Experimental Investigation of Heat Transfer Characteristics during Water Jet Impingement Cooling of Moving Steel Plate

Investigation of heat transfer characteristics and energy balance analysis of FLiNaK in turbulent boundary layers of pipe flow

Nanofluid plays a very crucial role in nuclear power plant for improving heat transfer. It opens a new portal for improving heat transfer for reducing thermal hydraulics problems in nuclear reactor. The aim of this study to represent the numerically investigated result of CuO/Water based nanofluid heat transfer in light water nuclear reactor. In this investigation the 1/6th part of hexagonal geometry of nuclear fuel rod assembly has been taken for simulation. For focusing the effect of nanoparticle concentration and flow rate on heat transfer fluid flow in triangular channel two phase model is used. For improving the thermal properties of conventional fluid CuO/water nanofluid is used. A uniform heat flux is applied at the inner wall. Profiles of heat transfer coefficient and wall adjacent temperature are shown and these are the function of flow rate of nanofluid and concentration of nanoparticles. For getting better result accuracy, k-ω SST turbulence model and mesh quality of fuel rod bundle in triangular array are studied. Results are compared with analytical equations of heat transfer. The results show that prediction of nanofluid heat transfer is very well by using two phase model in place of using single phase model. Results indicates that heat transfer coefficient is increasing by adding the nanoparticles which is in low concentration and heat transfer coefficient is also increasing with increase in Reynold Number. It also indicates that wall adjacent temperature is decreasing by adding the nanoparticles and heat transfer coefficient is also decreasing with increase in diameter of nanoparticles.

Nanofluid plays a very crucial role in nuclear power plant for improving heat transfer. It opens a new portal for improving heat transfer for reducing thermal hydraulics problems in nuclear reactor. The aim of this study to represent the numerically investigated result of CuO/Water based nanofluid heat transfer in light water nuclear reactor. In this investigation the 1/6th part of hexagonal geometry of nuclear fuel rod assembly has been taken for simulation. For focusing the effect of nanoparticle concentration and flow rate on heat transfer fluid flow in triangular channel two phase model is used. For improving the thermal properties of conventional fluid CuO/water nanofluid is used. A uniform heat flux is applied at the inner wall. Profiles of heat transfer coefficient and wall adjacent temperature are shown and these are the function of flow rate of nanofluid and concentration of nanoparticles. For getting better result accuracy, k-ω SST turbulence model and mesh quality of fuel rod bundle in triangular array are studied. Results are compared with analytical equations of heat transfer. The results show that prediction of nanofluid heat transfer is very well by using two phase model in place of using single phase model. Results indicates that heat transfer coefficient is increasing by adding the nanoparticles which is in low concentration and heat transfer coefficient is also increasing with increase in Reynold Number. It also indicates that wall adjacent temperature is decreasing by adding the nanoparticles and heat transfer coefficient is also decreasing with increase in diameter of nanoparticles.

Experimental investigation of subcooled flow boiling heat transfer in helical coils

In this paper, an investigation of heat transfer characteristics at supercritical pressure fluid flowing in a uniformly heated vertical tube has been carried out. In order to reduce thermal emissions and increase thermal efficiency, supercritical boilers were developed at various sizes. Above supercritical pressure, the distinction of liquid and gas phases disappears. This dispenses with the problem of critical heat flux and dry out phenomenon which occurs in subcritical pressure. However, the study of heat transfer behavior above supercritical pressure is indeed required due to the heat transfer deterioration operation at high heat flux to mass flux ratio. In the present work, numerical simulation has been employed in order to inquire about the effect of various parameters such as heat flux to mass flux ratio, diameter and pressure that causes heat transfer deterioration. Shear Stress Transport k-ω model has been applied in all the computations. It is observed that the metal temperature predicted by numerical simulation is more accurate than the empirical correlations available in the literature. A Visual Basic Program has also been developed to assess the empirical correlations in the context of predicting metal temperature under 5280 different operating conditions. Tube sizes of 10, 15 & 20 mm inner diameter with 4 m length, the pressure between 225 and 280 bar and heat flux to mass flux ratio between 0.27 and 0.67 have been chosen to explore the effect of diameter, pressure and heat flux respectively.

This paper describes local heat transfer for a round water jet on upward-facing and downward-facing static plates. Impinging liquid jets have high heat transfer rates. One of the technological issues in the steel making process is uniformity in cooling between the top and bottom sides of a plate. The objective of this study is to investigate the surface orientation effect on transient heat transfer experimentally. Experiments were conducted for a range of water flow rate, surface orientation. Both surface orientations were conducted on the same apparatus. The heat transfer plate was stainless steel to deal with both supercritical flow and subcritical flow regions. The plate length was wide for laboratory scale. Initial plate temperature was 800 degrees Celsius. Pipe Reynolds numbers were laminar flow regime. Inverse solution was employed to estimate transient local surface temperature and heat flux. Heat transfers between upward-facing and downward-facing surfaces are the same in the order of magnitude at downward-facing surface flow rate from 1.2 times to twice that of upward-facing surface. Local downward-facing surface temperature is higher than that of upward-facing temperature at the same flow rate. The following points can be given as reasons. Downward-flowing impinging jet velocity is larger than that of upward-flowing jet at the same flow rate due to gravity direction. Heat transfer is affected by a geometric arrangement relation of radial spreading liquid film, vapor and hot plate.

