DOCSLIB.ORG

9 Critical Flow

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
9 Critical Flow Summary Slides • Isentropic processes 3-7 NTEC Module: Water Reactor Performance and Safety • Propagation of small amplitude Lecture 9: Critical flow pressure wave 8-12 • Isentropic flow 13-20 G. F. Hewitt • Critical flow 21-27 Imperial College London • Example of critical flow of steam 28-31 • Homogeneous equilibrium model (HEM) for two-phase flow 32-38 1 2 Isentropic processes I Isentropic processes II Ideal gas law Definition of specific enthalpy Ru hupvuRT (ideal gas) pv RT R ' M u specific internal energy (J/kg) 1 3 v specific volume (m /kg) Definition of ccvp and p pressure (Pa) dh cp dT R gas constant (Nm/kg.K) du cv dT T temperature (K) Ru Universal gas constant Thus: 8314 (Nm/kmole.K) dh cpv dT du RdT c dT RdT ' M Molecular weight (kg/kmole) ccRpv 3 4 1 Isentropic processes III Isentropic processes IV Define c Work done given by p k ( often also used) cv dw pdv kR R Thus ccpv, kk11 du dq pdv Define: Chenge in internal energy du given by dq du dq dw ds dq heat added per kg (J/kg) T dw work done by system (J/kg) Thus: Tds du pdv 5 6 Isentropic processes V Isentropic processes VI But For an adiabatic, reversible ("isentropic") process ds 0. Thus: dT R dv dh d( u pv ) du pdv vdp 0 --- (1) Tcvv Tds dh vdp dT R dp 0 --- (2) Tcpp Subtracting (2) from (1) and dividing by R : Thus cv dpc dv du p dT dv p 0 ds dv cv R pcv TT T v v Integrating dh v dT dp ds dp c R c TTp T p lnpvp ln constant cv k 7 pv constant 8 2 Propagation of small amplitude pressure wave I Propagation of small amplitude pressure wave II Consider frame of reference moving with wave p + dp V = 0 a - dV a dV ρ + dρ V = dV p, ρ, T p + dp T + dT ρ + dρ p, ρ, T a T + dT • Long cylinder filled initially with motionless fluid Control volume moving with wave Continuity equation on control volume • Piston at one end given infinitesmal velocity dV aadVd( )( ) • Pressure wave moves at velocity a separating fluid moving at velocity dV and fluid which a a ad dV dVd remains stationary ad dV --- (3) 9 10 Propagation of small amplitude pressure wave III Propagation of small amplitude pressure wave IV But from equation 3 (continuity), dV ad Momentum equation for control volume: dp2 ad22 ad pA( p dpA ) aA22 ( d )( a dV ) A dp a2 Dividing through by A and expanding: d 2 For thin region around wave with a disturbance of p p dp a22 ( d )( a 2 adV dV ) infinitesmal amplitude, the process is essentially a22 a 2 adV dV2 a 2 d 2 adVd ddV 2 ADIABATIC AND REVERSIBLE, hence ISENTROPIC Thus 2 2 dp dp2 adV a d a d S 11 12 3 Propagation of small amplitude pressure wave V Isentropic flow I For ideal gas, isentropic process gives p pvk constant ( X ) k kk11p dp Xk dk k d Procedure: Derive continuity p V and momentum equations for kd element of length dx. ρ pkp kRT S x akRT 13 14 Isentropic flow II Isentropic flow III Momentum equation (steady flow without body or shear forces) Continuity equation (steady flow) d 11ppdA VA 0 pdxdApdxdx dx 22x xdx or VA M const pA pA dx pA x Differentiating 2 22 ρV A VA dx VA VAd VdA AdV 0 dx x ddAdV or 0 AV A A dA Momentum flux out – momentum flux in = sum of (pressure) forces on element 15 16 4 Isentropic flow IV Isentropic flow V 222 VA dx VA VA p x dx V2 A Adx 1 pA xx pA p dx dx pA dx pA p 2 xx x or VA2 A 0 xx VA222 dx VA VA p x or VVAA 0 ApAAp1 2 xx pA pdx dx pA pdx Adx x 2 xx x x Vp p VA V VA A 0 --- (4) dx V2 A Adx x xx xx 17 18 Isentropic flow VI Isentropic flow VII But from the continuity equation dV also follows from the continuity expression V VA 0 x dV dA d VA Thus equation 4 becomes (eliminating A) and introducing this into equation 5 we have: Vp dA d dp V 0 xx ApV 2 or dp VdV dA d dp dp V 2 1 dV dp 22 or --- (5) ApVpVdpd / VV 2 19 20 5 Isentropic flow VIII Critical flow I But adpd2222/ and VaM/ where M is the MACH NUMBER. Thus * * po p pd po > p > pd pdAA/ v in 22 When V = M at throat of VM1 V = a nozzle, further decrease