Heat Flow Transition Research Articles

New empirical flow-regime-based model of water boiling in rectangular microchannels

A new empirical flow-regime-based model of water boiling in rectangular microchannels is proposed and programmed using MATLAB code in the present paper. The prediction model divides the flow regime map into four parts: single-phase convection regime, sub-cooled boiling regime, saturated boiling regime, and partial dry-out boiling regime. Each zone is also divided into several sub-zones according to corresponding criteria. Suitable empirical heat transfer correlations and flow transition criteria are adopted for each flow pattern to reasonably capture the boiling heat transfer mode according to the vapor quality or the efficient heat flux. The prediction results generally present a similar trend to experimental results from the literature. The new model is also compared with the existing empirical flow-regime-based models in the literature. The Lee and Mudawar model and the Ma model can only capture up to 3 and 2 different trends of HTC, respectively. However, the new model considers a complete flow regime map and can capture up to 4 different trends of HTC.

海溝近傍の熱流量異常

Recent heat flow surveys in the Japan Trench and Nankai Trough areas delineate prominent heat flow anomalies correlated with the structure of the subducting oceanic crust. On the seaward side of the Japan Trench, anomalously high heat flow values are pervasively observed within 150 km of the trench axis. The broad high heat flow zone can be attributed to trenchward thickening of a permeable layer (aquifer) in the oceanic crust associated with fracturing due to plate bending. Fluid circulation in the thickening aquifer efficiently pumps heat up from the underlying unfractured part. Overlapping the broad anomaly, local variations at a scale of a few kilometers are detected, indicating heterogeneous development of fractures. On the floor of the Nankai Trough off the Kii Peninsula, observed heat flow varies from extremely high and variable values on the western side to normal values for the seafloor age on the eastern side. The transition occurs at around 136°E, which may correspond to the structural boundary in the Shikoku Basin between the seafloor formed by spreading in the NE–SW direction and that formed by spreading in the E–W direction. The high heat flow west of the boundary is considered to result from heat transport along the plate interface by fluid circulation in an aquifer in the subducted oceanic crust. The heat flow transition around 136°E may reflect a change in permeability structure across the boundary between the two spreading directions. The two types of hydrothermal heat transport, fluid circulation in the subducted aquifer in the case of the Nankai Trough and circulation in the thickening aquifer in the case of the Japan Trench, have distinctive features. The subducted-aquifer type is effective for heat transport in a young subducting plate with a highly permeable aquifer, while the thickening-aquifer type can transport heat even in an old plate. The subducted-aquifer type has a more significant influence on the temperature structure of the plate boundary. Some heat flow anomalies observed in other trenches may also be caused by either of these types of hydrothermal heat transport.

High Heat Flux Laser Testing of HfB2 Cylinders

Hafnium diboride (HfB2) is one of a family of ultra‐high temperature ceramics (UHTCs) which are being considered for application in environments with a substantial heat flux such as hypersonic flight. In order to characterize transitions in the material response with heat flux and therefore predict the in‐service behavior of UHTCs, a range of tests were conducted in which small cylindrical bars of HfB2 were laser heated using heat fluxes from 25 to 100 MW/m2. After testing, the external damage as well as damage observable in cross sections through the cylinders was characterized using photography, optical, and scanning electron microscopy. Experimental results were compared with finite element modeling of the heat flow, temperature distribution, and phase transition. Heat flux rather than total deposited heat was found to be the strongest determinant of the way in which damage develops in samples; for lower heat fluxes, the main damage mechanism is oxidation, progressing to oxidation‐induced melting and finally, at the highest heat fluxes, substantial ablation by melting irrespective of oxidation. The agreement between calculations and experimental observations indicates that such calculations can be used with confidence to guide the design of components.

Further Study of Sub-Tg Heat Flow Transition of a Cured Epoxy Resin

To further study the sub-Tg heat flow transition of a cured epoxy resin, cured samples with different thermal history were investigated using torsion pendulum analysis (TPA) and thermal mechanical analysis (TMA). The results indicate that sub-Tg heat flow transition could be related to the molecular relaxation from 20°C to the α-peak, and that frozen-in extra free volume is necessary for the appearance of sub-Tg heat flow transition.

