Heat flow in some regions of Siberia and the Far Eastern USSR

New heat flow values for three different geological regions (east Kamchatka, the Baikalian rocky area and the Altai-Sayan folded zone) have been obtained.The ranges of heat flow variations for each region are respectively: 39–66, 38–80 and 34–69 mW/m² (0.93–1.56; 0.9–1.9; 0.82–1.63 μcal/cm² sec). Heat flow anomalies have been established for the east-Baikalian region, 72 mW/m² (1.7 μcal/cm² sec) and the west Trans-Baikalian region, 59 mW/m² (1.4 μcal/cm² sec).A correlation has been established between heat flow and intensity of neotectonic movements for the Baikalian rift zone and the adjoining areas. The higher flow values correspond to the structural elements of the highest activity of Neogene and Quaternary.     

Terrestrial heat flow measurements near rosignano solvay (Tuscany), Italy

Heat flow measurements were made in three wells close together on the Tyrrhenian coast of Tuscany. The average value of the temperature gradient was 62.8 °C/km, that of thermal conductivity of the rocks was 3.79 mcal/(cm s °C). The heat flow obtained was 2.55 μcal/(cm²3) (107 mW/m²).These are values corrected for local effects (palaeoclimatic variations, the influence of the sea). In particular, a correction was made for the climatic variations of the last 10,000 years based on climatological evidence.     

Heat flow in Albania

As part of a joint geothermal project between Albania and the Czech Republic, a field expedition was organized to Albania in summer 1993 to measure temperature profiles in selected boreholes and to collect rock samples to determine their thermal conductivity. Fourteen localities were visited and nine detailed temperature-versus-depth profiles were obtained. These results were completed with numerous industrial temperature records from other deep holes. The regional patterns of temperatures at 100 m depth and of characteristic near-surface temperature gradients were constructed, and the effect of the topography on the subsurface temperature field was assessed to calculate a total of 49 heat flow density data. A generally low geothermal gradient exists in all of the country, ranging from 7–11 mK/m in the synclinal belt, 11–13 mK/m in southernmost Albania, to a maximum of 18–20 mK/m in the central part of the Pre-Adriatic Depression. These values correspond to a low heat flow zone of 30 to 45–50 mW/m² extending from the north and bordering the Adriatic coast. Heat flow generafly increases from west to east, but its distribution in the Inner Albanides is not clear.     

Temperature–depth relationships based on log data from the Los Azufres geothermal field,Mexico

Equilibrium temperatures based on log data acquired during drilling stops in the Los Azufres geothermal field were used to study the relationship between temperature, depth and conductive heat flow that differentiate production from non-production areas. Temperature and thermal conductivity data from 62 geothermal wells were analyzed, displaying temperature–depth, gradient–depth, and ternary temperature–gradient–depth plots. In the ternary plot, the production wells of Los Azufres are located near the temperature vertex, where normalized temperatures are over 0.50 units, or where the temperature gradient is over 165°C/km. In addition, the temperature data were used to estimate the depth at which 600°C could be reached (5–9 km) and the regional background conductive heat flow (≈ 106 mW/m²). Estimates are also given for the conductive heat flow associated with the conductive cooling of an intrusive body (≈ 295 mW/m²), and the conductive heat flow component in low-permeability blocks inside the reservoir associated with convection in limiting open faults (from 69 to 667 mW/m²). The method applied in this study may be useful to interpret data from new geothermal areas still under exploration by comparing with the results obtained from Los Azufres.     

Micro‐bubble emission boiling from horizontal and vertical surfaces to subcooled parallel flow water

Heat removal of more than 10 MW/m² in heat flux has been required in high‐heat‐generation equipment in nuclear fusion reactors. In some conditions of water subcooling and velocity, there appears an extraordinary high heat flux boiling in the transition boiling region. This boiling regime is called micro‐bubble emission boiling (MEB) because many micro‐bubbles are spouted from the heat transfer surface accompanying a huge sound. The study intent is to obtain heat transfer performance of MEB in horizontal and vertical heated surfaces to parallel flow of subcooled water, comparing with CHF of this system. Three types of MEB with different heat transfer performance and bubble behavior are observed according to the flow velocity and liquid subcooling. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(2): 130–140, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10077     

Surface heat flow density at the phlegrean fields caldera (SOUTHERN ITALY)