in Thus: M = 1 downstream pressure Subsonic flow MdpdA1: positive if positive (a) Nozzle does not change velocity (or mass flux) at throat or vena contracta or p*. dp negative if dA negative p* p p o d Hence MAXIMUM or vin Supersonic flow Mdp1: negative if dA positive CRITICAL flow observed in these conditions. V = a M = 1 dp positive if dA negative (vena contracta) 21 (b) Orifice 22 Critical flow II Critical flow III Kinetic energy per unit mass of fluid V 2 / 2. kRT V 2 kRT o First law of thermodynamics: kk12 1 V 2 hho constant 2 If V a kRT*2* then V kRT . Thus: ho STAGNATION ENTHALPY ** kRT kRT kRTo enthalpy of fluid brought to rest ( upstream enthalpy if Va) in kk12 1 kRT hcTp (Slide 5) k 1 * Dividing through by kRT and multiplying through by k 1 Thus: 2 kk11To kRT V kRTo 1 * kk12 1 22T 23 24 6 Critical flow IV Critical flow V * To obtain ppo / we use k Maximum (critical) mass rate of flow pv constant = c1 (isentropic expansion) aA* pv RT (ideal gas law) MaAAkRT ** ** * max v* RT vck constant ** v 1 AVaACAC is flow area at which ( , coefficient of discharge) c Tvk 1 constant 1 c 2 ** R We express TpT and in terms of (known) oo and 1 kk1/ k cc11k 1 * 2To v v T pp k 1 T p* constant * (ideal gas law) pkk1/ RT * Thus kk/1 kk/1 pToo 1 k ** pT 2 25 26 Critical flow VI Critical flow VII 2T T * o k 1 1 * po 11k * MA kRT * p crit1/k 1 o * (ideal gas law) RTo k 1 2 RT p 2 p* o kk/1 11 1 k 1/2 k12 * kk1 2 Apo RTo 2 * po 1 kk/1 1 k 1 1 k 1 k 1/2 RTo kk1 21k 2 2 * Apo p 1 RTo 2 o 1/k 1 RTo 1 k 2 27 28 7 Example of critical flow of steam I Example of critical flow of steam II • A 1100 MW(e) reactor operating at 150 bar is shut down due to a smqll break corresponding to an area of 0.011m2. A short time after For steam the shutdown, the rate of power generation has reduced to 200MW(t). Ru 8314 • The reactor has remained pressurised and the steam generators are R ' 461.9 not operating. Heat removal is by “feed and bleed” with water being M 18 injected by the HPIS and the heat being removed in the form of 7 steam which flows through the break. po 150 bar 1.5 10 Pa • Assuming that the specific heat ratio k (= cp/cv) is 1.3 for steam and that the steam is saturated at 343 C, calculate the maximum flow To 342 273 615 K rate of steam which could occur. Also, assuming a latent heat of vaporisation of 1000 kJ/kg, calculate the maximum amount of heat ACA* 1 0.011 0.011 which could be removed. Is this sufficient? • The molecular weight of water should be taken as 18 kg/kmole and the break treated as a nozzle with a discharge coefficient of unity. The Universal Gas Constant is Ru = 8314 J/kmole K 29 30 Example of critical flow of steam III Example of critical flow of steam IV k1 1/2 21k * kk1 Maximum rate of heat removal MAp crit o RTo 2 3 Mh max LG 206 1000 10 1/2 1.3 1 /2 1.3 1 7 1.3 1.3 1 0.011 1.5 10 206 MW 461.9 615 2 0.011 1.5 107 0.002139 1.15 3.833 (i.e. just sufficient to remove decay heat) 206 kg/s 31 32 8 Homogeneous equilibrium model Homogeneous equilibrium model (HEM) for two phase flow I (HEM) for two phase flow II Gas Temperature Tg Velocity ug Density of fluid ( ) given by Composition yi Mole fraction of th component 1 i xx/1/ gl Liquid Temperature Tl (lg and and liquid and gas densities) Velocity ul x quality (vapour mass flow as a fraction of total flow) Composition xi Mole fraction of ith component Assumptions: TTgl Applied along uu path of flow gl from upstream to throat yxii's in equilibrium with 's 33 34 Homogeneous equilibrium model Homogeneous equilibrium model (HEM) for two phase flow III (HEM) for two phase flow IV Method general and applies to both single component and multi-component fluids 35 36 9 Homogeneous equilibrium model (HEM) for two phase flow V Thermodynamic Equilibrium Tg = Tl Yes No Mechanical Equilibrium ul = ug Yes No Yes No Phasic Equilibrium xyii's in equilibrium with 's Yes No Yes NoYes No Yes No HEM Example: Dispersed Flow Model (DSM) 37 (Lemonier and Selmer Olsen) 10.
