Wall Temperature Measurements Research Articles

Wall temperature measurements at elevated pressures and high temperatures in sooting flames in a gas turbine model combustor

Wall temperatures were measured with thermographic phosphors on the quartz walls of a model combustor in ethylene/air swirl flames at 3 bar. Three operating conditions were investigated with different stoichiometries and with or without additional injection of oxidation air downstream of the primary combustion zone. YAG:Eu and YAG:Dy were used to cover a total temperature range of 1000–1800 K. Measurements were challenging due to the high thermal background from soot and window degradation at high temperatures. The heat flux through the windows was estimated from the temperature gradient between the in- and outside of the windows. Differences in temperature and heat flux density profiles for the investigated cases can be explained very well with the previously measured differences in flame temperatures and flame shapes. The heat loss relative to thermal load is quite similar for all investigated flames (15–16%). The results complement previous measurements in these flames to investigate soot formation and oxidation. It is expected, that the data set is a valuable input for numerical simulations of these flames.

Two-dimensional heat transfer coefficients with simultaneous flow visualisations during two-phase flow boiling in a PDMS microchannel

Infrared (IR) thermography was combined with simultaneous high speed flow visualisation and pressure measurements from integrated pressure sensors inside the microchannel, in order to produce two-dimensional (2D) high spatial and temporal resolution two-phase heat transfer coefficient (HTC) maps across the full domain of a polydimethylsiloxane (PDMS) high aspect ratio (a = 22) microchannel (Dh = 192 μm). High spatial and temporal resolution two-dimensional wall temperature measurements and pressure data were obtained for a range of mass fluxes (G = 7.37–298 kg m−2 s−1) and heat fluxes (q = 13.64–179.2 kW m−2) using FC-72 as the working liquid. The 3D plots of HTC provided fine details of local variations during bubble nucleation, confinement, elongated bubble, slug flow and annular flow regime. The optical images from the channel top revealed the local flow regimes and were correlated with simultaneous thermal images obtained from the channel base. The 3D plots of the 2D two-phase heat transfer coefficient with time across the microchannel domain were correlated with vapour-liquid dynamics and liquid film thinning (from the contrast of the optical images) which caused suspected dryout. The correlation between the synchronised at the same frame rate high-resolution thermal and optical images will assist in a better understanding of the heat transfer mechanisms during two-phase flow boiling in microchannels. This work intends to give a better insight into heat transfer coefficient spatial variation during flow instabilities with two-dimensional heat transfer coefficient plots as a function of time during a cycle of liquid–vapour alternations.

Air adsorption on the gas-liquid interface in vapor condensation across horizontal tube

Air adsorption on the gas-liquid interface in vapor condensation across horizontal tube was investigated experimentally. An air hole with a diameter of 0.006m was opened at z=0.755m and θ = 50° on the jacket tube wall. A total of 16 thermistors were mounted uniformly on the horizontal tube wall along the circumference of z=0.27m and z=0.72m to measure wall temperature. The relative air content, ending difference, heat transfer coefficient and Nusselt number were calculated, and the in-leakage air adsorption process on the gas-liquid interface was analysed. The key factors that affect air adsorption on the gas-liquid interface are relative air content, heat load, pressure, and temperature. The air adsorption amount on the gas-liquid interface improves with the increase in relative air content and reduces with the increase in heat load. The air adsorption on the gas-liquid interface in the condensation of vapor over the horizontal tube has a similar change rule as Langmuir’s isothermal adsorption law. The air adsorption amount on the gas-liquid interface increases with the increase in pressure and the reduction in temperature. Higher vapor condensation decreases the air adsorption amount on the gas-liquid interface, causing the adsorption equilibrium to move towards desorption. The error between the variation of experimental in-leakage air mass flux with the pressure drop rate and the results from a formula recommended by America Heat Exchange Institute (HEI) is within −28%–23%. The present experimental results were compared with the results of the works of Nusselt (1916), Sherkriladze and Gomelauri (1966), Rose (1984), Fujii et al. (1972) and Chen and Lin (2009).