The Phlegrean Fields area is a Holocene caldera located west of Naples, southern Italy. The recent post-caldera activity is characterized by several eruptive centers inside the collapsed area. In order to investigate the still active volcanic processes, surface heat flow measurements were carried out in 1995 in 30 sites of the Phlegrean Fields, and a heat flow map compiled. Filtering of the map reveals some well-defined anomalies superimposed on a general southward-increasing trend. Local anomalies are related to small magma bodies, whereas the observed general trend has been attributed to the effect of groundwater flow. This effect was calculated and removed. The undisturbed mean value of the surface heat flow density in the eastern sector is 149 mW\m², which is above the regional value of 85 mW\m² assigned to the eastern part of the Tyrrhenian Sea, and which is probably influenced by a very large, deep magmatic body.     

Heat flow map of South America

The results of geothermal investigations carried out in South America have been compiled with the purpose of preparing regional maps of terrestrial heat flow. The compilation revealed that 655 heat flow values had been determined, giving an overall data density of 37/10⁶ km² and a representative mean heat flow of 63+-36 mW/m². The quality of the data set is variable, depending on the nature of the primary geothermal data, and the geographic distribution of the data set is also non-uniform. In spite of such difficulties a careful analysis of the data set, following suitable priority schemes, has allowed not only the determination of reliable mean heat flow values for a large number of major geological structures in South America, but also the preparation of mosaics of regional heat flow variations. Heat flow is extremely variable in the Cordilleran regions, with the eastern and southern parts having relatively high values compared to the western and northern parts. The general trend of increasing heat flow from the western coastal regions towards inland areas is interrupted by a N-S trending low heat flow belt in the Pre-Cordilleran basins. In the eastern part of the continent heat flow is low to normal (<75 mW/m²) but there are indications that in the Patagonian Platform it is higher than in the Brazilian Platform. There are, however, several isolated localities of high heat flow in the northeastern and south-central parts of Brazil. The Mesozoic rift basins (Potiguar, Recôncavo and Taubaté) are also characterized by relatively high values.In order to examine the tectonic significance of variations in the regional geothermal regime, heat flow maps have been prepared using manual and automatic contouring methods. The comparative study of automatic contour maps generated by means of a variety of data interpolation and gridding schemes has led to the identification of some geothermal features that are believed to be related to tectonic processes affecting the South American continent. Prominent among these are E-W trending belts of low heat flow in northern Peru and in central Chile (extending into the Sierras Pampeans in Argentina), as well as high heat flow belts in northern Chile (extending into the Altiplano in Bolivia) and southern Chile (extending into western Argentina). The low heat flow belts coincide approximately with zones of sub-horizontal subduction, while the high heat flow belts are situated in regions of high-angle subduction. Some of these features correlate well with the results of studies on anelastic attenuation, electrical resistivity distribution and some patterns of global seismic tomography. On the other hand, many of these features are not evident in the recent spherical harmonic analysis of global heat flow, which suggests that the use of empirical predictors based on a heat flow-age relation in devising global heat flow maps should be restricted to tectonically stable areas.     

Thermal conduction between a heated microcantilever and a surrounding air environment

This paper investigates transient heat conduction between a heated microcantilever and its air environment. Continuum finite element simulations allow detailed analysis of heat flow within and from the resistively heated microcantilever. Heat generation of 8 mW excites the cantilever with heating that is either steady, pulse, sinusoidal, or pulse duty cycle. The time-averaged heat conduction from the cantilever leg to the nearby air is typically two to six times greater than the heat conduction from the heater to the air. The cooling time constant increases as the pulse heating time increases; for heating times of 1–1000 μs, the cooling time ranges 4.6–70 μs. The effective heat transfer coefficients around the heater and around the leg are considerably large; on the order of 1 kW/m² K. This study of heat transfer between a microcantilever and its surrounding air environment will aid the design and operation of microcantilever heaters.     

