High Exchange Research Articles

Optimal Design of Crossflow Heat Exchangers

The design of plate-fin and tube-fin crossflow heat exchangers is discussed. The transfer surface area of crossflow heat exchangers is used ineffectively because of the nonuniform distribution of the heat transfer across the volume of the exchanger. The optimal distribution of the transfer surface area for maximum heat exchanger effectiveness and constant total surface area is determined. It is found that a Dirac delta distribution of the transfer surface aligned along the diagonal of the crossflow exchanger gives the best performance; equal to that of a counterflow device. Design guidelines for optimal area allocation within crossflow heat exchangers are established. Compared to conventional designs, designs following these guidelines may lead to either a higher exchanger effectiveness for equal pressure drops and surface area, reduced pressure drops for equal exchanger effectiveness, or reduced weight and a near cubic form of the exchanger core for equal pressure drops and effectiveness.

Mass-transfer in rotating packed beds—II. Experimental results and comparison with theory and gravity flow

This paper presents the first reported set of experimental measurements, based on chemical absorption of CO 2 in NaOH, of gas—liquid interfacial areas and liquid-side gas—liquid mass-transfer coefficients in a rotating bed as a function of rotational speed and liquid flow rate. It is shown that both increase with rotational speed. Reasons for higher contacting efficiency and higher exchange in rotating beds than in gravity flow are outlined. Liquid—solid volumetric mass-transfer coefficients are also experimentally determined and found to be significantly higher than in gravity flow. The experimental data confirm the theoretical correlations developed in Part I of this paper.

Na+-K+ regulation in cultured vascular smooth muscle cell of the spontaneously hypertensive rat

Na+-K+ passive transport and activity of the Na+ pump were examined in serially passed cultured vascular smooth muscle cells originating from spontaneously hypertensive (SH), Wistar-Kyoto (WKY), and Wistar (W) rats. Measurements included 22Na+ and 86Rb+ (K+ analogue) uptake and washout rate constants as well as intracellular Na+ and K+ levels. The aforementioned variables were studied in cells subjected to either 2 mM Ca2+ or Ca2+-deficient media. In 2 mM Ca2+ medium, SH rat cells demonstrated the highest exchange (uptake and washout) rate constants for Na+ and Rb+ (K+) among cells of the three rat strains. At this extracellular Ca2+ concentration, the Na+ pump activity of SH rat cells was higher than that of WKY rat cells and was not different from that of W rat cells. Incubation in Ca2+-deficient medium resulted in increased magnitudes of Rb+ washout and Na+ uptake rate constants in all cell preparations associated with elevated intracellular Na+ concentrations and augmented activity of the Na+ pump. Under this condition, cells derived from SH rats showed the highest Na+ uptake and Rb+ washout rate constants associated with the highest Na+ pump activity. The increase in intracellular Na+ level in Ca2+-deficient medium was the highest in SH rat cells. These findings show that innate membrane defects and the response of the Na+ pump to these abnormalities can be demonstrated in in vitro-grown vascular smooth muscle cells of the SH rat.

Chapter I. The Home Economy

Sterling appreciated sharply between early May and late July. As compared with our May forecast, which assumed the effective index would be about 9 per cent lower than it is currently, our present forecast illustrates the typical effects of a higher exchange rate. The outlook for inflation is improved. Exports are now expected to be lower and consumer spending higher than in our last forecast, a switch in demand particularly unfavourable to manufacturing.

Photosynthetic Carbon Sources of Stream Macrophytes

Rates of photosynthesis of four submerged stream macrophytes were examined under varying pH and composition of inorganic carbon species. Callitriche stagnatis and Sparganium simplex used only CO2 for photosynthesis. Potamogeton crispus and P. pectinatus used HCO3 in addition to CO2, but with much lower efficiency. The photosynthetic rates at air equilibrium and a total inorganic carbon concentration of 5.0 mM were 2–3 times lower than maximum rates at CO2 saturation for the HCO3 users and 10–14 times lower for the CO2 users. The CO2 compensation point of entire plants of Callitriche (2.5 μM) and Sparganium (6.0μM) was well below the equilibrium concentration (15 μM). and the low saturation points (250–500 μM) also pointed to efficient use of CO2. Callitriche and Sparganium compete successfully with HCO3− users in hardwater streams, which have a higher exchange and generation capacity of CO2 than stagnant and more soft waters. Rates of photosynthesis of Potamogeton crispus and P. pectinatus decreased at high pH. Depending on the two alternative hypotheses for HCO3use, this decline can be explained by CO3−− inhibition of HCO3− uptake or by increasing capacity to buffer H+efflux from the plant. Habitats subject to high pH, e. g. small ponds with dense vegetation, may have a strong selection for efficient mechanisms of HCO3 use.