Estimating local heat transfer coefficients from thin wall temperature measurements

An approach to experimental estimation of local heat transfer coefficient on a plane wall has been described. The approach is based on measurements of heat-transfer fluid and wall temperatures during some certain time of wall cooling. The wall was a thin plate, a printed circuit board, made of composite epoxy material covered with a copper layer. The temperature field can be considered uniform across the plate thickness when heat transfer is moderate and thermal resistance of the plate in transversal direction is low. This significantly simplifies the heat balance written for the wall sections that is used to estimate the heat transfer coefficient. The copper layer on the plate etched to form a single strip acted as resistance thermometers that measured the local temperature of the wall.

Measurement of heat transfer coefficient and pressure drop during evaporation of R134a in new type facility with one pass flow through microchannel tube

A new facility has been built for experimental study on microchannel and introduced in this paper. Six heat transfer coefficient and six pressure drop measurements can be conducted simultaneously in one pass from vapor quality of 0 to 1 on the facility. Two water-jacket-design heat exchangers are placed top and bottom on each test section for heating the refrigerant. In each test section, the top and bottom sides are heated and controlled separately to ensure uniform conditions. The environmental heat loss and wall temperature measurements are corrected to increases confidence of results. Port geometry is measured with an optical microscope. Heat transfer coefficient and pressure drop of R134a are measured in a 24-port microchannel tube. The single-phase pressure drop follows the rule of round tube and fRe is 64. The single-phase Nusselt number is more sensitive to Reynolds number, compared to large tubes. As vapor quality increases, two-phase pressure drop increases until quality of 0.9, and then stops increasing or even drops; two-phase heat transfer coefficient increases until quality of 0.5 to 0.6 and then drops. Higher mass flux or lower saturation temperature will increase the pressure drop. Heat flux and mass flux have strong impact on heat transfer coefficient, and the effect of saturation temperature is not clear.

Parametric study of heat transfer in an electric arc furnace and cooling system

The present study deals with a numerical investigation of an electric arc furnace (EAF). A model based on radiative heat transfer has been generated to estimate the temperature distribution inside the furnace. The obtained results from this model provide realistic and reasonable predictions of the temperature, comparing with the results of the experimental measurements of wall temperature. Based on calculated temperatures fields, full numerical analysis of the cooling panel was performed. The numerical results from the cooling system simulation were also compared with experimental measurements of outlet water temperature from experimental apparatus and showed good accuracy. In addition, a parametric study was carried out to determine the influence of geometrical parameters and slag layer formation inside the furnace on temperature distribution within the furnace. It was concluded that the diameter of the furnace is the main geometrical parameter affecting temperature distribution in a furnace and the roof inclination angle appeared to be of secondary importance. The effects of slag layer thickness on the walls were also numerically investigated and it was observed that the formation of slag layer on the furnace walls has a significant impact on the safe operation of the furnace and improved furnace efficiency.

Experimental study of air accumulation in vapor condensation across horizontal tube

In this study, air accumulation in vapor condensation across a horizontal tube was investigated experimentally. A total of 16 thermistors were mounted uniformly on the horizontal tube wall along the circumference of z=0.17m and z=0.63m to measure wall temperature. Results show that vapor exists as a three-dimensional diffusion flow and air is carried by vapor toward the downstream at θ=135°–225° and z=0–0.6m, and forms a saturated moist air region there, whereas another region is full of moist vapor. A vapor flowing front lies at the joint of two regions, where interdiffusion between vapor and air is in dynamic equilibrium. In the saturated moist air region, the ratio of gas film layer to overall thermal resistance is within the range of 0.92–0.97, the air mole fraction on the gas–liquid interface is within the range of 0.75–0.87, and the heat transfer coefficient at the condensation side is less than 300Wm−2K−1. An increase in cooling water mass flux pushes the vapor flowing front forward, expanding the moist vapor region, ultimately enlarging the vapor condensation area. The present experimental results were compared with the results of the works of Zhou and Rose (1996), Sherkriladze and Gomelauri (1966), Rose (1984), Fujii et al. (1972), Memory et al. (1993), and Chen and Lin (2009). The wall temperature distribution and Nu‾/Rel0.5 variation are reasonable.

