Elsevier

Applied Thermal Engineering

Volume 199, 25 November 2021, 117567
Applied Thermal Engineering

Experimental study and comparative performance analysis on thermal-hydraulic characteristic of a novel longitudinal flow oil cooler

https://doi.org/10.1016/j.applthermaleng.2021.117567Get rights and content

Highlights

  • A novel longitudinal flow twisted trifoliate tube oil cooler is proposed.

  • The performance of a twisted trifoliate tube oil cooler is experimentally studied.

  • The novel longitudinal flow oil cooler obtains better heat transfer performance.

  • Correlations of Nu and f for a twisted trifoliate tube oil cooler are obtained.

  • The application of longitudinal flow heat exchangers at low Re is extended.

Abstract

The longitudinal flow heat exchanger possesses lots of merits but it exhibits poor heat transfer coefficient at low Re condition, which makes it difficult to be applied in the high viscosity fluid area. In this paper, a heat transfer augment solution for lubricating oil flowing on shell side of a novel longitudinal flow twisted trifoliate tube oil cooler was proposed. Experiments were conducted to comparatively investigate the thermal–hydraulic performance of a twisted trifoliate tube oil cooler and a conventional segmental baffle oil cooler. The tube side study demonstrates that the Nu and f of the twisted trifoliate tube are 17.5–75.8% and 16.9–62.9% larger than that of the smooth circular tube. The shell side study shows that at the same oil mass flow rate, the shell side heat transfer coefficient of the twisted trifoliate tube oil cooler is 66.3–148.9% higher than that of the conventional segmental baffle oil cooler with pressure drop increased by 31.6–65.2%. Furthermore, the shell side performance evaluation criterion h/ΔP of the twisted trifoliate tube oil cooler is 1.46 times larger than that of the conventional segmental baffle oil cooler on average. The possible mechanisms responsible for the heat transfer enhancement are analyzed. In addition, the predictive correlations of tube side and shell side of the twisted trifoliate tube bundles for Nu and f are deduced based on the experimental data. Results from current research could provide useful correlations and beneficial guidance for design and application of the longitudinal flow heat exchanger in low Re ranging of 40–250.

Introduction

Shell and tube heat exchangers are widely used in many engineering fields for heating and cooling processes. The characteristic of high viscosity, low Re flow and thick heat transfer boundary layer of lubricating oil result in a low heat transfer performance [1], [2], [3]. In the lubricating oil/water shell and tube heat exchangers, the lubricating oil usually flows in shell side of the oil cooler. The zigzag flow pattern of the conventional segmental baffle heat exchangers induces some disadvantages of hefty pumping power, large recirculation “dead” zones, risk of tube bundle vibration, etc. [4], [5]. Therefore, the research of highly efficient heat exchangers has always been a significant topic in industrial application [6].

Generally, new type of heat transfer tubes and novel shell side structures are the two main approaches to enhance heat transfer of shell and tube heat exchangers. A variety of enhanced heat transfer technologies have been applied to the tube side, such as corrugated tubes [7], [8], twisted tapes [9], [10] and finned tubes [11], [12]. On the shell side, the longitudinal flow heat exchanger is a new style of heat exchanger with a novel tube bundle support structure. This type of heat exchanger alters the shell side flow from traditional zigzag pattern to longitudinal pattern to reduce the fluid-induced vibration, the large pressure drop and dead zones problem [13]. The rod baffle heat exchanger (RBHXs) is a typical longitudinal flow heat exchanger originally proposed by Phillips Petroleum Company [14]. Since then, RBHxs has received extensive attentions [15], [16], [17], [18], [19], [20]. These studies showed that RBHxs has a higher shell side heat transfer coefficient to pressure drop ratio (h/ΔP) and cost-efficiency compared with the conventional segmental baffle heat exchanger. Nevertheless, RBHXs usually needs square arrangement of the tube bundles due to the complex shell side support structure. The shell side voidage of RBHXs is large and difficult to adjust. Hence, the low shell side velocity is still one of the most primary barriers to the application of RBHXs [13], [21], [22]. It is rarely reported in the opening literature that RBHXs is used to enhance the heat transfer with high viscosity fluid under low Re condition.

