Lower Wall Temperature Research Articles

Experimental test, numerical analysis and thermal calculation modeling of hundreds kWth-class supercritical CO2 fossil-fired boiler system

Boiler is one of the important parts for supercritical CO2 (S–CO2) power system. Currently, most studies are based on theoretical calculations and lack experimental validation. Besides, low flue gas temperature and high wall temperature significantly enhance convection heat transfer (CHT), resulting in the failure possibility of existing thermal calculation models (neglect CHT). This study aims to construct a thermal calculation model suitable for S–CO2 boiler. Firstly, the hundreds kWth-class S–CO2 diesel/coal-fired boiler system was built, and steady-state experiments were carried out. Secondly, to further evaluate CHT, a numerical model was established, and the reliability of simulation was verified. The results indicate that the proportion of CHT can reach 44.52%. The entrainment effect caused by high-speed jet leads to a negative velocity region near the cooling wall. Furthermore, there are velocity disturbances of non-mainstream direction near the cooling wall. These two lead to great enhancement of CHT. According to the above analysis, a proposed thermal calculation model (DCTCM-1D) considering CHT and wall temperature was constructed. Compared to existing models, DCTCM-1D has the lowest error, with the root mean square error of flue gas temperature, heat load, wall temperature and S–CO2 temperature being 22.54 °C, 0.94 kW/m2, 6.40 °C and 2.29 °C.

Enhancement of concentrator photovoltaic system through convergent-divergent microchannels

Concentrated photovoltaic technology is one of the evolving technologies that converts solar to electrical energy with a high efficiency percentage. Increasing concentrated photovoltaic cell’s temperature significantly reduces the performance of the system. Thus, in order to properly functioning of system, thermal management will be a rudimentary issue. This article focuses on the cooling performance of high-concentration photovoltaic system using microchannels attached to the bottom plate of solar cell. To this end, the effect of convergent-divergent microchannels at three amplitudes and three wave lengths at different Reynolds numbers is investigated, and results are compared with simple microchannels. The output results are presented via temperature, pressure, velocity contours as well as Nusselt number, friction factor, and effectiveness ratio. Compared to the simple microchannels, convergent-divergent microchannel lowers the wall temperature about 0.4–2 Kelvin by making velocity gradients along the channel. This leads to boosting the heat transfer capability up to 3 times in the best case and up to 1.5 times in the worst case. Increasing the wave length enhances the performance of system, while the opposite trend has been seen for greater wave amplitudes. For case A with lowest wave length, Nu increases 1.92 and 2.4 times at lowest and highest Re numbers while friction factor increases due to the higher contact surface area along the fluid stream. Moreover, increasing the wave amplitude leads to higher Nu number, higher friction factor and consequently lower effectiveness ratio. Finally, effectiveness ratio as a criterion to choose best case has shown that a higher wave length alongside with lower wave amplitude offers better heat transfer enhancement and lower pressure drop compared to simple channel. Case C-1 as a best case offers 0.8K lower wall temperature, 1.6 times better Nu number with only 1.3-time higher friction factor.

Gradient microstructures for flow-boiling enhancement

Herein, we apply grayscale lithography to produce novel gradient microstructures, demonstrating the enhancement of flow boiling through the manipulation of drag forces upon the forming bubbles. The use of engineered 3D anisotropy allowed directional control of boiling enhancement, with respective critical heat flux and peak heat transfer coefficient enhancements of up to 20% and 93% observed over the unstructured substrate. It is our suspicion that the sheltering of bubbles inside of cavity microstructures deteriorates their departure characteristics, and that the combination of induced turbulence and available surfaces to capture passing liquid is beneficial for protruding microstructures. We demonstrate the promising novel implementation of gradient microstructures in the boiling discipline, which may serve as a useful foundation for future work. The enclosed approach to boiling enhancement shows a potential future direction for engineered boiling microstructures, wherein bubble dynamics are directly manipulated on bespoke, 3-dimensional substrates, allowing the transfer of large heat fluxes at low wall temperatures.

