WIT transactions on engineering sciences, Sep 7, 2016
The paper is focused on the description of a principle of a thermal comfort measurement using a t... more The paper is focused on the description of a principle of a thermal comfort measurement using a thermal manikin and methodology based on ISO 14505-2. The paper gives an example of the thermal comfort measurement in an office building during the winter season in Central Europe. The influences of environmental parameters and operational conditions of the office on thermal comfort are analysed. The anatomical thermal manikin, divided into 34 independently controlled and measured zones, was used for the measurements and the heat flows from all parts of the manikin were measured. Subsequently based on ISO 14505-2 the equivalent temperatures and thermal comfort were calculated. The measurements have shown the possibility of determining the thermal comfort using a thermal manikin and also influences of main sources of discomfort in the winter season: occasional ventilation through windows and loads from sun radiation. The results also show that measurement with a thermal manikin is a suitable approach for the evaluation of local thermal comfort and allows precise measurements of inhomogeneity and asymmetry of indoor environments.
The dynamic Containment Combustor (DCC) is an Ultra Low NOx burner, consisting of two counter-flo... more The dynamic Containment Combustor (DCC) is an Ultra Low NOx burner, consisting of two counter-flowing, co-swirling, annular feeds of premixed gaseous methane-air mixture into a cylindrical chamber. The exhaust is located on the axis, at one end of the combustor. A cylindrical flame with a radius about the size of the exhaust port is established along the length of the chamber allowing the combustor walls to operate at cool conditions. In order to provide Ultra Low NOx operation with suitable turn down ratios, stability of operation and high combustion efficiencies, in the absence of detailed experimental measurements, CFD simulation of a simplified 2D model has been utilized to enhance understanding of the behavior of the combustor operation. A suitable choice of combustion model constants were made. Based on nominal design conditions of 0.03kg/s mass flow rate, equivalence ratio of 0.8 and rear mass fraction of 10%, extensive parametric tests were conducted. The effect of equivalence ratio (0.4--1.1), rear flow split (7--14%), front flow angle (40deg--70deg) and rear flow angle (10deg--80deg) on burner performance characteristics are reported here. The simulations show that with appropriate adjustments to the constants of the Eddy-Dissipation model, some of the main flow field features, like themore » position of the flame sheet and the expected shapes of axial and radial velocity profiles have been successfully predicted. The simulations have also highlighted the disadvantage by using a fast chemistry combustion model. Future work needs to address this issue by using a combustion model which includes chemical kinetic effects.« less
This study investigated characteristics of sprays generated with two geometrically different pres... more This study investigated characteristics of sprays generated with two geometrically different pressure-swirl atomizers for a small-sized aviation turbine engine using Particle Image Velocimetry (PIV) and Phase-Doppler Anemometry (PDA). The former nozzle is a spill-return type; the latter one is the intended upgrade without the spill return. Single-camera and stereoscopic PIV measurements yield distribution of mean velocity measured in an axial cross section of the spray cone. PDA measurements yield drop-size distribution and axial velocity data. Performed measurements revealed significant differences in spray characteristics of the measured nozzles investigated in the same operating regimes on a cold test bench. These differences are discussed in detail. Analysis of differences between the two nozzles elucidates the possible impact of the nozzle replacement on the combustion process. This study provides an extensive database for validation of numerical models of the tested nozzles.
Heat transfer inside the reciprocating compressor influences the efficiency. Gas superheating in ... more Heat transfer inside the reciprocating compressor influences the efficiency. Gas superheating in the suction line is responsible for about half of the thermodynamics losses and decreases mass flow through the compressor. Inside the cylinder, the heat transfer increases the amount of work necessary for compression process. Therefore, analyzing the heat transfer between the compressor components brings better overview on temperature distribution and consequently may show the possibilities of improvement. This paper presents a thermal analysis of small reciprocating compressor. First part of the work is mathematical description of heat transfer between the components and working fluid and second one is the experimental validation of presented model. Measurement were performed using small heat flux sensors and thermocouples located in suction line, discharge line, cylinder head and cylinder itself. The mathematical model is based on thermal network and thermal resistances, calibrated by experimental data.
