Surface Emissivity Research Articles

Analytical Model of Optical-Field-Driven Subcycle Electron Tunneling Pulses from Two-Dimensional Materials.

We develop analytical models of optical-field-driven electron tunneling from the edge and surface of free-standing two-dimensional (2D) materials. We discover a universal scaling between the tunneling current density (J) and the electric field near the barrier (F): In(J/|F|β) ∝ 1/|F| with β values of 3/2 and 1 for edge emission and vertical surface emission, respectively. At ultrahigh values of F, the current density exhibits an unexpected high-field saturation effect due to the reduced dimensionality of the 2D material, which is absent in the traditional bulk material. Our calculation reveals the dc bias as an efficient method for modulating the optical-field tunneling subcycle emission characteristics. Importantly, our model is in excellent agreement with a recent experiment on graphene. Our results offer a useful framework for understanding optical-field tunneling emission from 2D materials, which are helpful for the development of optoelectronics and emerging petahertz vacuum nanoelectronics.

Multi-scale remote sensing retrieval model for land surface emissivity and its impact on land surface temperature estimation

ABSTRACT As a fundamental parameter of the surface radiation process, land surface emissivity (LSE) is the most direct factor affecting the land surface temperature (LST) retrieval accuracy. Based on the measured data from 2017 to 2023, the characteristics of LSE changes were analysed, different timescale LSE retrieval models were developed, and the impact of LSE on pixel scale observational LST acquisition was evaluated by using unmanned aerial vehicle (UAV) remote sensing images. The results show that with changes in atmospheric environmental conditions, the LSE changes are relatively less pronounced at 3.99 µm and 4.02 µm in the mid-infrared band and at 10.8 µm and 11.8 µm in the thermal infrared band than in the other bands. At the timescale above day, the LSE is significant correlation with the normalized differential vegetation index (NDVI). Vegetation is the main parameter that dominates the LSE change under heterogeneous underlying surfaces. On a daily timescale, LSE exhibits typical diurnal variation characteristics, and the amplitude of diurnal variation is influenced mainly by shallow soil water and heat conditions. The developed LSE model based on Fengyun-4A (FY-4A) satellite remote-sensing data can effectively reproduce the daily variation characteristics of LST and avoid the ‘jumping’ phenomenon that may occur in the NDVI threshold method. The root-mean-square error (RMSE) between the retrieved LST and in situ data is reduced to 3.78°C, and the retrieval accuracy is better than that of the published LST product. When using UAVs to obtain pixel-scale LSTs, dry bare soil is more sensitive to LSE. When the LSE increases from 0.95 to 1.0, the average LST obtained by the UAV deviates by approximately 1.0°C. This study preliminarily provides some spatiotemporal variation patterns of LSE and lays a foundation for the later-modified LST retrieval algorithms.

PyRTlib: an educational Python-based library for non-scattering atmospheric microwave radiative transfer computations

Abstract. This article introduces PyRTlib, a new standalone Python package for non-scattering line-by-line microwave radiative transfer simulations. PyRTlib is a flexible and user-friendly tool for computing down- and upwelling brightness temperatures and related quantities (e.g., atmospheric absorption, optical depth, opacity, mean radiating temperature) written in Python, a language commonly used nowadays for scientific software development, especially by students and early-career scientists. PyRTlib allows for simulating observations from ground-based, airborne, and satellite microwave sensors in clear-sky and in cloudy conditions (under non-scattering Rayleigh approximation). The intention for PyRTlib is not to be a competitor to state-of-the-art atmospheric radiative transfer codes that excel in speed and/or versatility (e.g., ARTS, Atmospheric Radiative Transfer Simulator; RTTOV, Radiative Transfer for TOVS (Television Infrared Observation Satellite (TIROS) Operational Vertical Sounder)). The intention is to provide an educational tool, completely written in Python, to readily simulate atmospheric microwave radiative transfer from a variety of input profiles, including predefined climatologies, global radiosonde archives, and model reanalysis. The paper presents quick examples for the built-in modules to access popular open data archives. The paper also presents examples for computing the simulated brightness temperature for different platforms (ground-based, airborne, and satellite), using various input profiles, showing how to easily modify other relevant parameters, such as the observing angle (zenith, nadir, slant), surface emissivity, and gas absorption model. PyRTlib can be easily embedded in other Python codes needing atmospheric microwave radiative transfer (e.g., surface emissivity models and retrievals). Despite its simplicity, PyRTlib can be readily used to produce present-day scientific results, as demonstrated by two examples showing (i) an absorption model comparison and validation with ground-based radiometric observations and (ii) uncertainty propagation of spectroscopic parameters through the radiative transfer calculations following a rigorous approach. To our knowledge, the uncertainty estimate is not provided by any other currently available microwave radiative transfer code, making PyRTlib unique for this aspect in the atmospheric microwave radiative transfer code scenario.

