International Science Index


Simulation of Ammonia-Water Two Phase Flow in Bubble Pump


The diffusion-absorption refrigeration cycle consists of a generator bubble pump, an absorber, an evaporator and a condenser, and usually operates with ammonia/water/ hydrogen or helium as the working fluid. The aim of this paper is to study the stability problem a bubble pump. In fact instability can caused a reduction of bubble pump efficiency. To achieve this goal, we have simulated the behaviour of two-phase flow in a bubble pump by using a drift flow model. Equations of a drift flow model are formulated in the transitional regime, non-adiabatic condition and thermodynamic equilibrium between the liquid and vapour phases. Equations resolution allowed to define void fraction, and liquid and vapour velocities, as well as pressure and mixing enthalpy. Ammonia-water mixing is used as working fluid, where ammonia mass fraction in the inlet is 0.6. Present simulation is conducted out for a heating flux of 2 kW/m² to 5 kW/m² and bubble pump tube length of 1 m and 2.5 mm of inner diameter. Simulation results reveal oscillations of vapour and liquid velocities along time. Oscillations decrease with time and with heat flux. For sufficient time the steady state is established, it is characterised by constant liquid velocity and void fraction values. However, vapour velocity does not have the same behaviour, it increases for steady state too. On the other hand, pressure drop oscillations are studied.

[1] S. Kakaç, L. Cao. Analysis of convective two phase flow instabilities in vertical and horizontal in-tube boiling systems, International Journal of Heat and Mass Transfer 52 (2009) 3984–3993.
[2] S. Kakaç, H. Liu, Two-phase flow dynamic instabilities in boiling systems, in: X.J. Chen, T.N. Veziroglu, C.L. Tien (Eds.), Multi-phase Flow and Heat Transfer,vol. 1, Hemisphere, Washington, DC, 1991, pp. 403–444.
[3] S. Kakaç, B. Bon, A review of two-phase flow dynamic instabilities horizontal and vertical in-tube boiling systems, Int. J. Heat Mass Transfer. Available from :<>, 2007.
[4] Zhang, L., Wu, Y., Zheng, H., Guo, J. & Chen, D. 2006. An experimental investigation on performance of bubble pump with lunate channel for absorption refrigeration system. International Journal of Refrigeration: 815-822.
[5] Vicatos, G. & Bennet, A. 2007. Multiple lift tubes boost refrigeration capacity in absorption plants. Journal of Energy in Southern Africa: 49-57.
[6] A. Benhmidene. B. Chaouachi, M. Bourouis, S. Gabsi, (2011), “Numerical prediction of flow patterns in the bubble pump”, Journal of Fluid Engineering ASME, Vol.133 (3), pp 031302 (8 pages).
[7] A. Benhmidene, B. Chaouachi, S. Gabsi, M. Bourouis, (2011), “Modelling of the heat flux received by a bubble pump of absorption- diffusion machine”, Heat Mass Transfer, vol 47, pp1341–1347.
[8] A. Benhmidene, B. Chaouachi, S. Gabsi, M. Bourouis (2016), “Experimental investigation on the flow behaviour in a bubble pump of diffusion absorption refrigeration systems” Case Studies in Thermal Engineering, Vol.8.
[9] S. Mazouz, R. Mansouri, A. Bellagi, Experimental and thermodynamic investigation of an ammonia/water diffusion absorption machine, International Journal of refrigeration, Volume 45 (2014), Pages 464–4708 3-9 1.
[10] N. Ben Ezzine, R. Garma, M. Bourouis, A. Bellagi, Experimental studies on bubble pump operated diffusion absorption machine based on light hydrocarbons for solar cooling , Renewable Energy ,Volume 35, Issue 2, February 2010, Pages 464–470.
[11] S. Kakac, B. Bon, A Review of two-phase flow dynamic instabilities in tube boiling systems, International Journal of Heat and Mass Transfer 51 (2008) 399–433.
[12] Ishii, M. Hibiki, T. Drift-flux model. In Thermo-Fluid Dynamics of Two Phase Flow (2011), pages 361–395. Springer.