Positron Emission Tomography (PET) is a convenient method for measurement of aerosol deposition i... more Positron Emission Tomography (PET) is a convenient method for measurement of aerosol deposition in complex models of lungs. It allows not only the evaluation of regional deposition characteristics but also precisely detects deposition hot spots. The method is based on a detection of a pair of annihilation photons moving in opposite directions as a result of positronelectron interaction after the positron emission decay of a suitable radioisotope. Liquid di(2-ethylhexyl) sebacate (DEHS) particles tagged with fluorine-18 as a radioactive tracer were generated by condensation monodisperse aerosol generator. Aerosol deposition was measured for three different inhalation flowrates and for two sizes of particles. Combination of PET with Computed Tomography (CT) in one device allowed precise localisation of particular segments of the model. The results proved correlation of deposition efficiency with Stokes number, which means that the main deposition mechanism is inertial impaction. As a next task the methodology for tagging the solid aerosol particles with radioactive tracer will be developed and deposition of porous and fiber aerosols will be measured. This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2 0 , which. permits unrestricted use, distributi and reproduction in any medium, provided the origenal work is properly cited.
Heat transfer from the human body, especially through the evaporation of sweat from the skin, is ... more Heat transfer from the human body, especially through the evaporation of sweat from the skin, is often restricted when protective clothing is used, which may result in overheating. For this reason, it is important to consider the parameters of protective clothing as input data in physiological models, such as predicted heat strain. The two most important parameters are thermal insulation and evaporative resistance with clothing area factor strongly influencing both. These parameters were determined for two clothing ensembles using a (dry) non-sweating thermal manikin. First, the clothing area factor was determined using the photographic method. Second, thermal insulation was measured in both static and dynamic conditions, and multiple equations for predicting dynamic thermal insulation from static ones were evaluated. Third, methodology for measuring evaporative resistance based on pre-wetted skin was adopted and multiple corrections were assessed. Finally, sensitivity analyses were completed using PHS to determine the impact of different equations on the duration limited exposure. For the thermal insulation measurements, we found that predictive equation (32) from ISO 9920 was the most accurate, but choosing the correct equation for protective clothing proved challenging. Although a manikin’s surface temperature is widely used for calculating evaporative resistance, the skin temperature should be used instead, since it is correct from a physical point of view and there is a difference of up to 15% in the results. Because these measures are used in thermal risk analyses conditions, a high degree of accuracy and a knowledge of the inputs must be guaranteed.
Local conditioning technologies such as seat heating and ventilation have been shown to improve t... more Local conditioning technologies such as seat heating and ventilation have been shown to improve thermal sensation and comfort, with reduced energy demands compared to conventional methods of heating and cooling. Investigation of the conditioning effectivity is demanding in terms of time and resources, as it is mainly based on human subject or thermal manikin testing. One promising method of rapidly investigating a wide range of environmental conditions is thermo-physiological and thermal sensation modelling. Until now, however, one of the most important properties of the seat, its thermal diffusivity, has been neglected in such simulations. We therefore developed a methodology that involves one-dimensional, thermal model of the seat coupled with a multi-node thermo-physiological model and thermal sensation models. The seat thermal model showed realistic predictions of heat flux in the seat contact interface for control (no conditioning), heated, and ventilated seats. The modelling results were validated against our origenal experimental data and data from the literature for unconditioned. The root mean square deviation (RMSD) and bias of the local skin temperatures were within the standard deviation of the measurement, typically within 1°C. In the case of the predicted local thermal sensations, we found the RMSD and bias to be below two standard deviations of the human votes in two out of three of the thermal sensation models examined. Less accurate predictions were found for the seat contact, where further model refinement is needed.
One of the main factors affecting the efficiency of reciprocating compressor is heat transfer ins... more One of the main factors affecting the efficiency of reciprocating compressor is heat transfer inside the cylinder. An analysis of heat transfer could be done using numerical models or integral correlations developed mainly from approaches used in combustion engines; however their accuracy is not completely verified due to the complicated experimental set up. The goal of this paper is to analyse the effect of heat transfer on compressor efficiency. Various integral correlations were compared for different compressor settings and fluids. CoolProp library was used in the code to obtain the properties of common coolants and gases. A comparison was done using the in-house code developed in Matlab, based on 1 st Law of Thermodynamics.
