Publications

2023

Computational simulation of a vapor jet into a subcooled flow inside a capillary jet loop system operating in direct condensation mode

abstract

This work approaches numerical simulations applied for the investigation of vapor injection into a Capillary Jet Loop (CJL) system, aimed at the improvement of the injector design by investigating several parameters influencing its performance. Therefore, this paper will cover the influence of the entrainment ratio γ (ratio of the mass flow rate of the low-pressure flow – secondary flow - to the mass flow rate of the high-pressure flow - primary flow), the working fluid and the geometry on the pressure rise in the mixing region, the criterion chosen here for the injector efficiency. Considering that a full condensation is expected to occur, part of the simulation will also cover the numerical aspects related to phase-change. From Computational Fluid Dynamics (CFD) simulations, performed using the commercial software ANSYS-FLUENT 19.4, the parametric study showed a negative impact of the increasing injection angle on the pressure rise. The same negative impact was observed for the increase of the entrainment ratio. In terms of the working fluid, methanol and acetone proved to increase the pressure rise in the vapor injection region, inducing faster condensation, and consequently, affecting positively the injector efficiency.

Authors

Braga Vieira, C., Nicolle, T., Accorinti, F. de Ghelin, O. Goffaux, C. and Dupont, V.

Conference

Joint 21st IHPC and 15th IHPS

2023

Capillary Jet Loop in direct contact condensation mode used to perform ice protection function of a turboprop composite nacelle intake

abstract

In this experimental study a Capillary Jet Loop architecture (CJL-dcc) is proposed to transport the heat from a hot liquid (oil) as heat source to a composite material as coolant surface that is part of the nacelle in a turboprop transport aircraft (as used for Regional and Business Aviation). The application has dual usage, firstly ice protection in cold conditions and cooling of the oil in all conditions. The reduced scale demonstrator tested is a combination of a single capillary loop with a two-phase transport ring (TPR). The ring provides the liquid to the capillary structure and the capillary evaporator induces vapor jets thanks to four injector elements in parallel. The momentum exchange between the high velocity acetone vapor flows and the low velocity of the subcooled liquid ensures both transport and condensation functions before the connecting lines. This paper discusses the design, material and experimental performances of this demonstrator able to transfer 1.24 kW from a 90 x 90 mm² footprint heater. Two different cold sources are investigated with the same injector system and the results are discussed; a tube-in-tube ethylene-glycol water cooled (RS-0/1 demonstrator) and a carbon fiber composite panel (CFRP) with direct melting of an ice volume (RS-2C demonstrator).

Authors

Dupont, V., Accorinti, F., Henno, M. , Susana Serrano Perez, P. and Redondo Carracedo, F.

Conference

Joint 21st IHPC and 15th IHPS

2022

Flat-plate pulsating heat pipe for heat spreader for electronics with high-heat flux

abstract

A common thermal management solution for miniaturized electronic devices with high heat flux values is to integrate the heat spreader and the heat sink so that the forced or free convection is promoted. Taking advantages of thin and wickless simple structure of Pulsating Heat Pipes (PHPs), several studies proposed flat-plate PHPs for this application. In most of the PHP studies, the evaporator and the condenser are located at both ends the PHP. However, in many practical cases, the PHP configuration could be different: it could be used as to spread a centrally located heat source in a three-dimensional direction, achieving high temperature uniformity in a limited space. In the present study, in order to investigate this particular configuration with the evaporator in the centre, a flat-plate PHP is proposed for spreading heat of electronic devices with high heat flux up to 50 W/cm2 and its thermal performance experimentally investigated is shown. Methanol was charged as the working fluid. As the result of changing the filling ratio, the optimum filling ratio was estimated between 59 – 39 %. The thermal performance was evaluated with in four orientations. The thermal resistance in every orientation was less than on-half of that of the empty PHP. The results shown in this work could contribute to improve thermal management of the electronics generating high-heat flux by proposing an innovative heat spreader.

Authors

Iwata, N., Bozzoli, F., Accorinti, F., Dupont, V., de Ryckel, A.

