Thermohydraulics of a metal foam-filled annulus M.P. Orihuela a,1 , F. Shikh Anuar b,c,1 , I. Ashtiani Abdi b,⇑,2 , M. Odabaee b,2 , K. Hooman b a Dpto. de Ingeniería Energética, Escuela Técnica Superior de Ingenieros, Universidad de Sevilla, Camino de los Descubrimientos, s/n, 41092 Sevilla, Spain b School of Mechanical and Mining Engineering, The University of Queensland, Queensland, Australia c Centre for Advanced Research on Energy (CARe), Faculty of Mechanical Engineering, Universiti Teknikal Malaysia Melaka, Melaka, Malaysia article info Article history: Received 6 May 2017 Received in revised form 27 September 2017 Accepted 2 October 2017 Keywords: Metal foam Heat exchanger Pressure drop Temperature distribution CFD Thermal entrance length abstract This paper offers numerical and experimental analysis of forced convection through an annulus filled with aluminium foam. Effects of flow rate and foam pore density on the performance of the heat exchan- ger were investigated. Specifically, 5 and 20 pore per inch (PPI) aluminium metal foams were tested at three different airflow rates; 20, 85 and 150 standard litre per minute. In parallel, the problem has been simulated numerically. Once validated against experimental data, numerical simulations were conducted to add to the level of details obtained from experiments. The thermal study was done by analysing the temperature field throughout the porous volume and determining the thermal entrance length. This parameter, the thermal entrance length, establishes a reliable design criteria for metal foam-filled heat exchangers, since it marks the length beyond which heat transfer does not significantly increase while the pressure drop keeps growing. Ó 2017 Elsevier Ltd. All rights reserved. 1. Introduction Open-cell metal foams have been investigated extensively for heat exchanger applications due to their promising properties such as lightweight, high surface area, high thermal conductivity, tortu- ous flow paths and good mechanical strength and stiffness [1–4]. Many studies have proved that the metal foams can augment the heat transfer compared to an identical heat exchanger with no foams or even different surface extension techniques [1]. Accord- ingly, a great deal of information is available in the literature addressing metal-foam filled tubes [5,6], metal-foam wrapped tubes [7–10], fully-filled channels [11–18], partially filled channels [19,20] and other constructions [21,22] in order to match different applications. Due to significant improvement in heat transfer at the expense of higher pressure drop, many studies [9,10,21] have investigated the trade-off between the heat transfer and pressure drop increase. Odabaee et al. [9] numerically investigated a metal foam-wrapped tube with different foam thickness by varying the ratio of porous medium radius and surface radius from 1.025 to 2. Their results showed that the pressure drop and the heat trans- fer rate were increasing with the foam thickness. Odabaee and Hooman [23] extended their investigation on the same samples through an optimization study based on the first and second law of thermodynamics and concluded that the metal foam heat exchangers would have 2–6 times higher performance factor than finned-tubes in the air-cooled condenser application. Chumpia and Hooman [10] experimentally studied the thermo-hydraulic of five foam wrapped heat exchangers with different thickness (5– 20 mm). They showed that an optimum thickness of metal foam that provide a similar level of pressure drop to a finned tube will have better heat transfer performances. Mao et al. [24] also proved that the foam thickness of metal foam-wrapped tube has signifi- cant effects on the pressure drop and heat transfer performances. The study also claimed that only porosity has significant influence on the form coefficient, neither the pore size nor the pore shape. However, Hu et al. [3] demonstrated that a metal foam heat exchanger exhibited higher pressure drop and heat transfer rate as compared to a fin-and-tube heat exchanger when increasing the pore density and the relative humidity of the inlet air. Jin and Leong [25] also reported that the pressure drop was increasing with the pore density based on their study on steady and oscillat- ing flows within 10, 20 and 40 PPI foams. Huisseune et al. [21] numerically designed two tube rows in a staggered tube layout inside a metal foam block which was a comparable design to a lou- vered finned heat exchanger. The study showed that the high pore density metal foam (>40 PPI) would have better performance than the finned heat exchanger and six times higher heat transfer com- pared to the bare tube. https://doi.org/10.1016/j.ijheatmasstransfer.2017.10.009 0017-9310/Ó 2017 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: i.ashtianiadbi@uq.edu.au (I. Ashtiani Abdi). 1 Contributed equally as the first authors. 2 Contributed equally as the second authors. International Journal of Heat and Mass Transfer 117 (2018) 95–106 Contents lists available at ScienceDirect International Journal of Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ijhmt