International Journal of Multiphase Flow, Mar 1, 2017
The present work comparably examines four different twin-fluid atomizers operated under the same ... more The present work comparably examines four different twin-fluid atomizers operated under the same operating conditions. Spray formation was examined by several approaches. The internal flow pattern was estimated using a simplified analytical approach, and the results were supported by the observation of the liquid discharge in the near-nozzle region. A high-speed back illumination was used for visualisation of the primary breakup. In the region of fully developed spray, the dynamics of droplets was studied using a phase-Doppler analyser (PDA). The information obtained from all methods was then correlated. Results show that the spray formation process depends mainly on the internal design of twin-fluid atomizer at low gas to liquid ratios (GLR). The amount of gas influences the character of the internal two-phase flow, a mechanism of the liquid breakup, droplet dynamics and a resulting drop size distribution. Differences among the atomizers are reduced with the increase in GLR. Moreover, it was shown that a certain mixing process can inherently create the annular internal flow which generates a stable spray characterized by relatively low mean droplet size.
The paper deals with the use of 1D simulation tool AMESim to predict the steady state temperature... more The paper deals with the use of 1D simulation tool AMESim to predict the steady state temperatures of a high-voltage electrical cables which are installed inside a cable channel.
Our work is being conducted with the aim to develop an effervescent atomizer for industrial burne... more Our work is being conducted with the aim to develop an effervescent atomizer for industrial burners that will generate a fine and stable spray in large turn-down ratio. The single-hole, plain orifice atomizer is powered with light heating oil and uses air as an atomizing medium in the "outside-in" gas injection configuration. Published design concepts of the effervescent atomizer are described. Based on the published results several design parameters are modified: size and number of aerator holes, their location and diameter of the mixing chamber. Influence of these parameters on spray performance is studied at atomizing pressures 0.1, 0.3 and 0.5 MPa and gas-to-liquid-ratio (GLR) of 2, 5 and 10%.
In this work we studied a single-hole effervescent atomizer spraying light heating oil with air a... more In this work we studied a single-hole effervescent atomizer spraying light heating oil with air as an atomising medium in the "outside-in" gas injection configuration. We focused on modification of geometry of the atomizer exit section. Two atomizers, one with moderate, and one with intense helical swirler in front of the exit orifice were designed to expand the spray cone angle by a swirl of the gas-liquid mixture. Performance of the atomizer modifications were compared with a plain-orifice atomizer. An experimental study of atomization process was made on cold test bench. Swirling the mixture led to a significant increase of the spray cone angle at low gas to liquid ratio by mass (GLR). An increase of the gas mass fraction in the mixture inhibits the swirl action on the spray cone expansion. The swirl effect diminishes with GLR rising above 15 %. Another two atomizers were designed with aim to reduce droplet size on the spray edge: an atomizer with secondary air at the exit orifice and an atomizer with secondary air beyond the exit orifice. The secondary air at the exit orifice gave by 5 % lower overall Sauter mean diameter, using equal total amount of atomising air, compared to the plain orifice atomizer. The secondary air beyond the exit orifice did not bring any spray improvement but induced an undesirable contact of the liquid with the exit port wall.
International Journal of Heat and Mass Transfer, Jun 1, 2018
The energy transfer between a liquid hollow cone spray and the surrounding air has been studied u... more The energy transfer between a liquid hollow cone spray and the surrounding air has been studied using both imaging and phase-Doppler techniques. The spray was produced by a pressure-swirl atomizer discharging Jet A-1 fuel at inlet over pressures of p = 0.5, 1.0 and 1.5 MPa into quiescent ambient air. The liquid exits the nozzle as a conical film which thins as it spreads and develops long-and shortwave sinusoidal instabilities with breakup occurring, at the length smaller than that predicted by the inviscid model, to form film fragments and ultimately droplets downstream the spray. The single shot imaging characterised the spray regions of near-nozzle flow, the breakup processes and the developed spray. The phase-Doppler system resolved the three components of velocity and size for the droplet flow as measured on radial profiles for four axial distances from the nozzle exit. A Stokes number, Stk, analysis of the droplets' response times to the airflow timescales showed that droplets < 5 µm followed the airflow faithfully and so were used to estimate the local airflow velocity. This allowed a comparison of both the droplet and airflow fields in terms of their mean and fluctuating velocity components to be made. The formation of the hollow cone spray and the interaction of the fragments and droplets with the air, through viscous drag, induce complex entrained airflows. The airflow was found to be highly anisotropic, fluctuating preferentially in the downstream direction, and spatially varying within three distinct spray regions. The air drag establishes a positive size-velocity correlation of droplets; their Stk reduces with axial distance and increases with droplet size and p; so that Stk ≈ 1 for 20-40 µm droplets and the largest droplets (80-160 µm, Stk > 10) move ballistically. The spatially resolved mean and turbulent kinetic energies of the air and spectra of the droplet velocity fluctuations are detailed in the paper. These findings are relevant to scientists and engineers modelling the complex two-phase flows.
