Flow Heat Transfer In Tubes Research Articles

Thermal-hydraulic analysis of LBE flow in rod bundles with wire spacers based on heat transfer framework of OpenFOAM

The wire spacer allows for a compact layout in the core of lead-cooled fast reactor (LFR). However, it also introduces complexity to the flow and heat transfer of the coolant, lead-bismuth eutectic (LBE). This paper aims to analyze the effect of wire spacer in rod bundle and the applicability of heat transfer framework to LBE flow. Three Reynolds-Averaged Navier–Stokes (RANS) turbulence models with two representative turbulent Prandtl number (Prt) 1.5 and 2.0 are employed within the framework of OpenFOAM. The sensitivity of the models is examined based on turbulent heat transfer in tube flow. The simulations considered with an extensive mesh sensitivity study were analyzed. The buoyantSimpleFoam solver is compared with direct numerical simulation (DNS) data. Thermal-hydraulic analysis are conducted, considering temperature, velocity distribution, and local Nusselt (Nu) number, and pressure drop based on 7-rod and 19-rod bundle with wire spacers. The influence of wire initial starting angles from 0°, 10°, 20°, 30°, 40°, 50° on heat transfer is carried out. The study reveals that an optimum angle range from 20° to 40° exists in the sub-channels. This work validates the basic heat transfer solver for LBE using OpenFOAM.

CFD analysis of particle transport in axi-symmetric tube flows under the influence of thermophoretic force

In this study, we developed two frameworks to investigate the thermophoretic particulate deposition in non-isothermal tube flows conveying particles ranging from 10 to 300nm; a one dimensional model where the variables are assumed to be uniform in each cross section perpendicular to the tube axis and an axi-symmetric model where the aforementioned assumption is relaxed. In the one dimensional model, the rate of mass deposition along the inner surface of the tube is computed based on the local thermophoretic velocity of the particulate phase at the wall. This velocity is proportional to the radial gradient of the temperature at the wall and is calculated via some empirical correlations for heat transfer in tube flows. In the axi-symmetric model, the rate of deposition is computed through the Fick’s law after solving the species transport equation for the solid phase. We included the formation of the soot layer through moving the gas–solid interface in both models. The tube effectiveness (the ratio of actual heat transfer to the maximum possible heat transfer) decreases due to the formation of the layer. Model outputs including deposited mass along the tube wall and the tube effectiveness drop have been compared against experiments. While the computed results through both models agree with the trend of experimental data, the axi-symmetric results are closer to the experiments in most cases. The calculated deposited mass is smaller (and closer to experiments) for the axi-symmetric model compared to the one dimensional model in all cases. This indicates that the axi-symmetric model estimates the deposited mass more accurately.

Thermal analysis of mass concrete embedded with double-layer staggered heterogeneous cooling water pipes

Abstract Removal of hydration heat from mass concrete during construction is important for the quality and safety of concrete structures. In this study, a three-dimensional finite element program for thermal analysis of mass concrete embedded with double-layer staggered heterogeneous cooling water pipes was developed based on the equivalent equation of heat conduction including the effect of cooling water pipes and hydration heat of concrete. The cooling function of the double-layer staggered heterogeneous cooling pipes in a concrete slab was derived from the principle of equivalent cooling. To improve the applicability and precision of the equivalent heat conduction equation under small flow, the cooling function was revised according to its monotonicity and empirical formulas of single-phase forced-convection heat transfer in tube flow. Considering heat hydration of concrete at later age, a double exponential function was proposed to fit the adiabatic temperature rise curve of concrete. Subsequently, the temperature variation of concrete was obtained, and the outlet temperature of cooling water was estimated through the energy conservation principle. Comparing calculated results with actual measured data from a monolith of an arch dam in China, the numerical model was proven to be effective in sufficiently simulating accurate temperature variations of mass concrete.

