A parametric experimental study on the development of a round jet spray impacting a smooth, heate... more A parametric experimental study on the development of a round jet spray impacting a smooth, heated, flat plate has been accomplished. The main objective of this effort was to provide information characterizing the flow structure of a developing mist jet, issuing vertically towards an upward facing, horizontal heated plate, by means of simultaneous droplet size and velocity measurements. Phase Doppler Anemometry was used, providing also information on liquid volume flux. The fine spray of small atomized droplets (0.5-5.0 μm), was generated using a medical nebulizer. Two low Reynolds number jets (Re=2952, 3773) issuing from a cylindrical pipe have been tested. The distance between the jets ’ exit and the plate was 50 cm. A stainless steel non-magnetic flat plate of dimensions 1000x500x12mm 3 was used as target wall. Constant heat flux boundary conditions were established during measurements. Results indicate that the heat flux from the plate is influencing the evolution of the spray j...
In these days of heightened environmental consciousness, many countries are shifting their focus ... more In these days of heightened environmental consciousness, many countries are shifting their focus towards renewable energy sources for both large-scale uses (such as power plants that generate electricity) and smaller-scale applications (e.g., building heating and cooling). In this light, it is not surprising that there is a growing interest in technologies that are reliant on non-conventional sources of power, such as geothermal energy. This study is making an effort to provide a comprehensive understanding of the possible advantages and multiple uses of geothermal energy systems, in the context of their technical and environmental evaluation through Life Cycle Assessment. A brief description of the analyzing methods and the tools used to study a particular system or application is presented. The geothermal technologies and the applications of specific systems are discussed in detail, providing their environmental advantages and their technical barriers as well. District and domesti...
The interaction of a water mist jet with the thermally stratified turbulent field developing over... more The interaction of a water mist jet with the thermally stratified turbulent field developing over a horizontal heated flat plate, in an open top cavity, is investigated experimentally. The physical phenomena dominating this interaction, besides their importance for theoretical thermo-fluids, influence a wide spectrum of applications including fuel injection in internal combustion engines and burners, electronics cooling, meteorology, fire extinguishing, deposition and coating processes etc.Water mist, generated in a nebulizer, is sprayed through a cylindrical orifice of internal diameter 4mm, vertically, towards the horizontal surface and at considerable distance from it (50cm). In order to establish a reference case data base, a significant part of the work refers to data collection and study on the thermal convection field characteristics, in the absence of the spray mist, as well as on the isothermal mist jet development. The interaction field has been investigated for mist jets ...
With growing urban populations, methods of reducing the urban heat island effect have become incr... more With growing urban populations, methods of reducing the urban heat island effect have become increasingly important. Cool pavements altering the heat storage of materials used in pavements can lead to lower surface temperatures and reduce the thermal radiation emitted to the atmosphere. Cool pavement technologies utilize various strategies to reduce the temperature of new and existing pavements, including increased albedo, evaporative cooling, and reduced heat conduction. This process of negative radiation forces helps offset the impacts of increasing atmospheric temperatures. This paper presents an extensive analysis of the state of the art of cool pavements. The properties and principles of cool pavements are reviewed, including reflectivity, thermal emittance, heat transfer, thermal capacity, and permeability. The different types, research directions, and applications of reflective pavements are outlined and discussed. Maintenance and restoration technologies of cool pavements ar...
The paper presents a design and operation analysis of an Integrated Collector Storage (ICS) solar... more The paper presents a design and operation analysis of an Integrated Collector Storage (ICS) solar water heater, which consists of an asymmetric Compound Parabolic Concentrating (CPC) reflector trough, while the water tank comprises two concentric cylinders. The annulus between these vessels is partially depressurized and contains a small amount of water in the bottom of the outer vessel which dominantly contributes to the heat transfer from the outer to the inner cylinder. A multi-criteria optimization algorithm is applied to re-evaluate the design specifications of the parabolic surface, thus modifying the design of the entire ICS system and predict the necessary number of units for achieving the highest possible effectiveness with minimized fabrication costs and environmental impacts. The environmental footprint of the device is assessed through Life Cycle Assessment (LCA). The produced thermal energy in conjunction with the environmental and economic results are evaluated as a fu...
