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Heat Effects (heat + effects)
Selected AbstractsNumerical analysis of the single electrode heat effect in molten carbonate fuel cells: temperature analysis of the electrolyte plate by applying irreversible thermodynamicsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 15 2004Fumihiko Yoshiba Abstract A temperature analysis model of a molten carbonate fuel cells (MCFC) stack is used to calculate the single electrode heat effects. The magnitude of heat which evolves from the cathode and absorbed at the anode is large, and in similar value to the electrical output of a MCFC. This suggests that the heat evolution of a single electrode causes a temperature difference between the electrodes. The temperature distribution in the electrolyte plate is evaluated to establish more accurate results concerning the temperature analysis model of the stack. The temperature distribution in the electrolyte plate is studied by applying irreversible thermodynamics. When the operating current density is less than 3000 A m,2 and the thermal conductivity of the electrolyte is more than 2 W m,1 K,1, the temperature difference between cathode and anode is estimated to be less than approximately 1 K. This result proves that the temperature difference between the electrodes can be supposed constant in constructing the temperature analysis model of the MCFC stack. This results also allows us to construct a two-dimensional heat production distribution in the cell plane and discrete heat production distribution in the stacking direction for the practical use of the temperature analysis model. Copyright © 2004 John Wiley & Sons, Ltd. [source] Heat-exchange pressure swing adsorption process for hydrogen separationAICHE JOURNAL, Issue 8 2008Jang-Jae Lee Abstract A current focus in the energy field is on the use of hydrogen in fuel cells. Development of a hydrogen station system is important to the commercialization of fuel cells and fuel cell powered vehicles. In this study, the heat-exchange pressure swing adsorption (HE-PSA) was developed to design a compact H2 PSA process for small spatial occupancy in the hydrogen station. The adsorption dynamics and performance of the newly designed bed were compared with those of a conventional bed by using a quaternary mixture (H2/CO2/CH4/CO 69:26:3:2 vol %) which is generally obtained from the steam-reforming reaction of natural gas. Because the detrimental exothermic/endothermic heat effects accompanied by the adsorption/desorption steps were reduced by heat exchange between the adsorption beds, the separation performance of the HE-PSA was higher than that of a conventional PSA. In addition, the spatial occupancy of the beds could be significantly reduced, compared with a conventional PSA, because the single annular-type bed performed the function of two beds in the HE-PSA. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source] Analysis of multicomponent adsorption kinetics on activated carbonAICHE JOURNAL, Issue 4 2003L. P. Ding An integrated mathematical model for the kinetics of multicomponent adsorption on microporous carbon was developed. Transport in this bidisperse solid is represented by balance equations in the macropore and micropore phases, in which gas-phase diffusion dominates the mass transfer in the macropores, with the phenomenological diffusivities represented by the generalized Maxwell,Stefan (GMS) formulation. Viscous flow also contributes to the macropore fluxes and is included in the MS expressions. Diffusion of the adsorbed phase controls the mass transfer in the micropore phase, which is also described in a similar way by the MS method. The adsorption isotherms are represented by a new heterogeneous modified vacancy solution theory formulation of adsorption, which has proved to be a robust method for adsorption on activated carbons. The model is applied to the coadsorption and codesorption of C2H6 and C3H8 on Ajax and Norit carbon, as well as the displacement on Ajax carbon. The effect of the viscous flow in the macropore phase is not significant for the cases studied. The model accurately predicts the overshoot behavior and rollup of C2H6 during coadsorption. The prediction for the heavier compound C3H8 is always satisfactory, though at higher C3H8 mole fraction, the overshoot extent of C2H6 is overpredicted, possibly due to neglect of heat effects. [source] Permafrost thermal state in the polar Northern Hemisphere during the international polar year 2007,2009: a synthesisPERMAFROST AND PERIGLACIAL PROCESSES, Issue 2 2010Vladimir E. Romanovsky Abstract The permafrost monitoring network in the polar regions of the Northern Hemisphere was enhanced during the International Polar Year (IPY), and new information on permafrost thermal state was collected for regions where there was little available. This augmented monitoring network is an important legacy of the IPY, as is the updated baseline of current permafrost conditions against which future changes may be measured. Within the Northern Hemisphere polar region, ground temperatures are currently being measured in about 575 boreholes in North America, the Nordic region and Russia. These show that in the discontinuous permafrost zone, permafrost temperatures fall within a narrow range, with the mean annual ground temperature (MAGT) at most sites being higher than ,2°C. A greater range in MAGT is present within the continuous permafrost zone, from above ,1°C at some locations to as low as ,15°C. The latest results indicate that the permafrost warming which started two to three decades ago has generally continued into the IPY period. Warming rates are much smaller for permafrost already at temperatures close to 0°C compared with colder permafrost, especially for ice-rich permafrost where latent heat effects dominate the ground