Investigation Of Heat Transfer Characteristics Research Articles

Numerical Investigation of Heat Transfer Characteristics of Trapezoidal Fin Phase Change Thermal Energy Storage Unit

Abstract: In order to enhance the heat transfer performance of a phase change thermal energy storage unit, the effects of trapezoidal fins of different sizes and arrangement modes were studied by numerical simulation in the heat storage and release processes. The optimal enhancement solution was obtained by comparing the temperature distribution, instantaneous liquid-phase ratio, solid–liquid phase diagram and comprehensive heat storage and release performance of the thermal energy storage unit under different fin sizes. During the heat storage process, the results show that when the ratio of the length of the upper and lower base of the trapezoid h1/h2 is 1:9, the heat storage time is shortened by 9.03% and 18.21% compared with h1/h2 = 3:7 and 5:5, respectively. During the heat release process, the optimal heat transfer effect is achieved when h1/h2 = 5:5. To further improve the heat transfer effects, the energy storage unit is placed upside down; then, the least time is achieved when h1/h2 = 2:8. When heat storage and release are considered together, the energy storage unit with h1/h2 = 2:8 takes the shortest time to melt in upright placement and then to solidify in upside-down placement.

Development of a new criterion for predicting critical heat flux in rod bundles with supercritical water flowing upward

Investigations of heat transfer characteristics in channels with supercritical fluids are crucial for power cycle applications, such as supercritical water-cooled reactors. To ensure the safety of the system, heat transfer deterioration (HTD) should be avoided. The criteria to identify the onset of HTD in heated rod bundles are still not determined. This study summarizes indicators for the onset of HTD in a rod bundle with supercritical water flowing upward based on observations from experimental data. Existing criteria for the tube flow are assessed by comparing predicted critical heat flux (CHF) values with experimentally identified values. Considering effects of different operating parameters, a new criterion for predicting HTD behavior in rod bundles is developed. The results indicate that the new criterion has a better performance than all existing criteria, with a mean average relative deviation of 0.26 %. Predicted CHF values are within ± 20 % of the respective experimentally identified CHF values.

Interfacial heat transfer and melt-front evolution at a Fractal Cantor structured interface under various PCM melting conditions

With the aim to investigate heat transfer characteristics of PCM on micro-textured hot surface, this study numerically investigates the heat transfer process of PCM at fractal Cantor structured surfaces using the total enthalpy-based lattice Boltzmann method, which is partly validated by experimental testing. The thermal slip length and liquid velocity distribution are assessed as evaluation criteria. Results show that Fractal Cantor structure can significantly stimulate localized thermal convection, thereby reducing the average thermal slip length from 0.3 mm to approximately 0.14 mm. When the Fourier number exceeds 0.1, both thermal conduction and convection should be considered within the melted layer. With the fractal level increasing, a more uniform melt-front evolution can be observed, consequently, minimizing the total melting time by 500 s with the fractal level of 3. Elevating Ste and gravity can significantly increase the flow rate of liquid PCM by augmenting superheat degree and buoyancy effect, thereby enhancing convective heat transfer strength and reducing thermal slip length. According to the orthogonal design, though the fractal level demonstrates minimal range values for both maximum velocity and Rayleigh number, it elevates the sensitivity to the variation of boundary conditions. Ste yields the most significant enhancement in heat transfer performance.

Numerical investigation of heat transfer characteristics of supercritical CO2 and water flow in 2D self-affine rough fractures

