Energy Generation Processes Research Articles

Monte Carlo simulations of star clusters - III. A million-body star cluster

A revision of Stodolkiewicz's Monte Carlo code is used to simulate the evolution of million body star clusters. The new method treats each superstar as a single star and follows the evolution and motion of all individual stellar objects. A survey of the evolution of N-body systems influenced by the tidal field of a parent galaxy and by stellar evolution is presented. The process of energy generation is realized by means of appropriately modified versions of Spitzer's and Mikkola's formulae for the interaction cross section between binaries and field stars and binaries themselves. The results presented are in good agreement with theoretical expectations and the results of other methods. During the evolution, the initial mass function (IMF) changes significantly. The local mass function (LMF) around the half--mass radius closely resembles the actual global mass function (GMF). At the late stages of evolution the mass of the evolved stars inside the core can be as high as 97% of the total mass in this region. For the whole system, the evolved stars can compose up to 67% of the total mass. The evolution of cluster anisotropy strongly depends on initial cluster concentration, IMF and the strength of the tidal field. The results presented are the first step in the direction of simulating the evolution of real globular clusters by means of the Monte Carlo method.

A novel systems biology/engineering approach solves fundamental molecular mechanistic problems in bioenergetics and motility

A large number of new insights and further intricate details of the molecular mechanisms of ATP synthesis and muscle contraction have been offered from the perspective of the torsional mechanism of energy transduction and ATP synthesis and the rotation-uncoiling-tilt (RUT) energy storage mechanism of muscle contraction. In this paper, a new systems thermodynamics analysis of oxidative- and photo-phosphorylation has been performed. New experimental data has been reported on the inhibition of ATP synthesis by known specific anion channel blockers: the triorganotin compound, tributyltin chloride (TBTCl), and the stilbene compound 4,4′-diisothiocyanostilbene-2,2′-disulfonate (DIDS), and interpreted as supporting the new framework. A bioinformatic analysis of the interacting a–c regions in F O has been carried out to locate the anion binding pocket in the anion–proton symsequenceporter and insights into the coordination chemistry of the bound chloride in its internal cavity at the lipid–water interface have been obtained. The need to look at ATP synthesis in F O as a multisubstrate reaction has been emphasized and a detailed microscopic explanation of the mechanism of inhibition by these blockers and its relationship to the conformational cycle within F O has been postulated. Such detailed explanations of the role of membrane elements in a lipophilic region have been shown to lead to deeper understanding and to offer a more realistic and complete picture of biological energy transduction than considering the bilayer as “mere insulation”, as in chemiosmotic dogma. Details of the elementary force production events by myosin II have been provided within the novel molecular systems framework of the RUT mechanism in which the S-1, the S-1–S-2 hinge, and the S-2 coiled coil all have essential roles in the in vivo contractile process. The new paradigm is shown to be consistent with the great body of experiments usually considered to support the swinging crossbridge/lever arm models of muscle contraction, because these events also occur during the cycle but as events preliminary to the occurrence of the power stroke. The crucial role of energy storage in mechanically strained nonequilibrium conformational states of myosin, specifically as a high-energy state of S-2 with uncoiled first few N-terminal heptads is highlighted. The propensity of these heptads to recoil and regain the resting state of the coiled coil is postulated to be a primary driving force of the power stroke. The new paradigms of ATP synthesis/muscle contraction have been shown to remove the inconsistencies present in previous theories and to have the sound backing of the first and second laws of thermodynamics, the principle of electrical neutrality, the laws of Newtonian mechanics, and the great conservation laws of mechanics. A systems integration of muscle contraction has been successfully made and a systems electrical analog constructed. The unifying laws and principles in the new theories have been further applied to understand the functioning of other protein molecular machines such as kinesin, ncd and unconventional myosins. Finally, the major physical, chemical, biological and technological implications arising as a result of this research have been discussed. Taken together, the new paradigms have been shown to solve fundamental molecular mechanistic problems in bioenergetics and motility and to offer a most detailed, unified and appealing picture of energy generation, transduction, storage and utilization processes in systems of biological molecular machines.