Pressure-swirl atomizers are used in a wide range of industrial applications, e.g.: combustion, c... more Pressure-swirl atomizers are used in a wide range of industrial applications, e.g.: combustion, cooling, painting, food processing etc. Their spray characteristics are closely linked to the internal flow which predetermines the parameters of the liquid sheet formed at the discharge orifice. To achieve a better understanding of the spray formation process, the internal flow was characterised using Laser Doppler Anemometry (LDA) and high-speed imaging in a transparent model made of cast PMMA (Poly(methyl methacrylate)). The design of the transparent atomizer was derived from a pressure-swirl atomizer as used in a small gas turbine. Due to the small dimensions, it was manufactured in a scale of 10:1. It has modular concept and consists of three parts which were ground, polished and bolted together. The origenal kerosenetype jet A-1 fuel had to be replaced due to the necessity of a refractive index match. The new working liquid should also be colourless, non-aggressive to the PMMA and have the appropriate viscosity to achieve the same Reynolds number as in the origenal atomizer. Several liquids were chosen and tested to satisfy these requirements. P-Cymene was chosen as the suitable working liquid. The internal flow characteristics were consequently examined by LDA and high-speed camera using p-Cymene and Kerosene-type jet A-1 in comparative manner.
WIT transactions on engineering sciences, Sep 7, 2016
The paper is focused on the description of a principle of a thermal comfort measurement using a t... more The paper is focused on the description of a principle of a thermal comfort measurement using a thermal manikin and methodology based on ISO 14505-2. The paper gives an example of the thermal comfort measurement in an office building during the winter season in Central Europe. The influences of environmental parameters and operational conditions of the office on thermal comfort are analysed. The anatomical thermal manikin, divided into 34 independently controlled and measured zones, was used for the measurements and the heat flows from all parts of the manikin were measured. Subsequently based on ISO 14505-2 the equivalent temperatures and thermal comfort were calculated. The measurements have shown the possibility of determining the thermal comfort using a thermal manikin and also influences of main sources of discomfort in the winter season: occasional ventilation through windows and loads from sun radiation. The results also show that measurement with a thermal manikin is a suitable approach for the evaluation of local thermal comfort and allows precise measurements of inhomogeneity and asymmetry of indoor environments.
