Thermodynamic analysis data on vapour absorption heat pump working on R22-DMETEG pair

A thermodynamic analysis of the vapour absorption heat pump working on R22-DMETEG pair is made and the results are presented in the form of graphs and correlations. These data can be used to estimate the idealised system performance parameters such as heat quantities, flow rates, pump work, COP and second law efficiency. The procedure for using the data for above computations is described.     

Optimal choice of the performance parameters of an absorption heat transformer

The optimal performance of an absorption heat transformer, i.e. a type II absorption heat pump, is investigated by using the cyclic model with continuous flow. The effect of thermal resistances between the heat transformer and the heat reservoirs is considered in the model. A general expression related to the rate of heat-pumping, the coefficient of performance and the overall heat transfer area of the heat transformer is derived. The expression is used to optimise the main performance parameters of the heat transformer. The maximum rate of heat-pumping and the corresponding coefficient of performance are calculated. For a given overall heat transfer area of the heat transformer, the optimal relation of the heat transfer areas of the heat exchangers is obtained. The problems concerning the optimal choices of other performance parameters are discussed. The results obtained here can not only enrich the theory of finite time thermodynamics, but also provide some new theoretical bases for the optimal design and operation of real absorption heat transformers.     

Design and experimental performance evaluation of an absorption heat transformer with self-circulation

A 10 kW experimental absorption heat transformer unit operating with self-circulation has been thoroughly tested. The self-circulation is obtained according to the thermosyphon principle. The pressure difference in the unit is achieved through a difference in hydrostatic pressures. Theoretical relationships for the pressure profiles within the different components of the heat transformer have been derived. Stabilising the self-circulation has been the primary objective in this work, rather than the optimisation of the efficiency of heating and cooling areas. A satisfactory stable operation with self-circulation has been achieved.A reference heat transformer plant, delivering 100 kW, has been designed and installed in a major pulp and paper mill. This unit is directly incorporated with one of the evaporation plants of the mill. Plant operation data obtained under real industrial conditions are presented.     

Coupling a two-stage absorption heat transformer with finite heat sources and sinks

The coupling among a two-stage heat transformer (TSHT) and finite heat sources and sinks is considered. A novel configuration is proposed, in which the evaporator of the second stage is fed both by the absorber of the first stage and by the external source. A lumped-parameter mathematical model is used to compute the performance of the proposed TSHT. It has been found that the range of applicability is widened, when compared with the usual configuration. Moreover, the use of a two-stage apparatus allows one to noticeably increase the performance compared with that obtainable with a simpler single-stage transformer. Thus, it is possible to increase the output heat and/or the user temperature, to reduce the discharge temperature, or to use lower quality energy sources. The results also allow one to draw some more general conclusions on the applicability of absorption heat transformers of different configurations, when different heat sources/sinks are considered.     

Coupling a single-stage absorption heat transformer with finite heat sources/sinks

The coupling between a single-stage heat transformer and finite heat sources and sinks is considered. A simple lumped-parameter mathematical model shows that the performance is noticeably reduced in comparison with the simpler case of an infinite (constant temperature) heat source. The best performance is obtained when the evaporator and the generator are fed in series, the evaporator being placed upstream.     

Theoretical studies on adsorption heat transformer using zeolite-water vapour pair

An adsorption heat transformer can raise the temperature level of a fraction of waste heat by rejecting the remaining heat to a low temperature level. In this work some alternatives in the design of an adsorption heat transformer, such as a 2-tank system, 3-tank system and 4-tank system, are evaluated using zeolite-water vapour as the adsorbent-adsorbate pair. The values of coefficient of performance (COP) are computed for each system for various temperatures of waste heat source at which the heat is available and heat sink at which the heat is delivered.It is found that an adsorption heat transformer can be used for a gross temperature lift as high as 50°C with a fairly good COP value. Moreover the 4-tank system gives a much improved COP value as compared to the 2-tank and 3-tank systems for the same operating conditions. It is also found that the effect of temperature driving force for heat transfer on the COP value is quite pronounced.     

Thermodynamic analysis and design data for a double-effect absorption heat pump system using four working pairs

Performance analysis of a double-effect absorption heat pump system has been done for water-four working pairs (or mixture) by computer simulation. The coefficient of performance and mass flow ratio are investigated to compare these aqueous solutions [waterLiCl, waterLiBrLiBr waterLiClCaCl₂Zn(NO₃)₂] which was developed for only cooling, with conventional waterLiBr solution, based on mass, material and heat balance equations for each part.From this analysis, it is found that the performances of the new aqueous solutions are better than that of LiBrwater solution not only in cooling systems, but also in heating systems, although the operating temperature ranges of these new aqueous solutions are very narrow in heating. Theoretical thermodynamic performance data can be used and are given here by design data.     