Load more

Recommended publications
  • Advanced Organic Vapor Cycles for Improving Thermal Conversion Efficiency in Renewable Energy Systems by Tony Ho a Dissertation
    Advanced Organic Vapor Cycles for Improving Thermal Conversion Efficiency in Renewable Energy Systems By Tony Ho A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Engineering – Mechanical Engineering in the Graduate Division of the University of California, Berkeley Committee in charge: Professor Ralph Greif, Co-Chair Professor Samuel S. Mao, Co-Chair Professor Van P. Carey Professor Per F. Peterson Spring 2012 Abstract Advanced Organic Vapor Cycles for Improving Thermal Conversion Efficiency in Renewable Energy Systems by Tony Ho Doctor of Philosophy in Mechanical Engineering University of California, Berkeley Professor Ralph Greif, Co-Chair Professor Samuel S. Mao, Co-Chair The Organic Flash Cycle (OFC) is proposed as a vapor power cycle that could potentially increase power generation and improve the utilization efficiency of renewable energy and waste heat recovery systems. A brief review of current advanced vapor power cycles including the Organic Rankine Cycle (ORC), the zeotropic Rankine cycle, the Kalina cycle, the transcritical cycle, and the trilateral flash cycle is presented. The premise and motivation for the OFC concept is that essentially by improving temperature matching to the energy reservoir stream during heat addition to the power cycle, less irreversibilities are generated and more power can be produced from a given finite thermal energy reservoir. In this study, modern equations of state explicit in Helmholtz energy such as the BACKONE equations, multi-parameter Span- Wagner equations, and the equations compiled in NIST REFPROP 8.0 were used to accurately determine thermodynamic property data for the working fluids considered. Though these equations of state tend to be significantly more complex than cubic equations both in form and computational schemes, modern Helmholtz equations provide much higher accuracy in the high pressure regions, liquid regions, and two-phase regions and also can be extended to accurately describe complex polar fluids.
    [Show full text]
  • Compression of an Ideal Gas with Temperature Dependent Specific
    Session 3666 Compression of an Ideal Gas with Temperature-Dependent Specific Heat Capacities Donald W. Mueller, Jr., Hosni I. Abu-Mulaweh Engineering Department Indiana University–Purdue University Fort Wayne Fort Wayne, IN 46805-1499, USA Overview The compression of gas in a steady-state, steady-flow (SSSF) compressor is an important topic that is addressed in virtually all engineering thermodynamics courses. A typical situation encountered is when the gas inlet conditions, temperature and pressure, are known and the compressor dis- charge pressure is specified. The traditional instructional approach is to make certain assumptions about the compression process and about the gas itself. For example, a special case often consid- ered is that the compression process is reversible and adiabatic, i.e. isentropic. The gas is usually ÊÌ considered to be ideal, i.e. ÈÚ applies, with either constant or temperature-dependent spe- cific heat capacities. The constant specific heat capacity assumption allows for direct computation of the discharge temperature, while the temperature-dependent specific heat assumption does not. In this paper, a MATLAB computer model of the compression process is presented. The substance being compressed is air which is considered to be an ideal gas with temperature-dependent specific heat capacities. Two approaches are presented to describe the temperature-dependent properties of air. The first approach is to use the ideal gas table data from Ref. [1] with a look-up interpolation scheme. The second approach is to use a curve fit with the NASA Lewis coefficients [2,3]. The computer model developed makes use of a bracketing–bisection algorithm [4] to determine the temperature of the air after compression.