The Inhibitory Effects of Free Nitrous Acid on the Energy Generation and Growth Processes of an Enriched Nitrobacter Culture

The inhibitory effects of nitrite (NO2-)/free nitrous acid (HNO2-FNA) on the metabolism of Nitrobacter were investigated using a method allowing the decoupling of the growth and energy generation processes. A lab-scale sequencing batch reactor was operated forthe enrichment of a Nitrobacter culture. Fluorescent in situ hybridization (FISH) analysis showed that 73% of the bacterial population was Nitrobacter. Batch tests were carried out to assess the oxygen and nitrite consumption rates of the enriched culture at low and high nitrite levels, in the presence or absence of inorganic carbon. It was observed that in the absence of CO2, the Nitrobacter culture was able to oxidize nitrite at a rate that is 76% of that in the presence of CO2, with an oxygen consumption rate that is 85% of that measured in the presence of CO2. This enabled the impacts of nitrite/FNA on the catabolic and anabolic processes of Nitrobacter to be assessed separately. FNA rather than nitrite was likely the actual inhibitor to the Nitrobacter metabolism. It was revealed that FNA of up to 0.05 mg HNO2-N x L(-1) (3.4 microM), which was the highest FNA concentration used in this study, did not have any inhibitory effect on the catabolic processes of Nitrobacter. However, FNA initiated its inhibition to the anabolic processes of Nitrobacterat approximately 0.011 mg HNO2-N x L(-1) (0.8 microM), and completely stopped biomass synthesis at a concentration of approximately 0.023 mg HNO2-N x L(-1) (1.6 microM). The inhibitory effect could be described by an empirical inhibitory model proposed in this paper, but the underlying mechanisms remain to be revealed.

Stoichiometric and kinetic characterisation of Nitrosomonas sp. in mixed culture by decoupling the growth and energy generation processes

A novel method that relies on the decoupling of the energy production and biosynthesis processes was used to characterise the maintenance, cell lysis and growth processes of Nitrosomonas sp. A Nitrosomonas culture was enriched in a sequencing batch reactor (SBR) with ammonium as the sole energy source. Fluorescent in situ hybridization (FISH) showed that Nitrosomonas bound to the NEU probe constituted 82% of the bacterial population, while no other known ammonium or nitrite oxidizing bacteria were detected. Batch tests were carried out under conditions that both ammonium and CO2 were in excess, and in the absence of one of these two substrates. The oxygen uptake rate and nitrite production rate were measured during these batch tests. The results obtained from these batch tests, along with the SBR performance data, allowed the determination of the maintenance coefficient and the in situ cell lysis rate, as well as the maximum specific growth rate of the Nitrosomonas culture. It is shown that, during normal growth, the Nitrosomonas culture spends approximately 65% of the energy generated for maintenance. The maintenance coefficient was determined to be 0.14-0.16 mgN mgCOD(biomass)(-1)h(-1), and was shown to be independent of the specific growth rate. The in situ lysis rate and the maximum specific growth rate of the Nitrosomonas culture were determined to be 0.26 and 1.0 day(-1) (0.043 h(-1)), respectively, under aerobic conditions at 30 degrees C and pH 7.