Plume mode instability enhanced by emitter surface poisoning in hollow cathode

The unstable plume mode of hollow cathodes should be avoided in practical applications because it severely degrades the overall cathode lifetime. In this study, we investigate the spot-plume transition and plasma stability characteristics of an unused segmented lanthanum hexaboride emitter. The expansion of the unstable plume mode region is observed during a discharge experiment. Subsequently, the segmented emitter is retrieved, the inner surface of the emitter is observed, and the work function on the surface is measured at room temperature. The emitter surface exhibits color variations with oxygen and carbon detection. The downstream edge shows the original purple color and almost no degradation in the work function. The high temperature in this region promotes the desorption of carbon and oxygen. In the spot mode, this region mainly contributes to thermionic electron emission; therefore, the discharge voltage in the spot mode does not change during the discharge experiment. Carbon or carbide is detected in the middle of the axial direction on the emitter surface, where the surface temperature is not sufficiently high to desorb carbon during discharge. Based on the surface analysis results, the dominant substance in the region where carbon is detected was lanthanum carbide. An increase in the work function is indicated in the region, which appears to increase the plasma instability. According to previous studies, an increase in the work function results in a rise in the potential in the emitter, and an increase in the electron temperature in the outside plume region induces the plasma instability. Further investigation is needed to understand the mechanism connecting the rise in the work function and the rise in the electron temperature in the plume region.

Variability in surface CO2 flux: Implication for monitoring surface emission from geothermal fields

In the last decade the international push for the development of various renewable energy and the increase of the carbon tax for emitters, has put high enthalpy geothermal on a hot seat. Anthropic geothermal emissions in volcanic areas are not negligible due to the inherent nature of their volcanic setting but are counted regardless, similarly to a gas or coal power plant, despite their non-fossil carbon origin. Natural volcanic emissions are however poorly constrained due to the lack of field scale soil CO2 flux assessments. In this study, we analyse the temporal and spatial variations of soil CO2 flux and soil temperature in the Taupō region, Taupō Volcanic Zone, New Zealand, in the light of seasonal variation, field utilisation, and seismicity. Fortnightly monitoring between 2019 and 2023 at 8 sites across the Tauhara and Wairakei geothermal fields provides insight into changes of seasonal variations and geothermal activities. To understand the broader distribution of natural degassing and to compare the CO2 flux over decades, we repeated the CO2 flux survey between 2019 and 2023 and compared to previous results at Karapiti, Wairakei geothermal field (2004, 2018), Ring of Fire, Tauhara geothermal field (2006), and Rotokawa geothermal field (2003, 2011). Similar emissions but a change in the spatial distribution at Tauhara geothermal field suggests that human surface development has affected permeability in the shallow subsurface. In contrast, a similar spatial distribution of flux, but higher emissions, at Karapiti, Wairakei indicates the recovery or modification of reservoir pressure. Finally, a decrease of total emission flux of the natural geothermal features at Rotokawa coincides with the decrease of CO2eq emissions at the power stations. This study showcases the complexity and uncertainties of natural CO2 emission calculations and provides recommendations for future monitoring studies.

