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Review Paper a Review of Dough Rheological Models Review paper A review of dough rheological models used in numerical applications S. M. Hosseinalipour*, A. Tohidi and M. Shokrpour Department of mechanical engineering, Iran University of Science & Technology, Tehran, Iran. Article info: Abstract Received: 14/07/2011 The motivation for this work is to propose a first thorough review of dough Accepted: 17/01/2012 rheological models used in numerical applications. Although many models have Online: 03/03/2012 been developed to describe dough rheological characteristics, few of them are employed by researchers in numerical applications. This article reviews them in Keywords: detail and attempts to provide new insight into the use of dough rheological Dough, models. Rheological Models Rheology. Nomenclature Relative increase in viscosity due to Pa.sec A Apparent viscosity, gelatinization, dimensionless 1 b Index of moisture content effects on viscosity, Shear rate, sec dimensionless Rate of deformation tensor Strain history, dimensionless D K 11sec k ReactionArchive transmission coefficient, of Time SID-temperature history, K.sec a MC Moisture content, dry basis, decimal Yield stress, Pa 0 MC Reference moisture content, dry basis, decimal u Velocity, ms/ r m Fluid consistency coefficients, dimensionless Stress tensor n Flow behavior index, dimensionless E Free energy of activation, cal/g mol v 1.987cal / g mol K Pa R Universal gas constant, Stress, Index of molecular weight effects on viscosity, Relaxation time, sec dimensionless 1. Introduction *Corresponding author Email address: [email protected] www.SID.ir129 JCARME S. M. Hosseinalipour et al. Vol. 1, No. 2, March 2012 Bread is the most important daily meal of Thien-Tanner model [1,12,13]. In these studies people in the world. Furthermore, improving they often employed the Brabender Farinograph the quality of bread baked products and the to predict the measured rheological behavior of development of relevant apparatuses completely wheat flour dough at different moisture depend upon a comprehensive knowledge of contents. dough rheology. Therefore, it is essential to However, the limited application of their results gain a deep knowledge of dough behavior and and difficulties encountered in correlation to ensure the accuracy of the measured between the quality of the baked products and rheological data. However, finding a values obtained from them complicate the task constitutive model that has all accurate of characterizing the flow behavior of dough. molecular and structural arguments to simulate In 1954, Cunningham and Hlynka [14] tried to the linear and non-linear properties of wheat characterize the linear viscoelastic properties of flour dough is a tough challenge due to the dough using distribution of relaxation times. In complicated nature of wheat flour doughs 0. order to characterize the viscoelastic properties The challenge is due to the fact that once water, of flour dough, Bagley and Christianson [15] wheat flour dough and small amount of used the BKZ elastic fluid theory. Thereafter, ingredients such as salt, yeast, preservatives, the upper convected Maxwell model was used etc. are combined, a cohesive viscoelastic by Bagley et al.[16]. Till 1990, the aim of substance is produced called dough. All of studies had been to simulate the rheological these ingredients can considerably change the properties of wheat flour dough without rheological properties of the dough during considering its non linear behavior. Dus and mixing, and make it rheologically complex. In Kokini [6], therefore, tried to describe the fact, the combination of these ingredients steady state shear viscosity and oscillatory produces a three dimensional network called shear properties of hard flour dough using the gluten which has a crucial role in complex five-parameter Bird-Carreau model. Bagley viscoelastic behavior of wheat flour dough 0. [17] used of the upper-convected Maxwell Despite these complexities, the rheology of model to explain the dough behavior in biaxial wheat flour dough has been an important of extension flow. scientific researches topics. Over the years, Before 1995, less attention was paid to the several efforts have been made to measurements of uniaxial and biaxial experimentally and theoretically evaluate dough extensional rheological properties of wheat properties that affect its flow behavior. In this flour doughs in the strain rates region [12]. approach, Schofield and Scott Blair [2-5] might Therefore, Wang and Kokini [11], showed that be considered as pioneer researchers who one can profit by using the Wagner model to studied the flow behavior of the wheat flour predict transient shear properties and uniaxial doughs. They also demonstrated that dough and biaxial extensional