The Experts below are selected from a list of 816 Experts worldwide ranked by ideXlab platform

Elias Stefanakos - One of the best experts on this subject based on the ideXlab platform.

  • a review of solar thermo Mechanical Refrigeration and cooling methods
    Renewable & Sustainable Energy Reviews, 2015
    Co-Authors: Mehdi Zeyghami, Yogi D Goswami, Elias Stefanakos
    Abstract:

    Use of solar energy to produce Refrigeration and air conditioning can be a viable option to replace conventional cooling systems. Research and development activities on solar cooling systems started in the 1970s because of the energy crisis and has picked up again in the past few years due to greater awareness of the necessity to reduce emission of greenhouse and Ozone depletion gases. Although, most of the attention in the past has been on using solar heat to run absorption Refrigeration systems, solar thermo-Mechanical cooling systems have received a renewed attention in recent years due to the advantages such as, ability to produce low Refrigeration temperatures (<0°C) by using appropriate working fluids, ability to produce electricity when cooling is not needed by coupling the prime mover with an electric generator, maintaining high performance at off-design conditions and utilization of a wide range of temperatures from solar collectors. In a solar thermo-Mechanical cooling system, the heat gained from the solar collector is converted into Mechanical work, which is used to compress the working fluid in a vapor compression cycle directly (i.e. ejector cooling cycle) or indirectly (i.e. coupled with an organic Rankine cycle). Hybrid solar thermo-Mechanical cooling with conventional cooling systems also offers a great potential for energy demand reduction for buildings.

  • A review of solar thermo-Mechanical Refrigeration and cooling methods
    Renewable and Sustainable Energy Reviews, 2015
    Co-Authors: Mehdi Zeyghami, D. Yogi Goswami, Elias Stefanakos
    Abstract:

    Use of solar energy to produce Refrigeration and air conditioning can be a viable option to replace conventional cooling systems. Research and development activities on solar cooling systems started in the 1970s because of the energy crisis and has picked up again in the past few years due to greater awareness of the necessity to reduce emission of greenhouse and Ozone depletion gases. Although, most of the attention in the past has been on using solar heat to run absorption Refrigeration systems, solar thermo-Mechanical cooling systems have received a renewed attention in recent years due to the advantages such as, ability to produce low Refrigeration temperatures (

Ahmad K. Sleiti - One of the best experts on this subject based on the ideXlab platform.

  • Analysis of novel regenerative thermo-Mechanical Refrigeration system integrated with isobaric engine
    Journal of Energy Resources Technology, 2021
    Co-Authors: Ahmad K. Sleiti, Wahib A. Al-ammari, Mohammed Al-khawaja
    Abstract:

    Abstract Refrigerants of the conventional cooling systems contribute to global warming and ozone depletion significantly, therefore it is necessary to develop new cooling systems that use renewable energy resources and waste heat to perform the cooling function with eco-friendly working fluids. To address this, the present study introduces and analyzes a novel regenerative thermo-Mechanical Refrigeration system that can be powered by renewable heat sources (solar, geothermal, or waste heat). The system consists of a novel expander–compressor unit (ECU) integrated with a vapor-compression Refrigeration system. The integrated system operates at the higher-performance supercritical conditions of the working fluids as opposed to the lower-performance subcritical conditions. The performance of the system is evaluated based on several indicators including the power loop efficiency, the coefficient of performance (COP) of the cooling loop, and the expander–compressor diameters. Several working fluids were selected and compared for their suitability based on their performance and environmental effects. It was found that for heat source temperature below 100 °C, adding the regenerator to the system has no benefit. However, the regenerator increases the power efficiency by about 1% for a heat source temperature above 130 °C. This was achieved with a very small size regenerator (Dr = 6.5 mm, Lr = 142 mm). Results show that there is a tradeoff between high-performance fluids and their environmental effects. Using R32 as a working fluid at heat source temperature Th = 150 °C and cold temperature Tc1 = 40 °C, the system produces a cooling capacity of 1 kW with power efficiency of 10.23%, expander diameter of 53.12 mm, and compressor diameter of 75.4 mm.