Analysis of heat-loss mechanisms with various gases associated with the surface emissivity of a metal containment vessel in a water-cooled small modular reactor

In various small modular reactor (SMR) designs currently under development, the conventional concrete containment building has been replaced by a metal containment vessel (MCV). In these systems, the gap between the MCV and the reactor pressure vessel is filled with gas or vacuumed weakly, effectively suppressing conduction and convection heat transfer. However, thermal radiation remains the major mode of heat transfer during normal operation. The objective of this study was to investigate the heat-transfer mechanisms in integral pressurized water reactor (IPWR)-type SMRs under various gas-filled conditions using computational fluid dynamics. The use of thermal radiation shielding (TRS) with a much lower emissivity material than the MCV surface was also evaluated. The results showed that thermal radiation was always the dominant contributor to heat loss (48–97%), while the conjugated effects of the gas candidates on natural convection and thermal radiation varied depending on their thermal and radiative properties, including absorption coefficient. The TRS showed an excellent insulation performance, with a reduction in the total heat loss of 56–70% under the relatively low temperatures of the IPWR system, except for carbon dioxide (13%). Consequently, TRS can be utilized to enhance the thermal efficiency of SMR designs by suppressing the heat loss through the MCV.

Short and long time-scales variability of the H α double-peaked profile of Pictor A

ABSTRACT We present the results of the analysis of 18 optical spectra covering the H α profile region of the active nucleus of the galaxy Pictor A obtained in different epochs along 12 yr. With these data, we model the variability of the double-peaked H α emission of the nucleus of this galaxy. We find small variations in the integrated flux of the broad component of H α, occurring on short time-scales, of the order of 40 d. In addition, significant variations in the relative intensities of the red and blue sides of the broad profile occur on time-scales of years. In order to explain the observations, we propose a scenario in which the double-peak profile is produced by a flattened distribution of clouds surrounding the accretion disc with Keplerian and relativistic orbits, inclined in relation to the sky plane, and with axially asymmetric surface emissivity with the radius of maximum emissivity. We find that, for the theoretical time-scales of the disc-like BLR to conform the time-scales of variation observed for the double-peak profile, it is necessary for the gas in the disc to orbit a SMBH with a mass of M• $\approx \, 2\times$ $10^{8}\, \mbox{M}_\odot$. In this scenario, the physical extension of the line-emitting region extends by 6–48 light-days from the SMBH.

Numerical investigation of unsteady heat transfer from a vertical helical coil

A comprehensive investigation was conducted utilizing three-dimensional transient Computational Fluid Dynamics (CFD) to analyze conjugate heat transfer, with a specific focus on determining the cooling time of a hot vertical helical coil. The heat transfer characteristics of the helical coil are assessed numerically with respect to parameters within certain ranges such as Rayleigh number 104≤Ra≤108, surface emissivity 0≤ε≤1, and geometrical parameters of the coil, such as coil-to-rod diameter ratio 8≤D/d≤24, and pitch-to-rod diameter ratio 3≤p/d≤7.5. Furthermore, a lumped heat capacitance model is also proposed, which significantly reduces computational time while maintaining accuracy by utilizing the steady-state correlation of Nusselt number vs. Rayleigh number (Nu vs. Ra) and other pertinent geometrical parameters of the coil. Comparative analysis between the lumped heat capacitance model and transient simulations reveals a remarkable correspondence, with deviations not exceeding 2%. Validation of the computational model is conducted against experimental data, showing good agreement. Results indicate that coils with higher pitch-to-rod diameter ratio (p/d) and coil-to-rod diameter ratio (D/d) dissipate heat more quickly, while higher initial Rayleigh numbers lead to faster cooling rates. Temperature distribution and Nusselt number variations during the cooling process are analyzed and compared between steady and unsteady behavior. The study provides valuable insights into the cooling behavior of helical coils, crucial for industrial applications requiring efficient heat transfer.