Optical diagnosis study of fuel volatility on combustion characteristics of spray flame and wall-impinging flame

Finding suitable alternative fuels and reducing carbon emissions are important development directions for future engines. Many carbon-neutral fuels, such as alcohol fuels are widely used, and they are more volatile than traditional diesel fuel. Therefore, exploring the development characteristics of spray flames and near-wall flames of different volatile fuels has important theoretical significance and application value for the optimization of fuel characteristics and the development of efficient and clean combustion technology. In this paper, the flame structure, flame development characteristics and soot evolution of three fuels, including n-hexane, 74%v n-heptane mixed 26%v isooctane (PRF26) and 53%v n-dodecane mixed 47%v isooctane (D53) were tested, that the cetane number of three fuels is essentially same. High speed self-luminous imaging and RGB two-color method were used to investigated the effect of fuel volatility on combustion. Results can be seen as following. Firstly, during the early stages of n-hexane combustion, a blue premixed flame can be found, and there is a pale-yellow flame in the later stage. As the boiling point increases, the area of the blue flame in the first stage gradually decreases, the area of the yellow flame in the later stage gradually increases, and the spatially integrated natural luminosity (SINL) of flame gradually increases. In addition, as the boiling point increases, the initial spontaneous combustion ignition point is away from the nozzle, the ignition delay time reduces and flame area becomes larger. Furthermore, the flame of high boiling fuels result in higher soot emissions. Secondly, in the event of flame wall-impingement, the near-wall flame of the three fuels has higher flame SINL and more soot formation in comparison to the free spray flame. The flame development of the three fuels is similar. However, there are some differences in the flame brightness distribution. The bright flame areas in n-hexane and PRF26 are concentrated near the wall, while the bright flame area in the D53 flame is concentrated on the wall and the flame head area rolled up with a larger distribution area. The flame near the wall is impacted by the wall temperature that the lower wall temperature leads to prolonged fuel evaporation and mixing time, which increases the ignition delay time. In conclusion, fuel volatility has less influence on flame structure and development, but a significant impact on ignition delay time and emissions. Regardless of whether wall impingement occurs, higher volatile fuels can extend the ignition delay time, increase the flame area and decrease soot emissions from combustion.

Heat Transfer and Flow Structure Characteristics of Regenerative Cooling in a Rectangular Channel Using Supercritical CO2

At an extremely high Mach number, the regenerative cooling of traditional kerosene cannot meet the requirement of the heat sink caused by aerodynamic heating and internal combustion in a scramjet propulsion system. As a supplement of traditional regenerative cooling, supercritical CO2 is regarded as an effective coolant in severe heating environments due to its excellent properties of heat and mass transportation. In this paper, the heat transfer and flow structure characteristics of regenerative cooling in a rectangular channel using supercritical CO2 are analyzed numerically using a validated model. The effect of heat flux magnitude, nonuniform heat flux, acceleration and buoyancy and flow pattern are considered to reveal the regenerative cooling mechanism of supercritical CO2 in the engine condition of a scramjet. The results indicate that the heat transfer deterioration phenomenon becomes obvious in the cooling channel loaded with relatively high heat flux. Compared with the cooling channels loaded with increased heat flux distribution, the maximum temperature increased for the channel loaded with decreased heat flux distributions. When larger acceleration is applied, a relatively lower wall temperature distribution and higher heat transfer coefficients are obtained. The wall temperature distribution becomes more uniform and the high-temperature region is weakened when the coolants in adjacent channels are arranged as a reversed flow pattern. Overall, the paper provides some references for the utilization of supercritical CO2 in regenerative cooling at an extremely high Mach number in a scramjet.

