S. Rittidech

Application of silver nanofluid containing oleic acid surfactant in a thermosyphon economizer.

This article reports a recent study on the application of a two-phase closed thermosyphon (TPCT) in a thermosyphon for economizer (TPEC). The TPEC had three sections of equal size; the evaporator, the adiabatic section, and the condenser, of 250 mm × 250 mm × 250 mm (W × L × H). The TPCT was a steel tube of 12.7-mm ID. The filling ratios chosen to study were 30, 50, and 80% with respect to the evaporator length. The volumetric flow rates for the coolant (in the condenser) were 1, 2.5, and 5 l/min. Five working fluids investigated were: water, water-based silver nanofluid with silver concentration 0.5 w/v%, and the nanofluid (NF) mixed with 0.5, 1, and 1.5 w/v% of oleic acid (OA). The operating temperatures were 60, 70, and 80°C. Experimental data showed that the TPEC gave the highest heat flux of about 25 kW/m2 and the highest effectiveness of about 0.3 at a filling ratio of 50%, with the nanofluid containing 1 w/v% of OA. It was further found that the effectiveness of nanofluid and the OA containing nanofluids were superior in effectiveness over water in all experimental conditions came under this study. Moreover, the presence of OA had clearly contributed to raise the effectiveness of the nanofluid.

The Influence of Pretreatment Techniques on Ash Content of Cassava Residues

Cassava residues (cassava stalk and cassava rhizome) were subjected to pretreatment techniques with an aim to reduce their ash content. The effects of biomass size reduction, water washing, water-washing temperature, and acid washing on the ash content of the residues were investigated. The results showed that although most simple method, ash could be removed by biomass size reduction and selection. In washing biomass with water, it was found that both washing time and temperature were major variables affecting the ash content. The ash content decreased with washing time. Increasing the washing temperature to 80°C did not significantly reduce further ash until the washing time was 24 h. In addition, the acid washing was concluded to be the most effective technique for ash removal. The ash contents of the cassava stalk and rhizome were decreased from 5.04% to 1.94% and 4.99% to 2.26%, respectively, after washing with dilute HCl solution for 3 h.

Flow patterns and heat-transfer characteristics of a top heat mode closed-loop oscillating heat pipe with check valves (THMCLOHP/CV)

The aim of this research was to investigate the flow patterns and heat transfer of a top heat mode closed-loop oscillating heat pipe with check valves (THMCLOHP/CV). In this study, the heat pipe was made of a high-quality glass capillary tube with an inner diameter of 2.4 mm bent into 10 meandering turns. The number of check valves was 2 and the tube was filled with R141b at a filling ratio of 50% of internal volume of the tube. The combined lengths of the evaporator, adiabatic and condenser sections were equal to 50 mm. The pipe was operated at the top heat mode, and the angles of inclination were 20°, 40°, 60°, 80°, and 90°. The heat applied at the evaporator section was controlled at 85°Cto 105°C, and 125°C. The results show that in the evaporator section, bubbles are produced and grow as a result of the continuous nucleate boiling. They coalesced and their volume expanded. Similarly, in the condenser section the vapor plug condensate caused the bubbles to collapse and accumulate as a liquid mass at the lower section of the U-bend tube. A new slug then developed and the bubbles coalesced in an upward flow. Heat flux increased when the evaporator temperature and inclination angle increased causing the average length of the vapor plug to decrease and the average velocity of vapor plug to increase. The maximum heat flux occurred at an evaporator temperature of 125°C and an inclination angle of minus 90°.

Grey-Taguchi method to optimize the percent zinc coating balances edge joints for galvanized steel sheets using metal inert gas pulse brazing process

The objective of this work was to optimize the percent zinc coating balances edge joints of galvanized steel sheets using the metal inert gas pulse brazing process. The Taguchi method and grey relational analysis were used to determine the relationship between the metal inert gas pulse brazing process parameters and percent zinc coating balances edge joints. The metal inert gas pulse brazing process parameters used in this study included wire feed speeds, arc voltages, travel speed, peak currents, and pulse frequency. The characteristics of metal inert gas pulse brazing process that were considered to find response were percent zinc coating balances edge joints on the upper edge joint (PZBEJ1), the lower edge joint (PZBEJ2), and the back sides of the edge joint (PZBEJ3). Analysis of variance was performed to determine the impact of an individual process parameter on the quality parameters. The results showed that the optimal parameters in which grey relational grade increases at the highest level were wire feed speeds at 3.25 m/min, arc voltages at 16 V, travel speeds at 0.9 m/min, peak currents at 425 A, and pulse frequency at 35 Hz. These parameters gave a 74.90% higher response value than those of the initial parameters of metal inert gas pulse brazing process.

Loop Thermosyphon with Vapour Chamber: A Thermodynamic Study

This research presents a case study of the rating heat transfer of a loop thermosyphon with a vapour chamber (LTVC). The dimensions of the evaporator chamber were 200 × 200 × 55, 200 × 200 × 65 and 200 × 200 × 75 mm (W × L × H). The adiabatic and condenser section had an 8-loops thermosyphon. The length of the adiabatic and condenser section in each loop was 824 and 800 mm, respectively. The air velocity was 0.5, 1.0, and 1.5 m/s with the heat input being 600, 900, and 1,200 W. The three working fluids were: water, ethanol, and R-11 with filling ratios of 20, 40, and 60% with respect to the chamber volume. The experimental data showed that the LTVC yielded the value of the relative thermal efficiency of about 1 at R-11, a filling ratio of 60%, a velocity of 0.5 m/s, and an aspect ratio of 2.5 in the study conditions. It was further found that the larger vapour chamber was superior in the rating of the heat transfer over other vapour chambers in all experimental conditions in this study.