Stoichiometric and kinetic characterisation of Nitrobacter in mixed culture by decoupling the growth and energy generation processes

The growth, maintenance and lysis processes of Nitrobacter were characterised. A Nitrobacter culture was enriched in a sequencing batch reactor (SBR). Fluorescent in situ hybridisation showed that Nitrobacter constituted 73% of the bacterial population. Batch tests were carried out to measure the oxygen uptake rate and/or nitrite consumption rate when both nitrite and CO2 were in excess, and in the absence of either of these two substrates. The results obtained, along with the SBR performance data, allowed the determination of the maintenance coefficient and in situ cell lysis rate of Nitrobacter. Nitrobacter spends a significant amount of energy for maintenance, which varies considerably with the specific growth rate. At maximum growth, Nitrobacter consume nitrite at a rate of 0.042 mgN/mgCOD(biomass) . h for maintenance purposes, which increases more than threefold to 0.143 mgN/mgCOD(biomass) . h in the absence of growth. In the SBR, where Nitrobacter grew at 40% of its maximum growth rate, a maintenance coefficient of 0.113 mgN/mgCOD . h was found, resulting in 42% of the total amount of nitrite being consumed for maintenance. The above three maintenance coefficient values obtained at different growth rates appear to support the maintenance model proposed in Pirt (1982). The in situ lysis rate of Nitrobacter was determined to be 0.07/day under aerobic conditions at 22 degrees C and pH 7.3. Further, the maximum specific growth rate of Nitrobacter was estimated to be 0.02/h (0.48/day). The affinity constant of Nitrobacter with respect to nitrite was determined to be 1.50 mgNO2(-)-N/L, independent of the presence or absence of CO2.

Cellulose acetate reverse osmosis membranes: Optimization of the composition

AbstractMembranes based on cellulose acetate for reverse osmosis can possibly be applied to the so‐called salinity process of energy generation and water desalinization. The requirements for membranes for these two different applications are a relatively high water flux and low salt permeability. In this article, we present the optimization of the composition of such membranes. We started by producing membranes with a patented casting solution with the following composition: 45.77 wt % dioxane, 17.61 wt % acetone, and 8.45 wt % acetic acid (solvents); 14.09 wt % methanol (nonsolvent); and 7.04 wt % cellulose diacetate and 7.04 wt % cellulose triacetate. The membranes produced with this solution were analyzed comparatively, with the membranes obtained by the introduction of modifications to the following parameters: the solvent mix, the nonsolvent mix, the proportion of cellulose diacetate and cellulose triacetate in the casting solution, and the addition of reinforcing cellulose fibers. The results led us to conclude that the best membrane formulation had the following composition: 45.77 wt % dioxane, 17.61 wt % acetone, and 8.45 wt % acetic acid (solvents); 4.22 wt % cellulose triacetate and 9.86 wt % cellulose diacetate (polymers); 14.09 wt % methanol (nonsolvent); and 0.5 wt % cellulose fibers (with respect to the total polymer content). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4052–4058, 2006

Identification of a Ubiquinone-binding Site That Affects Autophosphorylation of the Sensor Kinase RegB

Rhodobacter capsulatus regulates many metabolic processes in response to the level of environmental oxygen and the energy state of the cell. One of the key global redox regulators of the cell's metabolic physiology is the sensor kinase RegB that controls the synthesis of numerous energy generation and utilization processes. In this study, we have succeeded in purifying full-length RegB containing six transmembrane-spanning elements. Exogenous addition of excess oxidized coenzyme Q1 is capable of inhibiting RegB autophosphorylation approximately 6-fold. However, the addition of reduced coenzyme Q1 exhibits no inhibitory effect on kinase activity. A ubiquinone-binding site, as defined by azidoquinone photo affinity cross-linking, was determined to lie within a periplasmic loop between transmembrane helices 3 and 4 that contains a fully conserved heptapeptide sequence of GGXXNPF. Mutation of the phenylalanine in this heptapeptide renders RegB constitutively active in vivo, indicating that this domain is responsible for sensing the redox state of the ubiquinone pool and subsequently controlling RegB autophosphorylation.

