Uniform Heat Flux Research Articles

Experimental study on heat transfer performance of high temperature heat pipe under axial non-uniform heat flux

Non-uniform high-temperature large heat flux is commonly encountered in engineering applications, posing challenges to heat transfer processes and affecting system performance. High temperature heat pipes offer an effective solution to mitigate the adverse effects of non-uniform heat flux by leveraging the unique characteristics of their inner alkali metal (or alloy) working fluid, such as high latent heat of vaporization, strong heat flux density, and ability to operate at elevated temperatures. These features enable high temperature heat pipes to achieve excellent isothermal and uniform heat transfer performance, thereby improving overall thermal management in heat transfer systems. Building upon the investigation of the original high temperature heat pipe, this study designed and fabricated a specially shaped high temperature heat pipe with a spherical crown surface as the evaporator. Experimental research was conducted to assess its frozen start-up performance and heat transfer characteristics under the influence of axial non-uniform heat flux. The results were also analyzed theoretically, providing valuable insights into the frozen start-up performance and heat transfer performance of the high temperature heat pipe in the presence of non-uniform heat flux conditions. The analysis results reveal several important findings: (1)The high temperature heat pipe demonstrates its capability to convert axial non-uniform high-temperature large heat flux into a uniform heat flux, thus achieving excellent uniform heat transfer performance. (2)The theoretical solution obtained through the lumped heat capacity analysis method shows satisfactory agreement with the actual frozen start-up process of the high temperature heat pipe. This theoretical reference can aid in the transient analysis of the frozen start-up process under the influence of axial non-uniform high-temperature large heat flux. (3)The experiment investigated the influence of heating power on heat transfer performance and temperature uniformity. The results indicate that the temperature uniformity of the high temperature heat pipe exhibits a trend of initially increasing and then decreasing. Specifically, the best temperature uniformity is achieved when the heating power is 1084.7 W. Moreover, when the heating power is 1197.9 W, the high temperature heat pipe exhibits the lowest equivalent thermal resistance of 0.0265 K/W, indicating the best heat transfer performance. (4) The variable power heating approach demonstrates that increasing the heating power leads to an extension of the effective length of the heat pipe. The most favorable heat transfer performance and temperature uniformity are observed when the heating power is set to 1133.7 W, allowing the full length of the condenser of the high temperature heat pipe to participate actively in the heat transfer process. These results can provide quantitative experimental data and theoretical references for improving the thermal shock of non-uniform high-temperature large heat flux.

The role of thermal effusivity on the incipient growth of the surface temperature in a semi-infinite region absorbing heat flux at the surface

Heat conduction theory stipulates that two thermo-physical properties of materials: the thermal conductivity “k” and the thermal diffusivity “ ” influence the temperature evolution in regular and irregular bodies as a response to various cooling/heating conditions. The traditional statement involving the two thermo-physical properties is examined at length in the present study for the case of a semi-infinite region. The primary objective of the present study is to investigate the influence of the less known thermo-physical property called the thermal effusivity “e” on the incipient surface temperature raise in a semi-infinite body affected by uniform surface heat flux. The secondary objective of the study is to identify a key figure-of-merit named the dimensionless threshold time that separates the incipient temperature elevation in a semi-infinite region from the incipient temperature elevation in a large wall of finite thickness under the same uniform surface heat flux. The outcome of the methodical analysis suggests that the accurate estimate for the dimensionless threshold time in the semi-infinite region should be 0.10.

