HEAT TRANSFER ENHANCEMENT IN A PIPE FLOW USING A ROTATING TWISTED TAPE INSERT

This is to prove that the thesis entitled, "ENHANCEMENT OF HEAT TRANSFER IN PIPE FLOW USING ROLLING TAPE" is a result of the investigation carried out by the author under the supervision of Col. Md. Nafis Bin Islam, Student ID. Their university thesis report on “ENHANCEMENT OF HEAT TRANSFER IN PIPE FLOW USING A ROTATING TAPE” under my supervision.

LIST OF TABLES

CHAPTER 1

INTRODUCTION

Introduction
Classification of Heat Enhancement Techniques
Convection Heat Transfer & Its Types
Background for Selecting the Project
Advantages of Rotating Twisted Tape Insert for Heat Enhancement
CHAPTER 2

Heat transfer is one of the important processes that involves a lot of application in our daily life. Convection heat transfer involves the transfer of heat between a surface at a given temperature (Ts) and a fluid at a higher temperature (Tb).

LITERATURE REVIEW

Recent Researches and Development

21] experimentally investigated the heat transfer enhancement, friction factor and thermal performance factor characteristics of tube equipped with V-cut twisted band. 29] investigated heat transfer enhancement, friction factor and thermal performance factor characteristics in a tube equipped with delta wing twisted band.

CHAPTER 3

General
Main Components for the Experimental Facility and Setup

A twisted bar insert is a flat rectangular bar whose length is comparatively much higher than its width, twisted around its longitudinal axis. The geometry of the twisted tape is mainly characterized by the twist ratio which is the simple mathematical ratio of its width. The twisted bar had specially designed ends so that it could be used to tighten for turning purposes.

The inlet section is specially designed so that the water can enter easily without obstructing the rotation system of the twisted tire. For this special shaft is designed to hold the twisted band and turning is without any vibration. Asbestos tape was used in this experiment to provide better heat insulation and prevent heat losses to the environment.

In this experiment, a 0.5 HP water pump was used to supply water through the pipe. In this experiment, a high-performance DC motor is used to keep the coiled tape rotating inside a copper tube.

Fig 3.2: Copper pipe with specification of different sections.

Program for Temperature Measurement Using PIC 18F452 Microcontroller

Fabrication of Twisted Tape
Experimental Setup
CHAPTER 4

Experimental Procedure
Experimental Conditions
Precautions

CHAPTER 5

The test piece is a section of copper pipe with an inner diameter of 39 mm and an outer diameter of 42 mm. The total length of the copper pipe is 1.2192 m, and the length of the test section is 900 mm. In addition, fiberglass cloth, aluminum foil tape, and asbestos tape were wound over the entire outer surface of the pipe.

Six LM35 sensors were placed on the outer surface of the pipe above the test section to measure the temperature at different local points of the test section. At first, the copper tube was heated with the help of Nichrome wire wound on the outer surface of the tube to be heated. The experiment begins by raising the temperature of the tube to a stable temperature.

Six LM35 temperature sensors were placed equidistantly on the outer surface of the tube containing the 900 mm test section. After this, the experiment was carried out in the same way as previous steps, except that the rotation of the twisted band was varied with a DC motor rotating at different revolutions.

Fig 3.24: Schematic diagram of experimental setup

CALCULATION METHODOLOGY

Data Reduction

The heat added by the heater was calculated from the heat added to the water. The temperature of the outer surface of the tube was calculated based on the average of six local temperatures of the outer surface of the tube.

CHAPTER 6

RESULT AND DISCUSSION

Result and Discussion

Nusselt number, heat flux, bulk temperature, inner surface temperature, heat transfer enhancement efficiency with respect to Reynolds number are illustrated in Figures 6.1 to 6.5. The effect of Reynolds number for different flow rates on Nusselt number is shown in Figure 6.1. The result suggests that the Nusselt number for pipes with tape inserts is relatively higher than the Nusselt number in smooth pipes.

On the other hand, the value of the Nusselt number keeps increasing significantly as the number of revolutions of the twisted belt increases. With increase of both RPM and Reynolds number, higher values of Nusselt number can be achieved. For the experiment, the highest value of Nusselt number was obtained at a mass flow rate of 0.2623 kg/sec and the rotation of twisted tape was at 600 RPM.

However, the results indicate that this Nusselt number could have been increased at a higher flow rate and speed.

Nusselt Number Vs Reynolds number

The effect of Reynolds number for different flow rates on heat flux is shown in figure 6.2. The result indicates that heat flux for tube with tape insert is relatively higher than heat flux in smooth tube. Initially for rotation of twisted belt between 0-400 RPM, the heat flux remains relatively lower than the heat flux at smooth pipe with Reynolds number in the range of 5000-8000.

