Antonio Lecuona | Universidad Carlos III de Madrid (original) (raw)

Papers by Antonio Lecuona

In the state-of-the-art PIV, image sensors are growing in size and PIV algorithms are increasing ... more In the state-of-the-art PIV, image sensors are growing in size and PIV algorithms are increasing in spatial resolution capabilities. These technological advances allow for the simultaneous measurement of increasingly larger spatial scales ranges in a single PIV snapshot. To take fully advantage of the available spatial scales range, PIV setup constraints establish a coupling between the laser sheet thickness and the time between laser pulses. This condition did not apply with older technologies. The resulting value for the optimum laser sheet thickness is in a range where the superposed flow information in the direction of the imaging sensor introduces special characteristics errors at the small scale limit. This may compromise the measurement of flow quantities like dissipation and turbulent kinetic energy (tke), for which the contribution of the small and medium scales may be relevant. Within this scenario the assessment of the smallest scale resolved in the PIV measurement is nec...

Sources/sinks Alternative to the Outside Air for Heat Pump and Air-conditioning Techniques (Alternative Sources - AS), Padua, Italy, April 5-7, 2011. / International Sorption Heat Pump Conference (ISHPC11), Padua, Italy, April 6-8, 2011., Apr 6, 2011

This paper presents the experimental evaluation of a fusion plate heat exchanger (FPHE) during bo... more This paper presents the experimental evaluation of a fusion plate heat exchanger (FPHE) during boiling conditions of a solution of lithium nitrate in ammonia. The data are representative of the working conditions of generators in single-effe ct absorption chillers used for trigeneration applications, among others. The solution flow rate and outlet temperature were modified in the ranges of 0.041 - 0.083 kg/s and 78 oC - 95 oC, res pectively. Correlations for single-phase-flow heat transfer, obtained in previous experiments, ar e used to characterize the boiling heat transfer. The influences of the heat flux and mass flux are analyzed. The region of the FPHE where bubbles begin to arise is estimated using a c orrelation for the wall superheat required for the onset of subcooled boiling. Results show that s ubcooled boiling is present in the generator and it takes up a significant part of the boiling r egion. Subcooled boiling heat-transfer coefficients and correlations for the Nussel...

This paper studies the effects caused by the optical losses on the calculated cross section of th... more This paper studies the effects caused by the optical losses on the calculated cross section of the measurement volume of a phase Doppler anemometer and consequently, in particle concentration and volume flux. It will be shown that as the optical l osses increase, the ca lculated d iameter of the measurement volume for the smaller particles presents an anomalous behaviour. Moreover, these small particles tend to disappear. As a consequence the particle range that the PDA can handle is restricted. A criterion to determine the minimum effective particle size that can be correctly measured is proposed.

Energy Conversion and Management, 2018

Two-phase gravity-driven and gravity-stratified flow regime inside a pipe, which is present in ma... more Two-phase gravity-driven and gravity-stratified flow regime inside a pipe, which is present in many engineering applications, is an attractive option for solar cooling/heating/power production using Rankine cycles, absorption cycles or any other thermodynamic application by means of vapor as working fluid. This paper offers a numerical model of this flow configuration that copes with transient phenomena, like unsteadiness of solar radiation, among others. The mathematical model consists of 1-D balance equations for mass and momentum for both fluids and energy for both fluids and the wall of the pipe that absorbs the solar radiation. The model is characterized by the fact that the area (or height) of the liquid layer is treated as a dependent variable forming part of the solution. The numerical method consists in a finite volume staggered grid discretization of the governing equations. Mass flow and liquid area are calculated with a semi-implicit pressure based method and the transient terms are treated with the explicit first stage singly implicit Runge-Kutta (ESDIRK) method. The calculation of the mass transfer rate from liquid to vapor is calculated iteratively by a guess-and-correct mass transfer algorithm, specially developed for stratified flows. The results show the applicability and benefits of this model for the not so well known counter-current stratified two-phase with evaporation/boiling. Additionally, the performance of the mass transfer algorithm is discussed showing that it is monotonic decreasing and linearly convergent.

