Heat transfer and rheology of stirred yoghurt during cooling in plate heat exchangers

Abstract

In the present work an experimental investigation was conducted to obtain a correlation for the determination of convective heat transfer coefficients of stirred yoghurt in a plate heat exchanger. A rheological study was carried out in order to characterise the stirred yoghurt flow behaviour, evaluating its dependency both on shear rate and temperature. A shift in the temperature dependency was evidenced at 25°C. It is also shown that the material shows a complex flow behaviour, changing from a Bingham fluid to a power-law fluid at shear stresses in excess of approximately 6.7 Pa. As regards the heat transfer behaviour of the non-Newtonian stirred yoghurt a correlation for the convective heat transfer coefficient was obtained that reveals the large effects of the thermal entry length due to the high Prandtl numbers and to the short length of the plate heat exchanger.

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

“…1), b, of 2.6 mm. A good agreement was found between the numerical thermal data (Fernandes et al, 2005(Fernandes et al, , 2006Maia et al, 2007) and the experimental data from Afonso et al (2003) for stirred yoghurt.…”

“…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.…”

Avaliação físico-química, microbiológica e reológica de bebida láctea e leite fermentado adicionados de probióticos

“…Porém, o modelo da lei da Potência não considera os efeitos de temperatura, sendo necessária para quantificar o efeito da temperatura na viscosidade aparente de fluidos alimentares, a Equação de Arrhenius (Equação 2), que leva em conta a energia de ativação (AFONSO et al, 2003;BARRETO et al, 2003;VELEZ-RUIZ;BARBOSA-CÁNOVAS, 1998 …”

Thermal behaviour of stirred yoghurt during cooling in plate heat exchangers

“…Plate heat exchangers (PHEÕs) are commonly used on food industry for tasks including the high-temperature short-time pasteurization of milk, beer and fruit juices (Gut & Pinto, 2003a) as well as the cooling of stirred yoghurt to stop lactic fermentation when a desired acidity is reached (Afonso, Hes, Maia, & Melo, 2003).…”