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Characteristic analysis of heat and mass transfer process within structured packing humidifier

  • Junjie Chen
  • Dong HanEmail author
  • Weifeng He
  • Chao Ji
  • Zetian Si
  • Mingrui Zheng
  • Jiming Gu
  • Yan Song
Technical Paper
  • 17 Downloads

Abstract

Humidifiers are the important devices for humidifying the air both in life and industrial production. This paper focuses on the heat and mass transfer processes inside the counter-flow packing humidifier at atmospheric pressure. Based on mass and energy balance, the mathematical model for the humidifier is established. The finite difference method is first adopted to calculate the specific scales of the packing and the relevant state distribution of the gas–liquid species at on-design conditions. Thus, the heat and mass transfer performance of the humidifier is also carried out at off-design conditions. The simulation results show that the required packing height at the design parameters is 3.38 × 10−1 m, while the supersaturation phenomenon begins at Z = 5.76 × 10−2 m, and the humidity ratio and supersaturated humidity ratio at humidifier outlet are 1.69 × 10−1 kg/kg and 1.64 × 10−3 kg/kg, respectively. In addition, for off-design analysis, as the liquid–gas ratio increases, the outlet water temperature and outlet air temperature increase by 14.3% and 7.47%, respectively, and the humid air reaches saturation earlier as the saturation point falls from 5.76 × 10−2 to 2.7 × 10−2 m. Within the range of the simulation conditions, the maximum account of droplets entrained in the humid air reaches 1.72 × 10−3 kg/kg, while the total packing pressure drop increases with the decrease in liquid–gas ratio. The effect of liquid–gas ratio and wet-bulb temperature of inlet air on the humidifier under design parameters can provide great reference significance for the design, optimization and regulation of humidifiers.

Keywords

Humidifier Heat and mass transfer Mathematical model Finite difference method On-design conditions Off-design conditions 

List of symbols

a

Specific surface area (m2/m3)

A

Surface area (m2)

AZ

Cross-sectional area (m2)

cp

Specific heat capacity (kJ/kg K)

C

Geometric coefficient

C1, C2, C3

Constants

Cp

Packing coefficient

d

Particle diameter (m)

dp

Equivalent diameter (m)

D

Packing diameter (m)

DG

Mass diffusivity in gas (m2/s)

f

Friction factor

g

Gravity acceleration (m/s2)

G

Mass flux of gas stream (kg/m2 s)

h

Specific enthalpy (kJ/kg)

hc

Heat transfer coefficient (W/m2 K)

hd

Mass transfer coefficient (kg/m2 s)

L

Liquid holdup

Lef

Lewis factor

m

Mass flow rate (kg/s)

mr

Mass flow rate ratio (mw/mda)

P

Pressure (kPa)

ΔP

Pressure drop (Pa)

ΔPv

Mass transfer pressure difference (kPa)

Re

Reynolds number

Sc

Schmidt number

T

Temperature (°C or K)

ΔT

Heat transfer temperature difference (°C)

u

Superficial velocity (m/s)

Z

Height (m)

Greek letters

ε

Void fraction of packing

φ

Relative humidity

ρ

Density (kg/m3)

μ

Dynamic viscosity (kg/m s)

σ

Surface tension (N/m)

ω

Humidity ratio (kg/kg)

Subscripts

a

Air above the loading point

b

Below the loading point

c

Control volume

d

Dry

da

Dry air

e

Environmental

G

Gas

i

Inlet

irr

Irrigated

max

Maximum

min

Minimum

o

Outlet

p

Packing

v

Vapor

s

Saturated

ss

Supersaturated

w

Water

wb

Wet bulb

Notes

Acknowledgements

The authors gratefully acknowledge the financial support by the National Natural Science Foundation of China (Grant No. 51406081) and the Fundamental Research Funds for the Central Universities (Grant No. NP2018107).

Funding

No support, financial or otherwise, has been received from any organization that may have an interest in the submitted work.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

