyclone separator unit has been simulated using SOLIDWORKS Flow Simulation software and the results were obtained. The design values of speeds in the SOLIDWORKS Flow Simulation model were theoretically calculated using the Navier-Stokes equations. The pressure, temperature, speed, on their basis, the dynamic viscosity of dust particles inside the unit have been studied, and the results have been obtained.

Understanding airflow pattern and temperature distribution in domestic refrigerators – A review analyzing recent developments and bridging knowledge gaps

Refrigerators have become an essential appliance in every household, and they consume approximately 30% of total electricity among other domestic appliances such as clothes washers, dryers, and air conditioners. With the refrigerator’s comparatively high energy consumption compared with other appliances, existing research has mainly focused on improving the energy efficiency of refrigerators by changing the design of the compressor, heat exchanger, refrigerant, and insulation. However, previous studies have paid very little attention to the research and development of the temperature distribution in the refrigerator, which is a key parameter in determining energy consumption and food safety. Therefore, this review aims to present an overview of recent design developments to improve the temperature distribution and air circulation in domestic refrigerators, including static refrigerators and no-frost refrigerators. This review article discusses the various operation and design factors that can affect the air circulation and temperature uniformity of the refrigerator, including shelf arrangement, the compressor on/off cycle, thermostat settings, evaporator design, ambient conditions, door opening frequency, and product loading temperatures. Additionally, this review provides a summary of the advanced vapor compression cycle based refrigerators that are expected to provide better energy efficiency and independent temperature control in freezer and refrigerator compartments. This review elaborates on the significance of improving the performance of the domestic refrigerator in terms of temperature distribution and air circulation.

ANALYSIS OF THE DETERMINING METHODS OF THE THERMAL FIRE DETECTORS TIME PARAMETERS

The article is devoted to substantiating the pulse method of time parameters determining - the thermal fire detectors' operation time and constant time with a thermal resist sensitive element. Significant research is that the time parameters of thermal fire detectors include the operation time and constant time that are interconnected. It is shown that the contribution of constant time to the operation time can be up to 20% at a speed of change in ambient temperature 0.50C per C-1. It is also found that their testing is used to determine the time parameters of thermal fire detectors, which are divided into stationary or autonomous and operational or object. The article specifies that the disadvantage of inpatient tests with the help of heat chambers is the asymmetry of the airflow distribution and temperature, and the lack of such tests employing standard combustion cells is that the thermal impact parameters on the fire detector sensitive element are not normalized. The research results have found that the amount of the fire detectors' constant time is not determined, and only control of the fire detectors' operation time is carried out according to the admission criteria. During the object tests, in most cases, the thermal impact on a fire detector's sensitive element with the help of small heat chambers is realized, the purpose of such tests is to check the fire detectors' performance without obtaining estimates of their operation time and constant time. It is worth noting that the thermal impact on the fire detector's sensitive element can be carried out with the help of both external and internal sources of heat. The second option is characteristic of fire detectors with a thermal resist sensitive element and is based on the use of the Joule-Lenz effect (heating of a conductor or semiconductor is directly proportional to its resistance, the duration of the current and the square of the current). In this case, new opportunities are opened to improve the efficiency of the fire detectors operation of this type. Keywords: fire equipment, detectors, improving the efficiency of the fire detectors operation, time parameters of thermal fire detectors.

How do caves breathe: The airflow patterns in karst underground.

Caves and their surrounding fracture systems in the vadose zone of karst regions host a unique atmospheric environment. Understanding the airflow patterns in caves is critical to understanding the properties of the subsurface atmosphere and the chemical interactions between air, water, and rock. The most common driver of airflow in caves is the density difference between the subsurface and the outside air, known as the chimney effect. Observations show that seasonal airflow patterns in caves also depend on the geometry of passages. In this work, I present and use a numerical model of a passage embedded and thermally coupled to a rock mass to study the relationship between the airflow pattern and passage geometry. As the outside air enters the subsurface, it approaches thermal equilibrium with the rock mass along a characteristic relaxation length. This determines the temperature and density contrast between the inside and outside air, and the resulting pressure difference, which drives the airflow. In passages with non-uniform outlines and/or cross-sections, the relaxation length may depend on the flow direction, resulting in different airflow velocities in cold and warm periods for the same absolute temperature difference between the massif and the external temperature. In a passage with a V-shaped longitudinal profile, the airflow is triggered by instability which causes the feedback between the relaxation length and airflow velocity. The airflow pattern can also be altered by snow and ice. Heat transfer in the rock and the thermal inertia of the rock also change the relaxation lengths and cause hysteresis in the curve presenting the airflow velocity vs. temperature difference.

Sensitivity and preference of local airflows beneath garments with personalised temperatures and velocities

Microclimate ventilation under garment is one of the effective means to relieve heat stress of human body, while the sensitivity and preference of airflow at different body parts are not thoroughly studied. This study investigates the local airflow sensitivity of five body segments by a psychophysical method, whereby twelve subjects were stimulated by three temperatures of ventilation under garment (Tsk - 5 °C, Tsk, or Tsk + 5 °C, Tsk is the initial local skin temperature); at the front chest, upper back, lower back, front thigh, and back thigh areas. Airflow sensitivity was tested to enhance when the airflow became warmer or cooler than the Tsk, showing that human skin can recognise variations in airflow velocity with a difference threshold of 0.23 ± 0.06 m/s. The front chest was the least sensitive of all three airflow temperatures, while the back thigh was the most sensitive to cool airflow. Twelve subjects then underwent controllable local ventilation at 35 °C, RH 40%. The airflow preference, psychological and physiological responses, and energy consumption were analysed. The preferred airflow temperature was approximately 26 °C (25.7 ± 1.8–25.9 ± 1.4 °C), while the preferred airflow velocity had a large individual variation. The lower back should be primarily ventilated, obtaining comfort enhancement with an energy saving of 30–40% compared to others; the front chest or the upper back should be added for higher cooling demand. This study helps us to understand the characteristics of airflow sensitivity on localised skin and optimises the design of individual ventilation.