System Mass Balance Research Articles

Systematic Generation of Identifiable Macroscopic Reaction Schemes

Mathematical modelling of bioprocesses is very useful for building simulators, software sensors, con trollers, etc. Th ese tools are generally based on simple models consisting of the system of mass balances for the macroscopic species involved in a reaction scheme. Although this reaction scheme plays a key role in bioprocess modelling, its determination usually relyon intuition, process knowledge and trials and errors. This paper focuses on a metho d to genera te and to co mpare, in a syste matic way, all the identifiable schemes given a set of components for which concentration measurements are available. “Identifiable schemes” means that the pseudo-stoichiometric coefficients can be (uniquely) identified, independently of the kinetics which are unknown. The method is illustrated on a case study.

Feedback stabilisation with positive control of a class of dissipative mass-balance systems

In many process control applications, the system under consideration is positive. This means that both the state variables and the control input are physically constrained to remain non-negative along the system trajectories. For such systems, the design of state feedback controllers makes sense only if the control function is guaranteed to provide a non-negative value at each time instant. The purpose of this paper is to present a positive control law for the feedback stabilisation of a class of positive mass-balance systems which are dissipative but can nevertheless be globally unstable. The approach is illustrated with an application to the control of an industrial grinding circuit.

EcoCELLs: tools for mesocosm scale measurements of gas exchange.

We describe the use of a unique plant growth facility, which has as its centerpiece four 'EcoCELLs', or 5x7 m mesocosms designed as open-flow, mass-balance systems for the measurement of carbon, water and trace gas fluxes. This system is unique in that it was conceived specifically to bridge the gap between measurement scales during long-term experiments examining the function and development of model ecosystems. There are several advantages to using EcoCELLs, including (i) the same theory of operation as leaf level gas exchange systems, but with continuous operation at a much larger scale; (ii) the ability to independently evaluate canopy-level and ecosystem models; (iii) simultaneous manipulation of environmental factors and measurement of system-level responses, and (iv) maximum access to, and manipulation of, a large rooting volume. In addition to discussing the theory, construction and relative merits of EcoCELLs, we describe the calibration and use of the EcoCELLs during a 'proof of concept' experiment. This experiment involved growing soybeans under two ambient CO2 concentrations (approximately 360 and 710 micromoles mol-1). During this experiment, we asked 'How accurate is the simplest model that can be used to scale from leaf-level to canopy-level responses?' in order to illustrate the utility of the EcoCELLs in validating canopy-scale models.

Pipeline leak detection based on mass balance: Importance of the packing term

After a brief survey of pipeline leak detection techniques, some mass balance systems are presented. Such systems use a pipeline flow model in order to compute the change in pipeline inventory during a transient flow. The packing term, whose importance is highlighted, is a function of the speed of sound in the pipeline. However, generally, the parameters on which the speed of sound depends are poorly defined. The consequences on leak detection thresholds are described.

Computer analysis of equilibrium data in solution. A method for computing the formation constants of two mass balance systems, from potentiometric measurements, applied to the hydrolysis of copper(II)

A computer program for two mass balance systems (in solution) has been written in FORTRAN IV. This program (ES3TM) refines the formation constants and some titration parameters (E0, analytical concentrations) from potentiometric data, using the Marquardt algorithm for the Gauss nonlinear least squares method. The program has been compared with some other programs reported in the literature. In order to test the ES3TM program and to obtain reliable values of formation constants for the species, [Cup(OH)q](2p−q)+, we studied the hydrolysis of copper(II) by pH-metric measurements at 37°C and I=0.15 mol dm−3 (NaNO3). The results of the refinement have been discussed in the light of the characteristics of the ES3TM program and of the reliability of the speciation models on copper(II) hydrolysis reported up to now.

A distributed model of peritoneal-plasma transport: theoretical considerations.

Transport of water-soluble substances between the peritoneal cavity and the plasma was modeled with a distributed approach. The model includes diffusion and convection through tissue as well as membrane transport across blood capillaries, which are assumed to be distributed uniformly in the tissue. Lymphatic uptake via the diaphragm is also included. Transport in the remainder of the body is modeled by a system of compartments. The resulting system of mass balances and rate equations is solved numerically to provide predictions of peritoneal volume and concentrations in plasma, peritoneal fluid, and tissue surrounding the cavity. The model sensitivity is explored by varying key parameters to determine whether the changes would have a significant effect on model output. Key parameters include peritoneal surface area, tissue diffusivity, capillary permeability, tissue void fraction, and hydrostatic and osmotic pressures in the capillaries and interstitium.

A System to Combine Stratigraphic and Annual Mass-Balance Systems: A Contribution to the International Hydrological Decade

AbstractMass-balance quantities at specific points on a glacier as defined in [IHD] (1970) relate either to annual maxima or minima in ice mass at that point (thestratigraphic system), or to values at the beginning and end of a hydrologic year (theannualorfixed-date system). Most quantities measured in the field relate to summer surfaces, which correspond to the annual minima at the measurement points. When stratigraphic system point values are integrated over a whole glacier, the result may be meaningless because annual maxima and minima and summer surfaces may form at different times at different places.The combined system utilizes several kinds of data to derive meaningful area-average results that can be directly related to other hydrologic and meteorologic information. Measurements to summer surfaces at certain specific times, including the beginning and end of a hydrologic year, are added together with proper recognition of the types of material involved: old firn and ice, snow and superimposed ice of the year under study, new firn formed during that year, and late snow deposited toward the end of the year. Other “balance increment” terms relate values at the beginning and end of a hydrologic year to corresponding area-average balance minima. As a result, two types of “net balance” and many other terms are given precise meaning for a glacier as a whole. The scheme is sufficiently versatile to be used on any glacier, although the terms relating to summer surfaces are not defined on a glacier in which ablation or accumulation is continuous throughout a year.

A System to Combine Stratigraphic and Annual Mass-Balance Systems: A Contribution to the International Hydrological Decade

AbstractMass-balance quantities at specific points on a glacier as defined in [IHD] (1970) relate either to annual maxima or minima in ice mass at that point (the stratigraphic system), or to values at the beginning and end of a hydrologic year (the annual or fixed-date system). Most quantities measured in the field relate to summer surfaces, which correspond to the annual minima at the measurement points. When stratigraphic system point values are integrated over a whole glacier, the result may be meaningless because annual maxima and minima and summer surfaces may form at different times at different places.The combined system utilizes several kinds of data to derive meaningful area-average results that can be directly related to other hydrologic and meteorologic information. Measurements to summer surfaces at certain specific times, including the beginning and end of a hydrologic year, are added together with proper recognition of the types of material involved: old firn and ice, snow and superimposed ice of the year under study, new firn formed during that year, and late snow deposited toward the end of the year. Other “balance increment” terms relate values at the beginning and end of a hydrologic year to corresponding area-average balance minima. As a result, two types of “net balance” and many other terms are given precise meaning for a glacier as a whole. The scheme is sufficiently versatile to be used on any glacier, although the terms relating to summer surfaces are not defined on a glacier in which ablation or accumulation is continuous throughout a year.