thermal regime. Colder permafrost sites are warming more rapidly. This improved knowledge about the permafrost thermal state and its dynamics is important for multidisciplinary polar research, but also for many of the 4 million people living in the Arctic. In particular, this knowledge is required for designing effective adaptation strategies for the local communities under warmer climatic conditions. Copyright © 2010 John Wiley & Sons, Ltd. [source] A heuristic approach of calculating spray water flux needed to avert fire-induced runaway reactions,,PROCESS SAFETY PROGRESS, Issue 3 2006BChE (Honors), Dilip K. Das BSc (Honors), MSChE In general all reactions have some heat effects. When the ability of the equipment to remove the heat is exceeded by the heat generated by a reaction, a hazardous situation called a runaway reaction may take place. Sometimes the exothermicity of runaway reactions is so high that the size of an emergency vent becomes impractical to install. A water spray system can sometimes be used to avert a fire-induced runaway reaction. Because the water spray system has a finite activation time, insulation helps to prolong the time required to reach the decomposition temperature. This article concludes that the required water flux to avert the fire-induced runaway reaction may be conservatively estimated by adding the water flux necessary to maintain an unbroken water film on the external surface of the equipment and the water flux necessary to absorb the fire heat after allowing for the splash loss and the in-flight loss. When adequate spray water is used, the metal temperature of the insulation jacket cannot theoretically exceed the boiling point of water thereby ensuring the avoidance of fire-induced runaway reactions whose adjusted onset decomposition temperature exceeds 100 ° C. Fire-induced runaway reactions with lower onset temperature can also be avoided depending on the initial temperature of the contents, mass of the contents and equipment, insulation thickness, and fire duration, for example, but a detailed calculation including dynamic simulation is necessary and the burden of proof lies with the designer. The reliability of the spray water system must be maintained high to include its credit as an environmental factor defined according to NFPA 30 to avoid the fire-induced runaway reaction as a scenario. Although API RP 521 does not allow any credit for sprinkler water, it allows credit, unlike NFPA 30, for insulation thickness and thus a runaway reaction can be avoided by using insulation alone according to API RP 521. © 2006 American Institute of Chemical Engineers Process Saf Prog, 2006 [source] CONSTRAINING HEAT INPUT BY TRAJECTORY OPTIMIZATION FOR MINIMUM-FUEL HYPERSONIC CRUISEASIAN JOURNAL OF CONTROL, Issue 4 2006M. Wächter ABSTRACT Unsteady heat input effects are considered for the range cruise of a future hypersonic vehicle equipped with a turbo/ram jet engines combination. A realistic mathematical model for describing the unsteady heat effects has been developed. It is coupled to the model for the dynamics of the vehicle. To compute the heat load in hypersonic flight, several points on the vehicle surface are treated simultaneously. A two-step technique consisting of an efficient optimization algorithm and an ordinary differential equations (ODE) solver is applied to generate a solution. The results show that the heat load can be significantly reduced, with only a small increase in fuel consumption. [source] Response surfaces for the combined effects of heat shock and smoke on germination of 16 species forming soil seed banks in south-east AustraliaAUSTRAL ECOLOGY, Issue 6 2007PAUL B. THOMAS Abstract There is limited understanding of how fire-related cues such as heat shock and smoke can combine to affect the germination response of seeds from fire-prone vegetation because combinations of multiple levels of both cues have rarely been investigated. Germination response surfaces were determined for the combination of heat shock and smoke by applying factorial combinations of temperature (up to 100°C) and aerosol smoke (0,20 min) to 16 species that form soil seed banks in the Sydney region of south-eastern Australia. Duplicate populations of three species were also examined to assess the constancy of a species response surface. Of the 19 populations examined, 16 showed a germination response to both the fire cues, which combined interactively in 14 populations, and independently in two. No population responded only to a single cue; however, seeds of 11 populations responded to heat in the absence of smoke, and nine responded to smoke in the absence of heat. Heat applied in the absence of smoke negatively affected germination in seven populations, either progressively as temperature increased, or above a set temperature. Negative germination responses over part of the temperature range were fully reversed at higher temperatures for unsmoked seeds of four populations (curvilinear heat response). Smoke effects were most frequently positive over all or part of the range of durations used, and when combined with heat frequently fully or partially reversed negative heat effects. Three populations required the obligatory combination of smoke and heat. A novel response to the cues was observed for three species, with smoke reversing negative heat effects at 75°C, being supplanted by a positive heat response of unsmoked seed at 100°C. The response surface for duplicate populations of two of the three species examined was variable. Heat shock and smoke frequently combined to affect germination, in both positive and negative ways. Consequently, to gain an accurate assessment of the response of seeds to fires, an experimental design that samples within the potential response zones of germination cues is essential. [source] | |||||||||||||