Nozzle Air Supply Research Articles

The influence of ventilation modes on oil mist particles diffusion in a machining workshop

Mechanical processing and operations are widely involved in modern industry. Large amount of oil mist is tended to be produced and will diffuse in the processing workshop when metalworking fluids are applied on the high temperature workpiece. The ventilation modes and air distributions can influence the air pollutants dilution in machining workshops. Therefore, this paper presents both experimental investigation and simulation study on the oil mist particles diffusion under different ventilation modes. The results identified PM2.5 as the primary component among different oil mist particles generated during a typical machining process. The distribution of oil mist particles in a full-scale machining workshop laboratory was investigated under two ventilation modes: high-sidewall nozzle air supply and low-sidewall air supply. Results revealed obvious influences of both air supply modes on the distribution of oil mist particles. Under the high-sidewall-nozzle air supply mode, the airflow and the oil mist distribution in the workshop was relatively uniform; while the low-sidewall-vent air supply mode led to an uneven distribution of oil mist particles, and the maximum oil mist concentration appeared at the height of 3 m. Under both modes, the attempts to increase the airflow rate are not always successful. Compared with low-sidewall-vent air supply mode, the high-sidewall-nozzle air supply mode presents better performance in achieving lower overall particle concentration level. Overall, the results of this study give useful reference to improve the air quality of industrial plant by properly designing the ventilation mode of machining workshop.

The Influence of Supply Channel Design on the Gas-Dynamic Structure of Air Flow in a Vertical Conical Diffuser

Vertical conical diffusers are used in power engineering, chemical industry, technological processes, and other industries. The efficiency of many machines and pieces of equipment is determined by the gas-dynamic and heat-exchange perfection of processes in diffusers. This study assesses the influence of the air supply method on flow structure in a diffuser. The studies were carried out on a test bench with thermal imaging for air flow rates ranging from 0.018 to 0.057 m3/s (42,500 < Re < 150,000). Two designs were examined: (1) a conventional air supply through one channel from below and (2) a nozzle air supply through four tubes at an angle of 45° to the vertical axis. In addition, the influence of the cross-sectional shape of the supply channels of both designs was studied. It is established that the use of a conventional air supply through one channel leads to the generation of a pronounced central flow along the vertical axis (all configurations of the supply channel) and the creation of stagnant zones in the corners of the diffuser (round and triangular channels; the use of a square supply channel causes the most uniform air distribution throughout the entire volume of the diffuser (while maintaining the central flow). It is found that with nozzle air supply, there are no stagnant zones in the corners and intense air movement generation in the centre of the diffuser (round and triangular tubes) can be observed; the use of square nozzle tubes causes intense flow movement at the base of the diffuser, which quickly collapses upstream, uniformly filling the entire volume of the diffuser’s cylindrical part. The presented data can be useful for designing various machines and pieces of equipment with vertical conical diffusers.

Prediction of vertical thermal stratification of large space buildings based on Block-Gebhart model: Case studies of three typical hybrid ventilation scenarios

Although nozzle air supply is considered to be dominant when creating the thermal environment of the occupied area in a large space building, natural ventilation and air infiltration can interact with nozzle jets, resulting in a complex air distribution inside the building. This study focuses on the prediction of indoor vertical temperature distribution in large space buildings under the coupling of multiple airflows. Based on the validated regional model, Block-Gebhart (B-G) model, three auxiliary models were introduced for three types of common building ventilation scenarios, namely nozzle air supply, natural ventilation, and air infiltration. The auxiliary models were combined with the basic model to predict the indoor thermal environment of large space buildings in three hybrid ventilation scenarios. Field measurements of the vertical air temperatures of these three buildings were carried out to verify the feasibility and accuracy of the composite model. The results showed that the average deviations of air temperature in the International Gymnastics Stadium, the Ecological Demonstration Building and the Engineering Training Plant were 0.85, 0.80, and 0.32 °C, respectively. The building with the minimum deviation was the training plant, because the prediction of air temperature of this building took into account both jet entrainment and air infiltration phenomenon, so that the description of its indoor airflow pattern was the most accurate. The composite model proposed in this paper extends the application of the B-G model in hybrid ventilation scenarios and supplements the present design system of air distribution in large space buildings.