Heat transfer enhancement using combined microchannel with vertical rectangular micro fins

This paper focuses on the numerical optimisation of a combined hybrid microchannel heat sink with rectangular solid fins. The axial length and volume are fixed, and external structure is allowed to vary. The simulation was performed on an elemental unit cell of the microchannel heat sink . The purpose of the optimisation is to discover an optimal geometric arrangement in internal and external configurations that minimises peak temperature in the microchannel heat sink. A high-density uniform heat flux of 250 W/cm2 is assumed to be dissipated on the bottom wall of the unit cell by microelectronics circuit boards devices. Computational fluid dynamic code was used to discretized the fluid domain and solve a set of governing equations. The influence of hydraulic diameter, external structural shape and fluid velocity on peak temperature and global thermal resistance, is discussed. Coolant or water of Reynolds number range 400 to 500 in a forced convection laminar flow is introduced through the inlet of the computational domain to remove the heat at the bottom of the rectangular block microchannel. The results show that when the fluid velocity is increased from 9.8 to 12.3 m/s across the axial length of the micro heat sink, more heat is removed from the bottom of the combined heat sink. The results revealed that the pump power increased by 37.1% in combined microchannels with fins and from by 27.2% in finless micro heat sink. The result of the study is validated with what is documented in open literature for a traditional micro heat sink with circular flow channel and the trends agree.

Experimental study on air impinging jet for effective cooling of multiple protruding heat sources

Air Impinging Jet is an effective cooling method for various applications, ensuring optimal performance and reliability of heat-generation systems. In the present work, a novel technique of cooling discrete protruding heat sources mounted in a rectangular channel by using a double air jet is introduced experimentally. A constant and uniform heat flux is produced from protruding heat source surfaces where the bottom and the upper channel walls are insulated. The effects of various parameters on the heat source cooling performance such as the Nusselt number for single and double air jets are obtained. Various parameters such as the air Reynolds number, aspect ratio, double jet position ratio, and jet inclination angle are investigated. The results show that those parameters effectively affect the average temperatures and the standard deviation of all protruding heat sources. It is indicated that the maximum value of the average Nu number occurs at the heat source just underneath the impinging air jet compared to other downstream heat sources. The highest average Nu is achieved at a position ratio of 3/7 and an inclination angle of 10o. The cooling system accomplishes an acceptable Nu and temperature uniform distribution for a position ratio of 4/7 compared to the other position ratios. The improved performance and longevity of heat sources are achieved by the innovative double-air jet method, which archives a consistent temperature distribution for all projecting heat sources.

Convective heat transfer across silicon rods under uniform wall heat flux in a laboratory-scale Siemens reactor

The effects of operating and geometric parameters on convective heat transfer (CHT) in Siemens reactor with a laboratory-scale are investigated. A dimensionless analysis of the CHT is performed considering the flow characteristics, rod diameter (d), rod length (L), number of rods, and the distance between adjacent silicon rods. A dimensionless parameter (Hou) is proposed to represent the number of rods and the distance between adjacent rods. Additionally, three dimensionless parameters that affect the CHT, namely, the Rayleigh number, d/L, and Hou, are obtained. The two-factor interaction effects of the dimensionless parameters on the CHT are analyzed, and their relationships are determined for calculating the CHT flux. Based on these relationships, the Nusselt number is calculated for 7- and 8-rod laboratory-scale Siemens reactors, and the relative errors between the predicted and calculated results are 1.4 and 3.2 %, respectively.

Fully developed opposing mixed convection of a Jeffery tri‐hybrid nanofluid between two parallel inclined plates subjected to wall‐slip condition

AbstractWe analyze the effect of wall slip on the fully developed reverse mixed convection of Jeffery nanofluids between two inclined parallel plates with uniform wall heat flux conditions. The theory of tri‐hybrid water‐based nanoparticles with unique shapes, namely, cylindrical (copper), spherical (titanium oxide), and platelet (aluminum oxide) for heat transfer enhancement is utilized since it has better heat performance applicable in a dynamic of fuels and coolant in automobiles as compared with regular Newtonian fluid and nanofluid. The equations describing the above transport phenomena are nondimensional through appropriate scale transformations. Analytical solutions for velocity, temperature, and pressure distributions are obtained. Four different flow regimes including no reversal, bottom reversal, top reversal, and on both walls reversal are found for different combinations of buoyancy and pressure. Particularly, we notice that the wall slip significantly affects flow reversal. Furthermore, we notice that Magyari 's conclusion that the results of the homogeneous nanofluid flow model can be recovered from the corresponding Newtonian fluid model has great limitations. Besides, the effect of several physical factors on velocity and temperature distributions and important physical quantities, including skin friction coefficient and Nusselt number, are analyzed and graphically discussed.

