Infrared Thermography Technique Research Articles

Improving turbine endwall overall cooling effectiveness using curtain cooling and redistributed film-hole layouts: an experimental and computational study

Abstract To enhance the cooling deficiency that occurs in a baseline endwall using axially-arranged cooling holes, this paper proposes a new locally-enhanced hole layout using curtain cooling and fan-shaped film holes being arranged on iso-Mach lines. The objective of cooling hole re-design is to minimize secondary flows and thus to provide better film coverage. In experiments, Infrared thermography techniques are applied to validate overall cooling effectiveness of the newly-designed endwall, and aero-thermal fields at the cascade exit are detected by five-hole and thermocouple probes. Additionally, computational fluid dynamic simulations are performed to provide complementary flow insights. A comparison with the baseline hole layout reveals that for a given total coolant flow rate, the newly-designed endwall significantly improves the cooling performance by up to 27% without a noticeable aerodynamic penalty, resulting in a lower and more uniform temperature field. Curtain coolant effectively suppresses the development of horseshoe vortex and provides adequate thermal protection for leading-edge junctures and pressure-side corner regions. The redistribution of fan-shaped film holes reinforces the cooling performance in the passage throat and trailing edge regions. At low and high total mass flow rates, the coolant split between various cooling sources has a substantial impact on cooling performance.

Optothermal characterization of vanadium dioxide films by Infrared Thermography

The thickness of vanadium dioxide (VO2) films is a crucial parameter for the study of their optical and thermal properties. In this paper we studied the effect of the film thickness on the thermal hysteresis loop during the phase transition of VO2 deposited on a sapphire substrate by pulsed laser deposition (PLD), by the application of the Infrared Thermography technique. We measure the main thermal hysteresis parameters of VO2 samples with different thicknesses in the LWIR range (8–14 μm) showing how the transition temperature during the heating and cooling cycles, and the width of the hysteresis loop, may change with thickness. We analyzed and compared the obtained results with, in situ Grazing Incidence X-Ray Diffraction (GI-XRD). A good agreement between the results obtained with the two techniques was found demonstrating the reliability of the IR Thermography as a quantitative characterization tool.The results show that the structural and IR emissivity properties of the VO2 layer exhibit a dynamic range dependent on the layer thickness due to a correlation with the crystalline grain size. This has important effects in view of a tailored energy management for the use of those materials as smart radiators or smart windows.

A Feasibility Study of Thermal Infrared Imaging for Monitoring Natural Terrain—A Case Study in Hong Kong

The use of infrared thermography (IRT) technique combining other remoting sensing techniques such as photogrammetry and unmanned aerial vehicle (UAV) platforms to perform geotechnical studies has been attempted by several previous researchers and encouraging results were obtained. However, studies using time-lapse IRT survey via a UAV equipped with a thermal camera are limited. Given the unique setting of Hong Kong, which has a high population living in largely hilly terrain with little natural flat land, steep man-made slopes and natural hillsides have caused significant geotechnical problems which pose hazards to life and facilities. This paper presents the adoption of a time-lapse IRT survey using a UAV in such challenging geotechnical conditions. Snapshot and time-lapse IRT studies of a selected site in Hong Kong, where landslides had occurred were carried out, and visual inspection, photogrammetry, and IRT techniques were also conducted. 3D terrain models of the selected sites were created by using data collected from the photogrammetry and single (snapshot) and continuous monitoring (time-lapse) infrared imaging methods applied in this study. The results have successfully identified various thermal infrared signatures attributed to the existence of moisture patches, seepage, cracks/discontinuities, vegetation, and man-made structures. Open cracks/discontinuities, moisture, vegetation, and rock surfaces with staining can be identified in snapshot thermal image, while the gradient of temperature decay plotted in ln(T) vs. ln(t) enables quantifiable identifications of the above materials via time-lapse thermography and analysis.

