Comparison of In‐line Consistency Measurement of Tomato Concentrates Using Ultrasonics and Capillary Methods

Abstract

This study focuses on the development of a noninvasive, in-line rheometer using ultrasonics and its comparison with data from a traditional capillary viscometer. The ultrasonic based pointwise viscosity measurement technique combines a measurement of the velocity profile and the pressure drop to determine the shear rate and the shear stress distributions, respectively in a pipe. The experiments were cam'ed out using tomato concentrates at 8.75%. 12.75%, and 17.10% total solids content. Thepow system consisted of a 53.2 mm diameter acrylic tube, a positive displacement pump and two pressure transducers. Multiple shear viscosity-shear rate data were recorded under actual pipeline conditions from a single combined measurement of the velocity profiles using ultrasonics and the pressure gradient, using the pressure transducers. The samples showed shear thinning behavior and a yield stress. Power law and Casson models were used to fit the data and both obtained values higher than 0.99. The yield stress was also directly determined from the velocity profiles. Shear viscosity versus shear rate data of the 12.75% total solids sample were obtained by capillary rheometty at four diflerent flow rates. These showed very good agreement with those obtained using the velocity profile technique.

Yield stress of pretreated corn stover suspensions using magnetic resonance imaging

“…The plug radius was calculated by fitting the velocity profile to that predicted for a Herschel–Bulkley rheological model. The pressure drop is combined with the plug radius to compute the yield stress (Dogan et al, 2003; McCarthy and McCarthy, 1997; McCarthy et al, 1992) using where Δ P is the pressure drop across the tube over a length L (2.08 m). The plug radius, R plug , is measured by fitting the velocity profile to a Herschel–Bulkley rheological model and determining the plug radius from the model.…”

Doppler Ultrasound‐Based Rheology

“…Dogan et al (2002) presented results on measured properties of diced tomatoes suspended in tomato juice including yield stress, consistency index and apparent wall slip. Dogan et al (2003b) investigated the flow of tomato concentrates with different solid content, the shear-thinning behaviour with a yield stress being fitted to power law and Casson models. In addition, the viscosity and plug radius (yield stress) were also determined directly from the profile.…”

“…in which r > R * and R * = 2Lτ 0 / P is the radius of the plug, which can also be determined directly from the flow profile (Dogan et al, 2003b). The local shear rate and viscosity are respectively given bẏ…”

“…Power law and Herschel-Bulkley are the two most often applied models, but literature also describes the use of Ellis (Wunderlich and Brunn, 1999), Casson (Dogan et al, 2003b), Eyring (Dogan et al, 2005b) and Sisko (Birkhofer, 2007;Wiklund, 2007) models.…”

A comparative study of UVP and LDA techniques for pulp suspensions in pipe flow

“…The UVP‐PD rheometric concept (UVP combined with pressure drop data) has been tested with great success in a large number of fluids and highly concentrated suspensions, mostly food related systems. The methodology and results are described in a number of publications 33–44. Choi et al45 compared velocity profiles and the rheological data obtained using UVP‐PD and MRI‐PD methods with good agreement.…”