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An experimental study and infrared thermography analysis on the effect of using various flute-type distributors in mini-channel evaporators employed by room air conditioners

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Abstract

In air conditioners, mini-channel heat evaporator/heat exchanger excels in performance over the traditional fin-tube counterpart. However, the uniformity of two-phase refrigerant flow distribution in mini-channel evaporators remains unclear. To enhance the flow distribution in mini-channels, a flute-type coaxial multi-opening distributor is inserted into the header of a vertical mini-channel evaporator. Using a room air conditioner (RAC) unit (cooling capacity at 7.5 kW and R410A as the refrigerant) as a sample, the opening direction and inter-opening distance along the distributor are changed to obtain the variation range where the two-phase flow distribution uniformity in the mini-channel evaporator performs the best. Considering the secondary throttle effect caused by the inserted flute-type distributor, the proper width of the preceding throttle opening is proposed based on the performance of the sample unit under the nominal condition of refrigeration. The thermal cycle pressure enthalpy diagrams of the sample unit and the infrared thermography of the mini-channel evaporator are used to verify the effect of the proposed flute-type distributor forms. The results reveal that, the most uniform refrigerant two-phase flow within the mini-channel is achieved when using a non-uniform distributor and β = 180°. It was also indicated that the CC and EER of the RAC unit are significantly increased by 2.62–6.43% and 4.04–11.39%. Additionally, the annual electricity consumption and total equivalent warming impact of the slotted distributor embedded in the microchannel evaporator were reduced by 0.40 MWh and 6.9%, respectively.

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Abbreviations

RAC:

Room air conditioner

EER:

Energy efficiency ratio

TEWI:

Total equivalent warming impact

P :

Pressure (bar)

T :

Temperature (oC)

WB :

Wet-bulb temperature (oC)

DB :

Dry-bulb temperature (oC)

q :

Indoor air volume flow (m3 s–1)

h a1 :

Enthalpy of evaporator inlet air (J kg–1)

h a2 :

Enthalpy of evaporator outlet air (J kg–1)

V n :

Specific volume of dry air corresponding to humid air at evaporator outlet (m3 kg–1)

W n :

Moisture content in the dry air at the evaporator outlet (g kg–1)

Q C :

Cooling capacity (kW)

u :

Uncertainty

u A :

Type-A uncertainty

u B :

Type-B uncertainty

s(X):

Standard deviation

n :

Number of measurements

x i :

Value of the i-th measurement

\(\overline{x }\) :

Arithmetic mean

PA :

Annual power consumption (kWh)

t :

Total cooling operation time during the cooling season (h)

Pr :

Rated power input

m :

Mass of refrigerant(kg)

l :

Leakage rate per year (%)

s l :

Service life of refrigeration system (years)

η :

Carbon dioxide emission factor

β :

The opening direction along the distributor

E :

Energy consumption (kWh)

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Acknowledgements

This research is supported by Postgraduate Research & Practice Innovation Program of Jiangsu Province, China (SJCX22_0599, SJCX22_0600). Jiangxi Provincial Education Department Science and Technology Research Project, China (GJJ214812).

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Authors and Affiliations

  1. School of Energy and Mechanical Engineering, Nanjing Normal University, Nanjing, 210042, China

    Yanzhen Feng, Zhongbin Zhang & Xiaotong Shao

  2. School of Civil Engineering and Architecture, Zhejiang Sci-Tech University, Hangzhou, 310018, China

    Wenting Zhang

  3. School of Engineering, The Australian National University, Canberra, ACT, 2601, Australia

    Xiaolin Wang

  4. School of Chemical Engineering and Technology, Xi’an Jiaotong University, Xi’an, China

    Xiaotong Shao

  5. Department of Chemical Engineering, Imperial College London, London, SW7 2AZ, UK

    Xiaotong Shao

  6. School of Architecture and Engineering, Jiangxi Vocational College of Finance and Economics, Jiangxi, 332000, China

    Peng Liu

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Contributions

ZZ: Conceptualization, Methodology, Funding acquisition. YF: Data curation, Writing—Original Draft. WZ: Investigation, Validation. XS: Supervision. XW: Writing—Review & Editing.

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Correspondence to Zhongbin Zhang.

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Feng, Y., Zhang, W., Zhang, Z. et al. An experimental study and infrared thermography analysis on the effect of using various flute-type distributors in mini-channel evaporators employed by room air conditioners. J Therm Anal Calorim 148, 8655–8673 (2023). https://doi.org/10.1007/s10973-022-11774-x

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