An experimental study of the thermal field developing over a horizontal heated plate in condition... more An experimental study of the thermal field developing over a horizontal heated plate in conditions of free convection, corresponding to Rayleigh numbers of 5.45 x 10 9 and 4.47 x 10 9 is presented. The modification of the thermal field due to the interaction with a fine spray discharging vertically towards the plate from significant distance, has also been investigated. The study of the thermal field was conducted using a fine chromel - constantan (type-E) fine thermocouple with a sensor diameter of 12 µm. Mean and turbulent characteristics of the thermal field such as t urbulent intensity, and probability density distributions (PDF) are presented and discussed. The study of the thermal statistical moments indicates that for the cases of free convection close to the wall, the thermal field is characterized by well organized motion of thermals or line plumes. Moreover the characteristic bulge in the fluctuating temperature distribution at the edge of the conduction layer, signify the presence of a boundary layer flow.
The interaction of a droplet cloud with a stratified turbulent environment, associated with a fre... more The interaction of a droplet cloud with a stratified turbulent environment, associated with a free convective flow field created above an isothermally heated horizontal surface is investigated experimentally. The droplet cloud created with a nebulizer, is injected normal to the plate and at significant distance from it, initially forming a two-phase jet. Droplet characteristics’ measurements are based on Phase Doppler Anemometry (PDA), providing information on droplet size, as well as mean velocity, rms values, skewness and flatness factors of the droplet turbulence velocity field under isothermal and stratified conditions, for two nebulizer flow rates. The single and two phase stratified thermal fields are also investigated. Temperature measurements are obtained with a fine thermocouple. Mean temperature along with rms values, skewness and flatness factors distributions, monitoring the stratified thermal field properties free of or, under the influence of the spray cloud, are presented and discussed.
The interaction of a water mist jet with the thermally stratified turbulent field developing over... more The interaction of a water mist jet with the thermally stratified turbulent field developing over a horizontal heated flat plate, in an open top cavity, is investigated experimentally. The physical phenomena dominating this interaction, besides their importance for theoretical thermo-fluids, influence a wide spectrum of applications including fuel injection in internal combustion engines and burners, electronics cooling, meteorology, fire extinguishing, deposition and coating processes etc. Water mist, generated in a nebulizer, is sprayed through a cylindrical orifice of internal diameter 4mm, vertically, towards the horizontal surface and at considerable distance from it (50cm). In order to establish a reference case data base, a significant part of the work refers to data collection and study on the thermal convection field characteristics, in the absence of the spray mist, as well as on the isothermal mist jet development. The interaction field has been investigated for mist jets...
ABSTRACT An experimental study of the thermal field established, over a horizontal heated plate (... more ABSTRACT An experimental study of the thermal field established, over a horizontal heated plate (1000x500x12 mm3) in an open top cavity, of aspect ratio Γ = 2 is presented. The working fluid was air at atmospheric pressure and the imposed temperature conditions correspond to a Rayleigh number Ra = 4.1x108, based on the cavity height and the temperature difference across it. Schlieren visualization was used to identify characteristic structures developing over the heated plate. Local temperature measurements along the vertical axis over the plate centre were accomplished using a fine thermocouple (d = 0.025 mm). Distributions of mean and rms temperatures are presented along with the corresponding skewness and flatness distributions. The exponential form of the PDF temperature distributions observed in the present experiments, as in several experiments in hard turbulence, is compatible with the intermittent presence of fluid structures with different origin and past history. Temperature PDFs have been approximated by mixtures of weighed Gaussian distributions to illustrate this concept
A parametric experimental study on the development of a round jet spray impacting a smooth, heate... more A parametric experimental study on the development of a round jet spray impacting a smooth, heated, flat plate has been accomplished. The main objective of this effort was to provide information characterizing the flow structure of a developing mist jet, issuing vertically towards an upward facing, horizontal heated plate, by means of simultaneous droplet size and velocity measurements. Phase Doppler Anemometry was used, providing also information on liquid volume flux. The fine spray of small atomized droplets (0.5-5.0 μm), was generated using a medical nebulizer. Two low Reynolds number jets (Re=2952, 3773) issuing from a cylindrical pipe have been tested. The distance between the jets ’ exit and the plate was 50 cm. A stainless steel non-magnetic flat plate of dimensions 1000x500x12mm 3 was used as target wall. Constant heat flux boundary conditions were established during measurements. Results indicate that the heat flux from the plate is influencing the evolution of the spray j...