The jet impingement technique is currently one of the most efficient cooling solutions for highly reinforced pistons of large two-stroke engines. To study the heat transfer characteristics of piston, experimental and numerical investigations with a piston cooling bore impinged by SAE 30 oil were carried out. To investigate the heat transfer coefficient distributions over the target bore, the wall temperatures of the cooling bore were measured by thermocouples, which will also be used in the numerical calculation. The jet Reynolds number (Re) ranges from 220 to 330, and the jet-to-plate spacing ratios (H/D) range from 10 to 30. Results show that jet-to-plate spacing ratios have a slight effect on the heat transfer coefficient for this low Reynolds numbers impingement which is quite different from high Reynolds numbers flow. There are both three peaks of the local heat transfer coefficient for Re = 330 and 280 along the x-axis direction. However, only two peaks occur when Re = 280. The heat transfer coefficient increases with the increase of Reynolds number when x/D < 0.22 or x/D > 1.77 while the variation is contrary when 0.22 < x/D < 1.77. The average heat transfer coefficient of the top surface region is far larger than other regions and decreases significantly in the upper chamfered region. While it is almost identical in the cylindrical region for different Reynolds numbers. This study provides the heat transfer characteristics of piston cooling with SAE30 oil and can be used for the piston optimization of large two-stroke engines with high cooling performance requirements.

Numerical investigation of heat transfer characteristics of high-speed and high-temperature air cooled open-cycle reactor

Experimental investigation of heat transfer characteristics of water in a vertically–upward tube under ultra-supercritical pressure and ultrahigh-temperature conditions

In this work, the heat transfer characteristics of supercritical pressure CO2 in vertical heating tube with 10 mm inner diameter under high mass flux were investigated by using an SST k-ω turbulent model. The influences of inlet temperature, heat flux, mass flux, buoyancy and flow acceleration on the heat transfer of supercritical pressure CO2 were discussed. Our results show that the buoyancy and flow acceleration effect based on single phase fluid assumption fail to explain the current simulation results. Here, supercritical pseudo-boiling theory is introduced to deal with heat transfer of scCO2. scCO2 is treated to have a heterogeneous structure consisting of vapor-like fluid and liquid-like fluid. A physical model of scCO2 heat transfer in vertical heating tube was established containing a gas-like layer near the wall and a liquid-like fluid layer. Detailed distribution of thermophysical properties and turbulence in radial direction show that scCO2 heat transfer is greatly affected by the thickness of gas-like film, thermal properties of gas-like film and turbulent kinetic energy in the near-wall region. Buoyancy parameters Bu < 10−5, Bu* < 5.6 × 10−7 and flow acceleration parameter Kv < 3 × 10−6 in this paper, which indicate that buoyancy effect and flow acceleration effect has no influence on heat transfer of scCO2 under high mass fluxes. This work successfully explains the heat transfer mechanism of supercritical fluid under high mass flux.

An experimental investigation of heat transfer characteristics for steam cooling and air cooling in a rectangular channel roughened with parallel ribs

The microstructure and mechanical properties of the hot rolled steel depend on the laminar jet cooling control on the runout table. An experimental and numerical study of the heat transfer during water jet impingement cooling of a hot steel plate (600 to 900°C) is presented. The effects of plate temperature upon the heat transfer were analyzed by the inverse heat conduction method that provided the heat fluxes on top surface from measured temperatures into the plate. Rewetting (liquid-solid contact) occurs on surface above 880°C. Higher initial temperatures enlarge the heat flux, but delay the onset of the rewetting and the advance of rewetting front radius (Rwet). Heat transfer coefficient (HTC) increases as surface temperature decreases. The size of the non-symmetric effective jet cooling zone depends on strip speed. Correlations to predict HTC and Rwet have been proposed. Results will contribute for enhancement of fast cooling system in hot strip mill.

Characterization of Two-Phase Flow Morphology Evolution during Boiling via High-Speed Visualization

Experimental investigation of heat transfer characteristics of circular tube fitted with straight half twist insert has been presented. The heat transfer coefficient increases with Reynolds number and decreases with spacer distance for both the single direction and left-right twist inserts. Also, there is no appreciable increase in heat transfer enhancement in straight half twist insert with 2-inch spacer distance. Experiments were carried out in turbulent flow using straight half twist insert with 4-inch spacer and similar trend of increasing Nusselt number with Reynolds number was observed. CFD simulation for the heat transfer augmentation in the plain tube and the tube fitted with half twist inserts has also been explained using Fluent version 6.3.26. The data obtained by simulation are matching with the experimental value with the discrepancy of less than ±10% for the plain tube and the tube fitted with straight-half twist inserts for Nusselt number and friction factor.

Investigation of Heat Transfer Characteristics of a Two-Phase Closed Thermosyphon