Experimental study on overall heat transfer coefficient of seawater on three tube arrangements for horizontal-tube falling film evaporator

Abstract

In this paper, two sets of experimental devices have been established for studying the falling film evaporation outside a horizontal tube and condensation inside a horizontal tube, with three different tube arrangements and seawater as the experimental fluid. The rules of the overall heat transfer coefficient (K) are determined by changing saturation temperature (T), Reynolds number (Re), total temperature difference (ΔT), inlet steam velocity (v_s), and vapor quality (x). Experimental results indicate that the overall heat transfer coefficient of the rotated square arrangement (K_rs) is higher than that of the triangular arrangement (K_t), and the square one (K_s) is the lowest with less impact on Re, T, ΔT, v_s, or x changing. With Re increasing, the K increases first and then declines, especially when Re > Re_cr, K_rs and K_t are almost the same. The increment of T and ΔT leads to the decreasing of the K, while v_s has little effect on the K. The growth of x contributes a lot to the increment of the K. In the evaporator, the vapor quality contributes a lot in the horizontal direction, while Re is more influential in the vertical direction.

Keywords:

• Horizontal-tube falling film
• Overall heat transfer coefficient
• Tube arrangement
• Desalination
• Seawater

Acknowledgment

The authors are gratitude for the financial supported by Chinese National Natural Science Foundation Project Numbers 51406024, 51336001, China Postdoctoral Science Foundation funded project (2014M551079), and Fundamental Research Funds for the Central Universities (DUT15LAB14).