Revised Fowler–Dubridge model for multiphoton over-barrier electron emission from two-dimensional materials

We revise the Fowler–Dubridge model for multiphoton over-barrier photoemission from two-dimensional (2D) materials to include the effects of reduced dimensionality, non-parabolic, and anisotropic energy dispersion of 2D materials. Two different directions of electron emission are studied, namely, vertical emission from the surface and lateral emission from the edge. Our analytical model reveals a universal temperature scaling of Tβ with β = 1 for the surface emission over a wide class of 2D materials and β = 3/2 for the edge emission from the 2D material with anisotropic parabolic energy dispersion, which are distinct from the traditional scaling of β = 2 originally derived for the traditional bulk materials. Our comparison shows good agreement with two experiments of photoelectron emitted from graphene for both surface and edge emission. Our calculations also show that the photoelectron emission is more pronounced than the coexisting thermionic emission for materials with low temperature and Fermi energy. This model provides helpful guidance in choosing proper combinations of light intensity, temperature range, and type of 2D materials for the design of photoemitters, photodetectors and other optoelectronics.

Bound states in the continuum and plasmonics in perovskite nanostructures for emission, detection, and sensing

We present photonic and plasmonic configurations on surfaces of perovskite materials which facilitate robust temporal confinement of light by means of photonic bound states in the continuum (BIC) and/or surface plasmonic resonance. Our three-dimensional finite-difference time domain simulation captures the intricate properties of BIC of photonic lattices and plasmonic cavities. We show that single crystal of MAPbBr3 can be utilized in developing new generation of nanostructured surface emitters, where with sufficient modulation depth high quality factors can be achieved with photonic BIC. We also show how gold thin film enhances the emission of FAPbBr3 NCs by plasmonic mechanisms

Characterization of Surface Spectral Emissivity Retrieved from EE9-FORUM Simulated Measurements

FORUM (Far-infrared Outgoing Radiation Understanding and Monitoring) has been approved to be the ninth Earth Explorer mission of the European Space Agency and is scheduled for launch in 2027. The core FORUM instrument is a Fourier transform spectrometer, which will, for the first time, measure the upwelling spectral radiance in the far-infrared (FIR) and mid-infrared (MIR) portions of the Earth’s spectrum. These radiances will be processed up to level 2, to determine mainly the vertical profile of water vapor, surface spectral emissivity, and cloud parameters. In this paper, we assess the performance of the FORUM surface spectral emissivity product based on all-sky sensitivity study. In the FIR, we find that the retrieval error is mainly driven by the precipitable water vapor (PWV) in clear-sky conditions. In dry atmospheres, FIR emissivity can be retrieved with an error less than 0.01. In cloudy conditions, small errors can be achieved for optically thin clouds, especially for small values of the PWV. In the MIR, we observe that a large thermal contrast between the surface and the lowest atmospheric layers increases the sensitivity of the measurements to the surface emissivity in clear-sky conditions and an emissivity retrieval error less than 0.01 can usually be achieved. In cloudy conditions, small errors can be achieved for optically thin clouds, especially for large values of the surface temperature. Applying a coarser retrieval grid further reduces retrieval error, at the expense of an increased emissivity smoothing error.

A normal form for synchronous land surface temperature and emissivity retrieval using deep learning coupled physical and statistical methods

