Positive heat flow anomaly in the Carpathian basin

Intensive geothermal investigations in the central Hungarian Tertiary sedimentary basin show uniform high temperature gradients between 45 and 70°C/km. New temperature measurements between 3000–5800 m depth confirm previous values between 400–2000 meters. Sixteen heat flow measurements showed values between 2.0 and 3.3 μcal/cm² s (84 and 138 mW/m² respectively). Sporadic measurements outside the Carpathian basin have shown invariably average or low heat flow and low temperature gradients.The investigation of the crustal structure in Hungary along 5 profiles indicates the depth of the Moho as being between 24.5 and 30.4 km. Comparing the isobaths of the Moho with the temperature gradient map there is an evident relation between high temperature gradients, the consequent high heat flow and the elevated position of the Moho. Areas with high heat flow are found where the Moho is 24.5–26 km deep. The Carpathian basin can be compared with the Black Sea depression where the Moho is 20 km deep.An interesting geothermal similarity exists between the Carpathian basin and the marginal basins of the western Pacific. The Okhotsk, Japan, Shikoku, Parace-Vela basins have a high mean heat flow above 2 μcal/cm² s. In the southwestern Pacific, the Fiji plateau and the Lau basin are also characterized by high heat flow. The Japan and Okhotsk seas may represent a subsidence similar to the Carpathian basin, caused by the uplift of the surrounding mountain ranges e.g., Kurili island arc.     

Hydrogeochemistry and geothermal characteristics of the White Lake basin, South-central British Columbia, Canada

Hydrogeochemistry and geothermal characteristics of the Tertiary White Lake basin are described in order to provide constraints on the hydrogeology and thermal regime of the basin. The basin can be divided into three flow subsystems on the basis of chemical and isotopic variations. The groundwaters evolve chemically from young Ca–Mg–HCO₃ type waters in the shallow surficial sediments to Na-dominated waters in the deeper intermediate system. Surface waters and shallow groundwaters collected from wells completed in overburden have undergone extensive evaporation as evidenced by their enriched δ¹⁸O and δ²H composition. Minor evaporation identified in the isotope composition of groundwater from domestic wells completed in bedrock, as well as from springs, suggests a local to intermediate origin for these waters, and perhaps mixing with shallow evaporative waters. In contrast, the uniform isotope signatures of deep basin waters measured both spatially and vertically suggest recharge at higher elevations, and a much deeper circulation system that is essentially isolated from the shallow subsurface. Chemical geothermometry indicates that spring waters and bedrock well waters have equilibrated at temperatures of less than 20 and 60°C, respectively. Groundwaters encountered by deep diamond drill holes, with equilibration temperatures of less than 80°C, are representative of intermediate flow systems, and may serve to modify the heat flow regime in the basin. Regional groundwater flow within the basin is complex due to numerous faults that exert a strong influence on fluid circulation patterns. Transport of heat in the subsurface, which has resulted in variations in the measured thermal gradients across the basin, occurs either at depths greater than those investigated in this study or has been significantly influenced by the circulation of cooler groundwater in the central part of the basin.     

Buoyancy-induced flow,heat, and mass transfer in a porous annulus

This paper reports on double-diffusive natural convection heat transfer in a porous annulus between concentric horizontal circular and square cylinders. A pressure-based segregated finite volume method is used to solve the problem numerically. The diffusion fluxes are discretized using the MIND fully implicit scheme. Furthermore, a modified pressure correction equation is derived that implicitly accounts for the nonorthogonal diffusion terms, which are usually neglected in the standard SIMPLE algorithm. Results indicate that convection effects increase with an increase in Rayleigh number, Darcy number, porosity, and enclosure aspect ratio. Further, at low Darcy values, porosity has no effect on the flow, temperature, and concentration fields.     

Analysis of the flow structure and heat transfer in a vertical mantle heat exchanger

The flow structure inside the inner tank and inside the mantle of a vertical mantle heat exchanger was investigated using a full-scale tank designed to facilitate flow visualisation. The flow structure and velocities in the inner tank and in the mantle were measured using a Particle Image Velocimetry (PIV) system. A Computational Fluid Dynamics (CFD) model of the vertical mantle heat exchanger was also developed for a detailed evaluation of the heat flux at the mantle wall and at the tank wall. The flow structure was evaluated for both high and low temperature incoming flows and for both initially mixed and initially stratified inner tank and mantle. The analysis of the heat transfer showed that the flow in the mantle near the inlet is mixed convection flow and that the heat transfer is dependent on the mantle inlet temperature relative to the core tank temperature at the mantle level.     