Endwall heat transfer in wedge channel with teardrop pin fins, circular fins and oblong pin fins

Abstract The turbine inlet air temperatures exhibit a significant degree of elevation, hence leading to potential adverse consequences such as the degradation of blade material integrity. Consequently, the necessity to cool the turbine blades has arisen, leading to the implementation of various cooling systems. This study aims to conduct a comparative analysis of three different types of pin fins, namely oblong, circular, and teardrop, in a wedge duct. The range of Reynolds number considered for the analysis is between 10,000 and 70,000, whereas the pin fins and endwalls are subjected to a uniform heat flux of 3280 W/m2. The findings suggest that the friction factor associated with teardrop pin fins is 28.4 % lesser than circular pin fins and when compared to oblong pin fins; it is reduced by 34.5 %. The findings suggest that the friction factor associated with teardrop pin fins is 14 % lower compared to oblong and circular pin fins. The TPF improves with Re, and it is 24.5 % higher than oblong pin fin geometry and 39.2 % higher than circular shaped pin fins.

Modeling and simulation of cryogenic propellant tank pressurization in normal gravity

The self-pressurization process of cryogenic propellant storage under a normal gravity condition often involves turbulent mixing in the liquid region and complex flow fields in the vapor region caused by heat leak into a cryogenic tank. Over time, the cryogenic tank pressurizes due to a temperature increase in the vapor phase and the heat and mass transfer across the liquid–vapor interface. A nodal simulation approach was employed to study the long term transients of tank self-pressurization. In this paper, mechanistic models and correlations were implemented to simulate the self-pressurization of Multipurpose Hydrogen Test Bed experiments with a commercial nodal code, namely, Systems Improved Numerical Differencing Analyzer with Fluid Integrator (SINDA/FLUINT). A lump number sensitivity study on the prediction of tank pressure and temperature was performed to determine the number of lumps appropriate for a 50% initial liquid fill level. Uniform heat flux boundary conditions were implemented on both phases during the tank self-pressurization with an estimated heat leak provided by NASA. Numerical simulation showed that the predicted pressure profiles of the 50% and 90% fill level cases agreed well with experimental data. In the liquid region, temperatures were primarily uniform and close to saturation due to turbulent natural convection mixing. Findings showed the current model overestimated the temperature profiles in the vapor region when assuming heat conduction transfer.

Numerical investigation of rocket engine cooling channel heat transfer for different LNG under trans-critical conditions

Hydrocarbon impurities in Liquified Natural Gas LNG may produce undesired phenomena such as pseudo boiling and two-phase flow. This can be an issue for rocket engine cooling channels. This study investigates the impacts of hydrocarbon impurities on LNG thermophysical and transport properties. It estimates the required relative roughness to improve the cooling capabilities with appropriate pressure drops for different LNG mixtures flowing in the rocket engine cooling channel. The Reynolds-averaged-Navier–Stokes equations are numerically solved for a straight cooling channel with a circular cross-section and uniform heat flux. LNG’s thermophysical and transport properties are calculated using the GERG equation of state and extended corresponding states, respectively. The turbulent models are validated numerically for supercritical LNG, vapor methane, and supercritical hydrogen. The results show that hydrocarbon compositions play a significant role in cricondenbar pressure. When the hydrocarbon impurities increase, the phase envelope develops, and cricondenbar pressure increases. The impacts of various relative wall roughness configurations on the cooling capabilities and pressure drops are sensitive under transcritical processes and hydrocarbon compositions. This study provides a systematic understanding of the relationships between cooling channel surface roughness, Nusselt Number, and LNG composition, offering designers the ability to optimize heat transfer in rocket engine cooling systems.