On the other hand, the heat flux value continues to increase significantly as the number of revolutions per minute of the coiled strip increases. By increasing the revolutions per minute and the Reynolds number, higher values of the heat flow can be achieved. For the experiment, the maximum value of the heat flux was obtained at a mass flow rate of 0.2623 kg/s and the rotation of the coiled strip at 600 RPM.

However, the results suggest that this heat flux could have been increased at higher flow rate and RPM.

Heat Flux vs Reynolds Number

The effect of Reynolds number for different flow rates on mass temperature is shown in figure 6.3. The result indicates that mass temperature for tube with tire insert is relatively higher than mass temperature in smooth tube. Initially for rotation of twisted belt between 0-400 RPM, the mass temperature remains relatively lower than the mass temperature at smooth pipe with Reynolds number in the range of 5000-8000.

On the other hand, the volume temperature value continues to increase significantly as the revolutions of the coiled strip increase. By increasing the rpm and Reynolds number, higher values of bulk temperature can be achieved. For this experiment, the maximum total temperature was achieved at a mass flow rate of 0.2623 kg/s and a coiled tape rotation of 600 RPM.

However, the results suggest that this bulk temperature could have been increased at higher flow rate and RPM.

Bulk Temperature vs Reynolds Number

40 | P a g e Fig 6.4: Variation of temperature of inner surface of tube with Reynolds number for different RPM of twisted tape. The effect of the Reynolds number for different flow rates on the temperature of the inner surface of the tube is shown in Figure 6.4. On the other hand, the value of the temperature of the inner surface of the tube continues to decrease significantly as the rotational speed of the twisted tape increases.

With an increase in both RPM and Reynolds number, lower values of the tube's internal surface temperature can be achieved. For this experiment, the lowest value of bulk temperature was obtained at a mass flow rate of 0.2623 kg/sec and the rotation of twisted tape was at 600 RPM. The effect of Reynolds number for different flow rates on the heat transfer enhancement efficiency is shown in Figure 6.5.

With increasing both RPM and Reynolds number higher values of heat transfer improvement efficiency can be obtained. For this experiment, the highest value of heat transfer enhancement efficiency was obtained at a mass flow rate of 0.2623 kg/sec and the rotation of twisted belt was at 600 RPM.

Heat Transfer Enhancement Efficeincy vs Reynolds Number

CHAPTER 7

CONCLUSIONS

RECOMMENDATIONS

Conclusions

This study presents the new experimental data on heat transfer characteristics using rotating twisted tape insert. The application of the approach results in a simple fast and easy implementation of the method. Although this method had helped us to understand the importance of RPM and flow rate controlling the heat transfer characteristics, further research is still needed to conclude the system behavior with response to the friction factor.

Heat transfer rate is greatly affected by the flow rate of the fluid flowing in the system. Higher heat transfer rate can be obtained at high RPM of twisted belt and flow rate of flowing water. Higher values of Nusselt number can be obtained at higher RPM of twisted tube and flow rate of flowing water.

Recommendation

Further analysis can be done with a modified geometry of the coiled strip and give it an appropriate rotation to investigate its relation to heat transfer enhancement. An alternative to the coupling system between the output shaft of the DC motor and the shaft connected to the coiled belt must be found to efficiently transmit the torque to the coiled belt. The housing design can be modified more efficiently by correct bearing arrangement and shaft locking position with separate temperature and pressure measurement openings.

Simulation based on Computational Fluid Dynamics (CFD) can be done to ensure the accuracy of experimental values compared to predicted values.

Eiamsa-ard, Heat transfer behavior in tubes with combined conical rings and twisted tape inserts, International Communication on Heat and Mass Transfer Vol. 16] Smith Eiamsa-ard, Chinaruk Thianpong and Pongjet Promvonge, Experimental Investigation of Heat Transfer and Flow Friction in a Circular Tube Equipped with Uniformly Spaced Coiled Tape Elements, International Communications in Heat and Mass Transfer Vol. Srinivasan, Heat transfer and pressure drop characteristics in a circular tube equipped with and without a V-cut coiled strip insert, International Communications in Heat and Mass Transfer Vol.

Thianpong, Pipe heat transfer enhancement using delta-winglet twisted ribbon inserts, Applied Thermal Engineering, Vol. Srinivasan, Heat Transfer and Pressure Drop Characteristics of Turbulent Flow in Tubes Equipped with a Trapezoidally Cut Twisted Tape Insert, International Journal of Academic Research, Vol. Chang, Yih Jena Jan and Jin Shuen Liou, Turbulent heat transfer and pressure drop in a tube equipped with a serrated twisted band, International Journal of Thermal Sciences Vol.

Murugeasan, A review of twisted tape heat transfer enhancement, International Journal of Scientific & Engineering Research, Vol. Bhuiya, Enhancement of heat transfer in tubes using rectangular cut twisted tape, BSME International Conference on Thermal Engineering, (2012).

APPENDIX

APPENDIX A

APPENDIX B