Influence of Longitudinal Fin Tubes Arrangement in LNG Ambient Air Vaporizers on the Wind Load

The article presents the results of computational fluid dynamics (CFD) analysis of the wind action on liquefied natural gas (LNG) ambient air vaporizers (AAVs). A study concerning AAV with a 6 × 6 tubes array is presented to demonstrate how the distribution of longitudinal finned tubes and wind direction affect the average load and wind pressure acting on the vaporizer structure. The main goal of the study is to estimate the wind load on the structure and wind pressure on individual tubes depending on the pitch of the tubes arrangement. The above parameters are crucial for the strength analysis of the vaporizer structure. The derived analysis results provide important data on the variation of pressure on individual tubes, wind velocity inside AVV structure and indicate a significant increase in the average wind load acting on the structure for a wind direction of 45 degrees compared to a perpendicular direction.

Influence of Fins Number and Frosting on Heat Transfer through Longitudinal Finned Tubes of LNG Ambient Air Vaporizers

The use of cryogenic liquefied gasses in industry is constantly increasing both for process purposes and for power supply needs. The liquefied natural gas (LNG) is stored at cryogenic temperature and its immediate use in gaseous form requires its evaporation. The heat needed to cause a phase change is usually delivered by means of vaporizers. This paper presents a numerical analysis of the influence of the fins number and frost accumulated within the fins surface on the heat transferred through the aluminum finned tubes of LNG ambient air vaporizers. The calculations were carried out applying finite element thermal analysis within Ansys software as well as using an analytical approach. As a result, the heat rate per unit length of the finned tube was obtained. The results were compared for different numbers of longitudinal fins both without frost and for total frosting of the tubes.

Applicability of The Equivalent Diameter Approach to Estimate Vortex Shedding Frequency and Acoustic Resonance Excitation From Different Finned Cylinders In Cross-Flow

This article explores the applicability of utilizing different equivalent diameter (Deq) equations to estimate the vortex shedding frequency and onset of self-excited acoustic resonance for various types of finned cylinders. The focus is on three finned cylinder types that are commonly used in industrial heat exchangers: straight, twist-serrated, and crimped spirally finned cylinders. Within each type of fins, at least three different finned cylinders are investigated. The results indicate that at off-resonance conditions, utilizing the appropriate equivalent diameter collapses the Strouhal number data within the typical Strouhal number variations of an equivalent diameter circular, bare cylinder. However, when acoustic resonance is initiated, the onset and the peak of resonance excitation in all of the finned cylinder cases generally occurred at a reduced flow velocity earlier than that observed from their equivalent diameter bare cylinders. This suggests that although utilizing the appropriate equivalent diameter can reasonably estimate the vortex shedding frequency away from acoustic resonance excitation, it cannot be used to predict the onset of acoustic resonance in finned tubes. The findings of this study indicate that the effective diameter approach is not sufficient to capture the intrinsic changes in the flow-sound interaction mechanism as a result of adding fins to a bare cylinder. Thus, a revision of the acoustic Strouhal number charts is required for finned tubes of different types and arrangements.

An Investigation of Heat Transfer and Pressure Drop Enhancement of Various Perforated Circular Finned Tubes at Different Tube Tilt Angles

The thermal and flow performance of the circular annular finned tube heat exchanger with perforated fins were investigated numerically using ANSYS Fluent 2020 software, RNG k-e model with enhanced wall treatment, global performance criterion was introduced as evaluation factor of the heat exchanger performance, the parameters to be investigated were the number of holes, size of hole, tilt angle of the finned tube, fin height and spacing between fins. Agreement was found with literature that the tilt angle causes increase in heat transfer rate and increase in the pressure drop as well, but the change the global performance criterion as function to tilt angle depends on the fin heights, for higher fin heights the effective change of the pressure drop become greater than the increase in the heat transfer rate and the contrast occur in the cases of smaller fin heights, we have found that the perforation in tilted annular circular finned tubes causes an increase in the heat transfer rate and an enhancement in the total heat exchanger performance, increasing the number of holes will enhance the performance of the heat exchanger and the spacing increase reduces the heat exchanger performance.

Convective Heat Exchange of Single-Row Bundles from Tubes with Rolled Aluminum Fins of Various Height at a Low Values of the Reynolds Number

The experimental study of the heat flow intensity of a single-row horizontal air-cooled tubular bundle of heat exchanger with spiral aluminum rolling fins at low Reynolds numbers (Re < 2000) is performed. The geometrical dimensions of the bimetallic finned tubes of the bundle, the following: the outer diameter of the fins d = 56.0 mm; the diameter of the tube at the base d0 = 26.8 mm; fin height h = 14.6 mm; pitch of fins s = 2.5 mm; the average fin thickness Δ = 0.5 mm; the coefficient of finned tubes φ = 19.3; heat transfer length l = 300 mm. The outer diameter of the load-bearing steel tube dн = 25 mm; wall thickness d = 2 mm. The research was carried out by the method of full thermal modeling at a specially designed experimental stand with electric heating of tubes and an exhaust shaft installed above the bundle. The air flow rate through the bundle was regulated by changing the height and cross-sectional area of the exhaust shaft. Calibration experiments were carried out and confirmed the reliability of the data obtained. Then the fins were sanded so to form new types of tubes, which were arranged in a single-row six-tube bundle with a constant relative cross-step σ1 = S1/d = 1.14 = const, and the thermal studies were repeated. As a result, a generalized criterion equation for heat transfer of a finned horizontal single-row bundle at small Reynolds numbers for various heights of the tube finning h = 0-14.6 mm was obtained. The effective height of the tube finning (h = 8 mm) for a single-row horizontal bundle was determined by dimensional and metal-intensive criteria.

Convective instability of air flows in the exhaust shaft above a four-row finned beam

Herein, multidirectional quasiperiodic air flows in an exhaust shaft above a four-order horizontal bundle consisting of bimetallic finned tubes used to remove heat in heat exchangers are considered. Modeling of the air movement is carried out on the basis of equations for thermogravitational convection in the Boussinesq approximation. It takes into account the viscosity of the air and the dependence of the air density on the temperature. An interpretation of quasiperiodic airstreams is proposed on the basis of Rayleigh – Bénard convection, as a result of which regular structures, called Rayleigh – Bénard cells, are formed in a liquid or gas. Rayleigh – Bénard cells are an analytical solution to the problem of the stability of hydrodynamics flows in the linear approximation. The appearance of two-dimensional (convective rolls) and threedimensional (rectangular cells) is possible. To estimate the number of emerging structures, the critical Rayleigh numbers were calculated, which characterizes the transition from an unstable mode of the convective fluid flow to a stable mode. For two experiments, the experimental Rayleigh numbers are compared with their critical values. The differences between the experimental conditions and the ideal boundary conditions used in the calculations and the partial destruction of quasiperiodic structures as a result of this are also discussed.