Irreversible Absorption Research Articles

06/00362 Irreversible absorption heat-pump and its optimal performance: Chen, L. et al. Applied Energy, 2005, 81, (1), 55–71

The energy audit of an operating distillery producing ethyl alcohol from low quality wine and wine dregs is presented. Three different processes were analyzed: the production of raw (unrefined) alcohol using stripping columns working at pressure lower than atmospheric, the same production using columns at higher pressure and the production of neutral (refined) alcohol. The operational and design data of these three processes were used to compute mass and energy balances. The liquid streams in a distillery are multicomponent nonideal solutions. The data reported in the literature for ethyl and methyl alcohol–water mixtures were utilized, together with purposely developed correlations for density, specific heat and vapor–liquid equilibrium and simplified exergy formulas. The methodologies used to study the alcohol production are based on the pinch technology approach: the detailed energy balances of the three industrial processes are presented. The main step was to present the heat sources and sinks of the production processes in the grand composite curve, laying out all the thermodynamic opportunities of any heat recovery. Thermodynamic analysis methods were used to minimize the heating energy needed by the production processes when using heat pump systems. The use of heat pump systems, mainly based on mechanical vapor re-compression, has proven to be effective in energy saving and profitable in other applications, as the concentration of gelatine, distillation of organic vapors, pulp drying and beer production. Different heat pump systems were investigated and compared with respect to fuel utilization and capital expenditures: electrical engine driven compressors, gas engine driven compressors, steam turbine driven compressors, gas absorption chillers, steam absorption chillers and thermo-vapor re-compression. It showed that the cogeneration of mechanical energy and heat to drive vapor compression (the so-called thermodynamic heating method of Frutschi et al.) is superior to other types of systems. Then, for mechanical vapor compression systems, two different applications to different production processes were analyzed: (a) a system using commercially available refrigerants and (b) a heat pump cycle using water from the bottom of the distillation columns or steam condensate as working fluid. The thermodynamic analysis, based on performance coefficients and fuel utilization, as well as the economic profitability in terms of costs, benefits and payback period, were discussed in detail.

Combined isotherm of adsorption and absorption on coal and differentiation of both processes

Sorption of hydrogen and helium on coal and activated charcoal was measured at 298 K within the pressure range 0–1 bar and the obtained isotherms were characterized by a maximum deviation of the desorption branch from the adsorption branch implied with their shape the process of irreversible absorption. At the sorption of carbon dioxide on coal, the simultaneously running adsorption and absorption were registered by a combined isotherm AD/AB, which desorption branch was for individual coals characterized with variously sized hysteresis. After separation of both partial sorption processes, a scheme of reconstruction of the combined isotherm AD/AB has been proposed. This provided a corrected isotherm of separate physical adsorption AD for calculation of parameters of the microporous structure according to Dubinin, as well as a pure absorption isotherm AB, for which the analysis of experimental values confirmed its linearity according to Henry’s equation. Since the isotherm AD/AB including besides filling of micropores also occupation of intramolecular voids within the macromolecular coal matrix complies very well with the interpretation in Dubinin’s coordinates, the designation nanoporous system has been suggested for this set of cavities. From the difference of the spatial parameters calculated from the isotherms AD/AB and AD, the effective size of intramolecular voids could be estimated.

Dispersion in steady and oscillatory flows through a tube with reversible and irreversible wall reactions

An asymptotic analysis is presented for the advection–diffusion transport of a chemical species in flow through a small-diameter tube, where the flow consists of steady and oscillatory components, and the species may undergo linear reversible (phase exchange or wall retention) and irreversible (decay or absorption) reactions at the tube wall. Both developed and transient concentrations are considered in the analysis; the former is governed by the Taylor dispersion model, while the latter is required in order to formulate proper initial data for the developed mean concentration. The various components of the effective dispersion coefficient, valid when the developed state is attained, are derived as functions of the Schmidt number, flow oscillation frequency, phase partitioning and kinetics of the two reactions. Being more general than those available in the literature, this effective dispersion coefficient incorporates the combined effects of wall retention and absorption on the otherwise classical Taylor dispersion mechanism. It is found that if the phase exchange reaction kinetics is strong enough, the dispersion coefficient is probably to be increased by orders of magnitude by changing the tube wall from being non-retentive to being just weakly retentive.

