In this paper cotton hollow yarns were obtained from the core spun yams which were produced on a little modified conventional experiment ring frame with water soluble staple PVA yam as the core. For comparison, yams w...In this paper cotton hollow yarns were obtained from the core spun yams which were produced on a little modified conventional experiment ring frame with water soluble staple PVA yam as the core. For comparison, yams with same linear densities, same twists of the sheath, different linear densities, different twist directions of the core were prepared. The results show that the tensile strengths of the hollow yarns decrease first, then increase and decrease again, at last the tensile strength trends to reach a steady state with the soluble PVA core extraction proceeding. And when the sheath linear densities of the core spun yams are constant, their twist and twist direction are same as that of the core it will be easier to remove the core of the yam with a higher core size. When the linear densities of the sheath and the core are all constant, the twists of them are same, it will be easier to remove the core of the yam with a different twist direction of core to the sheath.展开更多
The develop actuality and direction of FRP(fibre glass reinforced plastics) bolt in the world are analyzed The new type structure of FRP bolt was designed Trial data indicate that, all kinds of capability target o...The develop actuality and direction of FRP(fibre glass reinforced plastics) bolt in the world are analyzed The new type structure of FRP bolt was designed Trial data indicate that, all kinds of capability target of this FRP bolt all achieve and exceed the country standard, substitute present metal bolt,wood bolt and bamboo bolt and other side bolt, it can gain magnitude technology and economy benefit FRP bolt mechanization product line produce efficiency is high, its throughput a day are 750 base, this can meet demand of hit small mining company展开更多
The paper presents an experimental investigation on enhanced heat transfer and pressure loss characteristics by using single, double, triple, and quadruple twisted-tape inserts in a round tube having a uniform heat-fl...The paper presents an experimental investigation on enhanced heat transfer and pressure loss characteristics by using single, double, triple, and quadruple twisted-tape inserts in a round tube having a uniform heat-fluxed wall. The investigation has been conducted in the heat exchanger tube inserted with various twisted-tape numbers for co- and counter-twist arrangements for the turbulent air flow, Reynolds number （Re） from 5300 to 24000. The typical single twisted-tape inserts at two twist ratios, y/w = 4 and 5, are used as the base case, while the other multiple twisted-tape inserts are aty/w = 4 only. The experimental results of heat transfer and pressure drop in terms of Nusselt number （Nu） and friction factor 00, respectively, reveal that Nu increases with the increment of Re and of twisted-tape number. The values of Nu for the inserted tube are in a range of 1.15-2.12 times that for the plain tube while f is 1.9-4.1 times. The thermal enhancement factor of the inserted tube under similar pumping power is evaluated and found to be above unity except for the single and the double co-twisted tapes. The quadruple counter-twisted tape insert provides the maximum thermal performance.展开更多
Heat transfer enhancement is used in many applications including heat exchangers, air conditioning, and refrigeration systems; hence many researchers have conducted experimental and numerical researches on heat transf...Heat transfer enhancement is used in many applications including heat exchangers, air conditioning, and refrigeration systems; hence many researchers have conducted experimental and numerical researches on heat transfer enhancement and have developed various techniques and methods. As a passive heat transfer technique, twisted tapes are widely used in various industries for their cost savings, lower maintenance requirements and the fact that they are easily set up. This paper introduces the principle of heat transfer enhancement of twisted tapes and reviews some of the experimental works done by researchers on this technique in recent years. The variously modified twisted tape inserts are widely researched and used to enhance heat transfer efficiency for heat exchangers. Twisted tapes perform better in low Re conditions and in square tubes. However, they could also cause higher pressure drops. Twisted tapes have great potential and profound implications if they can be used in traditional heat exchangers. Besides this, some correlations between the Nusselt number and friction factors are presented in this paper.展开更多
Heat transfer,friction factor and thermal enhancement factor characteristics of a double pipe heat exchanger fitted with square-cut twisted tapes（STT） and plain twisted tapes（PTT） are investigated experimentally u...Heat transfer,friction factor and thermal enhancement factor characteristics of a double pipe heat exchanger fitted with square-cut twisted tapes（STT） and plain twisted tapes（PTT） are investigated experimentally using the water as working fluid.The tapes（STT and PTT） have three twist ratios（y=2.0,4.4 and 6.0） and the Reynolds number ranges from 2000 to 12000.The experimental results reveal that heat transfer rate,friction factor and thermal enhancement factor in the tube equipped with STT are significantly higher than those fitted with PTT. The additional disturbance and secondary flow in the vicinity of the tube wall generated by STT are higher compared to that induced by the PTT is referred as the reason for better performance.Over the range considered,the Nusselt number,friction factor and thermal enhancement factor in a tube with STT are respectively,1.03 to 1.14,1.05 to 1.25 and 1.02 to 1.06 times of those in tube with PTT.An empirical correlation is also formulated to match with experimental data of Nusselt number and friction factor for STT and PTT.展开更多
基金Supported by the Foundation of Tianjin Science and Technology Commission (No.043104711)
文摘In this paper cotton hollow yarns were obtained from the core spun yams which were produced on a little modified conventional experiment ring frame with water soluble staple PVA yam as the core. For comparison, yams with same linear densities, same twists of the sheath, different linear densities, different twist directions of the core were prepared. The results show that the tensile strengths of the hollow yarns decrease first, then increase and decrease again, at last the tensile strength trends to reach a steady state with the soluble PVA core extraction proceeding. And when the sheath linear densities of the core spun yams are constant, their twist and twist direction are same as that of the core it will be easier to remove the core of the yam with a higher core size. When the linear densities of the sheath and the core are all constant, the twists of them are same, it will be easier to remove the core of the yam with a different twist direction of core to the sheath.
