Study on flow and heat transfer characteristics for propane in twisted oval and the two-start twisted helically wound tube

In this paper, the numerical simulation was used to study the flow and heat transfer characteristics for twisted oval and two-start twisted helically wound tubes with Reynolds numbers 4000–16,000. The significant factors that affect the flow and heat transfer characteristics were analyzed. The range of twist pitch p is 0.02–0.10 m, and ellipse ratio r is 1.2–2 for twisted oval tube, the groove depth e is 0.4–2 mm for two-start twisted tube. The result showed that the relative friction coefficient and Nusselt number increased with the increase of ellipse ratio r and decreased with the increase of twist pitch p for twisted oval helically wound tube. With the growth of Reynolds number, the effects of twist pitch p and ellipse ratio r on the flow characteristics decreased. In addition, the average level of the thermal enhancement factor TEF of the two-start twisted was higher than that of the twisted oval helically wound tube. The maximum enhancements factor TEF of 1.1312 is obtained with groove depth of 2.0, twisted pitch of 0.02, and Reynolds number of 4000 for the two-start twisted tube. Finally, new empirical formulas for flow and heat transfer in helically wound tubes were proposed for two kinds of enhanced tubes.

Performance on Buoyancy Driven Flow in Square Duct Fitted with Twisted Strip

This experimental investigation aims to study the effect of inlet fluid on flow and heat transfer characteristics for buoyancy driven flow in square tube fitted with twisted strips. Twist pitch, heat supply, inclination of the tube and Inlet fluid temperature were changed during experimentation. The study revealed that with increase in pitch the percentage enhancement in heat transfer coefficient decreases. With decrease in the pitch the flow rate decreases. Moreover with increase in inlet fluid temperature both heat transfer coefficient and flow rate tends to decrease. Perhaps it is due to higher heat loss at the tube surface which results in reduction in Rayleigh number.

Influence of constructive features of symmetric data transmission chains on the process of optimizing the physical level of infocommunication systems

The influence of the twisting steps of twisted pairs of horizontal LAN cables of category 6 on the primary and key secondary parameters of the electrical transmission medium of infocommunication systems is investigated. The primary parameters are investigated, which make it possible to determine the secondary parameters of a symmetrical conductive path: wave impedance and attenuation coefficient. It is shown that, with respect to a twisted pair with the smallest twist pitch, it is expedient to apply the high-frequency model to calculate the electric transmission path.

Performance Study of a Cylindrical Parabolic Concentrating Solar Water Heater with Nail Type Twisted Tape inserts in the Copper Absorber Tube

This paper reports the overall thermal performance of a cylindrical parabolic concentrating solar water heater (CPCSWH) with inserting nail type twisted tape (NTT) in the copper absorber tube for the nail twist pitch ratios 4.787, 6.914 and 9.042 respectively. The experiments are conducted for a constant volumetric water flow rate and during the time period 9:00 h to 15:00 h. The useful heat gain, hourly solar energy collected and hourly solar energy stored of this solar water heater are found higher for nail twist pitch ratio 4.787. The above said parameters are found to be a peak at noon and observed to follow the path of variation of solar intensity. At the starting of the experiment, the value of charging efficiency is observed to be maximum. Whereas the maximum value of instantaneous efficiency and overall thermal efficiency are observed at noon. The key finding is that the nail twist pitch ratio enhances the overall thermal performance of the CPCSWH.