13,610 research outputs found
Cooling Towers, Energy Conservation Strategies
No full textCooling towers, because of their seeming simplicity, are usually orphans of the facilities operation. We are all aware that cooling towers are the step-children of the chemical process plant, electric power generating station, and refrigeration system.
While our engineers are pretty well convinced of the importance of their sophisticated equipment, and rightly so, they take the cooling towers and the cold water returning from them for granted.
Design Conditions are specified for the particular requirements before a cooling tower is purchased. After it is put on the line and the cold water temperature or volume becomes inadequate, they look to solutions other than the obvious. While all cooling towers are purchased to function at 100% of capability in accordance with the required Design Conditions, in actual on stream employment, the level of operation many times is lower, downwards to as much as 50% due to a variety of reasons: (1) The present service needed is now greater than the original requirements which the tower was purchased for; (2) 'Slippage' due to usage and perhaps deficient maintenance has reduced the performance of the tower over years of operation; (3) The installation could have been originally undersized due to the low bidder syndrome; and (4) New plant expansion needs colder temperatures off the tower
Cooling Towers, Energy Conservation Machines
No full textCooling towers, in all too many industrial plants, are often the neglected units of the process chain which are hidden bonanzas for energy conservation and dollar savings. By lowering the entire systems temperature by the use of colder water returning from the cooling tower, greater chemical product volume can be condensed and less energy is required to run compressors. This paper will discuss two case histories and the rapid cost-effective savings thereby accruing through retrofit
Cooling Towers, The Neglected Energy Resource
No full textLoving care is paid to the compressors,
condensers, and computer programs of
refrigeration systems. When problems arise,
operator: run around in circles with expensive
"fixes", but historically ignore the poor orphan,
the cooling tower perched on the roof or located
somewhere in the backyard. When the cooling
water is too hot, high temperature cut-outs occur
and more energy must be provided to the motors
to maintain the refrigeration cycle.
Cooling Towers:
1) . . . are just as important a link in the
chain as the other equipment,
2) ... are an important source of energy
conservation,
3) ... can be big money makers, and
4 ) .. . operators should be aware of the
potential of maximizing cold water.
Most towers designed over 20 years ago were
inefficiently engineered due to cheap power and
the "low bidder" syndrome. Operating energy
costs were ignored and purchasing criteria was to
award the contract to the lowest bidder.
This paper investigates internal elements of
typical towers, delineates their functions and
shows how to upgrade them in the real world for
energy savings and profitability of operation
Cooling Towers - Energy Conservation and Money Making Mechanisms
No full textThe utilization of colder water conserves energy, creates profits, increases product output. In an effort to obtain greater efficiencies and conserve both energy and dollars, all too many engineers neglect the potential of the cooling tower. Many cooling towers in operation are performing at levels as low as 50% of capability. This is energy wasteful and financially foolish. There are many reasons for this deficiency, among them the present service is greater than the original requirements, slippage due to age and deterioration, or the installation could have been originally installed undersized. This paper will investigate the various elements, their functions and methods of upgrading their performance by retrofit with the use of modern technology. Case histories will be examined in three major industries, chemicals, refrigeration and petrochemical illustrating how intelligent rebuilding can produce profits and conserve energy. Actual statistics will be cited showing that the return of investment (ROI) can be quite rapid by optimizing the performance of the cooling tower
Cosmic ray modulation with a Fisk-type heliospheric magnetic field and a latitude-dependent solar wind speed
No full textThe effect of a latitude-dependent solar wind speed on a Fisk heliospheric magnetic field [Fisk, L. A. Motion of the footpoints of heliospheric magnetic field lines at the Sun: implications for recurrent energetic particle events at high heliographic latitudes. J. Geophys. Res. 101, 15547–15553, 1996] was first discussed by Schwadron and Schwadron and McComas [Schwadron, N.A. An explanation for strongly underwound magnetic field in co-rotating rarefaction regions and its relationship to footpoint motion on the the sun. Geophys. Res. Lett. 29, 1–8, 2002. and Schwadron, N.A., McComas, D.J. Heliospheric “FALTS”: favored acceleration locations at the termination shock. Geophys. Res. Lett. 30, 41–1, 2003]. Burger and Sello [Burger, R.A., Sello, P.C. The effect on cosmic ray modulation of a Parker field modified by a latitudinal-dependent solar wind speed. Adv. Space Res. 35, 643–646, 2005] found a significant effect for a simplified 2D version of a latitude-dependent Fisk-type field while Miyake and Yanagita [Miyake, S., Yanagita, S. The effect of a modified Parker field on the modulation of the galactic cosmic rays. In: Proceedings of 30th International Cosmic Ray Conference. Merida, Mexico, vol. 1, 445–448, 2007] found a smaller effect. The current report improves on a previous attempt Hitge and Burger [Hitge, M., Burger, R.A. The effect of a latitude-dependent solar wind speed on cosmic-ray modulation in a Fisk-type heliospheric magnetic field. In: Proceedings of 30th International Cosmic Ray Conference. Merida, Mexico, vol. 1, pp. 449–450, 2007] where the global change in the solar wind speed and not the local speed gradient was emphasized. The sheared Fisk field of Schwadron and McComas [Schwadron, N.A., McComas, D.J. Heliospheric “FALTS”: Favored acceleration locations at the termination shock. Geophys. Res. Lett. 30, 41–1, 2003.) is similar to the current Schwadron–Parker hybrid field. Little difference is found between the effects of a Parker field and a Schwadron–Parker hybrid field on cosmic-ray modulation, in contrast to the results of Burger and Sello and Miyake and Yanagita [Burger, R.A., Sello, P.C. The effect on cosmic ray modulation of a Parker field modified by a latitudinal-dependent solar wind speed. Adv. Space Res. 35, 643–646, 2005 and Miyake, S., Yanagita, S. The effect of a modified Parker field on the modulation of the galactic cosmic rays. In: Proceedings of 30th International Cosmic Ray Conference. Merida, Mexico, vol. 1, pp. 445–448, 2007]. The two-dimensional approximation used by these authors is therefore inadequate to model the complexities of the actual three-dimensional field. We also show that a Fisk-type field with a latitude-dependent solar wind speed (Schwadron–Parker hybrid field) decreases both the relative amplitude of recurrent cosmic ray intensity variations and latitude gradients and yields similar constants of proportionality for these quantities as for the constant solar wind speed case
Cooling Tower Considerations for Energy Optimizations
No full textEnergy conservation strategies and production
economies involve more than examining the
cooling tower fan consumption of horse power.