05/01787 General performance characteristics of an irreversible vapour absorption refrigeration system using finite time thermodynamic approach: Bhardwaj, P. K. et al. International Journal of Thermal Sciences, 2005,44, (2), 189–196

05/01787 General performance characteristics of an irreversible vapour absorption refrigeration system using finite time thermodynamic approach: Bhardwaj, P. K. et al. International Journal of Thermal Sciences, 2005,44, (2), 189–196

Irreversible four-temperature-level absorption refrigerator

A refrigeration cycle is modeled as a demonstration of an irreversible absorption refrigeration cycle. This four-temperature-level model takes into account the heat resistance, heat leakage, and irreversibilities due to internal dissipation of the working fluid. The fundamental optimal relationships between: (1) the coefficient of performance (COP) and the cooling load; (2) the maximum COP and the corresponding cooling load; and (3) the maximum cooling load and the corresponding COP of the cycle, all coupled to constant-temperature heat reservoirs, are derived by using finite-time thermodynamics. The optimal distribution relationships of the heat-transfer surface areas are also presented. Moreover, the effects of the cycle parameters on the COP and the cooling load of the cycle are studied by detailed numerical examples. The results obtained herein are useful for optimal design and performance improvement of absorption refrigeration cycles.

Optical writing and reading with bilayer assemblies of photosensitive and fluorescent films

We have identified an efficient photochemical transformation involving the reaction of a [1,3]oxazine with tertiary amines. In aerated acetonitrile, the process is accompanied by the appearance of an intense absorption in the visible region. The irreversible formation of 4-nitrophenolate chromophores is responsible for the development of this band. The photogenerated absorption persists indefinitely upon storage in the dark or even under visible illumination. Furthermore, the process is particularly efficient when the [1,3]oxazine is reacted with triethylamine. The corresponding quantum yield is ca. 0.6. Their photoinduced reaction occurs also in poly(methylmethacrylate) matrices. Once again, the process is accompanied by the appearance of an intense absorption and induces pronounced changes in the refractive index of the dye–polymer composite. The irreversible absorption changes associated with these photosensitive materials can be exploited, in principle at least, to write information optically. The stored data can also be read optically relying on fluorescence measurements. Indeed, we have assembled a bilayer structure consisting of a photosensitive film overlaid on a poly(methylmethacrylate) film doped with naphthalene. The fluorescent dopant in the bottom layer emits light in a wavelength range where only the photogenerated state of the top layer absorbs. Thus, the emission coming from one component can be re-absorbed and filtered only by one of the two states of the other. On the basis of this mechanism, a simple fluorescence measurement can read the state of the photosensitive layer, which can, in turn, be written with an optical stimulation.

Irreversible absorption heat-pump and its optimal performance

On the basis of an endoreversible absorption heat-pump cycle, a generalized irreversible four-heat-reservoir absorption heat-pump cycle model is established by taking account of the heat resistances, heat leak and irreversibilities due to the internal dissipation of the working substance. The heat transfer between the heat reservoir and the working substance is assumed to obey the linear (Newtonian) heat-transfer law, and the overall heat-transfer surface area of the four heat-exchangers is assumed to be constant. The fundamental optimal relations between the coefficient of performance (COP) and the heating-load, the maximum COP and the corresponding heating-load, the maximum heating load and the corresponding COP, as well as the optimal temperatures of the working substance and the optimal heat-transfer surface areas of the four heat-exchangers are derived by using finite-time thermodynamics. Moreover, the effects of the cycle parameters on the characteristics of the cycle are studied by numerical examples.

General performance characteristics of an irreversible vapour absorption refrigeration system using finite time thermodynamic approach

This communication presents finite time thermodynamic analysis of vapour absorption refrigeration system considering both external as well as internal irreversibility. System is considered as consisting of an irreversible heat engine between the generator and absorber and an irreversible refrigerator between the evaporator and condenser. Optimization is made w.r.t. source/sink side heat exchanger areas, source/sink side heat transfer time and heat engine cycle and refrigeration cycle time. An optimal relation between overall coefficient of performance and maximum cooling load is obtained. Two internal irreversibility parameters (say, R Δ S is for generator–absorber assembly and R Δ S ′ is for evaporator–condenser assembly) have been introduced in the analysis, having fractional value for irreversible (real) system while R Δ S = R Δ S ′ = 1.0 corresponds to endoreversible system. A detailed parametric study shows that internal irreversibility parameters have more drastic effect on performance reduction than any other external irreversibility parameter. It is also found that internal irreversibility parameters are being dominant factor for performance reduction but out of these two parameters, internal irreversibility parameter of generator–absorber assembly is more sensitive for performance reduction than the internal irreversibility parameter of evaporator–condenser assembly.

