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Sorbents and Desiccants TC 8. Physical Properties of Materials TC 1. Energy Resources TC 2. Sustainability TC 2. Measurement and Instruments TC 1. Abbreviations and Symbols TC 1. Units and Conversions TC 1. Stored Energy.. Energy in Transition Second Law of Thermodynamics This chapter covers the Nuclear atomic energy derives from the cohesive forces hold- ing protons and neutrons together as the atom's nucleus. The second and third parts address compression and absorption refrigeration cycles, two common methods of thermal energy transfer.

Heat Q is the mechanism that transfers energy across the bound- aries of systems with differing temperatures, always toward the lower temperature. The surroundings include everything external to the system, and the system is separated from the surroundings by the system boundaries. These boundaries can be movable or fixed, real or imaginary. Entropy and energy are important in any thermodynamic system. Entropy measures the molecular disorder of a system.

The more mixed a system, the greater its entropy; an orderly or unmixed con- figuration is one of low entropy. Energy has the capacity for pro- ducing an effect and can be categorized into either stored or transient forms. Work is the mechanism that transfers energy across the bound- aries of systems with differing pressures or force of any kind , always toward the lower pressure.

If the total effect produced in the system can be reduced to the raising of a weight, then nothing but work has crossed the boundary. Work is positive when energy is removed from the system see Figure 1. Mechanical or shaft work W is the energy delivered or ab- sorbed by a mechanism, such as a turbine, air compressor, or inter- nal combustion engine. Flow work is energy carried into or transmitted across the system boundary because a pumping process occurs somewhere outside the system, causing fluid to enter the system.

It can be more easily understood as the work done by the fluid just outside the system on the adjacent fluid entering the system to force or push it into the system.

Flow work also occurs as fluid leaves the system. A property of a system is any observable characteristic of the system. Chemical energy is caused by the arrangement of atoms com- posing the molecules.

The third part is assigned to TC 8. The most common thermodynamic properties are temperature T, pressure p , and specific volume v or density p. Additional thermodynamic properties include entropy, stored forms of energy, and enthalpy. Frequently, thermodynamic properties combine to form other properties. Each property in a given state has only one definite value, and any property always has the same value for a given state, regardless of how the substance arrived at that state.

A process is a change in state that can be defined as any change in the properties of a system. A process is described by specifying the initial and final equilibrium states, the path if identifiable , and the interactions that take place across system boundaries during the process.

A cycle is a process or a series of processes wherein the initial and final states of the system are identical. Therefore, at the conclu- sion of a cycle, all the properties have the same value they had at the beginning. Refrigerant circulating in a closed system undergoes a cycle. A pure substance has a homogeneous and invariable chemical composition. It can exist in more than one phase, but the chemical composition is the same in all phases.

If a substance is liquid at the saturation temperature and pressure, it is called a saturated liquid. If the temperature of the liquid is lower than the saturation temperature for the existing pressure, it is called either a subcooled liquid the temperature is lower than the saturation temperature for the given pressure or a compressed liq- uid the pressure is greater than the saturation pressure for the given temperature.

When a substance exists as part liquid and part vapor at the sat- uration temperature, its quality is defined as the ratio of the mass of vapor to the total mass. Quality has meaning only when the sub- stance is saturated i. Pressure and temperature of saturated substances are not indepen- dent properties. If a substance exists as a vapor at saturation temperature and pressure, it is called a saturated vapor.

When the vapor is at a temperature greater than the saturation tem- perature, it is a superheated vapor. Pressure and temperature of a superheated vapor are independent properties, because the temper- ature can increase while pressure remains constant.

Gases such as air at room temperature and pressure are highly superheated vapors. The following form of the first-law equation is valid only in the absence of a nuclear or chemical reaction.

Nearly all important engineering processes are commonly mod- eled as steady-flow processes. Steady flow signifies that all quanti- ties associated with the system do not vary with time. The second law may be described in sev- eral ways. One method uses the concept of entropy flow in an open system and the irreversibility associated with the process.

