M.P. Maiya

Thermodynamic comparison of water-based working fluid combinations for a vapour absorption refrigeration system

Abstract Thermodynamic analysis of a water-based vapour absorption refrigeration system with four binary mixtures [H2O-LiBr, H2O-NaOH, H2O-LiI and H2O-LiCl], five ternary mixtures [H2O-LiBr+LiI (salt mole ratio 4:1), H2O-LiCl+LiNO3 (2.8:1), H2O-LiBr+LiNO3 (4:1), H2O-LiBr+ZnBr2 (2:1) and H2O-LiBr+LiSCN (1:1)] and seven quaternary mixtures [H2O-LiBr+LiCl+ZnCl2 (3:1:4), H2O-LiBr+ZnCl2+CaBr2 (1:1:0.13), H2O-LiBr+ZnBr2+LiCl (1:1.8:0.26), H2O-LiBr+LiI+C2H6O2 (3:1:1), H2O-NaOH+KOH+CsOH (4.3:3.6:2.4), H2O-LiNO3+KNO3+NaNO3 (5.3:2.8:1.9) and H2O-LiCl+CaCl2+Zn(NO3)2 (4.2:2.7:1)] has been carried out by computer simulation. Variations of performance parameters (cut-off temperature, circulation ratio, coefficient of performance and efficiency ratio) of these aqueous solutions are compared with operating temperatures (generator, evaporator, condenser and absorber temperatures) and heat exchanger effectiveness as parameters. Correlations for the performance parameters are obtained in terms of operating temperatures and heat exchanger effectiveness from the regression analysis. It has been concluded that the H2O-LiCl combination is better from the cut-off temperature and circulation ratio points of view and H2O-LiBr+LiCl+ZnCl2 combination is better from the coefficient of performance and efficiency ratio points of view.

Performance comparison of double-effect parallel-flow and series flow water–lithium bromide absorption systems

The double-effect parallel flow absorption refrigeration cycle with water–lithium bromide as working fluid is analysed based on the concept of equilibrium temperature at the low pressure generator. Coefficient of performance (COP) and its sensitivity to operating conditions are compared with those for series flow cycle. Maximum attainable COP for parallel flow cycle is greater than that for series flow cycle throughout the range of operating conditions considered here. Performance of parallel flow system is more sensitive to the effectiveness of low pressure heat exchanger than that of series flow system.

Equilibrium low pressure generator temperatures for double-effect series flow absorption refrigeration systems

Abstract The equilibrium temperatures at the low pressure (LP) generator for double-effect series flow lithium bromide–water vapour absorption chiller are evaluated and the system performance is estimated at these temperatures. Influence of temperatures at high pressure (HP) generator, evaporator, condenser and absorber, and the effectiveness of heat exchangers on equilibrium temperature and internal heat transfer at LP generator, circulation ratio, and coefficient of performance are studied. Dual-heat mode of operation of the system is also investigated utilising low grade waste heat at the LP generator. Correlations are presented for equilibrium LP generator temperature, internal heat transfer at the low pressure generator, circulation ratio, coefficient of performance, optimum HP generator temperature and optimum circulation ratio for maximum coefficient of performance in terms of operating temperatures, which are useful in the design and control of absorption system even at the off-design conditions.

Experimental analysis of a bubble pump operated H2O-LiBr vapour absorption cooler

Abstract Experimental analysis of a H 2 O–LiBr vapour absorption cooler based on bubble pump technique and hydrostatic principle are presented. Heat input to the bubble pump and boiler, pump lift/driving head and weak solution concentration are varied to analyze the system performance. The cooler is tested at different load conditions, i.e., at no load, pull down load and steady load conditions. Results indicate that coefficient of performance of about 0.50 could be attained for the boiler temperature of 85 °C and condenser and absorber temperatures in excess of 40 °C.

A Cell Based Approach to Determine the Minimum Weight of Metal Hydride Hydrogen Storage Devices

Determination of the minimum total weight is the main criterion in the design of a solid state hydrogen storage device for mobile or portable applications. The design should address additional requirements such as storage capacity, charge/discharge rates, space constraints, coolant temperature and hydrogen supply pressure. The typical metal hydride based storage device studied here consists of several filters to distribute hydrogen gas, and heat exchanger tubes to cool or heat the hydride bed based on whether hydrogen is absorbed or desorbed. The total weight of the system includes hydrogen storage material, heat exchanger tubes and associated heat transfer media, porous sintered filters and the cylindrical outer container. Systematic simulation of the heat and mass transfer during hydrogen sorption has been carried out for different feasible configurations. LaNi5 is used as the representative hydriding alloy in the device as its sorption performance is limited by heat transfer in the bed. The effect of geometric parameters on total system weight and charging time are plotted at specified operating conditions. These plots are used for the design of hydrogen storage devices with minimum system weight satisfying the imposed constraints.Copyright