Cooling Air Flow Rate Research Articles

Coupled effects of typical thermodynamic parameters on the flow and heat transfer in a high-pressure turbine outer ring with impingement-film composite cooling structure

The research focused on a high-pressure turbine outer ring with an impingement-film composite cooling structure. Two methods of experimental measurements and numerical calculations were employed to investigate the outer ring cooling performance under typical thermodynamic parameters, such as the blowing ratio (M), temperature ratio (τ), and Mach number (Ma). The study aimed to elucidate the coupling effects between different thermodynamic parameters. It is revealed that increasing M led to improved cooling performance as it increased the cooling air flow rate and film hole outlet momentum. However, increasing Ma resulted in a less effective coverage of cooling air film on the outer ring, resulting in reduced cooling performance. Elevating the τ lowered the temperature of cooling air and outer ring but decreased the efficiency of cooling air utilization, leading to poorer cooling performance. The influence of M on the outer ring cooling property was independent of the τ, but M affected the magnitude of the change in cooling characteristics at different τ. A lower M enhanced τ effect on the cooling performance, while a higher M had the opposite effect. Increasing τ effectively mitigated the Ma impact on the outer ring cooling performance, especially at lower τ. Ma altered τ influence trend on the cooling performance. When 0.2 ≤ Ma < 0.6, increasing τ led to a decrease in cooling performance, but the extent of this decline decreased. When 0.6 < Ma ≤ 0.8, increasing τ resulted in an increase in cooling performance, but the improvement rate was moderated. Elevating the Ma enhanced M effect on the outer ring cooling performance. Specifically, when Ma is 0.2, increasing M from 0.7 to 3.0 elevates the outer ring overall cooling effectiveness from 0.3 to 0.45, reflecting a change of approximately 50 %. Similarly, when Ma is 0.8, an increase in M from 0.7 to 3.0 raises the overall cooling effectiveness from 0.1 to 0.35, indicating a more significant change of around 250 %.

Brake Wear and Airborne Particle Mass Emissions from Passenger Car Brakes in Dynamometer Experiments Based on the Worldwide Harmonized Light-Duty Vehicle Test Procedure Brake Cycle

Brake wear particles, as the major component of non-exhaust particulate matter, are known to have different emissions, depending on the type of brake assembly and the specifications of the vehicle. In this study, brake wear and wear particle mass emissions were measured under realistic vehicle driving and full friction braking conditions using current commercial genuine brake assemblies. Although there were no significant differences in either PM10 or PM2.5 emissions between the different cooling air flow rates, brake wear decreased and ultrafine particle (PM0.12) emissions increased with the increase in the cooling air flow rate. Particle mass measurements were collected on filter media, allowing chemical composition analysis to identify the source of brake wear particle mass emissions. The iron concentration in the brake wear particles indicated that the main contribution was derived from disc wear. Using a systematic approach that measured brake wear and wear particle emissions, this study was able to characterize correlations with elemental compositions in brake friction materials, adding to our understanding of the mechanical phenomena of brake wear and wear particle emissions.

Performance Analysis for Battery Stability Improvement using Direct Air Cooling Mechanism for Electric Vehicles

Safety concerns about the battery are primary challenges for the maker of the electric vehicle (EV) system. At continuous work, maintaining the optimal temperature is a crucial scientific issue. It has restricted the widespread use of batteries. Hence, maintaining the optimal temperature for E-vehicles has been analyzed in this study. To achieve more energy density in charging, the discharging cycle and compact structure have been essential. In this study, a direct air-cooling system has been addressed to reduce the temperature of the battery pack, resulting in a significant improvement in system efficiency. The 1.44 kgwatt (kW) battery back has been constructed for the E-vehicle by Simulink diagram to analyze the system. In this study, two various scenarios have been made, such as with air cooling and without cooling, to validate the outcomes. Torque and speed characteristics have been analyzed for this study. Air-cooling-based batteries for e-vehicle simulation have delivered better outcomes, such as high power charging and discharging and a discharge depth of 92%. The differential battery pack temperature has been reduced by increasing the cooling air flow rate to 2 ms−1, 4 ms−1, and 6 ms−1. To attain an even delivery of coolant air flow, a design criterion has been suggested. The outcome of the study has been evaluated through numerical analysis.

