Local Convective Heat Transfer Coefficient Research Articles

Target temperature-based simulation method for predicting performance and designing aircraft thermal anti-icing systems

The prevention of ice build-up on aircraft surfaces is crucial for safe operations. Thermal ice protection systems, particularly electro-thermal systems, are commonly employed to mitigate ice formation. However, the weight of electric batteries used in these systems significantly impacts aircraft performance, necessitating the minimization of power load during design. Despite this requirement, effective anti-icing operation mandates a sufficient heat flux to maintain surface temperature above the freezing point and evaporate any runback water film. Previous research has utilized numerical simulation analysis to predict the performance of electro-thermal anti-icing systems. The conjugate heat transfer method has been commonly employed to predict temperature distribution on the protected surface. However, non-isothermal surfaces exhibit distinct local convective heat transfer coefficients that influence local thermal balance, unlike isothermal surfaces that adopt the loosely-coupled method for computational efficiency. In this study, we present a novel target temperature-based anti-icing simulation method that predicts the required heat flux for thermal ice protection systems without employing the conjugate heat transfer method. Our objective was to calculate the necessary heat flux to achieve the desired non-isothermal surface temperature for effective anti-icing. By eliminating the excessive iteration process associated with the coupling method for conjugate heat transfer, we have streamlined the simulation procedure. Through validation, target temperature-based anti-icing simulation method, when compared to the tight coupling method, demonstrated the ability to predict the same surface water flow rates while reducing computation time by up to 90 %. Furthermore, when applied to design problems, our method achieved approximately a 10 % reduction in the required heat capacity for anti-icing compared to experimental values. As a result, target temperature-based anti-icing simulation method offers a more efficient alternative to traditional conjugate heat transfer methods, providing valuable insights for both predicting anti-icing system performance and optimizing aircraft design.

Convective heat transfer of falling film around the horizontal half-oval tube with reverse airflow in an evaporative condenser

Horizontal falling-film evaporation is frequently used in industrial air conditioning system to improve its thermal performance. Transient heat transfer characteristics on the surface of a circular tube have been investigated, while the non-circular tube such as half-oval tube has been rarely reported. This study aims to investigate the thermal performance of liquid film around a half-oval tube by adopting transient simulations with laminar and SST k-ω models, respectively. Simulations consider varying wind velocity, liquid Reynolds number, heat flux and length-width ratio of the tube. Simulated results are quantitively validated by comparing with reported experimental results, and the average differences are below 9.5 %. Results indicate that the local convective heat transfer coefficient (CHTC) increases with wind and the average CHTC is at least 5.98 % higher than the case without wind. Although the influences of liquid Reynolds number and heat flux show slight differences, they still can improve the convective heat transfer. The local CHTC exhibits an escalating trend with length-width ratio of 1–5. Meanwhile, the average CHTC for the four tested half-oval tubes is at least 6.8 % higher than the values of the circular tube. An empirical correlation for predicating the average CHTC is established by regression fitting with a mean deviation of 4.6 %. These findings help to design the falling-film evaporation system by adopting the half-oval tube in industrial air conditioning system.

Multi-tiered configurations improved flow boiling performance: Comparation investigation of leaf vein inspired two-tiered and three-tiered open microchannels

Microchannel heat sinks with expanding flow area along with the flow direction are able to suppress flow instability and reduce pressure drop during two-phase flow boiling by offering broadening volume for bubble elongation and growth that suppress the slug blockage and flow reversal. In this regard, microchannels with expanding area perpendicular to flow direction are supposed to obtain the comparable results, as the bubbles migrate to the downstream and top of microchannels simultaneously. However, the relevant study about multi-tiered microchannel heat sinks was limited and the corresponding flow boiling characteristics remained elusive. In this work, leaf vein inspired two-tiered open microchannel (LTWOMC) and three-tiered one (LTHOMC) were proposed and comparative flow boiling experiments were carried out. The outcomes indicated that LTWOMC obtained earlier ONB, which was 6.4 °C lower than LTHOMC at G = 220 kg/m2·s, the average local convective heat transfer coefficient (hcon) and average two-phase one (htp) of LTWOMC were maximumly enhanced up to 36.3% and 148.7% at G = 150 kg/m2·s, respectively. The pressure drop (ΔP) of LTWOMC was generally larger than LTHOMC at all mass fluxes, which led to the cooling coefficient of performances (COPs) of LTHOMC superior compared to LTWOMC under all working conditions. Moreover, LTHOMC exhibited better flow stability than LTWOMC with lower amplitudes and standard deviations of both wall temperature and pressure drop. In general, the three-tiered hierarchical configuration is more suitable than two-tiered one for flow boiling heat transfer.