文摘The develop actuality and direction of FRP(fibre glass reinforced plastics) bolt in the world are analyzed The new type structure of FRP bolt was designed Trial data indicate that, all kinds of capability target of this FRP bolt all achieve and exceed the country standard, substitute present metal bolt,wood bolt and bamboo bolt and other side bolt, it can gain magnitude technology and economy benefit FRP bolt mechanization product line produce efficiency is high, its throughput a day are 750 base, this can meet demand of hit small mining company
基金the Thailand Research Fund(TRF)(Grant No.Ph D/0143/2552)
文摘The paper presents an experimental investigation on enhanced heat transfer and pressure loss characteristics by using single, double, triple, and quadruple twisted-tape inserts in a round tube having a uniform heat-fluxed wall. The investigation has been conducted in the heat exchanger tube inserted with various twisted-tape numbers for co- and counter-twist arrangements for the turbulent air flow, Reynolds number （Re） from 5300 to 24000. The typical single twisted-tape inserts at two twist ratios, y/w = 4 and 5, are used as the base case, while the other multiple twisted-tape inserts are aty/w = 4 only. The experimental results of heat transfer and pressure drop in terms of Nusselt number （Nu） and friction factor 00, respectively, reveal that Nu increases with the increment of Re and of twisted-tape number. The values of Nu for the inserted tube are in a range of 1.15-2.12 times that for the plain tube while f is 1.9-4.1 times. The thermal enhancement factor of the inserted tube under similar pumping power is evaluated and found to be above unity except for the single and the double co-twisted tapes. The quadruple counter-twisted tape insert provides the maximum thermal performance.
文摘Heat transfer enhancement is used in many applications including heat exchangers, air conditioning, and refrigeration systems; hence many researchers have conducted experimental and numerical researches on heat transfer enhancement and have developed various techniques and methods. As a passive heat transfer technique, twisted tapes are widely used in various industries for their cost savings, lower maintenance requirements and the fact that they are easily set up. This paper introduces the principle of heat transfer enhancement of twisted tapes and reviews some of the experimental works done by researchers on this technique in recent years. The variously modified twisted tape inserts are widely researched and used to enhance heat transfer efficiency for heat exchangers. Twisted tapes perform better in low Re conditions and in square tubes. However, they could also cause higher pressure drops. Twisted tapes have great potential and profound implications if they can be used in traditional heat exchangers. Besides this, some correlations between the Nusselt number and friction factors are presented in this paper.
文摘Heat transfer,friction factor and thermal enhancement factor characteristics of a double pipe heat exchanger fitted with square-cut twisted tapes（STT） and plain twisted tapes（PTT） are investigated experimentally using the water as working fluid.The tapes（STT and PTT） have three twist ratios（y=2.0,4.4 and 6.0） and the Reynolds number ranges from 2000 to 12000.The experimental results reveal that heat transfer rate,friction factor and thermal enhancement factor in the tube equipped with STT are significantly higher than those fitted with PTT. The additional disturbance and secondary flow in the vicinity of the tube wall generated by STT are higher compared to that induced by the PTT is referred as the reason for better performance.Over the range considered,the Nusselt number,friction factor and thermal enhancement factor in a tube with STT are respectively,1.03 to 1.14,1.05 to 1.25 and 1.02 to 1.06 times of those in tube with PTT.An empirical correlation is also formulated to match with experimental data of Nusselt number and friction factor for STT and PTT.
