Jean-Louis Joly

Spatial patterns in ant colonies

The origins of large-scale spatial patterns in biology have been an important source of theoretical speculation since the pioneering work by Turing (1952) on the chemical basis of morphogenesis. Knowing how these patterns emerge and their functional role is important to our understanding of the evolution of biocomplexity and the role played by self organization. However, so far, conclusive evidence for local activation–long-range inhibition mechanisms in real biological systems has been elusive. Here a well-defined experimental and theoretical analysis of the pattern formation dynamics exhibited by clustering behavior in ant colonies is presented. These experiments and a simple mathematical model show that these colonies do indeed use this type of mechanism. All microscopic variables have been measured and provide the first evidence, to our knowledge, for this type of self-organized behavior in complex biological systems, supporting early conjectures about its role in the organization of insect societies.

An experimental and theoretical investigation of the transient behavior of a two-phase closed thermosyphon

This paper presents an experimental and theoretical investigation of the two-phase closed thermosyphon (TPCT) behavior in transient regimes. Experimental results show two kinds of TPCT response. We focus on regular variations of operating system variables, where a mathematical model has been developed in order to obtain an analytical expression of the system response time. The dependence of this response time according to the various parameters is linked to geometry and heat transfer laws. The model can be considered as a simple and efficient tool for designing TPCTs in both transient and steady regimes.

Transient Modeling of Loop Heat Pipes for the Oscillating Behavior Study

A transient overall model has been developed to predict the thermal and hydrodynamic behavior of a standard loop heat pipe. The model of the loop has been divided into subsystems, for which transient mass, energy, or momentum conservation laws have been developed. The comparison of the calculation and experimental results for a transient test allows one to validate the proposed model. Then, the model is used to study the development mechanisms of an oscillating behavior during the loop heat pipe operation. Two different patterns of temperature fluctuation have been highlighted by modifying the loop heat pipe external conditions (heat load, sink temperature, ambient heat exchange with the liquid line). The characteristics of these oscillations are then compared quantitatively to available experimental tests: these comparisons highlight the ability of the model to accurately predict the frequencies and amplitudes as well as how they are affected by the design and operational parameters.

Complete Convective Condensation Inside Small Diameter Horizontal Tubes

An experimental study of complete convective condensation inside narrow channels is presented in this paper. Two-phase flows patterns and their transition (annular, annular-wavy, slug and bubbly flow) are visualized for the two tube diameters under study. A significant difference is observed for the two sizes of tube. Experimental results of the bubble radius decrease are then determined and compared to a model of bubble collapse in a subcooled and infinite liquid.Copyright

Modèle d'évaporateur d'une boucle fluide diphasique à pompage capillaire

Abstract Understanding the behaviour of such a complex and strongly coupled system as a capillary pumped loop (CPL) requires a modelling process involving physical study, experiments, numerical simulations and coupling analysis. In this paper, a transitory model of the vaporisation process at the wick outer surface of a CPL is presented. Energy balance, thermodynamical phase change and mechanical equilibrium at the meniscus are taken into account. In order to study the whole dynamical behaviour of the CPL and compare with experimental data, simple models of the other parts of the CPL are performed : so, the vapor pipe, the condensor and the control reservoir are modelled by a steady description. The experimental data exhibit an oscillatory behaviour, for applied steps of heat flux at the evaporator, or near the start-up. The simulation results show a dynamical behaviour compatible with that observed on the prototype, and point out that the evaporator model is intrinsically stable.