Heat Flux Measurements Research Articles

Experimental investigation on aerothermal effects of forward-facing cylindrical and parabolic cavity in hypersonic flow

Thermal protection of hypersonic vehicles is of great concern during ascent and re-entry conditions due to higher aerothermal loads. The passive forward-facing cavity is exhibited a substantial reduction of aero heating effects. The experimental studies on unsteady aspects of the flow considering the cavity geometries and heat transfer effects within the cavity are not abundant. In the present study, we investigated the heat transfer variations and nature of shock around a blunt body with cylindrical and parabolic cavity geometries. Experiments are conducted in hypersonic shock tunnels using air as the test gas for flow enthalpy conditions of 3.2 and 5.4 MJ/kg for a free-stream Mach number of 10.9 and 10.2 respectively. The cavity flow is established by verifying the measured heat flux, pressure, and shock oscillation results. The unsteady heat flux measurements and high-speed schlieren imaging is performed to study the effects. The results reveal that the flow with the parabolic cavity geometry shows a significant increase in the mean shock standoff position of about 14% and 30% compared to the blunt-nosed body, and about 7%–18% compared to the cylindrical cavity geometry, with a reduction of bow shock oscillations. As a result, a substantial reduction of heat flux about 34%–59% on the nose surface is noticed and found it is effective for mitigating the aerodynamic heating at higher flow enthalpy conditions. The flow with a cylindrical cavity geometry indicated the substantial increase in the heat flux due to the shock interaction and the significant heat flux variation in the cavity region is recognized and observed that such effects were not prevalent with the parabolic cavity geometry.

Closure in Surface Flux Estimation by Energy Balance Model: Comparison of Priestly-Taylor and Penman-Monteith Computations for a Tropical Site in Ibadan

Increasing demand to further understand complexity in surface energy flux partitioning necessitates the adaptation of numerous estimation methods to fit the site of observation. This is useful for reducing the uncertainty in physically measurable parameters especially those in tropical regions with high human interference in the atmospheric boundary layer. In this study, we used computations from two methods - the Priestley-Taylor (PT) and the Penman-Monteith (PM), based on the Energy Balance model to ascertain closure performance in the surface flux estimations. The study was carried out at the Nigerian Meteorological Experiment III site (7.38 o N and 3.93 o E, 224.2m) located in Ibadan, Southwest Nigeria. Thirty days of a year (2006) dataset were examined using the Bowen ratio (BR) energy balance model to validate the PT and PM methods. The systems were examined across daily and diurnal cycles to better understand the differences in energy partitioning. Results showed that both systems generally favored latent heat flux compared to sensible heat flux perhaps due to above-normal rainfall during the period. The PM method performed better than the PT method with a period average for the sensible heat and latent heat fluxes as 32.05 Wm -2 and 67.66 Wm -2 respectively, accounting for 29.22% and 61.39% of the total net radiation. The PT method underestimates the sensible heat flux by as much as 19.70 Wm -2 compared to the PM method, with a period average of 12.36 Wm -2 representing 11.26% of total net radiation. The PM method also gives a period average Bowen ratio estimate of 0.55, consistent with the standard range for grasslands. The study suggests that the performance of the PM method is related to its response to heat and water vapor transfer over humid regions and would contribute to further research on land-surface interactions over the tropics. Finally, we propose that the measurement of available energy, net radiation, and ground heat flux should be separated for different collocated systems in order to reduce the forcing of closure and aid in proper partitioning of the fluxes. Keywords: surface energy flux, energy balance model, Priestly-Taylor, Penman-Monteith, West Africa, latent heat, sensible heat, NIMEX_3 DOI: 10.7176/JEES/11-5-05 Publication date: May 31 st 2021

