Final Program EXPRES 2012 - Conferences

More documents

Recommendations

Info

V. FLOW PATTERN MAP FOR CONDENSATIONIN HORIZONTAL TUBESThe two-phase flow pattern map forcondensation proposed by El Hajal, Thome and Cavallini[6] is a slightly modified version of Kattan, Thome andFavrat [5] map for evaporation and adiabatic flows insmall diameter horizontal tubes. Thome and El Hajalhave simplified implementation of that map by bringing avoid fraction equation into the method to eliminate itsiterative solution scheme.The five principal flow patterns encounteredduring condensation inside horizontal tubes are: Annular flow (often referred to as shearedcontrolledregime) (A), Intermittent flow (heat transfer modeled likeannular flow), (I), Mist flow (annular flow heat transfer modelassumed for this regime) (MF) Stratified-wavy flow (SW), Stratified flow(S),Intermittent flow refers to both the plug and slugflow regimes (it is essentially a stratified-wavy flowpattern with large amplitude waves that wash the top ofthe tube). Also, stratified-wavy flow is often referred to inthe literature as simply wavy flow.A. FLOW PATTERN MAP OF THOME AND ELHAJAL (2003)This model can be easily applied and gives thevoid fraction as a function of total mass flux. Hence itmakes sense to use the same void fraction model in boththe flow pattern map and the flow boiling heat transfermodel for which the Rouhani-Axelson [8] model is abetter choice as a general method.The sectional area of the tube A and after calculating ε,the values and are directly determined by:A 1 Ald2D,A A vd 2DThe stratified angle can be calculated from anexpression evaluated in terms of void fraction proposedby Biberg [9] 2 P sinstratD 2 The transition boundary curve between Stratifiedflows to Stratified-wavy flow is:(6) 2 2226.2 A vd A vdG v l vstrat 2 3x 1 x 13 l g cos The transition boundary curve between Stratifiedflows to Intermittent/Annular flow is: 3 16A vd g D lv 2 220.5 x 1 2ld1Gwavy 2F2We 1 x 225 ldFr 0.51cos 50(7) F 1 (8) The transition boundary curve between Annularflows to Mist flow is:0.5 2 7680A vd g D v l WeGmist 2 2xFrphl (9) The transition boundary curve between Annularflows to Intermittent flow is:11 1.75 17 1 0.875 vvX IA 0.341 ll V. SIMULATION OF MATHEMATICALMODEL(10)Mathematical models are simulated by the use ofthe software tool MathCAD.The solution of thedeterministic mathematical models of the flow patternand heat transfer coefficients is complex. The appliednumerical simulation model for each variable isdiscretized. The input data and initial conditions in thedeterministic mathematical model clearly define the valueof flow pattern and heat transfer coefficient i.e. is theoutput of the model.The initial condition and values for the simulation: Refrigerant: R134a Mass velocity: G 100 kg 2 ms Vapor quality ranged: x = 0 – 1 [ - ]128
Tube diameter: d 6 mm W Heat flux:q 3000 2 m Temperature of evaporation: t o = 5 [°C] Temperature of condensation: t c = 40 [°C]section. (Figure 3.) On the contrary, in the condensingsection of the annular flow pattern the image did not evenappear. In the condensing sections the flow regime isstratified wavy. (Figure 4.) In practice, however, this isnot completely the case. If the cross section of wall isconsidered, the condenser tube wall is the coldest, hencethe vapor of the two-phase refrigerant is condensed in thewall, so there a degree of annular flow develops.Graphs are drawn for the considered evaporation andcondensation heat transfer coefficients and flow pattern infunction of different quality.VI.RESULTS AND DISCUSESThe motivation for the composition of this articlewas to investigate the flow pattern map and heat transfercoefficients in the horizontal tube of the condenser andthe evaporator.The flow pattern is of crucial definition. With thechange of flow pattern, the change of mass velocity ofrefrigerant occurs. The value of the two-phase heattransfer coefficient is determined by the mass velocity.The discrete value of the two-phase heat transfercoefficient is a function of the refrigerant mass velocity,the vapor quality, the refrigerant condensing orevaporation temperature and the inner diameter of tube.