Umbilical temperature correlation with core and skin temperatures at rest, in the heat and during physical activity

Purpose: to determine the correlation of umbilical temperatures (Tumb) with simultaneously recorded chest wall temperature (Tchest) and rectal temperature (Trectal) in adults during rest, heat exposure and exercise.Methods: A total of 28 healthy men, wearing different types of clothing (athletic garb, a spandex full body heating garment, firefighter bunker gear) had average and peak umbilical, chest wall and rectal temperature measurements taken during sedentary temperature stabilisation stages, heat exposure periods and active exercise phases.Results: Curvilinear relationships were noted between Tchest and Tumb compared with Trectal and their association became noticeably positive and linear at approximately 35.5 °C. Polynomial regression analysis of Trectal with linear and quadratic forms of Tchest and Tumb indicated an overall R2 of 0.657 and 0.767, respectively. Bivariate analysis of a restricted data set (where Tchest and Tumb ≥35.5°), indicated that Tumb was significantly associated with Trectal (raverage = 0.710, p <0.001; rpeak = 0.841, p <0.001) and Tchest was also significantly associated with Trectal, but less so (raverage = 0.570, p <0.001; rpeak = 0.699, p <0.001).Conclusions: the umbilicus offers a non-invasive, peripheral site for measurement of temperature that more closely correlated with body core temperature than Tchest when core temperature was ≥35.5 °C.

Buoyancy effects on turbulent heat transfer of supercritical CO2 in a vertical mini-tube based on continuous wall temperature measurements

Convection heat transfer of supercritical pressure fluid is important in industrial applications such as supercritical power stations, the supercritical CO2 Brayton cycle, Carbon Capture Utilization and Storage, and the thermal protection for rocket thrusters. Previous research has confirmed that there are three heat transfer regions for convection heat transfer of supercritical pressure fluid flowing inside vertical tubes: normal heat transfer, heat transfer deterioration, and heat transfer enhancement. However, existing research still carries inconsistent results, especially regarding the onsets of heat transfer deterioration of supercritical pressure fluid flow in vertical tubes. Here we propose a new view, by estimating the location where local fluid temperature, Tf(r) equals to the pseudocritical temperature, Tpc, in the transversal section inside the tube, then analyzing the relationship between the location where Tf(r)=Tpc and the turbulent boundary layers in the near wall region, to identify buoyancy effects on turbulent heat transfer. By taking advantage of infrared thermometry measurement to achieve continuous wall temperature, theoretical analysis was validated by experiments of supercritical pressure CO2 in a vertical mini-tube with inner diameter of 0.953mm. The experiments were performed for a pressure of 7.6–9.5MPa, inlet mass flux from 255kg/m2s to 685kg/m2s, and heat flux from 12kW/m2 to 63kW/m2. It is found that in contrast with the previous results, when the value of y+ at the location of Tf(r)=Tpc, y+|Tf(r)=Tpc, less than 5, heat transfer enhances for upward and decreases for downward flow due to the buoyancy effect. With the heat flux increasing or mass flux decreasing, the buoyancy effect on the turbulent convection heat transfer characteristics of supercritical pressure fluid in a vertical heated tube is be featured as the following regimes: for the upward flow, from no-effect to slight enhancement, significant reduction, recovery and then enhancement; for the downward flow, from no-effect to slight weaken, and then enhancement. Moreover, the experimental results showed that y+|Tf(r)=Tpc=5 is where there is an onset of heat transfer deterioration for the upward flow in a vertical heated tube induced by buoyancy effects. The results presented provide a better understanding of the special features of the turbulent convection heat transfer of supercritical pressure fluids in mini channels.