Heat Flux From a Vapor‐Dominated Hydrothermal Field Beneath Yellowstone Lake

AbstractWe report results from 149 heat flux measurements made over an ∼2‐year interval at sites in and around a vapor‐dominated geothermal field located at water depths of ∼100–120 m in Yellowstone Lake, Wyoming. Measurements of both in situ temperature and thermal conductivity as a function of depth were made with a 1 m probe via a remotely operated vehicle, and are combined to compute the vertical conductive heat flux. Inside the ∼55.5 × 103 m2 bathymetric depression demarcating the vapor‐dominated field, the median conductive flux is 13 W m−2, with a conductive output of 0.72 MW. Outside the thermal field, the median conductive flux is 3.5 W m−2. We observed 49 active vents inside the thermal field, with an estimated mass discharge rate of 56 kg s−1, a median exit‐fluid temperature of 132°C, and a total heat output of 29 MW. We find evidence for relatively weak secondary convection with a total output of 0.09 MW in thermal area lake floor sediments. Our data indicate that vapor beneath the thermal field is trapped by a low‐permeability cap at a temperature of ∼189°C and a depth of ∼15 m below the lake floor. The thermal output of the Deep Hole is among the highest of any vapor‐dominated field in Yellowstone, due in part to the high boiling temperatures associated with the elevated lake floor pressures.

Heat Flux Measurements in High Velocity Oxygen-Fuel Torch Flow for Testing High Thermal Materials

Heat Flux Measurements in High Velocity Oxygen-Fuel Torch Flow for Testing High Thermal Materials

Features for the design of a specialized information-measuring system for the study of thermoelectric properties of semiconductors

Methods for studying thermoelectric parameters of semiconductors that are optimal for the implementation of software and hardware have been analyzed and selected. It is based on the Harman method and its modifications, adapted for pulse measurements, which are convenient to implement on a modern element base. An important advantage of these methods is the absence of the need for accurate measurements of heat fluxes, which greatly simplifies and reduces the time for conducting experimental research. The required operating ranges for the voltage 10 µV–1 V, for the current 10 µA–300 mA and the element base performance at the processing level of 40–200 million samples per second have been determined. Structural and electrical circuits, as well as software for a specialized computer system for studying thermoelectric parameters of both bulk and thin-film thermoelectric materials, and express analysis of the operational characteristics of finished modules have been developed. It has been shown that the proposed scheme copes well with the task. And the use of FPGA and 32-bit microcontrollers provide sufficient processing speed up to 200 MSPS and the necessary synchronization modes for the implementation of the Harman pulse method even when studying films of nanometer thickness. Experimental studies of both bulk thermoelectric modules based on Bi2Te3 and thin-film thermoelectric material based on PbTe have been carried out. The effectiveness of the developed tools and techniques has been shown, which made it possible to more than halve the time for sample preparation and experiment. Based on the presented models, all the main thermoelectric and operational parameters have been determined, in particular, electrical conductivity, Seebeck coefficient, thermal conductivity, thermoelectric figure of merit. As a result of the development of specialized computer tools, it was possible to reduce the labor intensity of the process of measuring the main electrical and operational parameters of semiconductor thermoelectric materials and energy conversion modules based on them, as well as to automate the process of defects identification of thermoelectric modules. The labor intensity of the research process has decreased not only due to the automation of the measurement process, but also due to an optimized technique that allows research on a sample of one configuration, since the manufacture and preparation of samples are the most laborious

Analysis of Shroud and Disk Heat Transfer in Aero-Engine Compressor Rotors

Abstract Heat transfer within the rotating compressor cavity of an aero-engine is predominantly governed by buoyancy, which can be characterized by the Grashof number. Unsteady and unstable buoyancy-induced flow structures influence the temperatures and stresses in the compressor rotors, and these affect the radial growth of the disks. In addition, the heat transfer from the disks and shroud increases the temperature of the throughflow of cooling air. This paper contains two connected parts. First, a heat transfer correlation for the shroud of a rotating cavity was determined from steady-state heat flux measurements collected in the bath compressor-cavity rig at engine-simulated conditions. The Nusselt numbers were based on the cavity air temperature adjacent to the shroud, which was predicted using the Owen–Tang buoyancy model. Heat transfer from the shroud was consistent with free convection from a horizontal plate in a gravitational field. Maximum likelihood estimation was used with a Rayleigh–Bénard equation to correlate the shroud Nusselt number with the local Grashof number. Second, an energy balance was used to calculate the enthalpy rise of the axial throughflow from the measured disk and shroud heat fluxes. Disk fluxes were derived from radial distributions of measured steady-state disk temperatures using a Bayesian model and the equations for a circular fin. The calculated throughflow temperature rise was consistent with direct thermocouple measurements. The complex, three-dimensional flow near the cavity entrance can result in enthalpy exchange penetrating upstream in the throughflow, and rotationally induced flow can create upstream axial flow in the outer part of the annulus.

