Investigation Of Heat Transfer Behavior Research Articles

Fabrication and investigation of heat transfer behavior of copper nanofins by electrodeposition method in plate and frame heat exchangers (PHEs)

Fabrication and investigation of heat transfer behavior of copper nanofins by electrodeposition method in plate and frame heat exchangers (PHEs)

Exploring alteration of near-wellbore geothermal gradient during fluid circulation and production

Abstract The constant undisturbed formation temperature profile controlling heat transfer into the wellbore appears counterintuitive in light of transient cooling of the formation that occurs upon fluid circulation in drilling and also heating during fluid production. This study presents a mathematical model that shows that the heat transfer occurs from the wellbore/formation interface, not from some distance away from the wellbore wherein the initial formation temperature profile remains undisturbed. This new model allows investigation of heat transfer behavior from the formation into the wellbore during drilling or fluid circulation, and from the wellbore into the reservoir in the production mode. Application of the line-source solution for the temperature diffusivity equation for a steady-state system provides the necessary ingredients for computing the temperature behaviors at different times and radii. This line-source solution can be used throughout the wellbore to determine the undisturbed formation temperature, which may be used to obtain the geothermal gradient dependent on the radius and fluid circulation time. Therefore, the initial geothermal gradient works as a time-dependent variable, and the resultant second-order polynomial relationships can describe the undisturbed formation temperature. This study provides the required tools to assess the wellbore heat-transfer behavior and their effect on the wellbore temperature profiles. Also, the new mathematical model illuminates the impact of heat transfer by comparing its performance with the original formulations. Besides, this paper presents a complete derivation of the line-source solution of the temperature diffusivity equation to justify the proposed approach.

A combined CFD/visualization investigation of heat transfer behaviors during geyser boiling in two-phase closed thermosyphon

In order to promote the understanding of geyser boiling in two-phase closed thermosyphon, a combined CFD/visualization investigation was carried out in this work. The widely used phase change model, i.e., Lee model, is improved by introducing the consideration of superheat to increase its prediction performance. CFD modellings of heat transfer behaviors during geyser boiling were performed using both the improved and original Lee model based on VOF method. These results were analyzed and compared to the visualized observations from experimental tests. The experimental results show that a periodic geyser boiling with the cycle time at 80–100 s occurs under the conditions that the flow rate of heating water is controlled at 400 mL/min (95 °C) and cooling water at 300 mL/min (30 °C). The corresponding modelling results in accordance with these experimental conditions suggest that the improved Lee model has a better prediction performance. The rapid slug bubble growth in expulsion period, and the surface evaporation and thermally natural convection in liquid pool during the incubation period are in good agreement with the experimental observations. In addition, the temperature and velocity contours during geyser boiling are comprehensively revealed by use of the improved Lee model.

Numerical Investigation of Heat Transfer Behaviour During TIG Welding of Stainless Steel Pipes for Various Welding Heat Input Conditions

In the present work, tungsten inert gas (TIG) welding was carried out on stainless steel pipe joints and the heat transfer behaviour for various welding heat input was analysed. In this work austenitic stainless steel of grade 304L was used and the experiment was carried out on bead on plate and weld profile was analysed. The bead profile was obtained from the experiment and microstructure was characterized. The bead profile dimensions from the experiment were used in the calibration of heat source model during finite element heat transfer analysis. Based on the calibrated heat source model, TIG welding of stainless steel pipes was analysed. Numerical simulation was considered as conduction heat transfer analysis and weld pool convection was neglected in the model. The non-linear transient heat transfer analysis was carried out on pipes and thermal cycles at various locations were analysed.