Conference

39th International Conference on Heat and Mass Transfer

2022

A Loop Heat Pipe for Vehicle CPU Cooling: Peak Performance and Partial Flooding and Dryout Regimes

abstract

A Loop Heat Pipe (LHP) is assembled and tested for removing up to 400 W from two vehicle CPUs, while keeping their temperature under 95°C and using a 2 m-distanced, 45°C-air cooled condenser, and working fluid R1233zd(E). The capillary evaporator wick uses a liquid artery wick supplying liquid to a sawtooth copper wall evaporator. This novel sawtooth structure extends the evaporation area, spreads the liquid, and allows for the vapor escape space, while minimizing the evaporator resistance. For the application flexibility, it is preferred to place the condenser away from the CPUs. The air-cooled condenser fan-power consumption is also important, influencing the condenser thermal resistance. The loop thermal-hydraulics are analyzed (including the wick effective thermal conductivity, permeability, and maximum capillary pressure) and modeled. These include the role of the liquid accumulation on the evaporator, and the partial, local wick dryout under statistical variation in the microlayer wick thickness. The condenser thermal resistance and pressure drop, the transfer lines pressure drops, and the accumulator volume, which can dominate and limit the overall performance, are addressed in the design selection. The model predictions are compared with the performance of the fabricated LHP under variable thermal load and CPU-condenser separation distance. Good agreements are found, under partial flooding at low thermal load, under partial dryout at high thermal load, as well as under thermal loads with peak evaporator performance. Further improvements realized in the second-generation evaporator wick is expected to raise the peak performance and the maximum thermal load significantly.

Authors

Ferreira, J., Kaviany, M., Dupont, V., de Laet, O., Nicolle, T., Yen, E.

Conference

Proceedings of the ASME 2022 Summer Heat Transfer Conference

2021

Using Loop Heat Pipe solutions, and a dielectric fluid, to cool SiC MOSFET power modules for aircraft systems

abstract

In the scope of a technical exploration for an aircraft application four LHPs working with R-1233zd(E) have been designed and adapted to cool the four sides of the two specific double-sided power modules (DSPM). Four air exchangers equipped with fans reject the heat to the air. The present paper discusses the iterative thermal design methodology used to optimize the evaporator wall thickness to the location of the SiC chips on the substrate and the experimental performances of a demonstrator able to transfer up to 170W per MOSFET with an estimated heat flux of 675W/cm² at chip level.

Authors

Nicolle, T., Kapaun, F., Lasserre, P., Piaud, B., Dupont, V., Ybanez, L.

Conference

Joint 20th IHPC and 14th IHPS

2021

Performance analysis and simplified modelling of a capillary jet loop heat pipe

abstract

In this study, a prototype Capillary Jet Loop Heat Pipe has been tested to investigate its performances, and a lumped parameters simplified model has been developed to study the key parameters of the device. The tested Capillary Jet Loop is composed of an evaporator, a fluid loop with an ejector and a condenser. The working fluid used is R1233zd(e); an electric resistor of 40x40 mm2, dimensionally similar to a CPU, provides the thermal load, and a water cooling circuit removes it. An experimental investigation on the thermal behaviour has been conducted, varying the orientation, the thermal load from 40 W to 160 W, and the condenser cooling water temperature from 15 °C to 30 °C. The temperatures measured in different locations of the device have been used to estimate the equivalent thermal resistances. The results show a strong relation between performances and orientation and low dependence on thermal load and condensing temperature. The lowest equivalent thermal resistance value is obtained in the horizontal configuration with a value of 0.104 ± 0.005 K/W (CI 64%) at 80 W (5 W/cm2) while it reached the maximum value of 0.202 ± 0.002 K/W at 160 W (10 W/cm2) in vertical bottom heated orientation. The simulation includes a lumped parameter model focused on the two-phase evaporation condensation and capillary phenomena coupled with the fluid dynamics in the loop and in the ejector. Steady-state conditions are simulated. Under some simplified hypotheses, a parametric analysis was performed to investigate the influence on the thermal performances of the different construction and operative variables of the Capillary Jet Loop: loop length, tube diameter, ejector diameter, pore diameter, filling ratio, the fluid temperature. The maximum stable thermal load is calculated, and a stability map is found as a function of the fluid temperature. The matching point between the Loop and the ejector curve identifies the operating system point as a function of the studied parameters.

Authors

Araneo, L., Clavenna, R., Boubaker, R., Dupont, V.

Paper

Applied Thermal Engineering, Vol. 197

2019

New micro-evaporator for electronics cooling

abstract

Authors

Fourgeaud, L., Dupont, V., Mari, R., Figus, C.