Experimental study on the parallel-flow heat pipe heat exchanger for energy saving in air conditioning

Energy saving significantly and positively affects energy conservation and releases less carbon dioxide. This study aims to investigate the energy-saving characteristics of a novel parallel-flow heat pipe heat exchanger (PFHP-HE) in air conditioning. It merged the characteristics of high axial heat transfer performance of heat pipe with high external heat transfer performance of parallel-flow heat exchanger (PF-HE). The test rig for the PFHP-HE was built on the basis of the heat transfer wind tunnel in this work. The heat transfer performance of parallel-flow heat pipe heat exchanger charged with R600A as the working fluid was experimentally studied. The filling rate of the heat pipe was 26%, and its thermal behavior was analyzed. The evaporation section of the PFHP-HE was heated by heating belt. The experiment was conducted with heating power of 500W. The experiments were performed with cooling air flow rates ranging from 63.36 m3/h to 118.08 m3/h. The results indicate that when the airflow rate was 118.08m3/h, the minimum thermal resistance of the PFHP-HE was 0.06 K/W, and the heat transfer efficiency was up to 98% in the experiments. As the pulsation phenomenon was caused by its small diameter, the temperature distribution in condenser had stratified phenomenon in PFHP-HE. The PFHP-HE has excellent heat transfer performance and working stability. The PFHP-HE is a promising heat exchanger for energy-saving in air conditioning. Its superior heat transfer performance and working stability make it an attractive alternative to conventional heat pipe heat exchangers.

Through thickness changes to stiffness and thermal conductivity in thermal barrier coatings subjected to gradient exposure

Sintering-induced increases in the elastic modulus and thermal conductivity of thermally sprayed Thermal Barrier Coatings (TBCs) under constraint by a bond-coated substrate due to thermal gradient exposure have been measured. The results suggest the degree of sintering due to this constrained thermal exposure to be significantly lower when compared to free standing exposed specimens. Overall, a ∼30% increase in elastic modulus and ∼12% increase in thermal conductivity have been measured in a ∼ 450 µm thick TBC after 12 h of gradient exposure. Here, the top surface of the TBC was kept at 1250 °C, and the gradient was determined based on a constant backside cooling air flow rate. The elastic modulus, measured across the thickness of coating, reveals that in the region near the top surface, the elastic modulus increased by ∼ 50%. Contrastingly, no significant increase in elastic modulus was observed near the metal/coating interface. The dynamic evolution of thermal conductivity and sintering under gradient exposure and constraint was calculated using an analytical model which was then used to rationalize the experimental observations.

Wall heat loss effect on the emission characteristics of ammonia swirling flames in a model gas turbine combustor

Ammonia (NH3) combustion is regarded as one of the most promising solutions to realize zero CO2 emission. However, its low reactivity, low heat release result in a strong thermal effect (wall heat loss effect) which significantly affects flame macro structure and NOx emission characteristics. In this study, an air film cooling on the swirling combustion chamber was designed to investigate the wall heat loss effect on NOx emission. The flame structure and NO production were measured with the OH-/NO-PLIF techniques. The NOx emission was analyzed by the Gasmet DX4000 Fourier Transform Infrared (FTIR) gas analyzer. Large eddy simulation was also conducted with detailed chemistry to extend the understanding of the experimental findings. For the current combustion chamber, a larger convection heat loss was obtained when increasing the cooling air flow rate. NO emission shows a decreasing trend with heat loss which is mainly caused by the chemical reactions at near all region. This can be verified by the relatively farther NO profile from the combustor wall. By analyzing the LES results at near all region, the combustion efficiency is decreased due the lower temperature. As a result, NO production from HNO and NH pathway is suppressed due to the local OH decreasing in near-wall region. The larger unburned NH3 in the exhausted gas may also consumes NO by the NO reduction reactions. In comparison, N2O, around 300 times global warming potential than that of CO2, significantly increases as the heat loss increases. This is mainly because that the production of N2O from NO is promoted and N2O decomposition is suppressed within the thermal boundary. This study suggests that N2O might become a more serious emission component in NH3 fueled gas turbines. Furthermore, the heat loss effect on the NOx production should be fully considered when designing the gas turbine combustion chamber with strong wall cooling.