Applied Thermal Engineering, 2016

Abstract The two-stage configuration of a double-effect absorption cycle using ammonia/lithium ni... more Abstract The two-stage configuration of a double-effect absorption cycle using ammonia/lithium nitrate as working fluid is studied by means of a thermodynamic model. The maximum pressure of this cycle configuration is the same as the single-effect cycle, up to 15.8 bars, being an advantage over the double-effect conventional configuration with three pressure levels that exhibits much higher maximum pressure. The performance of the cycle and the limitation imposed by crystallization of the working fluid is determined for both adiabatic and diabatic absorber cycles. Both cycles offer similar COP ; however the adiabatic variant shows a larger margin against crystallization. This cycle can produce cold for external inlet evaporator temperatures down to −10 °C, but for this limit the crystallization could happen at high inlet generator temperatures. The maximum COP can be 1.25 for an external inlet generator temperature of 100 °C. This cycle shows a better COP than a typical double effect cycle with in-parallel configuration for the range of the moderate temperatures under study and using the same working fluid. Comparisons with double effect cycles using H 2 O/LiBr and NH 3 /H 2 O as working fluids are also offered, highlighting the present configurations advantages regarding COP , evaporation and condensation temperatures as well as crystallization.

This paper deals with the characterization of the resolution limits for the Stereo-PIV technique.... more This paper deals with the characterization of the resolution limits for the Stereo-PIV technique. The more relevant among these limits correspond to physical constrains like the overlapping of information along the oblique lines of view within the laser sheet, thus representing restrictions that are not algorithm-dependent. To establish situations in which the measurement is not physically feasible is not easy due to the large amount of parameters involved. Nevertheless, to ascertain situations that can be measured is an easier task. To analyze these limits, Stereo-LFC PIV and Stereo-Multigrid enhanced with image distortion are used in this paper. Both techniques have been tested in the past by the authors (Nauri et al. 2006 and 2008) in order to evaluate their performance in terms of robustness and accuracy for both large and small scale vorticity distributions. This work focuses on the study of the following limits: − The relation between the size of the smallest vortices that can be measured in a stereo configuration and the laser sheet width for different light intensity profiles across it. − The influence of the viewing angle of the stereo configuration in the previous resolution limit. It is relevant as it raises a trade-off between accuracy in the measurement of the out-of-plane component and spatial resolution. − The smallest size of the vortices under analysis if the laser sheet width is negligible. − The effect of individual variations of particle image grey level for each particle couple. This can be considered as a typical source of noise even in good real image acquisitions without stray light or reflections. (Nobach and Bodenschatz 2007). To conclude, the implications of the results obtained with synthetic images for the two advanced stereo techniques analyzed in this work are commented for actual cases of real images.

Among the renewable energy technologies, concentrating solar collectors are receiving growing int... more Among the renewable energy technologies, concentrating solar collectors are receiving growing interest as power source for heat and electricity production worldwide. The recent development of small scale parabolic trough collectors, PTCs, suggests extending their application to medium and low temperature facilities configuring solar integrated absorption machines for heating and cooling purposes. The innovative solution considered in this work uses the PTCs as a direct vapor generator/separator forming part of an absorption machine using ammonia/lithium nitrate dissolution as working fluid, thus flowing the dissolution inside the collector absorber tube. The gravity driven flow stratification and separation obtained inside the receiver tube ensures a continuous desorption of the refrigerant and enables a simplified system layout, reducing the overall costs and complexity. The 1-D steady-state numerical model of the PTC vapor generator proposed is suitable for approaching a first cha...

Particle Image Velocimetry: Recent Improvements, 2004

The presence of a large number of different software codes for image analysis, including several ... more The presence of a large number of different software codes for image analysis, including several variants for the image interrogation, suggests the need for testing the suitability and accuracy of the developed algorithms. One of the possible approaches is testing these systems with experiments of well-known flow properties. Otherwise, tests can be performed by analyzing synthetically generated images. The advantage of the latter approach is that there is no need to setup an experiment and the flow field is known in detail. On the other hand, there are obvious doubts on how close a synthetic image can describe the reality. This paper provides some insight on the relation between results on real and synthetic images both in a turbulent channel flow. A classical Particle Tracking Velocimetry (PTV) algorithm will be presented as well as the advanced PTV using Feature Tracking.

