Start-up,heat transfer and flow characteristics of silicon-based micro pulsating heat pipes

A simultaneous visualization and measurement study has been carried out to investigate the start-up, heat transfer and flow characteristics of three silicon-based micro pulsating heat pipes (MPHPs) with the trapezoidal cross-section having hydraulic diameters of 251 μm (#1), 352 μm (#2) and 394 μm (#3), respectively. Experiments were performed under different working fluids, filling ratios, inclination angles (bottom heating mode) and heating power inputs. It is found that (1) the silicon-based MPHPs could start up within 200 s when charged with R113 or FC-72, but they failed to start up at all inclination angle when charged with water or ethanol having lower (dP/dT)_sat, higher viscosity, higher latent heat and higher surface tension at the same temperature. During the start-up period, no obvious nucleation was observed. After the start-up period, MPHPs entered the operation period. The silicon-based MPHP could operate normally even at a Bond number of 0.26 and a hydraulic diameter of 251 μm, both smaller than the corresponding values in literatures; (2) the thermal performance of MPHPs depends greatly on the type of working fluid, filling ratio and inclination angle. At the lower power input, MPHPs charged with R113 showed better thermal performance than that charged with FC-72, however, the latter exceeded the former at the higher power input. For the same working fluid, there existed an optimal filling ratio corresponding to the best thermal performance of MPHPs, which was about 52%, 55% and 47% for MPHPs #1, #2 and #3 at the vertical orientation (90°), respectively. When the MPHPs turned from the vertical to the horizontal orientation, the thermal performance tended to be decreased, indicating that the gravity effect cannot be ignored in these silicon-based MPHPs. In MPHP #3 at the inclination angle from 70° to 90°, there appeared a special thermal resistance curve with two local maximum points, which is absent in the traditional PHPs; (3) in the operation period of larger MPHP #3, nucleation boiling, bulk circulation and injection flow were all observed, while these flow patterns were absent in the smaller MPHPs #1 and #2. Intense liquid film evaporation, instead of bubbles’ generation and expansion which usually activated the oscillation flow in macro-PHPs, drove the two-phase flow in the smaller MPHPs #1 and #2.     

Correlation of critical heat flux and two-phase friction factor for subcooled convective boiling in structured surface microchannels

Critical heat flux (CHF) and pressure drop of subcooled flow boiling are measured for a microchannel heat sink containing 75 parallel 100 μm × 200 μm structured surface channels. The heated surface is made of a Cu metal sheet with/without 2 μm thickness diamond film. Tests and measurements are conducted with de-ionized water, de-ionized water +1 vol.% MCNT additive solution, and FC-72 fluids over a mass velocity range of 820–1600 kg/m² s, with inlet temperatures of 15(8.6)°C, 25(13.6)°C, 44(24.6)°C, and 64(36.6)°C for DI water (FC-72), and heat fluxes up to 600 W/cm². The CHF of subcooled flow boiling of the test fluids in the microchannels is measured parametrically. The two-phase pressure drop is also measured. Both CHF and the two-phase friction factor correlation for one-side heating with two other side-structured surface microchannels are proposed and developed in terms of the relevant parameters.     

Effects of duct inclination angle on thermal entrance region of laminar and transition mixed convection

Experimental investigation was performed on the mixed convection heat transfer of thermal entrance region in an inclined rectangular duct for laminar and transition flow. Air flowed upwardly and downwardly with inclination angles from ?90° to 90°. The duct was made of duralumin plate and heated with uniform heat flux axially. The experiment was designed for determining the effects of inclination angles on the heat transfer coefficients and friction factors at seven orientations (θ = ? 90°, ?60°, ?30°, 0°, 30°, 60° and 90°), six Reynolds numbers (Re ≈ 420, 840, 1290, 1720, 2190 and 2630) within the range of Grashof numbers from 6.8 × 10³ to 4.1 × 10⁴. The optimum inclination angles that yielded the maximum heat transfer coefficients decreased from 30° to ?30° with the increase of Reynolds numbers from 420 to 1720. The heat transfer coefficients first increased with inclination angles up to a maximum value and then decreased. With further increase in Reynolds numbers, the heat transfer coefficients were nearly independent of inclination angles. The friction factors decreased with the increase of inclination angles from ?90° to 90° when Reynolds numbers ranged from 420 to 1290, and independent of inclination angles with higher Reynolds numbers.     