Influence of retro-reflective and high-reflective coatings on thermal performance of buildings in summer and winter: A contrast experiment

The solar radiation has a great effect on the thermal environment of regional buildings, and reflective coatings can increase the amount of solar reflectance and reduce the solar heat gain. In summer, it can effectively improve the regional thermal environment, but in winter, it may be ineffective, or even counterproductive. This study aimed to experimentally evaluate the thermal performance of retro-reflective coatings (RRC) with unique reflective mechanism in enclosed buildings in both summer and winter, and took high-reflective coatings (HRC) as the comparison. The regional albedos, wall temperatures, and air temperatures were measured, which showed that both in summer and winter, RRC had higher regional albedos, lower wall temperatures and air temperatures than HRC, however, the differences were smaller in winter, which would lead to more thermal benefits in summer caused by RRC than thermal penalties in winter. For the regional albedos, the maximum differences in summer and winter were 4.99% and 2.46%, and the values were 2.74 °C–11.61 °C and 1.39 °C–5.61 °C for the wall temperatures, 2.10 °C and 0.39 °C for the air temperatures in the enclosed space.

Flow Boiling Heat Transfer Enhancement Using Tuned Geometrical Contact-Line Pinning

Wettability patterning is a promising method to manipulate bubble dynamics in microscale boiling systems, allowing the transfer of large heat fluxes at low wall temperatures. Herein, we experimentally investigate the enhancement of flow boiling through exploitation of contact-line pinning using superbiphilic wettability patterns with a range of geometries and orientations. We compare the boiling performance on symmetrical (i.e., circular, square, and diamond-shaped) and asymmetrical (i.e., triangular) superhydrophobic patches and also create rings and chevrons through insertion of self-similar, recursive superhydrophilic cut-outs. Two main principles for boiling heat transfer enhancement are demonstrated: first, the ease of bubble departure from the superhydrophobic patches is shown to depend upon the interaction between the local contact angle and the bubble's tilt due to hydrodynamic drag; second, we find that ring-shaped superhydrophobic patches may trap droplets inside the forming bubbles, thus supplementing the heat transfer coefficient and critical heat flux through latent heat. Through application of these principles, the heat transfer coefficient and critical heat flux of heterogeneous surfaces was enhanced over the homogeneous analogues by 62% and 24%, respectively. Finally, we establish and validate a general model to estimate the ease of bubble departure through the use of geometric arguments.

Electrospray cooling characteristics in cone-jet and multi-jet modes

As a promising cooling technology, electrospray (ES) cooling has received increasing attention for its efficient thermal-dissipation capability and low coolant requirement. Previous investigations primarily focused on the ES cooling in single ES mode with solitary coolant. Here, we experimentally investigate the spray cooling performances in four ES modes and the effects of two coolants on ES heat transfer. Results show that smaller droplet size, higher speed and larger ES cone angle are observed in cone-jet and multi-jet modes, which are responsible for 32% and 74% of increments of heatflux compared to micro-droplet mode. Moreover, the widest nucleate-boiling zone is attained in multi-jet mode. Increasing coolant volume flux improves ES cooling performance due to the higher velocity and smaller droplet size. Ethylene glycol obtains better ES cooling performance than ethanol, except for at lower wall temperature with the same volume flux. In micro-droplet mode, the droplet bounced by the gas film connects with the fluid at nozzle outlet to form an oscillating liquid column, resulting in fluctuation of wall temperature. When the applied voltage is 3.7 kV and the wall temperature exceeds 110 °C, the ES switches randomly between cone-jet and multi-jet modes at nozzle outlet.

