Integration of solar thermal energy into processes with heat demand

An integration of solar thermal energy can reduce the utility cost and the environmental impact. A proper integration of solar thermal energy is required in order to achieve it. The objective of this study is to maximise the solar thermal energy delivered to the process. It is a result of trade-off between the captured solar thermal energy and maximal energy delivered to the process (process demand). Two novel curves are introduced to present this trade-off: (i) The Captured Solar Energy Curve (CSEC), which represents the available amount of heat from solar source and (ii) The Minimal Capture Temperature Curve (MCTC), indicating the minimal temperature making the heat transfer feasible. The crossing point of these two curves presents the minimal temperature of the capture being still sufficiently high to be usable for processes. The suitability of these curves for using in combination with standard heat integration methods is analysed and evaluated. The capture potential is revealed in full when the CSEC and MCTC are used with the Grand Composite Curve. In Total Site Profiles, the heat recovery is first maximised and then the CSEC and MCTC tool is applied. The implementation of CSEC and MCTC approach is illustrated by two case studies.     

Sensory,physical and chemical characteristics of cooked ham manufactured from rapidly chilled and earlier deboned M. semimembranosus

Effects of rapid chilling of carcasses (at − 31 °C in the first 3 h of chilling, and then at 2–4 °C) and earlier deboning (8 h post-mortem), compared to rapid (till 24 h post-mortem) and conventional chilling (at 2–4 °C, till 24 h post-mortem), on quality characteristics of pork M. semimebranosus and cooked ham were investigated. Quality measurements included pH value, colour (CIEL*a*b* values) and total aerobic count of M. semimebranosus, as well as sensory (colour, juiciness, texture, and flavour), physical (pH value, colour – CIEL*a*b* values and texture – Warner–Bratzler shear and penetration forces) and chemical (protein, total fat, and moisture content) characteristics of cooked ham. The cooked ham was manufactured from pieces of M. semimebranosus with ultimate lightness (CIEL* value) lower than 50. Rapid chilling and earlier deboning significantly increased quantity of M. semimebranosus desirable for cooked ham manufacturing. Earlier start of pork fabrication did not affect important quality characteristics of cooked ham.     

Cost optimization of the underground gas storage

The paper presents the cost optimization of an underground gas storage (UGS), designed from lined rock caverns (LRC). The optimization is performed by the non-linear programming (NLP) approach. For this purpose, the NLP optimization model OPTUGS was developed. The model comprises the cost objective function, which is subjected to geomechanical and design constraints. The geotechnical problem is proposed to be solved simultaneously. Geomechanical rock mass parameters are determined from geological conditions of a selected suitable UGS location and a special FE model is generated. The rock mass strength stability and safety of the system are then analyzed for various combinations between different design parameters like inner gas pressures, cavern depths, cavern diameters and cavern wall thickness. As a result, geomechanical constraints are approximated and put into the optimization model OPTUGS. This way, the optimization enables not only the obtaining of an optimal solution but also that the rock mass achieves sufficient strength stability and safety. The optimization is proposed to be performed for the phase of preliminary design. The numerical example at the end of the paper demonstrates the efficiency of the introduced optimization approach.     

Cooling of a sphere by natural convection – The applicability of the lumped capacitance method

Two approaches to predicting the sphere cooling process by laminar natural convection were compared in terms of the accuracy of the volume averaged sphere temperature and the heat transfer rate between the sphere and the surrounding fluid. The first approach is based on the formulation of conjugate heat transfer (heat conduction in the sphere and laminar natural convection in the fluid). The second approach includes the lumped capacity method based on the assumption that the temperature in the sphere is spatially uniform and on the Churchill correlation function. The solution to the problem depends on the Rayleigh number (Ra), the Biot number (Bi), the Prandtl number (Pr), and the sphere-to-fluid thermal diffusivity ratio (A). The lumped capacitance method gives fairly accurate results with respect to the conjugate heat transfer method (discrepancy in the volume averaged sphere temperature less than 5%) when A · Bi/Ra^0.452 < 0.05, for Bi < 0.15 and Pr > 1.     

New guidelines for prediction of antioxidant activity of Lactuca sativa L. varieties based on phytochemicals content and multivariate chemometrics

The aim of this study was to establish models for the antioxidant activity (IC₅₀) prediction of lettuce samples (Lactuca sativa L.) using their phytochemicals content (total phenols, chlorophylls, total carotenoids, and vitamin C) by using suitable chemometric methods. In order to select phytochemicals that best describe the antioxidant activity, classification, and regression analysis were conducted. Generalized pair correlation method (GPCM) gave insight which phytochemicals are the most important for the antioxidant activity prediction. That was confirmed using multiple linear regression (MLR) and establishing models that were validated. The sum of ranking differences (SRD) was applied in order to obtain and rank models with best predictive power. Both GPCM and MLR showed that the most important phytochemicals for the antioxidant activity prediction are chlorophyll a, chlorophyll a + b, and total carotenoids content. The obtained results should be considered as preliminary for the prediction of the antioxidant activity and further improvement in scientific research on this subject follows.

Practical applications

The models for the prediction of the antioxidant activity were obtained. Novel approach for variable selection was conducted and new method for the MLR model ranking was applied. Chemometric guidelines for the selection of lettuce cultivars with increased antioxidant activity were defined.     

Physikalisch-chemische Untersuchungsmethode zur Erforschung des Systems „Metall–Schlacke–Gas“ unter erhöhtem Gasdruck

Bericht über Anwendung der Schwebeschmelzmethode zur Untersuchung von Metall-Schlacke-Gas-Gleichgewichten unter erhöhtem Druck. Angaben über Versuchsergebnisse zur Stickstofflöslichkeit, zur Lösungsenthalpie und zur freien Reaktionsenthalpie des Stickstoffs bei Drücken bis 26 bar im Gleichgewicht mit legierten Schmelzen der bulgarischen Stahlsorte X 50 CrWMoVSiN 33 bei 1600 bis 1800°C sowie zur Schwefelverteilung zwischen Schmelze und einer Schlacke mit rd. 65% CaF₂, 30% Al₂O₃ und 4% CaO. Erörterung der Übertragbarkeit der Ergebnisse auf die Verhältnisse einer Druck-ESU-Anlage.     

Identification of critical points for the design and synthesis of flexible processes

Optimization problems for the design and synthesis of flexible chemical processes are often associated with highly discretized models. The ultimate goal of this work is to significantly reduce the set of uncertain parameter points used in these problems. To accomplish the task, an approach was developed for identifying the minimum set of critical points needed for flexible design. Critical points in this work represent those values of uncertain parameters that determine optimal overdesign of process, so that feasible operation is assured within the specified domain of uncertain parameters. The proposed approach identifies critical values of uncertain parameters a-priori by the separate maximization of each design variable, together with simultaneous optimization of the economic objective function. During this procedure, uncertain parameters are transformed into continuous variables. Three alternative methods are proposed within this approach: the formulation based on Karush–Kuhn–Tucker (KKT) optimality conditions, the iterative two-level method, and the approximate one-level method. The identified critical points are then used for the discretization of infinite uncertain problems, in order to obtain the design with the optimum objective function and flexibility index at unity. All three methods can identify vertex or even nonvertex critical points, whose total number is less than or equal to the number of design variables, which represents a significant reduction in the problem's dimensionality. Some examples are presented illustrating the applicability and efficiency of the proposed approach, as well as the role of the critical points in the optimization of design problems under uncertainty.