In recent years, efforts to maximize natural energy utilization have focused on harnessing energy from hot dry rocks (HDR) using supercritical carbon dioxide (SCCO2) or water as the heat transfer fluid. This study aims to enhance comprehension and evaluate the heat extraction performance of enhanced geothermal systems (EGS) by exploring the influence of various inlet velocities and fracture widths on the flow and heat transfer of SCCO2 and water within a rough single fracture in granite. This study utilized a 2D self-affine fractal function to create a rough-fractured rock with fractal properties in a φ50 × 100 mm granite sample. Investigating under 8 MPa conditions, we employed the thermophysical properties of SCCO2 and water to analyze the flow and heat transfer characteristics within the rough rock fractures. The results indicate the following: (1) Higher inlet velocities and wider fracture widths result in a broader temperature reduction range within the surrounding rock matrix for both SCCO2 and water. (2) Increasing the inlet flow velocity of SCCO2 and water leads to wider fracture widths, resulting in lower temperatures at the outlet end of the fracture. As the inlet flow velocity increases from 0.01 m/s to 0.04 m/s, the rate of temperature increase at the outlet can reach up to 19.8 % compared to water. (3) SCCO2, unlike water, exhibits significant reverse vortices at locations where the fracture surface morphology experiences substantial fluctuations. This behavior may be an indirect consequence of SCCO2’s higher velocity, with the direct cause being SCCO2’s lower viscosity and density than water. (4) Among the four conventional fluid thermodynamic parameters, specific heat capacity has the most significant impact on total energy flux rate (TEFR).

Investigation of heat transfer characteristics of the self driving temperature-sensitive magnetic fluid through a nonmagnetic porous in a heating pipe

A temperature-sensitive magnetic fluid (TSMF) is a functional fluid that can be driven by both a magnetic field and a temperature difference. In this research, non-magnetic porous materials are inserted into a circular pipe to enhance heat transfer and increase the driving force. To evaluate heat transfer performance, measurements are conducted on flow rates and thermal resistance for different lengths and porosity of porous materials. A one-dimensional numerical simulation is employed to compare and predict the heat transfer performance under various porosity conditions also used in this study. As a result, when the porosity of the porous body is 80 % and the length is 10 mm, the flow rate is maximized. This is because the effect of increasing the driving force is stronger than the flow-blocking effect of the porous materials. The numerical results show the same trend as the experiment, and the decrease in flow rate is directly dependent on the length of the porous material.

Investigation of heat transfer characteristics in air-to-air heat exchanger with steady flow, oscillating flow and sound waves

A steady flow with a high flow rate, oscillating flow, and audible sound waves can enhance the heat transfer performance in air-to-air heat exchangers, while the comparison of influence mechanisms and degrees of different methods is ignored. This study investigates flow instability and heat transfer characteristics in an air-to-air heat exchanger under steady flow, oscillating flow and sound waves. The results show that steady flow and oscillating flow with different amplitudes have little effect on the distribution characteristics of velocity and vortices. However, the vortices disappear and generate periodically under 140 dB. Moreover, oscillating flow and sound waves exert distinct influences on flow instability. The cold side experiences the highest increase in turbulence kinetic energy when subjected to high-amplitude oscillating flow, while the greatest increase on the hot side occurs under high-amplitude sound waves, and the influence of steady flow on turbulence kinetic energy is relatively low. Additionally, the steady flow enhances the heat transfer performance by increasing flow rate, while the oscillating flow and sound waves promote the heat transfer between the fluid and surface. Under the effect of steady flow, oscillating flow, and sound waves, the values of heat flux are 1.22, 1.24, and 1.31 times that of the initial condition with the amplitude increasing to 0.683 m/s (140 dB). The results demonstrate that with the increase in amplitude acting on the inlet, the sound waves have the greatest impact on heat transfer performance, followed by oscillating flow, and the effect of steady flow is relatively slight. The research can provide guidelines for the development of heat transfer enhancement in air-to-air heat exchangers.

Experimental investigation of heat transfer characteristics in a miniature flat heat pipe with multi-channels

The heat transfer characteristics of a miniatured flat heat pipe (MFHP) with multi-channels, featuring a port diameter of 1.18 mm, is investigated experimentally. Various operating parameters are considered, including the working fluid volume (Vf = 1.5, 2.5, and 3.5 ml), length of the liquid reservoir (Lres = No reservoir, 5, and 10 mm), orientation such as axial face (αa) or lateral side (αl), inclination angles (α = −15 to 90o), and cooling water flow rates (ṁi = 10, 15, and 20 LPH). Based on the experiments, the optimal values for the working fluid volume, reservoir length, and flow rate are determined as Vf = 2.5 ml, Lres = 5 mm, and ṁi = 20 LPH, respectively. Further analysis reveals that, the heat dissipation rate for the axial face is significantly higher than that of the lateral side, with an average percentage increase of 35.4 %. However, the lateral side outperforms the axial face in terms of stabilizing the evaporator wall temperature, reducing fluctuations by an average of 24.5 %. Moreover, the presence of multi-channels allows the MFHP in axial face orientation to dissipate a maximum heat load of 15 W against gravity at an inclination angle of αa = −15o. Finally, the variations in MFHP operation based on the orientation and its underlying physical mechanisms that contribute to enhancing heat transfer are discussed.

