Significant Heat Flow Research Articles

Intensification of heat transfer in high-power laser diode bars by means of porous metal heat-sink

To intensify a heat transfer in high-power emitters based on laser diode bars we propose the use of a heat sink from a porous permeable material cooled by a fluid flow [1-3]. The main advantage of this class of materials is the possibility of removing significant heat flows with compact heat sink. An analysis of the characteristic values of the thermal loads and their relations with the material and liquid parameters drawn from an one-dimensional model of stationary one-sided heat exchange shows the possibility of heat flow removal of more than 1.5 kW/cm 2 at room temperature in a liquid. Methods for improving the effectiveness of the strategy are considered.

Estimating late-winter heat flow to the atmosphere from the lake-dominated Alaskan North Slope

AbstractThe conductive heat flux through the snow cover (Fa) is used as a proxy to examine the hypothesis that there is a significant heat flow from the Alaskan North Slope to the atmosphere because of the large number of lakes in the region.Fais estimated from measurements of snow depth, temperature and density on tundra, grounded ice and floating ice in mid-April 1997 at six lakes near Barrow, northwestern Alaska. The meanFavalues from tundra, grounded ice and floating ice are 1.5, 5.4 and 18.6 W m2, respectively. A numerical model of the coupled snow/ice/water/soil system is used to simulateFaand there is good agreement between the simulated and measured fluxes. The flux from the tundra is low because the soils have a relatively low thermal conductivity and the active layer cools significantly after freezing completely the previous autumn. The flux from the floating ice is high because the ice has a relatively high thermal conductivity, and a body of relatively warm water remains below the growing ice at the end of winter. The flux from the grounded ice is intermediate between that from the tundra and that from the floating ice, and depends on the timing of the contact between the growing ice and the lake sediments, and whether or not those sediments freeze completely. Using the estimatedFavalues combined with the areal fractions of tundra, grounded ice and floating ice derived from synthetic aperture radar images, area-weightedFavalues are calculated for six areas.Favalues for the ice vary between 9.8 and 13.8 W m−2, and those from the ice plus tundra vary between 3.9 and 5.3 W m−2. TheFavalues are similar to those observed in the sea-ice-covered regions of the south and north polar oceans in winter. The North Slope of Alaska may thus make a significant contribution to the regional energy budget in winter.

Estimating late-winter heat flow to the atmosphere from the lake-dominated Alaskan North Slope

AbstractThe conductive heat flux through the snow cover (Fa) is used as a proxy to examine the hypothesis that there is a significant heat flow from the Alaskan North Slope to the atmosphere because of the large number of lakes in the region. Fa is estimated from measurements of snow depth, temperature and density on tundra, grounded ice and floating ice in mid-April 1997 at six lakes near Barrow, northwestern Alaska. The mean Fa values from tundra, grounded ice and floating ice are 1.5, 5.4 and 18.6 W m2, respectively. A numerical model of the coupled snow/ice/water/soil system is used to simulate Fa and there is good agreement between the simulated and measured fluxes. The flux from the tundra is low because the soils have a relatively low thermal conductivity and the active layer cools significantly after freezing completely the previous autumn. The flux from the floating ice is high because the ice has a relatively high thermal conductivity, and a body of relatively warm water remains below the growing ice at the end of winter. The flux from the grounded ice is intermediate between that from the tundra and that from the floating ice, and depends on the timing of the contact between the growing ice and the lake sediments, and whether or not those sediments freeze completely. Using the estimated Fa values combined with the areal fractions of tundra, grounded ice and floating ice derived from synthetic aperture radar images, area-weighted Fa values are calculated for six areas. Fa values for the ice vary between 9.8 and 13.8 W m−2, and those from the ice plus tundra vary between 3.9 and 5.3 W m−2. The Fa values are similar to those observed in the sea-ice-covered regions of the south and north polar oceans in winter. The North Slope of Alaska may thus make a significant contribution to the regional energy budget in winter.

