Investigation Of Local Heat Transfer Research Articles

Investigation of local heat transfer from a flat plate impinged by an inclined circular jet

Experiments are performed to study the influence of an oblique jet on convective heat transfer to a vertical heated plate. The local heat transfer coefficient is investigated parametrically for Reynolds numbers ranging from 10000 to 75000 and jet to plate spacing of 3–20 d for different inclinations of a jet in the range of 15°–75°. The experiments are carried out on a flat rectangular surface of 600 × 300 × 0.1 mm3, hit by a jet of 11.5 mm diameter, with air as the working fluid. The infrared technique is used to examine the temperature contours over the entire section of the test plate. The present investigation deals with the effect of inclination on cooling at different locations over the plate locally in all directions from the point of impingement. The effect of Reynolds number and jet to plate spacing due to inclined jet at different orientations on the longitudinal, lateral, and intercardinal axial location is studied. The study also focuses on the heat transfer phenomenon happening on the far side of the test plate. The correlation analysis is performed on the current experimental data. The local Nusselt number correlations for the inclined jet are suggested that predict the present experimental results as a function of the geometrical and flow parameters.

Investigation of Local Heat Transfer from a Flat Plate Impinged by an Inclined Circular Jet

Investigation of Local Heat Transfer from a Flat Plate Impinged by an Inclined Circular Jet

Investigation of local heat transfer in the vicinity of the contact line under steam bubbles during boiling of liquids

Investigation of local heat transfer in the vicinity of the contact line under steam bubbles during boiling of liquids

Heat and mass transfer are in the interaction of multi-pulsed spray with vertical surfaces in the regime of evaporative cooling

Sprays with a periodic supply drop phase have great opportunities to control the processes of heat transfer. We can achieve optimal evaporative modes of cooling by changing the pulse duration and the repetition frequency while minimizing flow of the liquid phase. Experimental data of investigation of local heat transfer for poorly heated large surface obtained on the original stand with multi nozzle managed the irrigation system impact of the gas-droplet flow present in this work. Researches on the contribution to the intensification of spray options were conducted. Also the growth rate was integral and local heat. Information instantaneous distribution of the heat flux in the description of the processes have helped us. Managed to describe two basic modes of heat transfer: Mode “insular” foil cooling and thick foil with forming of streams. Capacitive sensors allow to monitor the dynamics of the foil thickness, the birth-belt flow, forming and the evolution of waves generated by “bombing” the surface with the droplets.

Investigation of local heat transfer in random particle packings by a fully resolved LBM-approach

Static particle/fluid systems occur in a wide range of technical processes in chemical industry and in energy technology. Direct numerical simulations (DNS) can be applied to model the fluid flow in particle packings and thus to examine heat and momentum transfer in those systems. Besides traditional CFD simulations, the Lattice-Boltzmann method (LBM) has been established as an alternative and efficient approach. Thermal LBM (TLBM) relies on a set of two distribution functions which represent the fluid flow and its internal energy and cover convection-diffusion problems. In the present study a D3Q19 model with a multiple-relaxation-time (MRT) collision model for density distributions and a Bhatnagar–Gross–Krook (BGK) collision model for energy distributions is used. The fluid-solid boundaries are represented by interpolated bounce-back methods. Numerical investigations are performed for single sphere and random particle packings. Particle averaged and local heat transfer coefficients are considered. Obtained results are compared against available state of the art correlations and recent numerical results from the literature. The results demonstrate the accuracy of the derived LBM approach. Particle averaged and local heat transfer coefficients in sphere packings are presented in a range of Rep=20−100 and ε=0.6−1. A correlation of local heat transfer coefficients in random sphere packings is derived.

Coupling of Human Thermoregulation and URANS Computation for Investigation of Local Heat Transfer and Flow Structures in a Generic Car Cabin

Commonly used flow regimes, e.g. defrost and panel mode, are compared regarding human skin temperature and local comfort in dependence of the inlet direction, temperature levels and position of the driver. To avoid the standard application of a constant heat flux of about 50W/m2 for consideration of realistic thermal boundary conditions of the human, the heat emission of the driver is introduced using active and passive thermoregulation with application of the well-known Fiala model. The heat transfer through the seat is calculated using CHT method by coupling three regions, human - seat - environment. Computations using large computational resources allow for exploration of different climate control strategies as they relate to local flow structures and skin temperatures on the human body in a detailed manner.

Experimental investigation of local heat transfer for complex-shaped surfaces using thermochromic liquid crystals

This study presents the detailed description of an experimental test rig for local heat transfer measurements as well as the calibration technique and the postprocessing and test run data for a ribbed channel with 45 deg inclined ribs.

