Influence of tube diameter and steam flow rate on heat transfer in a vertical pipe of condenser: experimental investigation of copper pipes

journal article in Scopus

en

The overall condensing power at condensers is affected by many factors. A condensate film on the pipe wall plays a crucial role in heat transfer. The velocity of the gas phase inside the tubes has a fundamental influence on the movement of the liquid film and the specific course of the velocity profile in the condensate film. The magnitude of the shear stress at the steam-condensate interface affects the film thickness and its integrity. This paper presents a study to evaluate the effect of the flow velocity inside a vertical pipe on the heat transfer coefficient during water vapour condensation. Specifically, steam flow on heat transfer for two different pipes is evaluated, namely with inner diameters 16 and 26 mm. A common feature is a detailed investigation of the steam condensation process for a parallel flow and counterflow of steam and liquid film. Furthermore, the influence of the temperature and flow direction of the water cooling the outer side of the condenser tube on the transmitted power is evaluated. The condensation process is experimentally investigated on a copper pipe-in-pipe heat exchanger with a possible change of the direction of the cooling water flow. Determination of the condensation heat transfer coefficient is based on experimental identification of the overall heat transfer coefficient and subsequent inverse calculation of the condensation heat transfer coefficient. The condensation heat transfer coefficient ranges from 3,000 to 6,500 W/(m2∙K) for all configurations measured. The results generally show that as the Reynolds number of steam flow increases, the condensation heat transfer coefficient increases too. At Reynolds number of 35,000 the same heat transfer coefficient value is identified either for parallel flow or counterflow of cooling water. For higher Reynolds numbers, the parallel flow of cooling water enables to reach the higher heat transfer coefficient compared to counterflow configuration. At lower Reynolds numbers, the dependency is reversed.

The overall condensing power at condensers is affected by many factors. A condensate film on the pipe wall plays a crucial role in heat transfer. The velocity of the gas phase inside the tubes has a fundamental influence on the movement of the liquid film and the specific course of the velocity profile in the condensate film. The magnitude of the shear stress at the steam-condensate interface affects the film thickness and its integrity. This paper presents a study to evaluate the effect of the flow velocity inside a vertical pipe on the heat transfer coefficient during water vapour condensation. Specifically, steam flow on heat transfer for two different pipes is evaluated, namely with inner diameters 16 and 26 mm. A common feature is a detailed investigation of the steam condensation process for a parallel flow and counterflow of steam and liquid film. Furthermore, the influence of the temperature and flow direction of the water cooling the outer side of the condenser tube on the transmitted power is evaluated. The condensation process is experimentally investigated on a copper pipe-in-pipe heat exchanger with a possible change of the direction of the cooling water flow. Determination of the condensation heat transfer coefficient is based on experimental identification of the overall heat transfer coefficient and subsequent inverse calculation of the condensation heat transfer coefficient. The condensation heat transfer coefficient ranges from 3,000 to 6,500 W/(m2∙K) for all configurations measured. The results generally show that as the Reynolds number of steam flow increases, the condensation heat transfer coefficient increases too. At Reynolds number of 35,000 the same heat transfer coefficient value is identified either for parallel flow or counterflow of cooling water. For higher Reynolds numbers, the parallel flow of cooling water enables to reach the higher heat transfer coefficient compared to counterflow configuration. At lower Reynolds numbers, the dependency is reversed.

condensation; heat transfer; vertical tube

15.11.2021

The Italian Association of Chemical Engineering

Italská republika

2283-9216

88

2021

601–606

6