Experimental investigation of heat transfer characteristics of inclined aluminium two phase closed thermosyphon

Abstract A reduction in the size of electronic equipment increases the heat generation rate. Failure of electronic equipment occurs if the heat is not dissipated properly. This paper examines the performance of aluminium two-phase closed thermosyphon for cooling electronic equipment. Acetone charged aluminium two-phase closed thermosyphon was fabricated with an inside diameter of 17.05 mm and 1 mm thickness. A series of experimentations were performed for inclination angles of 10°–90° at selected filling ratios of 30, 60 and 100 %, along with heat inputs of 100, 200 and 300 W. The condenser section flow rate of water was maintained constant. Minimum thermal resistance was obtained at a 30° inclination angle for all filling ratios and heat inputs. The evaporator and condenser sections have a maximum heat transfer coefficient at a 30° inclination angle. Thermosyphon, with a 30 % or 60 % filling ratio, performed better than a 100 % filling ratio for all inclination angles and heat inputs. As the heat input was increased, the heat transfer coefficients of the evaporator and condenser section were increased, whereas total thermal resistance decreased. For 300 W heat input and 30 % filling ratio, the minimum thermal resistance at a 30° inclination angle was 0.158 °C/W. It is found that, the same heat input and filling ratio, the maximum heat transfer coefficient value for the evaporator and condenser section at a 30° inclination angle was 1602 W/m2 °C and 5652 W/m2 °C, respectively.

Numerical and theoretical investigations of heat transfer characteristics in helium–xenon cooled microreactor core

Numerical and theoretical investigations of heat transfer characteristics in helium–xenon cooled microreactor core

Design and numerical investigation of heat transfer characteristics in annular cooking bowl using food graded heat transfer fluid for NCCS

The design of non-centrifugal cane sugar (NCCS) preparation methods is paramount for jaggery production. A numerical analysis is performed on an Annular Cooking Bowl (ACB) in which food graded heat transfer fluid (FHTF) is used as heat transfer fluid. The effect of mass flow rates (10 lpm, 15lpm and 20 lpm) and inlet temperatures (403 K, 413 K, 423 K and 433 K) are studied. Transient numerical simulations are conducted to predict the temperature of inner ACB surface and sugar cane juice, heat transferred from FHTF to bowl for various inlet conditions. In addition to, thermal efficiency of ACB and its effectiveness is estimated. The present approach shows that it can replace the traditional sugar cane juice boiling methods with NCCS unit, which eliminates bagasse as fuel and reduces the carbon emissions. From the results, highest ACB’s thermal efficiency is seen with FHTF inlet temperature of 433 K at low mass flow rate. However, ACB’s thermal efficiency decreases drastically with increasing in mass flow rate due to uncontrolled heat losses to surroundings. It is concluded that ACB’s thermal efficiency is observed as 21 % when FHTF is suppled 10 lpm and 433 K. It is seen that at temperature of 433 K and mass flow rate, 15 lpm and 20 lpm ACB’s thermal efficiency is registered as 17 %, and 13 % respectively. Results reveal that higher heat transfer rates are seen with food graded heat transfer fluid, and relatively high convective losses are observed, which further reduces the bowl thermal efficiency.