The innovative normal form, named deep learning-couple-physical and statistical methods (DL-C-PS), has been developed for synchronously retrieving land surface temperature and emissivity (LST&E) from Japan's geostationary meteorological satellite Himawari-8 carrying the Advanced Himawari Imager (AHI). First, geophysical logical reasoning (GLR) and expert knowledge were used to formulate radiative transfer equations (RTEs). Then, a hybrid approach integrating physical and statistical methods was employed to derive the solution, with deep learning (DL) optimizing the solution process. Three band combination schemes were designed to assess the effectiveness of the DL-C-PS normal form. Simulation data from the MODerate spectral resolution atmospheric TRANsmittance mode (MODTRAN) yielded promising results during validation. Root mean square error (RMSE) values were below 1 K for LST and below 0.008 for LSE when using band combinations of four thermal infrared (TIR) bands or at least three TIR bands combined with water vapor information. Cross-validation and in situ validation showed consistent findings with simulation validation. Compared to MODIS LST&E products (MYD21), in most cases, the RMSE values for LST&E were approximately 2 K and less than 0.015 during daytime, and below 1.3 K and 0.017 during night, respectively. Validated against in situ observations, nighttime RMSE values for LST were approximately 1.5 K with correlation coefficient (R) values better than 0.93. The higher RMSE observed in daytime compared to nighttime can be attributed to the influence of the sun's illumination angle on satellite scanning imaging. Overall, this research presented a normal form for multi-parameter estimation by leveraging the optimal calculation of DL and incorporating physical interpretations.

High-Power Terahertz Photonic Crystal Surface-Emitting Laser with High Beam Quality

The photonic crystal surface-emitting laser (PCSEL) has attracted much attention due to the advantages of a small far-field divergence angle and high output power. Here, we report a high-power terahertz (THz) photonic crystal laser with high beam quality through the optimization of the absorption boundary condition and the introduction of the symmetrically distributed electrodes. Single-mode surface emission at 3.4 THz with the maximum peak output power of 50 mW is demonstrated. Meanwhile, a high symmetric far-field pattern with C6 symmetry and a small divergence angle is achieved. In this device, the integration of the stable single-mode operation, high beam quality and high output power is realized, which may have great significance for practical applications.

Neutron emission on the surface of Mars

The neutron emission of Mars is known to be produced due to the bombardment of Martian surface by Galactic Cosmic Rays (GCRs). As evidenced by numerical simulation, the intensity of neutron emission on the planetary surface is much larger than that of the neutron emission at the orbital altitude due to multiple reflections of the neutrons emitted from soil by the atmosphere. The code developed for simulations was validated using the experimental data of neutron emission acquired in the Gale crater by the RAD and DAN instruments aboard the NASA's Curiosity rover. Neutron emission was simulated for two Martian areas: the dry Solis Planum territory and the bottom of the Valles Marineris system of canyons, which is thought to be the most wet equatorial spot on Mars. For both areas a strong effect is found, showing a considerable difference between the neutron emission on the surface and at the altitude of a typical orbit. It was also shown that surface emission in these two areas is quite different due to the difference of mass fraction of water in the shallow subsurface. Finally, the seasonal variations of neutron emission in these areas due to the atmospheric seasonal changes are also estimated.

Joint 1DVar retrievals of tropospheric temperature and water vapor from Global Navigation Satellite System radio occultation (GNSS-RO) and microwave radiometer observations

Abstract. Global Navigation Satellite System radio occultation (GNSS-RO) and microwave radiometry (MWR) are two of the most impactful spaceborne remote sensing techniques for numerical weather prediction (NWP). These two techniques provide complementary information about atmospheric temperature and water vapor structure. GNSS-RO provides high vertical resolution measurements with cloud penetration capability, but the temperature and moisture are coupled in the GNSS-RO retrieval process and their separation requires the use of a priori information or auxiliary observations. On the other hand, the MWR measures brightness temperature (Tb) in numerous frequency bands related to the temperature and water vapor structure but is limited by poor vertical resolution (> 2 km) and precipitation. In this study, we combine these two technologies in an optimal estimation approach, 1D variation method (1DVar), to improve the characterization of the complex thermodynamic structures in the lower troposphere. This study employs both simulated and operational observations. GNSS-RO bending angle and MWR Tb observations are used as inputs to the joint retrieval, where bending can be modeled by an Abel integral and Tb can be modeled by a radiative transfer model (RTM) that takes into account atmospheric absorption, as well as surface reflection and emission. By incorporating the forward operators into the 1DVar method, the strength of both techniques can be combined to bridge individual weaknesses. Applying 1DVar to the data simulated from large eddy simulation (LES) is shown to reduce GNSS-RO temperature and water vapor retrieval biases at the lower troposphere while simultaneously capturing the fine-scale variability that MWR cannot resolve. A sensitivity analysis is also conducted to quantify the impact of the a priori information and error covariance used in different retrieval scenarios. The applicability of 1DVar joint retrieval to the actual GNSS-RO and MWR observations is also demonstrated through combining collocated COSMIC-2 and Suomi-NPP (National Polar-orbiting Partnership) measurements.