Start-up,heat transfer and flow characteristics of silicon-based micro pulsating heat pipes

A simultaneous visualization and measurement study has been carried out to investigate the start-up, heat transfer and flow characteristics of three silicon-based micro pulsating heat pipes (MPHPs) with the trapezoidal cross-section having hydraulic diameters of 251 μm (#1), 352 μm (#2) and 394 μm (#3), respectively. Experiments were performed under different working fluids, filling ratios, inclination angles (bottom heating mode) and heating power inputs. It is found that (1) the silicon-based MPHPs could start up within 200 s when charged with R113 or FC-72, but they failed to start up at all inclination angle when charged with water or ethanol having lower (dP/dT)_sat, higher viscosity, higher latent heat and higher surface tension at the same temperature. During the start-up period, no obvious nucleation was observed. After the start-up period, MPHPs entered the operation period. The silicon-based MPHP could operate normally even at a Bond number of 0.26 and a hydraulic diameter of 251 μm, both smaller than the corresponding values in literatures; (2) the thermal performance of MPHPs depends greatly on the type of working fluid, filling ratio and inclination angle. At the lower power input, MPHPs charged with R113 showed better thermal performance than that charged with FC-72, however, the latter exceeded the former at the higher power input. For the same working fluid, there existed an optimal filling ratio corresponding to the best thermal performance of MPHPs, which was about 52%, 55% and 47% for MPHPs #1, #2 and #3 at the vertical orientation (90°), respectively. When the MPHPs turned from the vertical to the horizontal orientation, the thermal performance tended to be decreased, indicating that the gravity effect cannot be ignored in these silicon-based MPHPs. In MPHP #3 at the inclination angle from 70° to 90°, there appeared a special thermal resistance curve with two local maximum points, which is absent in the traditional PHPs; (3) in the operation period of larger MPHP #3, nucleation boiling, bulk circulation and injection flow were all observed, while these flow patterns were absent in the smaller MPHPs #1 and #2. Intense liquid film evaporation, instead of bubbles’ generation and expansion which usually activated the oscillation flow in macro-PHPs, drove the two-phase flow in the smaller MPHPs #1 and #2.     

Parametric study of unsteady flow and heat transfer in a pin-fin heat exchanger

A numerical study has been carried out to analyze the unsteady three-dimensional flow and heat transfer in a parallel-plate channel heat exchanger with in-line arrays of periodically mounted rectangular cylinders (pins) at various Reynolds number and geometrical configurations. The three-dimensional unsteady Navier-Stokes and energy equations are solved using higher order temporal and spatial discretizations. The simulations have been carried out for a range of Reynolds number based on cylinder width (180-600) and a Prandtl number of 6.99 (corresponding to water). Conjugate heat transfer calculations have been employed to account for the conduction in the solid cylinder and convection in the fluid. The thermal performance factor (TPF) increases significantly when the flow becomes unsteady. The choice of aspect ratio of the cylinders is judged by their relative increase in friction factor and heat transfer at transitional Reynolds number. The TPF is found to increase with the increase in pitch of the cylinders. The increase in channel height enhances the TPF though the heat transfer decreases at higher channel height.     

The heat transfer and fluid flow of a partially heated microchannel heat sink

Numerical modeling of the conjugate heat transfer in microchannel heat sink is presented. As the most of the cooling applications deals with the partial heated sections, the influence of the heating position on the thermal and hydrodynamic behavior is analyzed. The laminar fluid flow regime and the water as a working fluid are considered. It is observed that partial heating together with variable viscosity has a strong influence on thermal and hydrodynamic characteristics of the micro-heat sink.     