    [Show full text]
  • Analysis of a CO2 Transcritical Refrigeration Cycle with a Vortex Tube Expansion
    sustainability Article Analysis of a CO2 Transcritical Refrigeration Cycle with a Vortex Tube Expansion Yefeng Liu *, Ying Sun and Danping Tang University of Shanghai for Science and Technology, Shanghai 200093, China; [email protected] (Y.S.); [email protected] (D.T.) * Correspondence: [email protected]; Tel.: +86-21-55272320; Fax: +86-21-55272376 Received: 25 January 2019; Accepted: 19 March 2019; Published: 4 April 2019 Abstract: A carbon dioxide (CO2) refrigeration system in a transcritical cycle requires modifications to improve the coefficient of performance (COP) for energy saving. This modification has become more important with the system’s more and more widely used applications in heat pump water heaters, automotive air conditioning, and space heating. In this paper, a single vortex tube is proposed to replace the expansion valve of a traditional CO2 transcritical refrigeration system to reduce irreversible loss and improve the COP. The principle of the proposed system is introduced and analyzed: Its mathematical model was developed to simulate and compare the system performance to the traditional system. The results showed that the proposed system could save energy, and the vortex tube inlet temperature and discharge pressure had significant impacts on COP improvement. When the vortex tube inlet temperature was 45 ◦C, and the discharge pressure was 9 MPa, the COP increased 33.7%. When the isentropic efficiency or cold mass fraction of the vortex tube increased, the COP increased about 10%. When the evaporation temperature or the cooling water inlet temperature of the desuperheater decreased, the COP also could increase about 10%. The optimal discharge pressure correlation of the proposed system was established, and its influences on COP improvement are discussed.
    [Show full text]
  • Eindhoven University of Technology MASTER Counterflow Pulse-Tube
    Eindhoven University of Technology MASTER Counterflow pulse-tube refrigerator Franssen, R.J.M. Award date: 2001 Link to publication Disclaimer This document contains a student thesis (bachelor's or master's), as authored by a student at Eindhoven University of Technology. Student theses are made available in the TU/e repository upon obtaining the required degree. The grade received is not published on the document as presented in the repository. The required complexity or quality of research of student theses may vary by program, and the required minimum study period may vary in duration. General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain Technische Universiteit Eindhoven Faculteit Technische Natuurkunde Capaciteitsgroep Lage Temperaturen Counterflow pulse-tube refrigerator R.J.M. Franssen Prof. Dr. A.T.A.M. de Waele (supervisor and coach) May 2001 Abstract Abstract In this report we discuss a new type of pulse-tube refrigerator. A pulse-tube refrigerator is a cooler with no moving parts in the cold region. This has the advantage that the cooler is simpler and more reliable, and it also reduces vibrations, which is useful in several applications.
    [Show full text]
  • Thermodynamic Modeling of an Atkinson Cycle with Respect to Relative AirFuel Ratio, Fuel Mass Flow Rate and Residual Gases R
    Vol. 124 (2013) ACTA PHYSICA POLONICA A No. 1 Thermodynamic Modeling of an Atkinson Cycle with respect to Relative AirFuel Ratio, Fuel Mass Flow Rate and Residual Gases R. Ebrahimi∗ Department of Agriculture Machine Mechanics, Shahrekord University, P.O. Box 115, Shahrekord, Iran (Received March 26, 2013; in nal form April 17, 2013) The performance of an air standard Atkinson cycle is analyzed using nite-time thermodynamics. The results show that if the compression ratio is less than a certain value, the power output increases with increasing relative airfuel ratio, while if the compression ratio exceeds a certain value, the power output rst increases and then starts to decrease with increase of relative airfuel ratio. With a further increase in compression ratio, the increase in relative airfuel ratio results in decrease of the power output. Throughout the compression ratio range, the power output increases with increase of fuel mass ow rate. The results also show that if the compression ratio is less than a certain value, the power output increases with increase of residual gases, on the contrast, if the compression ratio exceeds a certain value, the power output decreases with increase of residual gases. The results obtained herein can provide guidance for the design of practical Atkinson engines. DOI: 10.12693/APhysPolA.124.29 PACS: 05.70.Ln, 82.60.Fa, 88.05.−b 1. Introduction formance of an air standard Atkinson cycle under the re- striction of the maximum cycle temperature. The results The Atkinson cycle is a type of internal combustion show that the power output as well as the eciency, for engine, which was designed and built by a British engi- which the maximum power-output occurs, will rise with neer James Atkinson in 1882.
