Surachet Sichamnan , as a partial fulfillment of the requirements for the Doctor of Philosophy Mechanical Engineering at Mahasarakham University Examining Committee (Asst.

By coil flow pattern and the annular flow pattern affect the heat transfer rate of the TPCT with inner diameter of 7 mm, the inclination angles were 80 and 90°. Through the flow, flow pattern and stratified flow patterns affect the heat transfer rate for this test case.

Table 2.1 Silver nanoparticle properties [ 9 ]. ...............................................................

INTRODUCTION

Background
Objectives of this study
Scope of study
Benefits of this study

Chailangkar et al., study the visual of aspect ratio effects on the flow patterns within an inclined two-phase closed thermosyphon. They also study the effects of internal flow patterns of an inclined two-phase closed.

Literature Review

Theory and working principle of a two phase closed thermosyphon

Objectives of this study 1) To investigate the flow pattern of working fluids inside the thermosiphon on the inclined plane. Both thermosyphons use deionized water, ionized water mixed with nano silver.

Figure 2.2 Schematic of thermosyphon at the incline position [9].

Methodology

To summarize the internal flow models of rectangular cross section thermosyphon (RTPTC) and circular cross section thermosyphon (TPCT), respectively. It measures the bubble length in the axial direction of the thermosyphon with rectangular cross section. The internal flow pattern will be measured from the onset of vapor in the evaporator section until the bubbles float through the adiabatic section to the condensate section, respectively.

Gg+Gl (3.12) The quality of the steam can be calculated from the enthalpy or the specific volume of the two-phase and enthalpy. G = Gg+ Gl (3.14) Liquid mass flux is the product of the liquid density and the surface velocity of the working fluids in the liquid phase. Gl= ρlul (3.15) Vapor mass flux is the product of the vapor density and the superficial.

Figure 3.1 Outside surface area of fluid flow/Wetted perimeter [3].

Results and Discussion

The work and behavior of flow patterns within two phase closed thermosyphon

What characteristics of the steam flow are moving near the surface of the inner tube on both sides, from the gap in the middle of the tube is the liquid part that the gap in the middle of the tube turns out to be characteristic of the working fluids that are in the phase of liquids resulting from the condensation of the condenser section in the evaporator section. There is a liquid flow at the bottom of the tube and the vapor will flow along the top of the tube [33] as shown in Figure 4.2.

Figure 4.1 The working of two-phase closed thermosyphon.

Effect of the evaporator temperature and aspect ratio on flow patterns of two-

From the test, it found that at the evaporator temperature of 90 °C, three flow patterns were found consisting of bubble flow pattern (BF) formed a flow pattern of 6.32% and the average bubble velocity and average bubble length is 0.089 m / s, respectively 0.0051 m. The flux flow pattern (CF) formed a flow pattern of 17.34 % and the average bubble velocity and average bubble length is 0.208 m/s and 0.053 m, respectively. When considering the evaporator temperature of 70 °C as shown in Table 4.2, it was found that three flow patterns consist of the bubble flow pattern (BF) formed a flow pattern of 4.07 % and the average bubble velocity and average length of the bubble is 0.090 m /s, respectively 0.0049 m.

When considering the comparison of aspect ratios were 5 and 20, which affects the flow pattern of two-phase closed rectangular cross-section thermosyphon (RTPTC) inner diameters of 25.2 mm. It was found that the bubble flow pattern, slug flow pattern and churn flow are the basic flow patterns that can be found both in the test with the aspect ratio was 5 and 20. In addition, only the annular flow pattern is found in the test with the aspect ratio was 20.

Table 4.1 Effect of the evaporator temperature 50, 70 and 90 °C, aspect ratio was 20 and the inclination angle was 90°

Effect of the evaporator temperature and aspect ratio on heat transfer of two-

Considering the aspect ratio, it was 5, which has the length of the evaporator section and the condenser section is relatively short. This is another reason to move the vapor bubble using a short and fast moving distance to rise to cool the condenser section.

Effect of the evaporator temperature and inclination angle on flow patterns of

A biphasic flow pattern consisting of a gas flow phase and a liquid flow phase occurs due to an increase in evaporator temperature resulting in a liquid working fluid phase that boils and becomes vapor. Due to the large diameter of the TPCT, a binding force is created between the molecules of the working fluids and the particles that are formed between the lower edge of the TPCT tube. Therefore, we cause the test at an evaporator temperature of 50 °C with a TPCT inner diameter of 25.2 mm, an angle of inclination of 80 °.

As a result, the viscosity and density of the working fluids in the liquid phase are reduced at the same time. The result is the boiling of the working fluids, which are in the saturated liquid phase, with steam first forming at the edge of the pipe wall. From the size of a two-phase thermosyphon with a closed circuit cross-section (TPTC) with an internal diameter of 25.2 mm with a large diameter tube, which causes a binding force between the molecules of the working fluids with particles formed between the lower edge of the TPCTs. vent.

Table 4.3 Effects of the evaporator temperature 50, 70 and 90 °C, the inclination angles were 0, 80 and 90°

Effect of the evaporator temperature and inclination angle on heat transfer of

The flow properties of the vapor move on both sides near the surface of the tube because the slope being tested at slope angle 90° TPCT is placed in a straight and symmetrical location. Therefore, observed the flow of the vapor moving over the surface of both sides of the pipe and floating through the adiabatic section to transfer heat to a lower temperature source and condensation at the condenser section. When the working fluids are condensed and thereby change from vapor to liquid, the working fluids become weighted and move downward into the center of the pipe, the liquid being returned to the evaporator section by the gravity of the earth moving downward. .