The con- cept of irreversibility provides added insight into the operation of cycles. For example, the larger the irreversibility in a refrigeration cycle operating with a given refrigeration load between two fixed temperature levels, the larger the amount of work required to oper- ate the cycle.

Irreversibilities include pressure drops in lines and heat exchangers, heat transfer between fluids of different tempera- ture, and mechanical friction. Reducing total irreversibility in a cycle improves cycle performance, In the limit of no irreversibili- ties, a cycle attains its maximum ideal efficiency.

The change in entropy ofthe system is therefore zero. The irreversibility rate, which is the rate of entropy production caused by irreversibilities in the process, can be determined by rearranging Equation 1 0 : Equation 6 can be used to replace the heat transfer quantity. Note that the absolute temperature of the surroundings with which the system is exchanging heat is used in the last term.

If the temper- ature of the surroundings is equal to the system temperature, heat is transferred reversibly and the last term in Equation 1 1 equals zero. Equation 1 1 is commonly applied to a system with one mass flow in, the same mass flow out, no work, and negligible kinetic or potential energy flows.

Combining Equations 6 and 1 1 yields In a cycle, the reduction of work produced by a power cycle or the increase in work required by a refrigeration cycle equals the absolute ambient temperature multiplied by the sum of irreversibil- ities in all processes in the cycle. Usually the higher- temperature heat sink is the ambient air or cooling water, at temper- ature To, the temperature of the surroundings.

The first and second laws of thermodynamics can be applied to individual components to determine mass and energy balances and the irreversibility of the components. This procedure is illustrated in later sections in this chapter. Performance of a refrigeration cycle is usually described by a coefficient of performance COP , defined as the benefit of the cycle amount of heat removed divided by the required energy input to operate the cycle: 14 Useful refrigerating effect Net energy supplied from external sources For a mechanical vapor compression system, the net energy sup- plied is usually in the form of work, mechanical or electrical, and may include work to the compressor and fans or pumps.

Applying the second law to an entire refrigeration cycle shows that a completely reversible cycle operating under the same con- ditions has the maximum possible COP. Departure of the actual cycle from an ideal reversible cycle is given by the refrigerating efficiency: The Carnot cycle usually serves as the ideal reversible refrigera- tion cycle. For multistage cycles, each stage is described by arevers- ible cycle. When the system is in thermodynamic equilibrium, The principles of statistical mechanics are used to 1 explore the fundamental properties of matter, 2 predict an equation of state based on the statistical nature of a particular system, or 3 propose a functional form for an equation of state with unknown parameters that are determined by measuring thermodynamic properties of a substance.

A fundamental equation with this basis is the virial equation, which is expressed as an expansion in pressure p or in reciprocal values of volume per unit mass v as f! B' and B are the second virial coefficients; C' and C are the third virial coefficients, etc. The virial coefficients are func- tions of temperature only, and values of the respective coefficients in Equations 19 and 20 are related.

The universal gas constant R is defined as where pV , is the product of the pressure and the molar specific volume along an isotherm with absolute temperature 7: The current bestvalueofx is ThegasconstantRisequal to the universal gas constant R divided by the molecular mass Mof the gas or gas mixture.

Because lower-order interactions are common, contributions of the higher-order terms are succes- sively less. Thermodynamicists use the partition or distribution function to determine virial coefficients; however, experimental val- ues of the second and third coefficients are preferred. For dense fluids, many higher-order terms are necessary that can neither be sat- isfactorily predicted from theory nor determined from experimental measurements.

For higher densities, additional terms can be used and deter- mined empirically. Computers allow the use of very complex equations of state in calculating p-v-T values, even to high densities.

Stro- bridge 1 suggested a modified Benedict-Webb-Rubin relation that gives excellent results at higher densities and can be used for a p-v-T surface that extends into the liquid phase. Strobridge 1 suggested an equation of state that was devel- oped for nitrogen properties and used for most cryogenic fluids. This equation combines the B-W-R equation of state with an equa- tion for high-density nitrogen suggested by Benedict These equations have been used successfully for liquid and vapor phases, extending in the liquid phase to the triple-point temperature and the freezing line, and in the vapor phase from 10 to K, with pres- sures to 1 GPa.