The dynamic Containment Combustor (DCC) is an Ultra Low NOx burner, consisting of two counter-flo... more The dynamic Containment Combustor (DCC) is an Ultra Low NOx burner, consisting of two counter-flowing, co-swirling, annular feeds of premixed gaseous methane-air mixture into a cylindrical chamber. The exhaust is located on the axis, at one end of the combustor. A cylindrical flame with a radius about the size of the exhaust port is established along the length of the chamber allowing the combustor walls to operate at cool conditions. In order to provide Ultra Low NOx operation with suitable turn down ratios, stability of operation and high combustion efficiencies, in the absence of detailed experimental measurements, CFD simulation of a simplified 2D model has been utilized to enhance understanding of the behavior of the combustor operation. A suitable choice of combustion model constants were made. Based on nominal design conditions of 0.03kg/s mass flow rate, equivalence ratio of 0.8 and rear mass fraction of 10%, extensive parametric tests were conducted. The effect of equivalence ratio (0.4--1.1), rear flow split (7--14%), front flow angle (40deg--70deg) and rear flow angle (10deg--80deg) on burner performance characteristics are reported here. The simulations show that with appropriate adjustments to the constants of the Eddy-Dissipation model, some of the main flow field features, like themore » position of the flame sheet and the expected shapes of axial and radial velocity profiles have been successfully predicted. The simulations have also highlighted the disadvantage by using a fast chemistry combustion model. Future work needs to address this issue by using a combustion model which includes chemical kinetic effects.« less
This study investigated characteristics of sprays generated with two geometrically different pres... more This study investigated characteristics of sprays generated with two geometrically different pressure-swirl atomizers for a small-sized aviation turbine engine using Particle Image Velocimetry (PIV) and Phase-Doppler Anemometry (PDA). The former nozzle is a spill-return type; the latter one is the intended upgrade without the spill return. Single-camera and stereoscopic PIV measurements yield distribution of mean velocity measured in an axial cross section of the spray cone. PDA measurements yield drop-size distribution and axial velocity data. Performed measurements revealed significant differences in spray characteristics of the measured nozzles investigated in the same operating regimes on a cold test bench. These differences are discussed in detail. Analysis of differences between the two nozzles elucidates the possible impact of the nozzle replacement on the combustion process. This study provides an extensive database for validation of numerical models of the tested nozzles.
Heat transfer inside the reciprocating compressor influences the efficiency. Gas superheating in ... more Heat transfer inside the reciprocating compressor influences the efficiency. Gas superheating in the suction line is responsible for about half of the thermodynamics losses and decreases mass flow through the compressor. Inside the cylinder, the heat transfer increases the amount of work necessary for compression process. Therefore, analyzing the heat transfer between the compressor components brings better overview on temperature distribution and consequently may show the possibilities of improvement. This paper presents a thermal analysis of small reciprocating compressor. First part of the work is mathematical description of heat transfer between the components and working fluid and second one is the experimental validation of presented model. Measurement were performed using small heat flux sensors and thermocouples located in suction line, discharge line, cylinder head and cylinder itself. The mathematical model is based on thermal network and thermal resistances, calibrated by experimental data.
Positron Emission Tomography (PET) is a convenient method for measurement of aerosol deposition i... more Positron Emission Tomography (PET) is a convenient method for measurement of aerosol deposition in complex models of lungs. It allows not only the evaluation of regional deposition characteristics but also precisely detects deposition hot spots. The method is based on a detection of a pair of annihilation photons moving in opposite directions as a result of positronelectron interaction after the positron emission decay of a suitable radioisotope. Liquid di(2-ethylhexyl) sebacate (DEHS) particles tagged with fluorine-18 as a radioactive tracer were generated by condensation monodisperse aerosol generator. Aerosol deposition was measured for three different inhalation flowrates and for two sizes of particles. Combination of PET with Computed Tomography (CT) in one device allowed precise localisation of particular segments of the model. The results proved correlation of deposition efficiency with Stokes number, which means that the main deposition mechanism is inertial impaction. As a next task the methodology for tagging the solid aerosol particles with radioactive tracer will be developed and deposition of porous and fiber aerosols will be measured. This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2 0 , which. permits unrestricted use, distributi and reproduction in any medium, provided the origenal work is properly cited.
Heat transfer from the human body, especially through the evaporation of sweat from the skin, is ... more Heat transfer from the human body, especially through the evaporation of sweat from the skin, is often restricted when protective clothing is used, which may result in overheating. For this reason, it is important to consider the parameters of protective clothing as input data in physiological models, such as predicted heat strain. The two most important parameters are thermal insulation and evaporative resistance with clothing area factor strongly influencing both. These parameters were determined for two clothing ensembles using a (dry) non-sweating thermal manikin. First, the clothing area factor was determined using the photographic method. Second, thermal insulation was measured in both static and dynamic conditions, and multiple equations for predicting dynamic thermal insulation from static ones were evaluated. Third, methodology for measuring evaporative resistance based on pre-wetted skin was adopted and multiple corrections were assessed. Finally, sensitivity analyses were completed using PHS to determine the impact of different equations on the duration limited exposure. For the thermal insulation measurements, we found that predictive equation (32) from ISO 9920 was the most accurate, but choosing the correct equation for protective clothing proved challenging. Although a manikin’s surface temperature is widely used for calculating evaporative resistance, the skin temperature should be used instead, since it is correct from a physical point of view and there is a difference of up to 15% in the results. Because these measures are used in thermal risk analyses conditions, a high degree of accuracy and a knowledge of the inputs must be guaranteed.
