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The present article reports the heat transfer characteristics of a vertical stainless steel foil of 0.15 mm thickness (SS304) by circular impinging jets of various fluids such as pure water, nano-fluids (Al2O3-water, ф = 0.15%, 0.6%), and aqueous high-alcohol surfactant (HAS, i.e., 2-ethyl-hexanol, 100-400 ppm) studied using an infrared thermal imaging camera (A655sc, FLIR System). The enhancement in the heat transfer rates for Al2O3-water nano-fluids with ф = 0.15%, ф = 0.60%, and aqueous surfactant solution (150ppm) is found to be 140%, 207%, and 117% higher compared to pure water results, respectively. The surface characteristics of the foil after jet impingement by various fluids are also studied using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and surface wettability. [ABSTRACT FROM AUTHOR]

In the present study, an experimental investigation has been carried out to analyze the heat transfer characteristics of CuO-water nanofluids jet on a hot surface. A rectangular stainless steel foil (AISI-304, 0.15mm thick) used as the test surface is electrically heated to obtain the required initial temperature (500°C). The distribution of surface heat flux on the target surface is evaluated from the recorded thermal images during transient cooling. The effect of nanoparticle concentration and Reynolds number of the nanofluids on the heat transfer characteristics is studied. Tests are performed for varied range of Reynolds number (5000=Re=12,000), two different CuO-water nanofluids concentration (Ф=0.15%, 0.6%) and two different nozzle to plate distance (l/d=6, 12). The enhancement in Nusselt number for CuO-water nanofluids was found to be 14% and 90%, for nanofluids concentration of Ф=0.15% and Ф=0.60%, respectively, compared to pure water. The test surface characteristics after nanofluids jet impingement are studied using scanning electron microscope (SEM). Based on the investigation, a correlation among various parameters, namely, Reynolds number (Re), Prandtl number (Pr), nozzle to plate distance (l/d), and Nusselt number (Nu), is presented. [ABSTRACT FROM AUTHOR]

A theoretical model is proposed to study the fluid flow and heat transfer behavior of two dimensional impinging jet on a solid surface. Energy integral method is used to obtain the solution. Based on the analysis a generalized expression involving various modelling parameter such as Nusselt number, nozzle to plate distance, Prandtl number, Reynolds number and the modelling parameter k is obtained. Experimental investigation is performed to evaluate the heat transfer characteristics of a two dimensional impinging jets on the hot foil. Tests have been carried by using a two dimensional nozzle with length to diameter ( l/d h ) ratio of 70. Reynolds number based on nozzle exit condition is varied between 7000 and 17 000 and jet-to-plate spacing between 1 and 10. A hot foil of 0.15 mm (SS 304) is used as the test specimen and air is used as fluid during experiments. The local heat transfer characteristics are estimated from the thermal images obtained from infrared thermal imaging camera (A655sc, FLIR System). The results obtained from the theoretical model are compared with test data obtained during present experimental investigation. In addition, a correlation for Nusselt number is proposed as a function of nozzle to plate distance, Prandtl number, Reynolds number, radial distance. [ABSTRACT FROM AUTHOR]

• The quenching phenomena of multi-dimensional porous debris bed were studied using experiments. • Visualization of quenching of porous debris bed is performed. • Quench front movement inside the debris bed were mapped. • Different zones of heat transfer during quenching of porous debris bed are identified. In case of severe accidents in light water reactors (LWRs), the coolability of relocated corium from the reactor vessel is a significant safety issue. In a flooded cavity, a porous corium debris bed is expected to develop on the bottom of the cavity pool due to the melt jet breakup and fragmentation. The debris bed needs to be quenched by water either flooding from the top or flooding from the bottom until continuous cooling is established. If it is not quenched, this mass will begin to re-melt due to decay heat and leads to Molten Corium Concreate Interaction (MCCI). Most of the studies reported have conservative assumptions of one-dimensional homogeneous particulate beds with top or bottom flooding condition of coolant. Understanding of debris beds quenching with multi-dimensional characteristics are limited. To investigate the quenching behavior of the conical debris bed by means of experiments, a test facility MCCI-mitigatiON through passive cooling Effect Test (MONET) apparatus is established. Specifically, the objective is to understand the mechanism of heat transfer and quench front movement inside the conical heated debris bed during quenching by cooling water supplied from the bottom of the bed. Two different particle bed bottom wall boundary conditions are studied; closed bottom wall and open bottom wall to understand the effect of water ingression from the bottom wall. The particulate debris bed is formed with two different types of particles; Ø 3 mm SS 304 and Ø 3 mm alumina. In addition, the effect on the quench front movement inside the particle bed has been reported by using temperature measurements together with direct visualizations. [ABSTRACT FROM AUTHOR]

