Low capacity diffusion absorption refrigeration: Experiments and model assessment Ikram Saâfi #1 , Ahmed Taieb #*2 , Yosra Ben Salem #*3 , Ahmed Bellagi #4 # Higher Institute of Technological Studies of Kelibia Road Oued el Khatf 8090, Kelibia, Tunisia ikram.saafi@gmail.com ben-salem-yosra@live.fr * Thermodynamic and Thermodynamic Research Unit of Industrial Processes National School of Engineers of Monastir (ENIM) Avenue Ibn El Jazzar, 5060 Monastir, Tunisia hmed.taieb@gmail.com a.bellagi@enim.rnu.tn Abstract— In this paper, a low capacity commercial absorption- diffusion refrigeration machine using ammonia/water/hydrogen as working fluids, was tested under different operating conditions in order to master the operation of the refrigerator and to study its performances. A series of thirty experiments were realized which consisted of varying the electrical power supplied to the generator from 15W to 63W in order to identify the optimal operating conditions of the machine and to study the various operating modes. All these experiments are all performed in an air-conditioned room at 26°C. It is further noted that the optimal COP found is 0.15 for a cooling capacity of 7W. Keywords— Refrigeration machine; absorption-diffusion; experimental study; performance. I. INTRODUCTION The absorption-diffusion refrigeration machine, the subject of our study, was invented by Platen and Munters in 1928 [1] and has been recognized as one of the most encouraging sustainable technologies for cold production. The cycle of the machine (Figure 1) operates at a constant total pressure, and uses ammonia as a refrigerant, water as an absorber and hydrogen or helium as a non-absorbable auxiliary inert gas. This inert gas is necessary to reduce the refrigerant partial pressure in the evaporator to allow the evaporation process to take place in the uniform pressure device. The main feature of this machine is that it has no moving parts, hence its good reliability. The circulation of the aqueous ammonia solution is driven by a bubble pump and that of gas flows between the absorber and the evaporator by gravity. There are many theoretical and experimental studies on the analysis of the performance of this machine operated with different energy sources and using various mixtures of fluid work in the literature. Mansouri and al [2] has carried out experimental investigations of a commercial diffusion absorption refrigerator (DAR) cycle and developed a detailed steady state simulation model of this cycle using Aspen-Plus. He has found deviations between model predictions and experimental measurements in terms of cooling capacity and coefficient of performance are less than 1%. Experimental tests on a domestic DAR were performed by Ben Jemaa and al [3]. The refrigerator was modelled in dynamic mode for different electric heater powers input. He has used the black- box technique for the prediction of the transient behavior of the commercial DAR. Starace et al. [4] developed a thermodynamic model of the absorption-diffusion cycle without any hypothesis regarding the purity of the refrigerant leaving the rectifier. Using this model, he compared the performances of the machine with that of another thermodynamic model proposed by Zohar et al. [5]. Greater accuracy has been shown in predicting the actual state of the machine. In another study, Starace et al. [6] experimentally validated their model using a prototype of a bubble pump coupled to a home magnetron to reduce the start-up transient of the circuit. In order to validate the model, he varied the thermal power supplied to the heat pump, he tested the operating conditions of the machine in each element of the machine. In this paper, an experimental study is carried out on a low-power commercial refrigerator with a capacity of 25 liters, powered by an electrical resistance and which operates according to the Platen and Munters cycle. This machine involves the ammonia/water as refrigerant/absorbent and hydrogen, pressure equalizer, as an inert gas. It consists mainly of a generator, a rectifier, a condenser, an evaporator, a gas exchanger, an absorber, a liquid reservoir and a solution exchanger. All these elements are made of steel. II. EXPERIMENTAL APPARATUS A. Description of the cycle When the machine is energized, the electrical resistance begins to heat the ammonia-rich solution (1), Figure 1, with a thermal energy supply Q g in the lower part of the bubble pump. This energy supply is the origin of the evaporation of ammonia, the most volatile compound, and small amounts of