Laminar flow in chevron-type plate heat exchangers: CFD analysis of tortuosity, shape factor and friction factor

Abstract

Laminar or low Reynolds number flows are usually obtained when liquid foods with high viscosity are processed in plate heat exchangers (PHEs). The tortuosity coefficient is a key parameter used by PHEs manufacturers to estimate Fanning friction factors and convective heat transfer coefficients. Using the finite-element computational fluid dynamics program POLYFLOW ® , fully developed laminar flows in double-sine chevrontype PHEs passages are analysed in this work. The corrugation angle and channel aspect ratio of the passages vary in a broad range, PHEs with common area enlargement factors and with high area density being studied. The tortuosity coefficient and the coefficient K (Kozeny's coefficient in granular beds) from the friction factor correlations increase with the increase of the channels aspect ratio and the decrease of the chevron angle. The shape factor from the PHEs passages also increases with the decrease of the chevron angle and is weakly influenced by the channel aspect ratio. In this paper, relations to predict the tortuosity coefficient and shape factor are proposed, the coefficient K being predicted resorting to the tortuosity coefficient and shape factor. The coefficient K compares well with literature data in the region of common chevron angles, channels aspect ratio and area enlargement factor.

Friction factors of power-law fluids in chevron-type plate heat exchangers

“…(12)) for elaborate calculations. Fernandes et al (2007) found a good agreement between their numerical data (Eq. (10)) and the data from Wanniarachchi et al…”

“…1) developed by Fernandes et al (2007) differs from the unitary cell used by Ciofalo et al (1996) and Mehrabian and Poulter (2000) since it includes five contact points (four in the corners and one in the centre of the cell) instead of four (all in the corners). Fernandes et al (2007) established the referred unitary cell after observing the periodicity of the flow during the cooling of stirred yoghurt in half of a chevron-type PHE passage (Fernandes et al, 2005(Fernandes et al, , 2006Maia et al, 2007). In both approaches, the numerical results compared well with experimental data (Afonso et al, 2003;Wanniarachchi et al, 1995) from the literature; but the former approach (unitary cells) provides lower CPU times.…”

“…The simulations were performed using channels containing seven consecutive unitary cells (Ciofalo et al, 1996;Mehrabian and Poulter, 2000;Fernandes et al, 2007), since fully developed flows were achieved in the fifth or sixth consecutive cell, as in past works (Ciofalo et al, 1996;Fernandes et al, 2007).…”

“…The different channels had an inter-plates distance of 2.5 mm and the corrugation angle varied between 31°and 60°(31°, 35°, 40°, 45°, 50°, 55°and 60°) since b is typically located between 22°and 65° (Palm and Claesson, 2006;Ayub, 2003;Kakaç and Liu, 2002). The geometrical properties of the studied plates are presented in Table 1, this geometric properties being different from previous ones (Fernandes et al, 2005(Fernandes et al, , 2006Fernandes et al, 2007). A generalised Reynolds number is developed by extending an empirical methodology (Eq.…”

“…It is important to note that this methodology, developed under isothermal conditions, can be used successfully in non-isothermal situations (Delplace and Leuliet, 1995;Leuliet et al, 1987Leuliet et al, , 1988. Fernandes et al (2007) studied the relation between the geometrical properties of the chevron-type PHEs plates and the coefficient K, for Newtonian flows under laminar regime and developed the relation:…”