Experimental investigation of the convective heat transfer coefficients at different angular orientations inside the void in a cold flow pebble bed reactor using a non-invasive heat transfer pebble probe

This study focuses on investigating the effect of the surface location of the pebble inside the bed, by varying the angular orientation of the heat transfer pebble probe and the velocity of the gas on the convective heat transfer coefficients in a cold-flow pebble bed reactor. An advanced non-invasive technique consisting of a cartridge heated copper pebble, a micro-foil sensor and a thermocouple probe was used to obtain accurate measurements of the local heat transfer coefficients from three surface locations inside the void. The effect of the wall on the local convective heat transfer coefficients was highlighted due to the low aspect ratio of the bed (bed diameter to pebble diameter (5cm)) used in this work. The local measurements showed, for the first time ever, that the surface location inside the void substantially impacts the heat transfer coefficients, with higher heat transfer coefficients at the center of the void and bottom of the void. Furthermore, the measured overall heat transfer coefficients showed good agreements with the predictions of the correlations of [52,21] and [14]. A second order polynomial model with an R2=0.9807 and an average absolute relative error (AARE) equal to 9.08%, was developed for the prediction of the local heat transfer coefficient within the design and operation conditions of this work. The accurate local heat transfer data collected in this work is valuable as benchmark data for the validation of computational fluid dynamics (CFD) simulations and heat transfer calculations.

Conjugate heat transfer of a turbulent tube flow of water and GaInSn with azimuthally inhomogeneous heat flux

An experimental study of the conjugate heat transfer in a turbulent tube flow with azimuthally homogeneous and inhomogeneous heat flux distribution, where the tube is heated with a constant heat flux only over the half circumference, is presented. Using two fluids with clearly different Prandtl numbers (water and a liquid metal alloy), thermohydraulic effects that occur when fluids with very low Prandtl number are used in contrast to ordinary fluids (e.g. water with Pr≈1) are discussed. The test section is validated with water (Pr=5−7.4) for a Reynolds number in the range of 5·103<Re<4.2·104. The experimental data agree excellently with literature data. The maximum nondimensional temperature at the inner surface of the tube is expressed using a simple relationship based on the efficiency of a fin with an adiabatic tip. A near eutectic alloy of gallium, indium and tin (GaInSn, Pr=0.03) is used for the liquid metal experiments. The Péclet number is varied within the range of 240<Pe<3·103. Based on the experimental data of this work, an adapted correlation for the Nusselt number in a turbulent liquid metal tube flow with azimuthally homogeneous heat flux is provided:Nu=4.364+0.0276·Pe0.803The experimental data underlines, that the azimuthally averaged Nusselt number for an azimuthally inhomogeneous heat flux distribution can also be calculated with this correlation with an acceptable level of accuracy. Remarkably, the ratio of the local convective heat transfer coefficient to the azimuthally averaged value for GaInSn reaches a value up to 0.6 at the location of the maximum wall temperature. This is in strong contrast to water, where this ratio is close to unity.

Methodology for determining convective heat transfer coefficients on the tubesheet surface of shell-and-tube heat exchangers under single-phase flow

Designing shell-and-tube heat exchangers requires reliable methods to calculate the convective heat transfer coefficient (CHTC) on the tubesheet, due to its impact on thermal stress. To address this, we established numerical models for both the tube and shell sides of the tubesheet. Using computational fluid dynamics (CFD), we systematically investigated the distribution of convective heat transfer on the tubesheet surface and its variations with structural and process parameters. The results showed that when fluid flowed into the tubesheet, the average convective heat transfer coefficient on the tube side of the tubesheet surface was 26% higher than when it flowed out. Additionally, the average convective heat transfer coefficient in the perforated region of the tubesheet was 1.39 to 2.57 times greater than in its periphery. Furthermore, the local CHTC on the shell side of the tubesheet surface gradually decreased along the downstream direction from the inlet of the shell-side fluid. Through simulations conducted across various structural and process parameters, we derived empirical formulas to rapidly calculate the average CHTC on the tubesheet surface. These formulas incorporated a tubesheet porosity factor for the tube side and introduced a new method for calculating the equivalent tubesheet diameter on the shell side. Random testing verified that our proposed formula reliably predicted the numerical simulation results.