rheological properties of behaves both like a Hookean solid and also like gluten doughs and also to simulate nonlinear a Newtonian liquid. shear properties. Dhanasekharan and Kokini In order to provideArchive information on the [13] usedof the Phan SID-Thien Tanner model as a rheological properties of wheat flour dough, the more realistic model describing dough-like measurement of dough material properties has fluids for 3-D numerical modeling of been obtained using empirical instruments such viscoelastic flow in a single screw extrusion as Farinograph, Alveograph, Extensigraph and and then analyzed the effect of viscoelasticity Mixograph [6-8] and capillary rheometry (shear considering a stationary screw and rotating and extensional viscosities for dough) [9,10]. barrel. Phan-Thien and Safari-Ardi [18] derived Kokini et al. have attempted to simulate and relaxation spectra from both dynamic and compare dough-like rheological materials using relaxation data for Australian strong flour-water the Bird Carreau model [6, 8], the Wagner dough and reported dynamic oscillatory and model [11], the White-Mezner model, the stress relaxation data [1,19]. Giesekus-Leonov model [1,12] and the Phan- 130 www.SID.ir JCARME A review of dough . Vol. 1, No. 2, March 2012 Till that time, most of the reported models dough behavior in such a single screw extruder. simulating the rheological properties of wheat In this study, in order to take into account the flour doughs or their protein components had variations in the rheology of wheat flour dough, been either linear differential viscoelastic the Mackey and Ofoli viscosity model was models like the generalized Maxwell models or applied. With regards to attempts to examine nonlinear integral viscoelastic models such as the mixing ability of single and double screw the Bird-Carreau and Wagner models [19]. mixers, significantly Kokini et al. [23,24,26,27] Using the Phan-Thien Tanner, White-Metzner examined the effects of shear thinning and model and the Giesekus model applied by differential viscoelasticity on dough mixing Dhanasekharan et al. [12] to study whole wheat behavior. flour doughs, Dhanasekharan et al. 0 compared For the first time, Binding et al. [28] examined the validity of these models to predict the the combination of numerical and experimental steady shear and transient shear properties of studies of dough kneading in a partially filled gluten dough. Using the theory of rubber cylindrical mixer, with either one or two elasticity, Leonard et al. [19] studied the eccentric stirrers. The numerical procedure rheology of wheat flour doughs at large utilized a parallel numerical method based on a extensional strains and reported an intermediate finite element semi implicit time-stepping behavior between rubber elasticity and plastic Taylor-Galerkin/pressure-correction scheme. flow for dough. The same approach was then employed In order to evaluate the constitutive eqations [29,30,31] to analyze the wetting and peeling of introduced by Phan-Thien et al. [20], the large- dough like material on solid surfaces strain oscillatory shear flow of flour dough was considering the free surfaces, kinematics and studied by Phan-Thien et al. [21]. Their results stress fields produced by variations of stirrers’ indicated that a model with a shear-rate speed and changing geometry mixer. For fluid dependent viscosity alone is inadequate to rheology, Carreau–Yasuda, constant viscosity describe the response of flour dough since the Oldroyd-B and two shear-thinning Phan- material response is significantly non-linear Thien/Tanner constitutive models were which is mainly due to the strain softening employed. Velocity profiles and relevant behavior of the material. Furthermore, in order peeling stress were calculated using laser scatter to be able to differentiate between different technology, Laser Doppler Anemometry (LDA) flour types, tests at large-strain deformations and a video capture technique. Results revealed are required. good agreements between the numerical and Although, the literature has explored numerous experimental studies. papers dealing with both theoretical and It is not feasible here to even attempt to review experimental methods of characterizing dough many of efforts that have been made to explore like materials, there are only a few scattered both theoretical and experimental ways of references devoted to evaluating the application characterizing and evaluating dough; however, of reported constitutive equations of wheat Bagley [9], Kokini [19] and Phan-Thien et al. flour dough inArchive numerical simulations. In [21]of have cited SID some useful references. characterizing dough behavior and its effects on Despite all these attempts, there is still a great different flow patterns, the most notable
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