Investigation of heat transfer characteristics of deflected elliptical-tube heat exchanger in closed-circuit cooling towers

The core component in a closed-circuit cooling tower is the heat exchanger consisting of bundles of heat transfer tubes. To improve the heat transfer performance of closed-circuit cooling towers, this paper studies the elliptical-tube heat exchanger in closed-circuit cooling towers and proposes a deflected elliptical tube and its optimized tube. This study uses a combination of experiments and simulations to experimentally compare the heat transfer performance of elliptical tube heat exchangers in closed-circuit cooling towers under different operating conditions and simulation comparison and analysis of different wind speeds, spray water flow rate under the influence of the three elliptical tube flow field characteristics and heat transfer performance. The results show that in the wind speed of 2–3.2 m/s, due to the shortening of the tube bundle spacing, the growth rate of the heat transfer coefficient of the elliptical deflection optimized tube bundle is 16.27 %. The heat transfer performance of the deflected elliptical optimized tube is better than that of the elliptical tube and deflected elliptical tube, while the application of the optimized tubes shortens the overall unit structure by 24.03 %, which can reduce the material consumption of the closed cooling tower.

Natural convective Power law fluid flow in a crown cavity with heated cylinder: Application to energy transfer

The present study investigates heat transfer characteristics of power law fluid flow and energy transfer in a crown cavity with adjustment of the heated cylinder. The flow distribution is generated by the response of the heated cylinder. Additionally, the enclosure is partially adiabatic and the influence of cold interfaces is also taken. This whole setup generates a partial differential system in its mathematical translation. The numerical simulation is performed for the mathematical formulation by adopting the Galerkin Finite element method. The obtained results are analyzed against pertinent parameters of interest and presented via line graphs and contour maps for better explanation. The findings indicate that the K.E (energy motion) and Nu (Nusselt number) are higher for shear thinning While K.E energy motion) and Nu (Nusselt number) are higher is minimum for shear thickening.

A modified dynamic Lee model for two-phase closed thermosyphon (TPCT) simulation

A modified model consisting of a dynamic Lee model, volume of fluid model, and continuum surface force model is developed. The modified model investigates heat transfer characteristics of the vapor–liquid phase change process and details of the two-phase flow during operation of a two-phase closed thermosyphon. The mass transfer time relaxation parameters for the Lee phase change model are the most critical coefficients which determine the rate of the vapor–liquid phase change. A dynamic adjustment of the mass transfer time relaxation parameters for the Lee phase change model is realized based on the amount of mass transfer between the vapor and liquid phases and the values of the mass transfer time relaxation parameters become stabilized. The relative error between the modified model and experimental data for the temperature distribution is 5%, representing an acceptable agreement. Compared with the original model, the maximum thermal resistance errors in evaporation section and condensation section are reduced by 19.3% and 107.1%, respectively. These results indicate that the modified model can provide good corrections with high accuracy.

Investigation of heat transfer characteristics of Al2O3-water nanofluid in a coiled agitated vessel across varied operating conditions

Investigation of heat transfer characteristics of Al2O3-water nanofluid in a coiled agitated vessel across varied operating conditions

Mathematical Investigation of Heat Transfer Characteristics and Parameter Optimization of Integral Rolled Spiral Finned Tube Bundle Heat Exchangers

In this study, the effects of fin tip thickness and fin root thickness of integral rolled spiral finned tube bundles on flow resistance, heat transfer performance and heat transfer and flow exergy destruction were investigated via mathematical simulation. The correlations between heat transfer and flow resistance performance were fitted with dimensionless numbers. The optimized parameters with performance evaluation criteria (PEC) as the objective were obtained using methods involving computational fluid dynamics and machine learning. The results show the effects of fin tip thickness and fin root thickness on the Nusselt number (Nu), Euler number (Eu), PEC, heat transfer exergy destruction (ExT) and flow exergy destruction (ExP) as obtained via mathematical simulation. A new mathematical correlation is proposed for predicting the Nu and Eu of integral rolled spiral finned tube bundles. Among the four optimization models tested, the random forest regression algorithm was the most accurate algorithm for PEC prediction models. In the studied range, the optimal parameters were a fin tip thickness of 2 mm and a fin root thickness of 3.5 mm. Compared with the initial parameters, when the Reynolds number was 20,380, the PEC increased by 2.53%, the ExP increased by 2.37% and the ExT decreased by 7.96%.

