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In absorption systems using the aqueous lithium bromide mixture, the Coefficient of Performance is affected by the desorber. The main function of this component is to separate the refrigerant fluid from the working mixture. In conventional boiling desorbers, constant heat flux and vacuum pressure conditions are necessary to carry out the desorption process, and usually, the absorbers are heavy and bulky, thus, they are not suitable in compact systems. In this study, a membrane desorber was evaluated, operating at atmospheric pressure conditions with a water/lithium bromide solution with a concentration of 49.6% w/w. The effects of the solution temperature, solution mass flow, and condensation temperature on the desorption rate were analyzed. The maximum desorption rate value was 6.1 kg/m2h with the following operation conditions: the solution temperature at 95.2 °C, the solution mass flow at 4.00 × 10−2 kg/s, and the cooling water temperature at 30.1 °C. On the other hand, the minimum value was 1.1 kg/m2h with the solution temperature at 80.2 °C, the solution mass flow at 2.50 × 10−2 kg/s, and the cooling water temperature at 45.1 °C. The thermal energy efficiency, defined as the ratio between the thermal energy used to evaporate the refrigerant fluid with respect to the total thermal energy entering the membrane desorber, varied from 0.08 to 0.30. According to the results, a high solution mass flow, a high solution temperature, and a low condensation temperature lead to an increase in the desorption rate, however, a low solution mass flow enhanced the thermal energy efficiency. The proposed membrane desorber could replace a conventional boiling desorber, especially in absorption cooling systems that operate at high condensation temperatures as in warm weather regions.

The present work analyses an intermittent absorption cooling system using a hydrophobic porous membrane unit as desorber/condenser and powered by thermal solar energy. Experimental test runs were carried out in a membrane unit to experimentally determine the amount of refrigerant produced at different operating temperatures. With the obtained information, an intermittent absorption cooling system was modelled at a larger scale using information from real solar collectors and considering a 1 m2 membrane area. According to the experimental performance of the desorber/condenser unit, after 4 h of operation, the total amount of refrigerant produced was 14.50, 11.59 and 7.20 kg for desorber temperatures of 95.1, 85.2 and 75.1 °C, respectively. The designed solar system was composed of a 0.3 m3 storage thermal tank, and 30.2, 25.6 and 20.9 m2 of solar collector area for each desorber thermal level. According to the simulation of the absorption cooling system, evaporator temperatures of 18 and 14 °C were achieved for desorber temperatures of 75.1 and 85.2 °C, while evaporator temperatures of 17 and 12 °C were obtained at 95.1 °C. The COPs were 0.15, 0.21 and 0.26, which increased according to the increase in the desorber temperatures. Based on the clear desorber/condenser tendencies obtained from the refrigerant production, additional absorption conditions were calculated and may be useful for future designs. The lowest evaporator temperature was 6 °C when the initial LiBr concentration was 54.83% w/w, instead of 50.30% w/w at a temperature of 95.1 °C; however, the COP decreased 33%.

Parabolic Trough Collectors (PTC) provides thermal solar energy at medium temperature, and in order to increase the thermal level, the solar system can be coupled to upgrading devices, such as Absorption Heat Transformers (AHT). In this paper, a feasibility analysis of the PTC system operating as thermal source of an AHT is described. The PTC and AHT units were tested and, based on the experimental data of each system, a heat transfer analysis was carried out in order to propose a single system. Two case studies were analysed: In the first, the evaporator temperature was close to the generator temperature (84.6 and 85.2 °C respectively) and a simultaneous flow from the heat source was used; in the second case, the evaporator temperature was lower than the generator temperature (79.6 and 86.7 °C respectively) and a serial flow from the heat source was proposed. Results show that, for the absorber temperature of 101 °C, the calculated generator and evaporator heat loads were 1.50 and 1.34 kW respectively in Case 1, and 0.86 kW for both components in Case 2. For Case 1, the PTC system required 6.0 m 2 in order to provide two mass flows of 6.00 × 10 −02 and 5.35 × 10 −02 kg/s for generator and evaporator at 89 °C. For Case 2, one mass flow of 6.60 × 10 −02 kg/s at 89 °C for generator and evaporator must be satisfied by a 3.7 m 2 PTC system.

