Alberto Coronas

Liquid Densities, Kinematic Viscosities, and Heat Capacities of Some Ethylene Glycol Dimethyl Ethers at Temperatures from 283.15 to 423.15 K

Liquid densities and heat capacities at 1 MPa, and kinematic viscosities at atmospheric pressure of monoethylene glycol dimethyl ether (MEGDME), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TrEGDME), tetrathylene glycol dimethyl ether (TEGDME), pentaethylene glycol dimethyl ether (PeEGDME), and polyethylene glycol 250 dimethyl ether (PEGDME 250) were measured in the temperature range from 283.15 to 423.15 K. For each substance, experimental data were correlated with temperature using empirical polynomial equations. The experimental data were also used to evaluate the predictive capability of some estimation methods of liquid densities and heat capacities for the studied ethylene glycol dimethyl ethers. The densities estimated by the Yen–Woods equation agree with our experimental values with a root-mean-square relative deviation (RMSD) of 3.21% for all ethylene glycol dimethyl ethers. The best estimated results of liquid heat capacities were obtained from the Rowlinson equation based on the corresponding-states principle, with a RMSD of 1.12%. The group-contribution methods give the worst results, especially at high temperatures.

Absorption of water vapour in the falling film of water–lithium bromide inside a vertical tube at air-cooling thermal conditions

Abstract In the absorbers of air-cooled water–lithium bromide absorption chillers, the absorption process usually takes place inside vertical tubes with external fins. In this paper we have carried out an experimental study of the absorption of water vapour over a wavy laminar falling film of water–lithium bromide on the inner wall of a smooth vertical tube. The control variables for the experimental study were; absorber pressure, solution mass flow rate, solution concentration and cooling water temperature. Relatively high cooling water temperatures were selected to simulate air-cooling thermal conditions. The parameters considered to assess the performance of the absorber were; the mass absorption flux, the outlet solution degree of subcooling and the falling film heat transfer coefficient. The results indicate that in water cooling thermal conditions the mass absorption fluxes are in the range 0.001–0.0015 kg·m−2·s−1, whereas in air-cooling thermal conditions the range of mass absorption values decreases to 0.00030–0.00075 kg·m−2·s−1.

Double-lift absorption refrigeration cycles driven by low-temperature heat sources using organic fluid mixtures as working pairs

At present, much interest is being shown in absorption refrigeration cycles driven by low temperature heat sources, such as solar energy or low-grade waste-heat. Double-lift absorption cycles working with ammonia-water have been recommended for refrigeration applications which require cold at 0°C and which are activated by waste heat between 70 and 100°C. This paper discusses the potential of the organic fluid mixtures trifluoroethanol (TFE)-tetraethylenglycol dimethylether (TEGDME or E181) and methanol-TEGDME as working pairs in series flow and vapour exchange double-lift absorption cycles. The ammonia-water mixture was used for comparison purposes. The results show that the performances of these cycles improve significantly when they have the above mentioned organic fluid mixtures as working pairs. For example, the coefficient of performance of the vapour exchange cycle working with TFE-TEGDME is 15% higher than with ammonia-water. In this study, we used a modular software package, which we developed for the thermodynamic properties and cycles simulation of absorption systems.

Performance of double effect absorption compression cycles for air-conditioning using methanol–TEGDME and TFE–TEGDME systems as working pairs

Abstract The organic working pairs trifluoroethanol (TFE)–tetraethyleneglycol dimethyether (TEGDME or E181) and methanol–TEGDME have some advantages over classical water–LiBr and ammonia water working pairs in absorption cycles. One of the most important features is the wide working range caused by the absence of crystallization, the low freezing temperatures of the refrigerants and the thermal stability of the mixtures at high temperatures. The performance of a double effect absorption cycle for these organic mixtures can be improved if a compression stage is introduced between the evaporator and the absorber. The coefficient of performance (COP) and primary energy ratio (PER) values in the cooling mode are significantly increased over a wide working range: the cycle can work with temperature lifts of 50oC at 5oC in the evaporator or it can also be powered by low grade heat. For these conditions COP and PER values are higher than 1.0 and 0.7 respectively, and the power supplied to the compressor represents up to 15% of the thermal energy supplied to the generator. As it is possible to work at high temperatures lifts, the absorber and condenser can be air cooled.