The Impact of Inflation and Devaluation on the Selection of an International Borrowing Source: A Note

* In their recent article in this Journal, de Faro and Jucker addressed the problem of choosing international borrowing sources. Their approach consisted of identifying the effective interest rates in the various markets and comparing interest costs with expected devaluation-picking the source with least expected costs without consideration of the risk involved.1 Lower expected cost is likely to be a major reason for borrowing foreign currencies although not the only one. Other reasons may be thin domestic capital markets relative to financing requirements, comparative absence of disclosure rules and shorter lead time, hedging of balance sheet exposure by multinationals, as well as controls on capital flows-such as the U.S. program ending in January 1974. Yet, in the last few years, exchange rates have been more volatile, interest rates have been higher than in the past, and the average term to maturity in the Eurobond market has been a historically low 5-7 years. All of these developments imply a higher exchange risk for borrowers of foreign currencies. In other words, though such borrowing may have lower expected costs, these may be obtained at the risk of a considerable range of actual borrowing costs as time passes. The purpose of this short note is to bring into sharper focus this risk of actually higher than expected costs of borrowing foreign currencies. Some financial executives may not be at all concerned with the stability of borrowing costs; others, however, may not have a stomach for this added risk. Application of portfolio selection theory introduced by Markowitz2 and recently extended to this context by de Faro and Jucker themselves3 can help illustrate the problem of selecting an international borrowing source under uncertainty by making various assumptions about the degree of risk aversion. To concentrate on the main idea, we will simplify the problem to two sources of funds.4 And to lend realism to the discussion, we consider a Canadian borrower because Canada has traditionally had higher interest rates than the U.S., and Canadian firms have been heavy borrowers in foreign markets. Our hypothetical Canadian firm can borrow at effective interest rate RCAN. This cost is certain. Abroad-e.g., in the U.S. or in Europe-it can borrow at the nominal rate RUS, RUS<RCAN. The effective cost of a U.S. $ bond issue in terms of Canadian funds will, however, depend on exchange rate developments.

ChemInform Abstract: CONDUCTION AND RELAXATION OF CATIONS IN DEHYDRATED PARTIALLY COPPER(II)‐EXCHANGED SYNTHETIC FAUJASITES

Chemischer InformationsdienstVolume 7, Issue 5 Physical Inorganic Chemistry ChemInform Abstract: CONDUCTION AND RELAXATION OF CATIONS IN DEHYDRATED PARTIALLY COPPER(II)-EXCHANGED SYNTHETIC FAUJASITES ROBERT A. SCHOONHEYDT, ROBERT A. SCHOONHEYDTSearch for more papers by this authorFIRMIN VELGHE, FIRMIN VELGHESearch for more papers by this author ROBERT A. SCHOONHEYDT, ROBERT A. SCHOONHEYDTSearch for more papers by this authorFIRMIN VELGHE, FIRMIN VELGHESearch for more papers by this author First published: February 3, 1976 https://doi.org/10.1002/chin.197605015Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume7, Issue5February 3, 1976 RelatedInformation

A specific calcium requirement for potassium uptake by excised vetch roots

Compared to the behavior of excised barley roots, K uptake by excised roots of vetch was far more responsive to pH and required ambient Ca concentrations 100 fold higher to overcome the deleterious effect of low pH. At pH values above 7, however, the addition of very low concentrations of Ca markedly depressed the uptake of K by vetch roots, less so for barley. Potassium uptakes by vetch roots in the presence of Ca led to K being sequestered into a non-exchangeable form and this process was dependent upon aerobic metabolism. The degree of specificity for Ca appeared to be much higher for vetch roots than for barley roots. Some of the differences in response to Ca between vetch and barley may be related to the higher exchange capacity of vetch roots.

Scintigraphic Cholecystography — the Problem of Contrast Media Selection and Labelling

La possibilité d’obtenir „Biligraphine“ marquée par 131I d’une activité hautement spécifique a été examinée en vue d’obtenir une préparation convenable pour le diagnostic scintigraphique du tract hépato-biliaire avec l’emploi d’un volume réduit du moyen de contraste.Les résultats ont montré que la meilleure contribution de la réaction est obtenue quand le matériel est traité pendant 11 heures à une température de 150—180° C. Après cette période environ 90% de 131I est entré dans le Biligraphine. Le reste de l’iodide radioactif libre s’élimine por un échangeur d’ions.Nous pouvons conclure que la méthode de l’échange homogène offre de bonnes possibilités pour le marquage des moyens de contraste et qu’elle est réalisable par un procédé relativement simple.

