R. Best

Methodology for the energy analysis of an air cooled GAX absorption heat pump operated by natural gas and solar energy

Abstract In this work a methodological analysis and energy evaluation of an air cooled absorption system, with generator–absorber heat exchange (GAX), and operated by a hybrid natural gas–solar energy source is presented. Given the characteristic non-linearity of the resulting system of equations, the methodology proposed envisages a calculation sequence for the external currents and an iterative procedure for the internal currents. The system studied intents to be an alternative for space conditioning in the residential sector, the unit was designed with a capacity of 10.6 kW (3 Ton) of cooling and uses as working fluid ammonia–water. Giving priority to internal energy integration, an arrangement is proposed for the GAX cycle that allows 19% of solar contribution at full load, being greater at partial loads. In spite of using ambient air up to 40 °C with a relative humidity of 24% as cooling source, a COP value of 0.86 for cooling and 1.86 for heating was calculated, with an internal energy integration of 16.9 kW, 37% more than the energy that is supplied to the generator.

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.

Boiling heat transfer coefficients inside a vertical smooth tube for water/ammonia and ammonia/lithium nitrate mixtures

Abstract This paper describes the experimental results obtained on the heat transfer in forced convective boiling for the water/ammonia and ammonia/lithium nitrate mixtures flowing upward in a vertical tube uniformly heated. The concentration range for both mixtures was 38–48 wt%. Correlations were proposed to correlate the experimental local heat transfer coefficients with a mean deviation of ±16% for the ammonia/lithium nitrate mixture and ±25% for the ammonia/water mixture. The results showed that the local heat transfer coefficients are strongly dependent on Bo for the ammonia/lithium nitrate mixture and more dependent on quality and 1/ X tt for the ammonia/water mixture at the analysed conditions. Comparing the heat transfer coefficient values for both mixtures, it was observed that the lowest values were obtained with the ammonia/lithium nitrate mixture.

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.

Experimental evaluation of a single-stage heat transformer operating with the water/Carrol mixture

This paper describes experimental results obtained with a single-stage heat transformer (SSHT). Many combinations of fluid pairs have been proposed although only the water/lithium bromide mixture has been widely used. The experimental work was done using the water/Carrol™ mixture, where Carrol™ is a mixture of LiBr and ethylene glycol [(CH2OH)2] in the ratio 1:4.5 by weight. Flow ratios, gross temperature lifts, useful heat, and coefficients of performance are plotted for the heat transformer vs temperatures and solution concentrations. Because the water/Carrol™ mixture has higher solubility than water/lithium bromide and high experimental values are obtained for the gross temperature lift, it is a preferred mixture.

Theoretical comparison of performance of an absorption heat pump system for cooling and heating operating with an aqueous ternary hydroxide and water/lithium bromide

Abstract This paper compares the theoretical performance of the modelling of a heat pump system for cooling and heating operating with water/lithium bromide and an alternative aqueous ternary hydroxide mixture. The aqueous ternary hydroxide working fluid consists of sodium, potassium and caesium hydroxides in the proportions 40:36:24 (NaOH:KOH:CsOH). Plots of Carnot coefficients of performance and enthalpy based coefficients of performance are shown against the most important temperatures of the system. The results showed that similar coefficients of performance are obtained for both mixtures; however, it was found that the system operating with the alternative mixture may operate with a higher range of condenser and absorber temperatures and the heat delivered by these components can be easily removed by air.

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

Abstract 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.

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.

Experimental performance of ternary solutions in an absorption heat transformer

In this work, results from experiments with ternary solutions in an absorption heat transformer are presented. The experiments were performed under controlled conditions using water/lithium chloride/zinc chloride and water/calcium chloride/zinc chloride solutions as working pairs. The results showed that the gross temperature lift is increased with regard to the results obtained using binary solutions because the concentration of the solutions was enhanced. The water/lithium chloride/zinc chloride solution showed a generally better performance than the water/calcium chloride/zinc chloride mixture. The highest gross temperature lift for the former solution was 37.5°C for an absorber temperature of 96°C. This result compared favourably to that previously obtained for water/lithium bromide in the University of Salford.

Modelling of single-stage and advanced absorption heat transformers operating with the water/carrol mixture

Abstract A thermodynamic analysis was carried out to study the performance of single-stage, two-stage and double-absorption heat transformers operating with the water/Carrol mixture, where Carrol is a mixture of lithium bromide and ethylene glycol [(CH 2 OH) 2 ] in the ratio 1:4.5 by weight. A mathematical model to predict the theoretical performance of single-stage and advanced heat transformers operating with the water/Carrol mixture is also described. Coefficients of performance and gross temperature lifts are compared for the different heat transformers and plotted against the main temperatures of the system. A two-stage heat transformer consists of two single-stage heat transformers which can be coupled in three different ways. A double-absorption heat transformer is a single-stage heat transformer to which a dual-purpose absorber/evaporator unit has been added.