Super-high heat flux removal using sintered metal porous media

Introduction Recently there have been a demand for the technique to efficiently and steadily cool down extremely high heat flux of over 10 MW/m2, to fulfill not only the needs for plasma facing components in nuclear fusion reactors, but also the needs associated with sophisticated computers or downsizing of such devices as high-density laser equipment and power devices. However, existing cooling techniques in such high heat loading environment are basically based on high speed and highly subc…     

Zeolitic imidazolate framework ZIF-67 grown on NiAl-layered double hydroxide/graphene oxide as cathode catalysts for oxygen reduction reaction in microbial fuel cells

In this study, the cathode catalysts for microbial fuel cells (MFCs) were successfully synthesized by two-step feeding method. NiAl-layered double hydroxide (LDH) nanoparticle was attached efficiently on the surface of graphene oxide (GO) in situ, zeolitic imidazolate framework (ZIF-67) was modified on LDH surface layer; Highly crystalline NiAl-LDH/GO@ZIF-67 composite was flawlessly prepared, nano-hybrid had (003), (006), (011), (112) and (222) characteristic crystal planes attribute to NiAl-LDH/GO and ZIF-67 by X-ray diffraction (XRD), and the sheet-like structure and polyhedral structure were observed. The NiAl-LDH/GO@ZIF-67 nano-hybrid was rich in metal elements and provides a wealth of electrochemical active sites by EDS test. The study displayed that the maximum output voltage of NiAl-LDH/GO@ZIF-67-MFC was 516 mV and the stabilization time could last for about 8 d. The maximum output power was 501.26 mW/m², which was 1.31 times of NiAl-LDH/GO-MFC (381.92 mW/m²) and 2.76 times of ZIF-67-MFC (181.48 mW/m²). The GO with high conductivity was used as the substrate to ensure the stability of electrode cycle and the efficiency of power generation, the laminar structure of NiAl-LDH provided the specific surface area for the reaction, which facilitated the transport of electrons. The good structure of ZIF-67 increased the active sites of the composite. The excellent properties of the composites promoted the electrochemical stability and electricity production output of MFC. This study provided a method for the further application of MFC in the wastewater field.     

Effect of hydrogen producing mixed culture on performance of microbial fuel cells

This study examined the influence of H₂-producing mixed cultures on improving power generation using air-cathode microbial fuel cells (MFCs) inoculated with heat-treated anaerobic sludge. The MFCs installed with graphite brush anode generated higher power than the MFCs with carbon cloth anode, regardless heat treatment of anaerobic sludge. When the graphite brush anode-MFCs were inoculated selectively with H₂-producing bacteria by heat treatment, power production was not improved (about 490 mW/m²) in batch mode operation, but for slightly increased in carbon cloth anode-MFCs (from 0.16 to 2.0 mW/m²). Although H⁺/H₂ produced from H₂-producing bacteria can contribute to the performance of MFCs, suspended biomass did not affect the power density or potential, but the Coulombic efficiency (CE) increased. A batch test shows that propionate and acetate were used effectively for electricity generation, whereas butyrate made a minor contribution. H₂-producing mixed cultures do not affect the improvement in power generation and seed sludge, regardless of the pretreatment, can be used directly for the MFC performance.     

Study on falling film generation heat transfer of lithium bromide solution in vertical tubes

Falling film generation process in lithium bromide absorption refrigeration generation system is researched in this paper. To describe the coupled heat and mass transfer of laminar falling film in vertical generation tube, a mathematical model is developed, in which the effect of mass transfer on heat transfer is carefully evaluated. Moreover, an equation related Re number with solution volume flow was also obtained in given conditions. We carried out the experiments with the mass fraction of the inlet solution LiBr being 49.5% and obtained an empirical correlation of heat transfer with the film Re number and heat flux in different volume flow. Specifically, when 5kW/m² 2 and Re<500 the heat transfer correlation is given as: h=14009.87qw^0.0764Re^−0.5391.     

Evaluation of Jet Impingement,Spray and Microchannel Chip Cooling Options for High Heat Flux Removal

Thermal management for high heat flux removal from microelectronic chips is gaining critical importance in many earth-based and space-based systems. Heat fluxes greater than 1 MW/m² (100 W/cm²) have already been realized in high-end server applications, while cooling needs in next generation chips and advanced systems such as high-power electronics and electrical systems, pulsed power weapons systems, solid-state sensors, and phased-array radars are expected to reach 5–10 MW/m² (500–1000 W/cm²). After evaluating the contributions from different thermal resistances in the chip-to-ambient thermal path, this paper presents a critical review and research recommendations for three prominent contending technologies: jet impingement, spray cooling, and microchannel heat sinks.     

