The first ammonia loop heat pipe: Long-life operation test

An extensive development of two-phase thermal control systems based on two- and multi-phase devices (standard heat pipes, loop heat pipes, heat switches, etc.) offers a potential to assume an increasingly important position in the instrumental thermal control for a number of space and earth applications. However, experimental data regarding long-life testing for such systems is insufficient. The first ammonia loop heat pipe (LHP) was developed in 1976 in the Ural Polytechnic Institute under supervision of Prof. Gerasimov, Iu. F. (1921-2001) (Kiseev, 1977; Gerasimov et al., 1981; Maydanik, 2005)[1-3]. This paper features its long-life test, covering 41 years with varying operation times. The life test consists of two parts: permanent and periodic LHP operation (approx. 5000 h) and LHP stand-by storage (approx. 152,600 h). Experimental investigations were performed using the developed loop heat pipe based on composite nickel wick with effective pumping pores of 0.5-10 mu m in radius and 1 x 10(-14) m(2) to 4 x 10(-12) m(2) in permeability. We have provided experimental data demonstrating the impact of orientation, varying heat load and temperature on the LHP operation. In addition, a qualitative and quantitative chemical element analysis of the distilled water in a loop heat pipe without capillary structure (loop thermosyphon) was performed before and after its long-term operation (one year) to identify any possible interaction between the working fluid and the pipe materials. (C) 2017 Elsevier Ltd. All rights reserved.