Two-phase thermosyphon loop for cooling outdoor telecommunication equipments Ahmadou Samba a , Hasna Louahlia-Gualous a, * , Stéphane Le Masson b , David Nörterhäuser b a Université de Caen Basse Normandie/LUSAC, 120 rue de l’exode, 50000 Saint Lô, France b France Télécom, Orange Labs, 2 av Pierre Marzin, 22300 Lannion, France highlights < Passive loop is developed for cooling telecommunication equipment. < Optimal filling ratio determined from the experimental results, is about 9.2%. < Effects of power input and filling ratio on operating temperature are investigated. < The power of telecommunication equipment is increased from 250 to 600 W using thermosyphon loop. article info Article history: Received 8 December 2011 Accepted 15 May 2012 Available online 23 May 2012 Keywords: Thermosyphon loop Two-phase flow Heat transfer Passive cooling Evaporation Condenser Thermal resistance Fill ratio abstract Development of high bit rate services requires extension of the telecom network and then the power inside the France Telecom telecommunication outdoor cabinets. Traditional cooling systems through air forced convection become inefficient for high power supply. For this reason, thermosyphon loop is developed for cooling telecommunication equipments in the outdoor cabinet in order to keep equipments temperature below the operating temperature defined by European Telecommunication Standard Institute (ETSI). In this paper, experimental investigations using a France Telecom telecom- munication outdoor cabinet fitted with thermosyphon loop are presented. Transient and steady states analysis of the thermosyphon loop efficiency, the temperatures distributions, the thermal resistance, and mass flow rate and heat losses by convection in the walls of the cabinet as a function of heat load are studied. The n-pentane is used as the working fluid. Moreover, different working fluid filling ratios are tested and the results show that the optimal filling ratio is about 9.2%. This value corresponds to the minimum of operating temperature and also the minimum of system thermal resistance. In order to meet the ETSI norm, the traditional cooling system (air convection) currently used by France Telecom and the thermosyphon loop cooling system are compared. The results show that the maximum heat load of the telecommunication equipment obtained with the thermosyphon loop cooling system is twice as important than that given by, the traditional cooling system. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Recent significant improvement in the microelectronic devices performance requires development of very efficient cooling systems. Forced air convection has not achieved the satisfactory results for cooling systems with high heat flux. Other cooling technology must be developed for thermal control of high heat sources. Cooling systems using phase change heat transfer are the promising ways because of the latent heat transfer of working fluid is used for removing heat from devices. As known, the phase change cooling system allows high heat transfer with a very low mass flow rate of working fluid and slight temperature gradient. Additionally, due to their ability to improve the system energy efficiency, mini-channels and micro-channels are considered as the appropriate options for reducing the amount of working fluid and also greenhouse gas emissions. The process of phase change combined with a miniaturization of the channel hydraulic diameter offers a significant enhancement of heat transfer and of compactness of the cooling system. In this way, closed two-phase loops are the attractive cooling systems using two heat sources where heat is transferred from the hot source to the cold source separated by a long distance. The hot source (evaporator) is a heat exchanger where the working fluid changes * Corresponding author. Tel.: þ33 2 33 77 5518. E-mail address: hasna.louahlia@unicaen.fr (H. Louahlia-Gualous). Contents lists available at SciVerse ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng 1359-4311/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.applthermaleng.2012.05.023 Applied Thermal Engineering 50 (2013) 1351e1360