Isabel Pérez-Grande

Optimization of a commercial aircraft environmental control system

In this work, two optimization criteria, minimum weight and minimum entropy generation are simultaneously applied to deduce the main geometric characteristics of the two finned cross-flow heat exchangers that the environmental control system (ECS) of commercial aircraft normally incorporate. The performance of this system, described and modelled in this paper, is optimized as a whole instead of considering the optimal operation of isolated devices. The ECS is based on Brayton inverse cycle, where two air streams are involved, one to be conditioned or the main stream and a coolant one. The whole evolution of the two streams is analyzed. The main stream is studied starting from ambient conditions, before entering the aircraft engine, following with the bleed process until the turbine exit where the required temperature and pressure conditions are achieved. The coolant ram air stream is also considered from ambient conditions to the nozzle exit from where it is rejected. The heat exchanger surfaces have been selected using a compactness criterion but taking into account that compactness increases pressure losses. Once the parameters and variables are identified, the optimization task would lead to an optimum geometry by means of a trade-off solution. The numerical results found in this case illustrate the adequacy of this kind of optimization to study complex thermal systems.

Spacecraft thermal control

The space mission Space environment Keplerian orbits Conductive heat transfer Thermal radiation heat transfer Thermal control surfaces Insulation systems Radiators Louvers Mechanical interfaces Heat pipes Phase change capacitors Heaters Pumped fluid loops Thermoelectric cooling Cryogenic systems Thermal protection systems Thermal control design Thermal mathematical models Thermal control testing Conclusion.

NOMAD spectrometer on the ExoMars trace gas orbiter mission: part 1—design, manufacturing and testing of the infrared channels

NOMAD is a spectrometer suite on board ESAs ExoMars trace gas orbiter due for launch in January 2016. NOMAD consists of two infrared channels and one ultraviolet and visible channel allowing the instrument to perform observations quasi-constantly, by taking nadir measurements at dayside and nightside, and during solar occultations. In this paper, the design, manufacturing, and testing of the two infrared channels are described. We focus upon the optical working principle in these channels, where an echelle grating, used as a diffractive element, is combined with an acousto-optical tunable filter, used as a diffraction order sorter.

A global thermal analysis of multizone resistance furnaces with specular and diffuse samples

Abstract The heating process in multizone resistance furnaces, as applied to floating-zone crystal growth, is analyzed. A global model is formulated, where the temperature fields in the sample, the furnace and the insulation are coupled; the input thermal data is the electric power supplied to the heaters; the thermal conductivity of the insulation is modeled with the aid of experimental results. The radiation heat exchange between the sample and the furnace is formulated analytically, taking into account specular reflections on the sample; in general, for solid samples the reflectance is both diffuse and specular, and for some melts it is mostly specular. This behavior is modeled through the exchange view factors, which depend on whether the sample is solid or liquid, and, therefore, they are not known a priori. The effect of this specular behavior on the temperature field is analyzed, and compared with the case of diffuse samples; this effect is shown to be important in the analysis of the melt zone, for instance, differences of the order of 100% are obtained in parameters like the melt length or the maximum temperature difference in the melt when specular reflections are neglected. The model is used to simulate the heating process in the floating-zone technique in microgravity conditions; parameters like the Marangoni number or the temperature gradient at the melt–crystal interface are estimated. The model is validated comparing with experimental data.

Gas turbine turbocharged by a steam turbine: a gas turbine solution increasing combined power plant efficiency and power

A new design of a combined-cycle gas turbine power plant CCGT with sequential combustion that increases efficiency and power output in relation to conventional CCGT plants is studied. The innovative proposal consists fundamentally in using all the power of the steam turbine to turbocharge the gas turbine. A computer program has been developed to carry out calculations and to evaluate performance over a wide range of operating conditions. The obtained results are compared with those of combined cycles where the gas turbines are not turbocharged and the gas and the steam turbines have independent power exits; the advantages of the new design are stated.

