TUGAS BESAR CFD : Heat Transfer Enhancement Using Screw Insert Tapes

Introduction

In general, there are two methods that can be done to increase the heat transfer rate, namely through active and passive (Paneliya et al. 2020). The increase in the heat transfer rate through the active method is carried out by utilizing external energy such as forced convection using the aid of a fan. Meanwhile, increasing heat transfer through passive methods does not require external energy, including by using twisted insert tapes (Paneliya et al. 2020). The use of twisted insert tapes can increase the heat transfer rate of a passive stream. The twisted tapes insert is shaped like a ribbon that is twisted and placed in the middle of the pipe.

Twisted-tape inserts are beginning to be applied in a wide variety of areas due to their ability to improve heat transfer performance at a low cost (Paneliya et al. 2020). Basically, the presence of twisted insert tapes functions as a swirl generator and will modify the flow, especially in areas close to pipe walls (Martemianov and Okulov 2004; Paneliya et al. 2020; Smithberg and Landis 1964; Webb, Narayanamurthy, and Thors 2000). The swirl flow will increase the normal velocity gradient on the pipe and result in a reduction in the thickness of the thermal boundary layer, so that the heat transfer will be higher (Shinde, Patil, and Dange n.d.). Meanwhile, the use of twisted insert tapes has a consequence of increasing pressure drop in the flow and will have an impact on higher energy requirements to overcome this pressure drop (Paneliya et al. 2020). Therefore, increasing the heat transfer rate using twisted insert tapes needs to be considered so as not to produce too high a pressure drop.

Research and studies on the use of twisted insert tapes have been carried out by many researchers. Wang and Sunden, (2002) conducted a study on the heat transfer coefficient through the flow of water flowing in a tube equipped with a twisted insert tape. And it was found that there was a 3x and 3.5x increase in laminar and turbulent flow, respectively, to the water flow in the tube without inserts. Then, Agarwal and Rao, (1996) and Sarma et al., (2005), made a correlation between pressure drop and heat transfer on a tube using a conventional fitting model. From these studies, it was found that the presence of a tape insert would inhibit the transition jump from laminar to turbulent. However, because it causes a continuous fluctuation in turbulent flow, the heat transfer will be drastically decreased.

In addition to using inserts, finally various shapes and configurations to increase the heat transfer rate were studied further, such as twisted tape, corrugated / grooved tubes, and combination of turbulators (Paneliya et al. 2020). Sivashanmugam et al., (2008) conducted a study on the heat transfer and friction factor characteristics of circular tubes equipped with helical screw tape inserts. It was found that the helical twisted tapes produced better performance than the previously reported twisted tapes. Promvonge (2008) conducted an experiment using a wire coil connected to a twisted tape to increase the heat transfer rate and showed that the combination of wire coil and twisted tape produced better heat transfer, compared to only wire coil or twisted tapes. Piriyarungrod et al. (2015) conducted a study on the effect of twisted tapes with the shape of the tapper and the angle of the tapper on the heat transfer rate. From this research, it was found that the twisted tape in the form of a tapper will increase the heat transfer performance, friction loss, and thermal performance factor by increasing the angle of the tapper. He et al. (2018) have also conducted a study on the heat transfer characteristics of tubes equipped with cross hollow twisted tape inserts. However, the mechanism for increasing heat transfer with cross hollow insert tape is quite complex. Sarviya and Fuskele, (2018) conducted an experimental study on increasing heat transfer with circular tubes with a twisted tape insert that has a continuous cut edge. The result is the same: a reduction in the twist ratio will increase the heat transfer rate, but also increase the pressure drop.

