TIV and PIV based natural convection study over a square flat plate under stable stratification. (September 2019)

• Record Type: Journal Article
• Authors: Fan, Yifan; Li, Yuguo; Wang, Qun; Yin, Shi
• Is Part Of: International journal of heat and mass transfer. Volume 140(2019)
• Page Start: 660
• Page End: 670
• Publication Date: 2019-09
• Subjects: Natural convection -- Heat transfer -- Stable stratification -- Thermal image velocimetry -- Isolated square heat surface -- Urban heat island circulation; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2019.06.031
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: Natural convection under stable stratification is important and lack of study. TIV and PIV are used to investigate the convective flow and heat transfer. Different types of turbulent eddy structures are identified and analyzed. Diagonal inflow and side outflow present over an ideal square heated area. TIV results are verified by PIV and have potential applications in other fields. Abstract: Natural convection over an isolated horizontal plate in a stably stratified background condition is fundamental and challenging in industrial, atmospheric, geographical, and oceanic environmental studies, which, however, is still lack of investigation. In this study, the water tank modelling experiment with two main techniques, Thermal Image Velocimetry (TIV) and Particle Image Velocimetry (PIV), was conducted to investigate large eddy structures, the mean velocity field and heat transfer over an idealized square heated surface under the stable stratification. Shirking, growing and twisting eddy structures were identified in this study. By measuring the velocity fields at different horizontal planes with varied heights, an asymmetric flow structure over a square urban area is suggested by the PIV method to be characterized as the main diagonal inflow at lower levels and as the side outflow (perpendicular to edges) at upper levels. The mean flow speeds measured by TIV and PIV were quantitatively compared and analyzed by using cross-correlation coefficients. The low-level (2 mm or less above) velocity field measured by TIV also well presents the similar characteristics of near-surface diagonal inflow observed in the PIV measurements. Consequently, the reliability of the TIV method in this study is well verified for resolving the near-surface convective flow fields. The stable stratification is found to significantly impair the heat transfer efficiency as results indicated that the heat transfer in a stable environment is significantly weaker than that in a neutral environment by 71%.