Colder water provides vast potentials for
savings. Ask yourself, "What is the dollar
and energy utilization value if I can obtain 1��F
colder water off my cooling tower than I am
now getting?" Therefore, let us first examine
the elements of the cooling tower to determine
the areas of greatest potential improvement to
generate that colder water.
The air flow generated by the fan should first
be looked at In both counterflow or crossflow
towers to determine that maximum flow is
available through pitching fans up to within
the motor plate amperage limitations and fan
stall point calculations. If applicable, new
fiberglass state of the art fans can be installed
and additional motor horse power added.
However, the most dramatic improvement that
can be obtained in producing colder water is
to retrofit modern film fill to replace the old
fashioned wood splash bar slats
An extension of the Kolmogorov-Avrami formula to inhomogeneous birth-and-growth processes
No full textIt has been shown by a substantial body of literature that the hazard function plays an important role in the derivation of evolution equations of n-facet
densities of Johnson-Mehl tessellations generated by germ-grain
models associated with spatially homogeneous birth-and-growth
processes.
In this paper we analyze a more general class of space-time
inhomogeneous birth-and-growth processes emphasizing the role that
the hazard function plays in this generalization. A special result
is the extension of the well known formula that Kolmogorov and
Avrami had found in connection with problems of crystal growth.
Recent literature shows the relevance of a theory for the hazard
function in other important areas of application such as tumor
growth and angiogenesis, crystallization of sea shells, etc.
In this paper a detailed analysis of the hazard function in terms of
relevant volume and surface densities is carried out ; its
relationship with the local spherical contact distribution
function is also given
Les éléments: une trame d'histoire des religions
No full text(Résumé de l'ouvrage) Les articles du présent volume, issus d'un symposium international ayant eu lieu à l'Université de Lausanne en juin 1998, présentent la perception des éléments comme base de recherche de l'étude des religions (Maya Burger), exemplifiée à l'aide des traditions hindoues. Chaque élément est traité par un spécialiste d'une discipline académique particulière dans le but de souligner la variété des approches nécessaire à la discipline d'histoire des religions. L'éther (akasa) a été considéré sous l'angle de la philosophie (Wilhelm Halbfass), le vent sous celui de l'histoire des religions (Bettina Bäumer), le feu sous celui de la philologie classique (Peter Schreiner), l'eau par un spécialiste de la médecine indienne (Arion Rosu) et la terre sous l'angle de l'anthropologie (Gabriella Eichinger Ferro-Luzzi, se concentrant sur la littérature tamoule)
Is There a Role of Interim PSMA PET in Chemotherapy of Prostate Cancer?
No full textWhile RECIST 1.1 is well established in radiological response assessment, it is of limited use in prostate cancer (PCa) considering that the disease is often seen only as sclerotic bone changes on conventional imaging. Therefore, a molecular imaging-based response assessment including bone scans has been proposed and used in clinical trials, however, due to the flare phenomenon on bone scans this assessment leads to substantial delays in the detection of progression. Indeed, a robust and reliable imaging tool to assess response to chemotherapy in PCa is still warranted. Whether Positron Emission Tomography (PET) targeting the Prostate-Specific Membrane Antigen (PSMA) could achieve this, is still controversial. In this review, we summarized the available data on cytotoxic agents and their impact on PSMA expression, as well as the available data on PSMA PET imaging for response assessment
Porous medium equation and cross-diffusion systems as limit of nonlocal interaction
No full textThis paper studies the derivation of the quadratic porous medium equation and a class of cross-diffusion systems from nonlocal interactions. We prove convergence of solutions of a nonlocal interaction equation, resp. system, to solutions of the quadratic porous medium equation, resp. cross-diffusion system, in the limit of a localising interaction kernel. The analysis is carried out at the level of the (nonlocal) partial differential equations and we use gradient flow techniques to derive bounds on energy, second order moments, and logarithmic entropy. The dissipation of the latter yields sufficient regularity to obtain compactness results and pass to the limit in the localised convolutions. The strategy we propose relies on a discretisation scheme, which can be slightly modified in order to extend our result to PDEs without gradient flow structure. In particular, it does not require convexity of the associated energies. Our analysis allows to treat the case of limiting weak solutions of the non-viscous porous medium equation at relevant low regularity, assuming the initial value to have finite energy and entropy
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