    [Show full text]
  • Performance of a Combined ORC and VCC for Heat Activated
    Performance of a Combined Organic Rankine Cycle and Vapor Compression Cycle for Heat Activated Cooling Hailei Wang*, Richard Peterson, Kevin Harada, Erik Miller, Robbie Ingram-Goble, Luke Fisher, James Yih, Chris Ward School of Mechanical, Industrial, & Manufacturing Engineering 204 Rogers Hall, Oregon State University Corvallis, OR 97331, USA * Corresponding Author Phone: 541-713-1354, Fax: 541-758-9320, Email: [email protected] Abstract Heat activated cooling has the potential of utilizing thermal sources that currently go unused such as engine exhaust heat or industrial waste heat. Using these heat sources can provide enhanced energy utilization and reduced fuel usage in applications where cooling is needed. The concept developed here uses waste heat from stationary and mobile engine cycles to generate cooling for structures and vehicles. It combines an organic Rankine cycle (ORC) with a conventional vapor compression cycle. A nominal 5 kW cooling capacity prototype system was developed based on this concept and tested under laboratory conditions. In order to maintain high system performance while reducing size and weight for portable applications, microchannel based heat transfer components and scroll based expansion and compression were used. Although the system was tested off of its design point, it performed well achieving 4.4 kW of cooling at a measured heat activated COP of 0.48. Both the conversion and 2 nd law efficiencies were close to the model results, proving it to be an attractive technology. The measured isentropic efficiency of the scroll expander reached 84%, when the pressure ratio was close to the scroll intrinsic expansion ratio. The reduced cooling capacity was attributed to off design operation.
    [Show full text]
  • Design and Optimization of a Multicascade Refrigeration System for Use in Extreme Temperature Environments
    DESIGN AND OPTIMIZATION OF A MULTICASCADE REFRIGERATION SYSTEM FOR USE IN EXTREME TEMPERATURE ENVIRONMENTS A Thesis Presented to the Faculty of California State Polytechnic University, Pomona In Partial Fulfillment Of the Requirements for the Degree Master of Science In Mechanical Engineering By Christopher M. McNamara 2016 SIGNATURE PAGE THESIS: DESIGN AND OPTIMIZATION OF A MULTICASCADE REFRIGERATION SYSTEM FOR USE IN EXTREME TEMPERATURE ENVIRONMENTS AUTHOR: Christopher M. McNamara DATE SUBMITTED: Fall 2016 Mechanical Engineering Department Dr. Kevin R. Anderson Professor Mechanical Engineering Dr. Maryam Shafahi Assistant Professor Mechanical Engineering Dr. Angela Shih Professor & Chair Mechanical Engineering ii ACKNOWLEDGEMENTS I would like to thank my advisor, Dr. Kevin R. Anderson for his academic and professional guidance throughout the past years. Without his unique approach to teaching and sweeping mentorship I would not have found myself engaging in such rewarding research. To him I owe a lifetime of gratitude for assisting me both professionally and personally and cannot say that my experience thus far would be as excellent as it has been. I look forward to many more years of research and friendship. To my family, thank you for the years of support as I have continued this rollercoaster of an academic career. Without you I would not have been able to accomplish the lofty goals I have set out for myself. I have relied upon you greatly and for a lengthy time period for which I have not always been an easy person. Thank you for your unwavering support and love. iii ABSTRACT A novel refrigeration system concept is proposed to facilitate the cooling of electronics equipment operating in the atmosphere of Venus.