Enhancement of laminar and transitional flow heat transfer in tubes by means of wire coil inserts

This work presents an extensive experimental study on three wire coils of different pitch inserted in a smooth tube in laminar and transition regimes. Isothermal pressure drop tests and heat transfer experiments under uniform heat flux conditions have been carried out. The friction factor increases lie between 5% and 40% in the fully laminar region. The transition from laminar flow to turbulent flow is continuous, without the instabilities and the pressure drop fluctuations that a smooth tube presents. Heat transfer experiments have been performed in the flow ranges: Re = 10 – 2500 , Pr = 200 – 700 and Ra = 3 × 10 6 – 10 8 . At Reynolds numbers below 200, wire coils do not enhance heat transfer with respect to a smooth tube. For Reynolds numbers between 200 and 1000, wire coils remarkably increase heat transfer. At Reynolds numbers above Re ≈ 1000 – 1300 , transition from laminar to turbulent flow takes place. At Reynolds number around 1000, wire inserts increase the heat transfer coefficient up to eight times with respect to the smooth tube. A performance comparison between wire coils and twisted tape inserts has shown that wire inserts perform better than twisted tapes in the low Reynolds number range: Re = 700 – 2500 .

Oscillation-controlled heat-transport tube (heat transfer coefficient in tubes in heating and cooling regions)

In the present study, heat transfer coefficients of oscillatory flow at inner surfaces of the heating and cooling regions of oscillation-controlled heat-transport tubes (OCHTs) are investigated numerically. The numerical simulation is conducted under the following three conditions for the tube walls at the heating and cooling regions: isothermal, extremely thin, and actual wall systems. Based on the numerical results and Hausen's correlating equation for laminar flow heat transfer in tubes, a correlating equation of the heat transfer coefficient is developed which can be generally applied to these three conditions. Next, using this correlating equation and the authors' simplified model of overall thermal resistance in OCHTs, heat-transport rates are predicted, and it is found that the predicted results are in good agreement with the numerical results. Finally, numerical simulation is conducted also to compare the heat-transport rates of OCHTs with those of the conventional forced circulation type under the same pumping power. The results indicate that there exist oscillatory flow regions in which the heat-transport rate of the phase-shifted OCHTs is larger than that of the conventional circulation type. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(6): 415–430, 1998

Physical Properties and Heat Transfer in Tube Flows of Non-Newtonian Fluids

Physical Properties and Heat Transfer in Tube Flows of Non-Newtonian Fluids

Oscillation-Controlled Heat Transport Tube. Heat Transfer Coefficient in Tubes at Heating and Cooling Regions.

In the present report, first, heat transfer coefficients of oscillatory flow at inner surfaces of the heating and cooling regions of oscillation controlled heat transport tubes (OCHTs) are investigated numerically. The numerical simulation is conducted under the following three conditions for the tube walls at the heating and cooling regions : isothermal, extremely thin and actual wall systems. Based on the numerical results and Hausen's correlating equation for laminar flow heat transfer in tubes, a correlating equation of the heat transfer coefficient is developed which can be generally applied to these three conditions. Next, using this correlating equation and the author's simplified model of overall thermal resistance in OCHTs, heat transport rates are predicted, and it is found that the predicted results are in good agreement with the numerical results. Finally, numerical simulation is conducted also to compare the heat transport rates of OCHTs with those of the conventional forced circulation type under the same pumping power. The results indicate that there exist oscillatory flow regions in which the heat transport rate of the phase shifted OCHTs is larger than that of the conventional circulation type.

Augmentation of Laminar Flow Heat Transfer in Tubes by Means of Wire Coil Inserts

Experimental studies have been carried out on isothermal pressure drop and convective heat transfer to servotherm medium grade oil in laminar flow in one smooth tube and seven wire coil-inserted tubes of varying wire diameter and pitch of wire coil. The performance of these wire coil inserted tubes has been evaluated by two different criteria based on the objective of either maximizing heat transfer rate or minimizing exchanger size. The results indicated that as much as fourfold improvement can be obtained in laminar flow heat transfer coefficient using these tubes.

Augmentation of Laminar Flow Heat Transfer in Tubes by Means of Twisted-Tape Inserts

Heat transfer coefficients for laminar flow of water and ethylene glycol in an electrically heated metal tube with two twisted-tape inserts were determined experimentally. The Nusselt number for fully developed flow was found to be a function of tape twist ratio, Reynolds number, and Prandtl number. These Nusselt numbers were as much as nine times the empty tube constant property values. The correlation of these data is in fair agreement with the only available analytical predictions. The friction factor is affected by tape twist only at high Reynolds numbers, in accordance with analytical predictions. The performance of these augmented tubes is compared with that of empty tubes under similar heating conditions.

Reduction of turbulent heat transfer in tube flows of low-concentration polymer solutions

Reduction of turbulent heat transfer in tube flows of low-concentration polymer solutions