Efficient spreaders for cooling high-power computer chips

Investigated is the performance of composite spreaders, consisting of a top layer of porous graphite (⩾0.4 mm), for enhanced cooling by nucleate boiling of FC-72 dielectric liquid, and a copper substrate (⩽1.6 mm), for efficient spreading of the dissipated thermal power by the underling 10 × 10 mm or 15 × 15 mm high-power computer chips. The analysis assumes uniform thermal power dissipation by the chips and calculates the square surface area of the spreader, along with the spreading, boiling and total thermal resistances, the maximum chip temperature, and the removed thermal power from the spreader surface by saturation or subcooled nucleate boiling of FC-72 liquid. These performance parameters are determined as functions of the thickness of the copper substrate and the size of the underlying chip. When compared with those of copper and porous graphite spreaders of the same total thickness, 2.0 mm, the performance of the composite spreaders is superior for cooling high-power computer chips. When cooled by nucleate boiling of 30 K subcooled FC-72 liquid, the composite spreader removes 160.3 W and 98.4 W of dissipated thermal power by the underlying 10 × 10 mm and 15 × 15 mm chips, at total thermal resistances of 0.29 and 0.48 °C/W. When the same spreader is cooled by saturation boiling of FC-72, the removed thermal power decreases to 85.6 W and 53.4 W, and the total thermal resistances also decrease to 0.12 and 0.20 °C/W, respectively. Although the calculated surface temperatures of the chips are not uniform, the maximum temperatures are <71 °C and the temperature differential across the chips is <8 °C. For the same cooling condition, the calculated surface area of the copper spreaders, the total thermal resistance, and the maximum chip temperature are much higher, but the removed thermal powers from the surface of spreaders are much lower than with composite spreaders. The calculated surface areas of the porous graphite spreaders are smaller, the thermal powers removed from surface of these spreaders are much lower and both the total thermal resistance and the maximum chip temperature are higher than those with composite spreaders.     

Pool boiling of perfluorocarbon mixtures on silicon surfaces

The need for higher pool boiling critical heat flux (CHF) in electronic cooling applications has turned attention to the use of binary mixtures of dielectric liquids. The available literature demonstrates that the addition of a liquid with higher saturation temperature, higher molecular weight, higher viscosity and higher surface tension can lead to significant enhancement of CHF, beyond what can be achieved through changes in pressure, liquid subcooling, and the product of surface effusivity and heater thickness. The current study focuses on extending the available data on mixture CHF enhancement, as well as pool boiling, on polished silicon surfaces to FC-72/FC-40 mixture ratios of 10%, 15%, and 20% of FC-40 by weight, a pressure range of between 1 and 3 atm, and fluid temperature from 22 to 45 °C, leading to high subcooling conditions. It is found that peak heat flux can be increased to as high as 56.8 W/cm² compared to 25.2 W/cm² for pure FC-72 at 3 atm and 22 °C. It is believed that the increase in the mixture latent heat of evaporation and surface tension, accompanying the depletion of the lower boiling point fluid in the wall region plays the major role in enhancing the critical heat flux for binary mixtures.     

Saturated flow boiling heat transfer and associated bubble characteristics of FC-72 on a heated micro-pin-finned silicon chip

An experiment is carried out here to investigate flow boiling heat transfer and associated bubble characteristics of FC-72 on a heated micro-pin-finned silicon chip flush-mounted in the bottom of a horizontal rectangular channel. Besides, three different micro-structures of the chip surface are examined, namely, the smooth, pin-finned 200 and pin-finned 100 surfaces. The pin-finned 200 and 100 surfaces, respectively, contain micro-pin-fins of size 200 μm × 200 μm × 70 μm (width × length × height) and 100 μm × 100 μm × 70 μm. The pitch of the fins is equal to the fin width for both surfaces. The effects of the FC-72 mass flux, imposed heat flux, and surface micro-structures of the silicon chip on the FC-72 saturated flow boiling characteristics are examined in detail. The experimental data show that an increase in the FC-72 mass flux causes a delay in the boiling incipience. However, the flow boiling heat transfer coefficient is not affected by the coolant mass flux. But adding the micro-pin-fin structures to the chip surfaces can effectively enhance the single-phase convection and flow boiling heat transfer. Moreover, the mean bubble departure diameter and active nucleation site density are reduced for a rise in the FC-72 mass flux. A higher coolant mass flux results in a higher mean bubble departure frequency. Furthermore, larger bubble departure diameter, higher bubble departure frequency, and higher active nucleation site density are observed at a higher imposed heat flux. We also note that adding the micro-pin-fins to the chips decrease the bubble departure diameter and increase the bubble departure frequency. However, the departing bubbles are larger for the pin-finned 100 surface than the pin-finned 200 surface but the bubble departure frequency exhibits an opposite trend. Finally, empirical equations to correlate the present data for the FC-72 single-phase liquid convection and saturated flow boiling heat transfer coefficients and for the bubble characteristics are provided.     