Experimental Analysis of Bubble Behavior and Critical Heat Flux During Pool Boiling on Vertical Circular Tubes

Abstract The heat transfer during pool boiling incorporates a higher rate of heat dissipation capability at low-temperature differences. This technique is widely used in the nuclear industry for thermal management. In this study, the effect of tube diameter and length on critical heat flux (CHat atmospheric conditions in saturated water during pool boiling) is analyzed. The tubes of SS 304 are kept in the vertical orientation. The diameter of the tubes ranges from 1.2 mm to 9 mm. The experiments are performed with tubes having lengths varying from 50 mm to 1000 mm. It has been noted that tubes of smaller diameter show a greater magnitude of critical heat flux (CHF) for the given length. Compared to other tubes, the magnitude of CHF for a 1.2 mm diameter is higher. For a given diameter, a longer tube is found to have lower CHF than the ones having lesser length. The variation in the CHF magnitude is negligible for tubes with a diameter of more than 2.5 mm beyond a length of 200 mm. The location of occurrence of CHF is near the bottom end of the vertical tube. The study illustrates the behavior of bubble nucleation for various tube dimensions and heat fluxes. The inception and detachment of bubbles for different tubes are analyzed. The pool boiling regime is categorized and studied basing the behavior of the incepted and departed bubble while maintaining uniform heat flux. A mathematical relation that empirically accounts for the effect of tube dimensions , i.e., length and diameter on pool boiling CHF is proposed. The experimental CHF data obtained during pool boiling are tabulated toward contributing to the CHF databank.

Bubble behaviour and critical heat flux investigations on electrodeposited metallic tubes during pool boiling

There is colossal research scope in achieving greater functionality and durability in microelectronic devices as conventional air cooling systems cannot handle these devices' cooling requirements which may be due to their low heat transfer performance. In such instances, phase change heat transfer mechanisms are appropriate for heat extraction since they utilise both sensible and latent heat. The ability to remove huge amount of heat at low wall superheats and the lack of moving parts make pool boiling appealing. This experimental study emphasises the analysis of bubble behaviour and critical heat flux (CHF) on electrodeposited tubes developed via in-house built set-up. Copper has been deposited over SS 304 tubes of a length of 100 mm and diameter of 2.5–4.5 mm. Their surface morphologies have been investigated using various characterization techniques such as SEM, EDS, AFM, and XRD. The surface roughness measurement confirms that electrodeposition increases the roughness of the tube. The contact angle analysis confirms that the coated surfaces are hydrophobic in nature. The CHF visualization is carried out under uniform heat flux conditions. It is observed that with an increase in diameter, the magnitude of CHF reduces irrespective of the coated and uncoated surface. The hydrophobic surface exhibits a lesser CHF magnitude than the uncoated surface. The reduction in CHF magnitude is within a range of 4.27%–8.93%. At lower heat flux magnitude, the bubble nucleation is rigorous in coated tubes, making it efficient for phase change heat transfer applications.

Inclusion of unsteady heat conduction in regular bodies subject to uniform surface heat flux in a heat transfer course

The present study is concerned with the analysis of unsteady heat conduction in regular bodies (large plane wall, long cylinder, and sphere) with constant initial temperature, prescribed surface heat flux and thermal properties of the solid that are invariant with temperature. Surprisingly, this important topic is absent in textbooks on heat transfer. The exact evaluation of the dimensionless surface temperatures varying with the dimensionless time in the regular bodies over the entire dimensionless time domain [Formula: see text] is carried out with a symbolic algebra code. Thereafter, regression analysis is applied to the data gathered for the dimensionless surface temperatures varying with the dimensionless time of the regular bodies inside the dimensionless “small time” time sub-domains [Formula: see text]. The dimensionless threshold time [Formula: see text] is a decisive parameter that establishes the borderline between the “small time” sub-domain [Formula: see text] and the “large time” sub-domain [Formula: see text] comprising the entire dimensionless time domain [Formula: see text]. Based on regression analysis, compact asymptotes are constructed for the dimensionless surface temperatures varying with the dimensionless time inside the dimensionless “small time” sub-domain [Formula: see text]. At the end, agreements with the dimensionless exact, analytical surface temperature distributions (the baseline solutions) valid for the dimensionless time sub-domain [Formula: see text]. are considered of excellent quality.