Absorption heat pump with the TFE-TEGDME and TFE-H2O-TEGDME systems

Abstract The binary mixture trifluoroethanol (TFE)-tetraethylene glycol dimethyl ether (TEGDME) can be more advantageous for absorption cycles at high temperature levels than classical working systems such as H 2 OLiBr and NH 3 H 2 O. This system is non-corrosive, completely miscible over a wide temperature range, thermally stable up to 250°C and has low working pressures. The low thermal conductivity and enthalpy of evaporation of TFE can be improved by using the TFEH 2 O mixture as a refrigerant, instead of pure TFE, with TEGDME as an absorbent. The effect of adding water on the performance of a single-effect absorption heat pump has been analysed. The simulation of such a cycle with a partial evaporator has been carried out for binary and ternary systems, in order to recover thermal wastes at 80°C and upgrade them to 120°C. The maximum COP of about 1.6 obtained for the TFE-TEGDME system in these conditions is hardly affected by the addition of water, although the solution and reflux flow ratios increase with the water content. The results show that about 15 mass% of water gives optimum performance in terms of the COP and flow ratios. The thermodynamic properties of the pure compounds (TFE and TEGDME) and the binary and ternary mixtures needed to study the performance of the absorption cycles are also presented.

Review of optimization models for the design of polygeneration systems in district heating and cooling networks

Abstract The current increasing energy prices and the limitation of the existing energy resources promotes the use of new energy production systems, like hybrid integrated systems (using fossil fuels and renewable energy sources) with high-energy efficiency. These integrated systems, known as polygeneration systems, produce electrical, heating and cooling at different conditions at a higher efficiency than a conventional system, and involve a wide range of technologies with several possible configurations. Sometimes the design of these systems is carried out with the aid of mathematical models that are solved and optimized minimizing the investment and operational costs, but these optimization techniques are applied frequently for industrial applications and rarely for building or district heating and cooling (DHC) applications. The objective of this paper is to present a literature review of the optimization techniques that have been used so far for building or DHC applications. The main purpose of this review is to establish the basis for the development of an optimization tool for the synthesis and design of polygeneration systems for their use in district heating and cooling networks, that are optimized reducing their investment and operational cost. An example is presented to illustrate the application of this tool.

Measurement of the vapor pressure of 2,2,2-trifluoroethanol and tetraethylene glycol dimethyl ether by static method

New results of vapor pressure are presented for tetraethylene glycol dimethyl ether (TEGDME) and 2,2,2-trifluoroethanol (TFE) in the ranges of temperatures from 373.15 to 533.15 K, and 293.15 to 363.15 K, respectively. Measurements were made using the static method. The static vapor pressure apparatus developed is described. For the practical utility, vapor pressure data for TEGDME were fitted to Antoine equation and for TFE to a Wagner-type equation, combining in this case the experimental data with those of Sauermann et al. (1993) to cover a wide temperature range.

Densities and viscosities of the binary mixtures of interest for absorption refrigeration systems and heat pumps

Densities and kinematic viscosities were measured over the entire range of composition and at atmospheric pressure for methanol-tetraethylene glycol dimethyl ether and methanol-polyethylene glycol 250 dimethyl ether from 283.15 to 323.15 K at five isotherms. These properties were fitted by empirical equations stating their dependence on temperature and composition of the mixture. The kinematic viscosity was correlated by the methods of McAllister, Stephan and Heckenberger, Soliman and Marshall correlations.

Experimental and predicted excess enthalpies of the working pairs (methanol or trifluoroethanol + polyglycol ethers) for absorption cycles

In this work we report the excess molar enthalpies at 298.15 K and atmospheric pressure of the mixtures 2,2,2-trifluoroethanol (TFE)+poly(ethylene glycol) dimethyl ether 250 (PEGDME 250), methanol + tetraethylene glycol dimethyl ether (TEGDME) and methanol + PEGDME 250. In the case of mixtures with methanol, the UNIFAC and DISQUAC group contribution models have been used to compare the predicted and experimental results. We have used three versions of the UNIFAC model due to Tassios et al., Larsen et al. and Gmehling et al., for which three group assignments were made. The best predictions were found with the Gmehling version of the UNIFAC model.

Industrial heat recovery by absorption/compression heat pump using TFE–H2O–TEGDME working mixture

Abstract The thermodynamic performance of a single-stage absorption/compression heat pump using the ternary working fluid Trifluoroethanol–Water–Tetraethylenglycol dimethylether (TFE–H2O–TEGDME) for upgrading waste heat has been studied. A simulation program has been developed using a mathematical model based on mass and energy balances in all components of the cycle and thermodynamic equilibrium considerations. In order to establish the optimum operating conditions of the cycle for various thermal conditions, sensitivity studies of the coefficient of performance (COP), the flow rate of the weak solution and the compressor volumetric displacement, both per unit of upgraded energy, were carried out versus of water content in the vapour phase. The results obtained show that the operation of the cycle with this ternary system is still more advantageous than the TFE–TEGDME binary working pair. So, it is possible to upgrade thermal waste heat from 80 to 120°C, with a COP of about 6.4, with a compression pressure ratio of 4 at a low pressure of 100 kPa, the water mole fraction in the vapour being 42%. At these operating conditions, the necessary weak solution mass flow rate is about three times lower than the corresponding binary one. The performance comparison of such a cycle with other absorption cycles like the heat transformer or the single-effect heat pump, both of them using the ternary system, shows its interest and potential.