![Sample our Engineering & Technology journals, sign in here to start your access, latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5933/TOC-Subject-Sample-2021-Engineering-Tech.jpg"})
ABSTRACT
The enhanced heat transfer performance of falling film evaporation during desalination through altering smooth tubes by corrugated tubes was investigated. An experimental research on corrugated and smooth tubes was carried out using a horizontal-tube falling-film evaporation heat transfer experimental apparatus. The changes in heat transfer coefficient with the process parameters (sprinkling density, heat flux, heat transfer temperature difference, and evaporation temperature) were obtained according to the experimental data. The influence of tube type on liquid-film distribution outside the tube was also examined by numerical simulation. Results showed that within a certain scope increasing of any one variable of sprinkling density, heat flux, and evaporation temperature has a positive impact on the heat transfer coefficient. When the sprinkling density exceeded 0.178 kg/(m·s), the heat transfer coefficient tended to be stable. Compared with the simulation results, the liquid film coverage and thickness outside the tube significantly influenced heat transfer efficiency. When the heat flux exceeded 130kW/m2, the growth of the heat transfer coefficient significantly slowed down. Under the same experimental conditions, the heat transfer coefficient of corrugated tubes increased by 30% compared with that of smooth tubes. In addition, the content of non-condensable gas within the seawater affected the heat transfer coefficient significantly.
Nomenclature
| de | = | Equivalent diameter of heat-transfer tube, m |
| G | = | The mass flow rate of the water sprayed outside tube bundle, kg/s |
| G1 | = | Condensed water quantities of primary vapor, kg/s |
| G2 | = | Condensed water quantities of secondary vapor, kg/s |
| hg | = | Enthalpy of secondary saturated steam, kJ/kg |
| hw | = | Enthalpy of saturated water at corresponding temperature, kJ/kg |
| K | = | Heat-transfer coefficient, W/(m2·°C) |
| L | = | Length of heating zone, m |
| N | = | The number of heat transfer tubes each layer |
| Q | = | Heat flux, kJ/m2 |
| Q1 | = | The quantity of heat released during the condensation of the primary steam, kJ |
| Q2 | = | The quantity of heat absorbed by the spraying water during evaporation, kJ |
| Qav | = | The average energy exchanged by the evaporator, kJ |
| T | = | The feed liquid temperature, °C |
| T | = | The saturated steam temperature inside the tube, °C |
Greek Symbols
| γ | = | Latent heat of vaporization of primary saturated steam, kJ/kg |
| ρ | = | The density of condensate, kg/m3 |
| Δt | = | Heat-transfer temperature difference, °C |
| Γ | = | The sprinkling density, kg/(m·s) |
Acknowledgments
The authors are grateful for the support of the National Science & Technology Pillar Program during the Thirteen Five-year Plan Period No. 2016YFB0301205. This paper is also supported by the key technologies R&D program of Tianjin No. 17YFZCSF00910 and Tianjin technical cooperation R&D and industrialization projects for the belt and road initiative No.18YDYGHZ00100.