Issamu Muraoka

Experimental and theoretical investigation of a capillary pumped loop with a porous element in the condenser

Abstract A new CPL design is investigated experimentally and theoretically. In order to create a fixed physical interface between the liquid and the vapor phases inside the loop, the conventional tube condenser is replaced by a condenser containing a porous wick structure. The idea is to have a simple, light, and reliable system directed to applications where a high heat-transport capacity over long distances is needed, but a precise temperature control of the cold plate is not required. Experimental results, under different test conditions, are presented and illustrate the overall performance of the system. A CPL mathematical model, based on the nodal method, is described and validated experimentally.

Analysis of the operational characteristics and limits of a loop heat pipe with porous element in the condenser

This paper analyzes the operational characteristics and limits of a loop heat pipe (LHP) with flat porous elements in the condenser and evaporator. A mathematical model, based on the nodal method, was developed to simulate the thermal and hydrodynamic behavior of this specific type of LHP. Previously, the model was verified and validated by experiential data [I. Muraoka, F.M. Ramos, V. Vlassov, Int. Commun. Heat Mass Transfer 25 (1998) 1085]. The dry-out failure mechanisms of this device were investigated and its operational limits identified in terms of the heat load dissipated in the evaporator and the heat sink temperature at the condenser. Three distinct operational regimes were identified and characterized, taking into account the volume of vapor in the liquid core of the evaporator and the capillary pressure limit.

Spacecraft thermal design with the Generalized Extremal Optimization Algorithm

This article describes an application of the Generalized Extremal Optimization (GEO) algorithm to the inverse design of a spacecraft thermal control system. GEO is a recently proposed global search meta-heuristic (Sousa, F.L. and Ramos, F.M., 2002, Function optimization using extremal dynamics. In: Proceedings of the 4th International Conference on Inverse Problems in Engineering (cd-rom), Rio de Janeiro, Brazil.; Sousa, F.L., Ramos, F.M., Paglione, P. and Girardi, R.M., 2003, New stochastic algorithm for design optimization. AIAA Journal, 41(9), 1808–1818.; Sousa, F.L., Ramos, F.M., Galski, R.L. and Muraoka, I., 2005, Chapter III. In: L.N. De Castro and F.J. Von Zuben (Eds) Generalized Extremal Optimization: A New Meta-heuristic Inspired by a Model of Natural Evolution, Accepted for publication in Recent Developments in Biologically Inspired Computing (Hershey, PA: Idea Group Inc.).) based on a model of natural evolution (Bak, P. and Sneppen, K., 1993, Punctuated equilibrium and criticality in a simple model of evolution. Physical Review Letters, 71(24), 4083–4086), and specially devised to be used in complex optimization problems (Sousa, F.L., Vlassov, V. and Ramos, F.M., 2002, Heat pipe design through generalized extremal optimization. In: Proceedings of the IX Brazilian Congress of Engineering and Thermal Sciences – ENCIT 2002, Caxambu, MG, Brazil.). GEO is easy to implement, has only one free parameter to adjust, does not make use of derivatives and can be applied to constrained or unconstrained problems, and to non-convex or even disjoint design spaces with any combination of continuous, discrete, or integer variables. The application reported here concerns the optimum design of a simplified configuration of the Brazilian Multi-mission Platform (in Portuguese, Plataforma Multi-missão, PMM) thermal control subsystem, comprising five radiators and one battery heater. The PMM is a multi-purpose space platform to be used in different types of missions such as Earth observation, scientific, or meteorological data collecting. The design procedure is tackled as a multiobjective optimization problem, considering two critical cases, operational hot case (HC) and cold case (CC). The results indicate the existence of non-intuitive, new and more efficient design solutions.

Stochastic spacecraft thermal design optimization with low computational cost

This paper presents a strategy for a quick determination of the optimum configuration for radiators and solar absorbers in a spacecraft thermal design, to minimize heater power consumption and maximize temperature margins. It is particularly useful when applied to multimission platforms in which the thermal design is adapted for different orbits and operational modes. A two-step approach is adopted wherein a simplified thermal model is developed to search for the optimum radiator/solar absorber areas, and then the results are implemented in a detailed thermal model to verify the temperature distribution, thereby reducing computational time, a common drawback in complex engineering optimization problems. If necessary, small adjustments are then made in the radiator/solarabsorberconfiguration.Thesearchfortheoptimumdesignisaccomplishedusingarecentlyproposed global search metaheuristic, called generalized extremal optimization. Based on a model of natural evolution, it is easy to implement and has only one free parameter to adjust, making no use of derivatives. This paper presents the strategy as applied to the thermal design of the Brazilian Multimission Platform now under development. Nomenclature Ai = area of the radiator or solar absorber of node i, m 2 a = weighting factor for heater power consumption bl = weighting factor for temperature deviation for critical case l

Numerical and experimental investigation of thermal louvers for space applications

Thermal louvers, using movable or rotating shutters over a radiating surface, have gained a wide acceptance as highly efficient devices for controlling the temperature of a spacecraft. This paper presents a detailed analysis of the performance of a rectangular thermal louver with movable blades. The radiative capacity of the louver, determined by its effective emittance, is calculated for different values of the blades opening angle. Experimental results obtained with a prototype of a spacecraft thermal louver show good agreement with the theoretical values.