04/02996 An absorption heat-transformer and its optimalperformance: Qin, X. et al. Applied Energy, 2004, 78, (3), 329–346

On the basis of the endoreversible model of absorption refrigeration cycles, a new cycle model, which includes the heat leak from the heat sink to the cooled space and irreversibilities due to the internal dissipation of the working fluid besides the finite-rate heat transfer between the working fluid and the external heat reservoirs, is established and used to calculate the maximum coefficient of performance and cooling rate of the absorption refrigeration system for a given total heat-transfer area of the heat exchangers. The temperatures of the working fluid and the distribution of the heat-transfer areas of the heat exchangers are optimized for the two states of maximum coefficient of performance and maximum cooling rate. The behavior of the dimensionless specific cooling rate as a function of the coefficient of performance is presented, which may be used to describe the general performance characteristics of an irreversible absorption refrigerator. The practical operating regions of the cycle system are determined and the new bounds of the primary performance parameters are given.

An irreversible thermodynamic model for solar absorption refrigerator

A solar refrigerator is made of a solar collector and a refrigeration system. Real solar refrigerators usually operate between two limits, maximum coefficient of performance (COP) and maximum cooling load. A new model is presented to describe an irreversible absorption refrigerator, in which not only the irreversibilities of heat conduction but also those resulting from friction, eddy and other irreversible effects inside the working fluid are considered. The influence of these irreversible effects on the performance of an absorption refrigerator with continuous flow is investigated. The analytical expressions of the optimal refrigeration coefficient and the cooling rate of the refrigerator are derived. The predictions of the model are compared with semi-empirical cycle model of single-stage absorption refrigeration machines. The results obtained here can describe the optimal performance of a four temperature level absorption refrigeration affected simultaneously by the internal and external irreversibilities and provide the theoretical bases for the optimal design and operation of real absorption refrigerators operating between four temperature levels.

Quantum pumping and dissipation: From closed to open systems

Current can be pumped through a closed system by changing parameters (or fields) in time. The Kubo formula allows to distinguish between dissipative and non-dissipative contributions to the current. We obtain a Green function expression and an $S$ matrix formula for the associated terms in the generalized conductance matrix: the "geometric magnetism" term that corresponds to adiabatic transport; and the "Fermi golden rule" term which is responsible to the irreversible absorption of energy. We explain the subtle limit of an infinite system, and demonstrate the consistency with the formulas by Landauer and Buttiker, Pretre and Thomas. We also discuss the generalization of the fluctuation-dissipation relation, and the implications of the Onsager reciprocity.

Thermoeconomic optimization for irreversible absorption refrigerators and heat pumps : Kodal, A. et al. Energy Conversion and Management, 2003, 44, (1), 109–123

Thermoeconomic optimization for irreversible absorption refrigerators and heat pumps : Kodal, A. et al. Energy Conversion and Management, 2003, 44, (1), 109–123

か粒および成形体特性に及ぼすスラリー調製条件の影響

The effects of physical properties of MnZn-ferrite slurry on the quality of granules and compacts were discussed. Emphasis is laid on the order of addition of a dispersant and poly vinyl alcohol (PVA) to the starting ferrite slurry. The composite slurries were prepared either by simultaneous addition of dispersant and PVA (Slurry S), sequential addition of PVA followed by dispersant (Slurry D) or dispersant followed by PVA (Slurry P). The viscous flow behavior of all the composite slurries was analyzed on the basis of the Harschel-Bulkley model. Slurry P showed the highest yield point and plastic viscosity. The density of the granules produced from Slurry P was the lowest and its compacts showed the lowest bending strength and the smallest Weibull modulus. These phenomena were interpreted in terms of the irreversible absorption and interaction of dispersant and PVA.

