F.A. Holland

Thermodynamic study of advanced absorption heat transformers. I: Single and two stage configurations with heat exchangers

A thermodynamic analysis was carried out to study the effect of heat exchanger effectiveness (EF) on the performance of single stage heat transformers (SSHT). Moreover, an analysis of three different arrangements of two stage heat transformers was performed using a mathematical model assuming water/lithium bromide as the working fluid. An increase in the solution heat exchanger effectiveness (EF) greatly improved the performance of absorption heat transformers when the absorber temperature was at least 40°C higher than the temperature of the heat supplied to the system. In two stage heat transformers (TSHT), higher absorber temperatures were obtained by coupling the absorber of the first stage to the evaporator of the second. However, higher performance coefficients were obtained in general by coupling the absorber of the first stage to the generator of the second.

Thermodynamic design data for absorption heat transformers—Part II. Operating on water-calcium chloride

Abstract The Gibbs phase rule and the thermodynamic properties of the working pair limit the choice of operating temperatures. For any combination of the temperatures, the concentrations in the absorber and the generator and hence the flow ratio 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 absorption heat transformers operating on water-lithium bromide. The interaction of operating temperatures has been illustrated graphically.

Thermodynamic design data for absorption heat pump systems operating on water-lithium bromide part II: Heating

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 enthalpy-based coefficients of performance, have been presented for water-lithium bromide absorption systems for heating. The interactions of operating temperatures have been illustrated graphically.

Comparison of theoretical Rankine power cycle performance data for 24 working fluids

Abstract The boiling temperature T BO in a Rankine cycle power plant is largely determined by the temperature of the available heat supply. The gross temperature drop ( T BO − T CO ) is largely determined by the temperature of the coolant in the condenser. This means that for a given working fluid, the theoretical Rankine power cycle efficiency η R and the pressure ratio ( PR ) are determined automatically. The only way that the values of η R and ( PR ) can be varied is to choose another working fluid. Of the 24 working fluids for which comprehensive thermodynamic data are available, only 18 have critical temperatures high enough to be considered for use in Rankine cycle power plants with a boiling temperature of 120°C and only seven can be considered for a boiling temperature of 200°C. Values of η R are listed for gross temperature drops of 20, 30, 40, 50, 60 and 70 K for boiling temperatures of 80, 100, 120, 160 and 200°C respectively.

Ammonia/lithium nitrate absorption/compression refrigeration cycle. Part II. Experimental

The combination of an ammonia/lithium nitrate absorption refrigeration system with an ammonia mechanical vapour compression system can enhance the efficiency of the overall system. Based on the primary energy ratio this kind of hybrid system can operate more efficiently in developing countries than in developed ones. This is because electricity is generated and distributed less efficiently in developing countries. A 7 kWt prototype of a hybrid system was fabricated and commissioned, and the experimental results are presented. The maximum COP was obtained using 90% compression and 10% absorption. For this compression proportion, it was not necessary to supply heat to drive the absorption section, since the heat is supplied by the superheated ammonia at the compressor outlet.

Ammonia/lithium nitrate absorption/compression refrigeration cycle. Part I. Simulation

Ammonia/lithium nitrate absorption refrigeration combined with mechanical vapour compression in the same circuit permits higher efficiencies than individual compression or absorption cycles. The absorption cycle produces pure ammonia refrigerant and is thus suitable for retrofitting projects in existing ammonia mechanical vapour compression plants. The cycle is modelled over a range of proportions from 0 to 100% mechanical vapour compression. Different power generation and distribution efficiencies are considered in deriving the primary energy ratios. These efficiencies are related to the differences between the level of industrial development in various countries. In general it is possible to achieve up to a 10% increase in overall efficiency using combined absorption/compression refrigeration systems.

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.

An experimental integrated absorption heat pump effluent purification system. Part I: operating on water/lithium bromide solutions

Abstract The merits of single stage absorption heat pumps coupled to simple distillation for effluent treatment are discussed. An experimental integrated absorption heat pump effluent purification system (IAHPEPS) was built and operated with water–lithium bromide as a working mixture. This unit has been used to raise the temperature and hence, the vapour pressure of the impure water contained in one vessel, to the point where pure water vapour will distil from impure effluent solution (tap water or brine) and condense in a second vessel used to collect pure water. Pure effluent production rates of between 0.5 and 4.3 kg h −1 were obtained. The actual coefficient of performance ( COP A ) and the heat pump effectiveness varied from 1.1 to 1.4 and 0.58 to 0.72, respectively. The results from the small scale system indicate the likely results from industrial scale units which could be operated with low quality heat such as waste heat, solar or geothermal resources.

Thermodynamic study of advanced absorption heat transformers—II. Double absorption configurations

Abstract A thermodynamic analysis has been carried out to study the performance of double absorption heat transformers (DAHT) assuming water/lithium bromide as the working fluid. The performance of single (SSHT) and two stage heat transformers (TSHT) analyzed in Part I, was compared with the performance of double absorption heat transformers (DAHT) under the same operating conditions. The results showed that single stage heat transformers (SSHT) were the simplest and most efficient. Greater absorber temperatures were reached with two stage heat transformers (TSHT). However, these systems were in general less efficient than the others and technically the most complex. Double absorption heat transformers (DAHT) were technically simpler than two stage heat transformers (TSHT) and may reach absorber temperature as high as these systems.

Thermodynamic design data for absorption heat pump systems operating on water-lithium chloride—Part one. Cooling

Abstract The free choice of operating temperatures in absorption systems is limited by the Gibbs phase rule and the thermodynamic properties of the working pair. For a given combination of temperatures, the concentrations in the absorber and the generator are fixed automatically. This determines the flow ratio. Therefore 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 enthalphy based coefficients of performance have been presented for a water-lithium chloride absorption system for cooling. The interaction of operating temperatures has been illustrated graphically. The data obtained are also compared with published data for the water-lithium bromide absorption system under identical conditions.