Effect of gas–liquid phase change of axial rotating heat pipe on fluid-thermal-solid behaviors of high-speed spindle

The thermal deformation control (TDC) of the high-speed spindle (HSS) is difficult to be realized because the nonlinear, non-steady, and varying influencing factors, and traditional cooling system cannot effectively dissipate the internal heat and realize TDC. It is expected to effectively export the internal heat of HSS with a reasonable design and manufacturing. To effectively realize HSS cooling and TDC, the effect of gas–liquid phase change of axially rotating heat pipe (ARHP) on fluid-thermal-solid behaviors of HSS is investigated. The ARHP, which is suitable for HSS cooling and TDC, is designed. Then an experimental platform is constructed to study the operation performance and heat dissipation performance (HDP) of the designed ARHP under different working conditions. The effects of the rotational speed, heat flux, and cooling air flow rate on HDP of ARHP are investigated. The designed ARHP is embedded into the original HSS (O-HSS) to dissipate the internal heat, and the silicone grease (SG) is used to fill the gap between the ARHP and shaft core of HSS, increasing the contact area and enhancing heat transfer. Then the fluid-thermal-solid coupling behavior of HSS is simulated and experimentally studied. To verify the effectiveness of the designed ARHP and the proposed heat dissipation scheme, the fluid-thermal-solid coupling behaviors of O-HSS, HSS with ARHP (ARHP-HSS), and HSS with ARHP and SG (ARHP-SG-HSS) are compared. The results show that the maximum temperatures of ARHP-SG-HSS and ARHP-HSS are reduced by 50% and 43.5% compared with that of O-HSS, respectively. Moreover, the maximum thermal balance time of O-HSS, ARHP-HSS, and ARHP-SG-HSS is 1450 s, 800 s, 500 s, respectively. The maximum thermal deformation (TD) ranges of O-HSS, ARHP-HSS, and ARHP-SG-HSS are [-35 μm, 25 μm], [-20 μm, 10 μm], and [-20 μm, 10 μm], respectively. The maximum TDs of ARHP-SG-HSS and ARHP-HSS are reduced by 76.5% and 58.8% compared with maximum TD of O-HSS, respectively.

Research on active modulation of gas turbine cooling air flow

Gas turbines are the core power equipment for efficient energy conversion and clean utilization. Their hot components operate in environments that largely exceed the heat resistance limit of materials, using cooling air to maintain operation, but the cooling air is often in excess at low engine loads. Therefore, this paper proposes the active modulation of turbine cooling air flow to improve their cycle efficiency by appropriately reducing the cooling air flow rate at low engine loads. Accordingly, a dynamic gas turbine model applicable for the active modulation of turbine cooling air flow is established, along with an analytical turbine vane cooling model considering air-film cooling and thermal barrier coating. For the first time, this paper distinguishes between the hot gas parameters on the pressure and suction surfaces of turbine blades. Additionally, a new concept of equivalent air-film coverage is proposed and optimized by genetic algorithms to make the model calculation results closer to actual temperature distribution. A cooling air active modulation system combining open-loop and closed-loop control is the first ever designed. Studies indicate that active coolant modulation can significantly improve gas turbine efficiency at partial loads. Finally, the possibility of active coolant modulation to suppress blade overheating and enhance blade’s service life under off-design conditions is analyzed.