Numerical analysis for flow,heat and mass transfer in film flow along a vertical fluted tube

We conducted a three-dimensional numerical investigation of the flow, heat and mass transfer characteristics of the fluted evaporating tube with films flowing down on both the inside and outside tube walls. Condensation occurs along the outside wall while evaporation takes place on the free surface of the inside film. The three-dimensional transport equations for momentum and energy were solved by using the finite volume method (FVM). The free-surface shape is tracked by using the moving-grid technique that satisfies the space conservation law (SCL). Because of the secondary motion of the fluid, the film becomes thin at the crest whereas it thickens at the valley. The velocity and temperature fields were successfully predicted for various flute shapes.     

Transient thermal structure, turbulence, and heat transfer in a reattaching slot jet flow

The role of turbulent fluctuations on mean heat transfer coefficient in a reattaching slot jet flow is studied experimentally. Convective heat transfer rate and near-wall fluid flow are examined in the recirculation, reattachment, and post-reattachment regions for two nozzle-to-surface spacings of 0.25 and 0.75 times the width of the nozzle bottom plate. In the reattachment region, results indicate a strong correspondence between variances of near-wall velocity fluctuation and peak heat transfer rate for both spacings. Thermal structures that vary in the spanwise direction are identified in the recirculation region from low-frequency transient infrared thermographs of the heated surface. While these thermal structures are confined to regions in the vicinity of nozzle bottom plate for the low nozzle spacing, they span the entire recirculation region at larger spacings. Thermal streaks are observed past reattachment for the larger nozzle spacing, suggesting a periodic breakup and re-formation of the jet curtain. The scaling of heat transfer distribution is affected by the flow structure in the geometrically non-similar area of the recirculating flow beneath the nozzle. A correlation for peak Nusselt number is presented.     

An Investigation of the Swirling Flow and Heat Transfer in a Duct

This paper presents the results of experiments and numerical simulation of the turbulent swirling flow and heattransfer in a duct.The calculated results are in good agreement with data obtained by measurements.It isfound that the swirling flow promotes heat transfer to the wall of the duct;the swirl numbers are dependentupon the vane exit angles of the swirler,distance from the swirler and the duct Reynolds number.But the decayof swirling flow in streamwise direction is related to local Reynolds numbers and is independent of the swirlerexit angle.The swirl flow characteristics presented in this paper may be used for engineering purposes.     

Instability,heat transfer and flow regime in a two-phase flow thermosyphon loop at different diameter evaporator channel

In this study, the influence of different channel geometries on heat transfer, flow regime and instability of a two-phase thermosyphon loop, is investigated. Instabilities in flow regime and heat transfer, at low and high heat fluxes, are observed. Bubbly flow with nucleate boiling heat transfer mechanism, confined bubbly/slug flow with backflow for small channel height (H) and finally slug/churn flow at high heat fluxes are observed. This study shows that flow and thermal instability increases as channel height (H) decreases and also heat transfer coefficient increases with increasing channel height and heat flux. Bubbly flow characterizes the flow regime at high heat transfer coefficients while confined bubbles, backflow and intermittent boiling are more significant for low channel heights with lower heat transfer coefficient and critical heat flux.     

MHD flow and heat transfer in a backward-facing step

The laminar flow of a viscous incompressible electrically conducting fluid in a backward-facing step is investigated under the usual magnetohydrodynamic (MHD) hypothesis. Numerical simulations are performed for Reynolds numbers less then Re = 380 in the range of 0 ≤ N ≤ 0.2, where N is the Stuart number or interaction parameter which is the ratio of electromagnetic force to inertia force. Heat transfer is investigated for Prandtl number ranging from Pr = 0.02 corresponding to liquid metal, to Pr = 7 corresponding to water. It is found through the calculation of the reattachment length that external magnetic field acts to decrease the size of the recirculation zone. Velocity profiles show that, out of the recirculation zone, the basic flow is damped by the magnetic induced force, whereas flow near the walls channel is accelerated. Heat transfer is significantly enhanced by the magnetic field in the case of fluids of high Prandtl numbers.     