Experimental investigation of heat transfer characteristics of magnetic nanofluids (MNFs) under a specially designed revolving magnetic field effect

This study investigated the heat transfer characteristics of magnetic nanofluids (MNFs) under external magnetic field effects. Magnetic nanofluids used in the experiments were synthesised with Fe3O4 (iron oxide) nanoparticles (at mass ratios of 0.5, 1, and 2 %) in deionised water. Then, the thermal conductivity and viscosity values that directly affect the heat transfer results were measured after a comprehensive study on the stability of magnetic nanofluids. A unique set of experiments was designed to determine the effects of magnetic fields on different magnetic nanofluids. This system, which creates a rotating magnetic field effect, can be used stationary and with the effect of revolution at a certain speed. Heat transfer experiment results were evaluated considering average Nusselt numbers obtained from 3500 to 15,000 Reynolds numbers. The magnetic field acting on the magnetic nanofluids in heat transfer experiments was investigated for three circumstances. It was determined that the increasing rates of average Nu numbers in magnetic nanofluids with mass ratios of 0.5, 1 and 2% under the influence of constant magnetic field effects were 25, 38, and 60%, respectively, compared to deionised water. Moreover, when the magnetic field effects were constant, the increasing rates of average Nu numbers obtained 15, 20, and 33% in nanofluids with mass ratios of 0.5, 1, and 2%, respectively, compared to the case without magnetic field effects.

Experimental investigation of heat transfer characteristics for a shell and tube heat exchanger

Abstract In the present work, numerical investigations are conducted with 22 % cut segmental baffle heat exchanger (SB), 20°, 30°, and 40° helical baffles shell and tube heat exchangers (STHX) to estimate the overall heat transfer coefficient (OHTC), pressure drop (PD) and friction factor. Among the studied heat exchangers (HE), 40° helical baffles STHX provided the highest OHTC with minimum pressure drop. Hence, further investigations are conducted experimentally with 40° helical baffles STHX. OHTC increased by 2.65 % for 20° helical baffles, 5.37 % for 30° helical baffles, 9.78 % for 40° helical baffles when compared with 22 % cut segmental baffle heat exchanger. The deviation between experimental and numerical OHTC is 2.64 % 40° helical baffles.

Experimental and numerical investigation of heat transfer characteristics in solar flat plate collector using nanofluids

Experimental and numerical investigation of heat transfer characteristics in solar flat plate collector using nanofluids

Experimental and numerical investigations of heat transfer characteristics of vertical falling film heat exchanger in data center cabinets

To reduce the energy consumption in data centers, this paper proposes a novel structure that integrates a cabinet with a vertical falling film heat exchanger in data center to perform natural evaporative cooling. First, an experimental setup is built to verify the heat and mass transfer characteristics of a falling film in a vertical tube and to obtain the mass transfer coefficient 0.05. Then, the characteristics of tube length direction and heat and mass transfer are analyzed using compiled user-defined functions for different parameters of moist air and water in the tube. The maximum growth rates of heat transfer coefficient and mass transfer rate are 67.65% and 55.23% at increasing inlet moist air Rema,i, respectively. Finally, the heat transfer characteristics of the falling film heat exchanger with staggered and in-line are compared for inlet air velocities in the range of 1–3.5 m·s−1. The corresponding results demonstrate that the heat flow rate, heat transfer coefficient, and overall heat transfer performance PEC of the staggered are better than those of the in-line as the inlet air velocity of the heat exchanger continues to increase. The maximum PEC of the staggered heat exchangers is 40.07% higher than that of the in-line heat exchangers.

Investigation of heat transfer characteristics of graphene nanoplatelets dispersed aluminium composite

The thermal stability and specific heat capacity of Graphene Nanoplatelets (GNPs) dispersed aluminium composites are determined using Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). Results of DSC analysis of the Al/2.0 wt-% GNPs composite show a 174% enhancement in specific heat capacity. Compared to pure aluminium, the Al/2.0 wt-% GNPs composite’s TGA results show a 2% mass reduction. Heat transfer characteristics like heat transfer coefficient, fin efficiency, and heat transfer through a fin were determined using a pin-fin heat transfer apparatus under free and forced convection. Compared to pure aluminium, graphene nanoplatelets reinforcement in an aluminium matrix improves the heat transfer characteristics of prepared composites under both free and forced convection.