The gradient heat flux sensor made of a bismuth single crystal is calibrated. The volt–watt sensitivity of the sensor is determined and the method of data processing based on the 1D heat conduction ...equation for a thin plate is proposed. This method is tested on experimental data obtained for the initiation of a laser discharge in a calm atmosphere and in a supersonic gas flow.
Heat transfer during condensation of saturated water steam on the outer surface of a pipe has been investigated by the method of gradient heat flux measurement. Heat flux per unit area and heat ...transfer coefficients obtained for vertical, horizontal and inclined pipe are presented. The optimum angle of inclination of the pipe (ψ = 30 °) was experimentally determined. High informational content of gradient heat flux measurement has been revealed, which opens up new possibilities for studies of heat transfer during condensation.
The aim of the study is to determine optimum tilt of the pipe at film condensation by using of gradient heatmetry. Dependence of heat flux per unit area on time and azimuthal angle are presented for ...vertical, horizontal and inclined pipe. Maximal heat transfer coefficients for experimental conditions are observed for the angle 20° from vertical. The gradient heatmetry gives high informational content, which opens up new possibilities for studies of heat transfer during condensation.
"Thermophysics of Power Units" Department is based on pre-existed "Thermodynamics and Heat Transfer" and "Reactors and Boilers" Departments. The main goal of the new department (in addition to ...training students in basic courses of Thermodynamics, Heat and Mass Transfer, Fluid Mechanics, Metrology and Thermal Measurement) has become a new master's profile "Thermal Engineering, Energy Audit and Energy Service". It required radical restructuring of the whole educational process, and in the first place - its material resources and equipment. Over the last two years "Heat and Mass Transfer" lab and "Wind tunnel" lab are upgraded, and "Metrology and Thermophysical Measurement" lab is newly created. Tutorials of new generation are changing significantly the structure of our main courses. The members of our scientific group (2 - 6 year students) actively engaged in the work process. Now we hope to see the best of them among our future postgraduates.
The usage of gradient heat flux measurement for monitoring of heat flux on combustion chamber surface and optimization of diesel work process is proposed. Heterogeneous gradient heat flux sensors can ...be used at various regimes for an appreciable length of time. Fuel injection timing is set by the position of the maximum point on the angular heat flux diagram however, the value itself of the heat flux may not be considered. The development of such an approach can be productive for remote monitoring of work process in the cylinders of high-power marine engines.
Abstract
In the study of heat transfer during boiling, optical methods and thermometry are prevailing. The possibilities of experiment are significantly expanded by new technology – gradient ...heatmetry, in which heterogeneous gradient heat flux sensors with time constant of nanoseconds are used. When studying of boiling of subcooled water in a large volume on the surface of the titanium sphere, preheated up to 300-500 °C, heatmetry was combined with visualization of boiling modes using a high-speed camera Evercam 1000-4-M. It is possible to obtain the distribution of heat flux per unit area along the latitudinal coordinate and to relate the local heat flux per unit area with observed boiling regimes and initial temperatures of water and the model.
The new method for study of film boiling of subcooled water is proposed. Applying the heterogeneous gradient heat flux sensors (HGHFS) allows first the experimental determination of heat flux and ...heat transfer coefficient (HTC) when subcooled water is boiling at the spherical surface preheated up to 673 K. Maximum of the heat flux was fixed when the sphere contacted with subcooled water (ΔT = 80 K). Incessant and synchronous measurement of heat flux, surface temperature, and observation of vapor film were implemented. Traditional boiling curve was also obtained. Functionality of HGHFS under the complicated conditions of experiment was confirmed.
The flow and heat transfer of the finned cylinder are investigated by the methods of PIV, gradient heat flux measurement and thermometry. On the hollow model of a circular cylinder heated by ...saturated water vapor at atmospheric pressure, five annular fins of 20 mm high and of 10 mm thick are mounted. For the first model, the "acting" fin was hollow, for the second, it was solid and made of titanium alloy VT22. The remaining four fins simulated flow blockage. To visualize the flow in the intercostal space, the fin simulators were made of Perspex. Battery gradient heat flux sensors (GHFSs) with volt-watt sensitivity of 10 mV/W, were installed on the "acting" fin at different distances from the surface of the carrier cylinder. The cylinder rotated around its axis at an angle of φ = 0...180°, which made it possible to obtain the distribution of heat flux over the surface of the fin. By combining PIV diagnostics and gradient heat flux measurement, it was possible to obtain a complex 3D structure of the flow in the intercostal space and the distribution of heat flux on the surface of the fin. The values of the local heat transfer coefficients (HTCs) were also obtained. The dependence of HTC on flow mode and intercostal space is revealed. Comparison of the obtained characteristics for models with hollow and solid fins allowed us to determine in experiment fin efficiency for different intercostal spaces and free-stream velocities. The combination of all three technologies opens up new possibilities in study of flow and convective heat transfer.
Abstract
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/(m
2
• 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.
Abstract
The combination of methods of gradient heatmeatry and high-speed visualization made it possible to compare the distribution of the local heat flux and the hydrodynamics of the process during ...boiling of subcooled water on the surface of the sphere. The results are compared with the works of other authors and conclusions are drawn about the effect of subcooling of water on the intensity of heat transfer.
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