In these days of heightened environmental consciousness, many countries are shifting their focus ... more In these days of heightened environmental consciousness, many countries are shifting their focus towards renewable energy sources for both large-scale uses (such as power plants that generate electricity) and smaller-scale applications (e.g., building heating and cooling). In this light, it is not surprising that there is a growing interest in technologies that are reliant on non-conventional sources of power, such as geothermal energy. This study is making an effort to provide a comprehensive understanding of the possible advantages and multiple uses of geothermal energy systems, in the context of their technical and environmental evaluation through Life Cycle Assessment. A brief description of the analyzing methods and the tools used to study a particular system or application is presented. The geothermal technologies and the applications of specific systems are discussed in detail, providing their environmental advantages and their technical barriers as well. District and domesti...
The interaction of a water mist jet with the thermally stratified turbulent field developing over... more The interaction of a water mist jet with the thermally stratified turbulent field developing over a horizontal heated flat plate, in an open top cavity, is investigated experimentally. The physical phenomena dominating this interaction, besides their importance for theoretical thermo-fluids, influence a wide spectrum of applications including fuel injection in internal combustion engines and burners, electronics cooling, meteorology, fire extinguishing, deposition and coating processes etc.Water mist, generated in a nebulizer, is sprayed through a cylindrical orifice of internal diameter 4mm, vertically, towards the horizontal surface and at considerable distance from it (50cm). In order to establish a reference case data base, a significant part of the work refers to data collection and study on the thermal convection field characteristics, in the absence of the spray mist, as well as on the isothermal mist jet development. The interaction field has been investigated for mist jets ...
With growing urban populations, methods of reducing the urban heat island effect have become incr... more With growing urban populations, methods of reducing the urban heat island effect have become increasingly important. Cool pavements altering the heat storage of materials used in pavements can lead to lower surface temperatures and reduce the thermal radiation emitted to the atmosphere. Cool pavement technologies utilize various strategies to reduce the temperature of new and existing pavements, including increased albedo, evaporative cooling, and reduced heat conduction. This process of negative radiation forces helps offset the impacts of increasing atmospheric temperatures. This paper presents an extensive analysis of the state of the art of cool pavements. The properties and principles of cool pavements are reviewed, including reflectivity, thermal emittance, heat transfer, thermal capacity, and permeability. The different types, research directions, and applications of reflective pavements are outlined and discussed. Maintenance and restoration technologies of cool pavements ar...
The paper presents a design and operation analysis of an Integrated Collector Storage (ICS) solar... more The paper presents a design and operation analysis of an Integrated Collector Storage (ICS) solar water heater, which consists of an asymmetric Compound Parabolic Concentrating (CPC) reflector trough, while the water tank comprises two concentric cylinders. The annulus between these vessels is partially depressurized and contains a small amount of water in the bottom of the outer vessel which dominantly contributes to the heat transfer from the outer to the inner cylinder. A multi-criteria optimization algorithm is applied to re-evaluate the design specifications of the parabolic surface, thus modifying the design of the entire ICS system and predict the necessary number of units for achieving the highest possible effectiveness with minimized fabrication costs and environmental impacts. The environmental footprint of the device is assessed through Life Cycle Assessment (LCA). The produced thermal energy in conjunction with the environmental and economic results are evaluated as a fu...
