Necati Özkan

Characterization of stickiness and cake formation in whole and skim milk powders

A viscometer technique based on the measurement of the torque required to turn a propeller inserted into milk powders and a penetration test based on the measurement of force required to penetrate milk powder compacts were used to characterize stickiness and cake formation in whole and skim milk powders. These simple techniques were suitable for determining the sticky point temperature (SPT) of the milk powders. Furthermore, the techniques provided useful information regarding the sticking behavior of the milk powders prior to the SPT. The stickiness and cake formation in the whole and skim milk powders were quite different due to the significant variation in the surface composition of these powders. Effects of moisture content, applied load, temperature, and time on the stickiness of the milk powders were also established.

Combined ohmic and plate heating of hamburger patties: quality of cooked patties

Combined ohmic and conventional cooking of hamburger patties has recently been patented as a new method of cooking. The method is based on passing electric current through the meat patties causing internal heat generation. It has been found to reduce cooking time up to half the time usually required in conventional cooking. However, the effect of applying ohmic cooking on the quality of cooked patties is not known yet. This work summarises the experimental investigation made on the quality of hamburger patties cooked by conventional and ohmic-assisted cooking. Several properties of the patties cooked by the two methods were tested such as mechanical properties, oil and moisture contents. The results showed insignificant differences in the properties of the patties cooked by the two methods. It was concluded that ohmic heating has no effect on the quality of the cooked hamburger, which was also confirmed by non-expert tasting.

On-line fouling/cleaning detection by measuring electric resistance: equipment development and application to milk fouling detection and chemical cleaning monitoring

Abstract An electrical resistance method, which has the potential to measure the extent of soft material fouling such as milk fouling on the surface of process equipment in situ and in real time, is described. An experimental fouling unit with the appropriate attachments has been devised and used to monitor the fouling build-up using the electrical resistance method. Reconstituted skim milks with solid contents of 10–30 wt.% were used to produce milk foulings, and these milk foulings were cleaned using a cleaning solution with 0.5 wt.% NaOH. Using the fouling unit, it was possible to measure the thermal resistance (essentially measuring heat flux) and electrical resistance simultaneously. As a result, the relationship between the electrical resistance and the thermal resistance during both fouling build-ups and cleaning processes was established. It has been shown that this technique is effective for measuring the extent of fouling, and it has the potential to be modified further so that it can be adopted in real process industries.

Modeling of Powder Compaction: A Review

The compaction process involves stress transmission via rigid or flexible (die) walls and the propagation of stresses within a powder mass. The particles that comprise the powder distribute the stress by a variety of kinematic processes that involve sliding, rotation, particle deformation, and rupture. In practice the “particles” are often agglomerates of finer particles that have a range of properties. All of these factors must be considered in developing a comprehensive predictive model for compaction. The modeling of powder-compaction processes has a significant history that has been greatly advanced by the relatively recent general availability of powerful computers and their peripherals as well as by appropriate softwares. Compaction modeling may attempt to provide a basis for machine-loading specifications, or it may provide guidelines to help minimize “capping” defects where failure cracks form at the top of the green compact. It may also provide “green-body heterogeneity” through predicted stress and density distributions within a compact. Likewise compaction models may be combined with binder burnout and sintering models to predict internal microstructural features such as grain size and porosity, and the external shape of the sintered product. This article will deal only with the modeling of the compaction process; important elements such as powder flow for die filling and subsequent processing steps such as sintering and net shape predictions are not directly addressed.

Characterization of die-pressed green compacts

Abstract Die-pressed agglomerated alumina compacts, prepared as cylinders using single-ended nominally uniaxial compressive stresses, have been characterized by measuring their strength and density distributions. The strength of the alumina compacts, measured using the Brazilian configuration, increases up to an optimum compaction pressure; upon further increasing the compaction pressure, the strength of the green compacts decreases due to the formation of internal cracks. The density distributions in the alumina compacts have also been determined experimentally, using the coloured layer technique and also deduced indirectly from hardness measurements. The results obtained from these two experiments are shown to be in good agreement. The densest parts of the compacts, compressed uniaxially from the top planar surface adjacent to the compression source, are at the outer circumference at the top and the least dense parts are at the outer circumference at the bottom face. The density near the cylindrical surface of the compacts decreases with height from the top to the bottom of the compact. The density difference between the most dense and the least dense parts of the compacts increases with increasing aspect ratio; that is, the height-to-diameter ratio. The density distributions in the alumina compacts have also been estimated using a first-order predictive model. According to this model, the mean density variation along the height of the compact decreases linearly with height from the top to the bottom of the compact. These predictions are shown to be almost in accord with experiment.

