• Energy Research

More efficient systems and renewable energies are determinants of reducing the negative impact on the environment. A novel cogeneration system is modeled for the simultaneous production of power and cooling driven by geothermal energy utilizing an ammonia–water mixture. The system can be used in rural communities by using renewable energies or in industries where waste heat is available. The system is a modification of a Goswami cycle in which a separator has been added to produce an extra amount of ammonia vapor to increase the cooling effect. Energy and exergy analyses are conducted as a function of the main operating temperatures. From the optimization, it is found that the maximum energy utilization factor is 0.54, and the exergy efficiency is 0.37, producing 81.45 kW of power and 1068 kW of cooling. A case study is also conducted for a rural community located in the estate of Jalisco, México. The proposed system is capable of preserving 3750 L of milk/day while simultaneously producing 12.53 kW of power when 230.6 kW of geothermal energy is supplied at 120 °C.

Abstract A solar powered intermittent absorption refrigeration system has been developed and evaluated with the ammonia/lithium nitrate (NH3/LiNO3) and ammonia/lithium nitrate/water (NH3/LiNO3/H2O) mixtures. The system, designed to produce up to 8 kg/day of ice, was developed in the Centro de Investigacion en Energia of the Universidad Nacional Autonoma de Mexico. It consists of a Compound Parabolic Concentrator (CPC) with a cylindrical receiver acting as the generator/absorber during the generation and evaporation stages respectively, a condenser, an evaporator and an expansion device. The system operates solely with solar energy and no moving parts are required. Several test runs were carried out at different solution concentrations for both mixtures under study. Evaporator temperatures as low as −8 °C were obtained for a time period of 8 h. Comparing the performance of the system operating with the two mixtures, it was found that with the ternary mixture the solar coefficients of performance can be up to 24% higher than those obtained with the binary mixture, varying from 0.066 to 0.093. In addition, with the ternary mixture the initial generation temperatures resulted to be up to 5.5 °C lower than those obtained with the ammonia/lithium nitrate mixture, at the same time the maximum operating pressures were around 1.5 bar higher.

Abstract Desalination processes consume large amount of electricity and heat derived from fossil fuels to produce fresh water. In recent years, solar desalination emerged as a favorable method for sustainable fresh water production with less environmental impacts. A solar photovoltaic thermal collector is a combined system of solar photovoltaic and solar thermal collector that simultaneously generates electricity and thermal energy. The present work reviews photovoltaic thermal collector integrating desalination technologies such as solar still, humidification dehumidification, multiple effect distillation, reverse osmosis, multiple stage flash and membrane distillation. The primary focus is made on successful utilization of electricity and heat from the photovoltaic thermal collector in desalination systems to reduce cost, primary energy consumption and to improve overall system performance. Future opportunities and novel methods to improve/explore the photovoltaic thermal driven desalination systems are reported. Possibilities of photovoltaic thermal collector as energy source for other desalination technologies (electrodialysis, forward osmosis, vapor compression, adsorption desalination and etc.) are also presented. Comparative analysis shows that overall performance of photovoltaic thermal coupled desalination systems is better than desalination systems coupled with separate photovoltaic panel and/or solar thermal collector to meet the energy needs. The additional electricity generated from photovoltaic thermal desalination paves way for standalone desalination in remote location even though the initial costs are a tad higher.

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.

Abstract The need for an integrated energy system is increased especially in the field of cogeneration cycles for the simultaneos production of power and cooling. A standalone power or cooling cycle is less efficient compared to the integrated model. A new power and cooling cycle is proposed by integrating a dual and triple pressure cooling cogeneration cycle. The proposed system shares some common components like absorber, solution heat exchanger, pump, and generator. The system is analyzed in terms of the most influencing parameters such as operating and ambient temperatures, pressures, and solution concentrations in different components. The power and cooling are achieved in both dual and triple pressure cogeneration combinations. It is recommended to use low concentrations at higher ambient temperature conditions. A pressure fraction less than 0.5 is suggested to obtain higher amount of power and cooling produced. A maximum cogeneration output of 480 kW and cycle and plant energy utilization factor of 0.53 and 0.22 were obtained respectively, at an ammonia concentration of 0.58 and a heat source and ambient temperatures of 150 °C and 30 °C, respectively. The advantage of the present system is that the cooling or power production can be controlled by adjusting the pressure fraction.

The first and second law of thermodynamics have been used to analyze the performance of an experimental single-stage heat transformer operating with the water/lithium bromide mixture. Enthalpy coefficients of performance (COP), external coefficients of performance (COPEXT), exergy coefficient of performance (ECOP), exergy destruction or irreversibility in the system and components (I) and the improvement potential (Pot) have been calculated against the gross temperature lift and the main operating temperatures of the system. The results showed that the highest COP, COPEXT and ECOP values are obtained at the highest solution concentrations meanwhile the Pot and the I of the cycle remain almost constant against these parameters. Also it was shown that the COP, COPEXT and ECOP decrease with an increase with the absorber temperature, meanwhile the Pot and the I increase. Moreover, it was observed that in all the cases independently of the operating temperatures of the system, the absorber accounts with most of the half of the total irreversibility in the system. Finally, it was shown that the improvement potential is considerable for the system. Copyright © 2009 John Wiley & Sons, Ltd.

Abstract This investigation presents the results of the development and experimental assessment of a single-stage absorption cooling system built with plate heat exchangers as the main components and operated with the ammonia-water mixture thus resulting in a very compact design. The system utilized water as the auxiliary heating and cooling fluid. For the experimental assessment, the heating water was supplied to the generator at temperatures between 85 °C and 105 °C, for condensation/absorption temperatures between 20 °C and 32 °C. Several experimental curves describing parameters such as the internal cooling power, evaporation temperature and internal coefficient of performance as a function of generation and condensation temperatures are presented. The maximum values achieved for these parameters were close to 2.6 kW, −19 °C and 0.61, respectively. In addition, the effects of the expansion valve aperture on parameters such as the mass flow rate and stability of the produced refrigerant, evaporation temperature and internal coefficient of performance are presented. Due to the cooling temperatures achieved, the absorption system proposed can be operated either for food conservation or air-conditioning applications.

In the present study, the first and second law of thermodynamics have been used to analyze in detail the performance of a double absorption (lift) heat transformer operating with the water–lithium bromide mixture. A mathematical model was developed to estimate the coefficient of performance (COP), the exergy coefficient of performance (ECOP), the total exergy destruction in the system (ΨTD) and the exergy destruction (ΨD) in each one of the main components, as a function of the system temperatures, the efficiency of the economizer (EFEC), the gross temperature lift and flow ratio (FR). The results showed that the generator is the component with the highest irreversibilities or exergy destruction contributing to about 40% of the total exergy destruction in the whole system, reason why this component should be carefully designed and optimized. The results also showed that the COP and ECOP increase with increase in the generator, the evaporator and the absorber–evaporator temperatures and decrease with the absorber and condenser temperatures. Finally, it was observed that the COP and ECOP are very dependent of the FR and the economizer efficiency (EFEC) values. Also the optimum operating region of the analyzed system is shown in the present study. Copyright © 2009 John Wiley & Sons, Ltd.

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, including flow ratios, Carnot coefficients of performance nd enthalpy based coefficients of performance have been presented for absorption heat transformers operating on water-carrol (lithium bromide-ethylene glycol). The interaction of operating temperatures has been illustrated graphically.