Comparison of Life‐Cycle Inventory Databases: A Case Study Using Soybean Production

Three established life‐cycle inventories of agricultural operations were used to generate air emissions data for soybean production: the greenhouse gases, regulated emissions, and energy use in transportation (GREET) model; the economic input‐output life‐cycle assessment (EIO‐LCA) model; and SimaPro software equipped with the Franklin database. EIO‐LCA and GREET baseline data were compared to evaluate differences in boundary definitions that apply specifically to U.S. soybean agriculture and processing, which resulted in several major findings. The EIO model estimated for emissions of particulate matter less than 10 micrograms (PM10) resulting from wind erosion that were not included in GREET, but neglected indirect nitrous oxide (N2O) and nitrogen oxides (NOx) emissions from fertilizer application. EIO also assumed significantly lower process energy requirements and lower volatile organic compounds (VOC) for soybean crushing and oil extraction. The GREET and SimaPro models were compared using identical boundary and assumption data, to reveal major discrepancies in fundamental assumptions of energy inventories. Key emission factors varied by several orders of magnitude for basic energy generation and combustion processes, potentially impacting results for any inventory analysis that contains significant energy consumption. The Franklin database assumed VOC and sulfur oxides (SOx) emissions more than an order of magnitude higher than GREET for all categories investigated, with significantly lower N2O and methane (CH4) emission factors.

Modeling complex dispersed energy and clean water systems for the US/Mexico border

The technological advances have been accompanied by an enormous demand for energy. Non-renewable energy sources have supplied this energy so far, but it has also led to an erosion of the worldwide environment. The US/Mexico border region has some unique advantages and/or opportunities. The availability of high solar radiation, considerable amounts of non-potable water, and human and/or animal wastes can be used for generating hydrogen and biogas as alternative fuel sources. New technology can be used to produce hydrogen from salted water and this gas can be stored and later, used to fuel an electricity generator and consequently generate potable water as bi-product. Therefore, photovoltaic cells coupled to an electrolizer can be used to generate electricity in a sustainable manner. The research described here simulates complete energy systems based on commercial devices and developed using EXTEND software and has the capability to perform comparisons, predictions and evaluations among different processes for energy generation. In addition, it demonstrates alternatives in local energy production, and the feasibility of remote house hybrid system located in the El Paso/Juarez border area.

Methylglyoxal can completely replace the requirement of kinetin to induce differentiation of plantlets from some plant calluses

It is well known that cytokinins, a group of plant hormones are absolutely required for the differentiation of calluses for the regeneration of plantlets through organogenesis. In the present work, it had been observed that methylglyoxal could completely replace kinetin to initiate differentiation of plantlets from calluses of Solanum nigrum and Daucus carota. Moreover, the effect of methylglyoxal was more pronounced compared to that of kinetin and the optimum concentration for methylglyoxal had been determined to be 0.5Â mM. Parallel with the differentiation of calluses to plantlets, the chlorophyll contents increased whereas the endogenous level of methylglyoxal remained unchanged. This remarkable effect of methylglyoxal in plant differentiation had been found out to be specific because some related compounds such as pyruvate and -lactate could not replace the requirement for methylglyoxal in the differentiation process. The activities of several enzymes were monitored during both methylglyoxal and kinetin-induced differentiation. The activity of the enzyme glyceraldehyde-3-phosphate dehydrogenase (NADP-dependent) involved in energy generation process in photosynthesis, increased as the differentiation proceeded. Whereas, the activities of both glucose-6-phosphate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase (NAD-dependent) decreased with differentiation. The activity of glyoxalase I, which catalyzes the conversion of methylglyoxal and glutathione to S--lactoylglutathione, decreased with differentiation. The endogenous level of glutathione showed an initial decrease followed by an increase. It appears from the results presented above, that the effect of kinetin and methylglyoxal are similar in nature, the significance of which has been discussed.

Acetyl-coenzyme A synthetase (AMP forming).

