Figure 2. Set 1 of the fractal plates (Circular orifices).

It can be seen from the figures above that the introduction of fractal plates into the pipe flow increases the heat transfer from the centreline to the surrounding flow.

This is represented by the graphs spreading out and the peaks becoming flatter as the heat diffuses across the pipe.

The reason for the fractal plates increasing heat transfer from the centre line to the surrounding areas is due to the turbulence created down-stream of the fractal plate.

When the flow then passes through the orifices in the fractal plates the flow is disturbed causing turbulence. Turbulence creates vortices which are when the flow predominately rotates around an axis parallel to the flow which transfers heat.

It can be seen that the fractal plates with a higher iteration of fractal patterns create the most turbulence.

This may be due to the fact that the vortices created have a larger variation in size and number. This would allow for complete mixing as the vary-ing sized vortices can mix more readily.

The fractal plates with circular orifices can be seen to have mixed far quicker than the triangular orifices.

This is believed to be due to the circular orifices allowing the circular rotating vortices to be created more easily and faster. This would mean that mixing could occur earlier on downstream of the fractal plate.

The triangular orifices were still effective at mixing but this occurred much further downstream. If the experiment had not been limited by the number of stations available it would have been interesting to see whether the mixing reached the same stage of the circular orifices.

Figure 3. Set 2 of the fractal plates (Triangular orifices).

A STUDY INTO THE EFFECT OF FRACTAL PLATES ON THE

RATE OF HEAT TRANSFER Jacob Marlow // Supervisors: Dr F. Nicolleau and Dr W. Brevis

Department of Mechanical Engineering

Fractal plates are a relatively new concept in fluid dynamics, which possess inter-esting properties that can be exploited.

Fractal geometry uses the concept of identical shapes repeating itself on an ever di-minishing scale (self-similar geometry) to produce a pattern.

Fractal geometries are found in nature such as trees, rivers and shells.

It has been found that fractal shaped orifices have a significant effect on the pressure drop measured across them which in turn enhances their mixing properties.

This experiment aims to identify any links between shape and number of fractal itera-tions from the variety of plates tested using the relationship between heat transfer and turbulence.

Figure 1. Schematic of the experimental set up.

A variety of fractal plates were placed in a wind tunnel at position 3 and the rate of

heat transfer in the radial direction was used to calculate the turbulence produced.

The fluid used was air at room temperature (~20°C) travelling at a velocity of 4m/s which passed over a Nichrome wire heating element (1).

The centreline temperature at point 2 was measured as well as the temperature of the fluid at varying points along the diameter after the fractal plate to determine the temper-ature profile and heat transfer of the fluid.

The second thermocouple was moved to along four more stations and where the process repeated. The stations were 35.2mm apart.

The temperature was recorded using an Arduino connected to a K-type thermocouple. The K-type thermocouple used an amplifier which gave the temperature top an accuracy of ±1°C.

SUMMARY

INTRODUCTION

METHOD

DISCUSSION

Figure 4. These figures show the development of

the temperature profile down the pipe for vary-

ing fractal plates.

An experiment was done to find the most effective fractal plates at causing turbu-lence in a flowing fluid. The heat transfer within the fluid was used to determine the amount of turbulence created. The experiment found that the fractal plates with a higher iteration of a fractal pattern caused the most turbulence. It also identified that circular orifices are slightly more effective at creating turbulence than triangular orifices.