Effect Of Heat Transfer Characteristics Research Articles

Study on the Effect of Heat Transfer Characteristics of Energy Piles

The thermal performance of energy piles equipped with new metal fins to improve heat transmission is examined in this research. The solid heat transfer module of COMSOL Multiphysics was used to create a 2D numerical model of the energy pile, utilizing the energy pile at a field test site in Nanjing as an example. By contrasting the experimental data, the COMSOL Multiphysics model’s correctness was confirmed. After that, a new kind of energy pile fin was created to improve the heat transfer of the pile. The impact of the new fin type on the energy pile’s heat transfer efficiency was assessed, and the temperature change within the soil surrounding the pile before and after the fin was set was examined by contrasting the parameters of pipe configuration, buried pipe depth, and concrete thermal conductivity. The results indicate that after setting the fins to run for 336 h, the temperature of the concrete area increases by 10.8% to 12.3%, and the temperature of the region surrounding the pile increases by 5.3% to 8.7% when the tube diameter is chosen to be between 20 and 40 mm; The fins maximize the heat transfer temperature between the surrounding soil and the concrete, and as the tube diameter increases, the temperature drops. For 336 h of pile operation, the temperature of the concrete may be raised by 10.8% to 12.3% after the fins are set, and the temperature around the pile can be raised by 5.3% to 8.7%. The heat transmission efficiency of the energy pile can be improved by raising the temperature of the soil surrounding the pile through an increase in the concrete’s thermal conductivity; however, the degree of improvement diminishes as the conductivity rises. It is intended that this study will offer insightful information on the best way to design energy pile heat transfer efficiency.

Effects of Heat Transfer Characteristics of R32 and R1234yf with Al2O3 Nanoparticle through U-Bend Tube Evaporator

This study used the Ansys Fluent® computational fluid dynamics code in conjunction with a volume of fluid multiphase model and phase-change model to analyze the flow boiling evaporation heat transfer coefficient and flow patterns of R32 and R1234yf with Al2O3 nanoparticle through the U-bend tube with a curvature ratio for downward-oriented flow. The volume of fluid (VOF) model was used to follow the patterns at the interface, while the SST k-omega model was used to simulate the gas-liquid flow. This work has been validated by utilizing a R134a refrigerant. Simulations were performed at various mass fluxes, vapor qualities, and temperatures to determine the effects of these variables on heat transfer and frictional pressure decrease in the tube. R1234yf shows much better performance than the other pure refrigerants in terms of heat transfer and vaporization. The addition of nanoparticle Al2O3 with the refrigerants R32 and R1234yf significantly improved the heat transfer coefficient and increased the vapor fraction. The frictional pressure drop increases with increasing mass flux and decreases with increasing vapor quality due to a significant decrease in the liquid film thickness. The heat transfer coefficient, on the other hand, increases with increasing mass flux and decreases with vapor quality up to a point. There are certain changes in the heat transfer coefficient at the bend. After the bend, the frictional pressure drop increased at a higher rate than before the bend, and the vapor fraction increased at a higher rate.

The effect of heat transfer characteristics of macromolecule fouling on heat exchanger surface: A dynamic simulation study

AbstractAt the city gate gas pressure reduction stations (CGSs), to prevent natural gas from forming a hydrate in the throttle valve, the natural gas is heated by the heater before reaching the pressure relief valve. Heat exchangers are an essential component of industrial processes that contribute significantly to total system energy. Since the element impacting heat exchanger performance is the fouling process, all fouling processes and models were dynamically simulated in this study. Through coding in the C++ language and simultaneous use of fluent functions, or, in other words, user‐defined function (UDF), fouling‐related models were defined for this software. The dynamic simulation was performed, and parameters such as fouling strength and layer thickness were calculated. The effects of changing operating conditions, such as gas inlet velocity, surface temperature, and fouling species concentration on fouling growth, were also evaluated. As the concentration of fouling species increased, the fouling rate also increased. The amount of supersaturation and fouling rate increased as the surface temperature increased. Due to the operational limitations of the system, to reduce the fouling rate, the gas inlet velocity should be as high as possible, and the fluid inlet temperature, surface temperature, and concentration of fouling species should be as low as possible. In this study, the required time to reach the efficiency of 70% of the heat exchanger was calculated using the modelling of this chamber, which was equivalent to 190 days. Additionally, the critical thickness of the fouling layer at this time was 3.5 cm.