Flow condensation in parallel micro-channels – Part 1: Experimental results and assessment of pressure drop correlations

In this first part of a two-part study, experiments were performed to investigate condensation of FC-72 along parallel, square micro-channels with a hydraulic diameter of 1 mm and a length of 29.9 cm, which were formed in the top surface of a solid copper plate. The condensation was achieved by rejecting heat to a counter flow of water through channels brazed to the underside of the copper plate. The FC-72 entered the micro-channels slightly superheated, and operating conditions included FC-72 mass velocities of 68–367 kg/m² s, FC-72 saturation temperatures of 57.2–62.3 °C, and water mass flow rates of 3–6 g/s. Using high-speed video imaging and photomicrographic techniques, five distinct flow regimes were identified: smooth-annular, wavy-annular, transition, slug, and bubbly, with the smooth-annular and wavy-annular regimes being most prevalent. A detailed pressure model is presented which includes all components of pressure drop across the micro-channel. Different sub-models for the frictional and accelerational pressure gradients are examined using the homogenous equilibrium model (with different two-phase friction factor relations) as well as previous macro-channel and mini/micro-channel separated flow correlations. Unexpectedly, the homogenous flow model provided far more accurate predictions of pressure drop than the separated flow models. Among the separated flow models, better predictions were achieved with those for adiabatic and mini/micro-channels than those for flow boiling and macro-channels.     

Experimental study of evaporation heat transfer of R-134a inside a corrugated tube with different tube inclinations

Experimental heat transfer studies during evaporation of R-134a inside a corrugated tube have been carried out. The corrugated tube has been provided with different tube inclination angles of the direction of fluid flow from horizontal, α. The experiments were performed for seven different tube inclinations, α, in a range of − 90° to + 90° and four mass velocities of 46, 81, 110 and 136 kg m^− 2 s^− 1 for each tube inclination angle during evaporation of R-134a. Data analysis demonstrate that the tube inclination angle, α, affects the boiling heat transfer coefficient in a significant manner. The effect of tube inclination angle, α, on heat transfer coefficient, h, is more prominent at low vapor quality and mass velocity. In the low vapor quality region, the heat transfer coefficient, h, for the + 90° inclined tube is about 62% more than that of the − 90° inclined tube. The results also showed that at all mass velocities, the highest average heat transfer coefficient were achieved for α = + 90°. An empirical correlation has also been developed to predict the heat transfer coefficient during flow boiling inside a corrugated tube with different tube inclinations.     

Effects of high subcooling on two-phase spray cooling and critical heat flux

Experiments were performed with FC-77 using three full-cone spray nozzles to assess the influence of subcooling on spray performance and critical heat flux (CHF) from a 1.0 × 1.0 cm² test surface. The relatively high boiling point of FC-77 (97 °C at one atmosphere) enabled testing at relatively high levels of subcooling. Increasing the subcooling delayed the onset of boiling but decreased the slope of the nucleate boiling region of the spray boiling curve. The enhancement in CHF was relatively mild at low subcooling and more appreciable at high subcooling. CHF was enhanced by about a 100% when subcooling was increased from 22 to 70 °C, reaching values as high as 349 W/cm². The FC-77 data were combined with prior spray CHF data from several studies into a broad CHF database encompassing different nozzles, fluids, flow rates, spray orientations, and subcoolings. The entire CHF database was used to modify the effect of subcooling in a previous CHF correlation that was developed for relatively low subcoolings. The modified correlation shows excellent predictive capability.     