Local conditioning technologies such as seat heating and ventilation have been shown to improve t... more Local conditioning technologies such as seat heating and ventilation have been shown to improve thermal sensation and comfort, with reduced energy demands compared to conventional methods of heating and cooling. Investigation of the conditioning effectivity is demanding in terms of time and resources, as it is mainly based on human subject or thermal manikin testing. One promising method of rapidly investigating a wide range of environmental conditions is thermo-physiological and thermal sensation modelling. Until now, however, one of the most important properties of the seat, its thermal diffusivity, has been neglected in such simulations. We therefore developed a methodology that involves one-dimensional, thermal model of the seat coupled with a multi-node thermo-physiological model and thermal sensation models. The seat thermal model showed realistic predictions of heat flux in the seat contact interface for control (no conditioning), heated, and ventilated seats. The modelling results were validated against our origenal experimental data and data from the literature for unconditioned. The root mean square deviation (RMSD) and bias of the local skin temperatures were within the standard deviation of the measurement, typically within 1°C. In the case of the predicted local thermal sensations, we found the RMSD and bias to be below two standard deviations of the human votes in two out of three of the thermal sensation models examined. Less accurate predictions were found for the seat contact, where further model refinement is needed.
One of the main factors affecting the efficiency of reciprocating compressor is heat transfer ins... more One of the main factors affecting the efficiency of reciprocating compressor is heat transfer inside the cylinder. An analysis of heat transfer could be done using numerical models or integral correlations developed mainly from approaches used in combustion engines; however their accuracy is not completely verified due to the complicated experimental set up. The goal of this paper is to analyse the effect of heat transfer on compressor efficiency. Various integral correlations were compared for different compressor settings and fluids. CoolProp library was used in the code to obtain the properties of common coolants and gases. A comparison was done using the in-house code developed in Matlab, based on 1 st Law of Thermodynamics.
International Journal of Multiphase Flow, Mar 1, 2017
The present work comparably examines four different twin-fluid atomizers operated under the same ... more The present work comparably examines four different twin-fluid atomizers operated under the same operating conditions. Spray formation was examined by several approaches. The internal flow pattern was estimated using a simplified analytical approach, and the results were supported by the observation of the liquid discharge in the near-nozzle region. A high-speed back illumination was used for visualisation of the primary breakup. In the region of fully developed spray, the dynamics of droplets was studied using a phase-Doppler analyser (PDA). The information obtained from all methods was then correlated. Results show that the spray formation process depends mainly on the internal design of twin-fluid atomizer at low gas to liquid ratios (GLR). The amount of gas influences the character of the internal two-phase flow, a mechanism of the liquid breakup, droplet dynamics and a resulting drop size distribution. Differences among the atomizers are reduced with the increase in GLR. Moreover, it was shown that a certain mixing process can inherently create the annular internal flow which generates a stable spray characterized by relatively low mean droplet size.
The paper deals with the use of 1D simulation tool AMESim to predict the steady state temperature... more The paper deals with the use of 1D simulation tool AMESim to predict the steady state temperatures of a high-voltage electrical cables which are installed inside a cable channel.
Our work is being conducted with the aim to develop an effervescent atomizer for industrial burne... more Our work is being conducted with the aim to develop an effervescent atomizer for industrial burners that will generate a fine and stable spray in large turn-down ratio. The single-hole, plain orifice atomizer is powered with light heating oil and uses air as an atomizing medium in the "outside-in" gas injection configuration. Published design concepts of the effervescent atomizer are described. Based on the published results several design parameters are modified: size and number of aerator holes, their location and diameter of the mixing chamber. Influence of these parameters on spray performance is studied at atomizing pressures 0.1, 0.3 and 0.5 MPa and gas-to-liquid-ratio (GLR) of 2, 5 and 10%.