α f m,x,T,d Figure 3. Flow Pattern map and Heat Transfer model for in tubeboilingBesides the heat transfer coefficients, accuracy of thepressure drop and the void fraction value is determinedby the heat pump system of the accurate mathematicalmodel.The flow pattern map for boiling and flow boilingheat transfer model for refrigerant R134a on the inside ofhorizontal tubes are proposed of Wojtan et al. (2005).The flow pattern for condensation of refrigerantR134a on the inside of horizontal tubes are suggested byThome and El Hajal (2003). The condensation heattransfer model was used of Shah [10] correlation (1979).The existence of a particular flow regime depends ona variety of parameters, including the thermo physicalproperties of the fluid, the tube diameter, orientation andgeometry, force field, mass flux, heat flux and vaporquality.On the flow pattern maps, the value change of theheat transfer coefficients of evaporation and condensationcan be seen. It can be seen that the added input values, theannular flow is predominantly formed in the evaporatingFigure 4. Flow Pattern map and Heat Transfer model for in tubeCondensationFlow patterns that occur during condensation insidehorizontal tubes are similar to those for evaporation, withthe following exceptions:• The process begins without any entrainment ofliquid.• There is no dryout.129
Page 1 and 2:
4 4 th IEEE International Symposium
Page 3 and 4:
EXPRES 20124 th International Sympo
Page 5 and 6:
Application of Thermopile Technolog
Page 7 and 8:
Design of a Solar Hybrid System....
Page 9 and 10:
___________________________________
Page 11 and 12:
environmental protection and global
Page 13 and 14:
But can we use the human body sweat
Page 15 and 16:
IX. REFERENCES[1] Todorovic B. Cvje
Page 17 and 18:
QQ⎛ Λt⎞=⎜⎟⎝ Λ ⎠Nt Nwh
Page 19 and 20:
Analysis of the Energy-Optimum of H
Page 21 and 22:
V. OBJECTIVE FUNCTIONThe objective
Page 23 and 24:
The Set-Up Geometry of Sun Collecto
Page 25 and 26:
continuous east-west sun collector
Page 27 and 28:
continuously measure the thermal ch
Page 29 and 30:
CEvaluation of measurement resultsA
Page 31 and 32:
Application of Thermopile Technolog
Page 33 and 34:
Temperature of the components [C]90
Page 35 and 36:
nighttime, to weather or to the cha
Page 37 and 38:
η uη u0.50.40.30.20.1T 1 - 400K0.
Page 39 and 40:
Figure 10. . SPS Concept illustrati
Page 41 and 42:
[16] Zoya B. Popović: Wireless Pow
Page 43 and 44:
25.0020.0015.0010.005.000.00Figure
Page 45 and 46:
· ℃ 0.0738 · 1.209 0.0892
Page 47 and 48:
use may be advantageous not only in
Page 49 and 50:
To find the reasons for this disagr
Page 51 and 52:
Toward Future: Positive Net-Energy
Page 53 and 54:
EnergyPlus environment, we used mod
Page 55 and 56:
To keep future energy consumption d
Page 57 and 58:
A New Calculation Method to Analyse
Page 59 and 60:
On Fig. 3. can be seen the areas th
Page 61 and 62:
Present and Future of Geothermal En
Page 63 and 64:
TABLE II.THE TEMPERATURE DATA AND C
Page 65 and 66:
Error in Water Meter Measuring at W
Page 67 and 68:
III.RESULTS OF MEASURMENTSEach meas
Page 69 and 70:
TABLE I.THE AVERAGE VALUE OF THERMA
Page 71 and 72:
If the walls of the DHEs are made o
Page 73 and 74:
Environmental External Costs Associ
Page 75 and 76:
iodiesel production facility with a
Page 77 and 78:
Contribution of unit processesto ex
Page 79 and 80: Heat Pump News in HungaryBéla Ád
Page 81 and 82: Thermal Comfort Measurements In Lar
Page 83 and 84: IV.DISCUSSIONThe sample frequencies
Page 85 and 86: For a Clear View of Traditional and
Page 87 and 88: esults in geographically distribute
Page 89 and 90: Design of a Solar Hybrid SystemMari
Page 91 and 92: Maintaining the set point temperatu
Page 93 and 94: Decision system theory model of ope
Page 95 and 96: parameter of pump in the function o
Page 97 and 98: Importance and Value of Predictive
Page 99 and 100: D. Overview of existing boiler oper
Page 101 and 102: HEAVY FUEL OIL FIRED, STEAMNATURAL
Page 103 and 104: MATHEMATICAL MODEL AND NUMERICAL SI
Page 105 and 106: C. Energy balance equationMathemati
Page 107 and 108: Discretization energy balance equat
Page 109 and 110: T ulf=32 º C, A - m =0.00162 kg/s,
Page 111 and 112: Comparison of Heat Pump and MicroCH
Page 113 and 114: the microCHP development. The energ
Page 115 and 116: control and stabilizer must be deve
Page 117 and 118: In Figure 1, in relation to the ord
Page 119 and 120: NPCC BHXOBYNI x1I x2I x3I x4LO YKYO
Page 121 and 122: exchange, as in reality, economies
Page 123 and 124: esponsibilities for consequences, o
Page 125 and 126: Coca-Cola Enterprise Inc had approx
Page 127 and 128: Flow Pattern Map for In Tube Evapor
Page 129: circumference with a liquid film. T
Page 133 and 134: Realization of Concurrent Programmi
Page 135 and 136: applications the development, optim
Page 137 and 138: Renewable energy sources in automob
Page 139 and 140: commercial arrays can be built at b
Page 141 and 142: of multiple thin films produced usi
Page 143: EXPRES 20124 th International Sympo
show all

Final Program EXPRES 2012 - Conferences

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?