Normal fault thermal regimes: conductive and hydrothermal heat transfer surrounding the Wasatch fault, Utah

The thermal regime across an active normal fault is affected by tectonic processes of exhumation and erosion of the footwall and burial and sedimentation on the hanging wall. An enhanced thermal regime in the footwall is juxtaposed against a thermally depressed regime in the hanging wall causing significant two-dimensional (2D) heat flow. These thermal processes have been simulated with 2D numerical models and applied to the Wasatch fault of central Utah. Simulations included variable fault angles of 90°, 60°, and 45° and a vertical displacement profile accounting for hanging wall and footwall tilt. After 20 m.y. of fault movement, 60° fault, isotherms are displaced ∼1 km on the footwall and hanging wall. Furthermore, model surface heat flow is enhanced by 25% above the footwall and depressed by 15% above the hanging wall 10 km from the fault trace; the heat flow transition has a half width of 10 km. Present-day surface heat flow was compiled for 23 sites along the Wasatch Front. Heat flow has a mean value of 92 mW/m 2 (standard deviation 25 mW/m 2) but, unlike model predictions, does not show a discernible variation in heat flow across the fault. Part of the discrepancy between predicted and observed conductive heat flow may be caused by groundwater which recharges in the uplifted footwall, is heated in the subsurface, and discharges as thermal water along the range bounding fault or into the hanging wall valley. Flow rates and water temperatures from 29 tectonic hot springs along the Wasatch Front indicate a minimum hydrothermal thermal power loss of 90 MW or 0.24 MW per kilometer of strike along the fault. This thermal power is equivalent to a heat flow of 21 mW/m 2 captured uniformly between the range crest and range front, and discharged in hot springs.

Effects of Prior Cooling Rates on Tg and Sub-Tg Heat Flow Transitions of Cured Epoxy Resin

Effects of Prior Cooling Rates on <i>T</i>_g and Sub-<i>T</i>_g Heat Flow Transitions of Cured Epoxy Resin

A study of sub‐Tg heat flow transition of cured epoxy resin

AbstractThe physical aging behavior of fully and partially cured epoxy resins based on diglycidyl ether of bisphenol A(DGEBA) has been investigated by differential scanning calorimetry (DSC). A sub‐Tg heat flow transition (Tg1) could not be attributed to the phase separation or dynamic mechanical relaxation, as reported in the literature. In both fully and partially cured epoxy resins, it occurs only when the cooling rate is higher than that having the lowest Tg in the DSC scan. Therefore, it could be attributed to the motion of the internal stress‐relaxed molecular chain.

Terrestrial heat-flow estimates from petroleum bottom-hole temperature data in the Colorado Plateau and the eastern Basin and Range Province

Preliminary heat-flow estimates were calculated for 32 sites in the Colorado Plateau, the eastern Basin and Range Province, and the Middle Rocky Mountains. At 23 of these sites, the heat-flow estimates are believed to have merit. The heat-flow estimates often agree with nearby measurements and correlate reasonably well with interpretations from other geophysical techniques. The mean of the heat-flow estimates hi the northern Colorado Plateau interior (66 to 69 mWm −2 ) is within ∼5% or ∼18% of the mean of deep or shallow heat-flow measurements, respectively. Estimates in the peripheral areas of the plateau, in the San Juan Basin, agree with higher heat-flow measurements at sites approaching the San Juan volcanic field. Estimates along the western periphery of the Colorado Plateau are higher than in the interior and therefore suggest an anomalously shallow mantle (asthenosphere), extending ∼50 km under the plateau; this is consistent with previous studies. Above-average Basin and Range heat flows are estimated in the eastern Basin and Range Province (99–102 mWm −2 ), and this concurs with a high energy-flux zone proposed for the area. The transition from high to low heat-flow estimates between the eastern Basin and Range Province and the Middle Rocky Mountains seems to occur over a small distance (∼36 km). The narrow heat-flow transition implies shallow thermal sources in proximity to the Basin and Range–Middle Rocky Mountains transition; this may correspond to a shallow crustal low-velocity zone previously interpreted along the transition.