At the tilt angle of 80°, the liquid film with condensation in the condenser section will have some characteristics as a result, the viscosity of the working fluid that is in the liquid phase ready to flow back into the evaporator section is reduced. Together with the mixture of oleic acid as a surfactant that helps disperse nano-silver nanoparticles. Results in a higher rate of heat distribution than traditional working fluid or using working fluid in the group of coolants, which is useful for easy and quick boiling of working fluid.

Graph 4.2 Effects of the evaporator temperature and inclination angle on heat transfer of two - phase closed circle cross sectional thermosyphon (TPTC) inner diameters of 7 and 25.2 mm aspect ratio 5 and use silver nanofluid with oleic acid surfactant a

Effect of the diameter and inclination angle on flow patterns of two-phase

Working fluids that are in the liquid phase, when heat accumulates more in the evaporating part. Combined with the use of working fluids as silver nanoparticles and the addition of oleic acid to reduce surface tension. The addition of oleic acid, in addition to being a surface-active substance, also helps to disperse the nanoparticles of silver powder so that it is regularly dispersed in the working fluids.

From silver nanoparticles that are dispersed in working fluids regularly, the liquid-based working fluids also help to have more heat in the area, from the size of the nanoparticles and help to make boiling working fluids easier and better. With a pipe with a large pipe diameter, resulting in a strong surface tension between the molecules of the working fluids, which are drawn together at the surface of the working fluid and touch the edge of the pipe wall, will fall. For the reasons mentioned above, when heat is transferred from the pipe wall to the working fluids adjacent to the edge of the pipe wall.

Effect of the diameter and inclination angle on heat transfer of two-phase

Which is quite difficult since the bubble can move and collect, Due to the limited movement distance that leads to changes in the flow pattern from one flow pattern to another. This results in the convection coefficient of the two-phase flow pattern consisting of gas flow phase and liquid flow phase being too low.

Flow pattern map

Considering the flow pattern map, the vapor and liquid phase torque flux values are low. Find the annular/foaming/slug/bubble flow pattern that happens to working fluids with water, aspect ratio 5, two-phase closed-circuit cross-sectional thermosyphon (TPTC), 7mm internal diameter, 80 and 90o slope angle, 70 and 90oC evaporator temperature . Considering the flow pattern map, the momentum flux in the vapor and liquid phases is much higher than that in regions 1 and 2, it is found that the Churn/Slug/Bubble flow pattern occurring in the two-phase closed rectangular section thermosyphon (RTPTC) internal diameter 25.2 mm aspect ratio 5, inclination angle 80o, evaporator temperature 70 and 90 oC uses water as working fluid.

In addition, it happens with two-phase closed circuit thermosyphon (TPTC) with inner diameter 25.2 mm ratio 5, inclination angle 80o, evaporator temperature of 90 oC use silver nanofluid as working fluids. In ratio 5 in length is relatively short in the section of the evaporator during the boiling of working liquids. When the flow pattern map is considered, the momentum flux in the vapor phase and liquid phase is higher than all the flow patterns.

Conclusion

Summary of experimental results

Inclusion in the tilt angle of 80o also helps to reduce the flow problem between the working fluids in the condensed liquid state ready to flow back into the evaporator section and the working fluid that is in the vapor phase rising from the evaporator section. The working fluids that are in a fluid weight phase will flow next to the side of the pipe with an inclined position. Helps provide liquidity in the flow of two-phase flow patterns that are in the gas and liquid phases.

This directly affects the speed of movement of the vapor bubble moving upwards to cool the condenser section, leading to an increased heat transfer rate. Where the flow pattern region annular/churn/slug/bubble provided the highest heat transfer value per unit area with a two-phase closed circle thermosyphon (TPTC) with an inner diameter of 7 mm. And the flow pattern area Annular/Churn/Slug/Bubble gives the lowest heat transfer value per unit area by testing the working fluids as water, two-phase closed circle thermosyphon (TPTC), inner diameter 7mm, aspect ratio 5, inclination angle 80 and 90o, and two-phase closed thermosyphon with rectangular cross section (RTPTC) inner diameter 25.2 mm, aspect ratio 20, inclination angle 90o due to the working fluid with the latent heat of high evaporation.

Suggestions

Which directly affects the rate of heat transfer from the evaporator section to the bottom of the condenser. Parametthanuwat, “Heat transfer behavior of silver particles containing oleic acid surfactant: application to two closed phases. Srimuang W and kritacom B., "Waste heat recovery using two-phase flat closed thermosyphons (FTPCT) with silver nano powder - water mixture as working fluid for air preheater." Nakhon Ratchasima, Thailand, 2014.

9] Parametthanuwat T., Heat transfer characteristics of closed two-phase thermosyphon (TPCT) containing silver nanofluids with oleic acid surfactant. Inner diameter of rectangular closed two-phase transverse thermosyphon (RTPTC) 25.2 mm, length of evaporation section 126 mm. 50% filling rate of the volume of the evaporation section with thermosyphon with closed two-phase rectangular cross-section (RTPTC) internal 25.2 mm, length of the evaporation section 126 mm.