  • a combined thermo Mechanical Refrigeration system with isobaric expander compressor unit powered by low grade heat design and analysis
    International Journal of Refrigeration-revue Internationale Du Froid, 2020
    Co-Authors: Ahmad K. Sleiti, Mohammed Alkhawaja, Wahib A Alammari
    Abstract:

    Abstract Refrigeration and air conditioning systems consume about 17% of the world-wide electricity and their conventional refrigerants cause ozone depletion and global warming. In this study a novel thermo-Mechanical Refrigeration (TMR) system is developed and analyzed that is powered, instead of electricity, by thermal energy from waste heat or renewable sources in the ultra-low temperature range of 60–100 °C. A novel isobaric expander-compressor unit (ECU) is designed and combined with vapor compression Refrigeration cycle to constitute the TMR system. The technological solutions (mainly towards simplification of the design) are crucial components of the study novelty. The suitable refrigerants for the system are systematically investigated, analyzed and selected from a list of 43 refrigerants. Nine fluids for the power loop (the isobaric expansion cycle) and nine fluids for the cooling loop (the thermal Refrigeration cycle) were selected and compared based on their mode of operation (subcritical and supercritical), environmental effects and safety class. It is found that the HFO refrigerants such as R1234yf and R1234ze have acceptable performance with no ODP and very low GWP. Natural refrigerants R717 (ammonia) has the best performance in subcritical mode with toxicity as the main drawback. At heat source temperatures less than 85 °C, the system operation in subcritical mode is more efficient and more compact than in the supercritical mode. Thorough analysis and recommendations are made for the size of the ECU in terms of the diameters of the expander and the compressor.

  • Subcritical and Supercritical Operation of Innovative Thermal Mechanical Refrigeration System
    University of the Future: Re-Imagining Research and Higher Education, 2020
    Co-Authors: Ahmad K. Sleiti, Wahib A. Al-ammari, Mohammed Al-khawaja, Maxim Glushenkov, Alexander Kronberg
    Abstract:

    Around 17% of the globally generated energy is consumed for residential, commercial, and transportation Refrigeration. The current cooling technologies utilize refrigerants with high Ozone Depletion and Global Warming Potentials. Furthermore, the current technologies are expensive alongside with toxicity and flammability hazards. On the other side, energy produced by combustion of fossil fuels results in substantial amounts of waste heat. Therefore, it is necessary to develop new Refrigeration technologies that utilize waste heat as a source of energy with ecofriendly refrigerants with zero ozone depletion potential and zero global warming potential. In addition, this thermal Mechanical Refrigeration (TMR) technology improves the energy efficiency of the source of waste heat system and minimizes the emissions of the carbon dioxide (CO2). In this study, a novel thermo-Mechanical Refrigeration system is proposed. It operates with low-grade energy sources (such as waste heat) at temperature range of 60 oC to 100 oC. Furthermore, it has the advantage of working with low-frequency driver-compressor unit, which eliminates noise and increases its lifetime. Moreover, the TMR system is adaptable to commercial, transportation, and residential Refrigeration applications.

  • Heat Transfer Analysis of Regenerative Thermo-Mechanical Refrigeration System
    ASME 2020 Heat Transfer Summer Conference, 2020
    Co-Authors: Ahmad K. Sleiti, Mohammed Al-khawaja
    Abstract:

    Abstract Refrigeration systems contribute to the critical environmental concerns including global warming and ozone depletion. It is necessary to develop new systems that use renewable energy resources and waste heat to perform the cooling function with eco-friendly working fluids. This improves the energy efficiency of the power systems and minimizes the harmful effects of conventional Refrigeration systems. This paper introduces an analysis of a regenerative thermo-Mechanical Refrigeration system that is powered with renewable heat sources (solar, geothermal) or waste heat (from internal combustion engines, gas power plants, and steam power plants). The system operates at the supercritical conditions of the working fluids. The performance of the system is evaluated based on power efficiency, the COP, and the expander-compressor diameters. Also, a number of working fluids were compared with each other based on their performance and environmental effects. There is a trade-off between high-performance fluids and their environmental effects. Using R32 as a working fluid at Th = 150 °C and Tc1 = 40 °C, the system produces a cooling capacity of 1 kW with power efficiency of 10.23%, expander diameter of 53.12 mm and compressor diameter of 75.4mm. The regenerator increases the power efficiency by about 1%. However, the size of the regenerator is small (Dr = 6.5 mm, Lr = 142 mm].