After finding the fact that the use of insert tapes can increase the heat transfer rate, several other researchers conducted further studies, namely the effect of variations in the geometry of insert tapes on the heat transfer rate. Bhuiya et al., (2016) conducted an experimental study of several helix-shaped tape inserts that had different pitch ratios and were applied to turbulent flow. This study shows that if the pitch ratio value gets smaller, the heat transfer coefficient and pressure drop will increase. However, the increase in heat transfer is more significant than the increase in pressure drop, so the energy used will be more efficient. Garcia et al., (2018) Studied three different wire coil inserts and three different twisted insert tapes for applications in solar collectors and found that there was an increase in heat transfer and a decrease in temperature on the walls. Then, Yadav et al., (2012) Performed CFD simulations on applications of twisted tapes that have different lengths, namely the full length (from upstream to downstream), only half the length on the upstream side, and only half the length on the upstream side. downstream side. It was found that the full length twisted tape insert provided the highest heat transfer rates. Meanwhile, twisted tape inserts that are only half long on the downstream side have better performance than those that are only half long on the upstream side. Bhuyan et al., (2017) Conducted a numerical investigation regarding the comparison of heat transfer characteristics between twisted tapes inserts with full length and short ones under transient laminar flow conditions in U-loop shaped pipes. It was found that the highest exit temperature was generated in U-loop shaped pipelines with twisted insert tapes of full length and then followed by U-loop pipelines with short twisted insert tapes. Both result in higher outlet temperatures compared to ordinary pipes (plaint tubes). Another CFD simulation study on twisted insert tapes was carried out by Piriyarungrod et al., (2015). This study showed that twisted insert tapes with clearance ratio with value of 0.05 produced the highest performance compared to other clearance ratio values.

Based on a review conducted by Yousif, A.H. and Khudhair M.R. (2018), and also from some literature that the author has explored, until now there has been no study that discusses the use of insert tapes for use in evaporation applications. Referring to the results of studies that have been carried out, it is hoped that the use of insert tapes can also increase the rate of evaporation. This study is intended to find out the use of the screw tape insert as an heat transfer enhancement passive technique for evaporation process.

Materials

This study also compares two screw inserts geometry with different pitch length; 25 mm (left) and 25 mm(right). The length of the screw is 100 mm. The inner and outer diameter of the geometry sucessively are 15 mm and 20 mm. Both geometry is placed inside a channel with 120 mm long as shown in Fig.1 below.

Figure 1. Screws insert object

CFD Simulation Setup

The study is conducted through CFD simulation. The CFD simulation is performed by using CFDSOF software simulation. The simulation is set up as follows:

• Single phase simulation
• Turbulence flow by using SST K-ω RANS turbulence Model
• Steady-State
• Isothermal

Standard air is used as the working fluid. The resulting mesh for CFD simulation is shown in Fig. 2 below

Figure 2. Insert screw mesh

Result and Discussion

Pressure Distribution profile

It is obtained from the pressure contour that there is a significant rises of pressure drop occured in the by the presence of the twisted tape insert. It also compare that the geometry with the longer pitch will result a higher pressure drop. It can be seen from Fig.. that the pressure drop produced by the geometry with pitch ratio of 15mm is higher than the pressure drop produce by the geometry with pitch ratio of 25 mm. It is because the geometry with smaller pitch will have a longer screw and produce a more viscous frictions between the screw surface and the fluids. Thus, the geometry with the smaller pitch wil produce higher pressure drop.

Figure 3. Pressure distribution contour

The pressure distribution profile at the cross-sectional area is shown. It is obtained that at x=0.01, there are low area of pressure and high area of pressure. The high pressure area indicates that the fluid is blocked by the geometry and thus it produce stagnation pressure. While the low pressure zone indicates that there is a gap that fluid can move through it, hence it would now produce stagnation pressure. This contour is also have the same pattern in x = 0.02 until x=0.1 which is at the end of the geometry.

Figure 4. Pressure distribution contour at cross sectional area

Velocity Distribution

The velocity vector is also shown. According to the velocity vector above, it can be obtained that the screw geometry will generate swirling flow. In addition, it can also increase the velocity. According to the velocity distribution, the velocity of the flow is increased to almost 4 times. It is due tot eh swirling effect induced from the screw geometry. This dramatical increase would make the thermal boundary layer becomes thinner and thus enhance the heat transfer.

Figure 5. Velocity distribution vector

The geometry with pitch length of 15 mm give a higher velocity acceleration than the geometry with pitch length of 25 mm as shown in Fig 6 below. It is shown that the highest swirling velocity induces by the geometry with pitch of 15 mm reach to 20 m/s, while the highest swirling velocity induces by the geometry with pitch of 25 mm just only reach 16 m/s. It implies that the vortex flow induces by the smaller pitch length would produce higher centrifugal force to the flow, hence it would give a more strong swirling flow. However, it also need a higher energy to induce the swirling flow. Hence, it will give a higher pressure drop to the flow.

Figure 6. Velocity distribution contour at cross sectional Area

Conclusions

The study of the heat transfer enhancement by using passive screw insert tapes has been performed. It can be concluded that:

1. The addition of twisted tape insert could produce a higher pressure drop
2. The screw with smaller pitch length will produce a greater pressure drop
3. The screw insert geometry induces swirling flow that could enhance heat transfer.
4. The screw with smaller pitch length will generate a higher swirling velocity.