Renewable Energy, 2021

Linear Fresnel collectors offer great potential for producing solar heat for industrial processes... more Linear Fresnel collectors offer great potential for producing solar heat for industrial processes, both on a small and large scale. Thermal oil, pressurized water, or steam are used as heat transfer fluid in most applications, due to their suitable thermal properties. A heat exchanger is required for thermal power delivery to the user unless the heat transfer fluid is directly used as a medium in the industrial process. For those industrial applications using hot air as a process fluid, direct air heating inside linear Fresnel collectors can be an interesting solution aiming at simplification, cost reduction, and environmental and safety benefits. In this experimental study air is heated inside a commercial small-scale Linear Fresnel collector row of 79.2 m2 active surface, demonstrating the viability of direct air heating up to 500 °C at its outlet. A commercial turbocharger pressurizes the air and reduces the blowing power. The purposely designed test campaign carried out in Madri...

Applied Thermal Engineering, 2017

Photovoltaic cooking seems viable under some circumstances. Solar cooking during the night seems ... more Photovoltaic cooking seems viable under some circumstances. Solar cooking during the night seems an interesting capability as well as during cloudy intervals during the day. Electric energy storage in batteries can cost more than the rest of the Photovoltaic (PV) cooking system, namely: panel, wiring, controller and end converter into heat. The supply of the heavy batteries to remote locations can increase their price even more. When they are abandoned after their operative life as residues it involves the risk of pollution. Thermal energy storage can be an alternative to batteries for a lower price and complexity. Phase Change Materials (PCM) offer high energy density, viable for cooking if their melting temperature is above 100 oC. Erythritol is a PCM that offers advantages over some other candidates. Its thermal conductivity seems too low for a fast enough heating and cooking so that its enhancement seems a requirement. The paper offers the result of some experiences to develop a...

This paper presents the thermal characterization of a plate heat exchanger in a test rig for stud... more This paper presents the thermal characterization of a plate heat exchanger in a test rig for studying promising ammonia-salt solutions. With the aim of simulating the use of solar thermal energy to feed the absorption machine, oil temperatures between 55 and 113 ºC have been used in the generator. As a first step in the analysis heat transfer coefficients on the generator were determined using water as working fluid in single phase flow. The water and oil flow rate were varied from 2.5 to 9 and from 9 to 30 kg/min respectively. The modified Wilson plot method was used to determine the coefficients. Computed and experimental global coefficients were compared.

Volume 2: Coal, Biomass and Alternative Fuels; Combustion and Fuels; Oil and Gas Applications; Cycle Innovations, 1999

A high-pressure facility capable for testing Lean Premixed Pre-vaporized (LPP) combustor geometri... more A high-pressure facility capable for testing Lean Premixed Pre-vaporized (LPP) combustor geometries is reported. The proposed design enables the use of both single-point and whole-field non-intrusive measuring techniques when the combustor operates under conditions representative of gas turbines or jet engines operation, thereby enabling the complete characterization of the turbulent flow field that develops inside LPP combustors. The individual control of the air and fuel supplies, provided, respectively, by a number of industrial compressors and a specific LPG supply facility, allows the investigation of a wide range of operating conditions. In this paper, the facility specifications are explained and adequately justified. Preliminary results are presented, showing the suitability of the design.

