Systems of Gas Exchange

[...]... 5.74 1. 79 0. 41 0. 41 0.20 0 .13 0 .15 0 .15 19 ppm For C7+; mol wt = 14 7, Pc = 304psia, Tc = 1, 112 °R Condemate — 60 bbl/MMscf, 52.3 °APJ Initial free-water production — 0 bbl/MMscf Final free-water production — 15 bbl/MMscf (at surface conditions) Gas sales requirements — 1, 000 psi, 7 Ib/MMscf, '/4 grain H2S, 2% CO2 6 Design of GAS-HANDLING Systems and Facilities Chapter 9 discusses the refrigeration and. .. covered in Volume 1 Figure 1- 1 is a block diagram of a production facility that is primarily designed to handle gas wells The well flow stream may require heating prior to initial separation Since most gas wells flow at high pressure, a "•"Reviewed for the 19 99 edition by Folake A Ayoola of Paragon Engineering Services, Inc 1 2 Design of GAS-HANDLING Systems and Facilities Figure 1 -1 Gas field facility... oil and water * Reviewed for the 19 99 edition by K S Chiou of Paragon Engineering Services, Inc 8 Design of GAS-HANDLING Systems and Facilities MECHANISMS OF HEAT TRANSFER There are three distinct ways in which heat may pass from a source to a receiver, although most engineering applications are combinations of two or three These are conduction, convection, and radiation Conduction The transfer of. .. difference between the hot and cold liquid, and the heat transfer area It is expressed: 10 where Design of GAS-HANDLING Systems and Facilities q = heat transfer rate, Btu/hr A = heat transfer area, ft2 AT = temperature difference, °F h = film coefficient, Btu/hr~ft 2 ~°F The proportionality constant, h, is influenced by the nature of the fluid and the nature of the agitation and is determined experimentally... delivered to them, and periodic tests are made to ascertain that requirements are being fulfilled by the seller 4 Design of GAS-HANDLING Systems and Facilities Acid gases, usually hydrogen sulfide (H2S) and carbon dioxide (CO2) are impurities that are frequently found in natural gas and may have to he removed Both can be very corrosive, with CO2 forming carbonic acid in the presence of water and H2S potentially... understand the lectures and carry out their assignments Of more importance, the material that did exist usually contained nomographs, charts, and rules of thumb that had no reference to the basic theories and underlying assumptions upon which they were based Although this text often relies and builds upon information that was presented in Surface Production Operations, Volume I: Design of Oil-Handling Systems. .. pressure) of any pipe/equipment system is set by a relief valve For this reason, a section on pressure relief has been included Since safety considerations are so important in any facility design, Chapter 14 has been devoted to safety analysis and safety system design (Volume 1, Chapter 13 discusses the need to communicate about a facility design by means of flowsheets and presents general comments and several... several examples of project management.) Table 1 -1 describes a gas field The example problems that are worked in many of the sections of this text are for sizing the individual pieces of equipment needed for this field CHAPTER 2 Heat Systems of Gas Exchange Systems of Gas Exchange Bởi: OpenStaxCollege The primary function of the respiratory system is to deliver oxygen to the cells of the body’s tissues and remove carbon dioxide, a cell waste product The main structures of the human respiratory system are the nasal cavity, the trachea, and lungs All aerobic organisms require oxygen to carry out their metabolic functions Along the evolutionary tree, different organisms have devised different means of obtaining oxygen from the surrounding atmosphere The environment in which the animal lives greatly determines how an animal respires The complexity of the respiratory system is correlated with the size of the organism As animal size increases, diffusion distances increase and the ratio of surface area to volume drops In unicellular organisms, diffusion across the cell membrane is sufficient for supplying oxygen to the cell ([link]) Diffusion is a slow, passive transport process In order for diffusion to be a feasible means of providing oxygen to the cell, the rate of oxygen uptake must match the rate of diffusion across the membrane In other words, if the cell were very large or thick, diffusion would not be able to provide oxygen quickly enough to the inside of the cell Therefore, dependence on diffusion as a means of obtaining oxygen and removing carbon dioxide remains feasible only for small organisms or those with highly-flattened bodies, sucs as many flatworms (Platyhelminthes) Larger