Computational investigation of spray heat exchanger performance

الملخص EN

Enhancement of the heat transfer coefficient is important for the design and operation of heat exchangers.

In this study, a numerical model is built to investigate the performance of spray cooling heat exchanger as water is sprayed on a horizontal tube.

The objectives of the study are to evaluate evaporation rate of the falling water film on a horizontal tube evaporator and obtaining the effect of the distance from the nozzle to the hot tube location on the evaporation rate and on heat transfer effectiveness.

Moreover, the effect of droplet size distribution and the hot tube surface superheating temperature on the evaporation rate are also conducted.

For a certain distance from nozzle distributor to the hot tube surface and by using the equations of mass, momentum and energy of the sprayed droplets, the change on droplet velocity, droplet size and its temperature can be evaluated.

Vapor film is created around the hot tube surface.

In this study, the formed vapor layer thickness around the hot surface, evaporation rate and heat transfer effectiveness were also evaluated.

The heat transfer characteristics are investigated at the considered ranges of the various spraying parameters such as : sprayed mass velocity (sprayed mass flow rate per the unit area of the test tube) which ranged from 2532.1 to 5314.1 kg / m2.s, droplet size (ranged from 128.4 to 300 m), droplet velocity (ranged from 3 to 43.7 m / s ) and sprayed droplet subcooled (ranged from 70 to 7 oC).

The results show that, the evaporation rate and the heat transfer effectiveness are mainly increased by increasing the surface temperature.

Also, the evaporation rate and the heat transfer effectiveness are increased by decreasing the droplet velocity.

At high initial sprayed mass velocity, the evaporated mass flow rate and the heat transfer effectiveness are inversely proportional to the droplet size.

There is an optimum distance from nozzle distributor to the tube surface location at which the maximum evaporated rate will occur.

The comparison between the obtained results and the results due to others shows a good agreement in which the difference between these results was ranged from 4 to 15 %.