Estimating late-winter heat flow to the atmosphere from the lake-dominated Alaskan North Slope

AbstractThe conductive heat flux through the snow cover (Fa) is used as a proxy to examine the hypothesis that there is a significant heat flow from the Alaskan North Slope to the atmosphere because of the large number of lakes in the region. Fa is estimated from measurements of snow depth, temperature and density on tundra, grounded ice and floating ice in mid-April 1997 at six lakes near Barrow, northwestern Alaska. The mean Fa values from tundra, grounded ice and floating ice are 1.5, 5.4 and 18.6 W m2, respectively. A numerical model of the coupled snow/ice/water/soil system is used to simulate Fa and there is good agreement between the simulated and measured fluxes. The flux from the tundra is low because the soils have a relatively low thermal conductivity and the active layer cools significantly after freezing completely the previous autumn. The flux from the floating ice is high because the ice has a relatively high thermal conductivity, and a body of relatively warm water remains below the growing ice at the end of winter. The flux from the grounded ice is intermediate between that from the tundra and that from the floating ice, and depends on the timing of the contact between the growing ice and the lake sediments, and whether or not those sediments freeze completely. Using the estimated Fa values combined with the areal fractions of tundra, grounded ice and floating ice derived from synthetic aperture radar images, area-weighted Fa values are calculated for six areas. Fa values for the ice vary between 9.8 and 13.8 W m−2, and those from the ice plus tundra vary between 3.9 and 5.3 W m−2. The Fa values are similar to those observed in the sea-ice-covered regions of the south and north polar oceans in winter. The North Slope of Alaska may thus make a significant contribution to the regional energy budget in winter.

Seismological studies at Parkfield VI: Moment release rates and estimates of source parameters for small repeating earthquakes

AbstractWaveform data from a borehole network of broadband seismographic stations have been used to study microearthquakes along the Parkfield segment of the San Andreas fault (SAF). Analysis of almost 10 years of such data demonstrates that much of the seismicity in this region consists of repeating sequences, quasiperiodic sequences of earthquakes that are essentially identical in terms of waveform, size, and location. Scalar seismic moments have been estimated for 53 of these repeating sequences and combined with equivalent estimates from 8 similar but larger event sequences from the Stone Canyon section of the fault and the main Parkfield sequence. These estimates show that seismic moment is being released as a function of time in a very regular manner. Measurements of the moment release rate, combined with an assumed tectonic loading rate, lead to estimates of the seismic parameters source area, slip, and recurrence interval. Such parameters exhibit a systematic dependence upon source size over a range of 1010 in seismic moment that can be described by three simple scaling relationships. Several implications of these scaling relationships are explored, including the repeat time of earthquakes, average stress drop, strength of the fault, and heat generated by earthquakes. What emerges from this analysis of moment release rates is a quantitative description of an earthquake process that is controlled by small strong asperities that occupy less than 1% of the fault area. This means that the fault is highly heterogeneous with respect to stress, strength, and heat generation. Such heterogeneity helps to explain many of the apparent contradictions that are encountered in the study of earthquakes, such as why faults appear weak, why significant heat flow is not observed, how significant high frequencies can be generated by large earthquakes, and how various geologic features such as pseudotachylytes might form.

Thermal interaction of semiconductor devices on copper clad ceramic substrates

The temperature rise due to the spacing between two heat dissipating devices mounted on metallized or copper-clad ceramic substrates is presented. The thickness of the copper layer, the thermal conductivity of the substrate material, and the thermal resistance of the heat sink system are considered. Results for parameters typically found in power hybrid applications are presented in nondimensional form. The results indicate that increasing the thickness of the copper metallization requires that the devices be placed farther apart to prevent thermal interaction. An increase in the copper layer thickness can significantly decrease the device temperatures on alumina, but may increase temperatures on high thermal conductivity ceramic substrates such as beryllia (BeO). The results also demonstrate that the external heat sink thermal resistance can cause significant heat flow spreading and increased temperatures in the substrate. As the external resistance increases, the spacing required to prevent thermal interaction also increases.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Comparison of Two Test Methods for Determining Transfer Function Coefficients for a Wall Using a Calibrated Hot Box

This paper experimentally verifies and compares two dynamic test methods for a calibrated hot box to characterize the transient thermal performance of complex walls. In these methods, a wall specimen is sandwiched between the two conditioning chambers of a calibrated hot box. The exterior surface of the wall specimen is subjected to a time-varying excitation function in air temperature. At the interior surface, the air temperature is maintained steady, and the heat transfer response is measured. Conduction transfer function coefficients that relate the measured heat transfer response to the excitation function are derived. The two dynamic test methods were applied to an insulated hollow concrete block wall that contained significant thermal bridges and lateral heat flows. Empirical transfer function coefficients derived by the test methods predicted with good agreement the heat transfer response of this wall specimen when its exterior surface was subjected to excitation functions that differed markedly from those used to derive the coefficients.