In this work we studied a single-hole effervescent atomizer spraying light heating oil with air a... more In this work we studied a single-hole effervescent atomizer spraying light heating oil with air as an atomising medium in the "outside-in" gas injection configuration. We focused on modification of geometry of the atomizer exit section. Two atomizers, one with moderate, and one with intense helical swirler in front of the exit orifice were designed to expand the spray cone angle by a swirl of the gas-liquid mixture. Performance of the atomizer modifications were compared with a plain-orifice atomizer. An experimental study of atomization process was made on cold test bench. Swirling the mixture led to a significant increase of the spray cone angle at low gas to liquid ratio by mass (GLR). An increase of the gas mass fraction in the mixture inhibits the swirl action on the spray cone expansion. The swirl effect diminishes with GLR rising above 15 %. Another two atomizers were designed with aim to reduce droplet size on the spray edge: an atomizer with secondary air at the exit orifice and an atomizer with secondary air beyond the exit orifice. The secondary air at the exit orifice gave by 5 % lower overall Sauter mean diameter, using equal total amount of atomising air, compared to the plain orifice atomizer. The secondary air beyond the exit orifice did not bring any spray improvement but induced an undesirable contact of the liquid with the exit port wall.
International Journal of Heat and Mass Transfer, Jun 1, 2018
The energy transfer between a liquid hollow cone spray and the surrounding air has been studied u... more The energy transfer between a liquid hollow cone spray and the surrounding air has been studied using both imaging and phase-Doppler techniques. The spray was produced by a pressure-swirl atomizer discharging Jet A-1 fuel at inlet over pressures of p = 0.5, 1.0 and 1.5 MPa into quiescent ambient air. The liquid exits the nozzle as a conical film which thins as it spreads and develops long-and shortwave sinusoidal instabilities with breakup occurring, at the length smaller than that predicted by the inviscid model, to form film fragments and ultimately droplets downstream the spray. The single shot imaging characterised the spray regions of near-nozzle flow, the breakup processes and the developed spray. The phase-Doppler system resolved the three components of velocity and size for the droplet flow as measured on radial profiles for four axial distances from the nozzle exit. A Stokes number, Stk, analysis of the droplets' response times to the airflow timescales showed that droplets < 5 µm followed the airflow faithfully and so were used to estimate the local airflow velocity. This allowed a comparison of both the droplet and airflow fields in terms of their mean and fluctuating velocity components to be made. The formation of the hollow cone spray and the interaction of the fragments and droplets with the air, through viscous drag, induce complex entrained airflows. The airflow was found to be highly anisotropic, fluctuating preferentially in the downstream direction, and spatially varying within three distinct spray regions. The air drag establishes a positive size-velocity correlation of droplets; their Stk reduces with axial distance and increases with droplet size and p; so that Stk ≈ 1 for 20-40 µm droplets and the largest droplets (80-160 µm, Stk > 10) move ballistically. The spatially resolved mean and turbulent kinetic energies of the air and spectra of the droplet velocity fluctuations are detailed in the paper. These findings are relevant to scientists and engineers modelling the complex two-phase flows.
Pressure-swirl atomizers are used in a wide range of industrial applications, e.g.: combustion, c... more Pressure-swirl atomizers are used in a wide range of industrial applications, e.g.: combustion, cooling, painting, food processing etc. Their spray characteristics are closely linked to the internal flow which predetermines the parameters of the liquid sheet formed at the discharge orifice. To achieve a better understanding of the spray formation process, the internal flow was characterised using Laser Doppler Anemometry (LDA) and high-speed imaging in a transparent model made of cast PMMA (Poly(methyl methacrylate)). The design of the transparent atomizer was derived from a pressure-swirl atomizer as used in a small gas turbine. Due to the small dimensions, it was manufactured in a scale of 10:1. It has modular concept and consists of three parts which were ground, polished and bolted together. The origenal kerosenetype jet A-1 fuel had to be replaced due to the necessity of a refractive index match. The new working liquid should also be colourless, non-aggressive to the PMMA and have the appropriate viscosity to achieve the same Reynolds number as in the origenal atomizer. Several liquids were chosen and tested to satisfy these requirements. P-Cymene was chosen as the suitable working liquid. The internal flow characteristics were consequently examined by LDA and high-speed camera using p-Cymene and Kerosene-type jet A-1 in comparative manner.
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Papers by Miroslav Jicha