Experimental study on air cooling by spray in the upstream flow of a heat exchanger

Abstract

a b s t r a c tAn experimental study has been carried out on a water sprayed air flow aimed at cooling the air upstream of a heat exchanger in order to improve the heat transfer. A pilot has been built allowing injecting droplets in air in various conditions while controlling flow rates, temperature and humidity. The emphasis has been put on the spray evaporation resulting in a temperature decrease and humidity increase in the air flow. An actual increase in the heat exchanged (up to 3 times more) for an air initially entering in surrounding conditions (temperature between 293 and 308 K and relative humidity between 47.5% and 19.7%) has been reached when injecting upstream droplets smaller than 25 mm, in an air flow crossing the exchanger. A validation of a numerical study on the heat exchanges in the air flow has been also achieved. Results will be applied for the optimization of the water flow providing the best compromise between heat exchanged and water consumption.

Numerical simulation of water spray in natural draft dry cooling towers with a new nozzle representation approach

“…Spray cooling performance is also strongly influenced by air velocity [6,8,9]. Some of the other important parameters are: (a) nozzle cone angle, (b) water injection rate, (c) droplet velocity at nozzle exit, (d) injection direction, and (e) meteorological condition [8][9][10][11][12].…”

Modelling and experimental study of spray cooling systems for inlet air pre-cooling in natural draft dry cooling towers

“…˚C and Twb=9.11 ˚C), the results for 20 µm and 50 µm droplet diameters as well as the corresponding empirical predictions are shown in Figure 4-4 using equation (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19). The results…”

“…A number of experimental studies [15,19,33,37] and computational fluid dynamics models [5,33,38,42,43,45,118] have been carried out on spray cooling performance. Spray is a two-phase flow phenomenon and experience several actions when injected into air including heat, mass and momentum transfer.…”

“…The wetted media enhances evaporation by increasing the water-air contact surface area. However, significant pressure drop is created which reduce air mass-flow rate causing a decline in heat rejection rate [2,19]. Over the past decades, spray cooling has become more popular due to its simplicity, low capital cost, and ease of operation and maintenance [20].…”

“…Spray cooling performance is also strongly influenced by air velocity [20,40,45]. Some of the other important parameters are: (a) nozzle cone angle, (b) water injection rate, (c) droplet velocity at nozzle exit, (d) injection direction, and (e) meteorological condition [19,26,40,43,45].…”