Conference

14th European Advanced Technology Workshop on Micropackaging and Thermal management

2018

Capillary Jet Loop

abstract

In this study an innovative two-phase closed loop concept is proposed. This hybrid system is a combination of one or more local capillary loops with a two-phase ring (TPR). The ring provides the liquid to the capillary structure and each evaporator induces a vapor jet thanks to an injector element. The momentum exchange between the high velocity vapor flow and the low velocity single-phase, or two-phase, flow inside the ring insures the transport function. The paper discusses the governing equations of such a system and the experimental performances of a demonstrator able to transfer 470W from a 40 x 40 mm² footprint heater i.e. 29 W/cm².

Authors

Dupont, V., Paran, B., Van Oost, S. and Billet, C.

Conference

Joint 19th IHPC and 13th IHPS

2018

Multi-source miniaturized Loop Heat Pipes for electronics cooling

abstract

We present a novel architecture of a Loop Heat Pipe in which three auxiliary smooth-pipes evaporators have been added. Auxiliary evaporators feature the hot points of an electronic chip. Such a system would allow cooling down several hot spots by using a single-LHP and is of a broad interest for electronics cooling applications. This system preserves the main advantages of multi-capillary evaporators LHPs while avoiding numerous of their downsides. Our breadboard has the following characteristics: out of the main capillary evaporator, the LHP line crosses a first condenser, the three auxiliary evaporators-referred as "micro-exchangers", a second condenser, and then returns to the evaporator. The main capillary evaporator drives the mass flow rate while auxiliary evaporators are only dedicated to heat transfer. The working fluid is R245fa. Experimental investigations allow characterizing the loop behavior and the operating limits in order to deduce the operating conditions. Measurements agree with our multi-evaporators LHP model. We also point out that, before the onset of nucleate boiling within micro-exchangers, the liquid superheating may achieve 40 °C. In some cases, however, the ONB occurs immediately after applying the power to micro-exchangers.

Authors

Fourgeaud, L., Mari, R., Figus, C., Dupont, V.

Conference

32nd European Space Thermal Engineering Workshop

2018

Experimental investigations of a Multi-Source Loop Heat Pipe for electronics cooling

abstract

We present a novel architecture of a Loop Heat Pipe in which three auxiliary smooth-pipes evaporators have been added. Auxiliary evaporators feature the hot points of an electronic chip. Such a system would allow cooling down several hot spots by using a single-LHP and is of a broad interest for electronics cooling applications. This system preserves the main advantages of multi-capillary evaporators LHPs while avoiding numerous of their downsides. Our breadboard has the following characteristics: out of the main capillary evaporator, the LHP line crosses a first condenser, the three auxiliary evaporators – referred as “micro-exchangers”, a second condenser, and then returns to the evaporator. The main capillary evaporator drives the mass flow rate while auxiliary evaporators are only dedicated to heat transfer. The working fluid is R245fa. Experimental investigations allow characterizing the loop behavior and the operating limits in order to deduce the operating conditions. Measurements agree with our multi-evaporators LHP model. We also point out that, before the onset of nucleate boiling within micro-exchangers, the liquid superheating may achieve 40 °C. In some cases, however, the ONB occurs immediately after applying the power to micro-exchangers.

Authors

Fourgeaud, L., Mari, R., Dupont, V., and Figus, C.

Conference

Joint 19th IHPC and 13th IHPS

2018

Experimental investigation of a capillary-assisted high performance evaporator

abstract

A particular architecture for a miniaturized evaporator is proposed in which liquid is spread on the heat source using a thin capillary structure connected to two manifolds. The vapor produced by the heat source is extracted from the device using a separate outlet. A prototype has been designed, manufactured and integrated in a mechanically pumped loop in order to evaluate the evaporator efficiency in terms of heat transfer coefficient and induced pressure drop. In this paper, a capillary structure consisting in parallel rectangular micro-grooves is investigated with HFE7000 used as the working fluid. Results show that the evaporator is able to extract heat flux of the order of 10 W:cm^2 with heat transfer coefficients close to 10^4 W.m^-2.K^-1 while inducing pressure losses below a few hundred Pascal. Direct visualizations of the ow in the capillary structure allowed a precise characterization of the evaporator functioning mode, in particular the existence of two distinct two-phase flow regimes depending on the flooding of the capillary structure: nucleate boiling and liquid films evaporation. In order to predict the occurrence of these operating modes, a hydraulic model of the evaporator assembly has been developed and validated thanks to dedicated experimental campaigns. In particular, this model is able to predict the separation between the nucleate boiling and evaporation mode and highlights the fact that the capillary limit is not the main restricting factor in terms of the device maximum manageable heat flux.

Authors

Marie, A., Miscevic, M., Lavieille, P., Lachassagne, L., Dupont, V.

