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Natural convection energy recovery loop analysis, part I: energy and exergy studies by varying inlet air flow rate

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Abstract

The natural convection energy recovery loop is analyzed experimentally in different airflow rates. The system was introduced previously as a prototype of the standalone air conditioning system and its transient and steady performance was verified. As a new generation of energy recovery tool between the building return and fresh air, the system is rated from the viewpoints of energy and exergy. Different forms of effectiveness and 2nd law efficiency are studied and their values extracted for inlet airflow rates of 2–6 m3/h. The results show that the prominent factor that controls the system behavior is the concentration ratio from which the solution free- motion originated. The maximum sensible, latent, and total effectiveness of the system are 0.23, 062, and 0.54 respectively and are for the airflow rate of 2m3/h. It is confirmed that the number of a transfer unit (NTU) and capacity ratio (Cr*) are not independent and are varied oppositely to each other. By increasing the airflow rate, the mass flow rate and heat capacity rate of desiccant solution increase more than that of air streams. For flow rates less than 3.5m3/h, external heat transfer is just enough to induce natural motion of desiccant and in this way the loop performance is similar to a forced convection energy transfer loop which exchanges heat and moisture only between the air streams.

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Abbreviations

A:

Contact area (m2)

Abs:

Absorber

AC:

Air conditioning

AHRI:

American society of heating and refrigerating institute

ASTM:

American society of testing and materials

C:

Concentration (kgsalt/kgsol)

CC:

Cooling capacity (W)

Cr* :

Specific heat ratio

ECOP:

Electrical coefficient of performance

H:

Specific enthalpy (kJ/kg)

H:

Enthalpy (kJ)

H/M:

Heat and mass

HFM:

Hollow fiber membrane

\( \dot{\mathrm{m}} \),m:

Mass flow rate (kg/s)

MRR:

Moisture removal rate

NTU:

Number of transfer unit

PIV:

Particle imaging velocimetry

R:

Mass flow rate ratio

RAMEE:

Run around membrane energy exchanger

Reg:

Regenerator

SHR:

Sensible heat ratio

TCOP:

Thermal coefficient of performance

U:

Overall heat transfer coefficient (W/m2.K)

Um :

Overall mass transfer coefficient (kg/m2.s)

\( \dot{\mathrm{V}} \) :

Volume flow rate (m3/h)

\( \dot{\mathrm{W}} \) :

Electrical power (W)

∆:

Difference

ε:

Effectiveness

η:

Efficiency

ω:

Humidity ratio

Ψ:

Exergy flow (kJ)

0:

Dead state

A:

Air

abs:

Absorber

chiller:

Water chiller system

comp:

Compressor

cw:

Cold water

db:

Dry bulb

d, down:

Lower horizontal level of loop

f:

Liquid water

HMX:

Heat and mass exchanger

hw:

Hot water

in:

Inlet flow

l:

Latent

max:

Maximum value

min:

Minimum value

out:

Maximum value

reg:

Regenerator

s:

Sensible

sol:

Desiccant solution

tot:

Total

u, up:

Upper horizontal level of loop

v:

Water vapor

w:

Liquid water

wb:

Wet bulb

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Acknowledgements

This research is partially supported by the National Key Research and Development Program of China (2016YFB0100903) and JITRI Suzhou Automotive Research Institute Project (CEC20190404).

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Authors and Affiliations

  1. Suzhou Automotive Research Institute, Tsinghua University, Suzhou, 215134, China

    Yulin Ma

  2. Department of Mechanical Engineering, Khomeinishahr Branch, Islamic Azad University, Khomeinishahr, Iran

    Mohammad Ali Fazilati & Davood Toghraie

  3. Department of Mechanical Engineering, Australian College of Kuwait, Kuwait City, Kuwait

    Ahmad Sedaghat

  4. Department for Management of Science and Technology Development, Ton Duc Thang University, Ho Chi Minh City, Vietnam

    Pouyan Talebizadehsardari

  5. Faculty of Applied Sciences, Ton Duc Thang University, Ho Chi Minh City, Vietnam

    Pouyan Talebizadehsardari

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  1. Yulin Ma
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  2. Mohammad Ali Fazilati
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Correspondence to Pouyan Talebizadehsardari.

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Ma, Y., Fazilati, M.A., Sedaghat, A. et al. Natural convection energy recovery loop analysis, part I: energy and exergy studies by varying inlet air flow rate. Heat Mass Transfer 56, 1685–1695 (2020). https://doi.org/10.1007/s00231-019-02766-z

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