Investigation Of Heat Transfer Characteristics Research Articles

Influence of carbon-based hybrid nanofluids (GnP + MWCNT/H2O) on the heat transfer and entropy generation analysis for electronic cooling applications: an experimental study

The present article examined the thermophysical characteristics of functionalized carbon-based hybrid nanomaterials dispersed in H2O and EG, and studied the optimal combination for cooling electronic chips in a heat sink. Nanomaterials selected were functionalized graphene nanoplatelets (f-GnP) and multiwalled carbon nanotubes (f-MWCNT) mixed in the ratio of 1:1. The carbon-based hybrid nanofluids have been produced by a 2-step technique with vol% ranging from 0.1% to 1%. The thermophysical properties of carbon-based hybrid nanofluids were examined with standard techniques for the temperatures of 20 °C–60 °C in steps of 10 °C. The improvement of ∼100% and 246% for H2O-based hybrid nanofluids in thermal conductivity and thermal diffusivity was detected, while it was ∼95% and 152% for EG-based hybrid nanofluids at 1 vol%. The H2O-based hybrid nanofluids were advantageous in the laminar region for the entire vol% from the predicted effectiveness. Furthermore, the best-performing H2O-based hybrid nanofluids were studied in a microchannel heat sink for electronic cooling applications where Nu enhances by ∼47% at 200 W heat input. No work had been reported so far on the investigation of heat transfer characteristics and the entropy generation rate of carbon-based hybrid nanofluids in a microchannel heat sink, which shows the potential in the novelty of the current study. The addition of 0.2 vol% hybrid nanomaterials could be optimum for enhancing the effectiveness of microchannel heat sinks by enhancing the heat transfer phenomenon, which was evident from the performance evaluation coefficient and thermal entropy generation rate.

Numerical Investigation of Heat Transfer Characteristics for Various CPU Designs

Abstract Due to the rise in demand of computers with high computing power, there is significant advancement in electronic components inside the CPU cabinet every 6 months. The life of these electronic components is greatly affected by their working temperatures. Therefore, it is necessary to maintain the temperature of these devices within acceptable limits. Forced air cooling inside the CPU cabinet is a widely used technique for this purpose. Heat sinks are another way of increasing the heat transfer rate. The present study analyses the effect of different probable improvement cases implemented in the basic CPU cabinet. These improvement cases include changing the position and number of fans, changing the type of heat sink, and changing the inlet cross section. By making use of commercially available CFD softwares like Ansys Fluent and Icepak, the cooling effect in the CPU cabinet is analysed.

Experimental and numerical investigation of heat transfer characteristics of radiator using Graphene Amine-based nano coolant

This work presents experimental and numerical investigations on enhancing the heat transfer performance of automobile radiators with nano-coolant flowing with different mass flow rate and at different inlet temperatures conditions. Thermal management is critical as it dictates a system's overall power output, performance, efficiency and energy utilisation. Radiators and Thermal management systems for batteries are vital in keeping automobiles operating under optimal conditions. Conventional coolants lack the ability to keep up with the increasing performance requirements of thermal management systems. Nanocoolants represent a cutting-edge advancement in heat transfer fluid, boosting conductivity without compromising essential fluid dynamics of the cooling solutions. Several investigators have worked on various nanocoolants, but less work is done on radiators. In view of this, experimental and numerical investigations were done on radiator heat transfer performance using Graphene Amine based nanocoolant with varied coolant temperatures (50 °C–80 °C) and flow rates (3 l/min to 9 l/min). Thermophysical properties of nanocoolants, such as density, thermal conductivity, viscosity, specific heat, and Prandtl number, were determined by experimental and mathematical modelling techniques and were comparable with an average deviation of 5 %. Compared to the base fluids of De-ionised water and ethylene glycol combinations, Graphene Amine based nanocoolant has exhibited advancements in heat transfer properties, showing elevated Nusselt numbers, heat transfer coefficients and heat transfer rates. The investigation into the thermal transfer properties of nanocoolants utilizing theoretical and real-world experiments shows consistency with an average deviation of 20 %. Maximum heat transfer enhancement of 154.3 % and maximum heat transfer coefficient of 3209.52 W/m2K was found for Graphene Amine at 80 °C with coolant flowing at 9 l/min, which is 83.1 % higher when compared to De-ionised Water.