Experimental and Numerical Dynamic Investigation of a Swirling Jet: Application to Improve the Efficiency of Air Diffusion in an Occupied Zone

When reducing the energy prerequisites of buildings, the correct distribution of fresh air flows injected into the living rooms poses a problem. If the problem of mixing the injected air in the ambient air is not effectively solved, there will be a strong deterioration in air quality and comfort. In this research, a new design of swirling diffuser is investigated experimentally and numerically using large eddy simulations. The influence of fins is studied for the improvement of air diffusion and jet mixing with ambient air. The study was carried out for a fins angle of 30° with the jet's axis and 60° with the blowing orifice's plane with the condition of uniform heat flux of the air. The working fluid used is air. It has been validated that using fins leads to a greater spreading of the jet and good air mixing compared to those obtained from smooth tubes (circular nozzle). To enhance the accuracy of the turbulence models' predictions, three turbulence models are tested: the wall-adapting local eddy-viscosity turbulence model (LES/WALEVM), Smagorinski-Lilly (LES/S-LM) model and the kinetic-energy transport model (LES/K-ETM). It is worth highlighting that the LES/K-ETM model is well established in the prediction of swirling flows, which have been successfully compared with experimental results.

Refined Analysis of the Transient Temperature Effect during the Closing Process of a Cross-Sea Bridge

In order to study the transient temperature effect during the construction of a cross-sea bridge off the coast, based on the Hong Kong-Zhuhai-Macao Bridge-Pipe Bridge Crossing Cliff 13-1 Gas Field, a refined analysis was conducted and the prediction of transient temperature gradient and structural response was carried out under the conditions of strong solar radiation and atmospheric convection using the method of combining theoretical research and numerical simulation. Firstly, the partial differential equation of uniform heat flux density on the outer surface of the main girder under the action of solar radiation and atmospheric convection was established. The equation was realized by calculating the solar radiation intensity and the comprehensive heat transfer coefficient, as well as fitting the atmospheric temperature on the outer surface of the main girder, and the equivalent comprehensive temperature at any time on the main girder was obtained. Secondly, a numerical analysis model of the heat conduction of the main girder section was established, and the equivalent comprehensive temperature was input into the numerical model as the temperature field boundary to solve the transient temperature gradient of the section, and the result was verified in comparison with the measured data. Finally, the transient temperature gradient was applied to the girder, and the temperature effect of the main girder during the closing process was also calculated. Construction control measures were also discussed. The research results show that the predicted value of the transient temperature gradient is consistent with the measured value (the maximum deviation is less than 2 °C), and the predicted value is slightly larger than the measured value, which makes the structure safer. During the closing process, the temperature gradient of the main girder has obvious non-linear characteristics: the temperature gradient is relatively high within 0.4 m of the top surface of the roof while tending to zero outside 0.4 m. The best closing time for the main girder is from 21:00 in the evening of the closing day to 6:00 a.m. the next day. For the small angles at both ends of the closure segment during the best closing time, temporary adjustment jacks and temporary counterweights can be adopted to eliminate the small angles at both ends of the closure segment in order to facilitate the welding construction and meet the smoothness requirements of bridge alignment.