Burial and Heat Flux Modelling along a Southern Vøring Basin Transect: Implications for the Petroleum Systems and Thermal Regimes in the Deep Mid-Norwegian Sea

A key aspect on the evolution of rifted terranes and the prospectivity of the overlying sedimentary basins is heat. Temperature determines the deformation regime of crustal and mantle rocks and, thus, the style of rifting and geometry of rift basins. The generation of hydrocarbons from organic-rich rocks and reservoir conditions depend primarily on temperature. In this study, we model the thermal–burial history of the southern Vøring Basin (Mid-Norway Margin) along a regional transect (2-D), integrating basin- and lithospheric-scale processes. A model that accounts for the main extensional pulses that shaped the Mid-Norway Margin is in good general agreement with the present–past geothermal gradients inferred from borehole temperature and maturity data and the surface heat flux measurements in the proximal and intermediate margin. This supports a near steady-state, post-rift margin setting, following the break-up in the early Eocene. Significant discrepancies are, however, observed in the distal margin, where the borehole temperatures suggest (much) higher thermal gradients than model predicted and implied by the average surface heat flux. We speculate that the higher thermal gradients may result from deep-seated (mantle dynamics) thermal anomalies and/or recurrent hydrothermalism during periods of greater tectonic stress (regional compression and glacial loading rebound) and test the implications for the maturity of the Vøring Basin. The modelling results show, for example, that, depending on the thermal model assumptions, the depth and age of the optimal mid-Late Cretaceous source-rock horizons may vary by more than 2 km and 10 Ma, respectively.

Experimental study on the advective heat flux of a heat exchanger for passive cooling of spent fuel pools by temperature anemometry grid sensor

In commercial nuclear power plants spent fuel assemblies are usually stored in actively cooled water pools. The continuous decay heat release represents a potential risk in case of a station black out scenario. Thus two-phase passive heat removal systems are a key technology to enhance the safety of nuclear power plants. Such systems work only by the energy provided from the heat source, e.g. by the maintenance of a natural convection cooling. A heat transfer loop using air as an unlimited heat sink consists of a primary heat exchanger in the spent fuel pool water and a secondary heat exchanger located in ambient air. Thus the measurement of the heat flux, which gets transferred from the pool to the ambient air, is an important task. If one would measure heat flux, flow rates and temperatures in many positions by help of local probes, the natural flow would get strongly disturbed. For that reason we introduce a heat flux measurement around the secondary heat exchanger located in ambient air, which applies temperature and velocity measurement by an anemometric principle.A 6.5m long flow channel with an electrical heated finned tube heat exchanger was set up at the TOPFLOW facility at HZDR. Since the tubes of a heat exchanger would be tilted in a passive heat removal system, i.e. to allow drainage of the condensed heat transfer medium, different tiled angles were adjusted to 0° (horizontal), 20°,30° and 40°. The frontal velocity was varied between 0.5ms and 4ms and three thermocouples were placed up- and downstream of the heat exchanger respectively. A Temperature Anemometry Grind Sensor (TAGS) was located downstream the heat exchanger. It consists of a wire grid with platinum resistance elements, which are placed in the small sub-channels of a flow straightener to generate laminar flow profiles. Two methods were used to calculate the heat flux: arithmetical average and weighting of the flow area. The results of velocity was compared with the average velocity measured by the volume flow control and out of the velocity and temperature the heat flux was calculated and compared with electrical supplied heat flux. The calculated average velocity measured by the TAGS corresponds well with the velocity measured by the volume flow controller up to approximately 3ms with a maximum deviation of ±5%, but underestimates the velocity measured by the volume flow controller at higher velocities. The heat flux was calculated by five methods, 1.) from the three thermocouples up- and downstream of the heat exchanger, 2.) from the average temperatures measured by the TAGS, 3.) from the weighted temperature measured by the TAGS, 4.) from the average temperature and velocity measured by the TAGS and 5.) from the weighted temperature and velocity measured by the TAGS. In this order the accuracy of methods increases compared to the electrical supplied heat flux. For the last method the maximum deviation was 6.5% for all tilt angles. This measurement concept determines the heat flux without disturbing the flow in the loop.