Acetyl-coenzyme A synthetase (AMP forming; Acs) is an enzyme whose activity is central to the metabolism of prokaryotic and eukaryotic cells. The physiological role of this enzyme is to activate acetate to acetyl-coenzyme A (Ac-CoA). The importance of Acs has been recognized for decades, since it provides the cell the two-carbon metabolite used in many anabolic and energy generation processes. In the last decade researchers have learned how carefully the cell monitors the synthesis and activity of this enzyme. In eukaryotes and prokaryotes, complex regulatory systems control acs gene expression as a function carbon flux, with a second layer of regulation exerted posttranslationally by the NAD+/sirtuin-dependent protein acetylation/deacetylation system. Recent structural work provides snapshots of the dramatic conformational changes Acs undergoes during catalysis. Future work on the regulation of acs gene expression will expand our understanding of metabolic integration, while structure/function studies will reveal more details of the function of this splendid molecular machine.

Effect of cooling the recirculated exhaust gases on diesel engine emissions

Although combustion is essential in most energy generation processes, it is one of the major causes of air pollution. Spiral fin exhaust pipes were designed to study the effect of cooling the recirculated exhaust gases (EGR) of Diesel engines on the chemical composition of the exhaust gases and the reduction in the percentages of pollutant emissions. The gases examined in this study were oxides of nitrogen (NO x ), carbon dioxide (CO 2) and carbon monoxide (CO). In addition, O 2 concentration in the exhaust was measured. The two designs adopted in this study were exhaust pipes with solid and hollow fins around them. The first type uses air flow around the fins to cool the exhaust gases. The second type consists of hollow fins around the exhaust pipe to allow cooling water to flow in the hollow passage. Different combinations and arrangements of the solid and hollow fins exhaust pipes were used. It was found that decreasing the temperature of the EGR resulted in reductions in the oxides of nitrogen (NO x ) and carbon dioxide (CO 2) but increased the carbon monoxide (CO) in the exhaust gases. In addition, the oxygen (O 2) concentration in the exhaust was decreased. As a general trend, the percentages of reduction in the NO x gas concentrations were lower than the percentages of increase in the CO emissions as a result of cooling the EGR of a Diesel engine by a heat exchanger. Using water as a cooling medium decreased the exhaust gases temperature and the amount of pollutants more than did air as a cooling medium. In a separate series of tests, increasing the cooled EGR ratios decreased the exhaust NO x but increased the particulate matter concentrations in the exhaust gases.

Identification of androgen-coregulated protein networks from the microsomes of human prostate cancer cells.

Androgens play a critical role in the development of prostate cancer-dysregulation of androgen-regulated growth pathways can led to hormone-refractory prostate cancer. A comprehensive understanding of androgen-regulated cellular processes has not been achieved to date. To this end, we have applied a large-scale proteomic approach to define cellular processes that are responsive to androgen treatment in LNCaP prostate cancer cells. Using isotope-coded affinity tags and mass spectrometry we identified and quantified the relative abundance levels of 1,064 proteins and found that distinct cellular processes were coregulated by androgen while others were essentially unaffected. Subsequent pharmacological perturbation of the cellular process for energy generation confirmed that androgen starvation had a profound effect on this pathway. Our results provide evidence for the role of androgenic hormones in coordinating the expression of critical components involved in distinct cellular processes and further establish a foundation for the comprehensive reconstruction of androgen-regulated protein networks and pathways in prostate cancer cells.

Measurements of Polycyclic Aromatic Hydrocarbon Adsorption on Activated Carbons at Very Low Concentrations

The aim of this paper is to describe the existent equilibrium between polycyclic aromatic hydrocarbons (PAHs) and granular carbonaceous materials in adsorption processes occurring in carbon beds used for air pollution control. The adsorption of the most volatile PAHs listed by the USEPAnaphthalene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, and pyrenewas measured under the conditions at which they are emitted in energy generation processes, that is, with concentrations ranging from 0.020 to 25 ppm and at a temperature of 150 °C. Experimental results show that their adsorption capacity is dependent on PAH concentrations. From the measured adsorption capacities, original isotherms have been plotted and adsorption parameters based on the two-parameter models of Langmuir, Brunauer−Emmett−Teller, Freundlich, and Dubinin−Radushkevich have been calculated. Neither of the two-parameter models was able to fit the experimental data in all PAH concentration ranges studied. Furthermore, no relationship was found between the PAH physical propertiesmolecular volume, boiling point, and vapor pressure at 150 °Cand the parameters obtained in the four models.