An experimental study of the thermal field developing over a horizontal heated plate in condition... more An experimental study of the thermal field developing over a horizontal heated plate in conditions of free convection, corresponding to Rayleigh numbers of 5.45 x 10 9 and 4.47 x 10 9 is presented. The modification of the thermal field due to the interaction with a fine spray discharging vertically towards the plate from significant distance, has also been investigated. The study of the thermal field was conducted using a fine chromel - constantan (type-E) fine thermocouple with a sensor diameter of 12 µm. Mean and turbulent characteristics of the thermal field such as t urbulent intensity, and probability density distributions (PDF) are presented and discussed. The study of the thermal statistical moments indicates that for the cases of free convection close to the wall, the thermal field is characterized by well organized motion of thermals or line plumes. Moreover the characteristic bulge in the fluctuating temperature distribution at the edge of the conduction layer, signify the presence of a boundary layer flow.
The interaction of a droplet cloud with a stratified turbulent environment, associated with a fre... more The interaction of a droplet cloud with a stratified turbulent environment, associated with a free convective flow field created above an isothermally heated horizontal surface is investigated experimentally. The droplet cloud created with a nebulizer, is injected normal to the plate and at significant distance from it, initially forming a two-phase jet. Droplet characteristics’ measurements are based on Phase Doppler Anemometry (PDA), providing information on droplet size, as well as mean velocity, rms values, skewness and flatness factors of the droplet turbulence velocity field under isothermal and stratified conditions, for two nebulizer flow rates. The single and two phase stratified thermal fields are also investigated. Temperature measurements are obtained with a fine thermocouple. Mean temperature along with rms values, skewness and flatness factors distributions, monitoring the stratified thermal field properties free of or, under the influence of the spray cloud, are presented and discussed.
The interaction of a water mist jet with the thermally stratified turbulent field developing over... more The interaction of a water mist jet with the thermally stratified turbulent field developing over a horizontal heated flat plate, in an open top cavity, is investigated experimentally. The physical phenomena dominating this interaction, besides their importance for theoretical thermo-fluids, influence a wide spectrum of applications including fuel injection in internal combustion engines and burners, electronics cooling, meteorology, fire extinguishing, deposition and coating processes etc. Water mist, generated in a nebulizer, is sprayed through a cylindrical orifice of internal diameter 4mm, vertically, towards the horizontal surface and at considerable distance from it (50cm). In order to establish a reference case data base, a significant part of the work refers to data collection and study on the thermal convection field characteristics, in the absence of the spray mist, as well as on the isothermal mist jet development. The interaction field has been investigated for mist jets...
ABSTRACT An experimental study of the thermal field established, over a horizontal heated plate (... more ABSTRACT An experimental study of the thermal field established, over a horizontal heated plate (1000x500x12 mm3) in an open top cavity, of aspect ratio Γ = 2 is presented. The working fluid was air at atmospheric pressure and the imposed temperature conditions correspond to a Rayleigh number Ra = 4.1x108, based on the cavity height and the temperature difference across it. Schlieren visualization was used to identify characteristic structures developing over the heated plate. Local temperature measurements along the vertical axis over the plate centre were accomplished using a fine thermocouple (d = 0.025 mm). Distributions of mean and rms temperatures are presented along with the corresponding skewness and flatness distributions. The exponential form of the PDF temperature distributions observed in the present experiments, as in several experiments in hard turbulence, is compatible with the intermittent presence of fluid structures with different origin and past history. Temperature PDFs have been approximated by mixtures of weighed Gaussian distributions to illustrate this concept
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