Thermal Architecture

G. Medina Tanco, F. Trillaud, J. Evrard,

Main objective

to show that, from an extreme cold case to an extreme hot case, a suitable mechanical architecture, can comply with the thermal requirements of the instrument : -30°C / +50°C required for the electronic.

Results of this analysis are an input for the thermo-mechanical analysis performed by IRAP, in order to demonstrate that the safety requirement of “no falling parts” is fulfilled in any case for the instrument

The instrument: main elements to model

Styrofoam cover(flotation buffle)

Thermal controlBoyance & thermal control

Thermal modelling

Thermal environment of a stratospheric balloon is highly variable:

•Seasonal changes •Latitudinal changes•Presence of clouds under the instrument•Etc.

Two extreme cases:

- COLD CASE: coldest conditions to be encountered at the Kiruna launching site, with a ground temperature of -30˚C, a ceiling temperature of -100˚C and a minimum IR flux of 70 W/m2. - HOT CASE: hottest conditions encountered at Alice Springs, with ground and ceiling temperatures of 10˚C and 0˚C respectively and a maximum IR flux of 340 W/m2.

Thermal modelling: numerical model

A detailed thermal numerical model, based on a somehow simplified model of the mechanical architecture, has been achieved in a close collaboration between UNAM-México and CNES.

The model has been developed in: FEMAP 10.1.1

It includes:

•internal and external convection, •internal and external radiation, •heat dissipation of the equipment•conduction and thermal contacts between parts

Thermal modelling: numerical model - parameters

Thermal modelling: numerical model - grid

Global view of the model (grid) of two versions of the mechanical structure: (i) Left: upper plane completely covered by Styrofoam, =1, and (ii) Right, Styrofoam with a window for increased radiation, <1. The three lenses and part of the electronic shelf inside the Instrument Booth can also be seen in the left model.

Detail of the parts as they are included in the thermal numerical model inside the Instrument Boot, including the Styrofoam outer layer and lenses L2 and L3.

Thermal modelling: numerical model – grid / internal detail

Thermal modelling: numerical model – results #1

COLD case for a Styrofoam covering fraction ALU=0.9 of the whole Styrofoam upper surface (i.e, =0.75 in the analytical model)

for the COLD case, the thermal requirement can be met even without problems

Thermal modelling: numerical model – results #2

HOT case for a Styrofoam covering fraction ALU=0.9 of the whole Styrofoam upper surface (i.e, =0.75 in the analytical model)

The HOT case, requires more fine-tunning.

The two important parameters are Styrofoam thickness and covering factor . The Styrofoam thickness have been fixed here to 250 mm in order to improve buoyance of the gondola. With the Styrofoam in its present configuration the PDM is too hot inside. Nevertheless, a suitable range of temperatures can be found for both PDM and DP by playing with the thickness of the Styrofoam and the covering factor

• The thermal studies demonstrate that the mechanical design is able to accommodate the worst cold and hot extreme environmental conditions.

• That is, the design is adequate whatever the launch conditions.

• The tuning of design parameters, such as Styrofoam thickness and upper window size for the hot case in particular, will be done when the environmental conditions are be clearly known (first semester 2013), and after that for each particular flight.

• Furthermore, this model can also be used later to find an optimized configuration in case of long duration flight

Conclusions

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