Elman neural network-based temperature prediction and optimization for lithium-ion batteries

Reliable and precise temperature prediction is one of the most crucial challenges for improving battery performance and preventing thermal runaway. This paper uses a highly adaptive Elman neural network (Elman-NN) to construct a temperature prediction model for lithium-ion batteries in a metal foam aluminum thermal management system. Numerical modeling methods obtain experimental data sets for model training and testing. The input parameters of the neural network prediction model are ambient temperature, battery discharge rate, cooling air flow rate, and state of charge; the output parameters are the maximum, minimum, and average battery temperature. However, due to the limitations of the gradient descent algorithm, the training process of the Elman neural network tends to fall into local optimum solutions. To further improve the prediction accuracy, the Elman-NN structure was optimized using the PSO algorithm, and the model performance was tested and validated. Compared with the original Elman-NN, the hybrid PSO-Elman-NN has smaller MSE and MAE values, with a maximum reduction of 43% and 25%, respectively. For the three test conditions, the maximum predicted temperature difference does not exceed 1.5 K, and the temperature difference decreases further as the discharge time increases. Moreover, the hybrid model’s prediction accuracy is significantly improved, with the coefficients of determination ( R2) increasing by 1.736%, 0.706%, and 1.851%, respectively. The PSO-Elman-NN performed well in terms of compatibility and accuracy of the battery temperature prediction.

Results of conjugate modeling and analysis of the thermal state of a high-pressure turbine blade

Numerical modeling for the purpose of receiving the temperature field of cooled rotor blades and its improvement is an integral process of modern design of gas turbine engines since the issue of cooling at gas temperature at the combustion chamber outlet over 1800-2000 K is becoming one of the key ones. To ensure the specified parameters of turbine operation during its design, it is necessary to obtain reliable calculation data. The article presents an algorithm for forming a calculation model to determine the thermal state of the working blade of a high-temperature high-pressure gas turbine in the Ansys program. The process of preparation of geometric and grid models is described, the boundary conditions used to set up the project in Ansys CFX Pre are given. A method for determining the cooling efficiency factor using Ansys CFX Post is also presented. The distributions of the temperature field and the coefficient of cooling efficiency over the surfaces of the blade to be cooled are obtained. Integral values of the coefficient of cooling efficiency for the designed blade at various cooling air flow rates were compared with statistical data. On the basis of the comparison a conclusion was made that the working blade considered in the work corresponds to the modern level of cooling efficiency.

Decoupling strategy for react-air supply and cooling of open-cathode proton exchange membrane fuel cell stack considering real-time membrane resistance estimation

Open-cathode proton exchange membrane fuel cells are widely used in portable power and unmanned aircraft because of their portability and simple structure. To address the mismatch between gas supply and hydrothermal management resulting from the direct utilization of ambient air as both oxidant and coolant, this study proposes a decoupling strategy for the react-air supply and cooling based on a stack coupled with vapor chambers. Additionally, extended Kalman filter is utilized to estimate the change of proton exchange membrane internal resistance in real-time under varying operating conditions. Experiments show that the membrane internal resistance rises by 0.061 mΩ and stack voltage drops by 0.31V during the increase of react-air flow rate from 0.244 × 10−2 m3/s to 0.470 × 10−2 m3/s with a constant loading current of 30A operation before decoupling. Decoupling react-air supply from cooling effectively mitigates membrane dehydration, reducing internal resistance by 0.023 mΩ and improving performance by 5.41% at 35A compared to before decoupling. Furthermore, results indicate that increasing react-air and cooling-air flow rates under high loading currents can improve stack temperature uniformity and performance consistency but reduce system efficiency. The optimal react-air flow rate needs to balance stack heat dissipation and the increase in internal resistance caused by membrane dehydration.