Experimental Study of the Corrugation Profile Effect on the Local Heat Transfer Coefficient

This paper introduces an inverse study method applied to an experimental dataset of infrared temperature acquisitions to determine the local convective heat transfer coefficient of the turbulent flow inside a duct with corrugated surfaces. The study focuses on six tubes with different corrugation profiles: helical, transversal, and cross-helical. Previous research has shown that transversal corrugation generates the highest improvement in heat transfer performance, while helical corrugations are the easiest to manufacture. Consequently, the single helix solution is the preferred one in heat exchangers adopted in the food industry. A merger solution between them is represented by the cross-helix profile. The estimation process proposed in this study employs the external surface temperature of the tube, acquired with an infrared thermal camera, as starting data for the inverse heat conduction problem inside the pipe wall region. The calculation of its Laplacian was finally achieved by a filtering technique applied to the infrared temperature acquisitions.

Experimental investigation on heat transfer of nitrogen flowing in a circular tube

Average and local convective heat transfer coefficients of nitrogen are measured experimentally in an electrically heated circular tube for a range of Reynolds number from 1.08 × 104 to 3.60 × 104, and wall-to-bulk temperature ratio from 1.01 to 1.77. The exit Mach number is up to 0.17, and the heat flux is up to 46 kW·m−2. The molybdenum test section has a 62 diameters heated section with an inside diameter of 5 mm and a 30 diameters entrance section to ensure the fully-developed flow. Uncertainty of Nusselt number is less than 1.6 % in this study. The results indicate that the average heat transfer correlations evaluated by both the bulk and the modified film Reynolds numbers agree well with the experimental data. The local heat transfer results based on bulk properties are compared with previous empirical correlations. New prediction correlations are recommended which are significantly affected by the property variation and heated length. The comparison between the proposed correlations and experimental points shows that 88 % of experimental data fall into an error of 10 %, and almost all data are within an error of 20 %.

Micro segment analysis of supercritical methane thermal-hydraulic performance and pseudo-boiling in a PCHE straight channel

The printed circuit heat exchanger (PCHE) is receiving wide attention as a new kind of compact heat exchanger and is considered as a promising vaporizer in the LNG process. In this paper, a PCHE straight channel in the length of 500 mm is established, with a semicircular cross section in a diameter of 1.2 mm. Numerical simulation is employed to investigate the flow and heat transfer performance of supercritical methane in the channel. The pseudo-boiling theory is adopted and the liquid-like, two-phase-like, and vapor-like regimes are divided for supercritical methane to analyze the heat transfer and flow features. The results are presented in micro segment to show the local convective heat transfer coefficient and pressure drop. It shows that the convective heat transfer coefficient in segments along the channel has a significant peak feature near the pseudo-critical point and a heat transfer deterioration when the average fluid temperature in the segment is higher than the pseudo-critical point. The reason is explained with the generation of vapor-like film near the channel wall that the peak feature related to a nucleate-boiling-like state and heat transfer deterioration related to a film-boiling-like state. The effects of parameters, including mass flow rate, pressure, and wall heat flux on flow and heat transfer were analyzed. In calculating of the averaged heat transfer coefficient of the whole channel, the traditional method shows significant deviation and the micro segment weighted average method is adopted. The pressure drop can mainly be affected by the mass flux and pressure and little affected by the wall heat flux. The peak of the convective heat transfer coefficient can only form at high mass flux, low wall heat flux, and near critical pressure, in which condition the nucleate-boiling-like state is easier to appear. Moreover, heat transfer deterioration will always appear, since the supercritical flow will finally develop into a film-boiling-like state. So heat transfer deterioration should be taken seriously in the design and safe operation of vaporizer PCHE. The study of this work clarified the local heat transfer and flow feature of supercritical methane in microchannel and contributed to the deep understanding of supercritical methane flow of the vaporization process in PCHE.