References

1. Agarwal, S K, and M Raja Rao. 1996. “Heat Transfer Augmentation for the Flow of a Viscous Liquid in Circular Tubes Using Twisted Tape Inserts.” International Journal of Heat and Mass Transfer 39(17): 3547–57.
2. Bhuiya, Muhammad Mostafa Kamal, M S U Chowdhury, J U Ahamed, and A K Azad. 2016. “Heat Transfer Performance Evaluation and Prediction of Correlation for Turbulent Flow through a Tube with Helical Tape Inserts at Higher Reynolds Number.” Heat and Mass Transfer 52(6): 1219–30. https://doi.org/10.1007/s00231-015-1643-y.
3. Bhuyan, Md Moniruzzaman, Ujjwal K Deb, M Shahriar, and Simul Acherjee. 2017. “Simulation of Heat Transfer in a Tubular Pipe Using Different Twisted Tape Inserts.” Open Journal of Fluid Dynamics 7(3): 397–409.
4. García, A, R Herrero-Martin, J P Solano, and J Pérez-García. 2018. “The Role of Insert Devices on Enhancing Heat Transfer in a Flat-Plate Solar Water Collector.” Applied Thermal Engineering 132: 479–89.
5. He, Yan, Li Liu, Pengxiao Li, and Lianxiang Ma. 2018. “Experimental Study on Heat Transfer Enhancement Characteristics of Tube with Cross Hollow Twisted Tape Inserts.” Applied Thermal Engineering 131: 743–49.
6. Martemianov, Sergueï, and Vasiliev Leonid Okulov. 2004. “On Heat Transfer Enhancement in Swirl Pipe Flows.” International Journal of Heat and Mass Transfer 47(10–11): 2379–93.
7. Piriyarungrod, N et al. 2015. “Heat Transfer Enhancement by Tapered Twisted Tape Inserts.” Chemical Engineering and Processing: Process Intensification 96: 62–71.
8. Promvonge, Pongjet. 2008. “Thermal Augmentation in Circular Tube with Twisted Tape and Wire Coil Turbulators.” Energy Conversion and Management 49(11): 2949–55.
9. Sarma, P K, P S Kishore, V Dharma Rao, and TJIJoTS Subrahmanyam. 2005. “A Combined Approach to Predict Friction Coefficients and Convective Heat Transfer Characteristics in A Tube with Twisted Tape Inserts for a Wide Range of Re and Pr.” International Journal of Thermal Sciences 44(4): 393–98.
10. Sarviya, R M, and Veeresh Fuskele. 2018. “Heat Transfer and Pressure Drop in a Circular Tube Fitted with Twisted Tape Insert Having Continuous Cut Edges.” Journal of Energy Storage 19: 10–14.
11. Shinde, Mr D D, A M Patil, and H M Dange. “Review of Heat Transfer Parameters Using Internal Threaded Pipe Fitted with Inserts of Different Materials.”
12. Sivashanmugam, P, P K Nagarajan, and SJCEC Suresh. 2008. “Experimental Studies on Heat Transfer and Friction Factor Characteristics of Turbulent Flow through a Circular Tube Fitted with Right and Left Helical Screw-Tape Inserts.” Chemical Engineering Communications 195(8): 977–87.
13. Smithberg, E, and F Landis. 1964. “Friction and Forced Convection Heat-Transfer Characteristics in Tubes with Twisted Tape Swirl Generators.”
14. Wang, Lieke, and Bengt Sunden. 2002. “Performance Comparison of Some Tube Inserts.” International Communications in Heat and Mass Transfer 29(1): 45–56.
15. Webb, R L, R Narayanamurthy, and P Thors. 2000. “Heat Transfer and Friction Characteristics of Internal Helical-Rib Roughness.” J. Heat Transfer 122(1): 134–42.
16. Yadav, R J, and A S Padalkar. 2012. “CFD Analysis for Heat Transfer Enhancement inside a Circular Tube with Half-Length Upstream and Half-Length Downstream Twisted Tape.” Journal of Thermodynamics 2012.
17. Yousif, Ahmed Hashim, and Maher Rehaif Khudhair. 2019. “Enhancement Heat Transfer in a Tube Fitted with Passive Technique as Twisted Tape Insert-A Comprehensive Review.” American Journal of Mechanical Engineering 7(1): 20–34.