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Abstract

Plate fin-tube heat exchangers fins are bonded with tubes by means of brazing or by mechanical expansion of tubes. Various errors made in the process of expansion can result in formation of an air gap between tube and fin. A number of numerical simulations was carried out for symmetric section of plate fin-tube heat exchanger to study the influence of air gap on heat transfer in forced convection conditions. Different locations of air gap spanning 1/2 circumference of the tube were considered, relatively to air flow direction. Inlet velocities were a variable parameter in the simulations (1– 5 m/s). Velocity and temperature fields for cases with air gap were compared with cases without it (ideal thermal contact). For the case of gap in the back of the tube (in recirculation zone) the lowest reduction (relatively to the case without gap) of heat transfer rate was obtained (average of 11%). The worst performance was obtained for the gap in the front (reduction relatively to full thermal contact in the average of 16%).

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Authors and Affiliations

Dariusz Andrzejewski
Marcin Łęcki
Artur Gutkowski
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Abstract

The numerical simulation of the heat transfer in the flow channels of the minichannel heat exchanger was carried out. The applied model was validated on the experimental stand of an air heat pump. The influence of louver heights was investigated in the range from 0 mm (plain fin) to 7 mm (maximum height). The set of simulations was prepared in Ansys CFX. The research was carried out in a range of air inlet velocities from 1 to 5 m/s. The values of the Reynolds number achieved in the experimental tests ranged from 93 to 486. The dimensionless factors, the Colburn factor and friction factor, were calculated to evaluate heat transfer and pressure loss, respectively. The effectiveness of each louver height was evaluated using the parameter that relates to the heat transfer and the pressure drop in the airflow. The highest value of effectiveness (1.53) was achieved by the louver height of 7 mm for the Reynolds number of around 290.
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Authors and Affiliations

Artur Romaniak
1
Michał Jan Kowalczyk
1
Marcin Łęcki
1
Artur Gutkowski
1
Grzegorz Górecki
1

  1. Lodz University of Technology, Zeromskiego 116, 90-924 Łódz, Poland
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Abstract

The results of experimental investigations of heat transfer and a friction factor in an air channel of the minichannel heat exchanger are presented. The main aim of the analysis was to examine an influence of geometrical parameters of the fin shape with two geometries on heat transfer and flow characteristics of the air channel. The test rig was designed to monitor the parameters of the airflow during cooling by the minichannel heat exchanger. The analysis was conducted with the airflow in the range of 1–5 m/s. The temperature of the evaporation in a refrigeration system was set at 288.15 K. The energy balance of the refrigeration system was carried out. A numerical model describes the airflow through a part of the heat exchanger. Numerical simulations were validated with the experimental data. Numerical methods were used to evaluate the performance of the system and possibilities to improve the fin geometry. The characteristics of the friction factor (a measure of the pressure loss in the airflow) and the Colburn j-factor (heat transfer performance) were calculated. For the maximal velocity of the airflow, the Colburn factor was equal to 0.048 and the evaporator capacity equaled 1914 W.
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Bibliography

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[2] Muszynski T., Kozieł S.M.: Parametric study of fluid flow and heat transfer over louvered fins of air heat pump evaporator. Arch. Thermodyn. 37(2016), 3, 45–62.
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[5] Gunnasegaran P., Shuaib N.H., Abdul Jalal M.F.: The effect of geometrical parameters on heat transfer characteristics of compact heat exchanger with louvered fins. ISRN Thermodyn. (2012), 1–10.
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[7] Amirnordin S.H., Didane H.D., Norani Mansor M., Khalid A, Suzairin M.S., Raghavan V.R.: Pressure drop and heat transfer characteristics of louvered fin heat exchangers. Appl. Mech. Mater. 465-466(2014), 500–504.
[8] Chan Kang H., Jun G.W.: Heat transfer and flow resistance characteristics of louver fin geometry for automobile applications. J. Heat Transfer. 133(2011), 1–6.
[9] Okbaz A., Olcay A.B., Cellek M.S., Pinarbasi A.: Computational investigation of heat transfer and pressure drop in a typical louver fin-and-tube heat exchanger for various louver angles and fin pitches. EPJ Web Conf. 143(2017), 02084.
[10] Park J.S., Kim J., Lee K.S.: Thermal and drainage performance of a louvered fin heat exchanger according to heat exchanger inclination angle under frosting and defrosting conditions. Int. J. Heat Mass Transf. 108(2017), 1335–1339.
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[17] Kang, Hie-Chan & Jun, Gil.: Heat transfer and flow resistance characteristics of louver fin geometry for automobile applications. J. Heat Transf. 133 (2011), 101802.
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Authors and Affiliations

Michał Jan Kowalczyk
1
Marcin Łęcki
1
Artur Romaniak
1
Bartosz Warwas
1
Artur Gutkowski
1

  1. Lodz University of Technology, Institute of Turbomachinery, Wólczanska 217/221, 93-005 Łódz, Poland

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