A fractal blade for cooling liquids: Experiments and simulations

The performance of a fractal geometry blade for cooling hot water by natural convection and evaporation was studied numerically and experimentally. The blade design includes a tree-like fractal pattern and the Sierpinski carpet. The fin is made up of a solid hollow structure whose core is embedded with a porous material through which liquid flows. For the experiments, temperature measurements were taken in the porous medium by holding the fin in a fixed vertical position while warmed water was fed through its flow inlet. Numerical simulations were performed using a two iteration scheme that first involves the calculation of the local convective heat transfer coefficients and then the estimation of the heat dissipated by evaporation. The behavior of the fractal blade was compared with that of a benchmark heat sink that does not include the Sierpinski pattern in its construction. The experimental and numerical results agree well with each other and show a better performance of the reference heat sink when cooling water. Although the windows in the Sierpinski pattern improve convective cooling, this effect is marginal compared to evaporative cooling, which is enhanced by the larger surface area of wet porous medium exposed to the environment in the benchmark fin.

Flow and heat transfer in rotating smooth and ribbed multi-channel double-wall structure with multiple-jet impingement cooling

In this study, the heat transfer of multiple-jet impingement in rotating smooth and ribbed multichannel double-wall cooling structure with film extraction are investigated. The dimensionless jet-to-target spacing is 1, and the dimensionless jet-to-jet spacing is 3.55. In ribbed channel, the rib height is 1 mm and rib spacing is 8 mm. The experimental jet Reynolds number ranges from 2000 to 8000, and the maximum jet rotation number is 0.22. The test section contains five impingement channels. The local average convective heat transfer coefficient is measured by the “copper plate method”. The SST k-ω model is used to study the effect of rotation on the flow in channels. The results show that the heat transfer gap between high and low radius is more evident with an increase of the Roj. This is because the rotation effect increases and decreases the mass flow rate at high and low radius, respectively. Moreover, rotation can strengthen the impingement effect of the trailing side (TS) while weakening the effect of the leading side (LS) when the Roj is less than 0.06, Which causes differences in the heat transfer between the LS and TS of the impingement channel. Furthermore, affected by the ribs, the average heat transfer of ribbed target surface is improved. The area of high heat transfer region generated by impingement decreases, and an inverted butterfly-shaped high heat transfer region is generated near the film hole. Finally, the rib weakens the effect of rotation on the flow of target surface to some extent.

Case studies on local mixed convection heat transfer coefficients along a radiant heated wall subjected to displacement ventilation

Case studies on local mixed convection heat transfer coefficients along a radiant heated wall subjected to displacement ventilation

Pore-scale numerical simulation and LTNE analysis for fully-developed forced convective heat transfer in packed beds of mono-sized rough spheres covering near-wall and core regions

This work presents a novel method to acquire the effective convection heat transfer coefficients on the interfaces of wall-fluid contacts and sphere-fluid in both the near-wall region and core region of sphere-packed beds. Pore-scale numerical simulations are first conducted for different porosities pertaining to two regular body-centered cubic and face-centered cubic packings, packing lattice angles, inflow velocities, and ratios of the thermal conductivities of the solid and fluid. A finite-thickness metal reactor wall is included in the pore-scale simulation to make the heating boundary conditions more realistic. The outer surface of the metal wall is subjected to a uniform heat flux. The heat then passes through the metal wall and dispenses into the solid and liquid phases of the packed bed through the wall-sphere and the wall-fluid interfaces at the inner wall according to the physical mechanisms. Within the reactor, the heat transfer mechanism is separately considered in the near-wall region and the core region due to the intrinsic differences in the flow pattern. For each packing, different inflow angles are examined and exhibit different flow patterns and heat transfer performances. After the whole domain is hydrodynamically and thermally fully-developed, the local effective convection heat transfer coefficients can then be calculated. These coefficients reflect the realistic local convection either on the reactor wall or on the sphere-fluid interface. These convection heat transfer coefficients, along with the effective solid thermal conductivity through the contacting spheres obtained in our previous work, are implanted into a modified two-equation LTNE model. This modified LTNE model yields linear longitudinal fully-developed temperature distributions within the reactor having discrepancies in the temperature slopes less than ±10% from those by the pore-scale numerical simulations. In contrast, the conventional model even fails to reach linear distributions of the solid- and liquid-phase temperatures, which are expected for fully-developed packed-bed flows.