Transient analysis of modified cuboid solar integrated-collector-storage system

A novel solar water heating system, modified cuboid solar integrated-collector-storage (ICS) system with transparent insulation material (TIM) has been designed and developed, which combines collection and storage in a single unit and minimizes the nocturnal heat losses. A comprehensive study has been carried out to evaluate the heat transfer characteristics inside the enclosure of the system to enhance the collection and storage of solar energy. The transient behavior of the modified-cuboid solar integrated-collector-storage system is investigated numerically to evolve optimum configuration. The optimum design for the system is obtained by carrying out a numerical parametric study with different geometry parameters like the depth of the cuboid (d = 2, 5, 8, and 12 cm), and inclination angles (10°, 20°, 30°, and 50°). The inside heat transfer coefficient of the ICS system, stratification factor and water temperature distribution inside the enclosure have been predicted by numerical simulation. Average heat transfer coefficient at the bottom surface of absorber plate is 20% higher for depth of 12 cm as compared to the 2 cm depth of cuboid section, after 2 h of heating. The stratification factor also increases from 0.02 to 0.065 as depth of the system increases from 2 cm to 12 cm. There is a marginal effect of inclination angles of the system on the convection in the enclosure. As the inclination angle increases from 10° to 50°, the average heat transfer coefficient increases from 90 W/m² K to 115 W/m² K. But the stratification factor is comparatively high for lower inclination angles. With the optimum design parameters, a field experimental set-up was built and the numerical model was validated for efficient heat collection and storage in a modified cuboid ICS system. The model is in good agreement with the experimental results.     

Subcooled flow boiling heat transfer and associated bubble characteristics of FC-72 on a heated micro-pin-finned silicon chip

Experiments are conducted here to investigate subcooled flow boiling heat transfer and associated bubble characteristics of FC-72 on a heated micro-pin-finned silicon chip flush-mounted on the bottom of a horizontal rectangular channel. In the experiments the mass flux is varied from 287 to 431 kg/m² s, coolant inlet subcooling from 2.3 to 4.3 °C, and imposed heat flux from 1 to 10 W/cm². Besides, the silicon chips contain three different geometries of micro-structures, namely, the smooth, pin-finned 200 and pin-finned 100 surfaces. The pin-finned 200 and 100 surfaces, respectively, contain micro-pin-fins of size 200 μm × 200 μm × 70 μm (width × length × height) and 100 μm × 100 μm × 70 μm. The measured data show that the subcooled flow boiling heat transfer coefficient is reduced at increasing inlet liquid subcooling but is little affected by the coolant mass flux. Besides, adding the micro-pin-fin structures to the chip surface can effectively raise the single-phase convection and flow boiling heat transfer coefficients. Moreover, the mean bubble departure diameter and active nucleation site density are reduced for rises in the FC-72 mass flux and inlet liquid subcooling. Increasing coolant mass flux or reducing inlet liquid subcooling results in a higher mean bubble departure frequency. Furthermore, larger bubble departure diameter, higher bubble departure frequency, and higher active nucleation site density are observed as the imposed heat flux is increased. Finally, empirical correlations for the present data for the heat transfer and bubble characteristics in the FC-72 subcooled flow boiling are proposed.     

Experimental investigation of buoyant flows in inclined differentially heated cavities

This experimental investigation focuses on the effects of angle of inclination on buoyancy-driven flows inside tall, rectangular, differentially-heated cavities. It considers a rectangular cavity with an aspect ratio of 28.6, with its two long sides maintained at different temperatures and the two short, end-walls, thermally insulated. The spanwise aspect ratio is 6.82 and the side walls are also thermally insulated. The Rayleigh number, based on the temperature difference and spacing between the long sides, is 0.86 × 10⁶ for most cases and the working fluid is air (Prandtl number 0.71). Experimental data, for the flow and the thermal fields, using laser Doppler anemomentry and thermocouple traverses respectively, are presented for the cavity inclined at 60° and 15° to the horizontal, for both stable (the hot surface being the upper surface) and unstable orientations. The 15° stable case is investigated at a higher Rayleigh number of 1.54 × 10⁶ and some additional data for the 15° unstable case are also presented at this higher value of Rayleigh number. For moderate angles of inclination, the flow is two-dimensional and the effects of inclination are primarily confined to the fluctuating fields. For large angles of inclination, the flow becomes three-dimensional. In the unstable 15° angle of inclination case a set of four longitudinal vortices are formed over the entire length of the cavity, with four counter-rotating re-circulation cells within the cross-section parallel to the thermally active walls. The stable 15° angle of inclination leads to the formation of two longitudinal vortices and two re-circulation cells. At the 15° angle (stable and unstable), the enhanced mixing leads to uniform temperature in the cavity core and thus to only minor deviations from two-dimensionality in the thermal field. A modest rise in Rayleigh number, in the 15° unstable case, does not affect the mean motion, but causes an increase in the normalised turbulence intensities.     

