Varesa Chuwattanakul

Heat transfer and fluid flow behaviors in a five-start spiral corrugated tube

This paper presented a numerical investigation on turbulent periodic flow, heat transfer, pressure loss and thermal enhancement factor in a 3D five-start spiral corrugated tube. Air was used as the working fluids through the tube for Reynolds numbers of about 5000-20,000. In the current studied, the five-start spiral corrugated tube with six relative pitch ratios (p/D, PR=1.0, 1.5, 2.0, 2.5, 3.0 and 3.5) with constant depth ratio (e/D, DR=0.06). The numerical results reveal that the five-start spiral corrugated tube can generated a swirl flow, main swirl flow and five-secondary swirl flow. This behavior lead to the major change of temperature in transverse plane, reduced thermal layer thickness and enhanced heat transfer on the tube wall. The five-start spiral corrugated tube in range investigated provided the heat transfer rate and friction factor up to 2.02 and 6.12 times, respectively, over the straight circular tube. The thermal enhancement factor of the five-start spiral corrugated tube in the range of 0.89-1.16 where its maximum found as the optimum point is at PR=2.0.This paper presented a numerical investigation on turbulent periodic flow, heat transfer, pressure loss and thermal enhancement factor in a 3D five-start spiral corrugated tube. Air was used as the working fluids through the tube for Reynolds numbers of about 5000-20,000. In the current studied, the five-start spiral corrugated tube with six relative pitch ratios (p/D, PR=1.0, 1.5, 2.0, 2.5, 3.0 and 3.5) with constant depth ratio (e/D, DR=0.06). The numerical results reveal that the five-start spiral corrugated tube can generated a swirl flow, main swirl flow and five-secondary swirl flow. This behavior lead to the major change of temperature in transverse plane, reduced thermal layer thickness and enhanced heat transfer on the tube wall. The five-start spiral corrugated tube in range investigated provided the heat transfer rate and friction factor up to 2.02 and 6.12 times, respectively, over the straight circular tube. The thermal enhancement factor of the five-start spiral corrugated tube in the range ...

Simulation of turbulent heat transfer characteristics in a corrugated tube with five-channel twisted tape inserts

The article presents a numerical analysis of turbulent periodic flow and heat transfer characteristics in a five-start spiral corrugated tube combined with five-channel twisted tape. Influences of the five-channel twisted tape with tape width ratio, w/D=0.10, 0.20, 0.30, 0.40 and 0.44 at constant the twisted length ratio, y/D=2.0 were described. The results were reported in term of flow structure, temperature distribution, TKE field, local Nusselt number distribution on the wall, Nusselt number ratio, friction factor ratio and thermal enhancement factor. The five-start spiral corrugated tube combined with five-channel twisted tape showed a main swirl flow and secondary swirl flow along the tube due to the induction of the spiral groove while the smooth circular tube appeared the straight only and the five-start spiral corrugated tube with the five-channel twisted tape at w/D=0.44 appeared the main swirl flow only. The swirl flow help to increase fluid mixing and increase in heat transfer rate over the smooth circular tube. The increase in the w/D lead to the rise of Nusselt number and friction factor. The result showed that the optimum thermal enhancement factor of about 1.16was found at the five-start spiral corrugated tube without the five-channel twisted tape and at w/D=0.44.The article presents a numerical analysis of turbulent periodic flow and heat transfer characteristics in a five-start spiral corrugated tube combined with five-channel twisted tape. Influences of the five-channel twisted tape with tape width ratio, w/D=0.10, 0.20, 0.30, 0.40 and 0.44 at constant the twisted length ratio, y/D=2.0 were described. The results were reported in term of flow structure, temperature distribution, TKE field, local Nusselt number distribution on the wall, Nusselt number ratio, friction factor ratio and thermal enhancement factor. The five-start spiral corrugated tube combined with five-channel twisted tape showed a main swirl flow and secondary swirl flow along the tube due to the induction of the spiral groove while the smooth circular tube appeared the straight only and the five-start spiral corrugated tube with the five-channel twisted tape at w/D=0.44 appeared the main swirl flow only. The swirl flow help to increase fluid mixing and increase in heat transfer rate over the smo...

Heat transfer enhancement in turbular heat exchanger fitted with twin twisted tape swirl generators

An experimental investigation was made with aim to enhance heat transfer in a double-tube heat exchanger fitted with twin twisted tapes. The effects of the twin twisted tape inserts on heat transfer rate, friction factor and thermal performance behaviors were studied in turbulent region of Reynolds number between 5000 and 15,000. The twin twisted tapes with three twist ratios (y/w = 1.5, 2.0 and 2.5) were used for generating two longitudinal swirl flows along the test section. The experimental result indicates that heat transfer rate in term of Nusselt number (Nu) and friction loss in term of friction factor (f) increase as twisted ratio (y/w) decreases. The twin twisted tapes with y/w = 1.5 yield higher Nusselt number (Nu) than the ones with y/w = 2.0 and 2.5 up to 16% and 38%, respectively which are accompanied with the higher friction factor up to 15% and 35%, respectively. Among the tested twisted tapes, the twin twisted tapes with the smallest twist ratio (y/w = 1.5) offer the maximum thermal perform...

Impingement Cooling by Round Jets with a Longitudinal Swirling Strip

The objective of this research is to study the effect of swirling impinging jets on the heat transfer in an impinged plate using a thermochromic liquid crystal (TLC) sheet. In the experiments, a nozzle with a diameter of 20 mm (D) was installed with a four-channel twisted tape as a longitudinal swirling strip. Jet impingement was performed at jet-to-plate distances (L/D) of 2, 3, 4, 5, 6, and 7 and a constant Reynolds number (Re) of 5,000. The experimental results showed that the swirling jet (SJ) induced by the fourchannel twisted tape gave higher heat transfer rates than the conventional jet (CJ) at the same operating conditions. The highest average heat transfer rate was obtained at a jetto-plate distance (L/D) of 2. 