Performance Enhancement Using Porous Slabs in a Jet Impingement Microchannel Heat Sink

Numerical study of a novel microjet impingement microchannel heat sink with porous media is proposed. Hydrothermal performance of the hybrid heat sink is investigated and compared with no porous media heat sink at Reynolds number 200 to 500 for several configurations of the porous slabs such as fully filled porous channel, bottom porous slab, side porous slab and slotted porous slabs in between two jets. Hybrid heat sink with fully filled porous media and slotted porous slab yielded lower wall temperatures; however, higher rise in pressure drop obtained. Furthermore, pressure drop is lowered remarkably with a reasonable rise in wall temperature in heat sink with slotted porous slabs. The changes in porous slab size affected abruptly the overall performance such as figure of merit. Thus, optimal size of the porous slabs as a function of Reynolds number is investigated for different configurations. The heat sink with 0.15 mm thick porous slabs at the base exhibited better overall performance at high Reynolds numbers, whereas at low Reynolds numbers, slotted porous slab of 0.5 mm length in the middle of impingements showed better overall performance. Generalized correlations of Nusselt numbers are developed for different cases helping optimize the heat sink design.

Research on destructive knock combustion mechanism of heavy-duty diesel engine at low temperatures

ABSTRACT To clarify the mechanism of destructive knock combustion and piston ablation in heavy-duty diesel engines operating at low temperatures, CONVERGE simulation and wall temperature measurement were performed. The results show that as the initial temperature (intake valve closing instant) decreases from 380K to 307K, the spray wet-wall ratio increases from 12.8% to 22.2%. The fuel film evaporates slowly at low temperature before the hot flame, so the ignition is seriously delayed until the fuel injection ends, and the free-jet autoignition shifts to wall-attached combustion. However, the fuel film evaporation reverses after hot flame, and the maximum evaporation rate at 307K is about 54 times that at 380K. The wall temperature rises sharply to 350-450°C during wall-attached combustion. As the initial temperature decreases, the maximum pressure rise rate increases from 0.9MPa/°CA to 8.3MPa/°CA, and the pressure waves repeatedly oscillate along the end-center-end path in the cylinder. The highest pressure at the monitoring point is nearly an order of magnitude higher than the average, and the oscillation amplitude is as high as 6-10MPa, which far exceeds the failure threshold. The piston whose strength has been greatly reduced after thermal shock quickly undergoes ablation damage under strong pressure shock.

Jet Impingement Boiling on Monocrystalline Silicon Surfaces with Open Microchannels

Thermal management of electronic devices with great critical heat flux (CHF) and lower wall temperature is critical issues. To address it, the cooling method based on jet impingement boiling is experimentally explored. The effects of heat surface modification, vertical expansion angle of flow microchannels, and negative back pressure are emphasized. The vertical expansion angle, flow rate and average pressure are 0°–30°, 10–30 L/h, and 0.04–0.1 MPa, respectively. It is found that the CHF changes non-monotonically with the increase of the vertical expansion angle of the open flow microchannel since both flow resistance and bubble detachment performance. A maximum CHF reaches at 381 W/cm2 for the jet impingement boiling on a modified monocrystalline silicon surface with microcolumns under the condition of open microchannels with the vertical expansion angle of 20° and the pressure of 0.1 MPa. Moreover, compared with 0.04 MPa, a greater pressure of 0.1 MPa increases the boiling temperature, thus inhibiting explosive boiling and enhancing the CHF.

Effect of CO-to-H2 ratio on syngas flame behaviors in a micro flow reactor with controlled wall temperature gradient

Flame characteristics of CO/H2/O2/N2 mixture (O2:N2 = 1:7) with different CO/H2 ratios in a micro-channel with a controlled wall temperature gradient were investigated through numerical simulation. Five flame regimes were identified and their global diagram was drawn. The influence of CO/H2 ratio on two typical flame dynamics (one is stable and the other is unstable), i.e., “coexisting upstream normal flame (UNF) and downstream weak flame (DWF)” and “uninterrupted flame with repetitive extinction and ignition (UFREI)”, were discussed. It is revealed that in the UNF-DWF regime, a higher H2 proportion can strengthen OH generation in the UNF through H2-OH and H-HO2-OH reaction paths, which causes the UNF to propagate upstream. However, the upstream lower wall temperature results in weaker near-wall reaction intensity for the UNF, which brings about more CO residual and thus enhances the DWF. For the UFREI regime, both the period and the propagation distance of flame dynamics are reduced with the augmentation of CO/H2 ratio because of the weakened flame intensity. Moreover, the characteristic flame positions are also affected by the CO/H2 ratio. In details, the farthest position of UFREI moves upstream while the transition position slightly shifts downstream as the CO/H2 ratio is increased, which is substantially affected by the transport of residual fuel after the extinction of UFREI. In summary, the present investigation unraveled the complicated influence of CO/H2 ratio on the syngas flame dynamics in a micro-channel with a controlled wall temperature gradient.

