Study on Conjugate Thermal Performance of a Steam-Cooled Ribbed Channel with Thick Metallic Walls

In this work, a conjugate heat transfer model was established to numerically investigate the conjugate thermal performance of a steam-cooled ribbed channel with thick metallic walls. By employing the software of ANSYS CFX, the flow field in the channel and the temperature field in the solid channel were calculated. The flow behavior, heat transfer performance and temperature gradient distributions of ribbed channels with wall thickness (δ) of 1–5 mm, rib height-to-hydraulic diameter (e/D) of 0.047–0.188, rib pitch-to-height ratio (P/e) of 5–15 and rib angle-of-attack (α) of 30°–90° were compared and analyzed. The optimum structure parameters of thick-wall ribbed channel with higher heat transfer performance and lower maximum temperature gradient were obtained. The results show that the SST k-ω turbulence model is more suitable for the conjugate heat transfer problem of steam in the thick-wall ribbed channels. The friction factor reduces gradually with the increase of Re, increases greatly with the increase of e/D and α, and first increases then decreases with the increase of P/e. The average Nusselt number increases up to 8.81 times, while the maximum temperature gradient decreases about 45.35% when Reynolds number varies from 10,000 to 70,000. The rib angle of about 45°–60°, e/D of 0.188, and P/e of 10 are suitable to obtain the optimum thermal performance of steam flow in the ribbed channel. The influence of δ on the flow and heat transfer characteristics is non-significant.

Effect of encased concrete on section temperature gradient of corrugated steel web box girder

Thirty-two temperature sensors, a solar radiation sensor, wind speed, and direction sensor were installed on the bridge for the field monitoring of structural temperature, solar radiation, and wind. The frequency was set at 60 min for 211 days. Empirical equations were used to predict the maximum vertical and lateral temperature gradients, and the daily maximum and minimum mean temperatures of the corrugated steel web box girder. The results showed that the temperature gradient of the corrugated steel web box girder was closely related to the temperature gradient of air. The vertical maximum temperature gradient occurred at 4 pm. The height of the box girder had a significant effect on the accuracy of the predicted vertical maximum temperature gradient. Compared with the section without encased concrete, the maximum temperature gradient of the encased concrete section was reduced by 10.48%. Encased concrete showed minimal effect on both the vertical and lateral temperature gradient of the top plate part, however, the effect on the vertical temperature gradient of the haunch reduced by 17.19%. The maximum temperature gradient of corrugated steel with a composite encased concrete section was 4.12°C, which was less than that of the section without encased concrete at 5.06°C. The encased concrete had a significant effect on the maximum temperature gradient of corrugated steel web with a 26.99% deviation.

3D Thermal Finite Element Analysis of the SLM 316L Parts with Microstructural Correlations

In this study, a multitrack and multilayer finite element model was developed to simulate the temperature field and molten pool contours during selective laser melting (SLM) of 316L stainless steel powder under different scanning strategies. The simulated temperature field and its evolution over time were compared with experimental measurement results. Furthermore, a correlation was established by the presented results between the predicted thermal behavior and the microstructure of SLM specimens. It was found that the maximum temperature of the molten pool rose slightly with the increase of scanning tracks, but when laser scanned multilayer, the maximum temperature rose first and then decreased. There are large columnar crystals in molten pools, growing in the direction of the maximum temperature gradient. The microstructure defects are more likely to occur at the bonding regions between adjacent layers and islands, where the heat and stress are concentrated. Moreover, the results also showed that the scanning strategy affects the microstructure and microhardness. Also, the SLM 316L parts under the S-shaped strategy had finer grains and a higher Vicker hardness than that formed under the island strategy.

Effects of Averaging the Heat Transfer Coefficient on Predicted Material Temperature and Its Gradient

The heat transfer coefficient (HTC) is often averaged spatially when designing heat exchangers. Since the HTC could vary appreciably about a heat transfer enhancement feature such as a pin fin or a rib, it is of interest to understand the effects of averaging the HTC on design. This computational study examines those effects via a unit problem—a flat plate of thickness H and length L, where L represents the distance between pin-fins or ribs. This flat plate is heated on one side, and cooled on the other. Variable HTC is imposed on the cooled side—a higher HTC (hH) over LH and a lower HTC (hL) over LL = L − LH. For this unit problem, the following parameters were studied: abrupt versus gradual transition between hH and hL, hH/hL, LH/L, and H/L. Results obtained show that if the averaged HTC is used, then the maximum temperature in the plate and the maximum temperature gradient in the plate can be severely underpredicted. The maximum temperature and the maximum temperature gradient can be underpredicted by as much as 36.3% and 542%, respectively, if the Biot number is less than 0.1 and as much as 13.0% and 570% if the Biot number is between 0.25 and 0.4. A reduced-order model was developed to estimate the underpredicted maximum temperature.

