References of "Cuevas, Cristian"
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See detailExperimental Investigation on a Reversible Heat Pump for a Passenger Car
Lemort, Vincent ULg; Cuevas, Cristian; Declaye, Sébastien ULg

in Proceedings of the 21st International Compressor Conference, Purdue 2012 (2012, July)

This paper summarizes the first results of a research project dealing with the development of a reversible heat pump for a passenger car. Heat pump systems appear to be a more efficient alternative to ... [more ▼]

This paper summarizes the first results of a research project dealing with the development of a reversible heat pump for a passenger car. Heat pump systems appear to be a more efficient alternative to electrical resistance heaters for the purpose of heating the car indoor environment. Heat pump systems could be easily implemented into cars by allowing the air-conditioning system to run in reverse. In order to check the technical feasibility of a reversible heat pump system, and to point out technical barriers, a prototype was built and tested. Experimental data was also used to calibrate and validate simulation models of components. A heat pump system model was finally built to investigate the operating conditions of the system. The first part of the paper describes the test rig (architecture, components, and measurement devices) and the experimental campaign. Performance of components (compressor, evaporator, condenser and heater core) is evaluated in terms of variation with the operating conditions. The second part of the paper presents the steady-state semi-empirical models of the components. Such lumped models retain and concentrate the main physical phenomena inherent to the components into successive elementary processes (pressure losses, heat transfers, etc.). They require a limited number of parameters that can be identified based on experimental data. The calibration and the validation of the proposed component models are detailed. Finally, an overall simulation model of the reversible heat pump system is proposed and used to evaluate the energy performance of the system as function of the operating conditions. [less ▲]

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See detailAutomotive electric scroll compressor: Testing and modeling
Cuevas, Cristian; Fonseca, Nestor; Lemort, Vincent ULg

in International Journal of Refrigeration (2012)

The aim of this research is to characterize experimentally and by modelling an electrically driven automotive scroll compressor. The experimental characterization is carried out through 13 tests at ... [more ▼]

The aim of this research is to characterize experimentally and by modelling an electrically driven automotive scroll compressor. The experimental characterization is carried out through 13 tests at compressor speeds varying between 3000 and 5000 rpm. The DC/AC converter used to supply the compressor was characterized through a calorimetric balance, obtaining an efficiency that depends only on the compressor speed, ranging from 92.5 %, for a compressor speed of 1500 rpm, to 97.5%, for a compressor speed of 5000 rpm. The experimental results are used to identify the parameters of a semi-empirical compressor model, which is able to predict with an acceptable accuracy the main outputs of the mathematical model: confidence limits on the exhaust temperature of ± 1.0 K, on the refrigerant flow rate of ± 2 g s-1 and on the compressor power of ±60 W. This model is then used to determine the compressor cooling power at different compressor speeds and condensing pressures. [less ▲]

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See detailThermo-hydraulic characterization of an automotive intercooler for a low pressure EGR application
Cuevas, Cristian; Makaire, Danielle ULg; Ngendakumana, Philippe ULg

in Applied Thermal Engineering (2011), 31(14-15), 2474-2484

In this work an experimental study is carried out to determine the thermo-hydraulic performance of an intercooler (IC) with flat tubes provided with triangular plain internal fins and louvered external ... [more ▼]

In this work an experimental study is carried out to determine the thermo-hydraulic performance of an intercooler (IC) with flat tubes provided with triangular plain internal fins and louvered external fins when it is used on a car equipped with a low pressure EGR. The main unknowns to be answered are the thermo-hydraulic characteristics of the IC working under humid conditions induced by EGR, the conditions under which the water content in the mixture of air and exhaust gases begins to condense and the conditions under which the condensed water will be retained inside the IC. The exhaust gases are here replaced by a mixture of dry air and water vapour which are mixed upstream of the IC. The IC is submitted at the following testing conditions: on the ambient air side, the air temperature is fixed at around 20 °C and the air velocity is settled at 1, 2 and 4 ms/s; on the exhaust gases side, the supply temperature was varied between 90 and 150 °C, with dry gas flow rates of 20, 50 and 100 g /s, and water contents varying between almost 0 and 0.09 kgw kgg-1. At these conditions the IC transfers between 1 and 13 kW with overall heat transfer conductance varying between 0.05 and 0.38 kWK-1 and effectivenesses between 0.3 and 0.97. A water accumulation inside the IC was detected for the tests carried out at low dry gas flow rate of 20 g s-1 and for all the water content explored here (higher than 0.02 kgw kgg-1). [less ▲]

