The state of the art tunable VUV sources are used to produce excited C2H photofragments (C2H*) vi... more The state of the art tunable VUV sources are used to produce excited C2H photofragments (C2H*) via the photolysis of acetylene molecules. The quenching rate constants of the C2H emission by a number of species are determined. The collision free fluorescence lifetimes are measured at different excitation wavelengths. The excitation energy threshold for producing the observed emission is determined. In addition, a correlation between the excitation energy and the emission wavelength is observed.
ABSTRACT The state-of-the-art tunable vuv sources are used to produce excited CâH photofragments ... more ABSTRACT The state-of-the-art tunable vuv sources are used to produce excited CâH photofragments (CâH*) via the photolysis of acetylene molecules. The quenching rate constants of the CâH emission by a number of species are determined. The collision-free fluorescence lifetimes are measured at different excitation wavelengths. The excitation energy threshold for producing the observed emission is determined. In addition, a correlation between the excitation energy and the emission wavelength is observed. 27 refs., 6 figs., 2 tabs.
Time-resolved quenching rates are measured for the C2H(asterisk) product of acetylene photolysis ... more Time-resolved quenching rates are measured for the C2H(asterisk) product of acetylene photolysis using a high-resolution frequency-tripled laser source. It is noted that a simple harpoon model for an electron jump from the quencher to the C2H(asterisk) can be used to justify these quenching rates. It is also shown that the emission extends to 900 nm in the visible range.
Fuel cells are devices where electrical energy is produced by redox electrochemical reactions of ... more Fuel cells are devices where electrical energy is produced by redox electrochemical reactions of hydrogen or enriched hydrogen fuels and oxygen, or simply air. Powerful fuel cells or stacks have emerged as potential replacements for the internal combustion engine in automobile vehicles, because the use of fuel cells implies clean and efficient use of energy, and the unique by-products are water and heat when pure hydrogen is used as fuel. Fuel cells can find applications in transport, stationary power generation, supply of heat and electricity in buildings, in space missions for providing electricity and water, and military applications for providing electric power to electronic devices. The available energy of fuel cells is greater than the energy stored in primary or secondary batteries. This has led to a great interest in the development of fuel cells for many applications.
As already discussed in Chapter 1, energy is a finite resource and its rational use implies an in... more As already discussed in Chapter 1, energy is a finite resource and its rational use implies an increase in energy efficiency. The electric generation efficiency is always less than 100% due to resistive, transmission and distribution losses, which can be quantified as heat sent to the environment. This waste heat determines the quantity of energy that can be used by other systems in order to improve the process efficiency. A comfortable climate is required in offices, houses, and sport facilities. Therefore, cooling and heating requirements increase proportionally to the world population growth. According to the above idea, the suitability to satisfy these comfort requirements is in the use of waste energy to activate air conditioning machines. In this sense, fuel cells are a very attractive source of waste heat and therefore this possibility should be explored. This chapter describes the mathematical models and assumptions considered for coupling a fuel cell with air conditioning systems, specifically absorption heat pumps (AHP). Three absorption refrigeration systems, operating with different mixtures or working fluids for its operation, are simulated. The results for each case studied and a comparison in terms of efficiency is presented next.
From Chapter 1 it is clear that nowadays electricity and cooling demands are growing considerably... more From Chapter 1 it is clear that nowadays electricity and cooling demands are growing considerably worldwide, and that also there is a necessity to provide these by using more efficient and cleaner technologies, as the proposed in the present book. A profitability assessment is determinant to decide the implementation and use of some technologies; because of this in the present chapter, an economic analysis of a cogeneration system that consists of a PEM fuel cell coupled to an absorption air conditioning system PEMFC-AACS is presented. Several studies about the profitability of PEM fuel cells have been made by Farbir and Gómez (1996), Tsuchiya and Kobayashi (2004), Bar-On et al. (2002), Zoulias and Lymberopoulos (2007), and Chang et al. (2007). In these studies, the authors detail in a very precise way which are the elements and parameters determinant that make profitable the use of this technology. Also they show future scenarios where the PEM fuel cell can be introduced massively in the market. Because of the above, the present chapter does not show a detailed profitability assessment of the PEM fuel cells alone; the idea is to analyze the profitability of the cogeneration system in an integrated way considering that the use of a PEM fuel cell has already been decided.