The Helical Oscillating Heat Pipe: Flow Pattern Behaviour Study

This research aims to study the effect of evaporator temperature, pitch distance, and working fluid on the internal flow pattern and the heat transfer characteristics of the helical oscillating heat pipe. A Pyrex tube with an inner diameter of 2.4 mm was used to study the flow pattern in the evaporator section. The pitch distance varied at 1, 1.5, and 2 cm. Water and R-123 were used as working fluid with a filling ratio of 80% by total volume. In the evaporator section, the water temperature varied at 60, 75, and 90°C to supply heat to the heat pipe. In the condenser section, air with a temperature of 25°C was used as heat sink. From the results, it was found that 4 internal flow patterns, bubble flow, slug flow, annular flow, and stratified wavy flow, were observed in the evaporator section for both working fluids. The heat transfer rate decreased when the pitch distance was increased from 1 to 2 cm. The maximum heat flux was 2,132.6 and 1,773.4 W/m2 for the working fluid of R-123 and water, respectively. Both occurred at a pitch distance of 1 cm and an evaporator temperature of 90°C.

Three-dimensional transient mathematical model to predict the heat transfer rate of a heat pipe

A three-dimensional model was developed to simulate the heat transfer rate on a heat pipe in a transient condition. This article presents the details of a calculation domain consisting of a wall, a wick, and a vapor core. The governing equation based on the shape of the pipe was numerically simulated using the finite element method. The developed three-dimensional model attempted to predict the transient temperature, the velocity, and the heat transfer rate profiles at any domain. The values obtained from the model calculation were then compared with the actual results from the experiments. The experiment showed that the time required to attain a steady state (where transient temperature is constant) was reasonably consistent with the model. The working fluid r134a (tetrafluoroethane) was the quickest to reach the steady state and transferred the greatest amount of heat.

Two-phase flow patterns of a top heat mode closed loop oscillating heat pipe with check valves (THMCLOHP/CV)

This research is aimed at studying the two-phase flow pattern of a top heat mode closed loop oscillating heat pipe with check valves. The working fluids used are ethanol and R141b and R11 coolants with a filling ratio of 50% of the total volume. It is found that the maximum heat flux occurs for the R11 coolant used as the working fluid in the case with the inner diameter of 1.8 mm, inclination angle of −90◦, evaporator temperature of 125◦C, and evaporator length of 50 mm. The internal flow patterns are found to be slug flow/disperse bubble flow/annular flow, slug flow/disperse bubble flow/churn flow, slug flow/bubble flow/annular flow, slug flow/disperse bubble flow, bubble flow/annular flow, and slug flow/annular flow.

Corrosion mechanism in a closed-loop oscillating heat-pipe with check valves (CLOHP/CV)

Purpose – The purpose of this paper was to study the parameters affecting corrosion of the closed-loop oscillating heat-pipe with check valves (CLOHP/CV) in a system in clear that will be basic data to be used in future research. The majority of research focuses on the inner surface corrosion heat-pipe systems. The CLOHP/CV is commonly favored in cooling electronic devices, etc. Despite these common applications, limited reliable experimental research findings are available on the operation of the CLOHP/CV. Because of these reasons, the lack of detailed data, working fluids effect, working temperatures and duration of testing of the CLOHP/CV, this study focuses on determining the actual inner surface corrosion. Design/methodology/approach – Seven types of copper tubes used in the CLOHP/CV set were sectioned to observe their inner surfaces. Seven different specimens with tube corrosion were examined by a visual inspection, scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX). T...

A correlation to predict heat-transfer rates of a miniature loop thermosyphon

This research is aimed at enhancing the traditional thermosyphon by preventing flooding and drying out from the opposite directions of the vapor and liquid. A miniature loop thermosyphon (MLT) consists of three sections, namely, the evaporator, the adiabatic and condenser sections. The return liquid channel is connected between the condenser and the evaporator to convey the condensed liquid. The MLT has a ratio of internal diameter of the condenser section to internal diameter of the evaporator section (Idc/Ide), which is 1.4. The MLT was made from a copper tube of 15-mm, 19-mm, and 22-mm ID. The filling ratios of the working fluid were 30%, 50%, and 80% of evaporator volume with an inclination angle of 90°. The operating temperatures were 70°C, 80°C, and 90°C with ratios of Ide/Idr of 3, 3.8, and 4.4. The research reports the effect of dimensionless parameters on heat-transfer characteristics, namely, Bo, Pr, We, Fr, Ja, Ku, ρυ/ρl, and Ide/Idr. It was found that the Bo, Pr, Ja, Ku, ρυ/ρl, and Ide/Idr have no effect on heattransfer characteristics. The We, Fr, and Ku have an effect on the heat-transfer characteristics as with increasing We, Fr, and Ku, the heat-transfer characteristics decrease. The research established another modified Kutateladze number, which can also be used to predict MLT in the vertical position.