Experimental Investigation on Heat Transfer Characteristics of Liquid Nitrogen Spray Cooling for Large Area

Spray cooling has demonstrated advantages in the thermal control of avionic devices. In this study, a spray cooling system is established using liquid nitrogen (LN2) as a working fluid to investigate the effect of heat transfer characteristics on a large heating surface. The temperature response measurement and experimental analysis of the heating surface of a large-area shell structure under the boundary conditions of different heat flux and temperature regions were carried out. The temperature response curves for the outer surface of the shell structure from the initial temperature to the set temperature were obtained under different heat flows and temperature zones. The results show that the thermal response time of the surface spray phase cooling is less than 2 s, the stability time for the cooling temperature of the covering layer is longer than 60 s, and the cooling state can be maintained for 30 min under different working conditions. This study can provide a technical reference for the application of spray systems in the field of aircraft cooling.

Experimental research on heat transfer characteristics and temperature rise law of in situ thermal remediation of soil

With the advancement of industrialization, soil pollution has become a global environmental problem. In situ soil thermal remediation technology has attracted attention due to its wide application range, simultaneous removal of multiple pollutants and short time-consuming characteristics. In this study, using the principle of scale-down test, the law of temperature rise of the in situ thermal remediation of soil was experimentally studied; the heating construction period of the in situ soil remediation technology engineering application was predicted. The change law of temperature curve in different periods of soil heating is obtained. The results show that the soil temperature changes in three stages. Concentrated heating section: the temperature rises from the ambient temperature to the boiling point of water. Evaporation section: the water evaporates and the temperature maintains the boiling point temperature. Superheat section: the soil temperature continues to rise; the effect of heating power, water content and groundwater flow on heat transfer is studied. The results show that increasing the heating power, reducing the water content and preventing the seepage of surrounding water are all beneficial to the soil heating process. The research results provide favorable theoretical support for the laws of soil temperature rise, and the effect of heat transfer characteristics, simultaneously, provides a certain reference for actual soil remediation prediction, which is of great significance to the development of on-site soil thermal remediation technology.

Investigation In Electrical And Thermal Efficiency Of An Active Cooling Photovoltaic Thermal (Pv/T) Solar System With Taguchi Method

In this study, an attempt was made to optimize the default parameters in various experiments to improve the performance and heat transfer properties of the flat plate solar collector using the Taguchi method. An experimental investigation was carried out using air as working fluid at certain speeds (3.3, 3.9 & 4.5 m/s) on a PV/T collector. In this study, experiments were conducted to investigate the effects of heat transfer characteristics on performance, and the results are evaluated, since the above parameters have a great effect on the performance and heat transfer properties of the flat plate solar collector. Test Design for experiments were the Taguchi L36 Orthogonal Array Design. Experiments were carried out using the results of the outlet temperature of the air, the electrical and thermal efficiency of the collector, and the design of experiments by Taguchi method. The results showed that the selected parameters in this study had a significant effect on the selected responses and the verification results showed a significant improvement in the performance characteristics of the flat plate solar collector. The obtained results were analyzed in the ANSYS fluent program.

Effects of heat transfer characteristics between fluid channels and thermoelectric modules on optimal thermoelectric performance

Semiconductor thermoelectric generation technology has a promising application for waste heat recovery and is becoming a noticeable research field. This paper presents a mathematical thermoelectric generator (TEG) model applicable to engine exhaust gas heat recovery. This model considers the conduction along the heat exchanger and the contact thermal resistance of the exchanger plate between the fluid channel and the thermoelectric modules, which were neglected in a previous numerical analysis. Considering that there is an optimum module size corresponding to the maximum power output in a TEG system, the effects of heat transfer characteristics between the fluid channel and the thermoelectric modules on the optimal thermoelectric performance are investigated by using an engineering equation solver (EES) program. Numerical results show that there is a larger optimal area and a lower peak power when considering the conduction and contact thermal resistance factors mentioned above compared to traditional results, which are determined by considerably different factors such as internal heat transfer and temperature distributions. Moreover, an optimal thermal conductivity coefficient that corresponds to the peak power output exists when the conduction along the exchanger is considered. In the case when conduction along the exchanger is not considered, higher the thermal conductivity, the better is the thermoelectric performance. A thin-plate exchanger is recommended in the TEG system owing to its high power output. The optimal module area increases linearly, and the maximum power output exhibits an obvious decrease with an increase in the contact thermal resistance.