References

  1. 1.
    Kabeel AE, El-Said EMS (2014) A hybrid solar desalination system of air humidification–dehumidification and water flashing evaporation part I. A numerical investigation. Desalination 341(1):50–60.  https://doi.org/10.1016/j.desal.2014.02.035 CrossRefGoogle Scholar
  2. 2.
    Huang X, Zhang D, Zhang X (2017) Experimental research on the heat and mass transfer characteristics of corrugated plate spray humidification air coolers. Procedia Eng 205:1886–1892.  https://doi.org/10.1016/j.proeng.2017.10.276 CrossRefGoogle Scholar
  3. 3.
    Bae H, Ahn KY, Lee YD et al (2011) Basic analysis of heat and mass transfer characteristics of tubular membrane humidifier for proton exchange membrane fuel cell. Trans Korean Soc Mech Eng B 35(5):473–480.  https://doi.org/10.3795/ksme-b.2011.35.5.473 CrossRefGoogle Scholar
  4. 4.
    Srithar K, Rajaseenivasan T (2017) Performance analysis on a solar bubble column humidification dehumidification desalination system. Process Saf Environ Prot 105:41–50.  https://doi.org/10.1016/j.psep.2016.10.002 CrossRefGoogle Scholar
  5. 5.
    He WF, Zhang XK, Han D et al (2017) Performance analysis of a water-power combined system with air-heated humidification dehumidification process. Energy 130:218–227.  https://doi.org/10.1016/j.energy.2017.04.136 CrossRefGoogle Scholar
  6. 6.
    He WF, Han D, Zhu WP et al (2018) Thermo-economic analysis of a water-heated humidification–dehumidification desalination system with waste heat recovery. Energy Convers Manag 160:182–190.  https://doi.org/10.1016/j.enconman.2018.01.048 CrossRefGoogle Scholar
  7. 7.
    Traverso A (2009) Humidification tower for humid air gas turbine cycles: experimental analysis. Energy 35(2):894–901.  https://doi.org/10.1016/j.energy.2009.07.021 CrossRefGoogle Scholar
  8. 8.
    Han D, He WF, Ji C et al (2018) Thermodynamic analysis of a novel evaporation and crystallization system based on humidification processes at ambient temperature. Desalination 439:108–118.  https://doi.org/10.1016/j.desal.2018.04.016 CrossRefGoogle Scholar
  9. 9.
    He WF, Huang L, Xia JR et al (2017) Parametric analysis of a humidification dehumidification desalination system using a direct-contact dehumidifier. Int J Therm Sci 120:31–40.  https://doi.org/10.1016/j.ijthermalsci.2017.05.027 CrossRefGoogle Scholar
  10. 10.
    Ahmed HA, Ismail IM, Saleh WF et al (2017) Experimental investigation of humidification–dehumidification desalination system with corrugated packing in the humidifier. Desalination 410:19–29.  https://doi.org/10.1016/j.desal.2017.01.036 CrossRefGoogle Scholar
  11. 11.
    Xu Z, Xie Y, Zhang F (2018) Development of mass transfer coefficient correlation for a ceramic foam packing humidifier at elevated pressure. Appl Therm Eng 133:560–565.  https://doi.org/10.1016/j.applthermaleng.2018.01.092 CrossRefGoogle Scholar
  12. 12.
    Ramkumar R, Ragupathy A (2015) Optimization of cooling tower performance with different types of packings using Taguchi approach. J Braz Soc Mech Sci Eng 37(3):929–936.  https://doi.org/10.1007/s40430-014-0216-1 CrossRefGoogle Scholar
  13. 13.
    Velandia JS, Chery M, Lopez OD (2016) Computational study of the air flow dynamics in an induced draft cooling tower. J Braz Soc Mech Sci Eng 38(8):2393–2401.  https://doi.org/10.1007/s40430-015-0348-y CrossRefGoogle Scholar
  14. 14.
    Kloppers JC (2003) A critical evaluation and refinement of the performance prediction of wet-cooling towers. Ph.D. Thesis, Department of Mechanical Engineering. Dissertation, Stellenbosch UniversityGoogle Scholar
  15. 15.
    Merkel F (1925) Verdunstungskühlung. VDI-Verlag, GermanyGoogle Scholar
  16. 16.
    Jaber H, Webb RL (1989) Design of cooling towers by the effectiveness-NTU method. J Heat Transf 111(4):837–843.  https://doi.org/10.1115/1.3250794 CrossRefGoogle Scholar
  17. 17.
    Poppe M, Rögener H (1991) Berechnung von rückkühlwerken. VDI Wärmeatlas, pp. Mi.  https://doi.org/10.1007/978-3-540-32218-4_99
  18. 18.
    Kloppers JC, KröGer DG (2005) Cooling tower performance evaluation: Merkel, Poppe, and e-NTU methods of analysis. J Eng Gas Turbines Power 127(1):1–7.  https://doi.org/10.1115/1.1787504 CrossRefGoogle Scholar
  19. 19.
    Miller JA (2011) Numerical balancing in a humidification dehumidification desalination system. S.M. Thesis, Department of Mechanical Engineering. Dissertation, Massachusetts Institute of TechnologyGoogle Scholar
  20. 20.
    Zhang Y, Zhu C, Zhang H et al (2018) Experimental study of a humidification–dehumidification desalination system with heat pump unit. Desalination 442:108–117.  https://doi.org/10.1016/j.desal.2018.05.020 CrossRefGoogle Scholar
  21. 21.
    Zhang Y, Zhang H, Zheng W et al (2019) Numerical investigation of a humidification–dehumidification desalination system driven by heat pump. Energy Convers Manag 180:641–653.  https://doi.org/10.1016/j.enconman.2018.11.018 CrossRefGoogle Scholar
  22. 22.
    Mehta MSB, Paul A, Selokar GR (2012) Governing equation of heat and mass transfer in wet-cooling tower fills. Int J Eng Sci Res Technol 1(5):290–296Google Scholar
  23. 23.
    Reuter HCR (2010) Performance evaluation of natural draught cooling towers with anisotropic fills. Ph.D. Thesis, Department of Mechanical Engineering. Dissertation, Stellenbosch UniversityGoogle Scholar
  24. 24.
    Klimanek A (2013) Numerical modelling of natural draft wet-cooling towers. Arch Comput Methods Eng 20(1):61–109.  https://doi.org/10.1007/s11831-013-9081-9 MathSciNetCrossRefzbMATHGoogle Scholar
  25. 25.
    Onda K (1968) Mass transfer coefficients between gas and liquid phases in packed columns. J Chem Eng Jpn 1(1):56–62.  https://doi.org/10.1252/jcej.1.56 CrossRefGoogle Scholar
  26. 26.
    Gandhidasan P (2002) Prediction of pressure drop in a packed bed dehumidifier operating with liquid desiccant. Appl Therm Eng 22(10):1117–1127.  https://doi.org/10.1016/S1359-4311(02)00031-5 CrossRefGoogle Scholar

Copyright information

© The Brazilian Society of Mechanical Sciences and Engineering 2019

Authors and Affiliations

  • Junjie Chen
    • 1
  • Dong Han
    • 1
    Email author
  • Weifeng He
    • 1
  • Chao Ji
    • 1
  • Zetian Si
    • 1
  • Mingrui Zheng
    • 1
  • Jiming Gu
    • 1
  • Yan Song
    • 1
  1. 1.College of Energy and Power Engineering, Energy Conservation Research Group (ECRG)Nanjing University of Aeronautics and AstronauticsNanjingChina

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