Mechanical vapor compressio--Membrane distillation hybrids for reduced specific energy consumption

The energy efficiency of membrane distillation (MD) systems is low when compared to other thermal desalination systems. This leads to high water production costs when conventional fuels such as natural gas are used. In MD, separation of pure product water from feedwater is driven by differences in vapor pressure between the streams. Thus, the process can occur at low temperature and ambient pressure. As a result, MD is most frequently paired with waste or renewable sources of low temperature heat energy that can be economically more feasible. MD systems with internal heat regeneration have been compared to and modeled similar to counter-flow heat exchangers. In this study, MD is used to replace the preheater heat exchanger used for thermal energy recovery from the brine stream in mechanical vapor compression (MVC). Using MD in place of the heat exchanger results not only in effectively free thermal energy for MD, but also subsidized cost of capital, since the MD module is replacing expensive heat exchanger equipment. The MVC–MD hybrid system can lead to about 6% decrease in cost of water, compared to a stand-alone MVC system. The savings increase with: an increase in MVC operating temperature, a decrease in MVC recovery ratio, and with a decrease in MD capital cost. The conductive gap configuration of MD leads to maximum savings, followed by air gap and permeate gap systems, over a range of operating conditions, assuming equal specific cost of capital for these configurations.Masdar Institute of Science and Technology/MIT/Abu Dhabi, UAE (Cooperative agreement, Reference no.02/MI/MI/ CP/11/07633/GEN/G/00

Amex in Context: Tracing the Application of the Rule of Reason to Vertical Restraints

In his 1911 State of the Union address, President William Howard Taft, the former and future jurist, discussed the development of antitrust law since the Sherman Act’s passage: “Slowly the mills of the courts ground, and only gradually did the majesty of the law assert itself.” While Taft allowed for the possibility that some changes to the law may be beneficial, he also argued that the “object” of the Act was “near achievement,” and spoke against those calling to “abandon this work of twenty years and try another experiment[.]” Ultimately, the experiment was not abandoned, and the Sherman Act remains at the center of antitrust law in the United States. Meanwhile, the “mills of the courts” have continued to grind away. Various judges, justices—including the eventual Chief Justice Taft himself—and scholars have shaped the contours of antitrust law. One area of ongoing development is the organic rule of reason, which Taft played no small role in originating. The rule of reason was first articulated in United States v. Addyston Pipe & Steel Co.5 in 1898 and played an important role, not long after, in the titanic cases of Standard Oil of New Jersey v. United States6 and United States v. American Tobacco Co. During Taft’s presidency, however, the Supreme Court held that vertically imposed price restraints were per se illegal, and, over the decades that followed, the rule of reason began to wither and was gradually replaced, in significant part, by a series of per se rules

Sedimentation of an ellipsoid inside an infinitely long tube at low and intermediate Reynolds numbers

The motion of a heavy rigid ellipsoidal particle settling in an infinitely long circular tube filled with an incompressible Newtonian fluid has been studied numerically for three categories of problems, namely, when both fluid and particle inertia are negligible, when fluid inertia is negligible but particle inertia is present, and when both fluid and particle inertia are present. The governing equations for both the fluid and the solid particle have been solved using an arbitrary Lagrangian-Eulerian based finite-element method. Under Stokes flow conditions, an ellipsoid without inertia is observed to follow a perfectly periodic orbit in which the particle rotates and moves from side to side in the tube as it settles. The amplitude and the period of this oscillatory motion depend on the initial orientation and the aspect ratio of the ellipsoid. An ellipsoid with inertia is found to follow initially a similar oscillatory motion with increasing amplitude. Its orientation tends towards a flatter configuration, and the rate of change of its orientation is found to be a function of the particle Stokes number which characterizes the particle inertia. The ellipsoid eventually collides with the tube wall, and settles into a different periodic orbit. For cases with non-zero Reynolds numbers, an ellipsoid is seen to attain a steady-state configuration wherein it falls vertically. The location and configuration of this steady equilibrium varies with the Reynolds number

ULTRAPERMEABLE MEMBRANES FOR BATCH DESALINATION: MAXIMUM DESALINATION ENERGY EFFICIENCY, AND COST ANALYSIS

Reducing the energy consumption of membrane desalination is critical to reducing its cost of water and minimizing desalination’s CO₂ emissions. Hybrids of reverse osmosis (RO) with ul trapermeable membranes promise to address the efficiency, rejection, and fouling issues. In a batch reverse osmosis (BRO) process, salinity is varied over time so that the applied pressure better matches osmotic pressure, increasing efficiency. In this paper, the impact of ultrapermeable membranes in BRO are modelled, and a cost analysis is performed. The results show energetic advantages for the BRO over the best continuous RO configurations. Batch RO systems offer significant cost savings, and saves more energy than the use of ultrapermeable membranes in continuous RO systems. The two combined, BRO and ultrapermeable membranes, has the potential for the most efficient desalination systems yet proposed. However, low membrane cost is needed for ultrapermeable membranes to be viable