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See detailThermo-hydraulic Characterization of a Louvered Fin and Flat Tube Heat Exchanger
CUEVAS, Cristian; Makaire, Danielle ULg; DARDENNE, Laurent et al

in Experimental Thermal & Fluid Science (2011), (1), 154164

In the present study, a whole heat exchanger with a hydraulic diameter of 2.3 mm is tested, which is a minichannel heat exchanger according to the Kandlikar classification. This is a louvered fin and flat ... [more ▼]

In the present study, a whole heat exchanger with a hydraulic diameter of 2.3 mm is tested, which is a minichannel heat exchanger according to the Kandlikar classification. This is a louvered fin and flat tube heat exchanger currently used in car cooling systems, also known as radiator. A glycol-water mixture (60/40 in volume) circulates through the tubes at flows ranging from 100 to 7800 l/h and at a supply temperature of 90ºC. This fluid is cooled with ambient air at a temperature of 20ºC and at frontal air velocities varying between 0.5 and 7 m/s. The thermohydraulic performance of the heat exchanger is compared with the classical correlations given in the literature for the heat transfer and the friction factor calculation. On the glycolwater side the heat exchanger is characterized for Reynolds numbers from 30 to 8000. A first comparison is carried out with the correlations available in the literature with a purely predictive model by obtaining a predictive value with a systematic under prediction lower than 10%. In a second step a semi-empirical model is considered to identify the experimental heat transfer coefficients for this application. [less ▲]

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See detailExperimental Analysis of Radiant Ceiling Systems Coupled to its Environment
Fonseca, Néstor; Cuevas, Cristian; Lemort, Vincent ULg

(2010, July)

This paper presents the results of an experimental analysis of the radiant ceiling systems in both heating and cooling modes coupled to its environment (fenestration, walls, internal loads and ventilation ... [more ▼]

This paper presents the results of an experimental analysis of the radiant ceiling systems in both heating and cooling modes coupled to its environment (fenestration, walls, internal loads and ventilation system). The main objective of this study is to present the results of the systems performance and measurement methods used to evaluate the influence of some important parameters on the radiant ceiling capacity and comfort conditions. Two test chambers are adapted in a way to reproduce as good as possible the characteristics of the real offices located in Brussels. Forty-six tests were performed in which the main objective was to observe the influence of parameters such as the mass flow rate, supply water temperature and thermal load distribution, fenestration and ventilation system effects. Laboratory test results show that the influence of surfaces temperatures inside the room, especially the facade, is considerable. Therefore, the system must be evaluated together with its designed environment and not as separate HVAC equipment. [less ▲]

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See detailDynamic Modeling and Validation of Radiant Ceiling Systems Coupled to its Environment
Fonseca, Néstor; Cuevas, Cristian; Lemort, Vincent ULg

(2010, July)

This paper presents the results of a study performed in order to develop a dynamic model of radiant ceiling panels in heating or cooling modes coupled to its environment (fenestration, walls, internal ... [more ▼]

This paper presents the results of a study performed in order to develop a dynamic model of radiant ceiling panels in heating or cooling modes coupled to its environment (fenestration, walls, internal loads and ventilation system). The model considers the radiant panels as a dynamic-state finned heat exchanger connected to a detailed lumped dynamic model of the building (R-C network). The behavior of the radiant ceiling system and the interactions with its environment has been experimentally and numerically evaluated. Using as inputs the radiant ceiling and room dimensions, material properties and the transient measurements of air temperature at the adjacent zones, supply air and water temperatures and mass flow rates, the model allows for the estimation of the water exhaust temperature, radiant ceiling average surface temperature, resultant and dry air room temperatures, radiant ceiling power and internal surface temperatures of the room in order to compare with measurements taken during the commissioning process. Two dynamic tests in heating and cooling modes are used to validate the model. [less ▲]

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See detailRadiant ceiling systems coupled to its environment part 2: Dynamic modeling and validation
Fonseca, Nestor; Bertagnolio, Stéphane ULg; Cuevas, Cristian

in Applied Thermal Engineering (2010), 30

This paper presents the results of a study performed in order to develop a dynamic model of radiant ceiling panels in heating or cooling modes coupled to its environment (fenestration, walls, internal ... [more ▼]