Numerical Assessment of Nanofluids in Corrugated Minichannels: Flow Phenomenon and Advanced Thermo-hydrodynamic Analysis

The current study addresses the influence of the amplitude of distinct corrugation patterns on heat transfer and the performance of nanofluids as a coolant. A novel combined approach has been presented here to optimize the heat transfer, incorporating both geometry modification and coolant optimization. The computational model evolved for single-phase, and turbulent flow conditions in three-dimensional corrugated minichannels (i.e. rectangular, sine-shaped, and V-shaped) with Reynolds number varying from 10,000 to 30,000. Considering a uniform heat flux of 10,000 W/m2, the investigation evaluates the thermal-hydraulic performance of single nanofluids (CuO/water, Al2O3/water, TiO2/water) and hybrid nanofluids (Al2O3CuO/water, Al2O3-TiO2/water), with volume fractions ranging from 1% to 3%. Various nanoparticle compositions exhibited a 25–30% increased heat transfer coefficient in the corrugated minichannel relative to the smooth one. An enhanced Nusselt number is evident due to the sophisticated corrugated arrangement dependent on the amplitude and patterns of the corrugations. The obtained energy ratio quantifies the effectiveness of a heat exchanger, whereas the Bejan number signifies the heat transfer being characterized by higher irreversibility, leading to a notable dissipation of energy. To account for the PEC (performance evaluation criterion) value above one, the corrugated geometries can outperform smooth channels. With an optimal thermal performance improvement of 22.19%, the 3% Al2O3CuO/water has been found to be the most effective nanofluid in the rectangular corrugated minichannel with the amplitude-to-wavelength ratio of 0.12.

Experimental and numerical investigation of a single-phase microchannel flow under axially non-uniform heat flux

The design of microchannel based heat sinks for advanced electronic component continues to receive research interest, especially with the ever-increasing density of advanced chips with concomitant increase in heat generation. One aspect of microchannel heat sink design objectives is the optimum employment of non-uniform heat dissipation through the channel length. Two dominant schools in the performance optimization of non-uniform heat sinks are: 1) entropy minimization and 2) thermal resistance minimization. These two approaches usually result in contradictory conclusions: one recommending the use of increasing heat flux, the other recommending a decreasing heat flux. The current study seeks to explain this discrepancy by experimentally and numerically studying the heat transfer mechanisms in a single microchannel tube under the effect of non-uniform heat flux. This study presents an experimental framework capable of generating a wide range of pre-specified heat flux profiles over a single microchannel, mimicking actual heat flux profiles observed in thermo-electronic devices. We employ three flux profiles: 1) hotspots located at different locations with uniform background heat flux, 2) linearly ascending heat flux, and 3) linearly descending heat flux. The results show good agreement between numerical simulations and experimental measurements and provide insights into the microchannel tube's fundamental heat transfer mechanisms. Based on these insights, the study provides design guidelines to enhance microchannel heat sink performance under non-uniform axial heat fluxes. Finally, the discrepancy between entropy and heat resistance minimization approaches is explained.

Heat transfer enhancement in laminar water flow through a square channel by streamwise ultrasound irradiation

This research focuses on the heat transfer of laminar water flow in a square channel under 28–120 kHz and 60–120 W ultrasonic waves, irradiated along the streamwise direction. The experiment was conducted at Reynolds numbers of 400–2000, and the uniform surface heat flux of the pipe was set as 3.1–12.9 kW/m2. In this study, ultrasound-induced streaming was investigated using a particle image velocimetry (PIV) technique, and cavitation bubbles were detected using a digital camera. From the results, the maximum heat transfer enhancement was 155% with 28 kHz and 120 W ultrasound at q = 12.9 kW/m2, Re = 400, and x/Dh = 2.58. The Nu ratio, which represents the capability of ultrasound-induced heat transfer enhancement, was also determined. A maximum Nu ratio of 2.017 was achieved with 28 kHz and 120 W ultrasound at q = 7.2 kW/m2 and Re = 400 or St = 28.16 × 104. With a relatively low Re, the poorest heat transfer was observed at St values ranging from 40 × 104 to 120 × 104. This study provides a predictive formula for the Nu ratio, with deviations ranging from 6.89 to 13.2%. Furthermore, the PIV analysis suggested that acoustic streaming of Eckart type appears under the ultrasound irradiation and its velocity enhancement effect becomes maximal under the conditions for the maximum Nu ratio. It is also confirmed that the ultrasound irradiation can enhance the nucleation of bubbles at the pipe wall; ultrasound-induced dynamics of these nucleated bubbles are expected to further disturb near-wall liquid motion and contribute to heat transfer enhancement.