Hydration Absorption and Thermal Effects of Outcrop Porous Sandstone Based on Intelligent Experimental and Infrared Thermography Techniques

Sandstones are enriched in deep energy reservoirs and also exist as outcrop rocks, where the pore characteristics of sandstone are influenced by hydration absorption and thermal effects. To study the influence of the initial temperature on the hydration absorption characteristics of outcrop porous sandstone in the Mogao Grottoes, China, an intelligent experimental device for rock hydration was used. The hydration absorption characteristics and temperature effects of sandstone were analyzed by using infrared thermography techniques to monitor the infrared radiation characteristics of the sandstone’s surface during hydration absorption. The experimental results show that the higher the initial temperature of the rock samples, the shorter the time it takes for the sandstone to absorb enough water to reach saturation. The temperature variation of sandstone with different initial temperatures was also determined; the variation in the hydration absorption of sandstone conforms to certain rules, which can be expressed by formulae containing certain parameters. The changing trend of hydration absorption in outcrop porous sandstone shows that the hydration absorption increases rapidly at first, and then the rate of increase slows down until the hydration absorption remains unchanged after saturation. The experimental technique and method provide feasible means and techniques to evaluate the hydration absorption and thermal effects of outcrop porous sandstone, for further detecting the weathering degree of rock grottoes and revealing the damage mechanisms.

Receptivity and Stability Theory Analysis of a Transonic Swept Wing Experiment

Surface suction provides an efficient way to delay boundary layer transitions. In order to verify the suction effects and determine the mechanism of suction control in transonic swept wing boundary layers, wind tunnel transition measurements in a hybrid laminar flow control (HLFC) wind tunnel model uses an infrared thermography technique in the Aircraft Research Association (ARA) 2.74 m × 2.44 m low turbulence level transonic wind tunnel. Based on the experimental data of stationary crossflow dominant transitions without and with surface suction in transonic swept wing boundary layers, in this paper, the effects on the receptivity and linear and nonlinear evolution of stationary crossflow vortices have been analyzed with the consideration of curvature. Theoretical analysis agreed with the experimental observations in regard to the transition delay caused by boundary layer suction near the leading-edge region.

Experimental investigation of dual jet flow past a heated surface: Effect of Reynolds number

A dual jet flow comprises a wall jet, discharged immediately parallel to a solid boundary, flowing alongside a parallel jet whose exit is offset from the solid boundary by some distance. Despite the widespread industrial application of dual jet flows, experimental analysis of their flow and heat transfer characteristics is severely underrepresented in the published literature. As a result, the heat transfer capabilities and driving flow mechanisms associated with dual jet flows are not yet fully understood, meaning they cannot be optimised towards specific applications. The present study is thus concerned with characterising the transfer of heat to a dual jet flow for varying Reynolds number through experimental means. Using air as the working fluid, each jet Reynolds number is varied in the range 5500≤Re≤12,000 and the offset ratio and velocity ratio are each maintained at a constant value of 1. A constant heat flux generation of 1670W/m2 is maintained in the bounding wall and the surface Nusselt number distribution is measured using infrared thermography techniques. A distinct Nusselt number profile is observed with respect to downstream distance, which remains consistent regardless of the Reynolds number. The results indicate that increasing Re elevates the Nusselt number proportionally at all downstream locations, where the surface-averaged Nusselt number rises linearly with increasing jet Reynolds number.

Non-invasive methods to quantify the carcass parameters of sheep: Interaction between thermal environment and residual feed intake

The thermal environment is important in unit production because the perception of thermal stress can reduce fertility, and productive performance, therefore its management is necessary. The use of non-invasive methods, such as infrared thermography and real-time ultrasonography, are widely used to evaluate indicators in animal production, without the need to slaughter the animals. Thus, we aimed to assess the effect of the thermal environment on the physiological parameters and carcass characteristics of Dorper sheep with positive and negative residual feed intake (RFI) using infrared thermography and real-time ultrasonography techniques. Twenty uncastrated male Dorper sheep (17.8 ± 2.4 kg) were confined for 40 days for RFI classification. Sheep were separated into positive RFI (n = 10) and negative RFI (n = 10). The experimental design was in randomized blocks, in a 2 × 2 factorial arrangement, with 2 thermal environments (full sun or shade) and two feed efficiency groups (positive RFI or negative RFI), with 5 replications. The sheep remained in confinement for 60 days. The animals were slaughtered at the end of the experiment and the carcasses dissected for tissue separation. Rectal temperature (RT) and respiratory rate (RR) were measured at two times (14:00 h and 18:00 h) for periods of 5 days. The RR was determined by indirect auscultation of heart sounds at the level of the laryngotracheal region. The RT was measured introduced a digital clinical thermometer into the animal's rectum. Surface temperature (ST) was obtained using a thermographic infrared camera, collecting the temperatures of the eyeball and skin surface in the regions of the head, ribs, rump, flank and shin. Sheep confined in full sun showed higher RR (P = 0.0001), ST ribs (P = 0.0020), ST rumb (P = 0.0055), ST flank (P = 0.0001) and heat tolerance coefficient (HTC) (P = 0.0010). For sheep confined in full sun, a strong correlation was observed between the RR and the mean ST (MST; r = 0.6826; P = 0.0236) and between the final loin eye area (LEAf) with the real LEA (LEAr) (r = 0.9263; P = 0.0001) and slaughter body weight (SBW) (r = 0.7532; P = 0.0325). For negative RFI sheep, a positive correlation was observed between the RR and the ST rump (r = 0.7343; P = 0.0025) and ST ribs (r = 0.6560; P = 0.0178) and the MST (r = 0.7435; P = 0.0001), between the MST and the LEAr (r = 0.6837; P = 0.0025) and the final LEA (r = 0.6771; P = 0.0144), and between the final LEA and LEAr (r = 0.9942; P = 0.0001), BW (r = 0.8415; P = 0.0277) and MST (r = 0.6771; P = 0.0045). Positive RFI sheep confined to shade showed a high correlation between final LEA and LEAr (r = 0.9372; P = 0.0001). The use of shading in confined Dorper sheep, regardless of the RFI classification, reduces the effects of heat stress on physiological parameters.