The development trend of tube bundle supports is to further simplify the support structure. The twisted oval tube heat exchanger (TOTHXs) is another typical type longitudinal flow heat exchanger developed by Dzyubenko [23], [24], [25]. There is no baffle structure in shell side of TOTHXs and the tube bundles are self-supported by adjacent tubes. On the tube side, Yang et al. [26] summarized the correlations for thermal–hydraulic performance of TOTHXs and fitted the unified empirical equations for Re from 600 to 55000. Cheng et al. [27] numerically studied the performance inside the twisted oval tube for Re ranging of 50 to2000. They identified the laminar to turbulent flow transition point was at Re = 500. Yan et al. [28] investigated the heat transfer and pressure drop performance of epoxy flowing in horizontal twisted oval tubes with Re ranging from 20 to 120. The experimental results showed that the twisted oval tubes can enhance the heat transfer of high viscosity fluid. Guo et al. [29] specified and established the correlations of the intensity of secondary flow between the f and Nu. On the shell side, Tan et al. [30] experimentally investigated the heat transfer and pressure drop on shell side of TOTHXs under turbulent condition. A RBHXs is comparatively evaluated. The comparison results illustrated that the shell side h/ΔP of TOTHXs is superior to RBHXs. The heat transfer enhancement mechanism about shell side of TOTHXs was numerically investigated by Tan et al. [31] and Li et al. [32]. The studies showed it is the secondary flow that intensifies the heat transfer performance. Gu et al. [33] numerically studied a novel coupling-vortex chessboard-type square tube layout of the twisted oval tube bundle. Their results found that the coupling-vortex schemes possess higher overall performance compared with the corresponding parallel-vortex schemes. These researches mentioned above have indicated that the twisted oval tube excites the secondary flow and optimizes the distribution of temperature and velocity field. Besides, the special alternating surfaces of the heat transfer surface of twisted oval tubes promote the fluid disturbance, which intensify the heat transfer process. However, TOTHXs have the disadvantages of shell side low turbulence and poor heat transfer coefficient under low Re similar to RBHXs. Liu et al. [34] found the shell side heat transfer coefficient of TOTHXs is only 59.9–74.2% of that of the conventional segmental heat exchangers under the same oil volume flow rate with Re ranging from 50 to 600.

From above it is noted that the shell side heat transfer efficient of the longitudinal flow heat exchanger is poor under the low Re. The existing literature contains seldom experimental study on shell side performance of longitudinal flow heat exchanger with high viscosity fluid, which limits its further development. Wang et al. [35] proposed a novel type of the twisted trifoliate tube based on the twisted oval tube and conducted a numerical calculation on the heat transfer and flow resistance characteristic inside the tube with Re ranging from 4000 to 20000. Tang et al. [36] found the twisted trifoliate tube provides better heat transfer performance than that of the twisted oval tube on tube side, but the correlations of Nu and f with respect to Re were not given. The investigation on heat transfer enhancement of the twisted trifoliate tube has not been sufficient. Additionally, there is no work about shell side performance of the twisted trifoliate tube bundles in the open literature. In view of this, a novel longitudinal flow twisted trifoliate tube oil cooler (TTTOC) is developed and discussed in this paper. The working mediums of tube side and shell side of the novel oil cooler are water and lubricating oil. The Re of water and lubricating oil ranges from 2500 to 17,000 and 40 to 250, respectively. The heat transfer and pressure drop performance on tube side and shell side of the TTTOC are experimentally studied and compared with a conventional segmental baffle oil cooler (SGBOC). The predictive correlations for Nu and f based on the experimental result are obtained, which are beneficial for design and industrial application of the twisted trifoliate tube heat exchangers.

Section snippets

Experimental setup

Fig. 1 shows the schematic diagram of the twisted trifoliate tube, manufactured from a smooth circular tube Φ10 × 1 mm with a length of 1000 mm. The cross section of the twisted trifoliate tube is divided into three lobes zones composed of three 1/2 ellipses and three 1/6 arcs. The adjacent ellipses are connected by transition arcs. The characteristic parameters of the twisted trifoliate tube include twisted pitch P, inscribed circle diameter D, and transition arc diameter d. The specifications

Experimental setup

The configuration and photo of the TTTOC are shown in Fig. 7 and Fig. 8. The twisted trifoliate tubes contact at multiple pointes along the tube bundle length, which perform reliable self-support during the working condition. The partition plate and inner flow distributor are designed to avoid the leakage flow. A TTTOC and a SGBOC are tested in this experimental system. The main geometry parameters of the TTTOC and SGBOC are listed in Table 2. Fig. 9 is the schematic of shell side experimental

Conclusions

In the presented work, the thermal–hydraulic performance of a novel longitudinal flow twisted trifoliate tube oil cooler and a conventional segmental baffle oil cooler have been experimentally studied. The main findings are as follows:

  • (1)

    The tube side Nut and ft of the twisted trifoliate tube increase by 4.7–120.1% and 16.9–62.9% compared to the smooth circular tube under Ret ranging from 2500 to 17000. The secondary flow in the twisted trifoliate tube brings the heat transfer intensification,

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work is supported by the Natural Science Foundation of Guangdong Province (No. 2020A1515011318); Science and Technology Special Project of Guangdong Province (No. 2020ST008); Science and Technology Innovation Project of Foshan National High-tech Zone (No. 2020197000618); “Development of Energy-saving Integrated Technology for Aluminum Manufacturing Equipment“ (Sanshui District of Foshan City Government).

References (39)

Cited by (3)

  • Analysis of heat transfer characteristics and entransy evaluation of high viscosity fluid in a novel twisted tube

    2022, Applied Thermal Engineering
    Citation Excerpt :

    Talebi and Lalgani [13] analyzed the influence of different configuration of twisted tubes on heat delivery effect and claimed that the variable twist spiral tube significantly improved the heat delivery performance. Liu et al. [14,15] utilized the TOT and the twisted trifoliate tube to improve the energy efficiency of the oil cooler, and carried out experiments to prove that the novel oil cooler had excellent performance. Huang et al. [16] concluded that the TOT had a good comprehensive heat transfer intensification effect on oil products with higher viscosity when operating at low Re through experiments.

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