International Journal of Heat and Fluid Flow 58 (2016) 1–10 Contents lists available at ScienceDirect International Journal of Heat and Fluid Flow journal homepage: www.elsevier.com/locate/ijheatfuidfow Subatmospheric pressure boiling on a single nucleation site in narrow vertical spaces Florine Giraud a,b , Romuald Rullière a,∗ , Cyril Toublanc b , Marc Clausse a , Jocelyn Bonjour a a CETHIL UMR5008, Université de Lyon, CNRS, INSA-Lyon, Univ. Lyon 1, F-69621, Villeurbanne, France b Laboratoire de chimie moléculaire, génie des procédés chimiques et énergétiques (CMGPCE – EA 7341), CNAM, rue Saint-Martin, 75141, Paris Cedex 03, France article info Article history: Received 21 May 2015 Revised 9 October 2015 Accepted 3 December 2015 Keywords: Water pool boiling Subatmospheric pressure Narrow vertical space abstract Compact evaporators like plate heat exchangers can play a significant role in reducing the investment cost of low cooling power sorption systems. If water is used as refrigerant, their design remains mainly empirical. The objective of this paper is thus to investigate the specific characteristics of water pool boiling in narrow channel at subatmospheric pressure in order to acquire the fundamental knowledge needed to improve the design of compact evaporators in these sorption systems. An experimental test setup was thus designed and built to study water pool boiling in narrow channel at subatmospheric pressure (from 5 to 1.2 kPa) on a vertical heated copper disk. The influence of the thickness of the narrow channel and of the pressure on the heat transfer is discussed. As the pressure and the channel thickness decrease the occurrence of a specific subatmospheric pool boiling regime is observed, degrading heat transfer coefficient. Nevertheless, the general trends of evolution are in agreement with those generally observed in the literature: heat transfer is enhanced as the thickness of the narrow channel decreases but, depending on the pressure, decreasing too much the channel thickness could lead to a deterioration of the heat transfer coefficient. A particle image velocity (PIV) device was implemented to the experimental setup in order to highlight the effect of the wake-induced flow on the heat transfer. © 2015 Elsevier Inc. All rights reserved. 1. Introduction Compactness and cost are known to be the two main limitations for the development of efficient small cooling sorption systems. As the evaporator is one of the components which need to be improved, the implementation of compact heat exchanger is a key factor to allow the development of such systems. But, work- ing with water as refrigerant at such low pressure range (around 1 kPa for sorption systems used for air-conditioning applications such as LiBr/H 2 O absorption or, silicagel/H 2 O, zeolite/H 2 O adsorp- tion systems) requires a good understanding of the phenomena occurring inside the evaporator. This knowledge is all the more required as most of these phenomena limit the performance of the heat exchanger (presence of bubbles of several centimeters drying out the heat exchange area, low density of the vapour phase conducting to high velocities, onset of failure due to the influence of the hydrostatic pressure on the saturation temperature, etc.). Clausse et al. (2011) studied experimentally the feasibility to use plate heat exchangers in adsorption systems. They noticed that a too high secondary fluid temperature results in performance degra- ∗ Corresponding author. Tel.: +33472436305. E-mail address: romuald.rulliere@insa-lyon.fr (R. Rullière). dation. They explained that this might be due to a too high wall superheat resulting in a partial dry-out of the wall. Furthermore, they noticed the existence of an optimal evaporator filling for the achievable cooling power. Toublanc et al. (2014) visualized boiling regimes occurring in the channel of a single plate evaporator of dimension similar to the plate heat exchanger used by Clausse et al. (2011). They observed the occurrence of different boiling and evaporation flow regimes. Like Chang et al. (2012), they noticed that the evaporation flow regime is due to the consequence of the periodical growth of the bubbles: when the bubble deformed by the channel thickness surges out of the liquid, the liquid film that encapsulates the bubble is spread onto the evaporator wall above the liquid level. The splashed liquid droplets evolve into a liquid film above the newly formed liquid level. The evaporation process then immediately takes place. The presence of this first bubble thus seems to be necessary to initiate the heat transfer process and to avoid failure. However, although boiling under various conditions has been studied intensively in the last 3 decades, knowledge about water behavior in such conditions is scarce. This holds especially true when regarding boiling in narrow channels since, to the authors’ knowl- edge, no previous fundamental study was carried out both in narrow space and at subatmospheric pressure despite the fact that heat transfer mechanisms are different in confined space with respect to heat transfer mechanisms in free boiling. The few results obtained http://dx.doi.org/10.1016/j.ijheatfluidflow.2015.12.002 S0142-727X(15)00152-6/© 2015 Elsevier Inc. All rights reserved.