Experimental investigation on heat transfer and pressure drop of supercritical water flows in an inclined rifled tube

This paper presents an investigation of heat transfer behavior and pressure drop characteristics of subcritical and supercritical water flows inside an inclined rifled tube for near-supercritical and supercritical flows. The operating pressure range was from 15 to 28MPa, the mass flux range was from 600 to 1000kg/m2s and wall heat flux was from 300 to 500kW/m2. The maximum inner diameter of pipe was 19.5mm and the inclination angle of the tube was 20° with respect to the horizontal plane. The heat transfer to water and pressure drop gradients at various operating pressures for various heat fluxes and mass fluxes were studied. The results show that the effect of mass flux variations on heat transfer at supercritical pressures is more considerable than this effect at subcritical pressures. The same behavior was found for the pressure drop gradient. It was found that as the ratio of the mass flux to the heat flux exceeded 2.46kg/kWs, heat transfer enhancement occurred near the pseudo critical point for supercritical pressures while maximum heat transfer at subcritical pressures occurred at ratio of the mass flux to the heat flux value of 1.65kg/kWs for inclined rifled tube.

Double MRT-lattice Boltzmann model for simulating impinging jet flow and heat transfer

In this paper, the MRT (Multiple Relaxation Time)-D2Q9 model and the MRT-D2Q5 are employed to simulate the flow and heat transfer of laminar confined impinging jet flow. For impinging jet flows, the paper considers the effect of Reynolds numbers and jet-impingement surface distance ratio (H/W) on the flow and temperature fields. As for the investigation of heat transfer behaviors on stagnation Nusselt number, it is evident that the effect of H/W is not significant. The Nu number increases dramatically with increasing Reynolds number. And what’s more, this study presents flow and heat transfer predictions of slot jets impinging on cylinder and obtains distribution of Nusselt numbers around the cylinder for different Reynolds number.

Numerical and experimental investigation of heat transfer behavior in a round tube with the special conical ring inserts

In the present study an experimental investigation was carried out in order to find the role of the conical rings for the heat transfer enhancement and pressure drop change in a pipe with constant heat flux boundary condition. The conical rings were placed in two different arrangements: converging conical ring (CR array) and diverging conical ring (DR array). Also numerical study was performed through Computational Fluid Dynamics (CFD) calculations. The CFD predictions show suitable agreement with the experimental data of Nusselt number but overestimate pressure drop values. The predictions and the experimental results show that in the case of water as working fluid (despite air as working fluid), the conical ring inserts have an unfavorable effect on the enhancement efficiency of the heat-transfer in the heat exchangers.

Experimental Analysis of Hybrid Nanofluid as a Coolant

Investigation of heat transfer behaviour of hybrid nanofluid (HyNF) flow through the tubular heat exchanger was experimentally studied. In this analysis, the effects of thermal characteristics of forced convection, thermal conductivity and heat transfer coefficient were explored. The nanofluid was prepared by dispersing the copper-titanium hybrid nanocomposite (HyNC) in the water. The experiments were performed for various nanoparticle volume concentrations added in the base fluid ranging from 0.1% to 1.0%. The results showed that the convective heat transfer coefficient was found maximum by 48.4% up to 0.7% volume concentration of HyNC.

Heat transfer behaviors of a confined slot jet impingement

An experimental study on heat transfer behaviors of a confined slot jet impingement has been systematically performed. The parametric effects of jet Reynolds numbers and jet separation distance on heat transfer characteristics of the heated target surface are explored. With the measurement of jet mean velocity and turbulence intensity distributions at nozzle exit, two jet flow characteristics at nozzle exit, initially laminar and transitional/turbulent regimes, are classified. As for the investigation of heat transfer behaviors on stagnation, local and average Nusselt number, it is evident that the effect of jet separation distance is not significant; while the heat transfer performance increases with increasing jet Reynolds number. Comparisons of the present experimental data with the existing numerical and experimental results are made. Besides, two new empirical correlations for stagnation and average Nusselt numbers on the heated target surface are also reported in the study. Furthermore, a concept of effective cooling length is introduced to evaluate the average Nusselt number on a finite-length target surface, the existing numerical results are reasonably consistent with the present experimental data.