Hust and McCarty and Hust and Stewart 1 give further information on methods and techniques for determining equations of state. In the absence of experimental data, Van der Waals' principle of corresponding states can predict fluid properties. This principle relates properties of similar substances by suitable reducing factors i,e,, the p-v-T surfaces of similar fluids in a given region are assumed to be of similar shape.

The critical point can be used to define reducing parameters to scale the surface of one fluid to the dimensions of another. Modifications of this principle, as suggested by Kamerlingh Onnes, a Dutch cryogenic researcher, have been used to improve correspondence at low pressures. The principle of corresponding states provides useful approximations, and numer- ous modifications have been reported. More complex treatments for predicting properties, which recognize similarity of fluid properties, are by generalized equations of state.

These equations ordinarily allow adjustment of the p-v-T surface by introducing parameters. One example Hirschfelder et al. These properties have been tabulated for many substances, including refrigerants see Chapters 1, 30, and 33 , and can be extracted from such tables by interpolating manu- ally or with a suitable computer program.

This approach is appro- priate for hand calculations and for relatively simple computer models; however, for many computer simulations, the overhead in memory or input and output required to use tabulated data can make this approach unacceptable.

For large thermal system simu- lations or complex analyses, it may be more efficient to determine internal energy, enthalpy, and entropy using fundamental thermo- dynamic relations or curves fit to experimental data. Some of these relations are discussed in the following sections.

Also, the ther- modynamic relations discussed in those sections are the basis for constructing tables of thermodynamic property data. Further in- formation on the topic may be found in references covering system modeling and thermodynamics Howell and Buckius ; Stoecker At least two intensive properties properties independent of the quantity of substance, such as temperature, pressure, specific vol- ume, and specific enthalpy must be known to determine the remaining properties.

If two known properties are either p , v, or T these are relatively easy to measure and are commonly used in simulations , the third can be determined throughout the range of interest using an equation of state. Furthermore, if the specific heats at zero pressure are known, specific heat can be accurately determined from spectroscopic measurements using statistical mechanics NASA The second partial derivative of specific volume with respect to temper- ature can be determined from the equation of state.

Thus, Equation 31 can be used to determine the specific heat at any pressure. When entropy or enthalpy are known at a reference temperature To and pressurepo, values at any temperature and pressure may be obtained by combin- ing Equations 33 and 35 or Equations 34 and Combinations or variations of Equations 33 through 36 can be incorporated directly into computer subroutines to calculate properties with improved accuracy and efficiency.

However, these equations are restricted to situations where the equation of state is valid and the properties vary continuously. These restrictions are violated by a change of phase such as evaporation and condensation, which are essential processes in air-conditioning and refrigerating devices. Phase Equilibria for Multicomponent Systems To understand phase equilibria, consider a container full of a liq- uid made of two components; the more volatile component is des- ignated i and the less volatile componentj Figure 2A.

This mixture is all liquid because the temperature is low but not so low that a solid appears. If heat at constant pressure continues to be added, eventually the temperature becomes so high that only vapor remains in the container Figure 2C. A temperature-concentration T-x diagram is useful for exploring details of this situation. Figure 3 is a typical T-x diagram valid at a fixed pressure.

The case shown in Figure 2A, a container full of liquid mixture with mole fraction xi,o at temperature To, is point 0 on the T- x diagram. When heat is added, the temperature of the mixture increases. The point at which vapor begins to form is the bubble point.

Starting at point 0, the first bubble forms at temperature T, point 1 on the dia- gram. The locus of bubble points is the bubble-point curve, which provides bubble points for various liquid mole fractions xi. Rather, the mole fraction of the more volatile species is higher in the vapor than in the liquid.

Boiling prefers the more volatile species, and the T-x diagram shows this behavior. At T,, the vapor-forming bubbles have an i mole fraction of yi,,. If heat continues to be added, this preferential boiling depletes the liquid of species i and the tem- perature required to continue the process increases.

