Intensification of cooling by a pulsed gas-droplet flow: Equipment, parameters, and results

Flow structure and turbulent heat and mass transfer at the stagnation point of an impact impulse gas-droplet jet

“…This is most likely determined by the fact that an increase in the pulse duration causes an increase in the two phase coolant flow rate; therefore, the probability of the formation of a liquid film and spots on the impact surface increases. This explana tion is confirmed by the results of high speed video filming [20,21]. Within the present model, this effect is disregarded, and calculations of the authors show that when the amount of the gas droplet flow increases, the heat transfer appreciably intensifies because the obstacle surface is always dry and, in this case, the heat transfer will be higher than in the pres ence of a liquid film on the impact surface.…”

“…A large number of experimental, theoretical, and numerical studies have been devoted to investigations of the char acteristics of and heat and mass transfer in steady impact two phase jets [1][2][3][4][5][6][7][8][9][10][11][12]. In addition to acoustic action or the application of piezoelectric activators [13,14], supplying pulses of a two phase flow is one of the methods for active control of the flow structure and heat transfer [15][16][17][18][19][20][21]. It was noted in these papers that, as compared to a steady flow, the main features of pulsed impact jets are an intensified heat transfer, much thinner hydrodynamic and thermal boundary layers, an increased gas phase turbulence level, flow instability, etc.…”

“…The flow structure and heat transfer in a pulsed impact gas droplet jet were experimentally investigated in [19][20][21]. To create a pulsed two phase flow, a multiple nozzle device is used, which consists of 16 fluid sprayers that are arranged in the form of a 4 × 4 matrix and 25 air nozzles.…”

“…It was shown that an increase in the amount of evaporating droplets ini tiates an appreciable increase in the heat transfer (up to several times) in comparison to a single phase pulsed flow. According to data of video observations and a sensor for pressure pulsation measurements [20], when moving from the source to the heat exchanger surface, fluid particles are redistributed inside the air-droplet region of the pulsed spray. Large droplets (120-150 µm) concentrate in the front part of the two phase pulsed flow, and small droplets with sizes of 40-50 µm move in its "tail.…”

Characteristics of the behavior of a liquid film in a pulsed gas-droplet flow

“…The experimental installation is a multifunctional stand consisting of the following units: a programmable multi-jet source of pulsed gas-droplet flow, an automated calorimeter, an automated system for recording the parameters of the flow, which includes original capacitive sensors for recording the thickness and velocity of the liquid film waves [2]. The controlled source of the gas-droplet jet is structurally designed as a two-chamber unit: for air and water.…”