Queen Charlotte fault zone: heat flow measurements

The heat flow pattern from the deep sea across the Queen Charlotte Terrace to the west coast of the Queen Charlotte Islands has been determined through 20 marine heat flow measurements and by 11 borehole measurements at one land site. There is a continuous transition from very high deep sea heat flow, through intermediate values on the terrace, to low continental heat flow. The deep sea values are scattered, probably reflecting hydrothermal circulation in the crust, but their mean is in agreement with the theoretical value for the 7 Ma deep sea oceanic crust. The mean heat flow at the land site of 47 mW m−2 is similar to the average for the coast Insular Belt to the south and east. The measurements on the 30 km wide 2 km deep terrace are less scattered and much lower than those on the deep sea floor. The main thermal contrast is at the seaward edge of the terrace rather than near the coast where the earthquakes of the main plate boundary are located. Numerical models suggest that no reasonable steady state ocean–continent boundary can explain the observed heat flow transition. The data are consistent with a model of oblique underthrusting of the deep sea floor beneath the terrace. The continental margin heat flow transition will tend to mask any thermal anomaly generated by fault motion, but the results imply that there is no large frictional heat generated by motion on the Queen Charlotte fault.Nine marine heat flow measurements were made at the southwestern end of Queen Charlotte Sound south of the Queen Charlotte fault zone to test the hypothesis that the sound is a zone of recent crustal extension or rifting. The measurements were limited to isolated pockets of soft sediment and to sea floor depths greater than 800 m where bottom water temperature transients are negligible. The heat flow values are fairly uniform with an average of 86 mW m−2, which is about double the mean of other Insular Belt values. The Queen Charlotte Sound values could be affected by a nearby ocean spreading centre or by sediment erosion, but they are consistent with the rift hypothesis.

Heat flow in the north‐central Colorado Plateau

We report new heat flow measurements at 25 evenly distributed sites in the north‐central Colorado Plateau. Heat flow values computed for these new sites and one previously published site range from 43 to 116 mW m−2 but fall into the following distinct subsets related to physiographic and tectonic elements within the Plateau: (1) heat flow of 51 mW m−2 (12 sites; s.d. 6) in the San Rafael Swell and Green River Desert which constitute the core of the Colorado Plateau at this latitude, (2) heat flows of 69 mW m−2 (5 sites; s.d. 10) and 88 mW m−2 (4 sites; s.d. 19) in successive parallel north‐south bands approaching the Wasatch Plateau to the west but still 80 km east of the Basin and Range physiographic boundary, (3) heat flow of 64 mW m−2 (5 sites; s.d. 2) along the Salt Anticline trend which strikes northwest in the region of Moab, Utah. Heat flow results for the entire Colorado Plateau have been reexamined in view of our new results, and the overall pattern supports the concept of a low heat flow ‘thermal interior’ for the plateau surrounded by a periphery some 100 km wide having substantially higher heat flow. Average heat flow in the thermal interior is about 60 mW m−2 compared to 80–90 mW m−2 in the periphery. This regional heat flow pattern supports a model of Tertiary lithospheric thinning under the Colorado Plateau whereby the plateau is still in transient thermal response and a 15–20 m.y. lag between uplift and corresponding surface heat flow anomaly is to be expected. The position of the heat flow transition between our interior and peripheral regions in the northwest plateau is roughly consistent with lateral warming and weakening of the Colorado Plateau lithosphere initiated at the Basin and Range boundary some 20 m.y. ago.

Terrestrial heat flow in Arizona

New heat flow data in Arizona suggest that the southern Basin and Range has recently undergone less extension than other areas of the Basin and Range province. Heat flow–heat production data imply that magmatism and hydrothermal circulation in the crust and upper mantle beneath southern Arizona and northwestern Mexico may be less extensive than along the Rio Grande rift. A heat flow transition between the Basin and Range and the Colorado Plateau occurs within a lateral distance of 60 km in central Arizona. Predicted steady state temperatures suggest that the M discontinuity may be nearly coincident with an isotherm along this transition. The new heat flow measurements from depths greater than 650 m suggest that the mean value for the Arizona Basin and Range is 1.94 ± 0.12 HFU, indicating as little as 0.3 to 0.4 HFU difference between the Colorado Plateau and the Arizona Basin and Range. This difference could be attributed primarily to widespread magmatic intrusion in the Basin and Range.