    [Show full text]
  • Effect of an Internal Heat Exchanger on Performance of the Transcritical Carbon Dioxide Refrigeration Cycle with an Expander
    Entropy 2014, 16, 5919-5934; doi:10.3390/e16115919 OPEN ACCESS entropy ISSN 1099-4300 www.mdpi.com/journal/entropy Article Effect of an Internal Heat Exchanger on Performance of the Transcritical Carbon Dioxide Refrigeration Cycle with an Expander Zhenying Zhang 1,*, Lili Tian 2, Yanhua Chen 1 and Lirui Tong 1 1 Institute of Architecture and Civil Engineering, Hebei United University, Tangshan 063009, China; E-Mails:[email protected] (Y.C.); [email protected] (L.T.) 2 Department of Foreign Languages, Tangshan College, Tangshan 063000, China; E-Mail: [email protected] * Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel.: +86-315-2597-7073. External Editor: Kevin H. Knuth Received: 1 August 2014; in revised form: 24 September 2014 / Accepted: 29 October 2014 Published: 10 November 2014 Abstract: The effect of the internal heat exchanger (IHE) on the performance of the transcritical carbon dioxide refrigeration cycle with an expander is analyzed theoretically on the basis of the first and second laws of thermodynamics. The possible parameters affecting system efficiency such as heat rejection pressure, gas cooler outlet temperature, evaporating temperature, expander isentropic efficiency and IHE effectiveness are investigated. It is found that the IHE addition in the carbon dioxide refrigeration cycle with an expander increases the specific cooling capacity and compression work, and decreases the optimum heat rejection pressure and the expander output power. An IHE addition does not always improve the system performance in the refrigeration cycle with an expander. The throttle valve cycle with IHE provides a 5.6% to 17% increase in maximum COP compared to that of the basic cycle.
    [Show full text]
  • A Novel Transcritical CO2 Refrigeration Cycle with Two Ejectors
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Institutional Repository of GuangZhou Institute of Energy Conversion, CAS international journal of refrigeration 35 (2012) 2233e2239 Available online at www.sciencedirect.com www.iifiir.org journal homepage: www.elsevier.com/locate/ijrefrig A novel transcritical CO2 refrigeration cycle with two ejectors Jiwen Cen*, Pei Liu, Fangming Jiang Key Laboratory of Renewable Energy and Gas Hydrate, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, No. 2, Nengyuan Rd., Guangzhou 510640, China article info abstract Article history: In recent years, CO2 is being revisited as a fully environmentally friendly and safe refrig- Received 3 December 2011 erant. However, basic CO2 transcritical refrigeration cycle suffers from large expansion loss Received in revised form due to high pressure difference between gas cooler and evaporator. Then, it is crucial to 14 June 2012 find effective and economic way to reduce the expansion loss. Here, a novel cycle with two Accepted 1 July 2012 ejectors is proposed for the first time. Compared with conventional ejector-expansion CO2 Available online 23 August 2012 cycle with only one ejector, this novel cycle with two ejectors is able to recover more expansion loss, thus improving the system performance further. A computational model is Keywords: designed to simulate the double ejector CO2 cycle. Simulation results show its high system Carbon dioxide COP. Effects of parameters, such as ejector nozzle efficiency, gas cooler pressure, R744 entrainment ratios of the two ejectors, gas cooler outlet temperature, on the cycle Transcritical cycle performance are also analyzed by using the computational model.
    [Show full text]
  • Carnot Cycle, They Are Not Necessarily Externally Reversible
    Power Cycles Most power producing devices operate on cycles. To make simple thermodynamics analysis possible, we use the concept of ideal cycle. These idealized cycles serve as starting point for more in-depth studies. Heat engines are designed to convert thermal energy to work. The thermal efficiency, ηth, defines as: Benefit Wnet wnet th or th Cost Qin qin Ideal cycles are internally reversible, but unlike the Carnot cycle, they are not necessarily externally reversible. Thus, the thermal efficiency of an ideal cycle, in general, is less than that of a totally reversible cycle operating between the same temperature limits, i.e., Carnot cycle. Therefore, nobody can develop a cycle more efficient than the Carnot cycle. Common Assumptions in Idealizations Power Cycles 1- The cycles do not have any friction. Thus, no pressure drops in the working fluid. 2- All expansions and compressions are considered quasi-equilibrium. 3- No heat losses in pipes and other components. 4- Changes in kinetic and potential energies are negligible. Except for nozzles and diffusers which are specifically designed to change the velocity of passing fluid. T-s and P-v diagrams are useful as visual aids in the analysis of ideal power cycle. T Qin P 3 2 3 2 Wnet Wnet 1 4 4 Qout 1 s Fig. 2-1: Areas enclosed by the process curves in T-s and P-v diagrams represent the net work of the idealized cycle. Remember that an ideal power cycle does not involve any internal irreversibilities; thus one can conclude: 1- On a T-s diagram, a heat addition process proceeds in the direction of increasing entropy and vice versa.
