Equivalent Diameter for Predicting Vortex Shedding of Finned Cylinders in Cross-Flow

Sonare

2023

MMMS

PurposeThe prediction of critical velocity at instability threshold for shell and tube heat exchangers is important to avoid failure of tubes as a result of flow-induced vibrations due to water cross flow. The flow-induced vibration in finned tube heat exchangers is affected by various parameters such as fin height, fin pitch, fin material, tube array, pitch ratio, fin type, fluid velocity etc. In this paper, an experimental investigation of fluid elastic instability in shell and tube heat exchangers is carried out by subjecting normal square finned tube arrays of pitch ratio 1.79 to water cross flow.Design/methodology/approachThe five tube arrays, namely plain array, two finned tube arrays with 3 fpi and 9 fpi fin density, and two finned tube arrays with 3 mm and 6 mm fin height are tested in the experimental test setup with water flow loop and vibration measurement system. The research objective is to evaluate the effect of fin density and fin height on the instability threshold. The critical velocity at instability threshold is determined to characterize the fluid elastic instability behavior of different tube arrays. The vortex shedding behavior of the tube arrays is also studied by determining Strouhal number corresponding to the small peaks before fluid elastic instability.FindingsThe fluid elastic instability behavior of the tube arrays was found to be the function of fin tube parameters. The experimental results indicate that an increase in fin density and fin height results in delaying the instability threshold for finned tube arrays. It is also observed that critical velocity at instability is increased for finned tube arrays compared to plain tube arrays of the same pitch ratio. The design modifications in the outer box have resulted in further reduction in the natural frequency. This enabled to reach clear instability for all the five-tube arrays.Originality/valueThe research data add the value to the present body of knowledge by knowing the effect of fin height and fin density on the fluid elastic instability threshold of normal square finned tube arrays subjected to water cross flow.

Section: Resultsmentioning

confidence: 99%

Effect of fin density and fin height on flow-induced vibration behavior of finned tube arrays subjected to water cross flow

Sonare

2023

MMMS

“…The effective tube diameter compares the experimental results with the theoretical ones. The effective diameter depends on the fin thickness and fin pitch of the tube (Alziadeh and Mohany, 2021). For the present experimental condition, the equivalent diameter is obtained using the equation proposed by Mair et al (1975): …”

Section: Measurement Methodologymentioning

confidence: 99%

Fluid elastic instability and vortex shedding in finned tube arrays: the effects of tube material and fin density

Yadav¹,

Mohanty

2023

WJE

Purpose The purpose of this paper is to present investigations on the significant influence of the tube material and fin density on fluid elastic instability and vortex shedding in a parallel triangular finned tube array subjected to water cross flow. Design/methodology/approach The experiment was conducted on finned tube arrays with a fin height of 6 mm and fin density of 3 fins per inch (fpi) and 9 fpi. A dedicated setup has been developed to examine fluid elastic instability and vortex shedding. Nine parallel triangular tube arrays with a pitch to tube diameter ratio of 1.78 were considered. The plain tube arrays, coarse finned tube arrays and fine finned tube arrays each of steel, copper and aluminium materials were tested. Plain tube arrays were tested to compare the results of the finned tube arrays having an effective tube diameter same as that of the plain tube. Findings A significant effect of fin density and tube material with a variable mass damping parameter was observed on the instability threshold. In the parallel triangular finned tube array subjected to water cross flow, a delay in the instability threshold was observed with an increase in fin density. For steel and aluminium tube arrays, the natural frequency is 9.77 Hz and 10.38 Hz, which is close to each other, whereas natural frequency of the copper tubes is 7.40 Hz. The Connors’ stability constant K for steel and aluminium tube arrays is 4.78 and 4.87, respectively, whereas it is 5.76 for copper tube arrays, which increases considerably compared to aluminum and steel tube arrays. The existence of vortex shedding is confirmed by comparing experimental results with Owen’s hypothesis and the Strouhal number and Reynolds number relationship. Originality/value This paper’s results contribute to understand the effect of tube materials and fin density on fluid elastic instability threshold of finned tube arrays subjected to water cross flow.

“…The fins are not extensively modeled but are treated as a plain tube with an “effective diameter”. The effective diameter “ d eff ” depends on the fin pitch to the fin diameter ratio (Alziadeh and Mohany, 2021). For the tested tube arrays, the effective diameter of the tube based on volume is given as follows:where “ d b ” is the base diameter of the tube, “ d f ” is the fin diameter, “ p f ” is fin pitch, and “ t ” is the fin thickness.…”

Section: Methodology and Data Reductionmentioning

confidence: 99%

Investigation on vibration parameters in aluminum finned tube arrays subjected to water cross flow

Yadav

Mohanty

2022

MMMS

PurposePredicting the critical velocity is crucial at the instability threshold for shell and tube heat exchangers in order to prevent tube failure due to vibrations. In this study, the vibration response of an aluminum tube bundle subjected to water cross flow was analyzed experimentally. Aluminum tubes are preferred over steel tubes because of aluminum tubes' excellent corrosion resistance, ease of manufacture, and high thermal efficiency.Design/methodology/approachThe fluid elastic instability and vortex shedding mechanisms in a finned tube array of aluminum tubes with a base tube diameter of 19.05 mm and pitch of 34 mm were investigated. The current study considers parallel triangular finned tube arrays with fin heights of 3 mm and 6 mm with a uniform fin thickness and fin pitch. The plain tube array was tested to compare the finned tube array results. The tube vibration response was measured using an accelerometer mounted on the middle tube of the third row. In order to define the fluid elastic instability behavior of various tube arrays, the critical velocity at the instability threshold is measured. By finding the Strouhal number at the small peaks before instability, the vortex shedding behavior of the tube arrays is examined.FindingsThe results reveal that the critical velocity at instability for coarse finned tube arrays increases as the fin height increases. The effect of the tube material is evaluated by comparing the results with those previously reported for parallel triangular tube arrays made of steel. Finally, the occurrence of vortex shedding in a tube array is confirmed based on the Reynolds number and Strouhal number relationship. The instability constant K for the plain tube array of steel and aluminum material are 4.97 and 4.87, respectively.Originality/valueThis paper provides the research findings on the effect of fin height on coarse density finned tube array. This will add substantial knowledge to the literature in the field of fluid elastic instability and vortex shedding, which is needed for the safe functioning of shell and tube heat exchangers.