Preliminary heat flow and radioactivity studies in Wyoming

Twelve new heat flow values in Wyoming are in the range 0.6–2.1 μcal/cm2 s (25–88 mW/m2). Radioactive heat productions at eight localities range from ∼0 to ∼1.3 μμcal/cm3 s (∼0−5.4 μW/m3). These data are consistent with the following interpretations: (1) The Laramie Mountains‐eastern Wyoming Basin area is a zone of normal heat flow (0.6–1.6 μcal/cm2 s (25–67 mW/m2)) that is characterized by low flux (∼0.6 μcal/cm2 s (∼25 mW/m2)) from the lower crust and upper mantle. (2) The eastern boundary of the Yellowstone caldera heat flow high (≥2.5 μcal/cm2 s (≥105 mW/m2)) is narrow. (3) The heat flow is high (1.9–2.1 μcal/cm2 s (79–88 mW/m2)) in parts of the Black Hills in northeastern Wyoming and western South Dakota. From the data presented, a major heat flow transition occurs between the Medicine Bow and Laramie mountains in Wyoming (0.6–1.3 μcal/cm2 s (25–54 mW/m2)) and the Rocky Mountains in northern Colorado (2.2–3.0 μcal/cm2 s (92–125 mW/m2)). The high flux in this part of the Southern Rockies may mean that the zone of high heat flow associated with the Rio Grande rift extends to the Colorado‐Wyoming Border. The normal heat flow in the Laramie Mountains‐eastern Wyoming Basin area implies submelting temperatures in the upper mantle. In contrast, the very high flux in northern Colorado may be related to high‐temperature, nonradiogenic heat sources in the lower crust and upper mantle because the width of the transition to normal flux in the Laramie Mountains in southern Wyoming is narrow (≤70 km).

The mechanisms of heat transfer through the floor of the Indian Ocean

We present 206 new heat flow measurements in the Indian Ocean. These and approximately 300 previously published heat flow values are individually evaluated for sedimentary environment and instrumental performance. The relationship between average heat flow and age is found to be little affected by selection of the most reliable experiments, although the scatter about the mean is significantly lowered. The variation of mean heat flow with age is found to be very similar to that in the eastern Pacific and Atlantic oceans: There is a crestal low heat flow zone with large variability, a transition zone within which the heat flow increases from values considerably below to values in agreement with predictions from thermal models of the oceanic lithosphere, and a region where heat flow values are in accord with theoretical predictions. However, the transition zone occurs over different crustal ages from ocean to ocean: 40–60 m.y. in the Indian Ocean, 4–6 m.y. in the Galapagos spreading center, 10–15 m.y. on the East Pacific Rise, and 50–70 m.y. on the Mid-Atlantic Ridge. The transition zone generally corresponds to a sea floor age where (1) sedimentary thickness increases to ≥300 m, (2) sea floor roughness is significantly smoothed by sediment blanketing, and (3) the carbonate content of surface sediments decreases to ≤40%. The transition zone occurs where water circulation in the oceanic crust stops affecting the surface heat flow strongly. There are two possible explanations for the transition. First, a change in composition from carbonate to siliceous sediments results in a decrease in bulk permeability. This combined with general thickening of the sedimentary blanket with aging results in the deposition of an impermeable layer which prevents the convective exchange of heat from the oceanic crust to the ocean. Second, hydrothermal flow within the oceanic crust is plugged by filling of circulation cracks in the oceanic crust. The fact that in several basins of the Indian Ocean the heat flow transition corresponds with the carbonatesiliceous boundary is support for the former mechanism. However, the fact that locations of increases in velocity of seismic layer 2A generally correspond to the transition regions in the Atlantic and Pacific oceans provides support for the latter mechanism. Heat flow measurements in the world's oceans allow us to calculate the variations of bulk permeability and basal temperature in the oceanic crust as a function of age and to evaluate the geochemical implications of the variation in these parameters between oceans. The combination of conductive heat flow and elevation versus age observations in old lithosphere demonstrates the deviation from t1/2 cooling in the Indian Ocean and indicates that the Mozambique and western Somali basins are considerably older than preliminary deep-sea drilling results suggest. 1 Supplementary table is available with entire article on microfiche. Order from American Geophysical Union, Suite 1000, 1909 K Street, N.W., Washington, D.C. 20006. Document J77-003; $1.00. Payment must accompany order.