organisms had to evolve specialized respiratory tissues, such as gills, lungs, and respiratory passages accompanied by a complex circulatory systems, to transport oxygen throughout their entire body 1/11 Systems of Gas Exchange The cell of the unicellular algae Ventricaria ventricosa is one of the largest known, reaching one to five centimeters in diameter Like all single-celled organisms, V ventricosa exchanges gases across the cell membrane Direct Diffusion For small multicellular organisms, diffusion across the outer membrane is sufficient to meet their oxygen needs Gas exchange by direct diffusion across surface membranes is efficient for organisms less than mm in diameter In simple organisms, such as cnidarians and flatworms, every cell in the body is close to the external environment Their cells are kept moist and gases diffuse quickly via direct diffusion Flatworms are small, literally flat worms, which ‘breathe’ through diffusion across the outer membrane ([link]) The flat shape of these organisms increases the surface area for diffusion, ensuring that each cell within the body is close to the outer membrane surface and has access to oxygen If the flatworm had a cylindrical body, then the cells in the center would not be able to get oxygen This flatworm’s process of respiration works by diffusion across the outer membrane (credit: Stephen Childs) Skin and Gills Earthworms and amphibians use their skin (integument) as a respiratory organ A dense network of capillaries lies just below the skin and facilitates gas exchange between the external environment and the circulatory system The respiratory surface must be kept moist in order for the gases to dissolve and diffuse across cell membranes Organisms that live in water need to obtain oxygen from the water Oxygen dissolves in water but at a lower concentration than in the atmosphere The atmosphere has roughly 21 percent oxygen In water, the oxygen concentration is much smaller than that Fish and many other aquatic organisms have evolved gills to take up the dissolved oxygen from water ([link]) Gills are thin tissue filaments that are highly branched and folded When water passes over the gills, the dissolved oxygen in water rapidly diffuses across the gills into the bloodstream The circulatory system can then carry the oxygenated blood to the other parts of the body In animals that contain coelomic fluid instead of 2/11 Systems of Gas Exchange blood, oxygen diffuses across the gill surfaces into the coelomic fluid Gills are found in mollusks, annelids, and crustaceans This common carp, like many other aquatic organisms, has gills that allow it to obtain oxygen from water (credit: "Guitardude012"/Wikimedia Commons) The folded surfaces of the gills provide a large surface area to ensure that the fish gets sufficient oxygen Diffusion is a process in which material travels from regions of high concentration to low concentration until equilibrium is reached In this case, blood with a low concentration of oxygen molecules circulates through the gills The concentration of oxygen molecules in water is higher than the concentration of oxygen molecules in gills As a result, oxygen molecules diffuse from water (high concentration) to blood (low concentration), as shown in [link] Similarly, carbon dioxide molecules in the blood diffuse from the blood (high concentration) to water (low concentration) As water flows over the gills, oxygen is transferred to blood via the veins (credit "fish": modification of work by ...Heat Transfer Theory 1 1 Multiple Transfer Mechanisms Most heat transfer processes used in production facilities involve combi- nations of conduction and convection transfer processes. For example, in heat exchangers the transfer of heat energy from the hot fluid to the cold fluid involves three steps. First, the heat energy is transferred from the hot fluid to the exchanger tube, then through the exchanger tube wall, and finally from the tube wall to the cold fluid. The first and third steps are convection transfer processes, while the second step is conduction process, To calculate the rate of heat transfer in each of the steps, the individual temperature difference would have to be known. It is difficult to measure accurately the temperatures at each boundary, such as at the surface of the heat exchanger tube. Therefore, in practice, the heat transfer calcula- tions are based on the overall temperature difference, such as the differ- ence between the hot and cold fluid temperatures. The heat transfer rate is expressed by the following equation, similar to the conductive/convec- tive transfer process: where q = overall heat transfer rate, Btu/hr U = overall heat transfer coefficient, Btu/hr-ft 2 -°F A = heat transfer area, ft 2 AT = overall temperature difference, °F Examples of overall heat transfer coefficient and overall temperature difference calculations are discussed in the following sections. Overall Temperature Difference The temperature difference may not remain constant throughout the flow path. Plots of temperature vs. pipe length for a system of two concen- tric pipes in which the annular fluid is cooled and the pipe fluid heated are shown in Figures 2-2 and 2-3. When the two fluids travel in opposite direc- tions, as in Figure 2-2, they are in countercurrent flow. When the fluids travel in the same direction, as in Figure 2-3, they are in co-current flow. The temperature of the inner pipe fluid in either case varies according to one curve as it proceeds along the length of the pipe, and the tempera- ture of the annular fluid varies according to another. The temperature dif- ference at any point is the vertical distance between the two curves. 12 Design of GAS-HANDLING Systems and facilities Figure 2-2. Change in AT over distance, counter-current flow of fluids. Since the temperature of both fluids changes as they flow through the exchanger, an "average" temperature difference must be used in Equation 2-3. Normally a log mean temperature difference is used and can be found as follows: where LMTD = log mean temperature difference, °F ATj = larger terminal temperature difference, °F AT 2 = smaller terminal temperature difference, °F Although two fluids may transfer heat in either counter-current or co- current flow, the relative direction of the two fluids influences the value of the LMTD, and thus, the area required to transfer a given amount of Heat Transfer Theory 13 Figure 2-3. Change in AT over distance, co-current flow of fluids. heat. The following example demonstrates the thermal advantage of using counter-current flow. Given: A hot fluid enters a concentric pipe at a temperature of 300°F and is to be cooled to 20Q°F by a cold fluid entering at 100°F and heated to 150°F. Co-current Flow: Side Hot Fluid Inlet Hot Fluid Outlet Hot Fluid °F 300 200 Cold Fluid °F 100 150 AT op 200 50 14 Design oj GAS-HANDLING Systems and Facilities Counter-current Flow: Side Hot Fluid Inlet Hot Fluid Outlet Hot Fluid °F 300 200 Original article Stomatal and non stomatal limitation of photosynthesis by leaf water deficits in three oak species: a comparison of gas exchange and chlorophyll a fluorescence data D Epron E Dreyer INRA-Nancy, Laboratoire de Bioclimatologie et d’Écophysiologie Forestières, Station de Sylviculture et Production, Champenoux, F-54280 Seichamps, France (Received 5 April 1990; accepted 6 June 1990) Summary — Net CO 2 assimilation (A), stomatal conductance for CO 2 (g), intercellular mole fraction of CO 2 (C i ), kinetics of chlorophyll a fluorescence, and their half decay time (t 1/2 ), their ratio of fluo- rescence decrease (Rfd), and their adaptive index (A p) have been monitored on potted trees from 3 oak species (Quercus petraea, Q pubescens and Q ilex) grown in a climate chamber and submitted to drought. Use of A vs Ci representations for photosynthesis data revealed an apparent impairment of mesophyll photosynthesis, together with reduced CO 2 supply to mesophyll due to stomatal clo- sure. But in all species chlorophyll a fluorescence kinetics displayed very similar shapes, constant t 1/2 and stable R fd and Ap values until predawn leaf water potential dropped below -4.0 MPa. These observations led to the conclusion that photochemical energy conversion and photosynthetic carbon reduction cycle could be very resistant to leaf water deficits, and that observed decreases in meso- phyll photosynthesis had to be attributed to a possible artefact in Ci calculation. On the other hand, the susceptibility of leaves to photoinhibition increased as a consequence of water shortage, espe- cially in Q petraea and Q pubescens. Differences in drought adaptation between the studied species could probably be related to susceptibility to photoinhibition rather than to a direct sensitivity of pho- tosynthesis to leaf water deficits, at least in the range of stress intensities of ecophysiological signifi- cance. photosynthesis / water stress / chlorophyll a fluorescence / oak / stomatal conductance / drought / photoinhibition Résumé — Limitation d’origine stomatique et non stomatique de la photosynthèse de trois espèces de chêne soumises à la sécheresse : comparaison de mesures d’échanges gazeux et de fluorescence de la chlorophylle. Les échanges