In the present work the use of low-temperature solar heat is studied to produce cooling at 5°C, u... more In the present work the use of low-temperature solar heat is studied to produce cooling at 5°C, using a double-stage LiBr–H2O air-cooled absorption cycle. A solar plant, consisting of flat plate collectors feeding the generators of the absorption machine, has been modeled. Operating conditions of the double-stage absorption machine, integrated in the solar plant without crystallization problems for condensation temperatures

In the state-of-the-art PIV, image sensors are growing in size and PIV algorithms are increasing ... more In the state-of-the-art PIV, image sensors are growing in size and PIV algorithms are increasing in spatial resolution capabilities. These technological advances allow for the simultaneous measurement of increasingly larger spatial scales ranges in a single PIV snapshot. To take fully advantage of the available spatial scales range, PIV setup constraints establish a coupling between the laser sheet thickness and the time between laser pulses. This condition did not apply with older technologies. The resulting value for the optimum laser sheet thickness is in a range where the superposed flow information in the direction of the imaging sensor introduces special characteristics errors at the small scale limit. This may compromise the measurement of flow quantities like dissipation and turbulent kinetic energy (tke), for which the contribution of the small and medium scales may be relevant. Within this scenario the assessment of the smallest scale resolved in the PIV measurement is nec...

Sources/sinks Alternative to the Outside Air for Heat Pump and Air-conditioning Techniques (Alternative Sources - AS), Padua, Italy, April 5-7, 2011. / International Sorption Heat Pump Conference (ISHPC11), Padua, Italy, April 6-8, 2011., Apr 6, 2011

This paper presents the experimental evaluation of a fusion plate heat exchanger (FPHE) during bo... more This paper presents the experimental evaluation of a fusion plate heat exchanger (FPHE) during boiling conditions of a solution of lithium nitrate in ammonia. The data are representative of the working conditions of generators in single-effe ct absorption chillers used for trigeneration applications, among others. The solution flow rate and outlet temperature were modified in the ranges of 0.041 - 0.083 kg/s and 78 oC - 95 oC, res pectively. Correlations for single-phase-flow heat transfer, obtained in previous experiments, ar e used to characterize the boiling heat transfer. The influences of the heat flux and mass flux are analyzed. The region of the FPHE where bubbles begin to arise is estimated using a c orrelation for the wall superheat required for the onset of subcooled boiling. Results show that s ubcooled boiling is present in the generator and it takes up a significant part of the boiling r egion. Subcooled boiling heat-transfer coefficients and correlations for the Nussel...

This paper studies the effects caused by the optical losses on the calculated cross section of th... more This paper studies the effects caused by the optical losses on the calculated cross section of the measurement volume of a phase Doppler anemometer and consequently, in particle concentration and volume flux. It will be shown that as the optical l osses increase, the ca lculated d iameter of the measurement volume for the smaller particles presents an anomalous behaviour. Moreover, these small particles tend to disappear. As a consequence the particle range that the PDA can handle is restricted. A criterion to determine the minimum effective particle size that can be correctly measured is proposed.

Energy Conversion and Management, 2018

Two-phase gravity-driven and gravity-stratified flow regime inside a pipe, which is present in ma... more Two-phase gravity-driven and gravity-stratified flow regime inside a pipe, which is present in many engineering applications, is an attractive option for solar cooling/heating/power production using Rankine cycles, absorption cycles or any other thermodynamic application by means of vapor as working fluid. This paper offers a numerical model of this flow configuration that copes with transient phenomena, like unsteadiness of solar radiation, among others. The mathematical model consists of 1-D balance equations for mass and momentum for both fluids and energy for both fluids and the wall of the pipe that absorbs the solar radiation. The model is characterized by the fact that the area (or height) of the liquid layer is treated as a dependent variable forming part of the solution. The numerical method consists in a finite volume staggered grid discretization of the governing equations. Mass flow and liquid area are calculated with a semi-implicit pressure based method and the transient terms are treated with the explicit first stage singly implicit Runge-Kutta (ESDIRK) method. The calculation of the mass transfer rate from liquid to vapor is calculated iteratively by a guess-and-correct mass transfer algorithm, specially developed for stratified flows. The results show the applicability and benefits of this model for the not so well known counter-current stratified two-phase with evaporation/boiling. Additionally, the performance of the mass transfer algorithm is discussed showing that it is monotonic decreasing and linearly convergent.