Pumped fluid loops

The aim of this chapter is to introduce pumped fluid loops, explaining their application in the field of high heat loads, their basic physical principles, and their main types (single-phase, and two-phase flow fluid loops). Both types of fluid loops are outlined, including their main characteristics, the working fluids employed, and their main components (heat exchangers, pumps, additives to reduce pressure loads, evaporators, accumulators). Finally, the description of their operation is provided, as well as flight experiences.

Nonlinear analysis of a simple model of temperature evolution in a satellite

We analyze a simple model of the heat transfer to and from a small satellite orbiting round a solar system planet. Our approach considers the satellite isothermal, with external heat input from the environment and from internal energy dissipation, and output to the environment as black-body radiation. The resulting nonlinear ordinary differential equation for the satellite’s temperature is analyzed by qualitative, perturbation and numerical methods, which prove that the temperature approaches a periodic pattern (attracting limit cycle). This approach can occur in two ways, according to the values of the parameters: (i) a slow decay towards the limit cycle over a time longer than the period, or (ii) a fast decay towards the limit cycle over a time shorter than the period. In the first case, an exactly soluble average equation is valid. We discuss the consequences of our model for the thermal stability of satellites.

NOMAD spectrometer on the ExoMars trace gas orbiter mission: part 2-design, manufacturing, and testing of the ultraviolet and visible channel

NOMAD is a spectrometer suite on board the ESA/Roscosmos ExoMars Trace Gas Orbiter, which launched in March 2016. NOMAD consists of two infrared channels and one ultraviolet and visible channel, allowing the instrument to perform observations quasi-constantly, by taking nadir measurements at the day- and night-side, and during solar occultations. Here, in part 2 of a linked study, we describe the design, manufacturing, and testing of the ultraviolet and visible spectrometer channel called UVIS. We focus upon the optical design and working principle where two telescopes are coupled to a single grating spectrometer using a selector mechanism.

Surface tension and microgravity

The behaviour of confined liquids on board an orbiting spacecraft is mainly driven by surface tension phenomena, which cause an apparently anomalous response of the liquid when compared with the behaviour that can be observed on an Earth laboratory provided that the amount of liquid is high enough. The reason is that in an orbiting spacecraft the different inertial forces acting on the bulk of the liquid are almost zero, causing thus capillary forces to be the dominant ones. Of course, since gravity forces are proportional to the liquid volume, whereas surface tension forces are proportional to the liquid surface, there are situations on Earth where capillarity can be the dominant effect, as it happens when very small volume liquid samples are considered. However, work with small size samples may require the use of sophisticated optical devices. Leaving aside the neutral buoyancy technique, a way of handling large liquid interfaces is by using drop towers, where the sample falls subjected to the action of Earth’s gravity. This approach is suitable when the characteristic time of the problem under consideration is much smaller than the drop time. In this work the transformation of an out-of-use chimney into a drop tower is presented. Because of the miniaturization, hardiness and low cost of current electronic devices, a drop tower can be used as an inexpensive tool for undergraduate students to experimentally analyse a large variety of surface tension driven phenomena.

Comparative study of the effect of several trains on the rotation motion of ballast stones

The ballast pick-up (or ballast train-induced-wind erosion (BTE)) phenomenon is a limiting factor for the maximum allowed operational train speed. The determination of the conditions for the initiation of the motion of the ballast stones due to the wind gust created by high-speed trains is critical to predict the start of ballast pick-up because, once the motion is initiated, a saltation-like chain reaction can take place. The aim of this paper is to present a model to evaluate the effect of a random aerodynamic impulse on stone motion initiation, and an experimental study performed to check the capability of the proposed model to classify trains by their effect on the ballast due to the flow generated by the trains. A measurement study has been performed at kp 69 + 500 on the Madrid – Barcelona High Speed Line. The obtained results show the feasibility of the proposed method, and contribute to a technique for BTE characterization, which can be relevant for the development of train interoperability standards.