This paper presents the results of a study performed in order to develop a dynamic model of radiant ceiling panels in heating or cooling modes coupled to its environment (fenestration, walls, internal loads and ventilation system). The model considers the radiant panels as a dynamic-state finned heat exchanger connected to a detailed lumped dynamic model of the building (ReC network). The behavior of the radiant ceiling system and the interactions with its environment has been experimentally and numerically evaluated. Using as inputs the radiant ceiling and room dimensions, material properties and the transient measurements of air temperature at the adjacent zones, supply air and water temperatures and mass flow rates, the model allows for the estimation of the water exhaust temperature, radiant ceiling average surface temperature, resultant and dry air room temperatures, radiant ceiling power and internal surface temperatures of the room in order to compare with measurements taken during the commissioning process. Two dynamic tests in heating and cooling modes are used to validate the model. [less ▲]

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See detailRadiant ceiling systems coupled to its environment part 1: Experimental analysis
Fonseca, Néstor; Cuevas, Cristian; Lemort, Vincent ULg

in Applied Thermal Engineering (2010), 30

This paper presents the results of an experimental analysis of the radiant ceiling systems in both heating and cooling modes coupled to its environment (fenestration, walls, internal loads and ventilation ... [more ▼]

This paper presents the results of an experimental analysis of the radiant ceiling systems in both heating and cooling modes coupled to its environment (fenestration, walls, internal loads and ventilation system). The main objective of this study is to present the results of the experimental analysis and measurement methods and its discussion. Two test chambers are adapted in a way to reproduce as good as possible the characteristics of the real offices located in Brussels (Belgium). Forty-six tests are performed to observe the influence of parameters such as the mass flow rate, supply water temperature, fenestration and ventilation system effects and thermal load distribution. Laboratory test results show that the influence of surfaces temperatures inside the room, especially the facade, is considerable. Therefore, the system must be evaluated together with its designed environment and not as separate HVAC equipment. [less ▲]

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See detailCharacterization of a scroll compressor under extended operating conditions
Cuevas, Cristian; Lebrun, Jean ULg; Lemort, Vincent ULg et al

in Applied Thermal Engineering (2010), 30

Refrigeration and air-conditioning compressors are designed to work under well-defined conditions. In some applications it is interesting to observe their performances beyond these conditions, for example ... [more ▼]

Refrigeration and air-conditioning compressors are designed to work under well-defined conditions. In some applications it is interesting to observe their performances beyond these conditions, for example in the case of a high temperature two-stage heat pump or of a cooling system working at high temperature. In this study a compressor is characterized experimentally with refrigerant R134a and through 118 tests at condensing pressures varying from 8.6 up to 40.4 bar (tsat = 33.9°C to tsat = 100.8°C) and evaporating pressures varying from 1.6 up to 17.8 bar (tsat = -15.6°C to tsat = 62.4°C). Under these conditions the compressor motor was pushed at its maximal current in several tests. This compressor’s performance is mainly characterized by its isentropic and volumetric efficiencies. It presents a maximal isentropic efficiency of 72%, corresponding to a pressure ratio of around 2.5–2.6. The volumetric efficiency decreases linearly from almost 1.0 (for a pressure ratio of 1.3) to 0.83 (for a pressure ratio of 9.7). A slight degradation of the isentropic and volumetric efficiencies is observed when the compressor supply and exhaust pressures are increased for a given pressure ratio; this could be due to an internal leakage. The compressor tests are used to identify the six parameters of a semi-empirical simulation model. After parameter identification, experimental and simulated results are in very good agreement, except for some points at high compressor power where the compressor is pushed at its maximal current. [less ▲]

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See detailDevelopment and validation of a condenser three zones model
Cuevas, Cristian; Lebrun, Jean ULg; Lemort, Vincent ULg et al

in Applied Thermal Engineering (2009)

A general and simple ‘‘deterministic” model of a refrigeration condenser is presented. The model assumes that the condenser can be divided into three distinct zones on the refrigerant side: the vapour de ... [more ▼]

