Modeling pressure drop and heat transfer in plate heat exchanger channels

Hamoda, Mahmoud (2022) Modeling pressure drop and heat transfer in plate heat exchanger channels. Doctoral (PhD) thesis, Memorial University of Newfoundland.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (3MB)

Abstract

In compact heat exchangers, surface enhancements have been used for augmenting heat transfer due to the growing urgency for energy conservation and reduced environmental impact. Plates with corrugated walls are utilized in plate heat exchangers (PHEs) as they increase the effective heat transfer area, disrupt and reattach the boundary layer, and promote swirl flow resulting in a compact heat exchanger with high heat transfer performance. As a result, their applications have grown considerably to include a wide range of industries and processes, such as food, pharmaceutical, power generation, cooling engine oil, and dairy product processing. Due to heat exchanger size constraints, a compact heat exchanger's flow passages are often short in the automobile industry, especially for cooling engine oil and transmission oil. Hence, the heat exchanger is likely working with developing flow characteristics that have higher heat transfer and pressure drop compared to developed flow. A review of the open literature reveals a gap in the knowledge regarding the influence of the channel length on the thermal-hydraulic performance of PHE, which needs additional research. Also, no general models or correlations have been developed for predicting heat transfer and pressure drop in the entrance region of PHEs. Therefore, this thesis aims to experimentally investigate the effect of the channel length on the thermal-hydraulic performance of PHEs and to develop models for use in predicting pressure drop and heat transfer of PHEs, including the entrance region. An experimental facility is constructed to perform a series of single-phase flow tests on pressure drop and heat transfer of chevron PHE with two different channel lengths, 20.3 cm and 10.1 cm, and three different chevron angles, 30°,45°, and 60°. Mineral oil and water are used as the working fluids to cover laminar and turbulent flow regions. The results show that plates with a higher chevron angle experience higher pressure drop and heat transfer, which is consistent with the literature. Furthermore, the results of the effect of channel length on the Nusselt number of a PHE are very interesting as they demonstrate a significant impact of channel length on heat transfer performance of PHEs. The Nusselt number for short channels is considerably higher than for longer channels, indicating that thermal entrance effects are present. In addition, the Fanning friction factor results show that it is independent of the channel length at very low Reynolds numbers, while it is greatly impacted by the length of the channel at higher Reynolds numbers. The significance of these findings is that PHE channel length is an important factor that needs to be considered; however, it is often neglected due to assuming fully developed flow. This is important when designing a PHE and/or developing general models or correlations to predict the thermal and hydraulic performance of the PHE to cover a wide range of the Reynolds numbers. It is especially significant for applications where the length of the heat exchanger's flow passage is constrained. Finally, models for predicting the Fanning friction factor and Colburn factor are developed, which are a function of the plate length, corrugation depth, chevron angle, and Reynolds number. Agreement between the proposed models and the present experimental data is within ±20%. These models are also validated against numerical and experimental data from the literature and show good agreement within ±20% in most cases within the range of applicability. Thus, the proposed models may be used for preliminary designs of a chevron PHE.

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