Cathode catalyst selection for enhancing oxygen reduction reactions of microbial fuel cells: COF-300@NiAl-LDH/GO and Ti3AlC2/NiCoAl-LDH

In this study, a cathode catalyst for microbial fuel cells (MFCs) was successfully prepared by a simple step-by-step hydrothermal method. Graphene oxide (GO) and layered double hydroxide (LDH) composite substrate and three-dimensional covalent organic framework materials (COF-300) grown vertically on the surface were observed. (003), (006), (012), (018), (110) were the obvious crystal plane of the composite COF-300@NiAl-LDH/GO. C, O, N, Ni, Na, Al and other elements existed on the surface of the composite. The maximum power density produced by COF-300@NiAl-LDH/GO-MFC was 481.69 mW/m², which was 1.22 times of Ti₃AlC₂/NiCoAl-LDH-MFC (393.82 mW/m²) and 2.21 times of Ti₃AlC₂-MFC (217.73 mW/m²). The maximum voltage of COF-300@NiAl-LDH/GO-MFC was 518 mV and it could remain stable within 8 days. GO was used as the substrate to improve the conductivity; LDH was used to enhance the catalytic activity and electron transfer rate; The three-dimensional bulk COF-300 attached to the surface enhanced the surface area and catalytic properties; The above jointly promoted oxygen reduction reaction of cathode, so as to improve MFC performances.     

Optimization of substrates for Bioelectricity production by Ochrobactrum pseudintermedium KF026284 in a single chambered microbial fuel cell

A new strain of bacterium Ochrobactrum pseudintermedium KF026284 was isolated from a single chambered microbial fuel cell operated with rumen fluid. The bacterium produced maximum power density of 114 mW/m² (0.7 V, 0.6 mA) when nutrient broth was used as the growth medium. The optimization of electricity generation by O. pseudintermedium KF026284 was carried out using various substrates like cellulose, cellobiose, starch, sucrose, and glucose. The bacterium when fed with cellobiose showed an appreciable and sustainable electricity generation with a power density of 150 mW/m² from the 5th day and a maximum power density of 247 mW/m² on the 11th day.     

Power generation of microbial fuel cells (MFCs) with low cathodic platinum loading

This study aims at investigating the effects of platinum (Pt) loadings on the cathodic reactions in Single Chamber Microbial Fuel Cells (SCMFCs) and developing cost-effective MFC operational protocols. The power generation of SCMFCs was examined with different Pt loadings (0.005–1 mgPt/cm²) on cathodes. The results showed that the power generation of the SCMFCs with 0.5–1 mgPt/cm² were the highest in the tests, decreased 10–15% at 0.01–0.25 mgPt/cm², and decreased further 10–15% at 0.005 mgPt/cm². The SCMFCs with Pt-free cathode (graphite) had the lowest power generation. In addition, the power generation of SCMFCs with different Pt loadings were compared in raw wastewater (Chemical oxygen demand (COD): 0.36 g/L) and wastewater enriched with sodium acetate (COD: 2.95 g/L). The solution conductivity in SCMFCs decreased with the degradation of organic substrates. Daily polarization curves (V–I) showed a decrease in current generation and an increase in ohmic losses over the operational period (8 days). The SCMFCs (with 0.5–1 mgPt/cm² at cathode) fed with wastewater and sodium acetate (NaOAc) reached the highest power generation (786 mW/m²), while the SCMFCs (with 0.5–1 mgPt/cm² at cathode) fed only with wastewater obtained the lower power generation (81 mW/m²). The study demonstrated that lowering the Pt loadings in two magnitude orders (1 to 0.01, 0.5 to 0.005 mgPt/cm²) only reduced the power generation of 15–30%, and this reduction of the power generation become less substantial with the decrease in the solution conductivity of SCMFCs.     