Vertical temperature distribution in large space buildings in the heating season: On-site measurement and Block-Gebhart model prediction considering air infiltration

In the heating season, the air infiltration in large space buildings cannot be neglected, which will cause a complex movement of indoor air and affect the creation of the thermal environment. Existing thermal environment prediction models often treat the indoor space as a whole, and cannot consider the temperature gradient in the vertical direction. Therefore, in this investigation, based on the Block-Gebhart (B-G) model, combined with the air infiltration model, the indoor air temperature distribution and infiltration air volume in large space buildings were predicted. The on-site measurement was carried out in an engineering training plant in Shanghai, which used nozzle air supply as a stratified environment regulation method. The measurement results verified the accuracy of the indoor thermal environment predicted by the compound model. The influence of the outdoor temperature, the supply air temperature and velocity, and the height difference of the infiltration and exfiltration air outlets on the indoor air temperature and the infiltration air volume was analysed. The infiltration air volume was most significantly affected by the height difference. In addition, the influence of the above factors on the thermal comfort of the personnel activity area was discussed. In general, the proposed compound model can accurately predict the indoor thermal environment under air infiltration and provide a theoretical basis for the design of airflow distribution in large space buildings in winter.

Modelling dispersion of radioactive aerosols and occupational dose assessment of workers in a large nuclear plant industrial workshop with a stratified air conditioning system

Abstract Numerical simulations of radioactive aerosols dispersion were conducted to determine the potential radiation hazard on occupants due to radioactive aerosols emitted from the workbench in a large nuclear plant industrial workshop with a stratified air conditioning system. Different air organization schemes were evaluated based on the position of the workbench under the initial, mainstream and end locations of the jet stream. The two air distributions of ”unilateral nozzle air supply” (UNAS) and ”bilateral nozzle air supply” (BNAS) were considered based on experimental measurements. Results show a high removal efficiency of radioactive aerosols when the pollution source was in the main jet stream under ”BNAS”. Both air distributions worked well when the pollution source from the workbench was in the initial and end section of the jet air stream. In addition, increasing the local exhaust velocity was an effective solution to remove the radioactive aerosols. The maximum effective dose rate calculated for workers’ exposure to radioactive aerosols was 14.39mSv y−1 when the local exhaust system was operating normally in the work area, in the main jet stream under “UNAS”. Therefore, the average effective annual dose was under the International Commission on Radiological Protection (ICRP)’s recommended limit of 20.0mSv y−1.

Vertical Temperature Profiles and Cooling Load in Large Spaces Ventilated by Stratified Air-Conditioning Systems: Scale-Model Experiment and Nodal Modeling

Abstract An improved heat balance nodal model is proposed to predict the inner wall temperature profiles and calculate the stratified air-conditioning load in large spaces. The model aims to weaken the correlation between load calculation methods and indoor airflow patterns, and to ensure the synchronization of each heat transfer process, so as to be closer to actual situations. The scale-model experiments were conducted in an enthalpy different laboratory in University of Shanghai for Science and Technology (USST) in Shanghai, China. This paper took the air distribution of nozzle air supply system as an example to calculate the inner wall temperatures and the stratified air-conditioning load by the nodal model and verified by the scale-model experiments. The results showed the maximum deviations of the experimental and theoretical values for the inner wall temperatures, the heat transfer load from the nonair-conditioned (NAC) area and the stratified air-conditioning load were all within 5%. The effects of the air temperature in the NAC area on the heat transfer load from the NAC area and the stratified air-conditioning load were analyzed, and the load nomogram was produced. It was found the heat transfer load from the NAC area accounted for 10–30% of the stratified air-conditioning load. The load nomogram compared two methods for determining the air temperature in the NAC area and gave the recommended one. The findings in this paper can be used to further develop load calculation models for non-uniform thermal environments.

Nonlinear dynamics of self-organising bubble departures from twin nozzles

The nonlinear dynamics of self-organising bubble departures from twin nozzles in engine oils was analysed. Air bubbles were generated from twin brass nozzles with an inner diameter equal to 1 mm. The flow of bubbles in bubble chains was recorded using high-speed camera. The time series of air pressure oscillations and signal from laser–phototransistor identifying the presence of bubbles over the nozzles outlet were recorded simultaneously. The self-organising bubble departures were observed and their stability was analysed. It was found that self-organising bubble departures become unstable because of successive (during subsequent bubble departures) decrease of the mean air pressure in one of the nozzle air supply system. It was shown that instability of self-organising bubble departures leads to equalization of pressures in both nozzles air supply systems which causes that simultaneous bubble departures appear. In the present experiment, this process was repeated in a cyclic and chaotic way. It was shown that stable self-organising bubble departures are accompanied by periodic air pressure oscillations in one of the nozzles and chaotic air pressure oscillations in the second one.