Temperature-controlled focusing of Brownian particles in a channel.

The preferential motion of Brownian particles in a channel with heated or cooled walls was numerically simulated using a direct numerical simulation method, that is, the fluctuating-lattice Boltzmann method. The resulting focusing of Brownian particles on the channel centerline induced by heated walls is the focus of this study. The effects of wall temperature, fluid thermal diffusivity, and particle size and density were considered in terms of both the focusing efficiency and performance of Brownian particles. It was revealed that the particle focusing process follows a quadratic relationship with time at high wall temperatures or a linear relationship at low wall temperatures. For a fixed wall temperature, the focusing efficiency (i.e., how fast the Brownian particles aggregate) is dominated by the Prandtl number, that is, the relative importance of the heat transfer and momentum transfer in the fluid. Meanwhile, the Lewis number, that is, the ratio of the fluid thermal diffusivity to the particle self-diffusivity, controls the focusing performance (i.e., to what extent Brownian particles aggregate). The possible mechanisms behind this are discussed. Finally, the negligible influence of particle density on both the focusing efficiency and performance was revealed.

Simulation of single and two-phase refrigerant compression in rotary compressors

Liquid slugging, which often happens during startup and defrosting processes of the air conditioning, is a great threat to the reliability of rotary compressors, because of its high pressure in the compression chamber. In this paper, a coupled mathematical model that can predict the compression process of refrigerants in three different states in the compressor cylinder is proposed. The refrigerant phase change, heat exchange between refrigerant and wall, leakage through leak passage and refrigerant kinetic energy change rate are considered in the model. The coupled solution method and its Fortran calculation program are carried out. This mathematical model is experimentally verified by using R290 as refrigerant. The results show that the simulation results of pressure variation in the compressor cylinder during the refrigerant two-phase compression and discharge processes are consistent with the experimental values. The liquid slugging happens with the maximum pressure of 2400 kPa in the cylinder under low suction gas mass fraction. The R290 is more prone to condense during in-cylinder compression than that of R22 and R410A under low wall temperature condition. The larger the volume change rate of the compression chamber, the higher compressor rotation speed, and the smaller the flow area at the end of discharge process will exacerbate the liquid compression phenomenon.

Effects of wall temperature on two-point statistics of the fluctuating wall shear stress and heat flux in supersonic turbulent boundary layers

In the present study, we investigate two-point statistics of fluctuating streamwise wall shear stress τ′x and wall heat flux q′w by exploiting a direct numerical simulation database of supersonic turbulent boundary layers over a heated wall and a cooled wall at the friction Reynolds number around 800. By separately investigating positive and negative families of τx′ and qw′ with the aid of the conditional correlation analysis, we identify the asymmetrical deformation of τ′x and q′w, reminiscent of and ascribed to the asymmetrical deformations of sweeps and ejections events. The degree of such asymmetry is alleviated by the lower wall temperature. The spatial orientation of τx′ is insensitive to the wall temperature, whereas the spanwise elongated q′w that is closely related to the wall pressure is manifested merely in the cooled-wall case. The cross correlation between τx′ and the fluctuating streamwise velocity u′ reveals that low-speed streaks related to negative τx′ are more inclined to the wall than high-speed ones related to positive τx′ by 4°–5°, and that the phase lag between negative τx′ and u′ is larger than that between positive τx′ and u′ except in the near-wall region. Such a difference is proportional to the wall distance and should be considered for models predicting near-wall and wall quantities using signals in the logarithmic layer.

