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Materials and components for masonry
Published in Peter Domone, John Illston, Construction Materials, 2018
Taking the simplest geometry as an example it can be seen from Fig. 33.8 that the minimum cross-sectional area of the 5-slot unit resisting the load will be 80% on bed but 71% on edge and 25% on end. The ratios of the strengths in Table 33.5 follow approximately the ratios of the areas. Other factors such as the slenderness of the load-bearing sections and the effect of high local stresses at rectangular slot ends complicate the behaviour, and may explain the variations between different types. It can also be shown that porosity in the form of vertical perforations results in a smaller reduction in the strength of a material than does generally distributed porosity, and is the more efficient way of reducing the weight. This is illustrated in Fig. 33.9. More detailed information on clay brick properties is contained in BRE Digest 441 parts 1 and 2 (1999).
Numerical investigation of heat transfer augmentation and frictional loss characteristics in heat exchanger tube with the use of novel perforated rectangular cut twisted tape
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
Figure 5 depicts the temperature counters at the cross-section of pipe in case of PT, with STT and PRCTT at Re = 4000. It is perceived in the contours that in PT, large temperature gradients are presents, that is, temperature of fluid near the solid surface is higher and lower toward near the center. When STT is inserted in the tube, it disrupts the velocity and thermal boundary layer and augment the intensity of turbulence of the flow. Proper mixing of fluid occurs due to high intensity of turbulence in flow which leads to reduction in temperature near the tube wall and decrease in average temperature of cross-section. This reduction in temperature leads to higher rate of heat transfer. Further introduction of RCTT reduces the rate of heat transfer by very small amount. Due to rectangular cuts, turbulent mixing increases tries to intensify the rate of heat transfer but perforation in the tape give the passage for the flowing fluid to pass which reduces the turbulent effect up to certain limit which leads to reduce in rate of heat transfer by small amount. The main advantage of perforation is reduction in frictional losses due to extra passage for the flow.
Injection of discontinuities in concrete dams with cement-based grouts
Published in Journal of Structural Integrity and Maintenance, 2022
João Conde Silva, Carlos Serra
This type of perforations can be performed by rotary (core drilling) or percussion (hammer drilling) means. Drilling with rotary diamond drill bits should be accompanied by water injection which has the role of removing fine particles which, if not removed prior to injection, could block small cracks. Air-percussion drilling is faster and cheaper than rotary drilling and is preferable if core sample recovery is not required. This type of drilling can also be accompanied by water injection to clear and clean the cracks (ICOLD bulletin 107, 1997; Nordström et al., 2019).