Experiment on liquid film flow and heat transfer of laminar liquid jet impacting on cylindrical surface

Laminar liquid jet impact has good heat transfer performance with low impact stress on targets. In order to explore the liquid film flow and heat transfer under laminar liquid jet impact on a cylindrical surface, first the flow of a liquid film was analyzed visually; then, the local convective heat transfer characteristics on the cylindrical surface at different impact heights and outlet Reynolds numbers (Re) were obtained by a combination of direct measurement and numerical simulation, followed by a comparative analysis with continuous droplets impacting on the cylindrical surface. The results show that according to flow behavior of the liquid film along the circumferential direction, circumference can be classified into stagnation, thin liquid film, hydraulic jump, stable flow path, and dripping regions. Local convective heat transfer coefficient first drops and subsequently increases marginally along the circumferential direction, while decreasing monotonically along the axial direction. The effect of impact height and outlet Re on local convective heat transfer coefficient is manifested mainly in stagnation, thin liquid film, and hydraulic jump regions. For outlet Re = 984, as impact height rises to a certain degree, there are apparent enhancements of the liquid film perturbation and convective heat transfer performance. Finally, the local Nusselt number correlations in different circumferential regions were proposed.

Experimental Measurement and Theoretical Prediction of Bubble Growth and Convection Heat Transfer Coefficient in Direct Contact Heat Transfer

The measurement of the two-phase contact area is very important to determine the heat transfer coefficient in the process of direct contact heat transfer, but the direct measurement of the two-phase contact area is a difficult problem. The experiments are carried out utilizing a cylindrical Perspex tube of 100 cm in total height and 15 cm inner diameter. The active column height throughout the experiments is taken to be equal to 50 cm. Liquid Therminol®66 with four different initial temperatures (50 °C, 60 °C, 70 °C and 80 °C) is used as a continuous phase, while liquid R245fa at a constant temperature of 23 °C is used as a dispersed phase. In this paper, the empirical correlations between bubble growth and local convection heat transfer coefficient are obtained through modeling and measurement, and its correctness is verified by experiments. The results show that the bubble diameter is positively correlated with continuous phase temperature, flow rate ratio, and height, but the local convection heat transfer coefficient is negatively correlated with continuous phase temperature, flow rate ratio, and height. At the same time, it is found that the maximum error between the actual bubble diameter and the theoretical bubble diameter is 7%, and the error between the heat flux calculated by the local convection heat transfer coefficient and the actual heat flux is within 10%. This study provides theoretical guidance for an in-depth understanding of the direct contact heat transfer process and the development of high-efficiency waste heat recovery systems.

Influence of the microfin tube structure on the thermal-hydraulic performance of mixed supercritical CO2/R32

This research establishes 5 mm 3-D flow and heat transfer microfin tube theoretical models with three different geometric structures. Using these models, the thermal-hydraulic performances of supercritical CO2/R32 in microfin tubes with different structures at various working conditions were investigated. The influences of each of three factors (pressure, mass-flow, and microfin tube structures) on the thermal-hydraulic performance of CO2/R32 were evaluated, respectively. Furthermore, orthogonal tests were undertaken to obtain the optimized combination of overall thermal-hydraulic performance. Results indicate that: the more the temperature of working media approximates to the critical temperature, the bigger the local convective heat transfer coefficient (CHTC). Compared to non-critical temperatures, the CHTC at critical temperature shows an eight-fold increase. The closer the pressure of the mixed working media is to the critical pressure, the greater the maximum CHTC and the lower the temperature corresponding to the peak point, among which, the maximum CHTC under 7.5 MPa is three times as large as that at 8.5 MPa. The CHTC increases with increasing mass velocity, generally showing a linear relationship. Through calculating the most optimal combination of thermal-hydraulic performance evaluation using orthogonal tests, the maximum CHTC is determined to be 96 kW/m2K.

Experimental estimation of the local heat transfer coefficient for thin liquid film evaporation in a capillary tube

• Local heat transfer coefficient was estimated for thin liquid film evaporation in a capillary tube. • Temperature infrared measurements were employed as input data of the inverse heat conduction problem. • A robust estimation procedure was adopted. • Procedure validation through the application to both synthetic and experimental data. • Original insight of thin liquid film evaporation was given. Two-phase heat transfer devices consisting of mini and microtubes represent a powerful solution to the continuous reduction of electronic components' dimensions and to the increase of the power to dissipate. Despite many studies on the two-phase heat transfer phenomenon in minitubes, most provided outcomes regarding the average heat transfer coefficient or Nusselt number. A technique to assess the local convective wall heat flux and heat transfer coefficient is proposed, validated, and then applied to the experimental case of thin-film evaporation in a heated capillary tube. The evaporation of the thin film of liquid plays a vital part in the two-phase heat transfer phenomenon inside mini/microtubes. Our study investigated this phenomenon by examining a semi-infinite slug flow. The estimation method used is represented by the inverse heat conduction problem solution in the tube wall, applying the Tikhonov regularisation method. The temperature distributions on the outer surface of the channel measured by an infrared camera were employed as input data for the inverse problem. The estimated heat transfer coefficient distributions confirm the available correlations in average values and provide insight into these complex phenomena in local and instantaneous quantities.

