An evaluation of throughput time in closed loop operating systems

The purpose of this paper is to present a generalized and a special purpose method for the evaluation of throughput time. The general method presented represents a modification of Mason's Rule to a special case of flow evaluation encountered in production operations. The algorithm presented is for the special model wherein there is a single output and wherein all possible feedbacks are permissible. It is anticipated that the methods presented will aid greatly in the evaluation and understanding of throughput time. The methods should be equally applicable to normal manufacturing operations and to special major project type activities. Clearly the application of the methods is limited only by one's ability to establish the flow graph, the times for the operations and the yields for the various flows.     

INFLUENCE OF FRICTION, SAMPLE DIMENSIONS AND DEFORMATION RATE ON THE UNIAXIAL COMPRESSION OF RAW POTATO FLESH

The influence of surface friction and lubrication on the compression behavior, at compression rates of 5–100mm min^−l, of cylindrical samples of potato flesh have been examined with an Instron Universal Testing Machine at room temperature. The samples had length/diameter ratios of 0.2–0.8. Parameters derived from compression to failure were: failure stress; failure strain; and apparent modulus of elasticity. Stress relaxation with time was studied using samples with length/diameter ratios of 0.4–0.8 following compressions of 10 and 30%. The length/diameter ratio, rate of compression, surface friction and lubrication influenced the parameters derived from both the compression and the stress relaxation tests. Relaxation times increased following sample lubrication. The effect due to surface lubrication was smaller than in previous compression and relaxation tests on Gouda cheese. This was attributed to release of fluid from the damaged cellular tissue of the potato flesh which reduced the effectiveness of the lubricant film.     

DYNAMIC PROGRAMMING FOR PROCESS OPTIMIZATION 1. AN ALGORITHM FOR DESIGN OF MULTI-STAGE GRAIN DRYERS

A dynamic programming algorithm for determining the optimum operational parameters and size of a multi-stage concurrent flow dryer with intermediate tempering stages was developed. The objective function was based on energy and capital costs. The operational parameters were constrained by the desired final moisture content and the maximum allowable value of important grain quality factors. The two- and three-stage concurrent flow dryers have a higher investment cost than the single stage unit, but were less expensive to operate due to the decreased grainflow rate in the single-stage unit. On the basis of operating cost, the multi-stage concurrent flow dryer was preferable to a comparable crossflow dryer for drying corn.     

RHEOLOGICAL PROPERTIES AND APPLICATIONS OF MESQUITE TREE (PROSOPIS JULIFLORA) GUM. 1. RHEOLOGICAL PROPERTIES OF AQUEOUS MESQUITE GUM SOLUTIONS

The viscosities of aqueous mesquite gum solutions were measured at gum concentrations extending to 16.7% (w/v). Very dilute solutions exhibited typical polyelectrolyte behavior with respect to the influence of gum concentration on the reduced viscosity in the absence and presence of electrolyte. Shear thickening was exhibited at concentrations of 1–16.67% (w/v) when the shear rate exceeded ∼100 s⁻¹, whereas shear thinning was exhibited at lower shear rates. Shear thickening was attributed to configurational changes in the gum molecules at high shear rates. Electrolytes (0.1N NaCl and 0.1N CaCl₂) reduced the viscosity of concentrated solutions at high shear rates to a larger extent than increasing the pH. Charge screening by electrolyte permits the gum molecules to assume a more compact configuration.     

Retention of Micronutrients by Polymer Coatings Used to Fortify Rice

Nutrient deficiency diseases are public health problems in developing nations. Our objective was to design a rice-fortification method using materials approved for use in foods to retain significant quantities of added nutrients during the common practice of boiling rice in excess water and draining it. We accomplished this by applying nutrients to rice in edible polymer coatings. Various starches and cellulosic polymers were evaluated with respect to flexibility, strength, stickiness and nutrient retention. Combining hydroxypropyl methylcellulose and methylcellulose (3:1) gave the best results. Nutrient retentions for 1g of coated rice cooked in 100 ml water and drained were: Vitamin A, 70%; iron, 100%; niacin, 18%; thiamin, 18%, riboflavin, 21%.     

IDENTIFICATION OF STIMULI CONTROLLING THE SENSORY EVALUATION OF VISCOSITY II. Oral Methods

The stimulus associated with oral evaluation of the viscosity of liquid and viscous foods appears to embrace a range of shear rates extending from 10^-1 to 1000 s^-1. The value associated with a particular food depends on its flow characteristics. For liquid foods the stimulus appears to be the shear rate developed at an approximately constant shear stress (～ 100 dyn cm^-2), whereas for viscous foods it appears to be the shear stress developed at an approximately constant shear rate (～ 10 s^-1). Additional factors may be involved when evaluating highly viscous non-Newtonian foods or foods with an oil continuous medium. These are ‘plug flow’ or the spreading coefficient, respectively.     

RHEOLOGICAL ASPECTS OF THE RENNETING OF MILK CONCENTRATED BY ULTRAFILTRATION

The kinetics of clotting by rennet of ultrafiltrated milk were studied by determining induction and clotting times, and development of the rigidity modulus as a function of rennet concentration and protein content in the sample. Creep cmpliance-time studies were conducted on the resultant gels at three different stresses. Clotting time increased with protein content and decreased with rennet concentration. The protein effect on clotting time decreased with increasing rennet concentration and was practically nil at 200 mg enzyme/kg sample. The ultimate rigidity and the viscoelastic parameters of gels depended on the protein concentration in a double logarithmic relationship. The calculated values of the constants indicated that the viscosities were influenced to a greater degree by the protein concentration than were the elastic moduli. The renneted milk gels exhibited creep compliance-time response at low shear stresses indicative of the viscoelastic behaviour of an interlinked three-dimensional network. Gelation followed a second order reaction in its initial stages and an approximately third order reaction in the final stage. The results are discussed in terms of potential mechanism and type of bonds involved.