Heat flow and the thermal origin of hot spot swells: The Hawaiian Swell revisited

We present 150 new heat flow measurements obtained at eight sites along a 1230‐km‐long profile across the Hawaiian Swell about 700 km ESE of Midway Island. Most of the measurements include in situ thermal conductivity determinations, which helped to reduce the statistical uncertainties (95% confidence) at all sites to &lt;±2.l mW m−2. Surprisingly, there is no systematic variation in heat flow across the axis of the swell. With one exception, the mean heat flow (corrected for sedimentation) at each site is within ±10% of the mean value of 57.7±4.3 (S.D.) mW m−2 for all sites. At the two sites at either end of the profile, clearly located off the swell, the observed heat flow is &gt;59 mW m−2, about 20% higher than the predicted heat flow for 100 Ma seafloor based on simple lithospheric cooling models. Thus even though there is a small increase in heat flow with age along the swell, when compared with the off‐swell heat flux, the anomalous heat flow associated with the Hawaiian Swell is probably of the order of 5–10 mW m−2 and arguably may not exist at all. A previous investigation [Von Herzen et al., 1982] may have overestimated the magnitude of the heat flow anomaly associated with the Hawaiian Swell by comparing heat flux measurements on the swell with values expected for simple lithospheric cooling models. The heat flow anomalies associated with the Bermuda Rise and the Cape Verde Rise may also be smaller than previously estimated, given the uncertainties in the heat flux on the normal seafloor surrounding these swells. The lack of a significant heat flow anomaly associated with the bathymetric expression of the Hawaiian Swell is inconsistent with simple models of lithospheric reheating. Dynamic support, accompanied by modest temperature increases (&lt;100°–200°C) confined to the lower lithosphere, and underlying asthenosphere appear to be required to explain both the height of the swell and its small heat flow anomaly. However, detailed modeling of the origin of midplate swells, and their associated heat flow anomalies, is hampered by our lack of understanding of the thermal evolution of old (&gt;80 Ma) oceanic lithosphere.

On the high heat flow in the Nankai Trough area—a simulation study on a heat rebound process

A concentration of high heat flow (as high as 120–160 mW/m 2) has been observed in the Nankai Trough, off southwest Japan, where the Philippine Sea plate (Shikoku Basin) is subducting beneath the Japanese landmass. We interpret this high heat flow in the subduction zone as being caused by the recovery of conductive heat flow to the theoretically expected value for the young Shikoku Basin lithosphere after cessation of hydrothermal heat exchange through sediment. The thickening sedimentary cover suppresses the rapid heat exchange between basement and sea water, whereas the topmost part of the basement allows a hydrothermal circulation within it to pump up heat from the hot plate to the sediment cover. We propose to call this process “heat rebound”. Numerical simulation shows that significant heat flow recovery can occur and is largely influenced by the sedimentation rate. We believe that the high heat flow in the Nankai Trough is one of the heat rebound cases. However, rapid sedimentation in the trough also indicates that heat flow recovery expected by the simulation is not large enough to explain the trough high heat flow by the heat rebound process only.

Europa, tidally heated oceans, and habitable zones around giant planets

Tidal dissipation in the satellites of a giant planet may provide sufficient heating to maintain an environment favorable to life on the satellite surface or just below a thin ice layer. In our own solar system, Europa, one of the Galilean satellites of Jupiter, could have a liquid ocean which may occasionally receive sunlight through cracks in the overlying ice shell. In such a case, sufficient solar energy could reach liquid water that organisms similar to those found under Antarctic ice could grow. In other solar systems, larger satellites with more significant heat flow could represent environments that are stable over an order of Aeons and in which life could perhaps evolve. We define a zone around a giant planet in which such satellites could exist as a tidally-heated habitable zone. This zone can be compared to the habitable zone which results from heating due to the radiation of a central star. In our solar system, this radiatively-heated habitable zone contains the Earth.

Regional variations of heat flow differences with depth in Alberta, Canada

Summary. Differences between estimated average heat flow values for the Mesozoic and Cenozoic formations (el) and estimated average heat flow values for the Palaeozoic formations below the erosional unconformity (Q2) are calculated for the Alberta part of the western Canadian sedimentary basin. Significant heat flow differences exist for these two intervals and the map of AQ = Ql - Q2 shows that Q2 is generally greater than Ql in the western and south-western part of Alberta, while in the northern part of the province Q2 is generally less than Ql. The regional variations of AQ are large, with standard deviation of 26 mW m-’ and average value - 13.5 mW m-2. A regional trend of AQ correlates with topographic relief and the hydraulic head variations in the basin. It is shown that there is a heat flow increase with depth in water recharge areas and a decrease in heat flow with depth in the low topographic elevation water discharge areas when comparing the average heat flow in Mesozoic + Cenozoic and Palaeozoic formations.