Heat transfer deterioration in vertical sCO2 cooling in 3 mm tube

In this publication, the cooling heat transfer coefficient (htc) is investigated in a 3 mm diameter tube with vertical flow orientation. Commonly used calculation methods of the heat transfer coefficient are presented. Although developed for heating of sCO2, the mixed convection criterion is used to evaluate the heat transfer deterioration. The effects of the CO2 mass flux of 141−354kg/m²s and bulk fluid temperatures of 20−50°C with a constant pressure of 80bar on the heat transfer were examined. The upwards flow shows a steady decrease in the htc with the reduction of the mass flux. However, the downwards flow shows significant effects of buoyancy. At low mass flux the distinct peak in the htc at the pseudocritical temperature (Tpc) disappears. The deteriorated heat transfer in the downwards flow showed significant lower wall temperatures compared to the upwards flow. The separate evaluation of the liquid-like and gas-like region indicates that the deterioration may vary based on the fluid properties. The results were regressed within +-15% in the forced convection region and +-40% in the mixed convection region. The comparison with the literature data of vertical cooling in 6 mm showed different behaviour which indicates an influence of the tube diameter.

Analysis of spray/wall impingement using an ECN single-hole injector and a controlled-temperature wall under realistic engine conditions

Spray–wall interactions (SWI) directly affect fuel–air mixture and emissions formation. Therefore, they are considered among the most critical physical processes in engine research nowadays. However, the physics of the wall film formation, propagation, and breakup is not fully understood yet. This work aims to use a thermoregulated steel wall to study the spray–wall interaction phenomenon and its influence on the macroscopic spray behavior. A single-hole injector known as “Spray D” in the Engine Combustion Network was used. n-Dodecane was employed as fuel and the wall has been positioned in four different configurations, varying angle and distance respect to the injector tip. For this work, not only diesel combustion is reproduced in the test rig due to ambient gas engine-like thermodynamic conditions, but wall temperature has been controlled to emulate characteristic values that could be found in the piston of an internal combustion engine. This implies that the spray–wall heat transfer is simulated and its effects on ignition and spray development can be analyzed. Heat flux was measured by employing high-speed thermocouples fitted in the wall and by the use of an one-dimensional transient wall heat model. Three high speed cameras were simultaneously used to observe the SWI, one for the Schlieren optical technique which allows to study the vapor phase of the spray and to determine the ignition delay, another one to observe the natural luminosity of the flame, and finally, an intensified camera was used to determine the lift-off length by observing the chemiluminescence of the OH*. An interesting finding obtained in this work was a boundary layer formation due to the thermal diffusion that contributes to cool down the spray and to delay the high-temperature chemical reactions. Results show a substantial increment of the heat flux and the wall temperature variation with both ambient temperature and density by increasing the flame temperature and gas entrainment. The exposure to the cold wall affects the ignition delay variation with the injection pressure and the wall distance. It was found that the wall temperature (in the range of tested conditions) did not affect the lift-off length location. • The exposure to the cold wall delayed the ignition. • Flame thickness around the wall undergoes a narrowing at lower wall temperatures. • The injection pressure increments the convective coefficient. • A boundary layer due to thermal diffusion was formed on the wall.

