Thermodynamic analysis of humidification dehumidification desalination cycles

Humidification–dehumidification desalination (HDH) is a promising technology for small-scale water production applications. There are several embodiments of this technology which have been investigated by researchers around the world. However, from a previous literature [1], we have found that no study carried out a detailed thermodynamic analysis in order to improve and/ or optimize the system performance. In this paper, we analyze the thermodynamic performance of various HDH cycles by way of a theoretical cycle analysis. In addition, we propose novel high performance variations on those cycles. These high-performance cycles include multi-extraction, multi-pressure and thermal vapor compression cycles. It is predicted that the systems based on these novel cycles will have gained output ratio in excess of 5 and will outperform existing HDH systems.King Fahd University of Petroleum and MineralsCenter for Clean Water and Clean Energy at MIT and KFUP

Solar-driven refrigeration systems with focus on the ejector cycle

Interest in utilizing solar-driven refrigeration systems for air-conditioning or refrigeration purposes has grown continuously. Solar cooling is com-prised of many attractive features and is one path towards a more sus-tainable energy system. Compared to solar heating, the cooling load, par-ticularly for air-conditioning applications, is generally in phase with solar radiation. The objective of this thesis is to establish a fundamental basis for further research and development within the field of solar cooling. In this thesis, an overview of possible systems for solar powered refrigeration and air-conditioning systems will be presented. The concept of the ‘Solar Cool-ing Path’ is introduced, including a discussion of the energy source to the collector, and choice of cooling cycle to match cooling load. Brief infor-mation and comparisons of different refrigeration cycles are also pre-sented. The performance of solar cooling systems is strongly dependent on local conditions. The performance of a solar divan air-conditioning system in different locations will therefore be compared in this thesis. Solar cooling systems can be efficiently operated in locations where sufficient solar ra-diation and good heat sink are available. A solar-driven ejector refrigeration system has been selected as a case study for a further detailed investigation. A low temperature heat source can be used to drive the ejector refrigeration cycle, making the system suitable for integration with the solar thermal collector. Analysis of the solar driven ejector system is initiated by steady state analysis. System performance depends on the choice of working fluid (refrigerant), oper-ating conditions and ejector geometry. Results show that various kinds of refrigerants can be used. Also, thermodynamic characteristics of the re-frigerant strongly influence the performance of the cycle. An ejector re-frigeration cycle using natural working fluids generates good perform-ance and lower environmental impact, since traditional working fluids, CFC’s and HFC’s are strong climate gases. Further on, exergy analysis is used as a tool in identifying optimum operating conditions and investi-gating losses in the system. Exergy analysis illustrates that the distribu-tion of the irrervsibilities in the cycle between components depends strongly on the working temperatures. The most significant losses in the system are in the solar collector and ejector. Losses in the ejector pre-dominate over total losses within the system. In practice, the cooling load characteristic and solar radiation are not constant. Therefore, a dynamic analysis is useful for determining the characteristics of the system during the entire year, and dimensioning the important components of the solar collector subsystem, such as storage tanks. The final section of the thesis will deal with the ejector, the key compo-nent of the ejector refrigeration cycle. Characteristics of the actual ejector are shown to be quite complicated and its performance difficult to de-termine solely through theoretical analysis. Suggested design procedures and empirical equations for an ejector are offered in this thesis. Prelimi-nary test results for one fixed ejector dimension using R134a as the re-frigerant are also included.QC 2010091

Theoretical Study of a Carbon Dioxide Double Loop System

In the current research, a carbon dioxide double loop system is proposed. The system contains of two sub systems: a CO2power subsystem and a CO2refrigeration subsystem. The power subsystem is able to utilize the energy from the low-grade heat source to produce power. The power is then transferred to the refrigeration subsystem, partly or totally covering the power consumption of the compressor. Furthermore, it is also possible to take advantage of the temperature glides of both subsystems’ heat rejection processes to produce hot water. Engineering Equation Solver (EES) is employed to analyze the system performance. The results show that the proposed system is a very promising way to provide cooling, heating and hot water in a more efficient way comparing to traditional systems.QC 201120

Theoretical Study of a Carbon Dioxide Double Loop System

In the current research, a carbon dioxide double loop system is proposed. The system contains of two sub systems: a CO2power subsystem and a CO2refrigeration subsystem. The power subsystem is able to utilize the energy from the low-grade heat source to produce power. The power is then transferred to the refrigeration subsystem, partly or totally covering the power consumption of the compressor. Furthermore, it is also possible to take advantage of the temperature glides of both subsystems’ heat rejection processes to produce hot water. Engineering Equation Solver (EES) is employed to analyze the system performance. The results show that the proposed system is a very promising way to provide cooling, heating and hot water in a more efficient way comparing to traditional systems.QC 201120

Theoretical Study of a Carbon Dioxide Double Loop System

In the current research, a carbon dioxide double loop system is proposed. The system contains of two sub systems: a CO2power subsystem and a CO2refrigeration subsystem. The power subsystem is able to utilize the energy from the low-grade heat source to produce power. The power is then transferred to the refrigeration subsystem, partly or totally covering the power consumption of the compressor. Furthermore, it is also possible to take advantage of the temperature glides of both subsystems’ heat rejection processes to produce hot water. Engineering Equation Solver (EES) is employed to analyze the system performance. The results show that the proposed system is a very promising way to provide cooling, heating and hot water in a more efficient way comparing to traditional systems.QC 201120