gazeux foliaires et la fluorescence de la * Correspondence and reprints. Abbreviations : A = net CO 2 assimilation rate; A max = A at saturating Ci; A = adaptative index; Ci = intercellular CO 2 molar fraction; dA/dCi = carboxylation efficiency; Fp and Ft = maximal and terminal fluorescence levels; g = stomatal conductance for CO 2; LWC = leaf water content; Pi = inorganic phosphate; PPFD = photosynthetic photon flux density; PSII and PSI = photosystem II and I; R fd = ratio of fluorescence decrease; t 1/2 = fluorescence half-decay time; a = apparent quantum yield of photosynthesis; ψ wp = predawn leaf water potential; Δw : leaf to air water vapour molar fraction differ- ence chlorophylle ont été étudiés lors d’une sécheresse édaphique imposée en conditions contrôlées, sur de jeunes plants de Quercus patraea, Q pubescens et Q ilex. L’analyse des relations entre assimila- tion nette de CO 2 (A) et fraction molaire intercellulaire calculée de CO 2 (C i) semble indiquer que l’inhibition de A a résulté à la fois d’une fermeture des stomates, mais aussi d’une altération des pro- cessus mésophylliens de la photosynthèse. Par contre, la forme des cinétiques de fluorescence de la chlorophylle réalisées in Control of gas exchange: evidence for root-shoot communication on drying soil T. Gollan 1 W.J. Davies 2 U. Schurr J. Zhang 2 1 Universitit Bayreuth, Lehrstuhl Pflanzen6kologie, POB 10 f2 51, 8580 Bayreuth, F.R.G., and 2 University of Lancaster, Department of Biological Sciences, Bailrigg, Lancaster LA I 4YQ, U. K. Decrease in leaf conductance (stomatal closure) with drying soil is a common phe- nomenon and has been reported in myriads of publications. Stomatal closure with soil drying generally occurs in parallel with a deterioration of plant water status. With a decrease in relative water content, leaf turgor and water potential in general decline. Since both leaf conductance and leaf water potential decrease more or less at the same time during a drying cycle, the decrease in leaf conductance is often explained as a function of the decrease in leaf water potential. During the last few years, increasing evidence has been accumulated that stomatal closure at drying soil is not only related to a deterio- ration in shoot water potential but also to changes in soil conditions. In this paper, we summarize the experimental evidence that led us to hypothesize a communi- cation between root and shoot on drying soil. Changes in plant performance with drying soil have been widely discussed during the last 50 years. Martin (1940), Veihmeyer and Hendrickson (1950), and Veihmeyer (1956) had previously con- cluded that the rate of transpiration was maintained until a critical soil water content was reached. With the introduc- tion of thermodynamics in plant water rela- tions and the development of more sophisticated measurement techniques, leaf water potential became the controlling factor in most experimental hypotheses. It was an obvious thought, because stoma- tal movements operate via changes in tur- gor of the guard cells and the surrounding epidermal cells (e.g., Raschke, 1979). Also, in most experiments under normal conditions, we are unable to uncouple the decrease in leaf conductance and the decrease in water potential; both are com- mon plant responses to drying soil. Leaf water relation parameters, however, failed to explain the stomatal response due to drought. Often there is no unique relation- ship between leaf conductance and leaf water potential for different species (e.g., Schulze and Hall, 1982). Some species show a more linear relationship between the two, others an expressed threshold response, which means that, during a soil drying cycle, leaf conductance was main- tained at a high value until a critical leaf water potential was reached (Turner, 1974; Ludlow, 1980). However, Bates and Hall (1981) showed, that leaf conductance can decrease without any detectable changes in bulk leaf water potential. Turn- er et al. (1985) and Gollan et aL (1985) showed for a herbaceous and a woody species, that within one species there was no unique relationship between leaf conductance and leaf water potential with drying soil. In their studies, leaf conduc- tance of a single leaf was measured at constant high humidity with the remainder of the plant being either at high or low air humidity (Fig. 1 Depending upon the humidity treatment, transpiration of the shrub was high at low humidity and vice versa. High rates of transpiration caused a decrease in leaf water potential of the whole shrub, and also in the single leaf. Leaf conductance, however, did not decrease, as would have