Uses of Smartphone Thermal Imaging in Perforator Flaps as a Versatile Intraoperative Tool: The Microsurgeon's Third Eye

IntroductionIn this study, we evaluate the versatility of smartphone thermal imaging technology as a valuable intraoperative modality in different stages of perforator flap surgery aiming to minimize the complications and achieve the best postoperative outcome. Patients and methodsThermography was performed in 20 perforator flaps in 20 patients at different surgical stages in three different ways to identify the most dominant perforator: first, by measuring the surface temperature of the skin; second, by using the dynamic infrared thermography technique; and third, by assessing the perfusion pattern when the flap was supplied by each perforator separately. Thermography was used to help in discarding the least perfused area of the flap. After microvascular anastomosis, the flap reheating pattern was evaluated. ResultsSeventeen free and three pedicled perforator flaps were included. Intraoperatively, each of the selected perforators had a corresponding hotspot. The perforator with the hottest hotpot, best rewarming, and provision of best flap perfusion on thermography was found clinically dominant. After microvascular anastomosis in free flaps, rapid rewarming was recorded in 15 cases. In two deep inferior epigastric perforator flaps, no rapid rewarming was observed. The pedicle was kinked in one case and there was a venous insufficiency in another case that required a cephalic turndown. All flaps showed good perfusion on thermography after inset. ConclusionSmartphone thermography has proven to be a valuable, cheap, rapidly employed, and objective tool not only for the design of perforator flaps, but also for the decision making intraoperatively to achieve the best surgical outcome.

Fault Prediction in Electrical Assets Using Infrared Thermography

An infrared thermography technique is discussed in this paper to locate and diagnose the electrical equipment issue. Overheating is among major problems for an electrical device and entire power system. These overheated hotspots must be detected so that the fault can be predicted before it occurs. We used a thermal image of an electrical device taken from a infrared camera to apply our method to detect the hot region and find the maximum temperature and minimum temperature in the image. Image de-noising is done with the help of morphological reconstruction followed by Watershed transformation for image segmentation to identify and separate the region having high pixel intensity as we know that area with high pixel intensity will also have high temperature. Our method achieved near to exact maximum and minimum temperature of electrical device.

Infrared imaging for detection of defects in concrete structures

Deterioration of concrete structures is an issue that affects the entire world and is brought on by various causes like climatic conditions, aging, attack of aggressive media, etc. Periodic inspections and proper maintenance are crucial to prevent the degradation of structures. Conventionally, the condition of the structures is monitored visually but over a while, non-destructive evaluation (NDE) technologies have gained significance and are expected to be successfully used for the inspection and management of civil structures. Infrared imaging is an effective NDT tool to monitor the health of civil structures. In this study, Infrared Thermography (IRT), an image-based method, is introduced and implemented for the assessment of concrete structures. Experiments on cement concrete cubes were conducted to investigate and enhance the applicability of the infrared thermography technique. The results are quite promising and helps to detect defects like delamination, voids, and cracks, etc. as the IR camera can pick-up the difference in temperature between sound and defective regions. However, the utilization of IRT for inspection poses many challenges but they can be overcome by combining it with other techniques like finite element method, acoustic emission and ultrasonic guided waves. Hence, the infra-red thermography technique is an excellent technology for practically evaluating concrete structures.