Theoretical model for annular flow condensation in rectangular micro-channels

This study examines the pressure drop and heat transfer characteristics of annular condensation in rectangular micro-channels with three-sided cooling walls. A theoretical control-volume-based model is proposed based on the assumptions of smooth interface between the annular liquid film and vapor core, and uniform film thickness around the channel’s circumference. Mass and momentum conservation are applied to control volumes encompassing the liquid film and the vapor core separately. The model accounts for interfacial suppression of turbulent eddies due to surface tension with the aid of a new eddy diffusivity model specifically tailored to shear-driven turbulent films. The model predictions are compared with experimental pressure drop and heat transfer data for annular condensation of FC-72 along 1 × 1 mm² parallel channels. The condensation is achieved by rejecting heat to a counterflow of water. The data span FC-72 mass velocities of 248–367 kg/m² s, saturation temperatures of 57.8–62.3 °C, qualities of 0.23–1.0, and water mass flow rates of 3–6 g/s. The data are also compared to predictions of previous separated flow mini/micro-channel and macro-channel correlations. While some of the previous correlations do provide good predictions of the average heat transfer coefficient, they fail to capture axial variation of the local heat transfer coefficient along the channel. The new model accurately captures the pressure drop and heat transfer coefficient data in both magnitude and trend, evidenced by mean absolute error values of 3.6% and 9.3%, respectively.     

Effects of heater size and working fluids on nucleate boiling heat transfer

The present study is an experimental investigation of nucleate boiling heat transfer mechanism in pool boiling from wire heaters immersed in saturated FC-72 coolant and water. The vapor volume flow rate departing from a wire during nucleate boiling was determined by measuring the volume of bubbles from the wire utilizing the consecutive-photo method. The effects of the wire size on heat transfer mechanism during a nucleate boiling were investigated, varying 25 μm, 75 μm, and 390 μm, by measuring vapor volume flow rate and the frequency of bubbles departing from a wire immersed in saturated FC-72. One wire diameter of 390 μm was selected and tested in saturated water to investigate the fluid effect on the nucleate boiling heat transfer mechanism. Results of the study showed that an increase in nucleate boiling heat transfer coefficients with reductions in wire diameter was related to the decreased latent heat contribution. The latent heat contribution of boiling heat transfer for the water test was found to be higher than that of FC-72. The frequency of departing bubbles was correlated as a function of bubble diameters.     

Condensation heat transfer of R-134a inside a microfin tube with different tube inclinations

Experimental heat transfer studies during condensation of pure R-134a vapor inside a single microfin tube have been carried out. The microfin tube has been provided with different tube inclination angles of the direction of fluid flow from horizontal, α. The data are acquired for seven different tube inclinations, α, in a range of −90 to +90° and three mass velocities of 54, 81, and 107 kg/m²-s for each inclination angle during condensation of R-134a vapor. The experimental results indicate that the tube inclination angle of, α, affects the condensation heat transfer coefficient in a significant manner. The highest heat transfer coefficient is attained at inclination angle of α = +30°. The effect of inclination angle, α, on heat transfer coefficient, h, is more prominent at low vapor quality and mass velocity. A correlation has also been developed to predict the condensing side heat transfer coefficient for different vapor qualities and mass velocities.     

On thermal control of devices contained in inclined hemispherical cavities with dome oriented downwards and subjected to transient natural convection

In this study, relationships of Nusselt–Rayleigh–Fourier type are proposed for the case of air-filled hemispherical cavity whose dome is oriented downwards and maintained isothermal. Its disk is subjected to a constant heat flux and inclined at an angle varying between 90° (vertical position) and 180° (disk horizontal with dome oriented downwards). The numerical approach is performed in transient regime by means of the finite volume method for Rayleigh numbers in the range of 10⁴ − 5 × 10⁸. These results are confirmed at steady state by measurements done for some configurations in a previous study for the same Rayleigh and inclination ranges. Otherwise, they complete other surveys considering inclination angles varying between 0° (horizontal cavity with dome oriented upwards) and 90° (vertical cavity) for a wider range of Rayleigh numbers. The correlations allow thermal control of devices submitted to natural convection in hemispherical cavities during the time preceding the steady state after their switch on.     