  • A combined thermo-Mechanical Refrigeration system with isobaric expander-compressor unit powered by low grade heat – Design and analysis
    International Journal of Refrigeration, 2020
    Co-Authors: Ahmad K. Sleiti, Mohammed Al-khawaja, Wahib A. Al-ammari
    Abstract:

    Abstract Refrigeration and air conditioning systems consume about 17% of the world-wide electricity and their conventional refrigerants cause ozone depletion and global warming. In this study a novel thermo-Mechanical Refrigeration (TMR) system is developed and analyzed that is powered, instead of electricity, by thermal energy from waste heat or renewable sources in the ultra-low temperature range of 60–100 °C. A novel isobaric expander-compressor unit (ECU) is designed and combined with vapor compression Refrigeration cycle to constitute the TMR system. The technological solutions (mainly towards simplification of the design) are crucial components of the study novelty. The suitable refrigerants for the system are systematically investigated, analyzed and selected from a list of 43 refrigerants. Nine fluids for the power loop (the isobaric expansion cycle) and nine fluids for the cooling loop (the thermal Refrigeration cycle) were selected and compared based on their mode of operation (subcritical and supercritical), environmental effects and safety class. It is found that the HFO refrigerants such as R1234yf and R1234ze have acceptable performance with no ODP and very low GWP. Natural refrigerants R717 (ammonia) has the best performance in subcritical mode with toxicity as the main drawback. At heat source temperatures less than 85 °C, the system operation in subcritical mode is more efficient and more compact than in the supercritical mode. Thorough analysis and recommendations are made for the size of the ECU in terms of the diameters of the expander and the compressor.

Mehdi Zeyghami - One of the best experts on this subject based on the ideXlab platform.

  • a review of solar thermo Mechanical Refrigeration and cooling methods
    Renewable & Sustainable Energy Reviews, 2015
    Co-Authors: Mehdi Zeyghami, Yogi D Goswami, Elias Stefanakos
    Abstract:

    Use of solar energy to produce Refrigeration and air conditioning can be a viable option to replace conventional cooling systems. Research and development activities on solar cooling systems started in the 1970s because of the energy crisis and has picked up again in the past few years due to greater awareness of the necessity to reduce emission of greenhouse and Ozone depletion gases. Although, most of the attention in the past has been on using solar heat to run absorption Refrigeration systems, solar thermo-Mechanical cooling systems have received a renewed attention in recent years due to the advantages such as, ability to produce low Refrigeration temperatures (<0°C) by using appropriate working fluids, ability to produce electricity when cooling is not needed by coupling the prime mover with an electric generator, maintaining high performance at off-design conditions and utilization of a wide range of temperatures from solar collectors. In a solar thermo-Mechanical cooling system, the heat gained from the solar collector is converted into Mechanical work, which is used to compress the working fluid in a vapor compression cycle directly (i.e. ejector cooling cycle) or indirectly (i.e. coupled with an organic Rankine cycle). Hybrid solar thermo-Mechanical cooling with conventional cooling systems also offers a great potential for energy demand reduction for buildings.

  • A review of solar thermo-Mechanical Refrigeration and cooling methods
    Renewable and Sustainable Energy Reviews, 2015
    Co-Authors: Mehdi Zeyghami, D. Yogi Goswami, Elias Stefanakos
    Abstract:

    Use of solar energy to produce Refrigeration and air conditioning can be a viable option to replace conventional cooling systems. Research and development activities on solar cooling systems started in the 1970s because of the energy crisis and has picked up again in the past few years due to greater awareness of the necessity to reduce emission of greenhouse and Ozone depletion gases. Although, most of the attention in the past has been on using solar heat to run absorption Refrigeration systems, solar thermo-Mechanical cooling systems have received a renewed attention in recent years due to the advantages such as, ability to produce low Refrigeration temperatures (

Wahib A. Al-ammari - One of the best experts on this subject based on the ideXlab platform.