Thermodynamic criteria for optimal absorption heat pump media

The performance of absorption heat pump cycles is to a great degree dependent on the substances used as the working pair. It is therefore of great interest to know the influences of the pure component properties of the absorbent and the refrigerant, respectively, and the influence of a mixture of both on the performance parameters of an absorption heat pump.A methodological approach based on fundamental thermodynamic relations is proposed to estimate the influence of the working pair on heat pump performance. On this basis, criteria to preselect working media can be established.A thorough simulation of absorption heat pump cycles shows that three properties predominantly influence the COP of a heat pump. These are the heat of evaporation of the refrigerant at normal boiling point and the size and location of the extremum of the excess Gibbs free energy of mixing, g^E. Of these three properties the two properties of mixing exert the greatest influence.Good performances can be expected for working pairs which show high heats of evaporation for the refrigerants at normal boiling point and the extrema of the excess Gibbs free energy of −1000–2000 kJ kmol⁻¹. The extremum of g^E should preferably be located at high concentrations of the refrigerant.     

Energy recovery and plume reduction from an industrial spray drying unit using an absorption heat transformer

Spray drying is a widely used unit operation in the chemical industry. It is highly energy intensive, requiring hot, dry airstreams, at temperatures up to 550°C, to dry a wide range of products. Exhaust air from a dryer is usually vented to the atmosphere with little or no heat recovery. At best only the sensible heat associated with the air stream is recovered, although the majority of the stream's energy is in the form of latent heat associated with the evaporated water. Exhaust airstreams usually contain moisture to cause visible plumes upon leaving the dryer stack.A two-stage absorption heat transformer (A.H.T.) has been designed and contructed to investigate the potential for dehumidifying and reheating a simulated dryer exhaust stream to make it suitable for recycling to the dryer inlet. The amount of air vented to atmosphere and also the amount of wasted heat would be reduced by incorporating an A.H.T. into the drying operation. Performance data for the A.H.T. indicates that an airstream can be reheated to a temperature of 160°C, using a lithium bromide solution of 68% w/w, with a circulation ratio (LiBr: steam flow) of 14.8. Temperature lifts between 50 and 70°C are possible in the reheat column when using a low circulation ratio and a high LiBr concentration. Experiments show that a humid air stream can be dehumidified to a level suitable for recycling by direct contact with a concentrated lithium bromide stream.     

Thermodynamic design and assessment of hybrid double absorption solar cooling systems

This communication presents an investigation of the thermodynamic design and feasibility assessment of hybrid double-absorption solar cooling systems. The systems considered are conventional closed-cycle and open-cycle absorption systems with an additional open-absorber component through which the process room air is passed, cooled and dehumidified. The cooling produced in the evaporator is utilized to remove heat from the open absorber as well as the process air being circulated. Thermodynamic modelling of system components for a fixed set of operating conditions and with water-LiBr as working fluid have been carried out and the system COP predicted as a function of regenerator temperature, mass flow ratio and latent heat load in the process air and the ambient air. A comparative study of the open and closed cycle options has been made and detailed parametric results are presented. It is concluded that the hybrid double-absorption solar cooling systems are better in performance than conventional systems and an open-cycle double-absorption system is even more attractive and cost effective as compared to closed-cycle option.     

New working pairs for medium and high temperature industrial absorption heat pumps

The application of absorption cycles for high temperature heat recovery systems calls for the investigation of new working pairs. To qualify as a potential working pair, a mixture of two substances has to fulfill stringent requirements with respect to thermodynamic properties, corrosion and safety hazards like toxicity and inflammability.Based on a thermodynamic analysis of an absorption heat pump cycle a systematic search for new working pairs has been conducted. The investigation dealt exclusively with organic compounds. To get a first estimate of the properties of mixing, a molecular group contribution model (UNIFAC) was employed. This method has so far been widely used for chemical engineering purposes and renders agreeable estimates for the thermodynamic behavior of organic mixtures.With the help of the UNIFAC method, various pairings of functional molecular groups have been investigated for their possible potential to form effective working pairs for medium and high temperature absorption heat pump cycles. As a consequence of this analysis, ten alternative working pairs are proposed and their respective theoretical performance data and their toxicity characteristics are given.     

Thermodynamic design data for absorption heat transformers. Part six: Operating on water-carrol

The Gibbs phase rule and thermodynamic properties of the working pair limit the choice of operating temperatures. For any combination of temperatures, the concentrations in the absorber and the generator and hence the flow ratios are fixed. For any particular working pair, the coefficient of performance is related to the flow ratio.Tables of possible combinations of operating temperatures, including flow ratios, Carnot coefficients of performance nd enthalpy based coefficients of performance have been presented for absorption heat transformers operating on water-carrol (lithium bromide-ethylene glycol). The interaction of operating temperatures has been illustrated graphically.     