Effects of CO2 on the Phenanthrene Adsorption Capacity of Carbonaceous Materials

Three-ring polycyclic aromatic hydrocarbons (PAHs), and phenanthrene (Phe) in particular, are the main pollutants found in the waste flue gases from organic material combustion in energy generation processes. Quantitatively, the most abundant gaseous contaminant emitted in these processes is CO2. Therefore, the aim of this paper has been to study the influence of different CO2 concentrations on the phenanthrene adsorption in a postcombustion cleanup process when carbonaceous materials are used to remove low concentrations of phenanthrene from a hot exhaust gas stream. Adsorption isotherms were obtained using CO2 and phenanthrene concentrations in the ranges of 0−30% and 0.025−3.2 ppmv, respectively. The process temperature was fixed to 150 °C in all runs. All the obtained isotherms were properly fitted to the Freundlich adsorption model and their parameters determined by regression analyses. A negative influence of CO2 in phenanthrene adsorption capacity was observed, probably due to a competitive effect between CO2 and phenanthrene for the adsorption sites within the carbonaceous material. However, it was found that high CO2 concentrations did not affect the phenanthrene adsorption more negatively than low CO2 concentrations. It was thus concluded that the most suitable carbonaceous materials for phenanthrene abatement in flue gases were those having a wide pore distribution with a high average micropore diameter. The development of mesoporosity in adsorbents promotes phenanthrene adsorption because it favors both the access of phenanthrene molecules into the micropores and the phenanthrene multilayer adsorption. Finally, the Yoon and Nelson mathematical model was applied to simulate the breakthrough curves. This model was able to predict the adsorption breakthrough in all the runs. Nevertheless, problems arose when trying to fit breakthrough curves at relative concentrations higher than 70% in those adsorbents with narrow micropore distributions.

Mechanical Energy Generation during High Burnup Fuel Failure under Reactivity Initiated Accident Conditions

The dominant factor of mechanical energy generation during high burnup fuel failure under reactivity initiated accident (RIA) conditions is discussed on the basis of results from recent two RIA-simulating tests with burnup fuel rods and separate-effect tests with powder fuels. When cladding failed during the RIA conditions, solid fuel fragments were dispersed into the coolant water. The results from the recent two burnup fuel experiments indicated that the dominant factor of mechanical energy generation was thermal interaction of dispersed fuel fragments with the coolant water. To eliminate the effect of gas release from the fuel rod, and to evaluate the potential of the thermal interaction, powder fuel experiments were also performed as separate-effect tests. The results showed consistency in the mechanical energy generation process between the burnup fuel experiments and the powder fuel experiments. Accordingly, thermal interaction should be the dominant factor of the mechanical energy generation. Concerning the conversion ratio from thermal to mechanical energy, the finer fuel particles generated more mechanical energy at the same energy deposition level.

Monte Carlo simulations of star clusters -- II. Tidally limited, multimass systems with stellar evolution

A revision of Stodółkiewicz's Monte Carlo code is used to simulate evolution of large star clusters. The new method treats each superstar as a single star and follows the evolution and motion of all individual stellar objects. A survey of the evolution of N-body systems influenced by the tidal field of a parent galaxy and by stellar evolution is presented. The process of energy generation is realized by means of appropriately modified versions of Spitzer's and Mikkola's formulae for the interaction cross-section between binaries and field stars and binaries themselves. The results presented are in good agreement with theoretical expectations and the results of other methods (Fokker–Planck, Monte Carlo and N-body). The initial rapid mass loss, resulting from stellar evolution of the most massive stars, causes expansion of the whole cluster and eventually leads to the disruption of less bound systems (W0=3). Models with larger W0 survive this phase of evolution and then undergo core collapse and subsequent post-collapse expansion, like isolated models. The expansion phase is eventually reversed when tidal limitation becomes important. The results presented are the first major step in the direction of simulating evolution of real globular clusters by means of the Monte Carlo method.

