The interest in heat pipes as a capillary driven heat transfer device is based on its ability to transport thermal energy at high rates and with small temperature gradients. So the main objective of this project is to develop a European High Temperature Constant Conductance Heat Pipe (HTCCHP) for Alphabus, because the present trend is to increase the operational temperature of dissipating units and consequently, the working temperature range of heat pipe networks. Presently, with units qualified at +85Ã‚ºC, Al-NH3 constant conductances Heat Pipes are working at their limit temperature range.
The operation temperature range is specified to be between +20Ã‚ºC and +150Ã‚ºC. In this temperature range the commonly used and space-qualified material combination ammonia / aluminium cannot be applied. After a thorough trade off water/copper heat pipes are baselined. Therefore the main technical challenges are to find the best heat pipe design and to solve CTE mismatches between heat pipe and spacecraft structure materials.
An interesting possibility to produce deep and narrow grooves with high aspect ratio, which could meet the required heat transport capability, is the electroforming process. Wick designs based on this technology have the lowest weight of all designs investigated in this study. These wicks must be in any case inserted into an aluminum profile. Due to its potential with respect to performance and weight of such a sophisticated wick design, predevelopments and tests has been initiated in this contract.
Controlling high temperature units directly with High Temperature Constant Conductance Heat Pipes (HTCCHP) will allow significant mass saving (around -20% of radiating surface is foreseen).
The proposed activity was started with an extensive literature survey and trade off to identify the best heat pipe concept, relating to working fluids, container materials and potential wick structures.
Some test sample were manufactured to optimize and evaluate new manufacturing methods and processes like electroforming. A complete heat pipe assembly has been processed and filled with water for first performance testing. The main characteristics of this heat pipe are as follows:
The first very promising test results for the corrugated heat pipe for different temperatures and inclinations compared with theoretical data are shown in the following Figure. The required heat transport capability of greater or equal to 100 Wm (objective up to 200 Wm) at 120 Ã‚ºC will be exceeded by a factor of around four.