Applied Thermal Engineering, 2016

Abstract The two-stage configuration of a double-effect absorption cycle using ammonia/lithium ni... more Abstract The two-stage configuration of a double-effect absorption cycle using ammonia/lithium nitrate as working fluid is studied by means of a thermodynamic model. The maximum pressure of this cycle configuration is the same as the single-effect cycle, up to 15.8 bars, being an advantage over the double-effect conventional configuration with three pressure levels that exhibits much higher maximum pressure. The performance of the cycle and the limitation imposed by crystallization of the working fluid is determined for both adiabatic and diabatic absorber cycles. Both cycles offer similar COP ; however the adiabatic variant shows a larger margin against crystallization. This cycle can produce cold for external inlet evaporator temperatures down to −10 °C, but for this limit the crystallization could happen at high inlet generator temperatures. The maximum COP can be 1.25 for an external inlet generator temperature of 100 °C. This cycle shows a better COP than a typical double effect cycle with in-parallel configuration for the range of the moderate temperatures under study and using the same working fluid. Comparisons with double effect cycles using H 2 O/LiBr and NH 3 /H 2 O as working fluids are also offered, highlighting the present configurations advantages regarding COP , evaporation and condensation temperatures as well as crystallization.

This paper deals with the characterization of the resolution limits for the Stereo-PIV technique.... more This paper deals with the characterization of the resolution limits for the Stereo-PIV technique. The more relevant among these limits correspond to physical constrains like the overlapping of information along the oblique lines of view within the laser sheet, thus representing restrictions that are not algorithm-dependent. To establish situations in which the measurement is not physically feasible is not easy due to the large amount of parameters involved. Nevertheless, to ascertain situations that can be measured is an easier task. To analyze these limits, Stereo-LFC PIV and Stereo-Multigrid enhanced with image distortion are used in this paper. Both techniques have been tested in the past by the authors (Nauri et al. 2006 and 2008) in order to evaluate their performance in terms of robustness and accuracy for both large and small scale vorticity distributions. This work focuses on the study of the following limits: − The relation between the size of the smallest vortices that can be measured in a stereo configuration and the laser sheet width for different light intensity profiles across it. − The influence of the viewing angle of the stereo configuration in the previous resolution limit. It is relevant as it raises a trade-off between accuracy in the measurement of the out-of-plane component and spatial resolution. − The smallest size of the vortices under analysis if the laser sheet width is negligible. − The effect of individual variations of particle image grey level for each particle couple. This can be considered as a typical source of noise even in good real image acquisitions without stray light or reflections. (Nobach and Bodenschatz 2007). To conclude, the implications of the results obtained with synthetic images for the two advanced stereo techniques analyzed in this work are commented for actual cases of real images.

Among the renewable energy technologies, concentrating solar collectors are receiving growing int... more Among the renewable energy technologies, concentrating solar collectors are receiving growing interest as power source for heat and electricity production worldwide. The recent development of small scale parabolic trough collectors, PTCs, suggests extending their application to medium and low temperature facilities configuring solar integrated absorption machines for heating and cooling purposes. The innovative solution considered in this work uses the PTCs as a direct vapor generator/separator forming part of an absorption machine using ammonia/lithium nitrate dissolution as working fluid, thus flowing the dissolution inside the collector absorber tube. The gravity driven flow stratification and separation obtained inside the receiver tube ensures a continuous desorption of the refrigerant and enables a simplified system layout, reducing the overall costs and complexity. The 1-D steady-state numerical model of the PTC vapor generator proposed is suitable for approaching a first cha...

Particle Image Velocimetry: Recent Improvements, 2004

The presence of a large number of different software codes for image analysis, including several ... more The presence of a large number of different software codes for image analysis, including several variants for the image interrogation, suggests the need for testing the suitability and accuracy of the developed algorithms. One of the possible approaches is testing these systems with experiments of well-known flow properties. Otherwise, tests can be performed by analyzing synthetically generated images. The advantage of the latter approach is that there is no need to setup an experiment and the flow field is known in detail. On the other hand, there are obvious doubts on how close a synthetic image can describe the reality. This paper provides some insight on the relation between results on real and synthetic images both in a turbulent channel flow. A classical Particle Tracking Velocimetry (PTV) algorithm will be presented as well as the advanced PTV using Feature Tracking.

