Experimental investigation of heat transfer characteristics of steam generator with circular-ring turbulators

Heat transfer has been improved by creating turbulence in the fluid flow of heat exchangers through introducing various techniques. The present study investigated the heat transfer characteristics of steam generator with circular-ring tabulators with an inclination angle of 45° and a blocked ratio (BR) of 0.20 mm. The length ratios (LR) of 25%, 50%, 75% and 100%, pitch ratios (PR) of 1.0, 2.0, 3.0 and 4.0 and water flow rates of 12, 24 and 36 l/h were studied. The heat source used waste lubricating oil as fuel to produce steam. The results showed that the heat exchanger with circular-ring inserts provided a higher steam rate than that of a smooth tube by 6.88–10.35%, vapor quality (x) by 0.21–0.92, heat transfer by 1.27–1.55 times and the thermal efficiency by 0.46–0.68 depending on the PR, LR and FR. The optimum insert ratio was LR = 50% while 75% and 100% were not significantly different. The circular-ring inserts changed the flow behavior to turbulent flow. This increased the surface area, causing boundary layer interruptions leading to more heat exchange on the tube surface

Mathematical model to predict heat transfer in transient condition of helical oscillating heat pipe

This research aims to study the heat transfer with a numerical model and experimental evaluation of a helical oscillating heat pipe (HOHP). Firstly, we created a numeric model of the HOHP to predict the time required to reach the steady state temperature and the heat transfer of the HOHP under transient conditions. Secondly, we measured the temperature at the pipe wall and evaluated the heat transfer rate from experiments and compared them with the numeric model. The results showed that the transient temperature and the heat transfer profiles of the HOHP from the numerical model were similar with the results measured from the experimental data. The results from numeric model predicted temperature profiles for attaining a steady state temperature were in close agreement, when compared to the numerical simulation of Boothaisong et al. (2015)

The rectangular two-phase closed thermosyphon: A case study of two-phase internal flow patterns behaviour for heat performance

This research explored different types of two-phase flow patterns that influenced heat transfer rate by assessing rectangular two-phase closed thermosyphon (RTPCT) made from glass with the sides of equal length of 25.2 mm, aspect ratio 5 and 20, evaporation temperature of 50, 70, and 90°C, working substance addition rate of 50% by volume of evaporator, and water inlet temperature at condensation of 20°C. Upon testing with aspect ratios 5, three flow patterns emerged which were: bubble flow, slug flow and churn flow respectively. As per the aspect ratio 20, four flow patterns were discovered which were: bubble flow, slug flow, churn flow and annular flow, respectively. Aspect ratio 5 pertains characteristic which resulted in a shorter evaporation rate of the RTPCT than that of the aspect ratio 20, thus, a shorter flow distance from the evaporator section to heat releaser was observed. Therefore, flow patterns at aspect ratio 5 exhibited a faster flow velocity than that of the aspect ratio 20. Furthermore, changes of flow pattern to the one that is important for heat transfer rate can be easily achieved. Churn flow was the most important type of the flow for heat transfer, followed by slug flow. Moreover, with aspect ratio 20, annular flow was the most important flow for the heat transfer, followed by churn flow, respectively. Throughout the test, average heat flux as obtained from the aspect ratio 5 were 1.51 and 0.74 kW/m2 which were higher than those of the aspect ratio 20. The highest heat flux at the operating temperature of the evaporator section was 90°C, which was equivalent to 2.60 and 1.52 kW/m2, respectively

การทำนายอัตราการถ่ายเทความร้อนในเงื่อนไขสถานะชั่วครู่ของเครื่องแลกเปลี่ยนความร้อนชนิดท่อความร้อนโดยใช้แบบจำลองสามมิติ

วารสารวิชาการและวิจัย มทร.พระนคร, 10 (1) : 51-64The aim of this study was to develop a three-dimensional transient condition model to predict the heat transfer rate of a heat pipe heat exchanger. This paper presents the details of the calculated domains, which consist of the wall, wick, and vapor core. They were numerically simulated using the finite element method. The heat transfer rate values obtained from the model simulation can be used to design heat pipe heat exchangers. The values obtained from the model calculation were then compared with the results from experiments, and the differences were 10.3%, 10.4%, and 6.7% for the working fluids of distilled water, ethanol, and R134a, respectively. The working fluids of distilled water, ethanol, and R134a obtained heat transfer rates of 627.3 watts, 522.8 watts, and 836.4 watts from the experiments, respectively.Rajamangala University of Technology Phra Nakho