Numerical investigation of gas-solid heat transfer process and parameter optimization in shaft kiln for high-purity magnesia

As the core equipment for the production of high-purity magnesia, the determination of suitable structure and operating parameters has a significant impact on its efficient production. In present work, a three-dimensional numerical model of the high-purity magnesia shaft kiln is established to study the influence of different operating and structural parameters on outlet clinker temperature and outlet exhaust air temperature. The novelty is adding a convective term to the solid-phase equation of the energy model, as well as embedding the heat transfer coefficient and a modified Ergun’s correlation, obtained by a homemade experimental setup. Production data verify the accuracy and reliability of the model. The results indicate that with all other parameters being constant, the most significant impact on the outlet temperature of clinker and exhaust air is cooling air flow rate, followed by sintering gas flow rate, height below the burners and height above the burners. Finally, a combination of parameters for the 50,000 tons shaft kiln is obtained through orthogonal experiment and optimization, which is 2622 m3/h for sintering gas flow rate, 2422 m3/h for cooling air flow rate, 7.07 m for the height above the burners, and 12.14 m for the height below the burners.

Influence of cooling of high temperature vane systems on efficiency gas turbine units regarding working substance specific heat capacity dependence on temperature

BACKGROUND: Gas turbine units (GTU) are widely used in power plants, shipbuilding, aerospace and other industry sectors. Main performance indicators of units are effective cycle efficiency and useful internal power. It is known that gas turbine power grows on 1525% for each 100C of turbine inlet temperature increases in range of 10001400 K, which makes it possible to save fuel significantly. Further growth of turbine inlet temperature demands more drastic increase of cooling air flow rate for the sake of cooling of the GTU flow channel, that leads to decrease of effective efficiency of a GTU. Consequently, the research of cooling and heat capacity properties influence needs to be done in order to improve gas turbine unit performance in the turbine inlet temperature range of 10001400 K.&#x0D; AIMS: Issues of influence of cooling of high temperature GTUs as well as issues of influence of working substance specific heat capacity dependence on temperature are studied in the article.&#x0D; METHODS: The study contains comparative analysis of four gas turbine units (GTU) such as: the 3,13 MW Teeda GTU (Iran), the 4,13 MW UEC Perm Engines GTU-4P (Russia), the 5,1 MW Siemens SGT-100 (Germany) and the 5,67 MW Solar Turbines TAURUS 60 (USA).&#x0D; RESULTS: As a result, dependencies of efficiency, specific effective work and GTU useful work coefficient on cooling were obtained. Working substance specific heat capacity dependence on temperature was considered in order to increase accuracy of calculations.&#x0D; CONCLUSIONS: The completed calculation study allows judging on perfection of the heat layout of GTU, the flow channel of GTU and making a comparison of them for the sake of further optimization of operational processes.

Flow behaviour in vented brake discs with straight and airfoil-shaped radial vanes

This paper presents experimentally obtained flow characteristics inside the vane passage of a vented brake disc and at the brake disc exit. The flow conditions of three different brake discs were compared: a basic design with straight vanes and two prototypes with different vane heights, shapes (airfoil shape) and numbers. The possible effect on brake disc cooling performance was studies. Hot-wire anemometry was applied to measure the pumping performance of different discs, and particle imaging velocimetry was used to map the velocity field. All three discs were tested on a brake disc dynamometer according to the SAE J2522 standard, and the maximum temperature was measured during the thermal capacity test. No prototype outperformed the original brake disc. Moreover, the brake disc with the increased vane thickness and reduced vane height (prototype C) performed significantly worse, whereas prototype B, designed with an increased vane height and increased number of vanes, performed similarly to the original brake disc. A comparison of the flow characteristics of the three discs indicated that the significant decrease in the cooling airflow rate deteriorated the cooling performance of prototype C the most. On the other hand, the improved pumping performance did not improve the cooling performance of prototype B. Only the comparison of the internal cooling air flow pattern of the original and prototype B brake discs revealed the reason. While the characteristic jet-wake flow structure formed within the vane passage of the original brake disc, the inter-vane channel flow within brake disc B was distributed much more uniformly in a circumferential direction, with significantly lower flow velocities near the pressure vane side. This reduced the convective heat transfer on the brake disc vanes, which number, as well as the heat transfer surface area increased without the desired cooling effect.