Design of porous silicon /PECVD SiOx antireflection coatings for silicon solar cells

The meso-poreux porous silicon layer (PS) has become an interesting material owing to its potential applications in many fields including optoelectronics and photovoltaics. PS layers were grown on the front surface emitter n+ of n+ -p mono-crystalline Si junction. The thickness of the PS formed and the porosity were measured by an ellipsometer as a function of time duration of anodization, and the variation law of the PS growth kinetics is established. Single layers PS antireflection coating (ARC) achieved around 9% effective reflectivity in the wavelength range between 400 and 1000nm on junction n+ -p solar cells. To reduce the reflectivity and improve the stability and passivation properties of PS ARC, the design of PECVD oxide silicon layers were investigated. SiOx layers of thickness of 105nm deposited on PS ARC showed a decrease of ~3.8% in the effective reflectivity, compared to the single layer PS ARC, improve the reflectivity of 55%. Voc measurements were carried out on all the samples by suns-Voc method and showed an improvement of the quality of the passivation brought by the oxide layer. Using the experimental reflectivity results and taking into account the passivation quality of the samples, the PC1D simulations predict an enhancement of the photogenerated current exceeding 49%.

Performance of vacuum-insulated central pipes for deep borehole heat exchangers in geothermal systems

Abstract Geothermal energy is considered a promising future energy prospect, with the geothermal well outlet temperature being one of the important parameters affecting possible utilization options. For ground source heat pump applications or direct district heating, using lower temperatures can be acceptable. However, efficient electricity production requires a higher enthalpy gradient, which cannot be achieved without high temperature at the wellhead. The selection of the dry co-axial close-loop deep borehole systems (DBHE) may be, in some cases, very beneficial. The operating performance of co-axial DBHE can be optimized if the undesired heat transfer between the central pipe and annular fluid zones is minimized. Therefore, the operational performance of such a system depends strongly on the high thermal resistance of the central pipe. The most common option would be a low thermal conductivity material, such as high-density polyethylene (HDPE). In addition, vacuum-insulated tubing (VIT) used as the central pipe could be considered. The article presents results from the study aimed at the comparison of the homogeneous central pipe made of HDPE material and the gap-insulated central pipe. In the study, various air pressure levels as well as variations of surface emissivity were examined to reveal the effect on the heat transfer between the fluid channels. The simulation has been performed using a new purposely developed WellTH simulation software. A coaxial heat exchanger system using a VIT outperforms significantly the heat exchanger with an HDPE for deep geothermal wells. However, this advantage diminishes for shallow wells and therefore this tendency should be considered in the design stage.

Estimation of Land Surface Temperature from Chinese ZY1-02E IRS Data

The role of land surface temperature (LST) is of the utmost importance in multiple academic disciplines, such as climatology, hydrology, ecology, and meteorology. To date, many methods have been proposed to estimate LST from satellite thermal infrared data. The single-channel (SC) algorithm can provide an accurate result in retrieving LST based on prior knowledge of known land surface emissivity (LSE). The SC algorithm is extensively employed for retrieving LST from Landsat series data due to its simplicity and its reliance on just one thermal infrared channel. The Thermal Infrared Sensor (IRS) on the Chinese ZY1-02E satellite is a pivotal instrument employed for gathering thermal infrared (TIR) data of land surfaces. The objective of this research is to evaluate the feasibility of a single-channel approach based on water vapor scaling (WVS) for deriving LST from ZY1-02E IRS data because of its wide spectrum range, i.e., 7~12 μm, which is affected strongly by both atmospheric water vapor and ozone. Three study areas, namely the Baotou, Heihe River Basin, and Yantai Sea sites, were selected as validation sites to evaluate the LST inversion accuracy. This evaluation was also conducted via cross-comparison between the retrieved LST and MODIS LST products. The results revealed that the WVS-based method exhibited an average bias of 0.63 K and an RMSE of 1.62 K compared to the in situ LSTs. The WVS-based method demonstrated reasonable accuracy through cross-validation with the MODIS LST product, with an average bias of 0.77 K and an RMSE of 2.0 K. These findings indicate that the WVS-based method is effective in estimating LST from ZY1-02E IRS data.

