Q2. What contributions have the authors mentioned in the paper "Numerical investigation on heat transfer performance and flow characteristics in a roughened vortex chamber" ?
In this study, an investigation of a vortex chamber was carried out to gain a full understanding of the nature of the vortex flow and the cooling capability inside the chamber. The paper discusses the effects on flow and heat transfer rates when the inside surface of the vortex chamber was roughened by adding flow turbulators to its wall. The paper also presents the results of a comparative investigation of jet impingement and vortex cooling on a concave wall using different parameters, such as the total pressure loss coefficient, Nusselt number and thermal performance factor, to evaluate the cooling effectiveness and flow dynamics. Furthermore, the entropy generation in swirl flow with the roughened wall was assessed over a wide range of Reynolds numbers. Further increase in rib height has an adverse impact on thermal performance.
Q3. What is the effect of jet impingement cooling on the vortex chamber?
In the jet impingement cooling technique, the relatively high-pressure drop may be attributed to the kinetic energy loss after leaving the nozzle and frictional losses near the wall.
Q4. What is the effect of the ribs on the thermal performance of the chamber?
when the Reynolds number exceeds 50000, the ribs have a negative effect on the heat transfer compared to the smooth case 6- In a smooth chamber, the impact of heat transfer contributes significantly to the total entropygeneration over the range tested of Reynolds numbers.
Q5. What is the effect of the ribs on the flow?
When the rib height reaches 2.00 mm, the ribs divert the flow further from the wall towards the core, resulting in a circulation region near the heated wall between the first three ribs and decreasing the size of the core vortex.
Q6. What is the effect of ribs on flow and heat transfer in a vortex chamber?
Four square cross-section ribs of heights 0.25, 0.50, 1.00 and 2.00 mm were used, with a range of Reynolds number from 10000 to 100000.1- Numerical simulations were compared with experimental results for flow and heat transfer ina smooth vortex chamber.
Q7. What is the effect of ribs on flow in a vortex chamber?
2- The study indicates that the flow inside the vortex chamber is steady for a smooth wall andrib heights smaller than 0.25 mm, but as either the rib height or the Reynolds number increases the flow become quasi-steady.
Q8. What is the way to analyse the effects of the flow?
In order to analyse the effects of the flow with maximum efficiency, the same configuration with the same boundary conditions should be used for all flow rates.
Q9. Why was the RNG k model adopted for all the following calculations?
The RNG kε model was adopted for all the following calculations, not only because of its ability to predict the heat transfer and velocity profiles more accurately, but also its low computational cost.
Q10. How does the flow flow to the next rib?
As the flow advances to the following ribs, the peak from the reattachment decreases considerably until the last (fourth) rib, when the peak starts to fade away.
Q11. How much heat transfer is shown at high Reynolds numbers?
the value of Nu/Nuo for a rib height of 2.00 mm shows a 26% decrease in heat transfer at high values of Reynolds number compared to the smooth chamber.
Q12. What is the effect of the rib roughened wall on the thermal performance of the chamber?
5- The rib roughened wall produces superior thermal performance and heat transfer when theReynolds number is less the 50000 for rib height of 0.25 mm compared to the smooth case.
Q13. How much pressure loss coefficient is higher for the smooth vortex chamber?
At Reynolds number of 100000, the vortex chamber with rib heights of 2.00 mm and 1.00 mm has pressure loss coefficients higher by about twice and 1.6 times, respectively, than for the smooth vortex chamber.
Q14. What is the normalised Nusselt number for the smooth chamber?
For the smooth chamber, the normalised Nusselt number is high at the beginning of the chamber owing to the high tangential flow velocity entering the chamber and the beginning of the concave wall, which reduces the thermal boundary layer in that region.
Q15. What is the optimum Reynolds number for a rib?
At low Reynolds number, the region of maximum Nusselt number is near the inlet anddecreases towards the outlet for all ribs, except the rib of height 2.00 mm, where the heat transfer near the centre of the heated wall is greatest, primarily owing to the separation created by the first rib, which results in two large vortices being formed before and after the second rib.
Q16. What is the Reynolds number of the rib?
Increasing the Reynolds number to 20000 results in a heat transfer reduction for all cases, the maximum reduction being for the rib of height 2.00 mm, likely owing to the main flow being shifted away from the heated wall, as shown in Figure 8.
Q17. What is the average Nusselt number for the vortex chamber?
The normalised Nusselt number shows that heat transfer for low Reynolds numbers is higher in the vortex chamber and, as the Reynolds number increases, jet impingement rises compared to the vortex chamber at Re > 50000.
Q18. What is the maximum Nu/Nuo peak for a rib of height 0.50 ?
The highest Nu/Nuo peak occurs for a rib of height 0.50 mm and Reynolds number 10000;thereafter, for this height of rib, the initial peak progressively decreases with an increase in Reynolds number.
Q19. What is the maximum normalised Nusselt number at the beginning of the chamber?
as the Reynolds number increases, so the maximum normalised Nusselt number at the beginning of the chamber increases.