Enhanced boiling heat transfer in mesochannels

Heat transfer characteristics are studied for a hybrid boiling case that combine features of spray cooling and flow boiling. In such a hybrid system, a liquid is atomized and the surrounding vapor is entrained into the droplet cone to provide an initial quality for enhanced boiling. An in-house experimental setup was developed to obtain surface temperature and heat flux measurements in a series of converged mesochannels for hybrid boiling. To compare the heat transfer performance of this hybrid technique, a flow boiling module was also developed using the same series of converged mesochannels. The inlet and exit hydraulic diameter of the mesochannels was 1.55 and 1.17 mm, respectively. The heat flux was in the range of 15–45 kW/m² and the estimated mass flux varied from 45 kg/m²s at the channel inlet to 110 kg/m²s at the channel outlet. Moreover, a model was presented to predict surface temperatures and heat transfer coefficients for flow boiling and hybrid boiling in mesochannels. This model was developed based on Chen’s formulation (1966) [21] but with two essential modifications. First, the laminar entry length effect was taken into consideration for heat transfer coefficient calculation. Second, the boiling enhancement factor was calculated based on the fluid properties. The model was compared to the experimental data and several other correlations for both cases. This model shows good agreement with the experimental data (mean deviations on the order of 12–16%).     

Effect of ionic strength, cation exchanger and inoculum age on the performance of Microbial Fuel Cells

Power generation in Microbial fuel cells (MFCs) is a function of various physico-chemical as well as biological parameters. In this study, we have examined the effect of ionic strength, cation exchanger and inoculum age on power generation in a mediator MFC with methylene blue as electron mediator using Enterobacter cloacae IIT-BT08. The effect of ionic strength was studied using NaCl in the anode chamber of a two chambered salt-bridge MFC at concentrations of 5 mM, 10 mM and 15 mM. Maximum power density of 12.8 mW/m² was observed when 10 mM NaCl was used. Corresponding current density was noted to be 35.5 mA/m². Effect of cation exchanger was observed by replacing salt-bridge with a proton exchange membrane of equal surface area. When the salt-bridge was replaced by a proton exchange membrane, a 3-fold increase in the power density was observed. Power density and current density of 37.8 mW/m² and 110.3 mA/m² respectively were detected. The influence of the pre-inoculum on the MFC was studied using E. cloacae IIT-BT08 grown for 12, 14, 16 and 18 h. It was observed that 16 h grown culture when inoculated in the anode chamber gave the maximum power output. Power density and current density of 68 mW/m² and 168 mA/m² respectively were obtained. We demonstrate from these results that both physico-chemical as well as biological parameters need to be optimized for improving the power generation in MFCs.     

Heat transfer and entropy generation for laminar forced convection flow of graphene nanoplatelets nanofluids in a horizontal tube

The results are reported of an investigation of the heat transfer characteristics and entropy generation for a graphene nanoplatelets (GNP) nanofluid with specific surface area of 750 m²/g under laminar forced convection conditions inside a circular stainless steel tube subjected to constant wall heat flux. The analysis considers constant velocity flow and a concentration range from 0.025 wt.% to 0.1 wt.%. The impact of the dispersed nanoparticles concentration on thermal properties, convective heat transfer coefficient, thermal performance factor and entropy generation is investigated. An enhancement in thermal conductivity for GNP of between 12% and 28% is observed relative to the case without nanoparticles. The convective heat transfer coefficient for the GNP nanofluid is found to be up to 15% higher than for the base fluid. The heat transfer rate and thermal performance for 0.1 wt.% of GNP nanofluid is found to increase by a factor of up to 1.15. For constant velocity flow, frictional entropy generation increases and thermal entropy generation decreases with increasing nanoparticle concentration. But, the total entropy generation tends to decrease when nanoparticles are added at constant velocity and to decrease when velocity rises. Finally, it is demonstrated that a GNP nanofluid with a concentration between 0.075 wt.% and 0.1 wt.% is more energy efficient than for other concentrations. It appears that GNP nanofluids can function as working fluids in heat transfer applications and provide good alternatives to conventional working fluids in the thermal fluid systems.     

Boiling heat transfer in a hydrofoil-based micro pin fin heat sink

Flow boiling of R-123 in a hydrofoil-based micro pin fin heat sink was investigated. Average two-phase heat transfer coefficients were obtained over effective heat fluxes ranging from 19 to 312 W/cm² and mass fluxes from 976 to 2349 kg/m² s. The paper presents a flow map, which divides the data into three flow pattern regions: bubbly, wavy intermittent and spray-annular flows. Heat transfer coefficient trends and flow morphologies were used to infer boiling heat transfer mechanisms. Existing conventional scale correlations for circular tubes resulted in large scatter and were not able to predict the heat transfer coefficients accurately.