A novel heat exchanger for automotive applications developed by the Heat Transfer and Fluid Flow Laboratory at the Brno University of Technology, Czech Republic, is compared with a conventional commercially available metal radiator. The heat transfer surface of this heat exchanger is composed of polymeric hollow fibers made from polyamide 612 by DuPont (Zytel LC6159). The cross-section of the polymeric radiator is identical to the aluminum radiator (louvered fins on flat tubes) in a Skoda Octavia and measures 720 × 480 mm. The goal of the study is to compare the functionality and performance parameters of both radiators based on the results of tests in a calibrated air wind tunnel. During testing, both heat exchangers were tested in conventional conditions used for car radiators with different air flow and coolant (50% ethylene glycol) rates. The polymeric hollow fiber heat exchanger demonstrated about 20% higher thermal performance for the same air flow. The efficiency of the polymeric radiator was in the range 80–93% and the efficiency of the aluminum radiator was in the range 64–84%. The polymeric radiator is 30% lighter than its conventional metal competitor. Both tested radiators had very similar pressure loss on the liquid side, but the polymeric radiator featured higher air pressure loss.
Condensation during heat transfer processes can be very beneficially used due to the large amount of energy contained in phase change (vapor to liquid). This contribution focuses on the possible use of polymer hollow fiber heat exchangers (PHFHEs) in air conditioning. PHFHEs consist of hundreds or thousands of polymer hollow fibers with an outer diameter of around 1 mm. The wall thickness is approximately 10% of the outer diameter. PHFHEs are heat exchangers with such benefits as low weight, easy shaping, corrosion resistance, and resistance to many chemical solutions. In comparison with metal heat exchangers (made of copper, aluminum, or stainless steel) the plastic wall of PHFHEs has low thermal conductivity (between 0.1 and 0.4 Wm-1K-1). This seems to be their key disadvantage. However, due to the extremely small thickness of the fiber’s wall this disadvantage is negligible. PHFHEs are compact heat exchangers with a large heat transfer area with respect to their volume.
This paper shows the results of condensation tests for PHFHEs that consist of 6 equivalent layers of polypropylene fibers with a length of 190 mm. The total number of fibers is 798. The air humidity was set to 50% with an air temperature of 27°C, which are the typical conditions for such tests in air conditioning technology. Another important parameter was the velocity of the air. Testing velocities were chosen as 3 m s−1 and 1 m s−1.
The influence of gravity was studied by putting the PHFHEs in three different positions. The fibers were placed in horizontal and vertical positions, and in a position where fibers form an angle of 45° with the ground.
The study showed the ineffectiveness of placing the PHFHE in a horizontal position and suggests that it is better to have a larger distance between the layers of fibers.
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