COHEX: a computer model for solving the thermal energy exchange in an ultra high temperature heat exchanger. Part B: validation and results

The paper reports the development of a computer program that solves the thermal energy exchange and pressure drop characteristics for bayonet-element heat exchangers. The prime motivation for the study was to aid the design of a heat exchanger for the externally-fired combined cycle (EFCC) energy generation process. The essential feature of this high-efficiency process is the CMC (ceramic matrix composite) bayonet-tube gas–gas heat exchanger for use with shell-side temperatures up to 1600°C. It is envisaged that similar heat exchangers can be designed for applications in the metallic extraction and production industries. The program, named COHEX (composite heat exchanger), solves the basic governing equations of the exchanger. It makes use of a numerical iterative approach from an initial tube-side outlet temperature estimate to converge to a solution. For given inlet conditions, the program evaluates the heat transfer between the shell-side and tube-side streams and arrives at the outlet conditions. This two-part paper presents a computational solution method using accepted techniques for conduction, convection and radiation in the high temperature heat exchanger. Part A addresses the technological background of the EFCC application and the theoretical content of COHEX in terms of accuracy and sophistication of the code. The second part of this paper reported here, part B, describes the experimental facilities used to gather data in order to validate the program output. A comparison of computed and experimental data is presented. The paper progresses to illustrate the effects of parameter variation on heat exchanger output.

COHEX: a computer model for solving the thermal energy exchange in an ultra high temperature heat exchanger. Part A: computational theory

The paper reports the development of a computer program that solves the thermal energy exchange and pressure drop characteristics for bayonet-element heat exchangers. The prime motivation for the study was to aid the design of a heat exchanger for the externally-fired combined cycle (EFCC) energy generation process. The essential feature of this high-efficiency process is the ceramic bayonet-tube gas–gas heat exchanger for use with shell-side temperatures up to 1600°C. It is envisaged that similar heat exchangers can be designed for applications in the metallic extraction and production industries. The program, named COHEX ( Composite Heat Exchanger), solves the basic governing equations of the exchanger. It makes use of a numerical iterative approach from an initial tube-side outlet temperature estimate to converge to a solution. For given inlet conditions, the program evaluates the heat transfer between the shell-side and tube-side streams and arrives at the outlet conditions. This two-part paper presents a computational solution method using accepted techniques for conduction, convection and radiation in the ceramic heat exchanger. Part A addresses the technological background of the EFCC application and the theoretical content of COHEX in terms of accuracy and sophistication of the code. The second part of this paper, part B, describes the experimental facilities used to gather data in order to validate the program output. A comparison of computed and experimental data is presented. The paper progresses to illustrate the effects of parameter variation on heat exchanger output.

Boundary-layer flow and turbulence near porous obstacles

We derive a set of governing equations for flow through porous obstacles by employing a two-step averaging processes. The Navier-Stokes equations under the Boussinesq approximation that describe the air space of the porous obstacle are subjected to high-wavenumber a veraging, which leads to a set of high-frequency (wake) turbulence equations. We then use conventional Reynolds-averaging methods to obtain statistically steady mean and turbulence equations that include interactions between wake and shear turbulence. Our method provides a theoretical basis for the cascade of turbulent kinetic energy. We use this approach to analyze the constants and parameters of simpleK-theory and higher-order closure models. We also discuss qualitatively the theory of the turbulence energy generation process and the significance of interactions between different turbulent mechanisms.