Laser induced high temperature thermal-mechanical-oxygen coupling experimental system and method

In this paper, a thermal–mechanical–oxidation coupling experimental system based on laser heating is developed, containing two modes of Gaussian and flat-top lasers, which has a series of advantages such as high temperature range, rapid heating rate, and convenient observation. The system adopts active illumination and an optical filter to solve the problem where it is difficult for traditional digital-image correlation technology to image clearly under laser heating. A biaxial mechanical test machine is used to simulate the complex load by applying biaxial tension or compression loads on the material. Combined with the radiation temperature measurement and controllable flow field device, the thermal-mechanical-oxygen coupling experiment of high temperature resistant materials under aerobic environment can be carried out. The maximum uniform heat flux output density is 27.2 kW/cm2, and the maximum Gaussian heat flux output density is 105 kW/cm2. The thermal-mechanical-oxygen coupling experimental system and method are of great significance to the development of new high temperature resistant materials and thermal barrier coatings.

A novel design to optimize the optical performances of parabolic trough collector using Taguchi, ANOVA and grey relational analysis methods

Parabolic trough collectors (PTC) are the most widely used in the world's highest capacity solar power plants. This paper presents a novel design for a PTC that employs Monte Carlo Ray-Trace (MCRT) method to predict the solar flux distribution on the absorber tube surface. The optical modeling results are in good agreement with previous findings in the literature. Taguchi and ANOVA analysis methods are applied to simultaneously investigate multiple control parameters, and determine their contribution rates. Furthermore, the multi-objective optimization of optical efficiency and solar flux uniformity is achieved using the Grey Relational Analysis (GRA) method. The proposed design achieved an optical efficiency of 83.01% and a heat flux uniformity of 92.24%, demonstrating its effectiveness in balancing optical efficiency and heat flux uniformity. The innovative design can be insightful for future development in the concentrated solar energy field.

Numerical study of heat transfer, pressure drop and entropy production characteristics in inclined heat exchangers with uniform heat flux using mango bark/CO2 nanofluid

For sustainable low-carbon cities, using sustainable urban energy system solutions is imperative. CO2-based bionanofluid is one proposed energy system solution that is sustainable and environmentally friendly. This paper examines the thermal-hydraulic and entropy production properties of mango bark/CO2 nanofluid for industrial-inclined gas cooling applications. The influence of gravitational force (in terms of tube inclination angle), volume fraction, and Reynolds number on the heat transfer, pressure drop, and entropy production of CO2-based mango bark nanofluids in laminar flow through a circular aluminum tube are numerically studied. The bionanofluid flows through a tube with an inner radius of 2.25 mm, a length of 970.0 mm, and an initial temperature of 320.0 K. A constant heat flux of −10.0 W/m2 is applied to the flow at its walls. The laminar flow regime with Reynolds numbers of 100, 400, 700, and 1000 are subjected to flow inclinations of ±90°, ±60°, ±45°, ±30°, and 0° and bionanofluid volume fractions of 0.5%, 1.0%, and 2.0%. Results show that ±45° tube inclination angle offers the optimal heat transfer coefficient, maximum pressure drop, and minimum total entropy production rates for Re > 100; however, for Re = 100, these occur at the inclination angle of −30° and +60°. The pressure drop shows less sensitivity to the inclination angle; however, it offers peak values at the same inclination angles as the heat transfer coefficient for the respective Reynolds number values. The maximum thermal enhancements due to gravitational effect are 42%, 93.98%, 121.28%, and 150% for Reynolds numbers of 100, 400, 700, and 1000, respectively, while that due to nanofluid volume fraction are less than 16%.