Conference

Joint 19th IHPC and 13th IHPS

2018

Systèmes diphasiques CALYOS, développements récents

abstract

Authors

Dupont, V.

Paper

Systèmes diphasiques pour le contrôle thermique de l’électronique de puissance

2017

Temperature Swing Issue, How a Passive Two-Phase Cooling Loop Can Improve the Power Electronic Lifetime

abstract

Capillary Loops (CPL or LHP) can be used for passive cooling of high power electronics and are characterized by a variable heat transfer coefficient as a function of power i.e. if no power is applied no heat is transferred. This unique behavior associated with cold plate thermal inertia can be used to smooth the virtual junction cycling amplitude. The present paper describes the power duty cycle conditions and capillary evaporator characteristics (thermal inertia, heat transfer coefficient – HTC –, etc.) that permit to increase the power module lifetime compared with the active standard liquid cooling solutions.

Authors

Dupont, V., Nicolle, T., and Billet, C.

Conference

Proc. PCIM

2017

Etude experimentale de la condensation convective a vitesse massique interḿediaire en tube horizontal de section circulaire

abstract

Authors

El Achkar, G., Queekers, P., Ioro C.S., Rioboo, R. Dupont, V., Dubois, F

Conference

25ème Congrès Français de Thermique

2016

Capillary thermosyphon loop for high power electronic cooling by natural convection

abstract

The present paper describes an innovative coupling between a capillary loop system and a two-phase loop thermosiphon. The main benefit of this innovative configuration are to suppress the reservoir of the capillary side and allow to place the heat load anywhere on the complete height of the thermosiphon without significant change in the overall performances. The “double loop” concept has been validated by test with two demonstrators, one with liquid cooling (water) and the other with natural convection (air), with a total system power up to 3.2 kW (heat flux ranging from 5 to 35 W/cm²) and a fluid saturation temperature ranging between 36°C to 103°C. Full power startup capabilities has also be checked.

Authors

Dupont, V., Nicolle, T., and Billet, C.

Conference

Joint 18th IHPC and 12th IHPS

2016

Experimental investigation on condensation flow regimes, heat transfer and pressure drop in horizontal circular cross-section channel

abstract

Authors

El Achkar, G., Glushchuk, A., Chikov, S., Queekers, P., Ioro, C.S., Rioboo, R. Dupont, V., Dubois, F.

Conference

11th International Conference on Two-Phase Systems for Space and Ground Applications

2016

High Performances Passive Two-Phase Loops for Power Electronics Cooling

abstract

Capillary Loops (CPL or LHP) can be used for passive cooling of high power electronics. The present paper describes the recent advances in the field of high heat flux evaporator technology (up to 100 W/cm²) applied to IGBT modules cooling that dissipate several kilowatts Several application cases permit to demonstrate the benefits of such a passive system on existing and competing cooling systems in terms of junction temperature and life time.

Authors

Dupont, V., Billet, C., and Nicolle, T.

Conference

Proceedings of PCIM

2015

Performance Passive Two-Phase Cooling systems

abstract

Authors

Dupont, V.

Conference

ECPE Workshop, Advances in Thermal Materials and Systems for Electronics

2015

Thermal Performances of a fully passive capillary pumped loop with heat flux up to 90 W/cm² at evaporator

abstract

Authors

Dupont, V.

Conference

10th European Advanced Technology Workshop on Micropackaging and Thermal management

2013

Railways qualification tests of Capillary Pumped Loop on a train

abstract

Authors

Dupont, V., Van Oost, S., Barremaecker, L, S. Nicolau.

Conference

17th IHPC

2013

Experimental investigations of a CPL pressurized with NCG inside a centrifuge up to 10g

abstract

Capillary Pumped Loop can be used for cooling of high power electronics but must be pressurized in order to operate at low temperature. The present paper describes a new fully passive method (mechanical and electrical) to pressurize instantly the CPL. The pressurization with a non-condensable gas (NCG) located at reservoir level has been successfully tested with ICS-1 demonstrator. ICS-1 is a CPL with two flat evaporators in parallel and an air exchanger that use methanol as working fluid with a 6 microns nickel wick. The power transferred is up to 10 kW at 5g in a centrifuge. The investigated heat flux ranges from 4 to 37 W/cm². Up to 28 start-up at 8kW (30W/cm²) and acceleration cycles from 1.1g to 10g at 2kW are also presented.

Authors

Dupont, V., J.C. Legros, Van Oost, S., Barremaecker, L.

Conference

Proceedings of the 17th IHPC

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