Renewable Energy, 2021

Linear Fresnel collectors offer great potential for producing solar heat for industrial processes... more Linear Fresnel collectors offer great potential for producing solar heat for industrial processes, both on a small and large scale. Thermal oil, pressurized water, or steam are used as heat transfer fluid in most applications, due to their suitable thermal properties. A heat exchanger is required for thermal power delivery to the user unless the heat transfer fluid is directly used as a medium in the industrial process. For those industrial applications using hot air as a process fluid, direct air heating inside linear Fresnel collectors can be an interesting solution aiming at simplification, cost reduction, and environmental and safety benefits. In this experimental study air is heated inside a commercial small-scale Linear Fresnel collector row of 79.2 m2 active surface, demonstrating the viability of direct air heating up to 500 °C at its outlet. A commercial turbocharger pressurizes the air and reduces the blowing power. The purposely designed test campaign carried out in Madri...

Applied Thermal Engineering, 2017

Photovoltaic cooking seems viable under some circumstances. Solar cooking during the night seems ... more Photovoltaic cooking seems viable under some circumstances. Solar cooking during the night seems an interesting capability as well as during cloudy intervals during the day. Electric energy storage in batteries can cost more than the rest of the Photovoltaic (PV) cooking system, namely: panel, wiring, controller and end converter into heat. The supply of the heavy batteries to remote locations can increase their price even more. When they are abandoned after their operative life as residues it involves the risk of pollution. Thermal energy storage can be an alternative to batteries for a lower price and complexity. Phase Change Materials (PCM) offer high energy density, viable for cooking if their melting temperature is above 100 oC. Erythritol is a PCM that offers advantages over some other candidates. Its thermal conductivity seems too low for a fast enough heating and cooking so that its enhancement seems a requirement. The paper offers the result of some experiences to develop a...

This paper presents the thermal characterization of a plate heat exchanger in a test rig for stud... more This paper presents the thermal characterization of a plate heat exchanger in a test rig for studying promising ammonia-salt solutions. With the aim of simulating the use of solar thermal energy to feed the absorption machine, oil temperatures between 55 and 113 ºC have been used in the generator. As a first step in the analysis heat transfer coefficients on the generator were determined using water as working fluid in single phase flow. The water and oil flow rate were varied from 2.5 to 9 and from 9 to 30 kg/min respectively. The modified Wilson plot method was used to determine the coefficients. Computed and experimental global coefficients were compared.

Volume 2: Coal, Biomass and Alternative Fuels; Combustion and Fuels; Oil and Gas Applications; Cycle Innovations, 1999

A high-pressure facility capable for testing Lean Premixed Pre-vaporized (LPP) combustor geometri... more A high-pressure facility capable for testing Lean Premixed Pre-vaporized (LPP) combustor geometries is reported. The proposed design enables the use of both single-point and whole-field non-intrusive measuring techniques when the combustor operates under conditions representative of gas turbines or jet engines operation, thereby enabling the complete characterization of the turbulent flow field that develops inside LPP combustors. The individual control of the air and fuel supplies, provided, respectively, by a number of industrial compressors and a specific LPG supply facility, allows the investigation of a wide range of operating conditions. In this paper, the facility specifications are explained and adequately justified. Preliminary results are presented, showing the suitability of the design.

In the present work the use of low-temperature solar heat is studied to produce cooling at 5°C, u... more In the present work the use of low-temperature solar heat is studied to produce cooling at 5°C, using a double-stage LiBr–H2O air-cooled absorption cycle. A solar plant, consisting of flat plate collectors feeding the generators of the absorption machine, has been modeled. Operating conditions of the double-stage absorption machine, integrated in the solar plant without crystallization problems for condensation temperatures