=Paper=
{{Paper
|id=Vol-2348/short13
|storemode=property
|title=Air Flow and Heat Exchange Simulation of a Rotary Heat Exchanger of Polyethylene Terephthalate (PET) as a Sustainable Alternative for Aluminum
|pdfUrl=https://ceur-ws.org/Vol-2348/short13.pdf
|volume=Vol-2348
|authors=J. Ganzwind,M. Hammermeister,S. Dolata,F. Nebel,T. Schröder
|dblpUrl=https://dblp.org/rec/conf/cerc/GanzwindHDNS19
}}
==Air Flow and Heat Exchange Simulation of a Rotary Heat Exchanger of Polyethylene Terephthalate (PET) as a Sustainable Alternative for Aluminum==
https://ceur-ws.org/Vol-2348/short13.pdf
Nature Science and Engineering
Air flow and heat exchange simulation of a rotary heat
exchanger of polyethylene terephthalate (PET) as a
sustainable alternative for aluminum
J. Ganzwind, M. Hammermeister, S. Dolata, F. Nebel and T. Schröder
Gesellschaft zur Förderung technischen Nachwuchses GFTN e.V.
Institute at the University of Applied Sciences, Darmstadt
johann.ganzwind@h-da.de, thomas.schroeder@h-da.de
Abstract. This paper deals with the simulation of rotary heat exchangers made
of polyethylene terephthalates using CFD software. First steps for the simulation
of simplified flow processes within a heat exchanger are presented. The aim of
the project is the substitution of commercially available materials such as alumi-
num to plastic. The use of plastic as a storage mass material will create new pos-
sibilities which will make the heat exchangers even more efficient than their pre-
decessors made of aluminum. For this purpose, the two materials are compared
with each other using simulation models with ANSYS Fluent© and the resulting
temperature curve is examined. The results show that PET offers a more suitable
temperature profile than aluminum for heat exchanger.
1 Introduction and Objectives of the project
The PET rotary heat exchanger research project is being carried out in cooperation be-
tween the Gesellschaft zur Förderung technischen Nachwuchses GFTN e.V., Darm-
stadt, and Klingenburg GmbH, Gladbeck. The main focus of the research project is the
substitution of the aluminum by PET for the production of the storage mass. The PET
shall use the advantages of plastic and increase the efficiency of the rotary heat ex-
changer up to 90% by a geometrically optimized shaft structure. The design options for
aluminum are limited by the yield strength. This leads to a maximum efficiency of 85%.
A further advantage is the recyclability of the PET. The reuse of the material leads to a
sustainable and future-oriented alternative to the existing heat exchangers. The aim of
the project is to develop the complete production cycle in a process chain. The process
chain is to include extrusion, embossing and deep-drawing as well as the joining of the
films with subsequent winding. Once the life of the heat exchanger has been reached,
it will be taken back and recycled by Klingenburg GmbH.
2 Operating principle of a rotary heat exchanger
Rotary heat exchangers are used with permitted circulating air. The main task is the
supply and removal of heat energy in computer centers, office buildings, factory halls
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and cruise ships. Due to the large surface area and the associated large air volume,
rotary heat exchangers are considered to be the most effective heat exchangers. During
operation, two air streams flow through the storage mass, the supply air stream from
the outside and the exhaust air stream from the inside. Each of these two flows transfers
its heat energy to the storage mass. The energy absorbed is released again and the heat
is transferred by the rotation in the respective other stream. [1] The functional principle
of the rotary heat exchanger is shown in Figure 1. In the further course of this abstract,
the function of a rotary heat exchanger made of aluminum is compared with one made
of PET on the basis of simulation results.
Fig. 1. Functional principle of the rotary heat exchanger
3 Thermal basics of the model
In counterflow heat exchangers, the air flows are guided through a series of parallel
plates. Figure 2 shows the simplified principle of the heat exchanger as a volume body
in CATIA V5R20®. The arrows indicate the direction of flow of the two air streams.
The warm air flow directs the energy through the plate into the cold air flow, resulting
in heat exchange. The shown model was calculated under the theoretical basis of single-
layer walls.
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Fig. 2. Used simulation model in half section with displayed flow directions
The proportion of the heat flow absorbed depends on the design of the heat exchanger,
the size of the effective heat transfer surface and the material of the transfer surface.
The cooperation company Klingenburg GmbH has already carried out the first practical
tests in this field, in which the material of the heat exchanger mass was changed from
aluminum to PET. It has been shown that PET leads to a better efficiency as soon as
the layer thickness becomes very thin.
If the stationary heat conduction is considered in a single-layer wall, the following
relationship applies to the heat flow for a plate [2]:
−𝑇𝑇
𝑄𝑄̇ = 𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐
(𝑇𝑇 )
(1)
𝑅𝑅𝜆𝜆 ·𝑡𝑡
𝑅𝑅𝜆𝜆 = thermal resistance
𝑇𝑇𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤/𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 = temperature warm/cold
𝑡𝑡 = time
with the thermal resistance:
𝑠𝑠
𝑅𝑅𝜆𝜆 = (2)
𝜆𝜆·𝐴𝐴
𝑠𝑠 = wall thickness
𝜆𝜆 = thermal conductivity
𝐴𝐴 = trea flowed through
If the layer thickness in equation 2 is continuously smaller with the same denomina-
tor, the thermal resistance also becomes arbitrarily low. This means that the signifi-
cantly higher thermal conductivity of aluminum (approx. factor 1000 better than PET)
continuously has a considerable influence.
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4 Simulation of a counterflow heat exchanger with
ANSYS Fluent©
The first simulations were created with ANSYS 18.2 Fluent© CFD software. The ge-
ometry used for this was 2.1 mm wide, 0.5 mm high and 5 mm long. Two channels
were provided with a height of 0.15 mm and a width of 2 mm over the entire length of
this geometry. The dividing wall between them had a continuous thickness of 0.05 mm
(50 µm).
In Fluent©, a stationary state was simulated with an air velocity of 1 m/s flowing
through both channels. The temperature of the supply air flow duct is 0°C and the tem-
perature of the exhaust air flow is 25°C. The thermal boundary conditions on the outer
walls were defined as adiabatic and the material properties varied between aluminum
and PET.
Looking at the results in Figure 3, it can be seen that PET has a more favourable
temperature profile for heat exchangers. In the case of aluminum, a constant tempera-
ture has been set over the entire cross-section, while the PET volume body has a higher
temperature difference in the air flow channels.
Fig. 3. Temperature curve in the middle of the body for aluminum (top) and PET
(bottom)
5 Inference
This simulation is a first comparison of the two materials, aluminum and PET, with a
simplified model. The results obtained are similar to the practical tests carried out by
Klingenburg GmbH. In order to verify the simulation results, the model will be simu-
lated in practice in the next phase of the project.
6 Acknowledgement
The GFTN research team would like to thank the BMWi and the cooperation partner
Klingenburg GmbH for their support and cooperation in this research project.
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7 Bibliography
1. http://www.klingenburg.de/de/produkte/rotationswaermetauscher/rotoren-fuer-die-
raumlufttechnik/funktionsprinzip/ [Accessed 31.05.2018]
2. http://www.uni-magdeburg.de/isut/TV/Download/Waerme-
_und_Stoffuebertragung_Kapitel_1+2_WS0809.pdf [Accessed 31.05.2018]
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