Non-Linear Analysis of Air Pressure Fluctuations During Bubble Departure Synchronisation

Abstract In the recent paper, non-linear methods of data analysis were used to study bubble departure synchronisation. In the experiment, bubbles were generated in engine oils from two neighbouring brass nozzles (with an inner diameter of 1 mm). During the experiment, the time series of air pressure oscillations in the air supply system and voltage changes on phototransistor were recorded. The analysis of bubble departure synchronisation was performed using a correlation coefficient. The following methods of non-linear data analysis are considered. Fast Fourier Transformation, autocorrelation, attractor reconstruction, correlation dimension, largest Lyapunov exponent and recurrence plot analysis were used to examine the correlation between bubbles behaviour and character of pressure fluctuations. Non-linear analysis of bubble departure synchronisation revealed that the way of bubble departures from two neighbouring nozzles does not depend simply on the character of pressure fluctuations in the nozzle air supply systems. The chaotic changes of the air pressure oscillations do not always determine the chaotic bubble departures.

Study of convective heat transfer load induced by nozzle air supply in large spaces with thermal stratification based on Block-Gebhart model

The Block-Gebhart (B-G) model is proposed to predict the convective heat transfer load for the stratified air-conditioning system using nozzle air supply. The scale-model experiments were carried out in an enthalpy difference laboratory in Shanghai. The theoretical solutions of convective heat transfer load calculated by the B-G model were experimentally verified. The results showed the feasibility and accuracy of the B-G model in calculating the convective heat transfer load for the stratified air-conditioning system in large spaces. The key factors affecting the convective heat transfer load were analyzed. The nomogram of convective heat transfer load was made, which could be used to determine the relationship among the non-dimensional convective heat transfer load (ratio of convective heat transfer load to heat gain in non-air-conditioned area), the heat intensity ratio (ratio of heat intensity in non-air-conditioned area to heat intensity in air-conditioned area), and the exhaust heat ratio (ratio of exhaust heat to heat gain in non-air-conditioned area). Through this method, the convective heat transfer load can be effectively calculated in practical engineering applications, which provides the theoretical basis for the optimal design of airflow distribution in large spaces.

Study of indoor thermal environment and stratified air-conditioning load with low-sidewall air supply for large space based on Block-Gebhart model

At present, the commonly used mathematical calculation method of stratified air-conditioning load for large space building was proposed by the form of nozzle air supply. However, there is no complete cooling load calculation methods of stratified air-conditioning with low-sidewall air supply system for large space buildings which are widely used in recent years. This paper takes a scale model laboratory which has the airflow distribution of low-sidewall air supply system as study object and based on Block-Gebhart (B-G) model to predict the indoor thermal environment distributions. Afterwards, we used the calculation methods of radiative and convective heat transfer loads which were proposed by our research group to calculate the stratified air-conditioning load and verified by the experiments. The results show that the relative errors range of theoretical and experimental values of indoor air temperatures, inner wall temperatures and stratified air-conditioning load are ranging from −5.440% to 2.473%, −5.024%–3.277% and −6.47% to 4.04%, respectively. This indicates that the B-G model can accurately predict the indoor thermal environment distributions and the stratified air-conditioning load calculation method that described in this paper is also accurate and feasible. This study will make up for the insufficiency of traditional method which is unable to calculate the stratified air-conditioning load with low-sidewall air supply for large space buildings. In addition, the factors that influencing the indoor thermal environment and stratified air-conditioning load were analyzed, which it will contribute to the design and optimization of stratified air-conditioning system for large space buildings.

Experimental study on the comparison of thermal environment between nozzle air supply and column air supply in summer

In this paper, the air flow at the nozzle side and the column side were set up in a large space. The thermal environment of the two air supply modes were compared and analyzed by using the air diffusion performance index (ADPI), the draft sensation blowing index and so on. The results show that the uniformity of indoor air temperature and velocity of the column air supply is better than the nozzle; the percentage of dissatisfaction of the indoor average air blowing is less than that of the nozzle; The ADPI value of two airflow pattern changes with the air flow. The nozzle air supply shows a decreasing trend with the increase of air flow. The ADPI of the column air supply is higher than that of the nozzle, and both of them are less than 80%. Results of this paper provide a reference for airspace organization selection and the design of large space buildings.

Model for Indoor Air Vertical Temperature Distribution under Nozzle Air Supply System in Large Space Building

A model for indoor air vertical temperature and inner wall temperature is presented under nozzle air supply system in a large space building. Through discussion of the key parameters such as floor temperature and regional heat transfer coefficient, the floor heat transfer correction equation and modifier formula of zone heat transfer coefficient is founded. Through the summer experiment under nozzle air supply system in a large space building, the indoor air vertical temperature, inner wall temperature are tested and the modifier solving model is verified and promoted. The results show that the experiment data and the calculation results agreed well.

