Yanyang Wu

Experimental study on convective heat transfer in tube-side of water jacket-tube heat exchanger by electrohydrodynamics effect

The electrohydrodynamics (EHD) enhancement of convection heat transfer of water in a jacket tube heat exchanger was studied through an experimental method in this paper. In the experiment, a DC high voltage electrode was set in the central tube-side of the heat exchanger, and the high voltage electrode in the tube-side was adjustable in the range of 0–40 kV. Five different combinations of heat transfer enhancement experiments were conducted under the different voltage and rate of flow. The results indicate that the maximal enhancement coefficient θ is 1.224 when the flow rate of tube-side inlet is 0.1 m3/h. It is proved that, for the work medium of water, the convective heat transfer can be enhanced by applying high electric field. The performance of EHD-enhanced is sensitive to the variation of flow rate, and in the same flow rate, there exist an optimized voltage in the EHD-enhanced process rather than the monotonic positive-correlation relationship.

Numerical Simulation on Flow and Heat Transfer at Shell-Side of Flat-Tube Heat Exchangers

The fluid flow and heat transfer of the shell-side in one type of flat-tube heat exchangers (FHE) were studied through numerical simulation and experimental methods. In the numerical simulation, hot/cold air was set as working fluid, and the standard k-ɛ turbulence model supplemented by boundary conditions was used, and also the control volume method was used to the discrete control equations. Compared with the same type of circular-tube heat exchangers (CHE), the numerical simulation results show that the pressure drop at the shell-side of FHE decreases by 12%–20%, and heat transfer coefficient increases by about 24%. The coefficient of integral performance Nu/ζ 0.29 has an increment of 22%–34%. Under the same conditions, the experimental results of temperature and the overall pressure drop show that the deviation percentage with those of numerical simulation are less than 8% and 25%, respectively. Both results verify that the heat transfer efficiency and flow resistance characteristics of FHEs are superior to that of CHEs.

Numerical simulation on convection heat transfer of pulsating flow in corrugated tube

The influence of pulsating flow on convection heat transfer in corrugated tube is studied through numerical simulation at case of different pulsating amplitude and different. pulsating frequency. In the numerical simulation, heat transfer wall use constant wall temperature. the numerical simulation results show that pulsating flow can results in fluctuation of temperature and pressure lies on center of flow export around the steady state in corrugated tube; compared to steady state, with the introduce of pulsating flow, the average pressure drop Pave in corrugated tube has increased with the increase of the pulsating amplitude; the average Nusselt number Nuave in corrugated tube with the introduction of pulsating flow is less than the one in the steady state, it indicate that pulsating flow can not enhance the convective heat transfer in corrugated tube.

Influences of vertically staggered blades arrangement and draft-tubes spacing field on the flow shear stress in the vertical impinging stream reactor

Flow turbulence intensity is one of the most important indexes in measuring the shear performance of vertical impinging stream reactor (VCISR). The staggered forms of the upper and lower blades and the distances among draft-tube are the significant factors affecting the turbulence intensity in the reactor. In order to explore the law that the structure parameters impact the internal flow field, a series of the numerical simulations are employed to investigate the flow field under different conditions, including various vertically staggered arrangement and diverse draft-tubes spacing in the VCISR. The inclination angle of the blades is set as 45° and the rotate speed is adjusted as 900rpm. The staggered angles β of two paddles are set as 15°, 30°, 45°, 60°, respectively. Two draft-tubes spacing L are set as 8, 10, 12, 14 cm, severally. The computation results show that the turbulence intensity on the characteristics impact surface is the maximum under the condition of β=30°, L=12 cm, at the same time the shear stress is also maximal. In this paper, power consumption and rotating moment of blades are discussed in the reactor. When β=15° and L=8 cm, consuming energy of the reactor and the energy consumption under unit average intensity are minimum; the moment of the rotated blades is minimum at β=30°, L=12 cm. All the results provide the references for selection of the reactor motor and the materials of rotation axes as well as energy consumption.

Numerical simulational study on convective heat transfer process in tube-Side of Water Jacket-tube enhanced by Electrohydrodynamics

Aiming at the characteristics of Electrohydrodynamics(EHD)enhancement of boiling heat transfer, based on the fluid mechanics theory and the heat and mass transfer theory, theory of electromagnetism, heat-mass transfer, electromagnetic, the model of the tube-Side of Water Jacket-tube was established with water as working fluid, the numerical method was employed to simulate the EHD-enhanced coefficient in the different DC high voltage under the same conditions, then the numerical results compared to the experiment. The result shows that the convective heat transfer can be enhanced by applying high electric field. The growth of the heat transfer coefficient was not obvious when the applied electric voltage was 0 – 10kV. But the growth changes remarkably as the voltage continues to rise. The error of the strengthen heat transfer coefficient between the numerical simulation and experimental result is 43%.