A thermodynamic analysis of a half-effect absorption cooling system powered by a low-enthalpy geothermal source was carried out. This paper presents modeling of the half-effect absorption cooling system operating with an ammonia/lithium nitrate mixture and based on the first and second laws of thermodynamics, using as energy inputs real data from two geothermal wells located at Las Tres V&iacute, rgenes volcanic complex, Baja California Sur, M&eacute, xico. Plots of coefficients of performance and exergy efficiency against condenser, evaporator, and generator temperatures are presented for the half-effect cooling system. The results showed that the system was able to operate at generation temperatures between 56 and 70 &deg, C, which were supplied by the geothermal wells in order to produce cooling at temperatures as low as &minus, 16 &deg, C, achieving coefficients of performance between 0.10 and 0.36, while the exergy efficiency varied from 0.15 to 0.40 depending on the system operating temperatures.

Desalination driven by solar energy represents an appealing solution for agricultural irrigation in remote areas. In this work, a desalination system based on a photovoltaic-powered nanofiltration (NF-PV) membrane is studied. The experimental work explored the effect of the influent concentration and solar radiation on permeate production, energy consumption, recovery rate and quality of the permeate product. Four cases of different inlet conditions of influent concentrations were studied. In each set, the influent concentration was kept constant, varying only the irradiance along the solar day. In addition, a unit cost of permeated water was estimated. The maximum tested energy consumption was 1.55 Kwh m−3, with a concentration of 2,539 mg L−1 of total dissolved solids. The NF-PV system produces 2.16 to 4.8 m3 d−1, with a permeate water unit cost of 1.05–0.47 US$ m−3.

A conventional desorber in the Absorption Heat Transformer (AHT) cycle requires a constant heat flux and vacuum pressure conditions to boil the working mixture and separate the working fluid. In this paper, an Air Gap Membrane Distillation (AGMD) unit was adapted as desorber/condenser with water/Carrol mixture in order to demonstrate the feasibility of the desorption process at atmospheric pressure conditions. Two membranes with 0.22 and 0.45 μm pore sizes were used and three temperature levels were tested. The maximum increase in the concentration (Δ X ) was 1.54% w/w (from 60.63 to 62.17% w/w) with a membrane with pore size up to 0.45 μm and a solution temperature of 82.7 °C. The maximum thermal process effectiveness was 17.7% (on average) with a membrane with pore size up to 0.22 μm and a solution temperature of 84.4 °C. Due to the corrosion process, a fouling particle by iron oxide was found on the membrane; this fouling layer could promote the “wetting” process in the membrane after a long operating time.

In absorption cooling systems, the desorber is a component that separates the refrigerant fluid from the liquid working mixture, most commonly completed by boiling separation, however, the operation temperature of boiling desorbers is generally higher than the low-enthalpy energy, such as solar, geothermal, or waste heat. In this study, we used a hydrophobic membrane desorber to separate water vapor from an aqueous LiBr solution. Influencing factors, such as the H2O/LiBr solution and cooling water temperatures, were tested and analyzed. With the experimental data, a solar collector system was simulated on a larger scale, considering a 1 m2 membrane. The membrane desorber evaluation shows that the desorption rate of water vapor increased as the LiBr solution temperature increased and the cooling water temperature decreased. Based on the experimental data from the membrane desorber/condenser, a theoretical heat load was calculated to size a solar system. Meteorological data from Emiliano Zapata in Mexico were considered. According to the numerical result, nine solar collectors with a total area of 37.4 m2 provide a solar fraction of 0.797. The membrane desorber/condenser coupled to the solar system can provide an average of 16.8 kg/day of refrigerant fluid that can be used to produce a cooling effect in an absorption refrigerant system.

Radiative heat transfer in a solar thermochemical reactor for the thermal reduction of cerium oxide is simulated with the Monte Carlo method. The directional characteristics and the power distribution of the concentrated solar radiation that enters the cavity is obtained by carrying out a Monte Carlo ray tracing of a paraboloidal concentrator. It is considered that the reactor contains a gas/particle suspension directly exposed to concentrated solar radiation. The suspension is treated as a non-isothermal, non-gray, absorbing, emitting, and anisotropically scattering medium. The transport coefficients of the particles are obtained from Mie-scattering theory by using the optical properties of cerium oxide. From the simulations, the aperture radius and the particle concentration were optimized to match the characteristics of the considered concentrator.

The hybrid PV–thermal system was studied, with the photovoltaic panel (PVP) area much smaller than that of the solar collector. Performance of the different panels in the system was investigated, in particular, those made of crystalline (c-) Si, α-Si and CuInSe2 as well as different materials and constructions for the thermal contact between the panel and the collector. Our conclusion is that the PVP for application in a hybrid system needs a special design providing efficient heat extraction from it. PVP was designed and made. Its study has shown that this design provides the high electrical and thermal efficiency of the hybrid system.