Quantitative infrared investigation of local heat transfer in a circular finned tube heat exchanger assembly

This work deals with the local heat transfer coefficient evaluation over the fin of the second row of a staggered circular finned tube heat exchanger assembly. The coefficient distribution is determined by using a transient technique and by calculating the energy balance during the fin cooling. The calculation model takes into account radiation with the surrounding and lateral heat conduction into the material. The method uses infrared measurements and integration between time bounds that depend on space. It is proposed to choose the integration bounds with an original criterion based on local heat transfer. Validation is performed on the reference case consisting in a thin plate in an aerodynamically and thermally developing channel flow. Then, distributions of Nusselt number on the circular fin are presented for several Reynolds numbers. The high resolution of the whole method and set-up allow detecting thermal imprints of developing horseshoe vortices. These imprints are analyzed by following their angular evolution around the tube.

Infrared thermography investigation of local heat transfer in a plate fin and two-tube rows assembly

An experimental study is performed using an infrared thermography system. The experimental method uses the temperature transient variation of a thin plate (tested fin) in order to obtain detailed quantitative heat transfer coefficients. The method developed is similar to the lumped capacitance method usually used to measure heat transfer coefficient on heat exchanger fin models. But the method presented here exploits the capabilities of infrared thermography to measure surface temperatures in a transient technique in order to take into account errors effects due to tangential conduction and radiation of the tested fin. The method is validated using a two-dimensional channel experiment and its advantages are highlighted using a plate fin and two-tube rows assembly experiment. Moreover, convection coefficient variations with fin pitch and frontal air velocity of an automotive plate fin and two-tube rows assembly are also examined.

Experimental investigation of local heat transfer in the packing with triangular channels

Results of experimental studies on temperature distribution over the surface of a complex-shape heat exchanger like “Frenkel packing” are presented. Measurements were carried out with the airflow between two corrugated sheets with triangular crimps directed at 90° relative to each other. Microthermocouples glued on the outer surface of the heater were used for measurements. The effect of contact points, Reynolds number, and gap between corrugated sheets on temperature distribution over the heat exchanger surface is analysed under the turbulent mode of airflow. The main attention is paid to temperature distribution over the heating surface in an elementary cell. According to measurements performed, there is insignificant effect of contact points and gap on the type of temperature distribution over the perimeter of heated cell.

Experimental investigation of local heat transfer in a square duct with various-shaped ribs

In the present study, experimental studies are carried out to investigate the heat transfer and friction characteristics in a square duct roughened by various-shaped ribs on one wall. The ribs are oriented transversely to the main stream in a periodic arrangement. Liquid crystal thermography is employed to measure the local and average heat transfer coefficient on the ribbed surface. The rib height-to-duct hydraulic diameter ratio is fixed at 0.1; the rib pitch-to-height ratio varies from 8 to 15 and the test Reynolds number spans from 8,000 to 20,000. The results show that the trapezoidal-shaped ribs with decreasing height in the flow direction (case C) provide the highest heat transfer enhancement factor and are likely to be used to suppress the local hot spot which usually occurs in the region just behind the ribs.

Experimental Investigation of Local Heat Transfer in a Square Duct With Continuous and Truncated Ribs

In the present study, the turbulent heat transfer and fiction in a square duct roughened by continuous and truncated ribs on one wall has been investigated experimentally. The ribs are oriented transversely to the main stream in a periodic arrangement. For both cases, the rib height-to-hydraulic diameter ratio is 0.15, the rib pitch-to-height ratio is fixed at 12, and the Reynolds number varies from 8,000–20,000. Liquid crystal thermography is applied to demonstrate detailed distribution of heat transfer coefficient between a pair of ribs. The results show that the horseshoe vortices produced by truncated ribs are quite different from the flow structures altered by continuous ribs. It is noted that continuous ribs give higher heat transfer augmentation and pressure drop than truncated ribs. Moreover, the truncated ribs cannot be employed to eliminate hot spots which occur in the corresponding continuous types.

Experimental investigation of local heat transfer and skin friction in tube coils

Local heat transfer and skin friction around the tube perimeter of coils were studied in airflow. The heat transfer experiments were performed with two different coils D/d=23 and 15.6, and skin friction experiments were performed with three different coils D/d=25, 13.3 and 6.67 in the wide range of Re number from 4×103 till 105. Variation of the local heat transfer around the perimeter and along the tube was defined. The behavior of the shear stresses at the wall and of the flow modes were studied. Investigations of the heat transfer indicated that with the increase of D/d the difference between heat transfer in the initial thermal section and the stabilized heat transfer increases. Investigations of the shear stress and its fluctuations indicated that, in large-curvature coils, the transition from laminar-vortex flow to turbulent flow around the tube perimeter takes place at different values of Re. In the region of the external generatrix of the bend, the transition occurs at smaller Re, whereas at the internal generatrix, at larger Re.

