Cyril Romestant

Experimental Analysis of a Capillary Pumped Loop for Terrestrial Application

This paper reports on an experimental study of a capillary pumped loop for terrestrial application (CPLTA) that has been tested using ethanol, methanol, and N-pentane as working fluids. This CPLTA, designed for integrated power electronics cooling in railways, is capable of transferring total heat power of more than 5 kWwhen filled with methanol. First, experiments carried out under transient conditions show the high stability of this device for all the conditions tested, particularly with regard to a harsh rail cycle. Second, steady-state results convincingly show that conductance of the evaporator is independent of secondary fluid temperature, but strongly dependent on the nature of the fluid and the saturation temperature at the reservoir. A theoretical analysis has been undertaken in order to establish the thermodynamic operating curves of all tests carried out in steady-state condition by calculating the pressure difference between the reservoir and the evaporator; from these curves onemay determine the evaporation temperature, as well as the conductance restricted to the single evaporator, thereby underscoring the differences between the fluids. Finally, these results confirm that methanol is the maximally performing fluid for such devices, but also that N-pentane is useful with regard to the lowest heat powers applied, due to its lower density when compared with other fluids.

Transient Modeling of a Capillary Pumped Loop for Terrestrial Applications

Improvement of a new design for a capillary pumped loop (CPL) ensuring high dissipation electronics cooling in ground transportation has been carried out over recent years. Experimental studies on the hybrid loop, which share some characteristics with the standard CPL and loop heat pipe (LHP), have underlined the sizable potential of this new system, particularly with regard to its upcoming industrial applications. In order to obtain a reliable tool for sizing and design of this CPL for terrestrial applications (CPLTA), the present transient thermohydraulic modeling has been developed. Based on the nodal method, the model’s originality consists of transcribing balance equations under electrical networks by analogy. The model’s validation is provided by experimental results from a new CPLTA bench with three parallel evaporators. Large-scale numerical evaluation of loop behavior in a gravity field with a single evaporator shall facilitate understanding of the different couplings between loop parts. In addition, modeling of a multi-evaporator loop is introduced and compared with recent experimental results.

Transient thermohydraulic modeling of two-phase fluid systems

This paper presents a transient thermohydraulic modeling, initially developed for a capillary pumped loop in gravitational applications, but also possibly suitable for all kinds of two-phase fluid systems. Using finite volumes method, it is based on Navier-Stokes equations for transcribing fluid mechanical aspects. The main feature of this 1D-model is based on a network representation by analogy with electrical. This paper also proposes a parametric study of a counterflow condenser following the sensitivity to inlet mass flow rate and cold source temperature. The comparison between modeling results and experimental data highlights a good numerical evaluation of temperatures. Furthermore, the model is able to represent a pretty good dynamic evolution of hydraulic variables.

Visualization of Flow Patterns in Closed Loop Flat Plate Pulsating Heat Pipe Acting as Hybrid Thermosyphons under Various Gravity Levels

ABSTRACT A particular flat plate pulsating heat pipe (FPPHP), filled with FC72, is tested during the 62th and 64th ESA parabolic flight campaigns under vertical orientation. The FPPHP is made of a thin copper plate, in which a curved channel disposed with 11 U-turns is milled and closed on the top face by a transparent borosilicate plate. The particular characteristics is that the equivalent hydraulic diameter of the square channel (2.5 × 2.5 mm²) is above the working fluid capillary diameter on ground, inducing a stratification of the liquid/vapor phases under ground and hyper-gravity conditions, whatever the orientation. The energy transfer mode in such conditions is represented either by pure pool boiling inside the channels almost completely filled by the liquid phase or by an annular flow pattern inside the channels mostly filled by the refrigerant vapor. Instead, during the microgravity phases, the fluid regime naturally turns into a slug-plug flow pattern. During the transition from 1.8 g to 0 g a rapid dry-out may occur in some of the channels, followed by a similarly fast reaction of liquid plugs moving towards the evaporator from the condenser zone. Such stop-and-start motion events continue during the whole microgravity period, leading to strong temperature oscillations, but also to a still acceptable thermal performance of the device.