• Energy Research

This paper reports on a numerical and experimental study of a diffusion absorption refrigerator. The performance of the system is examined by computer simulation using MATLAB software and Engineering Equations Solver. A dynamic model is developed for each component of the system and solved numerically in order to predict the transient state of the diffusion absorption refrigeration. The experiment set included 0.04 m3 commercial absorption diffusion refrigerator working with the ammonia-water-hydrogen (NH3-H2O-H2) solution. The transient numerical results were validated with the experimental data. The investigations are focused on the dynamic profile of the temperature of each component. The results obtained agree with the experiment; the relative error between numerical and experimental models doesn’t exceed 15% for all temperatures of each component. The increase of the average ambient temperature from 23.04 °C to 32.56 °C causes an increase of the condensation temperature from 29.46 °C to 37.51 °C, and the best evaporation temperature obtained was 3 °C, with an ambient temperature of 23.04 °C. The results show that a minimum starting temperature of 152 °C and 63.8 W electric power are required to initiate the decrease of evaporation temperature.

This work presents the modeling and optimization of an indirectly irradiated solar receiver. A numerical model of the cavity-absorber block is put forward with the coupling of the net-radiation method using infinitesimal areas and a CFD code. An iterative method with a relaxation factor made it possible to obtain the temperature distribution and the developed code was implemented in the form of UDF and used as boundary conditions in the CFD model of the absorber to simulate the flow of air and heat transfer. The good ability of the receiver to transfer heat to the fluid is proved with a 92% thermal efficiency obtained. Then the combination of the Kriging surface response method and the MOGA allowed the mathematical optimization of the receiver. The multi-objective optimization made it possible to obtain 3 candidates giving the best combinations of design parameters from the fixed objectives. Three bullet points, highlighting the customization of the procedure. •A practical analysis using the net-radiation method using infinitesimal areas is applied for cavity radiative exchange model.•The code developed for the cavity is implemented in the boundary conditions at the level of the ANSYS Fluent CFD model allowing the simulation of the conjugated transfers within the absorber.•The optimization method proposed is the combination of the Kriging surface response method for quantitative and qualitative analysis of the design parameters and MOGA to obtain different combinations seeking to maximize or to minimize the chosen parameters.

This work presents an experimental study of H20-NH3-H2 diffusion absorption refrigeration under two types of energy sources, i.e. the conventional electric energy from grid (electric) and exhaust gas from internal combustion engine. Dynamic method is used to evaluate the behavior of the components of the system for both energy sources. Results obtained show that the performance of each component under different types of energy sources is almost coherent. For the generator, the electrical heater system requires more time to warm up, around three minutes, compared to the 40 s for system running with exhaust gas. For the evaporator, the decreasing rate is higher for the exhaust gas source and it took only about two hours to reach steady-state while for the electrical heat, the steady-state is reached after about seven hours of operation. For both energy sources, the evaporation temperature stabilizes to 3 °C and the minimum temperature to boil off ammonia is around 140 °C.