Ultrasonic Vibration Technology to Improve the Thermal Performance of CPU Water-Cooling Systems: Experimental Investigation

The rapid growth of the electronics industry and the increase in processor power levels requires new techniques to improve the heat transfer rate in their cooling systems. In this study, ultrasonic vibration technology was introduced as an active method to enhance the thermal performance of water-cooling systems. The effects of ultrasonic vibrations at power levels of 30, 60, and 120 watts for different cooling airflow rates were investigated experimentally. The results were validated with available empirical correlations to ensure the accuracy of the measurement systems. The findings indicated that the ultrasonic vibrations enhanced the heat transfer in the liquid-cooling heat exchangers. In addition, the thermal performance of the ultrasonic vibrations was improved by reducing the airflow rate and increasing the ultrasonic power. In addition to the feature of heat transfer improvement, ultrasonic waves are widely used for the cleaning of different types of heat exchangers. Regarding the anti-fouling and anti-accumulation effects of the ultrasonic vibrations, the introduced technology could provide a practical way for developing high-performance nanofluids-based computer cooling systems.

Energy and exergy analysis of a novel direct-expansion ice thermal storage system based on three-fluid heat exchanger module

Direct-expansion ice thermal storage (DX-ITS) system can overcome the mismatch between cold energy supply and demand, and also exhibit the characteristics of high energy efficiency, simple pipeline and minimal installation space. However, existing DX-ITS failed to achieve simultaneous high-efficiency heat transfer in the processes of charging and discharging, thereby limiting its widespread use. This study developed a novel DX-ITS system based on three-fluid heat exchanger modules employing micro heat pipe arrays to address the proceeding issue. Temperature distribution, pressure, charging and discharging power, energy efficiency ratio, exergy efficiency and ice packing factor during the charging and discharging processes at different compressor speeds, cooling-air temperature and flow rates were experimentally studied. Results demonstrated that maximum charging power, energy efficiency ratio, exergy efficiency, ice packing factor and discharging power of proposed system using a 4 HP compressor under experimental conditions reached 5.71 kW, 2.31, 11.12 %, 82.1 % and 4.99 kW, respectively. Moreover, cooling-air temperature had a more significant effect on system performance compared with cooling-air flow rate and compressor speed. The 11.7 %, 25.9 %, 24.3 %, and 20.6 % reductions in charging power, energy efficiency ratio, exergy efficiency, and ice packing factor were observed with an increase of cooling-air temperature from 18 °C to 35.5 °C.

A comprehensive study on energy and exergy analyses for an industrial-scale pyro-processing system in cement plant

The Pyro-processing system is the most important part of a cement plant, which is used to produce clinker. The energy and exergy evaluations for an industrial-scale Pyro-processing system (PS) were carried out in this study. The first and second law efficiencies of the PS were calculated to be 82.5% and 64%. The electrical energy and thermal energy consumption of the PS was calculated to be 0.0308 kWh/kg and 3,127.1 kJ/kg of clinker. Experimentally, the impacts of operating factors such as feed rate, cooling air flow rate, air temperature, and grate speed on the performance of the PS were also investigated. The effects of these parameters on the first and second law efficiencies of the PS were investigated. Finally, the electrical and thermal energy consumption of the PS compared with some domestic pyro-processing systems as well as the international best available technology (IBAT). According to the findings, the PS uses about 37% and 26.8% more electrical energy, as well as around 10% and 1.8% more thermal energy, to generate clinker than the IBAT system and the domestic best PS (DBPS).

