• Energy Research

Abstract A proposal for rational energy saving using wasted heat is showed in the present paper. Thermodynamicmathematical model is presented like an effort for water purification from waste heat. This paper describes computing results of heat transformer operation for water purification using low grade waste heat. Equations, parameters and simplifications used in the model are briefly described. The main parameter of the carried out study is the coefficient of performance (COP) defined for reversed heat pumps and the second main parameter is absorber temperature, both parameters has been showed and correlated between them. Main objective of this work is to show the optimal operating condition for different process which deliver low grade waste heat and requires water purification. Assisted computing simulation was used for obtain these results. The main conclusion is an ecological proposal for optimal recover of low grade waste heat. Many operating conditions are showed in graphical form and discussed for different environment conditions.

A reverse osmosis system driven by photovoltaic energy is an eco-friendly and sustainable way to produce freshwater in rural areas without connection to a power grid and with available brackish water sources. This paper describes a project where a photovoltaic-driven low-pressure reverse osmosis system (LPRO-PV) was designed, tested under laboratory conditions, and installed in Samalayuca, Chihuahua, Mexico, to evaluate the technical feasibility and social impact of this technology. The LPRO-PV system was tested with synthetic water with a salinity of 2921 ± 62.3 mg/L; the maximum freshwater volume produced was 1.8 ± 0.06 m3/day with a salinity value of 91 ± 1.9 mg/L. The LPRO-PV system satisfied the basic freshwater requirements for a local family of three members for one year, including the mobility-restriction period due to the COVID-19 pandemic. The social evaluation analysis reflects the importance of considering the technical aspects derived from the experimental tests, as well as the users’ perception of the performance and operation of the system. As a result of the implementation of this technology and the benefits described by the users, they committed to the maintenance activities required for the LPRO-PV system’s operation. This technology has great potential to produce fresh water in arid and isolated regions with high-salinity groundwater sources, thus fulfilling the human right to safe and clean drinking water.

The absorber is a major component of absorption cycle systems, and its performance directly impacts the overall size and energy supplies of these devices. Absorption cooling and heating cycles have different absorber design requirements: in absorption cooling systems, the absorber works close to ambient temperature, therefore, the mass transfer is the most important phenomenon in order to reduce the generator size; on the other hand, in heat transformer absorption systems, is important to recover the heat delivered by exothermic reactions produced in the absorber. In this paper a review of the main experimental results of different absorber designs reported in absorption heat pump cycles is presented.

Abstract This paper compares the theoretical performance of the modelling of a solar absorption air conditioning system operating with water/lithium bromide and an aqueous ternary hydroxide mixture consisting of sodium, potassium and cesium hydroxides in the proportions 40 : 36 : 24 (NaOH : KOH : CsOH). In this paper, plots of the coefficients of performance of a solar air conditioning system operating with these two mixtures are presented. The results showed that similar coefficients of performance are obtained for both mixtures, however, it was found that the system operating with the hydroxides may operate with a higher range of condenser and absorber temperatures and the heat delivered by these components can be removed by air.

High consumption of electricity represents an economic and social problem in warm places, caused by the massive use of cooling machines. Absorption systems are a sustainable method for air conditioning applications. However, environmental conditions should be analyzed to avoid crystallization problems of the working mixture. This article presents a thermal analysis of a solar absorption cooling system in dynamic conditions using NH3-H2O, H2O-LiBr, NH3-NaSCN, NH3-LiNO3, and H2O-LiCl working mixtures using Equation Engineering Solver (EES) and TRaNsient SYstem Simulation (TRNSYS) software. A solar collector area of 42.5 m2 was selected to carry out the thermal analysis. The results showed that H2O-LiCl obtained the maximum solar (0.67) and minimum heating (0.33) fraction. However, it obtained the maximum lost heat fraction (0.12), in spite of obtaining the best coefficient of performance (COP) among the other working mixtures, due mainly to a crystallization problem. The gain fraction (GF) parameter was used to select the adequate solar collector number for each working mixture. NH3-LiNO3 and NH3-H2O obtained the highest GF (up 6), and both obtained the maximum solar (0.91) and minimum heating (0.09) fraction, respectively, using 88.8 and 100.4 m2 of solar collector area, respectively.

Abstract The Gibbs phase rule and thermodynamic properties of the working pair limit the choice of operating temperatures. For any combination of temperatures, the concentrations in the absorber and the generator and hence the flow ratios are fixed. For any particular working pair, the coefficient of performance is related to the flow ratio. Tables of possible combinations of operating temperatures and concentrations, including flow ratios, Carnot coefficients of performance and enthalpy-based coefficients of performance for two effectiveness heat exchanger values have been presented for absorption heat transformers operating on an aqueous ternary hydroxide working fluid consisting of sodium, potassium and caesium hydroxides in the proportions 40:36:24 (NaOH:KOH:CsOH). The interactions of operating temperatures have been illustrated graphically.

Abstract Absorption Heat Transformer ( AHT ) is a device to recovery heat waste by a thermodynamic cycle. In this paper, an experimental AHT prototype operated with four temperature levels and two pressure levels was analyzed. This prototype was build with commercial Plate Heat Exchangers ( PHE ) and operates with water/Carrol mixture. The heat powers measured were 1.03, 1.48 and 1.51 kW for the generator, 1.19, 1.54 and 1.61 kW for the condenser, 1.21, 1.57 and 1.64 kW for the evaporator, and finally, 0.59, 0.98 and 1.09 kW for the absorber. Experimental Gross Temperature Lift ( GTL ) was 18.0, 17.4 and 16.5 °C and the dimensionless values of Coefficient of Performance ( COP ) calculated for those operating conditions were 0.26, 0.32 and 0.35. Absorber temperatures were 106.8, 105.3, 103.9 °C.

The energy consumption for space cooling is growing faster than for any other end-use in buildings, more than tripling between 1990 and 2016. Energy efficiency is an important topic in the drive to reduce the consumption of electricity, particularly in air conditioning. This paper presents a simulation of an absorption cooling system with a parabolic trough collector under dynamic conditions using TRaNsient SYstem Simulation (TRNSYS) software. The thermal analysis seeks to evaluate a storage tank at three different configurations: (1) sensible heat, (2) latent heat, and (3) latent heat incorporating a tempering valve. The latent heat storage tank is a rectangular heat exchanger using MgCl2·6H2O as the phase change material, programmed in EES software; in addition, water and synthetic organic fluid were analyzed as heating fluids. The process was analyzed while varying the solar collector area from 20 to 40 m2 and the storage tank volume from 0.25 to 0.75 m3. The results showed that the solar collector of configuration 1 is unable to satisfy the energy demand. Configuration 2 can satisfy the demand with water and a storage tank volume above 0.50 m3 and 30 m2, while configuration 3 can satisfy the demand above 0.50 m3 and 20 m2 with water.