Energy and exergy analysis of a downstream single-row air washer at different droplet diameters for air cooling application

This study proposes a downstream single-row air washer for air cooling. The theoretical energy and exergy balance models were established at different droplet diameters and verified by the experimental data. Based on the abovementioned theoretical relationship, the single performance indicator of heat exchange efficiency (HEE) and exergy efficiency was quantitatively analyzed; a comprehensive analysis method of two indicators was proposed, combining HEE and exergy efficiency, and a numerical simulation was carried out. Results show that the smaller the droplet diameter and the larger the water–air ratio, the lower the dry-bulb temperature of the outlet air and the higher the HEE and exergy flux destruction. When the droplet diameter is less than 440 μm, the droplet diameter does not affect exergy efficiency and dry-bulb temperature. When the droplet diameter is larger than 440 μm, the droplet diameter is positively correlated with the air outlet dry-bulb temperature and exergy efficiency; in contrast, the water–gas ratio is negatively correlated with the air outlet dry-bulb temperature. An engineering case reveals that when the air outlet temperature is less than 34°C, the critical water–gas ratio can be set as 2.6 (mass ratio). At this time, the HEE is more than 90%, the exergy efficiency is more than 60%, and the critical value of droplet diameter is 440 μm. The research results provide an essential theoretical basis for the optimization of engineering design calculation.

Effect of Two-Stage Cooling on the Microstructure and Tribological Properties of Steel–Copper Bimetals

In this paper, the solid–liquid composite method is used to prepare the steel–copper bimetal sample through two-stage cooling process (forced air cooling and oil cooling). The relationship between the different microstructures and friction properties of the bimetal copper layer is clarified. The results show that: the friction and wear parameters are 250 N, the speed is 1500 r/min (3.86 m/s), the friction coefficient fluctuates in the range of 0.06–0.1, and the lowest point is 0.06 at 700 °C. The microstructure of the copper layer was α-Cu, δ, Cu3P, and Pb phases, and Pb was free between α-Cu dendrites. When the solidification temperature is 900 °C, the secondary dendrite of α-Cu develops. With the decrease temperature, the growth of primary and secondary dendrites gradually tends to balance at 700 °C. During the wear process, Pb forms a self-lubricating film uniformly distributed on the surface of α-Cu, and the Cu3P and δ phases are distributed in the wear mark to increase α-Cu wear resistance.

Influence of Cooling Scenarios on the Evolution of Microstructures in Nickel-Based Single Crystal Superalloys

The reprecipitation and evolution of γ’ precipitates during various cooling approaches from supersolvus temperature are studied experimentally and via phase field simulation in nickel-based single crystal superalloys. The focus of this paper is to explore the influence of cooling methods on the evolution of the morphology and the distribution of γ’ precipitates. It is demonstrated that small and uniform spherical shape γ’ particles formed with air cooling method. When the average cooling rate decreases, the particle number decreases while the average matrix and precipitate channel widths increase. The shape of γ’ precipitates which changed from spherical to cubic and irregular characteristics due to the elastic interaction and elements diffusion are observed with the decrease of the average cooling rate. The phase field simulation results are in good agreement with the experimental results in this paper. The research is a benefit for the study of the rejuvenation heat treatment in re-service nickel-based superalloys.

Air-Hardening Die-Forged Con-Rods—Achievable Mechanical Properties of Bainitic and Martensitic Concepts

Three air-hardening forging steels are presented, concerning their microstructure and their mechanical properties. The materials have been produced industrially and achieve either bainitic or martensitic microstructures by air-cooling directly from the forging heat. The bainitic steels are rather conservative steel concepts with an overall alloy concentration of approximately 3 wt.%, while the martensitic concept is alloyed with 4 wt.% manganese (and additional elements), and therefore belongs to the recently developed steel class of medium manganese steels. The presented materials achieve high strengths (YS: 720 MPa to 850 MPa, UTS: 1055 MPa to 1350 MPa), good elongations (Au: 4.0 MPa to 5.9 MPa, At: 12.3 MPa to 14.9 MPa), and impact toughnesses (up to 37 J) in the air-hardened condition. It is shown that air-hardened steels achieve properties close to standard Q + T steels, while being produced with a significantly reduced heat treatment.

Analysis of Influence of 1000MW Unit Boiler Side Wind, Side Wind and Solar Radiation on Direct Air Cooling System

In the operation of direct air-cooled units, there are many factors that affect the safety and economy of the unit. The “hot air recirculation” and “backfill” phenomena caused by lateral wind, the influence of high ambient wind on the heat transfer performance of the air cooling unit near the windshield wall, and the “hot air recirculation” phenomenon caused by the back wind of the furnace, these may affect the direct air cooling unit. Safe and economical operation. Through carrying out on-site test research, collecting the actual operating conditions of the unit operation, the organic combination of laboratory simulation data and actual data is provided to provide a strong basis for the development of corresponding technologies.

Entropy analysis in spray cooling for dosing water injection

Spraying water in air improves air-cooling capacity, which then relies on the evaporation of water. Even for small drop sizes, literature reports that the evaporation remains limited inside the spray and below saturation limits. In this article, we describe the evolution of thermodynamic quantities in a mixture of air and evaporating liquid water. A complete and coherent formulation is used to express enthalpy, entropy and chemical potential. At constant enthalpy, we show that the chemical equilibrium corresponds to an intermediate state in which droplet evaporation is not complete and entropy is maximum under certain conditions. Results are compared with some experimental values measured in a wind tunnel downstream of a spray. The calculated values are consistent with observations. Cooling efficiency is discussed for the various parameters, which are the amount of water, air temperature and ambient humidity. Then, the numerical approach is inverted in order to forecast the amount of water needed to reach a target cooling temperature. This numerical approach is used to set water flow depending on inlet flow conditions and cooling objectives.