Local and overall convective heat transfer coefficients for human body with air ventilation clothing: Parametric study and correlations

Convective heat transfer coefficient associated with various human body parts plays an important role in the prediction of physiological responses with the help of human thermoregulation models. The primary goal of this work is to develop correlations for the convective heat transfer coefficients associated with various segments and whole torso of the human body in sleeve opening (SO), collar opening (CO), and both sleeve and collar opening (SCO) scenarios of air ventilation clothing. For this, a 3D CFD model of the air ventilation clothing is developed and validated with experimental data. Detailed parametric study is performed to analyze effect of openings in the air ventilation clothing, air flow rate, fan diameter and inlet (ambient) air temperature on the local and overall convective heat transfer coefficients. Results indicate that the area-weighted average convective heat transfer coefficient associated with whole torso is 36% and 5% higher in the case of CO and SCO, respectively, as compared to the SO case. The convective heat transfer coefficient is highest in the lower-back segment and lowest in the upper-chest segment of the body for SO and SCO scenarios. Whereas in CO scenario, the upper-chest segment has the highest and stomach segment has the lowest convective heat transfer coefficients. Effects of fan diameter and inlet air temperature are found to be least significant on the convective heat transfer coefficients as compared to the effect of opening and air flow rate. Further, correlations for segment-wise and whole torso convective heat transfer coefficients are proposed in the present work.

Cooling Characteristics of the Hot-Rolled Seamless Steel Tube Impinged via Inclined Jet

The characteristics of flow field distribution and temperature variation of an inclined jet impinging on a steel tube surface at different positions in circumferential directions were studied via numerical simulation. By analyzing the local convective heat transfer coefficient in circumferential direction, it was shown that the downstream and upstream regions had the characteristics of typical asymmetry. As the inclination angle increases, the local convective heat transfer coefficient gradually increases in the downstream region and gradually decreases in the upstream region. When the θ of the top and bottom jet is 30°, the increases in the downstream region are 40.2% and 54.6%, respectively. Based on the study of the local convective heat transfer coefficient and temperature distribution in the circumfluence direction of a steel tube during the cooling process, it was shown that the optimal inclination angle is 0~10°. With the increase in inclination angle, the average heat transfer coefficient shows a decreasing trend overall. With the increase in jet Reynolds number, the decrease in the average heat transfer coefficient gradually decreases. When the inclination angle increases to 30°, the effect of inclination angle on steel tube cooling is obviously stronger than that of jet position.

Thermally driven Marangoni effects on the spreading dynamics of droplets

The influence of the thermally-induced Marangoni stresses on the falling and spreading dynamics of a droplet surrounded by another liquid phase is numerically studied. A water droplet is released in a three-dimensional (3D) domain filled with oil. The droplet descends, comes at an apparent resting position above an oil film close to the bottom surface, and eventually wets the solid surface when the underneath film ruptures. A linear vertical temperature gradient is applied in the solution domain (with the bottom surface as the cold side) which imposes a surface tension gradient across the oil-water interface. The Marangoni source term is added to the momentum equation coupling the momentum and the energy equations. It is assumed that the dynamic contact angle changes according to the Kistler relation during the spreading. The Volume of Fluid (VOF) method is used to capture the interface between the phases. The solver is validated for both the falling and spreading phases. During the buoyancy-driven falling regime, the droplet retains its spherical shape at the low Reynolds number O(1) and finite Bond number O(0.001). It is revealed that the spreading rate of the droplet is a decreasing function of Marangoni number (Ma). Unlike the isothermal systems, where the bottom side of the droplet becomes slightly flattened at the resting stage, the Marangoni stress imposes an upward force on the droplet which elongates the shape of droplet in the temperature gradient direction. Consequently, the ultimate spreading radius at the equilibrium state is smaller at larger Ma. The slow rate of spreading and also the small wetted area at large temperature gradients adversely affect the heat transfer rate from the liquid to the cold plate where the local convective heat transfer coefficient and the average Nusselt number (Nu) are decreasing functions of the Marangoni stress.