Again, the T-x diagram reflects this fact; at point 2 the i mole fraction in the liquid is reduced to xi,2 and the vapor has a mole fraction ofyi,,. The tem- perature required to boil the mixture is increased to T,. Position 2 on the T-x diagram could correspond to the physical situation shown in Figure 2B. If constant-pressure heating continues, all the liquid eventually becomes vapor at temperature T3.

At this point the i mole fraction in the vapor yi,3 equals the starting mole fraction in the all-liquid mixture xi,1. We additionally allow variant types and in addition to type of the books to browse.

Example 3. PDF download. Of data centers cooling is the ashrae operating ranges, because they refer to. Jun 11, As temperature data center humidity levels in recommended over traditional systems, ashrae recommends that ashrae recommends the recommendations on. A one-year subscription to an eLearning ourse of the members choosing Members will also be presented with the option to add on additional benefits for a small fee during the join or renewing process 1.

A short summary of this paper. Samir Rabia. D Eastop and A. SI edition. Handbook contains supplemental features including online videos, spreadsheets, and case studies.

Relative humidity should be between 8 and Its more than 1, pages cover basic principles such as thermodynamics, psychrometrics, and heat transfer, and provide practical guidance on building envelope, indoor environmental quality, load calculations, duct and piping system design, refrigerants, energy resources, sustainability, a new.

This revised edition presents those chapter updates as originally intended by the cognizant Technical Committees TCs. Marino 18 Newsday, Inc. A82 ISBN Updated with research sponsored by ASHRAE and others, this volume includes 1, pages and 39 chapters covering general engineering information, basic materials, climate data, load and energy calculations, duct and pipe design, and sustainability, plus reference.

Committee Scope TC 6. Start at call number TH Yeni yaymlanan ASHRAE Handbook - HVAC Sistemleri ve Ekipmanlar, sistem tasarmclarnn ve operatrlerinin belirli bir uygulama veya senaryo iin en uygun ekipman semesine ve kullanmasna yardmc olmak iin yeni, gncellenmi bilgiler ieriyor.

Read Paper. Advertisement mooring for sale florida. For further guidance about the Space-by-Space Method for buildings greater than 25, sf, please contact. Elc values in recommended practices to begin the recommendations for people with a bit warmer. Ashrae handbook of fundamentals free download pdf Also known as Data Search, find materials and properties information from technical references. Letter from the president. Industrial refrigeration Chillers and plumbing training books and manuals are available.

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2009 ashrae handbook fundamentals free download pdf | Sound and Vibration TC 2. Yeni yaymlanan ASHRAE Handbook - HVAC Sistemleri ve Ekipmanlar, sistem tasarmclarnn ve operatrlerinin belirli bir uygulama veya senaryo iin en uygun ekipman semesine ve kullanmasna yardmc olmak iin yeni, gncellenmi bilgiler ieriyor. This book includes information on. Fre has completed distribution of complimentary copies to members and is now offering this resource to the public. Three kinds of profiles are defined:. Sustainability The compression process is completed by an isothermal compression fundamentalx from state b to state click. |

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My att native app | Chapter 18, Nonresidential Cooling and Heating Load Calcu- lations, has been updated to naruto mugen pc download new ASHRAE research results on climate data and on heat gains from office equipment, lighting, and commercial cooking appliances. All rights reserved. It can exist in more than funramentals phase, but the chemical composition is the same in all phases. Residential Cooling and Heating Load Calculations This equation combines the B-W-R equation of state with an equa- tion for high-density nitrogen suggested by Benedict The entire risk of the use of any information in this publication is assumed by the asbrae. These parameters are useful inenergy estimating methods. |

2009 ashrae handbook fundamentals free download pdf | The compression process is completed by an isothermal compression process from state b visit web page state c. ASHRAE has requested that fundamentaos attendees please register for the conference as there is a free comittee meeting option. Pipe Sizing Ventilation and Infiltration TC 4. June 22, Monthly percen-tile values of dry-bulb or wet-bulb temperature may be higheror lower than the pef conditions corresponding to the samenominal percentile, depending on the month and the seasonaldistribution of the parameter at that location. Mass Transfer 7. |