Determining transient heat transfer coefficient for dropwise condensation in the presence of an air flow

It is necessary to understand humid air condensation because of its various applications, such as water harvesting. In this study, the influence of airflow on the condensation heat transfer coefficient of humid air on a horizontal surface was investigated experimentally. Airflow velocities from 1 to 15 m/s were investigated, because the condensate's shedding usually happens in this range. A relative humidity of 10–80% and subcooling temperature (Tsc) of 0–10 °C were used to achieve both single-phase and condensation regimes. To study the relationship between condensate morphology and heat transfer coefficient (HTC), transient and instantaneous heat flux measurements were required. To facilitate this, a transient inverse heat conduction method was developed to characterize the time-varying surface heat flux and associated heat transfer coefficient. A 5-fold decrease in response time was found for the transient method compared to the steady-state method. The effect of condensation parameters on the heat transfer coefficient, as well as the relationship between condensate morphology and heat transfer coefficient, is discussed. The results show that HTC for the subcooling of T = 0 °C is smaller than for other temperatures. Also, the effect of RH on condensation was investigated and higher HTC was found for higher RHs. The results clearly show that the shedding of condensate kept the average droplet size low and doubled heat transfer performance improvement.

A Na density lidar method and measurements of turbulence to 105 km at the Andes Lidar Observatory

This study presents a method of measuring atmospheric turbulence from resonance-fluorescence lidar observations of atmospheric Na layer density fluctuations, which is used to characterize turbulent eddy diffusion (kzzTurb) from 85 km to 105 km altitude over the Andes Lidar Observatory (ALO) in Cerro Pachón, Chile, (30.3°S, 70.7°W) at timescales between 12 seconds and 78 seconds. Na lidar measurements of heat, momentum, and constituent fluxes at turbulence scales have traditionally been limited to the 85–100 km region due to signal limitations; however, the ”Na density” method described herein offers a 3x signal-to-noise ratio improvement over Doppler heat flux measurements, enabling determination of eddy diffusion to higher altitudes and at shorter timescales. The presented mean turbulent eddy diffusion profile is determined from 115 h of zenith data acquired over 25 nights via the Na density method. Results are supplemented by off-zenith data for all 25 nights, which is used to examine atmospheric stability. Mean kzzTurb over the timescales analyzed ranged between 1.2×105 cm2s−1 and 5.7×105 cm2s−1 in the 85–100 km region and increased from a minimum at 98 km to a maximum of 4.5×106 cm2s−1 near 105 km altitude. The mean profile is compared with the Doppler method for (i) the same ALO dataset discussed herein and (ii) vertical-only ALO data between 85 km and 100 km altitude. The critical region (95–110 km) of diffusive coupling in the mesosphere and lower thermosphere (MLT) differs in forcing uniquely with a dominance of wind shear and associated instabilities. Source investigations pertaining to the induced transport difference from the critical to the lower MLT region (80–95 km), where the effects of damped atmospheric gravity waves and convective instabilities are well-established, require an ability to gather data on the variability of turbulence with altitude, latitude, and season, as well as atmospheric wave activity.

Natural convection from a triangular array of isothermal horizontal cylinders

Natural convection heat transfer from three isothermally heated horizontal cylinders submerged in water in a triangular arrangement is investigated. Two configurations, named here as one over two and two over one, are characterised for three cylinder spacings (S = 2, 3 and 4 cylinder diameters) and Rayleigh number conditions (Ra = 2×106, 4 × 106 and 6 × 106). Combined local heat flux measurements and flow velocity measurements using particle image velocimetry are employed to examine the governing heat transfer mechanisms. For many cases of the one over two configuration, substantial differences from the single cylinder case are noted. The buoyant plumes generated from the two lower cylinders interact with the flow field and heat transfer around the upper cylinder, altering the local fluid velocities and temperature fields. This effect is dependent on both the inter-cylinder spacing and the Rayleigh number condition. For the two over one setup, both upper cylinders for all cases, except S=4D and Ra = 6 × 106, behave in the same manner as a single cylinder. This is due to the competing effects of the buoyant plume rising from the lower cylinder and the restriction of flow through the gap between the two upper cylinders.

