Experimental study of heat transfer of ultra-supercritical pressure water in vertical upward internally ribbed tube

Under ultra-supercritical pressure, the heat transfer characteristics of water in vertical upward 4- head internally ribbed tubes with a diameter of 28.65mm and thickness of 8mm were experimentally studied. The experiments were performed at P = 25- 34MPa, G = 450- 1800kg/（m^2·s） and q = 200 600kW/m^2. The results show that the pressure has only a moderate effect on the heat transfer of uhra-supercritical water when the water temperature is below the pseudocritical point. Sharp rise of the wall temperature near the pesudocritical region occurs earlier at a higher pressure. Increasing the mass velocity improves the heat transfer with a much stronger effect below the pesudocritical point than that above the pesudocritical point. For given pressure and mass velocity, the inner wall heat flux also shows a significant effect on the inner wall temperature, with a higher inner wall heat flux leading to a higher inner wall temperature. Increasing of inner wall heat flux leads to an early occurrence of sharp rise of the wall temperature. Correlations of heat transfer coefficients are also presented for vertical upward internally ribbed tubes.

Experimental Study on Cross-Flow Induced Vibrations in Heat Exchanger Tube Bundle

Vibration in heat exchangers is one of the main problems that the industry has faced over last few decades. Vibration phenomenon in heat exchangers is of major concern for designers and process engineers since it can lead to the tube damage, tube leakage, baffle damage, tube collision damage, fatigue, creep etc. In the present study, vibration response is analyzed on single tube located in the centre of the tube bundle having parallel triangular arrangement （60-） with P/D ratio of 1.44. The experiment is performed for two different flow conditions. This kind of experiment has not been reported in the literature. Under the first condition, the tube vibration response is analyzed when there is no internal flow in the tube and under the second condition, the response is analyzed when the internal tube flow is maintained at a constant value of 0.1 rn/s. The free stream shell side velocity ranges from 0.8 rn/s to 1.3 m/s, the reduced gap velocity varies from 1,80 to 2.66 and the Reynolds number varies from 44500 to 66000. It is observed that the internal tube flow results in larger vibration amplitudes for the tube than that without internal tube flow. It is also established that over the current range of shell side flow velocity, the turbulence is the dominant excitation mechanism for producing vibration in the tube since the amplitude varies directly with the increase in the shell side velocity. Damping has no significant effect on the vibration behavior of the tube for the current velocity range.

Ammonia corrosion analysis of copper tubes and experimental research on non-copper improvement for heat exchanger in power plant

Ammonia corrosion in copper tube will affect the safety of boiler running in power plant. Therefore, no copper in heating system has become a technical orientation in heat exchanger reconstruction, This paper analyzes the condition and mechanism of ammonia corrosion occurring in copper tube used in coal-fired power plants. Using a general steam condensation testing equipment only for horizontal single tube, with water vapor and water as working fluid, on two types of steel tube with 2-side enhancement heat transfer, namely, a spirally fluted tube and a ratchet tube with internal spiral groove （RISG tube） which was developed recently, a set of experimental tests are conducted to investigate the characteristics of heat transfer and hydromeehanics. In order to compare easily, both one copper smooth tube and one steel smooth tube are also used in the experiment. The experimental results, which get from single horizontal tube, show that the overall heat transfer coefficient of steel spirally fluted tube are improved by 10%o to 17%, and that of the steel RISG tube（22%-28%） is better than steel spirally fluted tube, its flow resistance coefficient is only increased by 22% to 66% when compared with smooth tube. Based on a lot of experimental data, the steel spirally fluted tube and the steel RISG tube were applied in a low pressure preheater and an oil-cooler of some or other power plant respectively. The field testing results showed that their heat transfer coefficient with each types of enhancement heat transfer tubes were improved by 2.5% and 21%-45% comparing with copper smooth tube heat exchangers. Both basic and field experiment indicates that the steel tube with 2-side enhancement heat transfer is an ideal choice for heat exchanger reconstruction in no copper issue in power plants.

Thermal test and numerical simulation of cooling stave with internal ribbed tube

A new type of cooling stave with internal ribbed tube was proposed,and the heat transfer performance of the stave was studied by means of thermal test and numerical simulation.The temperature of cooling stave was monitored in the conditions of furnace gas temperature of 200-700 C and cooling water velocity of 0.2-1.0 m/s.The thermal test results show that the internal rib structure can form swirl in the water pipe and improve the cooling capacity of the cooling stave.The higher the furnace temperature or the lower the cooling water flow rate,the more obvious the advantage of the cooling stave with internal ribbed tube.The mathematical model of the cooling stave with internal ribbed tube was established by FLUENT software,and the influence of the internal rib structure parameters on the heat transfer performance of the cooling stave was discussed.It is suggested that the parameters of the internal ribbed tube should be 4 ribs,1 mm in height,5-7 mm in width,and 20-30 mm in lead.In the same common working conditions of the cooling stave,the maximum temperature of the newly designed cooling stave with internal ribbed tube is reduced by 5.6%compared with that of common cooling stave with round tube.The water flow rate in the internal ribbed tube only needs 0.9 m/s to reach the cooling effect of 2 m/s in the common tube cooling stave,which can save 55%of water.In case of water shortage accident of cooling stave,the maximum temperature of the cooling stave with internal ribbed tube is decreased by 22.4%compared with that of common round tube,which can effectively reduce the harm of water shortage and protect the cooling stave.

Heat Transfer Characteristics of Laminar Flow in Internally Finned Tubes under Various Boundary Conditions

Numerical solutions for fully developed laminar flow in internally finned tubes with trapezoidal and triangular fin profiles were given with Finite Element Method (FEM): The heat transfer characteristics were obtained and compared under the boundary conditions of uniform heat flux, uniform wall temperature, and the third boundary condition with finite wall thermal conductivity considered. The numerical results show that boundary conditions have pronounced effects on the temperature field.Furthermore, a new mechanism on the heat transfer augmentation of internally finned tubes is proposed.