  • Analysis of novel regenerative thermo-Mechanical Refrigeration system integrated with isobaric engine
    Journal of Energy Resources Technology, 2021
    Co-Authors: Ahmad K. Sleiti, Wahib A. Al-ammari, Mohammed Al-khawaja
    Abstract:

    Abstract Refrigerants of the conventional cooling systems contribute to global warming and ozone depletion significantly, therefore it is necessary to develop new cooling systems that use renewable energy resources and waste heat to perform the cooling function with eco-friendly working fluids. To address this, the present study introduces and analyzes a novel regenerative thermo-Mechanical Refrigeration system that can be powered by renewable heat sources (solar, geothermal, or waste heat). The system consists of a novel expander–compressor unit (ECU) integrated with a vapor-compression Refrigeration system. The integrated system operates at the higher-performance supercritical conditions of the working fluids as opposed to the lower-performance subcritical conditions. The performance of the system is evaluated based on several indicators including the power loop efficiency, the coefficient of performance (COP) of the cooling loop, and the expander–compressor diameters. Several working fluids were selected and compared for their suitability based on their performance and environmental effects. It was found that for heat source temperature below 100 °C, adding the regenerator to the system has no benefit. However, the regenerator increases the power efficiency by about 1% for a heat source temperature above 130 °C. This was achieved with a very small size regenerator (Dr = 6.5 mm, Lr = 142 mm). Results show that there is a tradeoff between high-performance fluids and their environmental effects. Using R32 as a working fluid at heat source temperature Th = 150 °C and cold temperature Tc1 = 40 °C, the system produces a cooling capacity of 1 kW with power efficiency of 10.23%, expander diameter of 53.12 mm, and compressor diameter of 75.4 mm.

  • Subcritical and Supercritical Operation of Innovative Thermal Mechanical Refrigeration System
    University of the Future: Re-Imagining Research and Higher Education, 2020
    Co-Authors: Ahmad K. Sleiti, Wahib A. Al-ammari, Mohammed Al-khawaja, Maxim Glushenkov, Alexander Kronberg
    Abstract:

    Around 17% of the globally generated energy is consumed for residential, commercial, and transportation Refrigeration. The current cooling technologies utilize refrigerants with high Ozone Depletion and Global Warming Potentials. Furthermore, the current technologies are expensive alongside with toxicity and flammability hazards. On the other side, energy produced by combustion of fossil fuels results in substantial amounts of waste heat. Therefore, it is necessary to develop new Refrigeration technologies that utilize waste heat as a source of energy with ecofriendly refrigerants with zero ozone depletion potential and zero global warming potential. In addition, this thermal Mechanical Refrigeration (TMR) technology improves the energy efficiency of the source of waste heat system and minimizes the emissions of the carbon dioxide (CO2). In this study, a novel thermo-Mechanical Refrigeration system is proposed. It operates with low-grade energy sources (such as waste heat) at temperature range of 60 oC to 100 oC. Furthermore, it has the advantage of working with low-frequency driver-compressor unit, which eliminates noise and increases its lifetime. Moreover, the TMR system is adaptable to commercial, transportation, and residential Refrigeration applications.

  • A combined thermo-Mechanical Refrigeration system with isobaric expander-compressor unit powered by low grade heat – Design and analysis
    International Journal of Refrigeration, 2020
    Co-Authors: Ahmad K. Sleiti, Mohammed Al-khawaja, Wahib A. Al-ammari
    Abstract:

    Abstract Refrigeration and air conditioning systems consume about 17% of the world-wide electricity and their conventional refrigerants cause ozone depletion and global warming. In this study a novel thermo-Mechanical Refrigeration (TMR) system is developed and analyzed that is powered, instead of electricity, by thermal energy from waste heat or renewable sources in the ultra-low temperature range of 60–100 °C. A novel isobaric expander-compressor unit (ECU) is designed and combined with vapor compression Refrigeration cycle to constitute the TMR system. The technological solutions (mainly towards simplification of the design) are crucial components of the study novelty. The suitable refrigerants for the system are systematically investigated, analyzed and selected from a list of 43 refrigerants. Nine fluids for the power loop (the isobaric expansion cycle) and nine fluids for the cooling loop (the thermal Refrigeration cycle) were selected and compared based on their mode of operation (subcritical and supercritical), environmental effects and safety class. It is found that the HFO refrigerants such as R1234yf and R1234ze have acceptable performance with no ODP and very low GWP. Natural refrigerants R717 (ammonia) has the best performance in subcritical mode with toxicity as the main drawback. At heat source temperatures less than 85 °C, the system operation in subcritical mode is more efficient and more compact than in the supercritical mode. Thorough analysis and recommendations are made for the size of the ECU in terms of the diameters of the expander and the compressor.