In this chapter the basic thermodynamic and electrochemical principles behind fuel cell operation... more In this chapter the basic thermodynamic and electrochemical principles behind fuel cell operation and technology are described. The basic electrochemistry principles determining the operation of the fuel cell, the kinetics of redox reactions during the fuel cell operation, the mass and energy transport in a fuel cell, etc., are described briefly to give an understanding of practical fuel cell systems. The ideal and practical operation of fuel cells and their efficiency are also described. This will provide the framework to understand the electrochemical and thermodynamic basics of the operation of fuel cells and how fuel cell performance can be influenced by the operating conditions. The influence of thermodynamic variables like pressure, temperature, and gas concentration, etc., on fuel cell performance has to be analyzed and understood to predict how fuel cells interact with the systems where it is applied. Understanding the impact of these variables allows system analysis studies of a specific fuel cell application.
Before going into the details of cogeneration combined heat and power (CHP) processes, it is nece... more Before going into the details of cogeneration combined heat and power (CHP) processes, it is necessary to establish the operation principles and performance characteristics of the most common fuel cells for consideration in CHP processes. According to the phenomena governing the performance of fuel cells, it is worth noting that fuel cells are electrochemical energy conversion devices, where redox reactions occur spontaneously and the fuel and oxidant are consumed, and the electrochemical energy is transformed into electricity to produce work. The thermodynamic reversible potentials and over-potential losses are the principal factors that control the net efficiency to convert chemical energy to electrical energy. The fuel cell operating conditions depend on the electrochemical nature of the electricity production. Normally, activation over-potentials predominate at low current densities and they are also controlled by mass transport over-potentials at high current densities. Thus, the application of fuel cells in CHP processes implies a more detailed knowledge of the operation of every kind of fuel cell. Therefore, in this chapter, the fundamentals of the four typical fuel cells considered for CHP applications are explained, taking electrochemical operation principles and the consequent heat and electricity production into consideration. Generally, fuel cell classification is according to the type of electrolyte used and the operating temperatures.
The word energy is derived from the Greek in (in) and ergon (work). The accepted scientific energ... more The word energy is derived from the Greek in (in) and ergon (work). The accepted scientific energy concept has been used to reveal the common characteristics in diverse processes where a particular type of work is produced. At the most basic level, the diversity in energy forms can be limited to four: kinetics, gravitational, electric, and nuclear. Energy is susceptible to being transformed from one form to another, where the total quantity of energy remains unchanged; it is known that: “Energy can neither be created nor destroyed, only transformed”. This principle is known as the first law of thermodynamics, which establishes an energy balance in the different transformation processes. When the energy changes from one form to another, the energy obtained at the end of the process will never be larger than the energy used at the beginning, there will always be a defined quantity of energy that could not be transformed.
Sorption cooling systems have been used commercially for some decades for different applications ... more Sorption cooling systems have been used commercially for some decades for different applications including air conditioning and refrigeration, using a diverse range of thermodynamic cycles and technologies for many size and capacities. However, their use has been limited mainly because of their low efficiency and high investment costs, at least compared with compression systems that are widely used all over the world. Because of this, sorption and desiccant systems have been used, in general, only when large amounts of waste thermal energy that can be used as the energy supplied to the system are available, and recently with, for example, solar and geothermal technologies. As will be explained in the next chapter, desiccant cooling (DEC) and sorption systems are in fact heat pumps since they have the capacity to absorb heat from a source at low temperature and to pump it to a heat sink at a higher temperature level. Depending on the use, common sorption systems are classified as sorption refrigeration systems when they are used for refrigeration and air conditioning, heat pumps when they are used for heating and heat transformers when they are used also for heating but the temperature of the useful heat is higher than the temperature of the heat supplied to the system.
The knowledge of the basic principles of thermodynamics allows us to understand the conditions an... more The knowledge of the basic principles of thermodynamics allows us to understand the conditions and necessary limitations in order to transform heat in work, transferring heat from a thermal source of high temperature to a smaller one. Thermal machines work under this principle, however, there are machines that consume work (external) and produce heat, that is to say in the inverse sense of a thermal machine operation according to the cycle of Carnot, this it is the case of a refrigerating machine. A particular case is refrigeration cycles based on the sorption process, which operate with thermal energy and consume their own work that they self-produce, this being the coupling among a thermal machine and a refrigeration machine. There are great variety of sorption refrigeration systems, in general those of absorption and adsorption cycles. In this chapter, the introduction of the sorption theory, its applications to refrigeration thermodynamic cycles, and its efficiencies are presented and analyzed, as well as the different possibilities of work fluids for diverse applications, showing different examples of refrigeration cycles.