Inverse heat conduction estimation of inner wall temperature fluctuations under turbulent penetration

Turbulent penetration can occur when hot and cold fluids mix in a horizontal T-junction pipe at nuclear plants. Caused by the unstable turbulent penetration, temperature fluctuations with large amplitude and high frequency can lead to time-varying wall thermal stress and even thermal fatigue on the inner wall. Numerous cases, however, exist where inner wall temperatures cannot be measured and only outer wall temperature measurements are feasible. Therefore, it is one of the popular research areas in nuclear science and engineering to estimate temperature fluctuations on the inner wall from measurements of outer wall temperatures without damaging the structure of the pipe. In this study, both the one-dimensional (1D) and the two-dimensional (2D) inverse heat conduction problem (IHCP) were solved to estimate the temperature fluctuations on the inner wall. First, numerical models of both the 1D and the 2D direct heat conduction problem (DHCP) were structured in MATLAB, based on the finite difference method with an implicit scheme. Second, both the 1D IHCP and the 2D IHCP were solved by the steepest descent method (SDM), and the DHCP results of temperatures on the outer wall were used to estimate the temperature fluctuations on the inner wall. Third, we compared the temperature fluctuations on the inner wall estimated by the 1D IHCP with those estimated by the 2D IHCP in four cases: (1) when the maximum disturbance of temperature of fluid inside the pipe was 3°C, (2) when the maximum disturbance of temperature of fluid inside the pipe was 30°C, (3) when the maximum disturbance of temperature of fluid inside the pipe was 160°C, and (4) when the fluid temperatures inside the pipe were random from 50°C to 210°C.

Effects of Double Wall Cooling Configuration and Conditions on Performance of Full-Coverage Effusion Cooling

Experimental results are presented for a double wall cooling arrangement which simulates a portion of a combustor liner of a gas turbine engine. The results are collected using a new experimental facility designed to test full-coverage film cooling and impingement cooling effectiveness using either cross flow, impingement, or a combination of both to supply the film cooling flow. The present experiment primarily deals with cross flow supplied full-coverage film cooling for a sparse film cooling hole array that has not been previously tested. Data are provided for turbulent film cooling, contraction ratio of 1, blowing ratios ranging from 2.7 to 7.5, coolant Reynolds numbers based on film cooling hole diameter of about 5000–20,000, and mainstream temperature step during transient tests of 14 °C. The film cooling hole array consists of a film cooling hole diameter of 6.4 mm with nondimensional streamwise (X/de) and spanwise (Y/de) film cooling hole spacing of 15 and 4, respectively. The film cooling holes are streamwise inclined at an angle of 25 deg with respect to the test plate surface and have adjacent streamwise rows staggered with respect to each other. Data illustrating the effects of blowing ratio on adiabatic film cooling effectiveness and heat transfer coefficient are presented. For the arrangement and conditions considered, heat transfer coefficients generally increase with streamwise development and increase with increasing blowing ratio. The adiabatic film cooling effectiveness is determined from measurements of adiabatic wall temperature, coolant stagnation temperature, and mainstream recovery temperature. The adiabatic wall temperature and the adiabatic film cooling effectiveness generally decrease and increase, respectively, with streamwise position, and generally decrease and increase, respectively, as blowing ratio becomes larger.

Evaluation of swirl effect on the Global Energy Balance of a HSDI Diesel engine

In the last years, a growing interest about increasing engine efficiency has led to the development of new engine technologies. Since air motion in the chamber is a key issue in internal combustion engines to improve the air-fuel mixing process and achieve faster burning rates, modern Diesel engines are designed to generate gas vorticity (swirl) that lead to enhanced turbulence in the combustion chamber. However, the use of swirl has a direct effect on fuel consumption due to the changes in the in-cylinder processes, affecting indicated efficiency, and also on the air management. An analysis, based on the engine Global Energy Balance (GEB), is presented to thoroughly assess the behavior of a high speed direct injection Diesel engine under variable swirl levels at different operating points. The tests have been performed keeping constant both the conditions at intake valve closing and combustion phasing, thus minimizing the variability due to in-cylinder conditions and the combustion process. The analysis includes a combination of theoretical (0D models) and experimental tools (heat rejection and wall temperature measurement) used to ensure control of in-cylinder conditions and to provide detailed explanation of the different phenomena affecting engine efficiency when swirl ratio is modified. Based on these tools, impact of swirl on the engine GEB is analyzed in detail paying special attention to engine efficiency and heat transfer in the chamber. Results show that increasing swirl has two main effects regarding the gross indicated efficiency (ηi): on one hand chamber heat rejection increases and therefore ηi diminishes about −0.5% at low load and −0.4% at high load; on the other hand combustion development is affected and thus a ηi improvement higher to 1.5% is achieved at low load and speed. The combination of these effects leads to a gross indicated efficiency increase higher to 1% at an optimum swirl ratio that diminishes when engine speed increases. In addition, pumping losses effect dominates brake efficiency behavior, which always diminishes (from −0.9% to −1.4%) when swirl increases.