On tuning passive black-box macromodels of LTI systems via adaptive weighting

This paper discusses various approaches for tuning the accuracy of rational macromodels obtained via black-box identification or approximation of sampled frequency responses of some unknown Linear and Time-Invariant system. Main emphasis is on embedding into the model extraction process some information on the nominal terminations that will be connected to the model during normal operation, so that the corresponding accuracy is optimized. This goal is achieved through an optimization based on a suitably defined cost function, which embeds frequency-dependent weights that are adaptively refined during the model construction. A similar procedure is applied in a postprocessing step for enforcing model passivity. The advantages of proposed algorithm are illustrated on a few application examples related to power distribution networks in electronic system

On velocity and reactive scalar spectra in turbulent premixed flames

AbstractKinetic energy and reactive scalar spectra in turbulent premixed flames are studied from compressible three-dimensional direct numerical simulations (DNS) of a temporally evolving rectangular slot-jet premixed flame, a statistically one-dimensional configuration. The flames correspond to a lean premixed hydrogen–air mixture at an equivalence ratio of 0.7, preheated to 700 K and at 1 atm, and three DNS are considered with a fixed jet Reynolds number of 10 000 and a jet Damköhler number varying between 0.13 and 0.54. For the study of spectra, motivated by the need to account for density change, which can be locally strong in premixed flames, a new density-weighted definition for two-point velocity/scalar correlations is proposed. The density-weighted two-point correlation tensor retains the essential properties of its constant-density (incompressible) counterpart and recovers the density-weighted Reynolds stress tensor in the limit of zero separation. The density weighting also allows the derivation of balance equations for velocity and scalar spectrum functions in the wavenumber space that illuminate physics unique to combusting flows. Pressure–dilatation correlation is a source of kinetic energy at high wavenumbers and, analogously, reaction rate–scalar fluctuation correlation is a high-wavenumber source of scalar energy. These results are verified by the spectra constructed from the DNS data. The kinetic energy spectra show a distinct inertial range with a $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}-5/3$ scaling followed by a ‘diffusive–reactive’ range at higher wavenumbers. The exponential drop-off in this range shows a distinct inflection in the vicinity of the wavenumber corresponding to a laminar flame thickness, $\delta _L$, and this is attributed to the contribution from the pressure–dilatation term in the energy balance in wavenumber space. Likewise, a clear spike in spectra of major reactant species (hydrogen) arising from the reaction-rate term is observed at wavenumbers close to $\delta _L$. It appears that in the inertial range classical scaling laws for the spectra involving the Kolmogorov scale are applicable, but in the high-wavenumber range where chemical reactions have a strong signature the laminar flame thickness produces a better collapse. It is suggested that a full scaling should perhaps involve the Kolmogorov scale, laminar flame thickness, Damköhler number and Karlovitz number.This is the accepted manuscript. The final version is available from CUP at http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9317552&fileId=S0022112014003929

Camera distortion self-calibration using the plumb-line constraint and minimal Hough entropy

In this paper we present a simple and robust method for self-correction of camera distortion using single images of scenes which contain straight lines. Since the most common distortion can be modelled as radial distortion, we illustrate the method using the Harris radial distortion model, but the method is applicable to any distortion model. The method is based on transforming the edgels of the distorted image to a 1-D angular Hough space, and optimizing the distortion correction parameters which minimize the entropy of the corresponding normalized histogram. Properly corrected imagery will have fewer curved lines, and therefore less spread in Hough space. Since the method does not rely on any image structure beyond the existence of edgels sharing some common orientations and does not use edge fitting, it is applicable to a wide variety of image types. For instance, it can be applied equally well to images of texture with weak but dominant orientations, or images with strong vanishing points. Finally, the method is performed on both synthetic and real data revealing that it is particularly robust to noise.Comment: 9 pages, 5 figures Corrected errors in equation 1

On the present and future economic viability of stand-alone pressure-retarded osmosis

Pressure-retarded osmosis is a renewable method of power production from salinity gradients which has generated significant academic and commercial interest but, to date, has not been successfully implemented on a large scale. In this work, we investigate lower bound cost scenarios for power generation with PRO to evaluate its economic viability. We build a comprehensive economic model for PRO with assumptions that minimize the cost of power production, thereby conclusively identifying the operating conditions that are not economically viable. With the current state-of-the art PRO membranes, we estimate the minimum levelized cost of electricity for PRO of US$1.2/kWh for seawater and river water pairing,$0.44/kWh for reverse osmosis brine and wastewater, and $0.066/kWh for nearly saturated water (26$0.074/kWh. We show two methods for reducing this cost via economies of scale and reducing the membrane structural parameter. We find that the latter method reduces the levelized cost of electricity significantly more than increasing the membrane permeability coefficient.National Science Foundation (U.S.) (Graduate Research Fellowship Program, Grant No.1122374) )Kuwait Foundation for the Advancement of Sciences (KFAS) (Project No. P31475EC01