2009 ashrae handbook fundamentals free download pdf | It can exist in more than one phase, but the chemical composition is the same in all phases. For Dummies. Mean temperature of coldest month between 27F 3C learn more here 65F 18C b. Volunteer members of ASHRAE Technical Committees and others compiled the infor- mation in this handbook, and it is generally reviewed and updated every four years. Additions and correc- tions to Handbook volumes in print will be published in the Handbook published the year following their click and, as soon as verified, on the ASHRAE Internet Web site. June 0. Sorbents and Desiccants TC 8. |

Its members worldwide are individuals who share ideas, identify needs, support research, and write the industry's standards for test- ing and practice. The result is that engineers are better able to keep indoor environments safe and productive while protecting and pre- serving the outdoors for generations to come. The ASHRAE Tech- nical Committees that prepare these chapters strive not only to provide new information, but also to clarify existing information, delete obsolete materials, and reorganize chapters to make the Hand- book more understandable and easier to use.

Also new for this volume, chapter order and groupings have been revised for more logical flow and use. Some of the other revisions and additions to the volume are as follows: Chapter 1, Psychrometrics, has new information on the composi- tion of dry air, and revised table data for thermodynamic proper- ties of water and moist air.

Chapter 6, Mass Transfer, has added examples on evaluating diffu- sion coefficients, and on heat transfer and moisture removal rates. Chapter 7, Fundamentals of Control, includes new content on dampers, adaptive control, direct digital control DDC system architecture and specifications, and wireless control.

Chapter 9, Thermal Comfort, has a new section on thermal com- fort and task performance, based on multiple new studies done in laboratory and office environments. Chapter 10, Indoor Environmental Health, was reorganized to describe hazard sources, health effects, exposure standards, and exposure controls. New and updated topics include mold, Legio- nella, indoor air chemistry, thermal impacts, and water quality standards.

Chapter 14, Climatic Design Information, has new climate data for stations an increase of new stations compared to Fundamentals on the CD-ROM accompanying this book. A subset of data for selected stations is also included in the printed chapter for convenient access. Chapter 15, Fenestration, has been revised to include new exam- ples of solar heat gain coefficient SHGC calculations, and new research results on shading calculations and U-factors for various specialized door types.

Chapter 18, Nonresidential Cooling and Heating Load Calcu- lations, has been updated to reflect new ASHRAE research results on climate data and on heat gains from office equipment, lighting, and commercial cooking appliances. Chapter 21, Duct Design, has new data for round and rectangular fittings in agreement with the ASHRAE Duct Fitting Database, as well as new content on duct leakage requirements, spiral duct roughness, and flexible duct pressure loss correction.

Chapter 24, Airflow Around Buildings, has added a detailed dis- cussion on computational evaluation of airflow, plus new refer- ences including updated versions of design standards and manuals of practice. Chapters 25, 26, and 27 carry new titles, reorganized as chapters on Heat, Air, and Moisture Control Fundamentals, Material Prop- erties, and Examples, respectively, with updated content through- out. Chapter 29, Refrigerants, has new content on stratospheric ozone depletion, global climate change, and global environmental char- acteristics of refrigerants.

Chapter 36, Measurement and Instruments, has revised content on measurement of air velocity, infiltration, airtightness, and outdoor air ventilation, plus new information on particle image velocime- try PIV and data acquisition and recording. Reader comments are enthusiastically invited.

Mark S. Psychrometrics TC 1. Thermodynamics and Refrigeration Cycles TC 1. Heat Transfer TC 1. Two-Phase Flow TC 1. Fluid Flow TC 1. Mass Transfer TC 1. Fundamentals of Control TC 1. Sound and Vibration TC 2. Thermal Comfort TC 2. Odors TC 2. Air Contaminants TC 2. Indoor Environmental Modeling TC 4. Climatic Design Information TC 4.

Fenestration TC 4. Ventilation and Infiltration TC 4. Space Air Diffusion TC 5. Duct Design TC 5. Pipe Sizing TC 6. Insulation for Mechanical Systems TC 1. Airflow Around Buildings TC 4. Combustion and Fuels TC 6. Refrigerants TC 3. Thermophysical Properties of Refrigerants TC 3. Sorbents and Desiccants TC 8. Physical Properties of Materials TC 1. Energy Resources TC 2. Sustainability TC 2.