Experimental study on vibrating fluidized bed solids drying

Enhancing the gas–solid contacting inside a fluidized bed leads to improved solids drying characteristics. This can be achieved by mechanical vibration, resulting in so-called vibro-fluidized beds. In this study, experiments in a pseudo-2D vibro-fluidized bed setup are performed in order to better understand this improved drying behavior. A coupled particle image velocimetry - infrared thermography technique is applied to characterize the local solids velocity and temperature fields. The added vibration results in a significantly increased solids drying rate compared to a traditional gas-fluidized bed due to enhanced meso-scale particle agitation. Furthermore, it is shown that the gas-bubble appearance and the particle temperature standard deviation are highly dependent on the applied vibration amplitude and frequency.

Soil moisture content estimation using active infrared thermography technique: An exploratory laboratory study

Small scale laboratory testing was conducted to estimate the moisture content of sandy soils using a non-destructive and non-contact infrared thermography (IRT) technique. Tests were carried out by applying an external halogen lamp light (400 ​W). In this study, the aim was to explore the feasibility of using IRT to assess the moisture content of sandy soil. The laboratory tests conducted included evaluating soil physical characteristics such as grain size distribution. Soil samples were prepared with five different moisture content percentages. The soil moisture content was then evaluated using two different techniques. The first is the gravimetric oven dry method as per (ASTM D2216, 2019). The second is the IRT Technique. During the second procedure the samples were photographed with an ICI IR-Pad 640 ​P Series camera, which had an image resolution of 640 ​× ​480 pixels and a capture rate of 6 frames/minute. The emissivity correction used was 0.98. The soil surface temperature was captured in both the heating and the cooling phase, with the temperature taken from a specific thermal image area called the region of interest (ROI). Moisture content measurements were taken for each sample using the oven-drying method at the initial stage, and at the end of the heating and cooling phases. The procedure produced a good correlation between moisture content and surface temperature in the heating phase. The soil moisture content and surface temperatures were inversely related and formed a linear line with a high degree of accuracy (r2 ​= ​0.9138). A validation check is done at the end for a sample with random moisture content using the IRT technique where the moisture content was found to be 6.81%, this value was confirmed with the oven dry procedure. It was found that IRT successfully estimated soil moisture content.

A Feasibility Analysis of the Infrared Thermography Technique in Surface Crack Detection for High-Speed Rail Slab Track

The surface crack on track slab is the main cause of the service reliability deterioration of the high-speed rail (HSR) slab track. To realize the rapid and accurate detection of these cracks, infrared thermography (IRT) can be regarded as an effective way in HSR application. However, the performance of IRT can be significantly affected by the testing environment. This study aims to analyze the feasibility of IRT in crack detection for HSR slab track by investigating the key factors affecting the detection accuracy. Firstly, the principle of IRT in detecting surface crack of track slab is given, and the key factors influencing the detection performance are discussed. Considering the difficulty in conducting field tests for slab tracks, this study establishes a finite element (FE) model to simulate the temperature field of track slab with surface cracks. This model is verified by using the field measurement results of track slab temperature. With the FE model, the effects of detection time, ambient temperature, and sensitivity of the thermal imager on the detection accuracy are revealed. The results show that, during the window time for track maintenance (0:00 am–3:00 am), the difference of temperature between crack areas and noncrack areas gradually increases with time, so it is recommended to conduct detection during 2:00–3:00 am; under the condition of no auxiliary heat source, the crack detection is suggested to be arranged in summer with a high incidence of crack; the minimum limit of thermal sensitivity of thermal imager is below 108mk@25°C. The findings in this research can offer guidance for the implementation of IRT-based crack detection for HSR slab crack.

Experimental gas-fluidized bed drying study on the segregation and mixing dynamics for binary and ternary solids

Fluidized bed drying is an evolving process: The bed hydrodynamics, including the segregation and mixing tendencies, and its interplay with mass and heat transfer change in time. In this study, pseudo-2D fluidized bed experiments are performed using binary (50/50%) and ternary (33.3/33.3/33.3%) solids mixtures. A coupled particle image velocimetry infrared thermography technique provides local solids velocity and temperature fields. Furthermore, a machine learning algorithm is applied to characterize the bed segregation and mixing dynamics. Significant hydrodynamic changes and various segregation and mixing tendencies due to the evaporation of water from the porous γ-Al2O3 material were observed. A competition between size and density-based segregation and mixing dynamics resulted in changing bed configurations, which are correlated to the local solids drying behavior. Besides, it showed that drying of wider size distributions could lead to more complex efficient process operation.