The state of the art tunable VUV sources are used to produce excited C2H photofragments (C2H*) vi... more The state of the art tunable VUV sources are used to produce excited C2H photofragments (C2H*) via the photolysis of acetylene molecules. The quenching rate constants of the C2H emission by a number of species are determined. The collision free fluorescence lifetimes are measured at different excitation wavelengths. The excitation energy threshold for producing the observed emission is determined. In addition, a correlation between the excitation energy and the emission wavelength is observed.
ABSTRACT The state-of-the-art tunable vuv sources are used to produce excited CâH photofragments ... more ABSTRACT The state-of-the-art tunable vuv sources are used to produce excited CâH photofragments (CâH*) via the photolysis of acetylene molecules. The quenching rate constants of the CâH emission by a number of species are determined. The collision-free fluorescence lifetimes are measured at different excitation wavelengths. The excitation energy threshold for producing the observed emission is determined. In addition, a correlation between the excitation energy and the emission wavelength is observed. 27 refs., 6 figs., 2 tabs.
Time-resolved quenching rates are measured for the C2H(asterisk) product of acetylene photolysis ... more Time-resolved quenching rates are measured for the C2H(asterisk) product of acetylene photolysis using a high-resolution frequency-tripled laser source. It is noted that a simple harpoon model for an electron jump from the quencher to the C2H(asterisk) can be used to justify these quenching rates. It is also shown that the emission extends to 900 nm in the visible range.
Fuel cells are devices where electrical energy is produced by redox electrochemical reactions of ... more Fuel cells are devices where electrical energy is produced by redox electrochemical reactions of hydrogen or enriched hydrogen fuels and oxygen, or simply air. Powerful fuel cells or stacks have emerged as potential replacements for the internal combustion engine in automobile vehicles, because the use of fuel cells implies clean and efficient use of energy, and the unique by-products are water and heat when pure hydrogen is used as fuel. Fuel cells can find applications in transport, stationary power generation, supply of heat and electricity in buildings, in space missions for providing electricity and water, and military applications for providing electric power to electronic devices. The available energy of fuel cells is greater than the energy stored in primary or secondary batteries. This has led to a great interest in the development of fuel cells for many applications.
As already discussed in Chapter 1, energy is a finite resource and its rational use implies an in... more As already discussed in Chapter 1, energy is a finite resource and its rational use implies an increase in energy efficiency. The electric generation efficiency is always less than 100% due to resistive, transmission and distribution losses, which can be quantified as heat sent to the environment. This waste heat determines the quantity of energy that can be used by other systems in order to improve the process efficiency. A comfortable climate is required in offices, houses, and sport facilities. Therefore, cooling and heating requirements increase proportionally to the world population growth. According to the above idea, the suitability to satisfy these comfort requirements is in the use of waste energy to activate air conditioning machines. In this sense, fuel cells are a very attractive source of waste heat and therefore this possibility should be explored. This chapter describes the mathematical models and assumptions considered for coupling a fuel cell with air conditioning systems, specifically absorption heat pumps (AHP). Three absorption refrigeration systems, operating with different mixtures or working fluids for its operation, are simulated. The results for each case studied and a comparison in terms of efficiency is presented next.
From Chapter 1 it is clear that nowadays electricity and cooling demands are growing considerably... more From Chapter 1 it is clear that nowadays electricity and cooling demands are growing considerably worldwide, and that also there is a necessity to provide these by using more efficient and cleaner technologies, as the proposed in the present book. A profitability assessment is determinant to decide the implementation and use of some technologies; because of this in the present chapter, an economic analysis of a cogeneration system that consists of a PEM fuel cell coupled to an absorption air conditioning system PEMFC-AACS is presented. Several studies about the profitability of PEM fuel cells have been made by Farbir and Gómez (1996), Tsuchiya and Kobayashi (2004), Bar-On et al. (2002), Zoulias and Lymberopoulos (2007), and Chang et al. (2007). In these studies, the authors detail in a very precise way which are the elements and parameters determinant that make profitable the use of this technology. Also they show future scenarios where the PEM fuel cell can be introduced massively in the market. Because of the above, the present chapter does not show a detailed profitability assessment of the PEM fuel cells alone; the idea is to analyze the profitability of the cogeneration system in an integrated way considering that the use of a PEM fuel cell has already been decided.