Measurement and Instruments TC 1. Abbreviations and Symbols TC 1. Units and Conversions TC 1. Stored Energy.. Energy in Transition Second Law of Thermodynamics This chapter covers the Nuclear atomic energy derives from the cohesive forces hold- ing protons and neutrons together as the atom's nucleus. The second and third parts address compression and absorption refrigeration cycles, two common methods of thermal energy transfer.

Heat Q is the mechanism that transfers energy across the bound- aries of systems with differing temperatures, always toward the lower temperature.

The surroundings include everything external to the system, and the system is separated from the surroundings by the system boundaries. These boundaries can be movable or fixed, real or imaginary. Entropy and energy are important in any thermodynamic system. Entropy measures the molecular disorder of a system. The more mixed a system, the greater its entropy; an orderly or unmixed con- figuration is one of low entropy.

Energy has the capacity for pro- ducing an effect and can be categorized into either stored or transient forms. Work is the mechanism that transfers energy across the bound- aries of systems with differing pressures or force of any kind , always toward the lower pressure.

If the total effect produced in the system can be reduced to the raising of a weight, then nothing but work has crossed the boundary. Work is positive when energy is removed from the system see Figure 1. Mechanical or shaft work W is the energy delivered or ab- sorbed by a mechanism, such as a turbine, air compressor, or inter- nal combustion engine. Flow work is energy carried into or transmitted across the system boundary because a pumping process occurs somewhere outside the system, causing fluid to enter the system.

It can be more easily understood as the work done by the fluid just outside the system on the adjacent fluid entering the system to force or push it into the system. Flow work also occurs as fluid leaves the system. A property of a system is any observable characteristic of the system.

Chemical energy is caused by the arrangement of atoms com- posing the molecules. The third part is assigned to TC 8. The most common thermodynamic properties are temperature T, pressure p , and specific volume v or density p.

Additional thermodynamic properties include entropy, stored forms of energy, and enthalpy. Frequently, thermodynamic properties combine to form other properties. Each property in a given state has only one definite value, and any property always has the same value for a given state, regardless of how the substance arrived at that state. A process is a change in state that can be defined as any change in the properties of a system.

A process is described by specifying the initial and final equilibrium states, the path if identifiable , and the interactions that take place across system boundaries during the process.

A cycle is a process or a series of processes wherein the initial and final states of the system are identical. Therefore, at the conclu- sion of a cycle, all the properties have the same value they had at the beginning. Refrigerant circulating in a closed system undergoes a cycle. A pure substance has a homogeneous and invariable chemical composition. It can exist in more than one phase, but the chemical composition is the same in all phases.

If a substance is liquid at the saturation temperature and pressure, it is called a saturated liquid. If the temperature of the liquid is lower than the saturation temperature for the existing pressure, it is called either a subcooled liquid the temperature is lower than the saturation temperature for the given pressure or a compressed liq- uid the pressure is greater than the saturation pressure for the given temperature. When a substance exists as part liquid and part vapor at the sat- uration temperature, its quality is defined as the ratio of the mass of vapor to the total mass.

Quality has meaning only when the sub- stance is saturated i. Pressure and temperature of saturated substances are not indepen- dent properties. If a substance exists as a vapor at saturation temperature and pressure, it is called a saturated vapor. When the vapor is at a temperature greater than the saturation tem- perature, it is a superheated vapor.

Pressure and temperature of a superheated vapor are independent properties, because the temper- ature can increase while pressure remains constant.

Gases such as air at room temperature and pressure are highly superheated vapors. The following form of the first-law equation is valid only in the absence of a nuclear or chemical reaction. Nearly all important engineering processes are commonly mod- eled as steady-flow processes.

Steady flow signifies that all quanti- ties associated with the system do not vary with time. The second law may be described in sev- eral ways. One method uses the concept of entropy flow in an open system and the irreversibility associated with the process.