Spectral analysis of laser speckle contrast imaging and infrared thermography to assess skin microvascular reactive hyperemia.

Post-occlusive reactive hyperemia (PORH) test with signal spectral analysis coupled provides potential indicators for the assessment of microvascular functions. The objective of this study is to investigate the variations of skin blood flow and temperature spectra in the PORH test. Furthermore, to quantify the oscillation amplitude response to occlusion within different frequency ranges. Ten healthy volunteers participated in the PORH test and their hand skin temperature and blood flow images were captured by infrared thermography (IRT) and laser speckle contrast imaging (LSCI) system, respectively. Extracted signals from selected areas were then transformed into the time-frequency space by continuous wavelet transform for cross-correlation analysis and oscillation amplitude response comparisons. The LSCI and IRT signals extracted from fingertips showed stronger hyperemia response and larger oscillation amplitude compared with other areas, and their spectral cross-correlations decreased with frequency. According to statistical analysis, their oscillation amplitudes in the PORH stage were obviously larger than the baseline stage within endothelial, neurogenic, and myogenic frequency ranges (p<0.05), and their quantitative indicators of oscillation amplitude response had high linear correlations within endothelial and neurogenic frequency ranges. Comparisons of IRT and LSCI techniques in recording the reaction to the PORH test were made in both temporal and spectral domains. The larger oscillation amplitudes suggested enhanced endothelial, neurogenic, and myogenic activities in the PORH test. We hope this study is also significant for investigations of response to the PORH test by other non-invasive techniques.

Condition and characterization analysis of a twentieth century cultural heritage through non-destructive testing (NDT) methods: the case of the Sivas industry school ironworking atelier in Turkey

Before the conservation and restoration of many types of cultural heritage, it is necessary to perform careful examination. This study aimed to determine the original building state and deterioration by applying non-destructive testing (NDT) methods in the case of a heritage building. Another goal was to determine, via NDT methods, whether the limestones observed in this study of different forms, colours, and textures were truly different. The Sivas Industry School Ironworking Atelier, which constitutes the research object, is one of the important public buildings in the city of Sivas, Turkey. Within the scope of the study, non-destructive infrared thermography (IRT), Schmidt hammer rebound (SHR) tests, and X-ray fluorescence (XRF) spectroscopy were applied. Accordingly, through IRT, deteriorations, anomalies, and material differences were investigated, and via SHR testing, uniaxial compressive strength (UCS) estimates, strength levels and hardness classes of stones were obtained. Moreover, via XRF spectroscopy, characterization analysis of stones was conducted. The data obtained could provide information to establish a basis for subsequent conservation. The innovation of this study is that although the infrared thermography technique is typically used in the investigation of materials, it was revealed that another technique such as XRF analysis is needed to better determine whether stones that seem different based on IRT are actually different. With IRT technique, anomaly and material detorioration can be determined. In addition to these two techniques, SHR tests that are non-destructive methods are needed to think about mechanical features of the material. Therefore, when determining the conditions and for characterization analysis of a cultural heritage before restoration, different techniques should be jointly used to complement each other.

UAS IR-Thermograms Processing and Photogrammetry of Thermal Images for the Inspection of Building Envelopes

Infrared thermography techniques (IRT) are increasingly being applied in non-invasive structural defect detection and building inspection, as they provide accurate surface temperature (ST) and ST contrast (Delta-T) information. The common optional or off-the-shelf installation, of both low- and high-resolution thermal cameras, on commercial UAS further facilitates the application of IRT by enabling aerial imaging for building envelope surveys. The software used in photogrammetry is currently accurate and easy to use. The increasing computational capacity of the hardware allows three-dimensional models to be obtained from conventional photography, thermal, or even multispectral imagery with very short processing times, further improving the possibilities of analysing buildings and structures. Therefore, in this study, which is an extension of a previous work, the analysis of the envelope of a wine cellar, using manual thermal cameras, as well as cameras installed on board an Unmanned Aerial System (UAS), will be presented. Since the resolution of thermal images is much lower than that of conventional photography, and their nature does not allow for accurate representation of three-dimensional objects, a new, but simple, digital image pre-processing method will be presented to provide a more detailed 3D model. Then, the three-dimensional reconstruction, based on thermal imagery, of the building envelope will be performed and analysed. The limitations of each technique will be also detailed, together with the anomalies found and the proposed improvements.