Origin of the irreversible microwave absorption versus the state of vortex matter in Bi 2Sr 2CaCu 2O x single crystals

We have investigated properties of hysteretic microwave absorption (MWA) by the Bi 2Sr 2CaCu 2O x single crystals in the temperature range from 10 K to T c. It was found that the shape of the MWA hysteresis loop and its dependence on the magnetic field modulation amplitude undergo essential changes with temperature. The analysis has shown that near 50 K, the origin of the signal detected by electron spin resonance spectrometer with magnetic field modulation changes. It is due to crossover to another pinning type. At T<50 K where the bulk pinning is the most effective pinning mechanism, the signal registered by a spectrometer is the magnetically modulated MWA. At high temperatures, 50 K< T< T c, when vortices are pinned by the surface or the edge barrier, the signal is the derivative of the absorption power with respect to field d P/d H. The shape of the MWA hysteresis loop and its modulation enable one to determine unambiguously the pinning type (bulk or surface) controlling the irreversible properties of a superconductor.

Absorption and Desorption Behavior of Ammonia with Alkali Earth Halide and Mixed Halide

Abstract Alkali earth metal halides were studied for the use as ammonia storage material operated below 60 kPa. Reversible and irreversible absorption were observed for each samples. MgCl2, CaCl2, and CaBr2 were found to be adequate for TSA method (between 298 and 473 K), and these storage capacities were much higher than that of Na–Y zeolite. CaCl2–CaBr2 mixed halides proved to be a useful material with large absorption for PSA cycling between 10 and 60 kPa of ammonia.

Thermoeconomic optimization for irreversible absorption refrigerators and heat pumps

A performance analysis using finite time thermodynamic based on a thermoeconomic objective function has been performed for absorption irreversible refrigerators and heat pumps. The optimal design parameters at the maxima of the thermoeconomic objective functions for an absorption refrigerator and heat pump have been derived analytically, and the effects of the internal irreversibility, the economical parameter and the external temperatures on the global and optimal performances have been discussed.

Optimal performance of an irreversible absorption refrigerator

On the basis of endoreversible absorption refrigeration cycle model with the sole irreversibility of heat transfer between the working fluid and the heat reservoirs, an irreversible model of absorption refrigeration cycle with heat transfer law of q∝Δ(T−1), which includes the heat leak from the heat sink to the cooled space and irreversibilities due to the internal dissipation of the working fluid besides the finite-rate heat transfer between the working fluid and the external heat reservoirs, is established and used to derive the relation between the optimal coefficient of performance and the cooling load and the optimal distribution of the heat-transfer surface areas of the heat exchangers. The practical optimal regions of the cycle are determined and new bounds of the primary performance parameters are given. A numerical example is provided to illustrate the performance characteristic of endoreversible and irreversible cycles.

Thermodynamic modeling of an ammonia–water absorption chiller

This article develops a general thermodynamic framework for the modeling of an irreversible absorption chiller at the design point, with application to a single-stage ammonia–water absorption chiller. Component models of the chiller have been assembled so as to quantify the internal entropy production and thermal conductance (UA) in a thermodynamically rigorous formalism, which is in agreement with the simultaneous heat-and-mass transfer processes occurring within the exchangers. Local thermodynamic balance (viz. energy, entropy, and mass balance) and consistency within the components is respected, in addition to the overall thermodynamic balance as determined by the inlet and outlet states of the components. For the absorbers, Colburn-and-Drew mass transfer equations are incorporated to describe the absorption process. Furthermore, the impact of various irreversibilities on the performance of chiller is also evaluated through the use of a general macroscopic equation.

Optimum performance of an irreversible solar-driven cogeneration heat pump system

By employing the energetic optimization technique, the optimal performance of a focusing collector-driven, irreversible Carnot cogeneration heat pump system which consists of an irreversible Carnot heat engine, an irreversible Carnot vapor compression heat pump and an irreversible Carnot absorption heat pump, is investigated. The optimum temperature and minimum operating parameter of the solar collector are obtained. A minimum value for the total solar insolation needed to overcome internal irreversibilities for start-up of the system is defined, and the effect of the collector design parameters on this value is investigated.

Temperature–entropy diagram for an irreversible absorption refrigeration cycle

This article develops the theoretical foundation for the temperature–entropy (T–s) diagram for irreversible absorption chillers that employ either a volatile or nonvolatile working pair. The representation of a real absorption refrigeration cycle on a T–s diagram can directly depict the energetic superiority of one design over another. For practical usage, this diagrammatic approach only requires as inputs the inlet and outlet state points that can be computed based on the corresponding temperatures, pressures, and component concentrations of each of the heat-and-mass exchanger modules within a chiller system and can therefore also be employed as a useful tool for system analysis and diagnosis. The same method is also applicable to any continuously operating thermodynamic system that is wholly or partially driven by thermal power.