Thermal contact resistance evaluation of a thermoelectric system by means of three I-V curves

To achieve a suitable performance in a thermoelectric (TE) device it is important to minimize the thermal contact resistances between the device external surfaces and the heat exchangers of the system (heat source and heat sink). Despite its relevance, there are not many methods available for the evaluation of the thermal contact resistance, and the existing ones typically employ complex setups. Here, we present a new method to determine the thermal contact resistance of a TE device thermally contacted to a heat sink and a heat source. The method is based on performing three current-voltage (I-V) curves at different system conditions under a small temperature difference. First, an I-V curve with a high voltage scan rate, which avoids the variation of the initial temperature difference, provides the ohmic resistance. A second I-V curve performed with a constant input heat power (or the device suspended) provides the TE resistance. Finally, a third I-V curve with a constant temperature difference between the heat exchangers allows obtaining the thermal contact resistance. Using this method, a thermal contact resistivity value of 3.57 × 10−4 m2KW−1 was obtained for a commercial Bi-Te TE module contacted with a heat source and a heat sink using thermal grease as thermal contact interface material, which is in good agreement with reported values. The new method is highly advantageous, since neither involves complex setups nor requires the measurement of heat fluxes. Moreover, it measures directly under operating conditions for small temperature differences.

Method for increasing upper limit of heat flux measurement of slug calorimeter in high enthalpy plasma jet

The temperature of the high-power inductively coupled plasma jet is very high, and its temperature is difficult to measure directly. The heat flux becomes a thermodynamic characteristic to measure the plasma jet. The existing heat flux calculation method is based on the temperature change rate after the response time. The slug is required to stay in the high enthalpy jet area for a longer time. With the slug temperature reaching the melting point as the upper limit, the shorter the residence time, the greater the upper limit of the measured heat flux. In this paper, the first-order transient solution is added to the steady-state solution of temperature (the calculation equation of the existing method), which can shorten the response time. The shortening of the response time can reduce the residence time of the slug in the jet region, and the reduction in the residence time can increase the upper limit of the calorimeter heat flux measurement. This paper uses numerical simulation and experimental methods to verify that the steady-state solution method and the first-order transient solution method can obtain consistent heat flux results. Using the first-order transient solution method can reduce the residence time of the slug calorimeter in the jet region. According to the shortening of the residence time, the method of using the first-order transient solution can increase the upper limit of the heat flux measurement by more than 25%.

Intraoperative Temperature Monitoring with Zero Heat Flux Technology (3M SpotOn Sensor) in Comparison with Tympanic and Oesophageal Temperature and Hypotermia Risk Factors: An Observational Study.

ObjectiveInadvertent hypothermia (body temperature below 35°C) is a common and avoidable challenge during surgery under anaesthesia. It is related to coagulation (clotting) disorders, an increase in blood loss, and a higher rate of wound infection. One of the methods for non-invasive monitoring of the core body temperature is the 3M SpotOn zero heat flux method. In this approach, sensors placed at the frontal region of the patient measure the skin temperature by creating an isothermic channel. The study aimed to determine the risk factors for hypothermia and compare the 3M SpotOn zero heat flux method with the tympanic membrane (eardrum) and oesophageal (food pipe) temperature measurement methods.DesignObservational.Data sourcesThe patients’ data were collected, including age, gender, weight, BMI, other illnesses, smoking history, type of anaesthesia, duration of surgery, operating room temperature, pulse rate, blood pressure, blood loss, and transfusions. Body temperature was measured by the tympanic membrane method before and after surgery, oesophageal method during surgery, and SpotOn measurements throughout all three periods were recorded.Eligibility criteriaInclusion criteria was: adult patients, both genders, who had undergone major abdominal cancer surgery at the trialists’ institution, in whom the SpotOn zero heat flux, tympanic membrane, and oesophageal temperature measurement methods had all been used. Participant exclusion criteria was the absence of recorded data.ResultsIn this study, inadvertent intraoperative hypothermia incidence was 38.1% in the recovery room. Although gender, presence of comorbidities, history of smoking, administration of epidural anaesthesia, and requirement of blood transfusion [red blood cells (RBCs) and fresh frozen plasma (FFP)] did not affect hypothermia significantly during admission to the recovery room, prewarming the patient throughout the operation prevented the occurrence of hypothermia significantly (p=0.004). Additionally, as the American Society of Anaesthesiologists (ASA) physical status score worsened, the rate of hypothermia increased significantly (Frequency: 1st degree, 29.4%; 2nd degree, 47.5%; 3rd degree, 66.7%; X2Slope- p=0.047).ConclusionThe most significant risk factor was found to be not prewarming the patient as a strict procedure, and as the ASA physical status score worsened, the rate of hypothermia increased significantly. Besides, the SpotOn method provided temperature measurements as good as the oesophageal temperature measurements. Clinical Trial registration: ISRCTN 14027708.