Embedded thermocouple wall temperature measurement technique for scraped surface heat exchangers

Heating and cooling processes involving viscous fluids, crystallization processes or with fouling tendency require often the employment of scraped surface heat exchangers to enhance the heat transfer. In these cases, obtaining the heat transfer coefficient is complex due to the difficulty of measuring the wall temperature. The present work introduces an innovative measurement technique to retrieve the scraped wall temperature based on embedded thermocouples, welded directly into the wall plate. The thermocouple wires were introduced into a knockout and welded with a filler material. Once welded, the entire set was calibrated in a cold room at controlled temperature. A total of 26 T-type thermocouples were welded to a stainless steel wall substrate, tested later in a rotating scraped surface heat exchanger employed in the ice slurry production. The thermocouples presented a variance of 0.3°C and an accuracy after calibration of 0.2°C. The deviation between the scraped wall temperature and the thermocouple measurement was assessed by 2D numerical simulations of the transient heat conduction across the wall substrate. The influence of the wall substrate thickness, thermocouple location and scraping velocity has been considered.

Validation of magnetic resonance concentration measurements with adiabatic wall temperature measurements

Adiabatic wall temperature measurements were obtained in a high subsonic Mach number airflow experiment and compared with concentration measurements near the surface from a low-speed liquid flow experiment. Excellent agreement between the temperature and concentration measurements validates the investigation of turbulent mixing phenomena in compressible gas flows through the study of incompressible liquid flows with magnetic resonance techniques.

Experimental Study on Fluid Flow and Heat Transfer from a Rectangular Prism Approaching the Wall of a Wind Tunnel

AbstractExperimental investigations in fluid flow and heat transfer have been carried out to study the effect of wall proximity due to flow separation around rectangular prisms. Experiments have been carried out for the Reynolds number 2.6 × 104, blockage ratios are 0.1, 0.2, 0.3, and 0.4, aspect ratios (d/c) are 1.5, 1.33, 0.667, and 0.333, with different height‐ratios and various angles of attack. The static pressure distribution has been measured on all faces of the rectangular prisms. The results have been presented in the form of pressure coefficient, drag coefficient for various height‐ratios and blockage ratios. The pressure distribution shows positive values on the front face whereas on the rear face negative values of the pressure coefficient have been observed. The drag coefficient decreases with the increase in angle of attack as the height‐ratio decreases. The heat transfer experiments have been carried out under constant heat flux conditions. Heat transfer coefficients are determined from the measured wall temperature and ambient temperature and presented in the form of a Nusselt number. Both local and average Nusselt numbers have been presented for various height‐ratios. The variation of the local Nusselt number has been shown with nondimensional distance for different angles of attack and blockage ratios. The variation of the average Nusselt number has also been shown with different angles of attack for blockage ratios. The local as well as average Nusselt number decreases as the height‐ratio decreases for all nondimensional distances and angles of attack, respectively, for rectangular prisms. Empirical correlations for the average Nusselt number have been presented for a rectangular prism as a function of the Reynolds number, Prandtl number and relevant nondimensional parameters.

Transient boiling crisis induced by heat-load step pulses in a helium vertically heated natural circulation loop with static initial condition

Boiling helium natural circulation loops are used as cooling system of some large superconducting magnets. Their thermalhydraulic behavior has already been studied quite thoroughly in steady state operation. However, the transient response of these systems remains up to date poorly studied, and transient boiling experiments in other fluids or heating configurations are difficult to extrapolate. In this work, an experimental study of helium natural circulation loops is conducted in which the system is excited by a step-pulse power wave function from a static initial condition (no power applied). The measurements of wall temperature on the heated section allowed the detection of boiling crisis onset during the transient. Different boiling crisis onset mechanisms could be determined from the dependence of the nucleate boiling lifetime on applied heat flux. The simultaneous analysis of thermal aspects and mass flow rate evolution allowed determining a semi-empirical local criterion based on the evolution of vapor fraction along the section for the prediction of transient boiling crisis.