A digital and non-destructive integrated methodology for heritage modelling and deterioration mapping. The case study of the Moorish Castle in Sintra

The development of non-destructive, non-contact and autonomous unmanned techniques is extremely important for the preservation of heritage integrity. This paper presents a digital integrated methodology combining Terrestrial Laser Scanning (TLS), Aerial Digital Photogrammetry (ADP) and Infrared Thermography (IRT), which accelerate data collection and facilitate the creation of point clouds, the deterioration mapping and the state of conservation monitoring of historic structures. Both Digital Photogrammetry and Infrared Thermography were coupled with unmanned aerial vehicle (UAV). The proposed methodology was applied to the Moorish Castle in Sintra, Portugal. Manual Infrared Thermography, complemented with other traditional non-destructive techniques, were also applied in a pilot area for comparison purposes. Resultsdemonstrate the high potential of the integration of TLS, ADP and IRT techniques for heritage modelling digitalization, inspection and deterioration mapping with a positive impact on conservation and restoration projects.

Digital Rock Mass Analysis for the Evaluation of Rockfall Magnitude at Poorly Accessible Cliffs

The analysis of a digital rock cliff model, built by airborne photogrammetric data and infrared thermal images, is herein presented as an alternative tool for rock mass study in restricted and poorly accessible areas. Photogrammetric and infrared thermography techniques were combined for the geostructural and morphological characterization of an unstable cliff located in a nature reserve, where the rock mass extension and the environmental preservation rules required the use of minimally invasive surveying solutions. This methodological approach provided quantitative and qualitative data on both the spatial orientation of discontinuities and the location of major structural features, jutting blocks and past rockfall source areas. The digitally derived spatial data were used to carry out a rock mass kinematic analysis, highlighting the most recurring unstable failure patterns. Thermal images were overlapped to the photogrammetric cliff model to exploit the data combination and to analyze the presence of protruding rock mass volumes to be referred to as potential unstable volumes. Based on this activity, rock volumes were quantified on the digital model and the results were used to provide a zonation map of the potential magnitude of future rockfalls threatening the reserve. Digital data were validated by a field surveying campaign, which returned a satisfactory match, proving the usefulness and suitability of the approach, as well as allowing the quick and reliable rock mass characterization in the frame of practical use and risk management purposes.

Experimental and analytical study on local heat transfer distribution between smooth flat plate and free surface impinging jet from a circular straight pipe nozzle

The present study describes the heat transfer characteristics of free surface single-phase circular liquid jet impinging on a thin smooth flat surface subjected to uniform heat flux. The experimental setup is developed to measure the local temperature of a thin stainless steel metal foil using the infrared thermography technique. The effects of nozzle diameter (d = 2.5 to 10.8 mm), nozzle to plate spacing (z/d = 2 to 10), and Reynolds number (Re = 5000 to 24,000) on the local Nusselt number (Nu) distributions are studied. The local Nu is maximum in the stagnation region, and it decreases in the downstream flow following the stagnation region. The nozzle with a larger diameter shows maximum Nu compared to other nozzles. For a given z/d of 2 and a Reynolds number of 15,000, a maximum increment of 67% in local Nu is observed for a 10.8 mm nozzle in comparison to a 2.5 mm nozzle. The local Nu in the viscous boundary layer is found to be a function of the Reynolds number, Prandtl number, dimensionless r/d, and Weber number. The Nu increases with an increase in Reynolds number, however, the effect of the nozzle to plate spacing is negligible. The off-stagnation peak is observed for the 10.8 mm nozzle in the region of 0≤r/d≤0.7. The existing correlations reported in the literature are not able to capture the measured local Nusselt number distribution. Therefore, in the present study, an effort has been made to propose semi-empirical correlations for local Nu in the stagnation and viscous boundary layer region which will incorporate the diameter effect of the nozzle. The proposed correlations are able to predict the local Nusselt number distribution within the maximum deviation of 20%. The comparison between the free surface and submerged jet has been made which suggests that the local Nu for the submerged jet is higher compared to the free surface jet.