Observation of pair absorption in calcium

Pair absorption has been observed in calcium using broad band absorption. The absorption peaks at the sum energy of the (4s4p) ¹P° and (4s3d) ¹D atomic states. A cross section of 1.3 × 10^-22 (P/A) cm² is measured corresponding to a reduced absorption coefficient of 1.3 × 10^-35 cm⁵. An error in earlier calculations predicting the reduced absorption coefficient for pair absorption in barium is noted. Simple scaling laws, our experimental results, and the assumption that the barium process is dominated by the resonant dipole-dipole interaction are used to deduce an upper limit for the calcium (4s3d) ¹D→(4s4p) ¹P° oscillator strength of 6.5 × 10^-4.     

A study of the optimum interaction between the working fluid and the absorbent in absorption heat pump systems

The operating efficiency of an absorption heat pump is critically dependent on the chemical, thermophysical and thermodynamic properties of the working fluid, the absorbent and their solution. The desirable properties are discussed in the light of the operating parameters and the thermodynamic limits. Deviations from ideality are considered with specific reference to water/salt systems. Plots of the heat of hydration and heat of solution against the effective ionic radius, the lowering of vapour pressure against the heat of solution and the solubility against the melting point have been made for aqueous alkali metal halide solutions. It is demonstrated that an optimisation procedure is necessary to select suitable working fluid-absorbent combinations from the hundreds of possible combinations based on the operating conditions and the field of application.     

Thermodynamic design data for absorption heat pump systems operating on ammonia-lithium nitrate-part one. Cooling

The free choice of operating temperatures in absorption systems is limited by the Gibbs phase rule and the thermodynamic properties of the working pair. Tables of possible combinations of operating temperatures and concentrations, including flow ratios, Carnot coefficients of performance and enthalpybased coeffecients of performance have been presented for Ammonia-lithium nitrate absorption systems for cooling. The interactions of operating temperatures have been illustrated graphically.     

Thermodynamic modelling of absorption-resorption heating cycles with some new working pairs

This paper presents the results of a thermodynamic cycle analysis of single stage resorption heat pump (RHP) and resorption heat transformer (RHT) cycles with the new working pairs R22-NMP and R22-DMA. The coefficients of performance (COP) are correlated with the low grade source temperature, temperature at which useful heat is obtained and ambient temperature. The COPs are in the range 1.20–1.60 for the RHP mode and 0.25–0.45 for the RHT mode. Absorber temperatures (useful temperatures) as high as 50°C in the RHP mode and 87°C in the RHT mode have been obtained. It is observed that absorption-resorption systems are inflexible in their range of operating temperature and necessitate a higher pump work as compared with simple single-stage absorption heating systems. However, single stage RHTs show higher temperature boosts than simple absorption heat transformers.     

Optical fiber sensor for oxygen detection working on an absorption basis

Painstaking spectrophotometric investigation was carried out on organo-metallic compounds to identify the most suitable compound for the detection of oxygen. A bis (histidinato) cobalt(II) solution was chosen, characterized by an absorption change at λ-408 nm as a function of the molecular oxygen concentration in the surrounding environment. An optical fiber system was developed that makes use of a halogen lamp as the source and an appropriate electronic circuit as a detection system. The optrode is a very small hollow fiber membrane filled with the solution and coupled with optical fibers.     

Thermodynamic design data for absorption heat pump systems operating on monomethylamine-water. Part I: Cooling

The Gibbs phase rule and thermodynamic properties of the working pair limit the choice of operating temperatures. For any combination of temperatures, the concentrations in the absorber and the generator and hence the flow ratios are fixed. For any particular working pair, the coefficient of performance is related to the flow ratio.Tables of possible combinations of operating temperatures and concentrations, including flow ratios, Carnot coefficients of performance and enthalpy-based coefficients of performance have been presented for monomethylamine-water absorption systems for cooling. The interactions of operating temperatures have been illustrated graphically.     

Thermodynamic design data for absorption heat pump systems operating on monomethylamine-water. Part II: Heating

The Gibbs phase rule and thermodynamic properties of the working pair limit the choice of operating temperatures. For any combination of temperatures, the concentrations in the absorber and the generator and hence the flow ratios are fixed. For any particular working pair, the coefficient of performance is related to the flow ratio.Tables of possible combinations of operating temperatures and concentrations, including flow ratios, Carnot coefficients of performance and enthalpy-based coefficients of performance have been presented for monomethylamine-water absorption systems for heating. The interaction of operating temperatures have been illustrated graphically.     

Thermodynamic design data for absorption heat pump systems operating on water-carrol. Part I: Cooling

The Gibbs phase rule and thermodynamic properties of the working pair limit the choice of operating temperatures. For any combination of temperatures, the concentrations in the absorber and the generator and hence the flow ratios are fixed. For any particular working pair, the coefficient of performance is related to the flow ratio.Tables of possible combinations of operating temperatures and concentrations, including flow ratios, Carnot coefficients of performance and enthalpy based coefficients of performance have been presented for water-carrol (lithium bromide-ethylene glycol, ratio 4.5) absorption systems for cooling. The interaction of operating temperatures have been illustrated graphically.