Dependence of the blowout limit on flow structure,heat transfer,and pressure loss in a bluff-body micro-combustor

In this study, we numerically investigated the main factors affecting the flame blowout limit of bluff-body micro-combustors with a blockage ratio (δ) varying from 0.3 to 0.8; the combustion performance of these combustors is investigated as well. Measurements from the literature (Fan et al., 2012, Int J Hydrogen Energy, 37, 19,190–19,197) were used to validate the present numerical models. The predicted results are in good agreement with the experimental data, with a relative error of less than 10%. The results show that the blowout limit increases with δ in a non-monotonic manner. The establishment of a low-velocity recirculation behind the bluff body and recirculation of heat and key radicals help increase the flame blowout limit, whereas the stretching of reaction zones has an unfavorable effect. In contrast, heat loss contributes negligibly to the difference between the blowout limits in the micro-combustors for different values of δ. An extra pressure loss or initial power input is required to improve the blowout limits. An available size of the in-built bluff body should be carefully selected to maximize its efficiency and to considerably improve the blowout limit; however, this should be realized while ensuring a low cost of pressure loss when designing a micro-combustor. In general, δ = 0.5 is relatively optimal and recommended for the straight combustion channel discussed herein.     

Combined heat flow and heat generation measurements in the Bohemian massif

All available heat flow data together with temperature gradients and thermal conductivities of rocks from deep holes in the area forming the contact zone between the Bohemian massif and the western Carpathians are summarized. These data include 20 previously published values and 12 new values. The technique of measurement of the underground temperature, as well as the laboratory determination of the coefficient of thermal conductivity is briefly described. The most important result is the increase of the geothermal activity along the Carpathian foredeep from the south to the north and the generally high heat flow in the area of Permo-carboniferous sedimentation known as the Ostrava-Karviná coal basin in the north.     

Mathematical model for turbulent flow,heat transfer,and solidification

A steady‐state, two‐dimensional numerical model has been used to describe coupled liquid steel's turbulent flow and heat transfer with solidification for Fe‐C binary alloy in a crystallizer of inverse casting. The solid‐liquid phase change phenomena have been modeled by using continuum formulations and considering the mushy zone as porous media. The turbulence flow in the crystallizer has been accounted for using a modified version of the low‐Reynolds‐number κ?ε turbulence model. The flow pattern in the liquid zone and the temperature distribution in the solid, mushy, and liquid regions have been predicted. The numerical analysis indicates that the residence time of the mother sheet in the crystallizer is one of the key parameters. The effects of some other main parameters on the solidification behavior have also been studied, such as the thickness and the initial temperature of the mother sheet, and the superheat degree of liquid steel. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(7): 582–592, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10112     

Simulation study of flow and heat transfer in a thermosyphon

By establishing a mathematical model in the thermosyphon system, the numerical simulation method is used for the temperature field, flow field distribution in heat pipe simulated calculation in recent years. In this article, we combine the thermosyphon engineering actuality, build up the Nusselt model, write the visual program with the VB code, and make use of the computer to carry on imitating the calculation. Meanwhile, the calculation predicted temperature profile in the thermosyphon was compared with experimental measurements and a good agreement was observed. Through the research, it can provide theoretical basis for the optimization of heat pipe model in the future.     

CFD modeling of flow and heat transfer in a thermosyphon

In the present study a gas/liquid two-phase flow and the simultaneous evaporation and condensation phenomena in a thermosyphon was modeled. The volume of fluid (VOF) technique was used to model the interaction between these phases. Experiments in a thermosyphon were carried out at different operating conditions. The CFD predicted temperature profile in the thermosyphon was compared with experimental measurements and a good agreement was observed. It was concluded that CFD is a useful tool to model and explain the complex flow and heat transfer in a thermosyphon.     

Second-law analysis of flow and heat transfer inside a microannulus

The purpose of this work is to investigate the entropy generation in a microannulus flow. Fully developed laminar flow is considered with uniform heat flux at the walls. The viscous dissipation effect, the velocity slip and the temperature jump at the wall are taken into consideration. The velocity and temperature profiles are obtained analytically and used to compute the entropy generation rate. The effects of Kn, Br, Br/Ω and r? on velocity, temperature profiles, entropy generation rate and average entropy generation are discussed. The present analytical results for the case with and without the viscous dissipation effect are compared with those available in the literature and an excellent agreement is observed. Entropy generation is shown to decrease with an increase in Kn while increasing Br, Br/Ω and r? results in increasing entropy generation.