An Investigation of Local Heat Transfer in a Slot with Various Injection Types for a Gas Turbine Combustor

An Investigation of Local Heat Transfer in a Slot with Various Injection Types for a Gas Turbine Combustor

Investigation of local heat transfer in compact heat exchangers by holographic interferometry

Compact heat exchangers are key components for the development of future aircraft devices. An enhancement of the heat transfer results in a decrease in the heat exchanger size and thus in lower weight and lower investment costs. Exact knowledge of the temperature distribution in the boundary layer is necessary for a specific augmentation of heat transfer. Holographic interferometry was applied to visualize the temperature field. This optical measuring method offers the advantage of delivering information about the temperature distribution without disturbing the flow pattern. A digital image processing system was used for evaluation of the interferograms. The local Nusselt number was determined from the isotherms at the wall. Two types of geometries for compact plate heat exchangers were investigated using air as test fluid: plain fin arrangements of plate-fin heat exchangers and circular segment shaped turbulence promoters in plate heat exchangers. The test section was heated by hot water to obtain a constant wall temperature as a thermal boundary condition. During the experiments Re was varied between 500 and 3000, a range where low pressure losses occurred. Investigations of the plate-fin arrangements show that the Nusselt number for the geometry with 1-mm radii is about 15% higher than that for the duct with radii of 5 mm. In the case of the circular segment shaped turbulence promoters, a staggered, a nonstaggered, and an inclined arrangement were investigated. The overall Nusselt number shows that the nonstaggered ribs lead to the best heat transfer. To compare the results with the heat transfer in a flat duct, the Nusselt number distribution between parallel plates was calculated by equations taken from the literature. The present results show that an enhancement of heat transfer of 100% for low Reynolds numbers and approximately 300% for Re = 2500 can be achieved.

Investigation of local heat transfer associated with the evaporation of a liquid film on a horizontal ribbed tube

The heat-transfer enhancement effect of longitudinal ribs on a horizontal tube is discussed on the basis of experimental data on the local heat-transfer Co-efficients.

Experimental investigation of local heat transfer in a turbulent boundary layer at supersonic speed

The authors present results of an experimental investigation of coefficients of local heat transfer in a turbulent boundary layer over a wide range of M and Re numbers and values of the temperature ratio.

Local heat transfer in the intertube space of a heat exchanger with spiral tubes

The article explains the methods and presents the results of the experimental investigation of local heat transfer in bundles of spiral tubes with heat supply to the heat carrier that is nonuniform over the cross section.

Heat transfer and hydrodynamics of an array of round impinging jets with one-sided exhaust of the spent air

The paper presents the results of an experimental investigation of local heat transfer at the surface blown by an array of round impinging jets with the spent air exhaust on one side. The experiments were carried out in the following range of parameters: f ̄ = 0.006–0.18 ; h d = 1–10 ; d = 1–5 mm; Re d = 1.1 × 10 3−17 × 10 3. Applicability of the collector relationships to calculate air distribution over the length of perforation, the jet flow and stalling flow velocity ratio and the coefficients of the total hydraulic resistance of the jet arrays, is considered. The channel technique is suggested to correlate the data on heat transfer in an array of impinging jets with one-sided exhaust of air. The validity and sufficient universality of this technique has been also confirmed by recalculation of the reported data. With power losses for air pumping through the system taken into account, the relationship has been established between the optimum open surface of perforation f ̄ opt and the relative spacing h L . Empirical relationships are suggested for calculation of heat transfer in an array of impinging jets with flow exhaust on one side.

An Investigation of Local Heat Transfer during Grinding Process—Effects of Porosity of Grinding Wheel

The thermal boundary condition around the workpiece surface is one of important factors to analyze the thermal deformation of a workpiece, which is in close relation to the machining, accuracy of grinding. The heat dissipation from the workpiece surface which is influenced by the flow pattern, may govern this thermal boundary condition. In consequence, it is necessary to clarify the convection heat transfer coefficient and the flow pattern of air and/or grinding fluid around surroundings of a rotating grinding wheel and of a workpiece. Here experiments were carried out in a surface grinding process to measure the flow velocity, wall pressure and local heat transfer by changing the porosity of the grinding wheel. The air blowing out from the grinding wheel which is effected by the porosity may be considered to have large influences on the local heat transfer coefficient, which is found to be neither symmetric nor uniform over the workpiece surface.