Heat flow measurements in the inlets of southwestern British Columbia

The geothermal heat flux has been measured at 15 sites in the inlets of southwestern British Columbia by using the ocean probe technique. Corrections have been applied for variations in bottom water temperature, sedimentation, thermal refraction by the sediment prism, topography, warm-rim effect, Pleistocene thermal history, uplift, and erosion. The accuracy of the values is about ±0.3 μcal cm−2 s−1 (±13mW m−2). The relative accuracy between the values is about half of this range. The data indicate a pattern of low heat flow from the coast inland about 200 km to the heads of the inlets (13 values average 0.9 μcal cm−2 s−1 or 37 mW m−2). Stations at the heads of two inlets (1.5 μcal cm−2 s−1 or 63 mW m−2) mark the transition to high heat flow further inland (about 2.0 μcal cm−2 s−1 or 84 mW m−2). From west to east the heat flow transition coincides with the first occurrence of recent volcanic centers and hot springs, the transition from high to low Bouguer gravity, and the transition to low deep crustal and upper mantle electrical resistivity and to recent regional uplift. The coast low heat flow is explained partly by low crustal radioactive heat production and in part by the heat sink effect of the cold oceanic Juan de Fuca plate being subducted along the continental margin. The high inland heat flow probably is produced by the upward convective transport of heat by magma and thinning of the lithosphere that occurs when the sinking plate reaches a depth where temperatures are sufficient for partial melting. Low mantle temperature and thus high density in both the continental lithosphere and the underlying subducted oceanic lithosphere under the coast zone explain the high Bouguer gravity and thick crust in this region compared with the low gravity and thin crust inland. To the north of about 51°N where at present there is transform fault motion along the continental margin, there probably was subduction prior to about 10 m.y. ago. The gravity and crustal thickness data suggest that the high density in the subducted oceanic lithosphere has disappeared but that upwelling and a hot thin continental lithosphere persist inland of 200 km from the continental edge.

Heat flow and gravity interpretation across the Rio Grande Rift in southern New Mexico and west Texas

Recent heat flow measurements at 10 separate localities in southern New Mexico and West Texas range from 0.9 to 3.6 HFU (1 HFU = 1 × 10−6 cal/cm2 s). Radiogenic heat production determinations at eight of these localities range from 2.2 to 4.9 HGU (1 HGU = 1 × 10−13 cal/cm3 s). When the heat flow measurements are reduced by the heat from bedrock radioactivity, the Rio Grande rift and immediately adjacent areas are characterized by very high reduced flux (≥1.8 HFU), which contrasts strongly with 1.2 to 1.5-HFU values in bordering portions of the Basin and Range province and a 0.8-HFU value assumed for the southern Great Plains. Analyses of 2000 gravity observations in the Basin and Range province and the Great Plains reveal that a positive gravity ridge of about +30 mGal occurs along the Rio Grande rift in the Franklin and San Andres mountains and the Tularosa Valley. This relative gravity high can be caused by crustal thinning and/or shallow sills and dikes of mafic rocks in the crust under the rift. Gravity anomalies and a thin crust are compatible with a low-density upper mantle beneath most of the Basin and Range province. The new heat flow and radioactivity data indicate that the Basin and Range-Great Plains heat flow transition is marked by unusually high observed and reduced flux in the neighborhood of the Rio Grande rift. The combined thermal and gravity observations may be explained by shallow crustal intrusions, a hot abnormal upper mantle, and relative crustal thinning beneath the rift.