Investigation of heat transfer characteristics and optimization design of platen superheaters in the furnace of a 350 MWe supercritical CFB boiler

With the scale-up of circulating fluidized bed (CFB) boilers, the size of the platen heating surface within the furnace increases. Deformation, crack, and tube explosion of the platen heating surface threaten the safe and stable operation of CFB boiler. Large wall temperature deviation and overtemperature of partial tubes of heating surfaces are two of main reasons resulting in above problems. To identify the causes of large wall temperature deviation and decrease them, the heat transfer characteristics and wall temperature distribution uniformity of platen superheaters in the furnace of a 350 MWe supercritical CFB boiler were studied by experimental tests, and the structure of the high temperature superheater was optimized by numerical simulation to improve the temperature distribution uniformity. The steam parameters and wall temperatures of the platen superheaters were measured at boiler loads of 50 % BMCR, 75 % BMCR, and 100 % BMCR. The heat transfer coefficient, heat flux, and wall temperature uniformity of the platen superheaters were analyzed. At 100 % BMCR boiler load, the average heat transfer coefficient and heat flux of the medium temperature superheater IIs were 165.5 W/(m2·°C) and 56 kW/m2, respectively; while those of the high temperature superheaters were 179.7 W/(m2·°C) and 53.2 kW/m2, respectively. The wall temperature distribution uniformity among six medium temperature superheater IIs or six high temperature superheaters was relative good, while the temperature distribution uniformity of a single platen superheater required improvement. An optimized structure of the high temperature superheater was obtained from eight structures by numerical simulation, achieving a steam temperature deviation of less than 8 °C at the boiler load of 100 % BMCR.

Experimental Investigation of Heat Transfer Characteristics of Copper Nanofluid Under Subcooled Flow Boiling Conditions

Experimental Investigation of Heat Transfer Characteristics of Copper Nanofluid Under Subcooled Flow Boiling Conditions

Experimental and numerical investigation of heat transfer characteristics on the whole turbine vane surface

Experimental and numerical investigation of heat transfer characteristics on the whole turbine vane surface

Numerical investigation of heat transfer characteristics of hydrogen flow in a randomly packed bed

In this study, two randomly packed beds with small tube-to-particle diameter (D/d) ratios of D/d = 4 (PB-4) and D/d = 5 (PB-5) are constructed using the discrete element method (DEM). The pore-scale heat transfer characteristics of hydrogen flow at low pore Reynolds numbers (Rep < 100) are investigated using a DEM-CFD simulation approach, with the temperature-dependent thermo-properties of hydrogen being considered. Distinct local channeling flow patterns are revealed by detailed analyses of the flow fields in PB-4 and PB-5. The overall friction factors for both beds are found to agree well with empirical correlations. Notably, a faster spatial temperature increase is exhibited by PB-5, with a larger D/d ratio, as evidenced by a shorter axial distance for fully-heated hydrogen flow compared to PB-4. For the pore-scale heat transfer in the packed beds, the radial temperature profiles are compared at various heights of the packed beds depending on the radial porosity oscillation, in which the wall effect should be especially considered in the near-wall region. Furthermore, the axial pore-scale Nusselt number (Nup,axial) exhibits an inverse fluctuation with the axial porosity oscillation. Finally, the global Nusselt numbers (Nu) in the packed beds are analyzed under different operating conditions, which are in good agreement with empirical correlations.

Experimental and numerical investigations of heat transfer characteristics of a piston cooling bore impinged by SAE 30 oil

The jet impingement technique is currently one of the most efficient cooling solutions for highly reinforced pistons of large two-stroke engines. To study the heat transfer characteristics of piston, experimental and numerical investigations with a piston cooling bore impinged by SAE 30 oil were carried out. To investigate the heat transfer coefficient distributions over the target bore, the wall temperatures of the cooling bore were measured by thermocouples, which will also be used in the numerical calculation. The jet Reynolds number (Re) ranges from 220 to 330, and the jet-to-plate spacing ratios (H/D) range from 10 to 30. Results show that jet-to-plate spacing ratios have a slight effect on the heat transfer coefficient for this low Reynolds numbers impingement which is quite different from high Reynolds numbers flow. There are both three peaks of the local heat transfer coefficient for Re = 330 and 280 along the x-axis direction. However, only two peaks occur when Re = 280. The heat transfer coefficient increases with the increase of Reynolds number when x/D &lt; 0.22 or x/D &gt; 1.77 while the variation is contrary when 0.22 &lt; x/D &lt; 1.77. The average heat transfer coefficient of the top surface region is far larger than other regions and decreases significantly in the upper chamfered region. While it is almost identical in the cylindrical region for different Reynolds numbers. This study provides the heat transfer characteristics of piston cooling with SAE30 oil and can be used for the piston optimization of large two-stroke engines with high cooling performance requirements.

Investigation of heat transfer characteristics in heat pipe heat exchanger for space application

Investigation of heat transfer characteristics in heat pipe heat exchanger for space application

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.

Experimental and numerical investigation of heat transfer characteristics on the whole turbine vane surface

Experimental and numerical investigation of heat transfer characteristics on the whole turbine vane surface

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.