been expected if a simple decrease in leaf water potential is a controlling factor for stomatal Page 1 of 2 (page number not for citation purposes) Available online http://ccforum.com/content/11/6/182 Abstract While the principles underlying alveolar gas exchange have been well-known for over 50 years, we still struggle to assess gas exchange in hypoxemic patients. Unfortunately, simple measure- ments lack discrimination while complex measurements are infeasible in clinical care. The paper by Karbing et al. in this issue seeks a middle ground based on the arterial P O 2 (PaO 2 )/inspired O 2 fraction (F IO 2 ) ratio measured at different F IO 2 s with the out- comes fed into proprietary software to account for both shunting and ventilation/perfusion inequality. Whether this is the optimal compromise between measurement difficulty and information available will have to be answered by those willing to test the approach in their own patients. It never ceases to amaze me that the primary function of the lungs — gas exchange — can be accurately described by one simple mass conservation equation. Such cannot be said for any other organ. However, while this was well established over 50 years ago [1,2], we continue to struggle for ways to quantify abnormal gas exchange in patients with hypoxemia. The problem boils down to the complexity of gas exchange in diseased lungs, where hypoxemia can stem from, firstly, insufficient overall ventilation; secondly, shunting of blood through unventilated vascular channels; thirdly, non-uniform distribution of ventilation, perfusion, or both throughout the 300 million or so alveoli; and fourthly, diffusion limitation of O 2 exchange across the alveolar wall [3]. Added to these four well- known causes of hypoxemia is the also well-known modulation of arterial oxygenation by so-called extra-pulmonary factors: O 2 consumption, ventilation, cardiac output, acid/base state, Hb P 50 and concentration, and body temperature [4]. Thus, when any of these extra-pulmonary factors change, so too will arterial oxygenation even if the lungs themselves remain unchanged. As if that were not enough, as inspired O 2 fraction (FIO 2 ) is altered, the arterial O 2 saturation changes, but the response is different depending on these various factors [5]. It should therefore come as no surprise that to fully assess gas exchange in any given patient, one really needs to be able to pin down each and every factor just mentioned. That of course is impractical (although technically feasible). That leaves us wondering what the compromise should be. We want the most information at the least experimental cost. We want methodology that will quantify a gas exchange problem in a manner that allows reliable pulmonary patho- physiological insights and also filters out the “noise” from factors outside the lungs that, as mentioned above, affect gas exchange. Unfortunately, full understanding requires complex measurements — there is no short cut, and you get what you pay for. At the simplest extreme, arterial P O 2 (PaO 2 ) or saturation do not do it, being sensitive to all the above factors: low experimental cost but poor discrimination between lung pathologies and between lung pathologies and the extra- pulmonary modulating factors. At the most complex extreme, the multiple inert gas elimination technique is currently the best tool to fully understand the nature of gas exchange [6,7], but the experimental cost is too high for routine clinical use. The paper by Karbing et al. in this issue [8] tackles this optimization problem by re-examining the PaO 2 /FIO 2 ratio, an index which has gained favor in recent years. They correctly point out that this ratio is NOT independent of F IO 2 despite its intent. They explore the behavior of this ratio under two common circumstances: two of the four causes of hypoxemia noted above — shunting and ventilation/perfusion (V • A/Q • ) inequality. Applying this ratio to several sets of patients they show that while in some the ratio behaves as if the lung has a pure shunt, in others it behaves as ... system 5/11 Systems of Gas Exchange The trachea and bronchi are made of incomplete rings of cartilage (credit: modification of work by Gray's Anatomy) Lungs: Bronchi and Alveoli The end of the trachea... via the veins (credit "fish": modification of work by Duane Raver, NOAA) 3/11 Systems of Gas Exchange Tracheal Systems Insect respiration is independent of its circulatory system; therefore, the.. .Systems of Gas Exchange The cell of the unicellular algae Ventricaria ventricosa is one of the largest known, reaching one to five centimeters