A general and simple ‘‘deterministic” model of a refrigeration condenser is presented. The model assumes that the condenser can be divided into three distinct zones on the refrigerant side: the vapour de-superheating zone, the two-phase zone and the sub-cooled liquid zone. The model inputs are the air supply temperature, the air mass flow rate, the refrigerant supply temperature (or the over-heating), the exhaust sub-cooling and the refrigerant mass flow rate. The model is able to identify the pressures and temperatures in each zone and the corresponding heat flows. The model also gives the geometrical repartition among the zones and the pressure drop on air-side. The condenser model is validated with a total of 183 tests. Testing conditions cover a very wide domain, including pressures up to 40 bars with refrigerant R134a. The model is able to predict with a probability of 95% the condenser supply pressure within a confidence interval of +0.5 and 0.1 bar. This means a condenser power confidence interval within 200 and +100 W, which is considered here as acceptable. Refrigerant pressure drop is predicted with a higher error, but it is attributed to measuring uncertainty. On the other hand, air pressure drop is predicted with a very poor accuracy. Undoubtedly, this is due to the friction factor correlation used in this study which is not the most adequate. Here a difference of 40% is obtained. [less ▲]

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See detailTesting and modeling a scroll expander integrated into an Organic Rankine Cycle
Lemort, Vincent ULg; Quoilin, Sylvain ULg; Cuevas, Cristian et al

in Applied Thermal Engineering (2009), 29

Organic Rankine Cycles (ORC’s) are particularly suitable for recovering energy from low-grade heat sources. This paper first presents the results of an experimental study carried out on a prototype of an ... [more ▼]

Organic Rankine Cycles (ORC’s) are particularly suitable for recovering energy from low-grade heat sources. This paper first presents the results of an experimental study carried out on a prototype of an open-drive oil-free scroll expander integrated into an ORC working with refrigerant HCFC-123. By exploiting the overall expander performance measurements, the eight parameters of a scroll expander semi-empirical model are then identified. The model is able to compute variables of first importance such as the mass flow rate, the delivered shaft power and the discharge temperature, and secondary variables such as the supply heating-up, the exhaust cooling-down, the ambient losses, the internal leakage and the mechanical losses. The maximum deviation between the predictions by the model and the measurements is 2% for the mass flow rate, 5% for the shaft power and 3 K for the discharge temperature. The validated model of the expander is finally used to quantify the different losses and to indicate how the design of the expander might be altered to achieve better performances. This analysis pointed out that the internal leakages and, to a lesser extent, the supply pressure drop and the mechanical losses are the main losses affecting the performance of the expander. [less ▲]

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See detailDevelopment of simple cooling coil models for simulation of HVAC systems
Lemort, Vincent ULg; Cuevas, Cristian; Lebrun, Jean ULg et al

in ASHRAE Transactions (2008), 114(1), 319-328

This paper presents two simple cooling coil models. The first part of the paper describes and validates the first one (“reference model”). This model only necessitates 3 parameters, which can be estimated ... [more ▼]

This paper presents two simple cooling coil models. The first part of the paper describes and validates the first one (“reference model”). This model only necessitates 3 parameters, which can be estimated by using commissioning or manufacturer information. The second part of the paper presents and validates the second simple model (“simplified model”). The paper shows how the latter can be built from the reference model, when there is no need to describe what happens on the refrigerant side. This simplified model can be easily integrated in the model of a global HVAC system in order to calculate the cooling coil energy consumption over large time periods. The simplified model is appropriate to decrease the computational time and avoid numerical instabilities. [less ▲]

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See detailContribution à l'étude des cycles de Rankine de récupération de chaleur
Lemort, Vincent ULg; Cuevas, Cristian; Teodorese, Ion et al

(2007, May)

Ce papier présente tout d’abord un modèle de cycle de Rankine, dont l’expanseur est de type spiro-orbital. Ce modèle doit permettre d’orienter le design des différents éléments du cycle, mais aussi de ... [more ▼]

Ce papier présente tout d’abord un modèle de cycle de Rankine, dont l’expanseur est de type spiro-orbital. Ce modèle doit permettre d’orienter le design des différents éléments du cycle, mais aussi de prédire les performances du cycle pour des conditions opératoires imposées. Une méthode de comparaison des performances réalisées par différents fluides est ensuite proposée. Les résultats d’une étude expérimentale menée sur un prototype de cycle de Rankine de récupération de chaleur sont finalement présentés. Le modèle du cycle et la méthode de comparaison des performances des fluides ont été utilisés pour orienter le design de l’expanseur spiro-orbital et sélectionner le fluide de travail. [less ▲]

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See detailCO emissions of fuel oil boilers used in domestic heating
Cuevas, Cristian; Ngendakumana, Philippe ULg

Conference (2006, August)

To assess the CO emissions of fuel oil boilers, tests have been performed on a boiler in transient and steady state regimes. The tests were performed so that the output power (about 370 kW) was kept ... [more ▼]