• The quenching phenomena of multi-dimensional cylindrical particle bed were studied using experiments. • Visualization of quenching of porous debris bed were performed. • Quench front movement inside the homogeneous and radially stratified particle bed were mapped and analyzed. • Internal configurations of the beds have a substantial influence on the coolant and vapor movement. In case of a severe accident in nuclear reactor, a debris bed may be formed from the fragmentation of the molten core at different stages of the accident. Debris bed coolability is an important issue, as it will determine the accident progression, its termination, and mitigation. One of the major concerns of debris bed coolability investigations is to understand and evaluate the effect of water re-flooding. Many experiments have been conducted to study the two-phase flow and heat transfer in porous medium configuration. However, the understanding of debris bed quenching with multi-dimensional characteristics are limited. Here, a test facility MCCI-mitigatiON through passive cooling Effect Test (MONET) apparatus is established to conduct the porous debris bed re-flooding investigation. The objective is to understand the mechanism of heat transfer and quench front movement inside the cylindrical heated debris bed during quenching by cooling water supplied from the bottom of the bed. Specifically, the effect of Homogeneous bed (with different external boundary conditions) and radially stratified bed (with different internal porosity configurations) conditions of the cylindrical debris bed on the quench front movement has been investigated. The particulate debris bed is formed with two different types of particles (SS 304, alumina) and sizes (2–3.5 mm). The effect on the quench front movement inside the particle bed has been reported by using temperature measurements together with direct visualizations. Present findings suggest non-uniform quench front propagation pattern even for the homogeneous bed conditions. While the tests with the stratified bed indicate a clear influence of low porosity region on the quench front and vapor movement. [ABSTRACT FROM AUTHOR]

A theoretical model is proposed to evaluate the heat transfer characteristics of axisymmetric impinging fluid jets on the horizontal hot surface in the stagnation region using the energy integral method. A generalized expression involving various modeling parameters such as Nusselt number, nozzle-to-plate distance, Prandtl number, Reynolds number, and the modeling parameter k is obtained from the analysis. Present predictions are found to agree well with the test data involving a wide range of coolant type, Reynolds number, and nozzle-to-plate distance. In addition, a mechanistic correlation is suggested between the modeling parameter k and flow parameter, i.e., Reynolds number. [ABSTRACT FROM AUTHOR]

• Generalized semi-mechanistic model for maximum heat flux of sub-cooled jet quenching is presented. • Model for evaporative heat flux is based on the work of Katto's Model of Helmholtz instability. • Convective heat transfer was derived from the model of bubble-induced turbulent heat transfer using integral analysis. • Several modeling parameters were identified and model was compared with tests data and previous findings. In the present analysis, a semi-mechanistic maximum heat flux (qmhf) model has been developed for sub-cooled jet impingement cooling of the heated surface. The model for evaporative heat flux is based on the work of Katto's Model of Helmholtz instability theory of liquid thin film. While the convective heat transfer is derived from the model of bubble-induced turbulent heat transfer using integral analysis. Subsequently, the semi-mechanistic model of maximum heat flux is developed utilizing the assumption of infinite thermal conductivity of heated surface. In addition, experiments were performed on a heated vertical stainless steel foil of 0.15 mm thickness (SS-304) by circular horizontal impinging jets. Number of experimental parameters were studied including, initial surface temperature, nozzle to plate distance, flow rate, and effect of additives like surfactants and nanofluids. Finally, a generalized model for the maximum heat flux of sub-cooled jet is presented by incorporated different empirical parameters into the model using regression analysis with test data. Various modeling parameters are identified in the present investigation and comparisons of the present model with present tests data and previous findings are presented. [ABSTRACT FROM AUTHOR]

An experimental investigation has been carried out to analyze the heat transfer characteristics of a hot vertical stainless steel foil by circular impinging jets of pure water and Al 2 O 3 –water nanofluids. The local heat transfer characteristics are estimated from the thermal images obtained from infrared thermal imaging camera (A655sc, FLIR System). Tests are performed for different Reynolds number (Re = 5000–12000), nanofluids concentration (Φ = 0.15%, 0.6%) and for a different nozzle to plate distance (l/ d = 6, 12). The results indicated that the heat transfer characteristics of Al 2 O 3 –water nanofluids were better compared with water. Based on the investigation a correlation among various parameter, namely, Nusselt number (Nu), Prandtl number (Pr), nozzle to plate distance (l/ d ), Reynolds number (Re) and particle volume fraction (Φ) is presented. [ABSTRACT FROM AUTHOR]

In the present study, an experimental investigation has been carried out to analyze the heat transfer characteristics of CuO-water nanofluids jet on a hot surface. A rectangular stainless steel foil (AISI-304, 0.15 mm thick) used as the test surface is electrically heated to obtain the required initial temperature (500 °C). The distribution of surface heat flux on the target surface is evaluated from the recorded thermal images during transient cooling. The effect of nanoparticle concentration and Reynolds number of the nanofluids on the heat transfer characteristics is studied. Tests are performed for varied range of Reynolds number (5000 ≤ Re ≤ 12,000), two different CuO-water nanofluids concentration (Φ = 0.15%, 0.6%) and two different nozzle to plate distance (l/d = 6, 12). The enhancement in Nusselt number for CuO-water nanofluids was found to be 14% and 90%, for nanofluids concentration of Φ = 0.15% and Φ = 0.60%, respectively, compared to pure water. The test surface characteristics after nanofluids jet impingement are studied using scanning electron microscope (SEM). Based on the investigation, a correlation among various parameters, namely, Reynolds number (Re), Prandtl number (Pr), nozzle to plate distance (l/d), and Nusselt number (Nu), is presented. [ABSTRACT FROM AUTHOR]