Detailed heat flow measurements over the Juan de Fuca Ridge System

Eleven detailed profiles of heat flow measurements have been completed over young oceanic crust of the Juan de Fuca ridge system. Individual measurements were spaced typically 0.4–1 km apart along multiple‐penetration lines from 3 to 20 km in total length, and each measurement was located with respect to structural and sedimentary features by simultaneous seismic reflection profiling. In all cases, the average heat flow is well below that predicted by simple conductively cooled spreading models, even when the sediment cover is thick and the nearest basement outcrop is 15 km away. This disparity is attributed to ventilated convective circulation of water in the crust. Large heat flow variability is common along all profiles. Variations are present at two scales. Small‐scale variations (from 1 km to a few kilometers between significant heat flow maxima), present in the younger profiles, probably reflect the influence of local venting and permeability variations on permeable layer cellular convection. Large‐scale variations (10–20 km between significant heat flow maxima), present in all profiles, may reflect the influence of regional circulation driven by cold water recharge at isolated basement outcrops. Laboratory experimental data indicate that normal cellular convection can coexist with larger‐scale bilateral flows, so that there is no simple way to extract the permeable layer thickness from the surface heat flow data. There is a considerable reduction in the amplitude of small‐scale heat flow variability over the range of crustal age studied (0.1–12.5 m.y.). This is probably caused by the thermal filtering effects of the sediment cover which increases from about 50 m near the ridge crests to over 700 m on the flanks.The appendix is available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N. W., Washington, D.C. 20009. Document J79‐007; $1.00. Payment must accompany order.

Prospects for geothermal energy applications and utilization in Canada

Like the sun, the earth is a vast energy source. The utilization of this geothermal furnace is still in its infancy, the heat flow from the mantle to the surface (9 × 10 −1 cal/cm 2/min; 0.063 W/m 2) is the energy equivalent to 2 × 10 11 barrels of oil per yr (3 × 10 10 tons or about fourfold greater than the present yearly total world energy consumption). Although today only local hot spots yielding dry and wet steam, and shallow hot-water sites are used economically, future technology may well lead to a much greater utilization. This will be done through additional imaginative and sophisticated exploitation of available regions of dry hot rock, geopressure-geothermal fields, and even deep areas of significant heat flow. Such potential utilization of geothermal resources should provide for relatively pollution-free, steam-generated electrical power, steam and hot-water for home and industry, mineral and chemical by-products, as well as numerous uses where hot water is required in agriculture, horticulture, fisheries, mining, pulp and paper and other industries. Canadian developments in these areas are still relatively dormant. The problem areas are not of a technological nature but rather of an institutional type in passing a geothermal act that would provide the incentives for exploration and economical development.

Analytic solution for transient heat flow in a shocked composite slab

An analytical solution and computational procedure has been obtained for transient heat flow in a three-slab finite-length composite solid with symmetry about the center. Each material has different initial temperatures and there are constant temperatures on the boundaries. The solutions are of interest in thermal quenching procedures and in the shock compression of sandwich configurations of materials. The results of a computation corresponding to the temperatures reached in shock-wave compression indicate that there is significant heat flow into a metal foil, which is sandwiched between two epoxy layers, in less than 1 μsec of heat flow. This paper presents a mathematical discussion of the heat-flow problem along with sample computational results. One conclusion from these results is that they demonstrate the important effect of heat flow on electrical resistance changes in certain geometries of shock-wave compression of metals.

Temperature rise of solid junctions

SEMICONDUCTOR DEVICES always contain a junction; i.e., a plane zone of vanishing thickness. Current pulses through the device generate heat, mostly in the zone, from which it diffuses into the adjoining metallic body. Heat causes an increase of temperature in the junction, depending on the size of the current pulse and the rate of heat dissipation. Measurements on alloy junction diodes lead to a curve of temperature rise against pulse duration which does not agree with any single theory of heat transfer. Investigating the problem reveals the need to consider a multitude of factors (materials, dimensions, shapes) which cannot be fitted to a single mathematical model. Satisfactory analysis, without undue complications, can be achieved in four successive steps, described in Table I. Considering each step, we assume that the preceding step is transferring heat at a steady rate (i.e., neglecting heat storage) and the following step is not yet subjected to a significant heat flow. Careful selection of boundaries and time limits leads to a valid approximation; or, inversely, an observed pulse-time characteristic can be interpreted by the theory to gain an insight into the modes of internal heat transfer.