The appropriate airflow rate for a nozzle in commercial aircraft cabins based on thermal comfort experiments

Personal air supply is important for both thermal comfort and air quality for individuals. However, no appropriate airflow rate for a nozzle in aircraft cabins is included in the existing standards. To study the effect of the nozzle air supply on thermal comfort and optimize the airflow rate for a nozzle, both measurements of the air flow field and a human thermal comfort survey were carried out in an experimental three-row aircraft cabin. The experiments used four airflow rates (0 L/s, 0.67 L/s, 0.96 L/s and 1.45 L/s) for a nozzle and three different cabin temperatures (24 °C, 26 °C, 28 °C). The air velocity distribution was obtained to calculate the air velocity for the nozzle jets at any point. This study provides an understanding of the effect of the nozzle air supply on passengers' thermal comfort and the optimal designs for a nozzle air supply system. The nozzle airflow rate for thermal comfort was calculated for a personal air supply at different cabin temperatures. The thermal comfort map for a nozzle can be referenced for the design of a personal air supply system in aircraft cabins.

Effect of nozzle air supply temperature and volume flowrate on the jet flow from a typical ventilation nozzle in aircraft cabins

A ventilation nozzle’s airflow characteristics could have an influence on a passenger’s thermal comfort and dispersion of pollutants in an aircraft cabin, but there is little published research in this area. In this article, the temperature and air velocity from a nozzle jet were measured in a simulated three-row aircraft cabin at more than 220 points for both isothermal and non-isothermal jets. The non-isothermal jets were tested for air supply temperature differences of ± 5 and 10℃, and the isothermal jets for volume flowrates of 1.86 × 10−7, 2.67 × 10−7, and 4.03 × 10−7 m3/h. The results show that both the nozzle jet’s temperature and air velocity distributions are axially symmetrical and that the decay of the jet is rapid. The equation for the air velocity distribution was used to calculate the air velocity at any point in the main jet region for different volume flowrates. The temperature difference was shown to have little effect on the air velocity distribution for the main region of a nozzle jet, whereas the air flowrate was shown to significantly affect the air velocity distribution. This suggests that the effect of nozzle jet on passenger’s thermal comfort is mostly due to its air velocity distribution rather than temperature distribution.

Performance analysis of the air-conditioning system in Xi’an Xianyang International Airport

Reducing the energy consumption of air-conditioning systems is becoming increasingly important. This paper focuses on the air-conditioning system in Terminal 3 in Xi’an Xianyang International Airport, the first airport terminal to adopt radiant cooling in China. In the large spaces of this airport terminal, a temperature and humidity independent control (THIC) system has been adopted instead of a conventional nozzle air supply method, which significantly reduces the energy consumption of the air supply. The radiant floor is the main mechanism for indoor temperature control, while a liquid desiccant outdoor air processor combined with displacement ventilation is responsible for humidity control. Ice storage is adopted to reduce operating costs, and the supplied chilled water temperature can be as low as 3°C. This paper examines the performance of the THIC system in detail. The indoor environment is determined through measurements to be comfortable, and the on-site performances of key components in both the airport terminal and the cooling plant are investigated. The outdoor air processor supplies air of appropriate temperature and humidity ratio; two kinds of radiant floors are used for temperature control, both with measured cooling capacities of about 30–40W/m2; and the energy efficiency ratio (EER) of the cooling plant is 2.62.

Velocity statistics along the stagnation line of an axi- symmetric stagnating turbulent flow

Velocity statistics along the stagnation line of an axi-symmetric wall stagnating turbulent flow are studied experimentally. A low turbulence, uniform air flow from a nozzle type air supply with an exit diameter of 50 mm stagnates at a wall located 50 mm downstream. A flow velocity is set to 3 m/s, 10 mm downstream from the exit of the air supply. Instantaneous values of streamwise and radial velocities are measured by laser-Doppler velocimetry. The turbulence level in the air flow is changed by use of turbulence generator. When the turbulence generator is not installed in the air supply, the mean velocity profile in the streamwise direction fits well with that of a laminar viscous flow with the rms value of velocity fluctuations low near the wall. With the turbulence generator installed, a significant turbulence structure appears near the wall. When the wall is approached, the rms value of velocity fluctuations in the streamwise direction decreases monotonically while the profile of the rms value in the radial direction reaches a maximum near the wall. The increase in the rms value of velocity fluctuations in the radial direction near the wall is attributed to the bi-modal histogram of the fluctuating velocity in the radial direction. Near the wall, the instantaneous stagnation streamline fluctuates and the probability of the mean location of the stagnation point reaches a maximum not at the stagnation line but on a circle around the stagnation line, resulting in the bi-modal histogram. Turbulence statistics, the rms value of velocity fluctuation and the turbulent kinetic energy, can be normalized successfully by similarity parameters based on the strain rate and the reference turbulent kinetic energy introduced by Champion and Libby.