Changqing Tian - One of the best experts on this subject based on the ideXlab platform.

  • Simulation on the performance and free cooling potential of the thermosyphon mode in an integrated system of Mechanical Refrigeration and thermosyphon
    Applied Energy, 2016
    Co-Authors: Hainan Zhang, Hongbo Xu, Mingsheng Tang, Shuangquan Shao, Changqing Tian
    Abstract:

    Free cooling based on thermosyphon is a promising technology for energy-saving in data centers. Integrated system of Mechanical Refrigeration and thermosyphon does not need auxiliary Refrigeration system, therefore it is an ideal way of free cooling based on thermosyphon. To study its free cooling performance and potential, it is built that a distributed-parameter model of the thermosyphon mode in an integrated system of Mechanical Refrigeration and thermosyphon and validated by experimental data. The simulation results show that the cooling capacity and circulation flow rate increase with the increase of height difference mainly due to higher driving force of gravity, while the increase is little when the height difference is higher than 0.5m. The cooling capacity and circulation flow rate decrease with the increase of connection pipe length due to higher flow resistance, therefore the connection pipe should be as short as possible. The cooling capacity increases rapidly with the temperature difference and reaches 5.3kW when the temperature difference is 15°C, with an EER of 14.3. Also with the performance model and weather data of China, annual free cooling potential in China and corresponding energy-saving and economic benefits are analyzed. For the studied cities in China except those in the hot summer & warm winter zone, the free cooling percentages are approximately 30–70%, the annual energy-saving rates are 16–49% and the payback period is 1.7–4.3years. Therefore, free cooling based on integrated system of Mechanical Refrigeration and thermosyphon has great application potential for energy-saving of data centers.

  • Simulation of the Thermosyphon Free Cooling Mode in an Integrated System of Mechanical Refrigeration and Thermosyphon for Data Centers
    Energy Procedia, 2015
    Co-Authors: Hainan Zhang, Shuangquan Shao, Changqing Tian
    Abstract:

    Abstract Integrated system of Mechanical Refrigeration and thermosyphon (ISMT) is an ideal solution for energy-saving of data centers. The performance of the thermosyphon mode of an ISMT is very important and has great effect on its annual energy-saving rate. To investigate and optimize the performance of the thermosyphon mode, a distributed-parameter model is built and verified by experimental results. With this model, the performance of different air flow rate and geometric parameters is studied. The results show that the cooling capacity and circulation flow rate both increase with air flow rate and riser diameter, and decrease with tube length. Combined with these performance simulation results, the annual working time of thermosyphon mode is also calculated for a small data center in Beijing. The method to achieve the optimal design is given for different design requirements.

  • integrated system of Mechanical Refrigeration and thermosyphon for free cooling of data centers
    Applied Thermal Engineering, 2015
    Co-Authors: Hainan Zhang, Hongbo Xu, Shuangquan Shao, Changqing Tian
    Abstract:

    Abstract The number of data centers is increasing rapidly in recent years. Huge amount of energy is consumed by the cooling equipment of data centers for its year round working. Cutting down the energy consumption of cooling equipment becomes an urgent need and free cooling is an ideal way. It is proposed an integrated system of Mechanical Refrigeration and thermosyphon (ISMT) by combining two independent loops, Mechanical Refrigeration loop and thermosyphon loop, with a three-fluid heat exchanger. The new ISMT has three modes: Mechanical Refrigeration, thermosyphon free cooling and dual mode. The experimental results show that it has sufficient cooling capacity of all these three working modes. The EER of the thermosyphon mode reaches 10.7 and 20.8 when the indoor and outdoor temperature difference is 10 °C and 20 °C, respectively, and the AEER of the ISMT is 12.6, which is much higher than traditional air conditioners (TAC). The annual energy consumption in four cities located in different climate zones of China is calculated and compared to TAC in a small data center. The annual energy-saving rate is 5.4%–47.3% when the indoor temperature is set on 27 °C, and it is higher in colder zones for longer working time of thermosyphon free cooling.