The effect of radiative heat transfer characteristics on vacuum directional solidification process of multicrystalline silicon in the vertical Bridgman system

In the vertical Bridgman system for multicrystalline silicon vacuum directional solidification process, the radiation heat transfer characteristics have a significant impact on the quality of crystal growth. In this paper, the effect of heat transfer characteristics under different pulling-down rates on the vacuum directional solidification process was investigated. Simplified radiation view factor dependent on pulling-down rate in pilot-scale vertical Bridgman system was derived. Combined with the transient simulation results, we obtained the heat transfer characteristics inside the furnace, and proposed the optimization scheme by using a rate of slowly first and then faster to pull down the crucible, which can not only satisfy thermal conditions of crystal growth, but also shorten the solidification time and effectively reduce the energy consumption. In addition, according to the characteristics of the radiative heat transfer under vacuum condition and the change of view factor, it was found that an improved design by widening the cold zone of the furnace can narrow the temperature gradient in the silicon ingot, and greatly decrease the thermal stresses, which in turn can aid in the design of future industrial equipment and process improvements.

The Effect of Heat Transfer on Unsteady Hydromagnetic Flow in a Parallel-Plate Channel of an Electrically Conducting, Viscous, Incompressible Fluid

An analytical study has been performed to examine the effect of heat transfer characteristics on the flow of a viscous, incompressible electrically conduction fluid in a parallel plate channel under the action of transverse magnetic field when (i) the two plates are kept at different but constant temperatures, (ii) the upper plate is given to move with constant velocity while the lower plate is adiabatic. The governing partial differential equations of this problem, subject to boundary conditions are solved analytically for fluid velocities, magnetic field and temperature distributions. The graphical representation for the velocity, the induced magnetic field, temperature distributions and the heat transfer are depicted graphically for different values of dimensionless parameters of the problem and the analysis of the results showed that the flow field is appreciably influenced by the applied magnetic field.

Optimum thermal performance of microchannel heat sink by adjusting channel width and height

A three-dimensional numerical model of the microchannel heat sink is presented to study the effects of heat transfer characteristics due to various channel heights and widths. Based on the theory of a fully developed flow, the pressure drop in the microchannel is derived under the requirement of the flow power for a single channel. The effects of two design variables representing the channel width and height on the thermal resistance are investigated. In addition, the constraint of the same flow cross section is carried out to find the optimum dimension. Finally, the minimum thermal resistance and optimal channel width with various flow powers and channel heights are obtained by using the simulated annealing method.

1819 地下水流が存在する系内の含水土壌の凍結挙動に関する数値解析

1819 地下水流が存在する系内の含水土壌の凍結挙動に関する数値解析

Transport phenomena in vertical reactors for metalorganic vapor phase epitaxy: I. Effects of heat transfer characteristics, reactor geometry, and operating conditions

Effects of operating conditions, reactor geometry, and heat transfer characteristics on flow patterns and growth rate uniformity in vertical, axisymmetric reactors for metalorganic vapor phase epitaxy (MOVPE) are described. Finite element solutions of two- and three-dimensional models of transport phenomena in vertical MOVPE reactors identify regions of inlet flow rates, susceptor rotations, and pressures where flow recirculations due to natural convection are minimized and good deposition rate uniformity is achieved. Particular attention is placed on understanding the influence of reactor geometry and heat transfer characteristics on flow fields and film thickness variations. The numerical computations demonstrate that modifications in the orientation of the reactor, the inlet size and its distance from the susceptor as well as the shape of the reactor enclosure can be used effectively to optimize reactor performance. Baffles can also be used advantageously to improve uniformity in existing reactor enclosures but at the expense of more complex flow patterns. The simulations underscore the importance of including accurate heat transfer treatments in MOVPE models by illustrating that different flow fields result from the commonly used thermal boundary conditions and a detailed heat transfer model. The model predictions are shown to be in good agreement with experimentally observed flow fields, wall temperatures and growth rates for GaAs. Nonlinear transport phenomena lead to the existence of multiple steady flows for the same operating parameters as well as the breaking of axisymmetry and development of fully three-dimensional flow patterns. An example of a non-axisymmetric flow field is given and the assumption of axisymmetry in models of vertical reactors is discussed.