To assess the CO emissions of fuel oil boilers, tests have been performed on a boiler in transient and steady state regimes. The tests were performed so that the output power (about 370 kW) was kept constant in steady state regime (same water flow rate and inlet and outlet temperatures). On the other hand, the oxygen content of the flue gas in the chimney was kept constant (around 3%). Classical gas analysers were used to measure the CO2, O2, CO and NOx concentrations in the flue gas. The two main parameters investigated are the nozzle capacity and the corresponding fuel injection pressure to keep the same burner consumption. Four nozzles whose capacity ranges from 30 to 45 kg/h (at a fuel supply pressure of 20 bar) were fitted on the burner equipping the fuel oil boiler. All the nozzles used are spill return and 45° spray angle type. The tests performed showed that in steady-state regime, the CO emissions are very low compared to the limits established by the European standard (110 mg/kWh of energy consumption). A comparison with calculated CO emissions shows also that the values obtained in equilibrium conditions are too high. On the other hand, in the transient regime (start-up regime for a cycling boiler), the CO emissions are not negligible and increase significantly if a high capacity nozzle is fitted on the fuel oil burner. In short, the paper demonstrates that in order to increase the boiler thermal efficiency and thus to reduce CO2 emissions (for the same output power), one has to avoid the CO emissions in the transient regime. When performing a replacement of the burner nozzle, a low capacity nozzle associated with an adjustment of a high fuel injection pressure is recommended, since a reduction of CO emissions in the starting-up regime is achieved and, on the other hand, the thermal efficiency and the pollutants emissions of the fuel oil boiler in steady state regime are not affected. [less ▲]

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See detailRéalisation et validation d’un banc du système de refroidissement pour pile à combustible de véhicule
Cuevas, Cristian; Duysinx, Pierre ULg; Hannay, Jules et al

Report (2006)

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See detailEnergy conservation and CO emissions of fuel oil boilers used in domestic heating
Cuevas, Cristian; Ngendakumana, Philippe ULg

Conference (2006, May)

According to the European standard, the CO emissions of new fuel oil boilers, whose output power is lower than 400 kW, are limited in steady-state regime to 110 mg/kWh of energy consumption. In order to ... [more ▼]

According to the European standard, the CO emissions of new fuel oil boilers, whose output power is lower than 400 kW, are limited in steady-state regime to 110 mg/kWh of energy consumption. In order to assess the performance of actual fuel oil boilers, an experimental work has been performed on a boiler available in the laboratory and whose output nominal power is about 370 kW. The two main parameters investigated are the nozzle capacity and the corresponding fuel injection pressure to keep the same burner consumption. Four nozzles whose capacity ranges from 30 to 45 kg/h at 20 bar were fitted on the burner equipping the fuel oil boiler. All the nozzles used are spill return and 45° type. To assess the CO emissions of the fuel oil boiler, tests have been performed in transient and steady-state regimes. The tests were performed so that the output power was kept constant in steady-state regime (same water flow rate and inlet and outlet temperatures). That is why for each nozzle tested, the fuel injection pressure has been adjusted in order to maintain the fuel mass flow rate at around 37.7 kg/h. On the other hand, the oxygen content of the flue gas in the chimney was kept constant (around 3%) by adjusting only the position of the burner air damper (the position of the flame holder was kept constant) and thus the air combustion mass flow rate. Classical gas analysers were used to measure the CO2, O2, CO and NOx concentrations in the flue gas. The tests performed showed that in steady-state regime, the CO emissions are very low compared to the European standard. On the other hand, in the transient regime (start-up regime for a cycling boiler), the CO emissions are not negligible and increase significantly if a high capacity nozzle is fitted on the fuel oil burner. In short, the paper demonstrates that in order to increase the boiler thermal efficiency and thus to reduce CO2 emissions (for the same output power), one has to avoid the CO emissions in the transient regime. When performing a replacement of the burner nozzle, a low capacity nozzle associated with an adjustment of a high fuel injection pressure is recommended, since a reduction of CO emissions in the starting-up regime is achieved and, on the other hand, the thermal efficiency and the pollutants emissions of the fuel oil boiler in steady state regime are not affected. [less ▲]

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See detailDéveloppement et validation d’un modèle de radiateur de voiture
Cuevas, Cristian; Ngendakumana, Philippe ULg

Report (2006)

Detailed reference viewed: 9 (1 ULg)