Full-scale three-dimensional simulation of air-cooled proton exchange membrane fuel cell stack: Temperature spatial variation and comprehensive validation

This study presents one of the first full-scale stack three-dimensional (3D) simulations for proton exchange membrane (PEM) fuel cell to investigate temperature distribution, cell/stack performance, and impact of air cooling. The stack consists of 30 cells with the active area of 50 mm × 200 mm for each fuel cell. The manifold and all the basic components are included in the computational domain, while the flow field structure is treated as porous media in order to reduce the computational burden. The model predictions are validated against the experimentally measured voltage and detailed temperature distribution under different currents. It is found that significant differences in temperature are present between the fuel cells at the two sides and that in the middle, and the oxygen content becomes lower at a higher temperature site due to the local increased water vapor concentration. As a consequence, thermal behavior has a decisive effect on the distributions of temperature, reactant concentration, membrane hydration, current density, etc., inside this air-cooled stack. It is also found that increasing the cooling air flow rate not only decreases the stack temperature, but also reduces the temperature variation, which further benefit the uniform distributions of oxygen, water vapor, etc. in the stack.

Novel industrial gas filling station with an internal cooling system dedicated for speeding up cylinder charging process - Energy and exergy analysis

In the paper, a novel patented system which meets the demand to shorten gas cylinder charging times is described and investigated. It has been analytically proven that the charging time of a 50-L gas cylinder can be reduced to 15 min (twice as fast as in conventional systems) and keep its temperature within safe limits when the cylinders are cooled. The second advantage of the introduced novel system is the cold exergy recovery from the evaporation process of the liquefied gas. The recycled cold fully covers the demand for cooling power, making the system self-sufficient. A very useful and common method to evaluate the thermal performance of any recovery system is energy and exergy analyzes, which are also applied to the presented system. The paper provides numerical simulations based on linear thermodynamic analysis, supported by CFD simulations. To optimize the cold exergy recovery and cylinder cooling process, three different cooling intensities are compared: ΔT = 10, 20, 30 K. These are defined by the assumed growth of the gas temperature during the filling process. A smaller temperature increase means a higher cooling airflow rate, which results in a more intense cooling process. Analyses were carried out for three selected gases: argon, nitrogen, and oxygen, all compressed to the same final pressure of 30 MPa. In total, it gives nine different cases, which are analyzed and compared. Analysis brings a deeper insight into the system and provides indications for designing a real installation.

Improving Combined Flow and Thermal Network Accuracy for Radially Air-Cooled Generators by Considering the Nonlinear Resistance Characteristics of T-Junction Flow

This work aims to improve the combined flow and thermal network (CFTN) accuracy for radially air-cooled generators by investigating the possible error stemming from the flow part. The nonlinear resistance characteristics of the T-junction dividing flow are first time considered for such cooling arrangement, which is achieved by employing the Gardel equations and the blend equation as the governing equations. Compared with the CFD model results as the benchmark, the nonlinear CFTN predicts an accurate flow rate in the radially extended airducts, making only 9% root mean square (rms) error for all the airducts. On the contrary, the linear CFTN fails to obtain a reliable flow distribution, as the rms error is as large as 34%. As a result, the nonlinear CFTN improves the accuracy of the maximum winding temperature by 6.4% over the linear CFTN and gives a more reasonable temperature gradient in the axial direction. Furthermore, the relative difference between the linear and nonlinear CFTNs is found to be even larger in the following conditions: large cooling air flow rate, wide airgap, low slot fill factor, and large airduct number. The proposed nonlinear CFTN modeling approach is also validated against experimental measurements for a prototype. The modeled temperatures match well with the measurements at different axial positions. According to the aforementioned findings, the nonlinear CFTN modeling approach is considered to be a reliable thermal analysis tool for the radial air-cooling arrangement.