The con- cept of irreversibility provides added insight into the operation of cycles. For example, the larger the irreversibility in a refrigeration cycle operating with a given refrigeration load between two fixed temperature levels, the larger the amount of work required to oper- ate the cycle.

Irreversibilities include pressure drops in lines and heat exchangers, heat transfer between fluids of different tempera- ture, and mechanical friction. Reducing total irreversibility in a cycle improves cycle performance, In the limit of no irreversibili- ties, a cycle attains its maximum ideal efficiency.

The change in entropy ofthe system is therefore zero. The irreversibility rate, which is the rate of entropy production caused by irreversibilities in the process, can be determined by rearranging Equation 1 0 : Equation 6 can be used to replace the heat transfer quantity.

Note that the absolute temperature of the surroundings with which the system is exchanging heat is used in the last term. If the temper- ature of the surroundings is equal to the system temperature, heat is transferred reversibly and the last term in Equation 1 1 equals zero. Equation 1 1 is commonly applied to a system with one mass flow in, the same mass flow out, no work, and negligible kinetic or potential energy flows.

Combining Equations 6 and 1 1 yields In a cycle, the reduction of work produced by a power cycle or the increase in work required by a refrigeration cycle equals the absolute ambient temperature multiplied by the sum of irreversibil- ities in all processes in the cycle. Usually the higher- temperature heat sink is the ambient air or cooling water, at temper- ature To, the temperature of the surroundings. The first and second laws of thermodynamics can be applied to individual components to determine mass and energy balances and the irreversibility of the components.

This procedure is illustrated in later sections in this chapter. Performance of a refrigeration cycle is usually described by a coefficient of performance COP , defined as the benefit of the cycle amount of heat removed divided by the required energy input to operate the cycle: 14 Useful refrigerating effect Net energy supplied from external sources For a mechanical vapor compression system, the net energy sup- plied is usually in the form of work, mechanical or electrical, and may include work to the compressor and fans or pumps.

Applying the second law to an entire refrigeration cycle shows that a completely reversible cycle operating under the same con- ditions has the maximum possible COP.

Departure of the actual cycle from an ideal reversible cycle is given by the refrigerating efficiency: The Carnot cycle usually serves as the ideal reversible refrigera- tion cycle.

For multistage cycles, each stage is described by arevers- ible cycle. When the system is in thermodynamic equilibrium, The principles of statistical mechanics are used to 1 explore the fundamental properties of matter, 2 predict an equation of state based on the statistical nature of a particular system, or 3 propose a functional form for an equation of state with unknown parameters that are determined by measuring thermodynamic properties of a substance.

A fundamental equation with this basis is the virial equation, which is expressed as an expansion in pressure p or in reciprocal values of volume per unit mass v as f! B' and B are the second virial coefficients; C' and C are the third virial coefficients, etc. The virial coefficients are func- tions of temperature only, and values of the respective coefficients in Equations 19 and 20 are related. The universal gas constant R is defined as where pV , is the product of the pressure and the molar specific volume along an isotherm with absolute temperature 7: The current bestvalueofx is ThegasconstantRisequal to the universal gas constant R divided by the molecular mass Mof the gas or gas mixture.

Because lower-order interactions are common, contributions of the higher-order terms are succes- sively less. Thermodynamicists use the partition or distribution function to determine virial coefficients; however, experimental val- ues of the second and third coefficients are preferred. For dense fluids, many higher-order terms are necessary that can neither be sat- isfactorily predicted from theory nor determined from experimental measurements. For higher densities, additional terms can be used and deter- mined empirically.

Computers allow the use of very complex equations of state in calculating p-v-T values, even to high densities. Stro- bridge 1 suggested a modified Benedict-Webb-Rubin relation that gives excellent results at higher densities and can be used for a p-v-T surface that extends into the liquid phase. Strobridge 1 suggested an equation of state that was devel- oped for nitrogen properties and used for most cryogenic fluids. This equation combines the B-W-R equation of state with an equa- tion for high-density nitrogen suggested by Benedict Web icon An illustration of a computer application window Wayback Machine Texts icon An illustration of an open book.

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