Aqua-ammonia Absorption Refrigeration System Research Articles

Experimental Investigation of Solar Absorption Refrigeration System.(Dept.M)

In this paper, an investigation of aqua-ammonia solar absorption refrigeration system for domestic use is presented. The refrigeration system investigated here is a conventional aqua-ammonia absorption refrigeration system powered by solar heater. The solar heater used is a stationary, hyperbolic sprial solar concentrator equipped with a glass tube for convection loss suppression. A generator temperature as high as 140°C is reached. The lowest temperature reached in evaporator is 2°C, with an additional external heating Source. The various parameters affected the cycle performance and cooling ratio, such as, the generator temperature, evaporator temperature, collector performance and condenser temperature are presented. For fixed initial conditions, higher generator temperature and lower condenser temperature increases the coefficient of performance and improves the operation of the system.

Effect of heat exchangers on performance of absorption refrigeration systems

In this study, the effect of heat exchangers on the system performance in an aqua–ammonia absorption refrigeration system has been investigated. For this purpose, the thermodynamic performance of the system is analysed, and the irreversibilities in the thermal processes have been determined for three different cases. These cases are: both of the heat exchangers are included in the system, only the refrigerant heat exchanger is included in the system and only the mixture heat exchanger is included in the system. It is assumed that the ammonia concentration at the rectifier outlet is independent of the other parameters, constant and equal to 0.999. The coefficient of performance, exergetic coefficient of performance, circulation ratio ( f) and non-dimensional exergy loss of each component of the system are calculated separately. After these calculations, some graphics indicating the change of the variables with the system parameters have been plotted.

Performance of a packed bed absorber for aqua ammonia absorption refrigeration system

A mathematical model of a packed bed absorber for aqua-ammonia absorption refrigeration system is presented. The model is used to predict the performance of the bed at various design and operating conditions. The governing equations and the boundary conditions are derived to predict the bed performance. A numerical integral method and an iteration scheme are used to solve the governing one dimensional, non-linear simultaneous differential equations which are subjected to three point boundary value problem. A computer program is prepared and carefully debugged to solve the governing equations with the help of some supporting equations to describe the properties of the working fluids and the heat and mass transfer coefficients in the bed. The analysis show that the absorption process is affected by the following parameters: the volumetric heat rejection model, bed height, vapor and solution flow rates to the bed and the inlet conditions; and packing material type. The effect of changing each of those parameters on the performance of the bed is studied after suggesting a model for the volumetric heat rejection from the bed. The results showed that changing the bed pressure and/or the vapor inlet temperature have negligible effect on the performance of the bed. Changing other parameters are found to affect the performance of the bed by different degrees. Also, the results show that within the present range of parameters, a bed height less than 0.7 m guarantees an absorption efficiency better than 91%.

THE AQUA-AMMONIA ABSORPTION SYSTEM: AN ALTERNATIVE OPTION FOR FOOD REFRIGERATION

Food refrigeration is one of the largest applications in the refrigeration market. At present, this market is dominated by mechanical vapor compression systems. The availability of aqua-ammonia absorption refrigeration systems provides an alternative to vapor compression systems. The study describes the aqua-ammonia absorption refrigeration system. A detailed mathematical model for simulating its operation is presented with complete sources of H2O-NH3 mixture thermodynamic data. Based on the model, a computer software is developed. With this software, the performance characteristics of the aqua-ammonia absorption system are analyzed. Optimizing the system performance is also carried out and some optimum results are presented.

Optimization of the thermodynamic model of aqua-ammonia absorption refrigeration systems

This work deals with optimization of the aqua-ammonia absorption refrigeration system (ARS) in the light of the first law of thermodynamics. The system consists of an evaporator, a generator, a condenser, a pump, expansion valves and two heat exchangers. A theoretical model is developed for the ARS. The coefficient of performance (COP) is maximized for various evaporator, condenser and absorber temperatures.

Comparative study of irreversibilities in an aqua-ammonia absorption refrigeration system

Irreversibilities in components of an aqua-ammonia absorption refrigeratio system (ARS) have been determined by second law analysis. The components of the ARS are as follows: condenser, evaporator, absorber, generator, pump, expansion valves, mixture heat exchanger and refrigerant heat exchanger. It is assumed that the ammonia concentration at the generator exit is, independent of the other parameters, equal to 0.999 and at the evaporator exit the gas is saturated vapour. Pressrre losses between the generator and condenser, and the evaporator and absorber are taken into consideration. In the results the dimensionless exergy loss of each component, the exergetic coefficient of performance, the coefficient of performance and the circulation ratio are given graphically for each different generator, evaporator, condenser and absorber temperature.

Thermodynamic evalaution of a modified aqua-ammonia absorption refrigeration system

This short communication presents a modified version of the basic aqua-ammonia absorption refrigeration system. The heat released during the absorption process is utilized to heat the strong solution coming out of the absorber. Thus, the heat required for further heating the solution in the generator is considerably reduced and, hence, yields enhanced coefficients of performance. Detailed thermodynamic analysis of the modified aqua-amonia absorption system is carried out to study the effects of various operating parameters, such as generator temperature, condenser temperature, absorber temperature, rectification column and the effectiveness of the heat exchangers, on the COP and various heat/mass transfer rates. It is found that an improvement of about 10% in the COP for the modified absorption cycle is achieved at an evaporator temperature of 0°C.

Cut-off temperatures of aqua-ammonia absorption refrigeration system

The cut-off temperature, i.e. the minimum temperature at which the binary solutions just starts boiling, is dependent on the evaporator pressure, absorber temperature and generator pressure. Thus, the heat source temperature should be more than the cut-off temperature for the operation of vapour absorption refrigeration systems. Two methods have been developed to determine this temperature; one using a pressure-temperature-concentration chart and the other an emperical equation for aqua-ammonia binary mixtures. These methods will be very useful for assessing the potential use of waste heat as heat input to aqua-ammonia vapour absorption systems.

Simulation of a solar driven aqua-ammonia absorption refrigeration system Part 2: viability for milk cooling at remote Brazilian dairy farms

Refrigeration at dairy farms in Brazil would contribute substantially to improving the rate and quality of milk production. Farmers would be able to milk twice a day or more, and keep the milk refrigerated until it was transported to the delivery station. The 1980 rural electricity consumption in Brazil's major milk-producing state was only 0.93% of the national total 2. This low consumption can be attributed to the high costs associated with the electrification of the rural regions. In these areas, cooling cycles based on the absorption principle may be especially suitable. Solar energy, coupled with methane generated from cattle herd wastes, has been investigated as a source of auxiliary energy.

Simulation of a solar driven aqua-ammonia absorption refrigeration system Part 1: mathematical description and system optimization

A theoretical thermodynamic analysis was performed on an aqua-ammonia refrigeration (AAR) cycle coupled to a solar water heating system using CPC-collectors and augmented with auxialiary energy. Thirteen AAR cycles were considered in the search for the maximum coefficient of performance. Also investigated was the exergetic performance of the AAR cycle. The adopted temperature and mass flow rate control strategy on the storage tank-auxiliary heater-AAR generator loop ensured operation of the refrigeration systems at design conditions. Consequently, the ratio between the pumps' electrical power and the designed evaporator heat transfer rate was kept to a minimum.