Heat transfer by free convection from the inside surface of the vertical and inclined elliptic tube

Free convection from the inside surface of vertical and inclined elliptic tubes of axis ratio (a:b) 2:1 with a uniformly heated surface (constant heat flux) is investigated experimentally. The effects of orientation angle (α) and inclination angle (ϕ) on the heat transfer coefficient were studied. The orientation angle (α) is varied from 0° (when the major axis is horizontal) to 90° (when the major axis is vertical) with steps of 15°. The inclination angle (ϕ) is measured from the horizontal and varied from 15° to 75° with steps of 15°. The vertical position is considered as a special case of the inclined case when ϕ = 90. The experiments covered a range of Rayleigh number, Ra from 2.6 × 10⁶ to 3.6 × 10⁷. The local and average Nusselt numbers are estimated for different orientation angles and inclination angles at different Rayleigh numbers. The results obtained showed that the local Nu increased with the increase of axial distance from the lower end of the elliptic tube until a maximum value near the upper end, and then, it gradually decreased. The average Nu increases with the increase of α or ϕ at the same Ra. The results obtained are correlated by dimensionless groups and with the available data of the inclined and vertical elliptic tubes.     

Single-phase and two-phase cooling with an array of rectangular jets

Experiments were performed to explore the effects of jet width, impingement velocity, and inlet subcooling on the cooling performance of an array of three confined rectangular FC-72 and ethanol jets impacting a 3.0 cm × 3.0 cm heated surface. The single-phase heat transfer coefficient increased with increasing jet velocity and/or jet width. A correlation for single-phase cooling was constructed by dividing the flow into impingement zones and confinement channel flow regions that are dominated by wall jet flow. Increases in jet velocity, jet width, and/or subcooling broadened the single-phase region preceding the commencement of boiling and enhanced critical heat flux (CHF). A new correlation was developed which fits the CHF data with good accuracy. Overall, better cooling performance was realized for a given flow rate by decreasing jet width. Pressure drop was for the most part quite modest, even for the smallest jet width and highest velocity tested. Overall, these results prove the present cooling scheme is highly effective at maintaining fairly isothermal surface conditions, with spatial variations of less than 1.2 and 2.6 °C for the single-phase and boiling regions, respectively. These results demonstrate the effectiveness of the present jet-impingement scheme for thermal management of next generation electronics devices and systems.     

Natural convection of water-based nanofluids in an inclined enclosure with a heat source

This study investigates natural convection heat transfer of water-based nanofluids in an inclined square enclosure where the left vertical side is heated with a constant heat flux, the right side is cooled, and the other sides are kept adiabatic. The governing equations are solved using polynomial differential quadrature (PDQ) method. Calculations were performed for inclination angles from 0° to 90°, solid volume fractions ranging from 0% to 20%, constant heat flux heaters of lengths 0.25, 0.50 and 1.0, and a Rayleigh number varying from 10⁴ to 10⁶. The ratio of the nanolayer thickness to the original particle radius is kept at a constant value of 0.1. The heat source is placed at the center of the left wall. Five types of nanoparticles are taken into consideration: Cu, Ag, CuO, Al₂O₃, and TiO₂. The results show that the average heat transfer rate increases significantly as particle volume fraction and Rayleigh number increase. The results also show that the length of the heater is also an important parameter affecting the flow and temperature fields. The average heat transfer decreases with an increase in the length of the heater. As the heater length is increased, the average heat transfer rate starts to decrease for a smaller inclination angle (it starts to decrease with inclination at 90° for ? = 0.25, 60° for ? = 0.50, 45° for ? = 1.0, respectively).     

Natural convective flow in an inclined lid-driven enclosure with a heated thin plate in the middle

Natural convection heat transfer from a heated thin plate located in the middle of a lid-driven inclined square enclosure has been analyzed numerically. Left and right of the cavity are adiabatic, the two horizontal walls have constant temperature lower than the plate’s temperature. The study is formulated in terms of the vorticity-stream function procedure and numerical solution was performed using a fully higher-order compact (FHOC) finite difference scheme on the 9-point 2D stencil. Air was chosen as a working fluid (Pr = 0.71). Two cases are considered depending on the position of heated thin plate (Case I, horizontal position; Case II, vertical position). Governing parameters, which are effective on flow field and temperature distribution, are Rayleigh number values (Ra) ranging from 10³ to 10⁵ and inclination angles γ (0° ? γ < 360°). The fluid flow, heat transfer and heat transport characteristics were illustrated by streamlines, isotherms and Nusselt number (Nu). It is found that fluid flow and temperature fields strongly depend on Rayleigh numbers and inclination angles. Further, for the vertical located position of thin plate heat transfer becomes more enhanced with lower γ at various Rayleigh numbers.