Effect of High-Pressure Homogenization on the Structure of Cassava Starch

Cassava starch suspension was homogenized at different pressures (0, 20, 40, 60, 80, and 100 MPa) with a high-pressure homogenizer. To investigate the effect of high-pressure homogenization on the structure of cassava starch, the samples were characterized using microscopy, laser scattering, and X-ray diffraction techniques, with native and heat gelatinized cassava starches as controlled samples. The temperature of starch suspension increased linearly with applied pressure at a rate of 0.187°C/MPa. Microscopy studies showed that cassava starch was partly gelatinized after high-pressure homogenization, and the degree of gelatinization increased with homogenizing pressure. Results of laser scattering measurements suggested a considerable increase in particle size after homogenization at 100 MPa as a result of granule swelling. The X-ray diffraction pattern showed that there was no evident change after homogenization suggesting that the crystalline structure of starch granules was resistant to high-pressure homogenization.

Drying kinetics of water-based ceramic suspensions for tape casting

Abstract An experimental study is described which seeks to characterise the drying kinetics of water-based ceramic (alumina) suspensions in controlled environments. The drying process of the ceramic suspensions is shown, to a first approximation, to follow a two stage mechanism (initial stage: ‘external’ evaporation controlled process; and second stage: ‘internal’ diffusion-controlled process). It has been shown that the temperature, the humidity and the surface area of the samples strongly affects the drying kinetics of these suspensions in the initial stage of the drying. The thickness of the samples is more influential in the second stage of the drying. There are no noticeable effects of the initial solid content and the nature of binder content of the suspensions on the drying kinetics. A first order empirical relationship is provided in order to predict the drying time and drying curve for these ceramic suspensions. The drying curves of tape cast suspensions is shown to be predicted accurately by the use of this relationship.

Prediction of overall shape of sintered alumina compacts

Abstract The effects of the final aspect ratio on the overall shape of cylindrical sintered compacts, prepared by a uniaxial die pressing technique, are measured and described. An empirical compaction equation, which describes the compaction behaviour of a spray dried AKP-30 alumina powder, is presented. The density distribution along the axis of the compacts was predicted by using an established first-order analysis. From these predicted density distributions, the overall shapes of the sintered compacts were quite accurately predicted by using a set of sintering simulation equations obtained in separate experiments.

Stickiness, Functionality, and Microstructure of Food Powders

Three major aspects of food powder are described and discussed. Stickiness is one issue that can cause production and product handling difficulties. Stickiness has been interpreted in a number of ways and thus measured differently. Functionality of the primary (single) particles or agglomerated powders is of practical interest to the consumers. The desired quality will have to be matched or exceeded by the powder manufacturers. Finally, microstructure provides a key linkage between the production and the functionality. Its formation has impacts on both the stickiness and functionality.

Evaluation of alkaline pretreatment temperature on a multi-product basis for the co-production of glucose and hemicellulose based films from lignocellulosic biomass.

Cotton stalks were subjected to alkaline pretreatment for the co-production of glucose and hemicellulose based films with a multi-product approach. Three pretreatment temperatures (25, 60 and 90 °C) were evaluated for their effects both on the glucose yield and on the properties of hemicellulose based films. Compared to untreated cotton stalks, the glucose yields were enhanced 3.9, 4.1 and 4.2 times for pretreatments conducted at 25, 60 and 90 °C, respectively. The pretreatment temperature of 90 °C was detrimental in terms of film formation. Tensile energy to break values of the films obtained after pretreatments conducted at 25, 60 and 90 °C were 1.1, 0.8, and 0.4 MJ/m3, respectively. The hemicellulosic part of the process, which considers the production of hemicellulose based films, should govern the pretreatment temperature since it was more responsive to the changes in the pretreatment temperature compared to the cellulosic part that accounts for glucose production.