Assessment of subchannel code ASSERT-PV for supercritical applications

The Canadian subchannel code ASSERT-PV has been modified and used in the development of a fuel assembly concept for the Canadian Supercritical Water-cooled Reactor (SCWR). This paper describes the modification to ASSERT-PV for the SCWR applications, and presents an assessment of the code against available experimental data. Full-bundle tests for the SCWR fuel assembly are not yet available; therefore, partial-bundle tests with a reduced number of rods and a shortened channel length were considered in the assessment. Three heat transfer experiments at supercritical pressures were selected for the assessment: (i) a Japanese 7-rod bundle water experiment; (ii) a Chinese 2×2 rod bare-bundle water experiment; and (iii) a Russian 7-rod bare-bundle Freon experiment. The rod surface temperature was taken as the key parameter in the assessment since the maximum fuel cladding temperature is a key criterion used in developing the SCWR fuel assembly concept. The ASSERT-PV predictions of rod surface temperature were compared against experimental data of measured wall temperatures. Six widely-known heat transfer correlations were assessed for their suitability in predicting the wall temperatures in rod bundles under conditions relevant to the Canadian SCWR. Overall, the Jackson correlation was found to be the most suitable for predicting the wall temperatures in the range of conditions covered by the selected experiments.

Formation of Urea-Based Deposits in an Exhaust System: Numerical Predictions and Experimental Observations on a Hot Gas Test Bench

Using a generic configuration of an exhaust system, the formation of deposits due to urea-derived byproducts is examined. For this purpose, the temporal profile of the formation of deposits is visually observed and the resulting deposit composition is analyzed. Based on the experimental results, the most important deposit regime can be identified depending on the measured wall temperatures and is compared with the prediction of a suitable reaction mechanism.

Prediction of dryout and post-dryout heat transfer using a two-phase CFD model

This study focuses on development of an integrated CFD model for diabatic high quality two-phase flow including tarns-dryout regions from annular-mist regime to mist regime. One unified three-field CFD model accounting for droplets, gas, and liquid film was developed to simulate both pre and post dryout regions, with local models to determine the dryout occurrence. The thin liquid film model was coupled to the gas core flow model, which is described using the Eulerian–Eulerian approach. For the post-dryout region, the various heat and mass transfer mechanisms between the wall, the gas phase, and the droplets were identified, including the wall-gas convective heat transfer, the droplet evaporation, the droplet-wall direct contact heat transfer and the thermal radiation, to calculate the temperature of the wall and the fluid. Of the most interests, dryout location and wall temperature measurements from a post-dryout heat transfer experiment have been used for the validation. Simulation results show that the dramatic temperature excursion could be well captured using current models. Nevertheless, more work will be continued to improve the accuracy of the results.

Study of argon–oxygen flowing afterglow

The reaction kinetics in argon–oxygen flowing afterglow (post-discharge) was studied using NO titration and optical emission spectroscopy. The flowing DC post-discharge in argon–oxygen mixture was created in a quartz tube at the total gas pressure of 1000 Pa and discharge power of 90 W. The O(3P) atom concentration was determined by NO titration at different places along the flow tube. The optical emission spectra were also measured along the flow tube. Argon spectral lines, oxygen lines at 777 nm and 844.6 nm and atmospheric A-band of were identified in the spectra. Rotational temperature of was determined from the oxygen atmospheric A-band and also the outer wall temperature of the flow tube was measured by a thermocouple and by an IR thermometer. A zero-dimensional kinetic model for the reactions in the afterglow was developed. This model allows the time dependencies of particle concentrations and of gas temperature to be calculated. The wall recombination probability for O(3P) atoms and wall deactivation probability for (b ) molecules were determined from the fit of model results to experimental data. Sensitivity analysis was applied for the analysis of kinetic model in order to reveal the most important reactions in the model. The calculated gas temperature increases in the afterglow and then decreases at later afterglow times after reaching the maximum. This behavior is in good agreement with the spatial rotational temperature dependence. A similar trend was also observed at outer wall temperature measurement.