The subcellular distribution and nucleotide specificities of Na+, K+-stimulated adenosine triphosphatase and [14C]adenosine diphosphate-adenosine triphosphate exchange reactions in rat brain.

Abstract—(1) The subcellular distributions of Na‐K ATPase and [14C]ADP‐ATP exchange activities were studied in rat brain. The data presented are not consistent with a discrete localization of these enzymes in any given fraction, but nerve endings and microsomes had similar specific activities. The supernatant fraction had the highest exchange and the lowest Na‐K ATPase activities, measured at a concentration of 3 mm‐MgCl2.(2) Nucleotide specificity of the Na‐K ATPase was determined in all fractions, and this enzyme system showed an absolute requirement for ATP. The [14C]ADP‐ATP exchange, measured at 3mm‐MgCl2, possessed broader specificity and also was active toward ITP, UTP and GTP; this serves to differentiate it from the Na‐K ATPase.(3) Treatment of nerve ending fractions with NaI medium removed the bulk of the [14C]ADP‐ATP exchange activity without loss in Na‐K ATPase activity.(4) The exchange activity in NaI‐insoluble fractions was insensitive to NaCl in the presence of 3 mm‐MgCl2, but it was stimulated 502‐820 percent at low MgCl2 concentrations, a finding which may be consistent with the postulated role of this exchange reaction in the Na‐K ATPase system.

Título en español.

Los suelos Catalina y Cialitos difieren en su capacidad para el intercambio de cationes a pesar de que contienen cantidades similares de materia orgánica y arcilla. Las fracciones arcillosas de estos suelos se sometieron a exámenes con rayos X y a análisis térmicos diferenciales (DTA) para determinar si las diferencias en la capacidad de intercambio de cationes podían atribuirse a diferencias en la composición mineralógica de la fracción arcillosa. Los análisis revelaron que la caolinita predomina en dicha fracción en ambos casos. Sin embargo, se encontró que en la arcilla Cialitos la caolinita cristaliza pobremente, mientras que en la arcilla Catalina los cristales son bien definidos. Como se ha comprobado que mientras menos definida es la cristalización más alta es la capacidad de intercambio, se considera que esto podría explicar la razón por la cual la arcilla Cialitos posee una capacidad mayor de intercambio. Otro factor que puede explicar en parte la diferencia en capacidad de intercambio es el contenido de óxidos de hierro libres del suelo, que es mayor en el suelo Catalina arcilloso. Está comprobado que los óxidos de hierro libres bloquean las posiciones que normalmente ocuparían los cationes reemplazables en las arcilla caoliníticas.

Deposition of C-14-labelled cholesterol in the atheromatous aorta.

The results suggest that circulating cholesterol exchanges with available cholesterol pools of intima of human aorta. This exchange is slow. Cholesterol in the atheromatous plaques appears to exchange or accept circulatory cholesterol with the greatest difficulty. The highest exchange or depositions were observed for area of the arch of human aorta; abdominal part of aorta showed a smaller exchange. The media showed about the same cholesterol rate of exchange through length of aorta. A disk technic suitable for various types of quantitative assays of intima, media, etc. of the aorta was described.

Título en español.

Se determinó la capacidad de cambio de la materia orgánica de un grupo de suelos típicos de Puerto Rico usando tres métodos de análisis: (1) Variación en la capacidad de cambio de las muestras de suelo al destruirse la materia orgánica. (2) Titulación potenciométrica de los coloides orgánicos extraídos del suelo con carbonato de sodio. (3) Correlación entre el contenido de materia orgánica y la capacidad de cambio de un grupo considerable de muestras de suelos similares. El primer método resultó ser el más práctico y fácil de llevar a cabo. Dio resultados muy parecidos a los obtenidos usando el método de correlación que es probablemente el más preciso. Este último método es, sinembargo, poco práctico. El segundo método dio los resultados más altos. La capacidad de cambio de la materia orgánica en las distintas muestras varió considerablemente, estando, la mayoría entre 100 y 150 m.e./100 gramos. Los resultados demostraron que la materia orgánica contribuye alrededor de un 25 por ciento de la capacidad de cambio total en los suelos estudiados. Se demostró que la fracción de la materia orgánica que se puede separar por medio de la flotación en agua, tiene una capacidad de cambio mayor que ninguna otra porción. Igualmente, la fracción mas propensa a la oxidación mostró una capacidad de cambio mayor que las fracciones más resistentes. Aparentemente, una parte considerable de la materia orgánica de los suelos de Puerto Rico está combinada íntimamente con la porción mineral y contribuye muy poco a la capacidad de cambio total del suelo. Esta fracción orgánica es muy resistente a la oxidación y esto explica el alto contenido de materia orgánica aún en suelos cultivados continua e intensivamente.