Laser Dynamic Control of the Thermal Emissivity of a Planar Cavity Structure Based on a Phase-Change Material.

Tailoring the thermal emission of a material in the long-wave infrared (IR) range of 8-13 μm is crucial for many IR-adaptive applications, including personal thermal management, IR camouflage, and radiative cooling. Although various materials and surface structures have been proposed for these purposes, space-selective and dynamic control of their emissivity is challenging. In this study, we present a planar surface cavity structure consisting of a Ge2Sb2Te5 (GST) film on top of a thin metal reflector to modulate its emissivity by using an ultraviolet laser beam. A laser-induced phase change in GST allowed for the local control of emissivity. The average emissivity in the long-wave IR range was tunable from 0.15 to 0.77 simply by changing the laser energy deposited on the GST film. This enabled the laser printing of high-contrast emissivity patterns, which were erasable by subsequent thermal annealing. Emissivity-modulated GST cavities could be fabricated on not only rigid substrates but also flexible plastic substrates such as polyimide. The GST surface cavity was highly flexible and remained stable upon repeated bending to a curvature radius of 0.5 cm. This study provides a promising route for realizing scalable and flexible thermal emitters with tunable surface emissivity.

Numerical and experimental study of a multiphase flow inside a self-contained drum motor drive system

The multiphase Taylor-Couette flow of air and oil enclosed within the annular space between two concentric cylinders has been studied experimentally and numerically. The outer cylinder rotates at a constant speed and exchanges heat by convection and radiation with ambient air. The inner cylinder is stationary and subjected to a constant uniform heat flux. Such flow can be found in a self-contained drum motor drive system (SCDMDS). The heat flux imposed on the inner cylinder mimics the amount of heat generated due to several thermal losses within the SCDMDS. A layer of lagging material is sometimes added to the outer cylinder to enhance belt traction.The effect of the inner-to-outer cylinder radius ratio (RR), Reynolds number (Re), oil volume (OV), outer cylinder surface emissivity (ε), and lagging material thickness (δ) on the flow and heat transfer between the two cylinders and the ambient has been investigated considering a quasi-steady state analysis. The current investigation considered the following ranges found in a typical SCDMDS: RR = 0.35–0.85, Re = 200–3000, OV = 50–100 %, ε = 0–0.95, and δ = 0–100 mm. The numerical part of the present study has been carried out using ANSYS-CFX software package. The numerical results have been validated using experimental data. Resultsindicated that increasing RR, Re and ε enhanced the heat transfer within the SCDMDS. The rate of heat transfer within the annular space reached its highest value at OV = 65 % above which the rate of heat transfer is deteriorated. Because the lagging material is acting as an insulation over the outer cylinder, a critical thickness of δ = 35 mm resulted in the minimum overall resistance above which the rate of heat transfer is deteriorated.The parametric study revealed that the best overall thermal performance was attained at RR = 0.85, Reynolds number = 3000, OV = 65 %, ε = 0.95 and δ = 35 mm. In this case, the heat transfer coefficient between the inner cylinder and the oil reached its highest value of 410 W/m2 °C, giving the lowest possible inner cylinder temperature. A correlation of Nusselt number in terms of the geometrical and operating parameters of a SCDMDS considered in the current study has been developed and validated. The developed correlation gave a maximum deviation of ±8 %.