An analog period method for gap‐filling of latent heat flux measurements

AbstractPractically all records of eddy‐covariance flux measurements are affected by gaps, caused by several reasons. In this work, we propose analog period (AP) methods for gap‐filling, and test them for filling gaps of latent heat flux at five AmeriFlux sites. The essence of the methods is to look for periods in the record that bear a strong resemblance, in the variable to be filled, to the periods immediately before and after the gap. Similarity between periods is gauged by the coefficient of determination, and the search for similar periods and their ranking is straightforward. The methods are developed in a univariate version (that uses only the latent heat flux data series itself) and several multivariate ones, that incorporate sensible heat flux, ground heat flux and net radiation data. For each set of independent variables used for gap‐filling, the methods are tested against an existing gap‐filling procedure with similar data requirements. Thus, the univariate version is tested against the mean diurnal variation method, and the multivariate versions are tested against corresponding simple and multiple linear regression techniques that use energy‐budget data, and in one case the evaporative fraction as well. In our tests, the proposed univariate version performs better than the mean diurnal variation method, and the multivariate versions perform better than simple/multiple linear regression methods. An often used available computer package, REddyProc, was also tested as a basis of comparison. In general, the proposed methods (in univariate and multivariate versions) and simple/multiple linear regressions performed better than REddyProc. For the datasets analysed, gap filling via the evaporative fraction method performed poorly.

The study of heat transfer during condensation on inclined pipes by gradient heatmetry

The paper presents results of studying of heat transfer during condensation on the outer surface of inclined pipe by using gradient heatmetry. The proposed approach made it possible to estimate distribution of local heat flux per unit area in several sections along the pipe’s length. Combination of gradient heatmetry and thermometry allows us to show dependence of heat transfer coefficient from the angle of pipe inclination. Under experimental conditions the maximal average heat transfer coefficient, α = 6.94 kW/(m2 • K), was observed when the pipe was tilted at the angle of ψ = 20° from vertical. The relative uncertainty of measured heat flux per unit area was of 7.5 %, and for heat transfer coefficient it does not exceed the level of 8.4%. The use of gradient heatmetry in this study provides us information about films thickness distribution over the pipe surface without optical visualization, which is especially important in experiments at industrial heat exchangers.

Air-Sea Interactions over Eddies in the Brazil-Malvinas Confluence

The Brazil–Malvinas Confluence (BMC) is one of the most dynamical regions of the global ocean. Its variability is dominated by the mesoscale, mainly expressed by the presence of meanders and eddies, which are understood to be local regulators of air-sea interaction processes. The objective of this work is to study the local modulation of air-sea interaction variables by the presence of either a warm (ED1) and a cold core (ED2) eddy, present in the BMC, during September to November 2013. The translation and lifespans of both eddies were determined using satellite-derived sea level anomaly (SLA) data. Time series of satellite-derived surface wind data, as well as these and other meteorological variables, retrieved from ERA5 reanalysis at the eddies’ successive positions in time, allowed us to investigate the temporal modulation of the lower atmosphere by the eddies’ presence along their translation and lifespan. The reanalysis data indicate a mean increase of 78% in sensible and 55% in latent heat fluxes along the warm eddy trajectory in comparison to the surrounding ocean of the study region. Over the cold core eddy, on the other hand, we noticed a mean reduction of 49% and 25% in sensible and latent heat fluxes, respectively, compared to the adjacent ocean. Additionally, a field campaign observed both eddies and the lower atmosphere from ship-borne observations before, during and after crossing both eddies in the study region during October 2013. The presence of the eddies was imprinted on several surface meteorological variables depending on the sea surface temperature (SST) in the eddy cores. In situ oceanographic and meteorological data, together with high frequency micrometeorological data, were also used here to demonstrate that the local, rather than the large scale forcing of the eddies on the atmosphere above, is, as expected, the principal driver of air-sea interaction when transient atmospheric systems are stable (not actively varying) in the study region. We also make use of the in situ data to show the differences (biases) between bulk heat flux estimates (used on atmospheric reanalysis products) and eddy covariance measurements (taken as “sea truth”) of both sensible and latent heat fluxes. The findings demonstrate the importance of short-term changes (minutes to hours) in both the atmosphere and the ocean in contributing to these biases. We conclude by emphasizing the importance of the mesoscale oceanographic structures in the BMC on impacting local air-sea heat fluxes and the marine atmospheric boundary layer stability, especially under large scale, high-pressure atmospheric conditions.