Analysis on the Loading Stress, Thermal Stress and Coupling Stress in PCC-AC Composite Pavement

PCC-AC composite pavement has the advantages of high carrying capability and excellent comfort. The maximum temperature gradient formula of PCC-AC composite pavement in Guangxi region is fitted. The loading stress, thermal stress and coupling stress in AC layer of with dowel bar can significantly reduced. All kinds of stresses are also decreased with the narrow dowel bar space. Therefore, the Shrinking joints of composite pavement with dowel bars can greatly reduce the probability of reflection crack initiation. As the thickness of AC layer, there is greater influence on thermal stress and coupling stress than on loading stress, The loading stress, thermal stress and coupling stress in PCC layer decreases with the thickness increasing of AC layer, their relationship is linear. The loading stress and coupling stress of PCC layer reduce significantly with increasing the PCC thickness. AC layer also plays a role in reducing the loading stress and coupling stress of PCC layer.

Freeze-thaw dynamics and the implications for stratification and brine geochemistry in meltwater ponds on the McMurdo Ice Shelf, Antarctica

A high resolution record of water column temperatures was measured in a coastal meltwater pond on the McMurdo Ice Shelf, Antarctica. The maximum temperature gradient measured through the water column was 35°C, with an annual temperature range of 52.1°C within the pond. For most of the year the pond shows reverse temperature stratification with the lowest temperatures measured at the surface of the pond, with the exception of brief periods of normal stratification over winter caused by regional warming events. During freezing, the freezing front propagated downwards from the pond surface, excluding major ions and releasing large amounts of latent heat, both of which had a dramatic effect on the thermal and compositional evolution of the pond. Thawing is dominated by changes in surface air temperatures and the differential absorption of solar radiation. A new conceptual model of the physical freeze-thaw process has been developed that explains the presence of an ‘ice plug’ during melting, which reduces wind-induced mixing, forms a physical barrier to chemical processes, and encourages thermal and chemical stratification. It may also explain the persistence of anoxic and hydrogen sulphide bearing basal brines in summer stratified ponds that are otherwise fully oxidized.

Further Results on Studies of Temperature-Gradient Metamorphism

A correlation between temperature gradient in snow–pack and material strength is found to exist in laboratory studies on temperature gradient metamorphism of snow. These results are in agreement with earlier field investigations and eliminate diurnal solar and temperature variations as reasons for the existence of the maximum temperature gradient in the zone of minimum strength. Also the laboratory studies have indicated that locally dense layers such as ice crusts tend to enhance weakness directly below the crust due to local alteration of the thermal regimen. Further studies are continuing to describe the thermodynamic process of temperature gradient metamorphism more exactly.

Further Results on Studies of Temperature-Gradient Metamorphism

A correlation between temperature gradient in snow–pack and material strength is found to exist in laboratory studies on temperature gradient metamorphism of snow. These results are in agreement with earlier field investigations and eliminate diurnal solar and temperature variations as reasons for the existence of the maximum temperature gradient in the zone of minimum strength. Also the laboratory studies have indicated that locally dense layers such as ice crusts tend to enhance weakness directly below the crust due to local alteration of the thermal regimen. Further studies are continuing to describe the thermodynamic process of temperature gradient metamorphism more exactly.

Modelling of Tgs Growth in Space

ABSTRACTTo maintain a constant growth rate in the absence of convection it is necessary to program down the temperature. Trial and error numerical computations were performed to find the first approximation for the required isothermal dissolution period, linear ramp; and polynomial temperature variation period. The linear ramp rate was limited by the specified maximum temperature gradient. The isothermal dissolution turned out to be unnecessary. The linear ramp had to be stopped before the polynomial period was begun to avoid overshooting the specified maximum growth rate. After a few hours the temperature profile approached steady state behavior.