Thermohydraulic performance of Al2O3-water nanofluid during single-phase flow and two-phase subcooled flow boiling

This study presents the thermohydraulic performance of Al2O3-water nanofluid in single-phase and two-phase subcooled flow boiling in a horizontal copper tube. The results of a three-dimensional Eulerian-Eulerian CFD model are validated with the experimental data. Having the model validated, a comprehensive parametric analysis is conducted on the effect of Reynolds number, heat flux, and volume concentration of nanoparticles on the hydrothermal performance of the heat exchanging tube. The HTC in the flow boiling regime is increased by ∼73% compared to the single phase. The heat transfer and pressure drop increased through the addition of nanoparticles to the base fluid in single-phase and two-phase flows. However, its effect is more pronounced in case of single-phase flow. Increasing the heat flux on the tube wall is associated with a slight increase in the heat transfer coefficient (HTC) and a significant decrease in the pressure drop. The HTC and pressure drop increase by moving to higher Reynolds number. The vapor volume fraction of nanofluid was lower than pure water due to a higher heat transfer and lower wall temperature. The maximum PEC (performance evaluation criterion) of 1.25 and 1.19 is found in case of single- and two-phase flows.

Analytical analysis of non-boiling heat transfer during droplet impact on heated wall and the effect of thermophysical properties

Droplet impact process exhibits excellent heat and mass transfer characteristics. Analytical solution with simple explicit form and certain accuracy can clearly reflect the correlation of physical parameters, however the analytical study on droplet impact heat transfer is quite insufficient and limited to flow field analysis. In this paper, the analytical solutions of heat flux and temperature variation of droplet impact on heated wall in non-boiling regime were obtained based on boundary layer asymptotic matching method. Parameter analysis of thermophysical properties was conducted to explore the decisive properties of droplet and wall materials. The results showed that the analytical solutions are appropriate to predict non-boiling heat transfer at low impact velocity and low initial wall temperature. Parameter analysis showed that thermal effusivity is the decisive property rather than the thermal diffusivity. Wall thermal effusivity could independently determine heat flux, but should determine temperature variation together with wall thermal conductivity. Droplet thermal effusivity and Prandtl number were the decisive properties, however the effect of Prandtl number in reality can be ignored. Wall materials and droplet liquids with higher thermal effusivity showed higher heat transfer capacity. The importance of thermal effusivity was demonstrated and high thermal effusivity was preferred in future thermal management.

Air curtains for reduction of natural convection heat loss from a heated plate: A numerical investigation

Concentrating solar power (CSP) plants encounter inefficiencies at all stages of electricity generation. Convection from the solar-thermal receiver is a significant mode of heat loss in CSP systems, and is challenging to mitigate. This study investigates the reduction of convection losses by using a planar jet that disrupts the buoyant flow arising from the heated surface of an external CSP receiver. An isothermal flat plate with a height of 1.8 m was used to model the receiver, and a planar jet air curtain with a nozzle thickness of 3 mm was introduced near the upper edge of the wall. A computational fluid dynamics model was first validated and subsequently implemented to conduct a parametric study on the heat transfer from the isothermal plate with an air curtain varying four parameters: jet speed, jet angle, plate temperature and plate inclination. The results showed that the air curtain generates a stagnation zone adjacent to the wall which successfully reduces local convective heat losses. The effectiveness of an air curtain is defined here as the relative reduction in the local heat loss due to the air curtain, compared to the case of natural convection alone. A local maximum of 31.2% effectiveness is achieved in the stagnation zone below the jet outlet for a vertical wall with a jet speed of 2.5 ms−1 and jet angle of 45∘. The air curtain effectiveness at the stagnation region was found to decrease with increasing jet speeds, whereas the effectiveness increased near the laminar-to-turbulent transition region with increasing jet speed. Smaller air curtain angles relative to the wall resulted in lower effectiveness. A 45∘ air curtain on a vertical wall can offer performance benefits that are similar in magnitude to inclining a wall from the vertical. A higher wall temperature was accompanied by better effectiveness near the jet outlet, particularly in the stagnation region, while lower wall temperatures produced higher effectiveness further from the jet. Therefore, an air curtain can be used to reduce convective heat losses locally from a heated flat surface, including potentially when applied to CSP receivers.