Fast-Response transient heat flux measurements in a plasma wind tunnel

A fast response heat transfer gauge has been developed to measure the radial distribution and the fluctuations of heat flux in a supersonic arcjet plasma wind tunnel. The heat flux gauge consists of 3.2 mm diameter coaxial surface junction thermocouple which was positioned behind a thin layer of PTFE and mounted in a ESA standard 50 mm diameter flat faced copper probe head. A non-dimensional impulse response for the heat flux gauge was identified using pulsed optical power deposition from a laser. The impulse response was used in combination with reference measurements from a calorimeter at a single location to determine the distribution and fluctuations in heat flux. Eight traverses of the PWK4 jet at the University of Stuttgart confirmed a symmetric Gaussian-like heat flux distribution with a centreline heat flux consistent to within ±6%. These distributions were measured in less than one second, representing a significant gain in productivity when compared to calorimeter-based heat flux measurements where probes must be held stationary at a number of locations in order to resolve spatial distributions. At this particular PWK4 operating condition, which had a flow stagnation enthalpy of approximately 15 MJkg−1, heat flux fluctuations of up to ± 140 kWm-2 (corresponding to a relative variation of 15% of the centreline heat flux) were identified near the vicinity of the nozzle centreline for frequencies from 4 Hz to 1 kHz.

Experimental investigation of blunt cone model at hypersonic Mach number 7.25

Experiments were carried out in hypersonic shock tunnel in Defence Research and Directorate Laboratory at hypersonic Mach number of 7.25 using an 11.37° apex-angle blunt cone model. Heat flux measurement was carried out on cone model at different angles of attack with angle of rotation ϕ = 0° to 360° in steps of 45° with vacuum sputtered platinum thin film sensors. The measured experimental value of heat transfer data at stagnation point was compared with theoretical value estimated Fay and Riddell correlation. As angle of rotation was increased from ϕ = 0° to ϕ = 180°, the shock wave became closer to model surface due to high density ratio across the shock wave and consequently heat transfer rate became higher.

The Wildland Fire Heat Budget-Using Bi-Directional Probes to Measure Sensible Heat Flux and Energy in Surface Fires.

Sensible energy is the primary mode of heat dissipation from combustion in wildland surface fires. However, despite its importance to fire dynamics, smoke transport, and in determining ecological effects, it is not routinely measured. McCaffrey and Heskestad (A robust bidirectional low-velocity probe for flame and fire application. Combustion and Flame 26:125–127, 1976) describe measurements of flame velocity from a bi-directional probe which, when combined with gas temperature measurements, can be used to estimate sensible heat fluxes. In this first field application of bi-directional probes, we describe vertical and horizontal sensible heat fluxes during the RxCADRE experimental surface fires in longleaf pine savanna and open ranges at Eglin Air Force Base, Florida. Flame-front sensible energy is the time-integral of heat flux over a residence time, here defined by the rise in gas temperatures above ambient. Horizontal flow velocities and energies were larger than vertical velocities and energies. Sensible heat flux and energy measurements were coordinated with overhead radiometer measurements from which we estimated fire energy (total energy generated by combustion) under the assumption that 17% of fire energy is radiated. In approximation, horizontal, vertical, and resultant sensible energies averaged 75%, 54%, and 64%, respectively, of fire energy. While promising, measurement challenges remain, including obtaining accurate gas and velocity measurements and capturing three-dimensional flow in the field.