    [Show full text]
  • On the Reversed Brayton Cycle with High Speed Machinery
    LAPPEENRANNAN TEKMLLINEN KORKEAKOULU UDK 536.7: LAPPEENRANTA UNIVERSITY OF TECHNOLOGY 621.57: 62-135: 62-947 TIETEELLISIA JULKAISUJA RESEARCH PAPERS LTKK-Tj— S'L’ JARIBACKMAN ON THE REVERSED DRAYTON CYCLE WITH HIGH SPEED MACHINERY Thesis for the degree of Doctor of Technology to be presented with due permission for public examination and criticism in Auditorium of the Student House of Student Union at Lappeenranta University of Technology, Lappeenranta, Finland on the 19th of December 1996, at noon Lappeenranta 1996 OJSIRStmi OF THIS DOCUMENT IS WTH) DISCLA1 Portions of this document may be illegible in electronic image products. Images are produced from the best available original document Jari Backman On the Reversed Brayton Cycle with High Speed Machinery UDK 536.7: 621.57: 62-135: 62-947 Key words Reversed Brayton cycle, heat pump, refrigeration, dehu­ midifier, high speed technology ABSTRACT This work was carried out in the laboratory of Fluid Dynamics, at Lappeenranta University of Technology during the years 1991-1996. The research was a part of larger high speed technology development research. First, there was the idea of making high speed machinery applications with the Brayton cycle. There was a clear need to deepen the knowledge of the cycle itself and to make a new approach in the field of the research. Also, the removal of water from the humid air seemed very interesting. The goal of this work was to study methods of designing high speed machinery for the reversed Brayton cycle, from theoretical principles to practical applications. The reversed Brayton cycle can be employed as an air dryer, a heat pump or a refrigerating machine.
    [Show full text]
  • Status of Not-In-Kind Refrigeration Technologies for Household Space Conditioning, Water Heating and Food Refrigeration
    International Journal of Sustainable Built Environment (2012) 1,85–101 Gulf Organisation for Research and Development International Journal of Sustainable Built Environment SciVerse ScienceDirect www.sciencedirect.com Review Status of not-in-kind refrigeration technologies for household space conditioning, water heating and food refrigeration Pradeep Bansal ⇑, Edward Vineyard, Omar Abdelaziz Building Equipment Program, Oak Ridge National Laboratory (ORNL), One Bethel Valley Road, P.O. Box 2008, Oak Ridge, TN 37831-6070, USA Received 2 February 2012; accepted 19 July 2012 Abstract This paper presents a review of the next generation not-in-kind technologies to replace conventional vapor compression refrigeration technology for household applications. Such technologies are sought to provide energy savings or other environmental benefits for space conditioning, water heating and refrigeration for domestic use. These alternative technologies include: thermoacoustic refrigeration, ther- moelectric refrigeration, thermotunneling, magnetic refrigeration, Stirling cycle refrigeration, pulse tube refrigeration, Malone cycle refrigeration, absorption refrigeration, adsorption refrigeration, and compressor driven metal hydride heat pumps. Furthermore, heat pump water heating and integrated heat pump systems are also discussed due to their significant energy saving potential for water heating and space conditioning in households. The paper provides a snapshot of the future R&D needs for each of the technologies along with the associated barriers. Both thermoelectric and magnetic technologies look relatively attractive due to recent developments in the mate- rials and prototypes being manufactured. Ó 2012 The Gulf Organisation for Research and Development. Production and hosting by Elsevier B.V. All rights reserved. Keywords: Efficiency; Thermoacoustics; Thermoelectricity; Stirling; Magnetic refrigerator Contents 1. Introduction . 86 2. Thermoacoustic refrigeration .
    [Show full text]