In this chapter the basic thermodynamic and electrochemical principles behind fuel cell operation... more In this chapter the basic thermodynamic and electrochemical principles behind fuel cell operation and technology are described. The basic electrochemistry principles determining the operation of the fuel cell, the kinetics of redox reactions during the fuel cell operation, the mass and energy transport in a fuel cell, etc., are described briefly to give an understanding of practical fuel cell systems. The ideal and practical operation of fuel cells and their efficiency are also described. This will provide the framework to understand the electrochemical and thermodynamic basics of the operation of fuel cells and how fuel cell performance can be influenced by the operating conditions. The influence of thermodynamic variables like pressure, temperature, and gas concentration, etc., on fuel cell performance has to be analyzed and understood to predict how fuel cells interact with the systems where it is applied. Understanding the impact of these variables allows system analysis studies of a specific fuel cell application.
Before going into the details of cogeneration combined heat and power (CHP) processes, it is nece... more Before going into the details of cogeneration combined heat and power (CHP) processes, it is necessary to establish the operation principles and performance characteristics of the most common fuel cells for consideration in CHP processes. According to the phenomena governing the performance of fuel cells, it is worth noting that fuel cells are electrochemical energy conversion devices, where redox reactions occur spontaneously and the fuel and oxidant are consumed, and the electrochemical energy is transformed into electricity to produce work. The thermodynamic reversible potentials and over-potential losses are the principal factors that control the net efficiency to convert chemical energy to electrical energy. The fuel cell operating conditions depend on the electrochemical nature of the electricity production. Normally, activation over-potentials predominate at low current densities and they are also controlled by mass transport over-potentials at high current densities. Thus, the application of fuel cells in CHP processes implies a more detailed knowledge of the operation of every kind of fuel cell. Therefore, in this chapter, the fundamentals of the four typical fuel cells considered for CHP applications are explained, taking electrochemical operation principles and the consequent heat and electricity production into consideration. Generally, fuel cell classification is according to the type of electrolyte used and the operating temperatures.
The word energy is derived from the Greek in (in) and ergon (work). The accepted scientific energ... more The word energy is derived from the Greek in (in) and ergon (work). The accepted scientific energy concept has been used to reveal the common characteristics in diverse processes where a particular type of work is produced. At the most basic level, the diversity in energy forms can be limited to four: kinetics, gravitational, electric, and nuclear. Energy is susceptible to being transformed from one form to another, where the total quantity of energy remains unchanged; it is known that: “Energy can neither be created nor destroyed, only transformed”. This principle is known as the first law of thermodynamics, which establishes an energy balance in the different transformation processes. When the energy changes from one form to another, the energy obtained at the end of the process will never be larger than the energy used at the beginning, there will always be a defined quantity of energy that could not be transformed.
Sorption cooling systems have been used commercially for some decades for different applications ... more Sorption cooling systems have been used commercially for some decades for different applications including air conditioning and refrigeration, using a diverse range of thermodynamic cycles and technologies for many size and capacities. However, their use has been limited mainly because of their low efficiency and high investment costs, at least compared with compression systems that are widely used all over the world. Because of this, sorption and desiccant systems have been used, in general, only when large amounts of waste thermal energy that can be used as the energy supplied to the system are available, and recently with, for example, solar and geothermal technologies. As will be explained in the next chapter, desiccant cooling (DEC) and sorption systems are in fact heat pumps since they have the capacity to absorb heat from a source at low temperature and to pump it to a heat sink at a higher temperature level. Depending on the use, common sorption systems are classified as sorption refrigeration systems when they are used for refrigeration and air conditioning, heat pumps when they are used for heating and heat transformers when they are used also for heating but the temperature of the useful heat is higher than the temperature of the heat supplied to the system.
The knowledge of the basic principles of thermodynamics allows us to understand the conditions an... more The knowledge of the basic principles of thermodynamics allows us to understand the conditions and necessary limitations in order to transform heat in work, transferring heat from a thermal source of high temperature to a smaller one. Thermal machines work under this principle, however, there are machines that consume work (external) and produce heat, that is to say in the inverse sense of a thermal machine operation according to the cycle of Carnot, this it is the case of a refrigerating machine. A particular case is refrigeration cycles based on the sorption process, which operate with thermal energy and consume their own work that they self-produce, this being the coupling among a thermal machine and a refrigeration machine. There are great variety of sorption refrigeration systems, in general those of absorption and adsorption cycles. In this chapter, the introduction of the sorption theory, its applications to refrigeration thermodynamic cycles, and its efficiencies are presented and analyzed, as well as the different possibilities of work fluids for diverse applications, showing different examples of refrigeration cycles.
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