Experimental study of crosswind effects on the performance of small cylindrical natural draft dry cooling towers

• A 1:12.5 scaled NDDCT model equipped with a round electric heater has been tested in a wind tunnel.
• The experimental results match well with those of the same-size CFD cooling tower model.
• The experiment verifies that the reversed hot airflow exists near the heat exchanger.
• The heat dumping of NDDCTs under crosswind is a combination of a natural convection and a forced one.
• In small NDDCTs, the forced convection is comparable with the natural convection under fast winds.

Crosswind effect is a common issue which limits the cooling efficiency of natural draft dry cooling towers (NDDCTs) of all sizes. On short NDDCTs with total heights less than 30 m, this effect might be much more significant. Following the authors’ previous numerical investigation on crosswind effects in a 15 m-tall cylindrical NDDCT, an experimental study was carried out and is presented in this paper. The study used a 1:12.5 scaled cooling tower model equipped with an electric resistance heater simulating horizontally placed heat exchangers. The air velocity, temperature, and the heat input on the model were measured at different crosswind speeds in a wind tunnel. Comparisons against CFD models show good agreement between the experimental and numerical results when the similarity conditions between the CFD model and the experimental model are fully satisfied. Based on these results, the total heat transfer rate of NDDCTs was proposed to be a combination of a natural convective heat transfer term and a forced convective one. In small cooling towers, the natural convection term is comparable with the forced convection term. This explains why the correlation of the total heat transfer with the wind speed has a turnabout point below which the heat transfer decreases with increasing crosswind speed and above which it does the reverse. The turnabout point occurs when the sum of natural and forced convection terms is the minimum.