Comparative study on steady and unsteady heat transfer analysis of a spherical element using air/water mist two-phase flow

Abstract

In this study, two approaches to investigating the process cooling of a heated sphere were performed using air as well as air/water mist two-phase flow. Steady-state and unsteady heat transfer analysis were compared in the terms of the average surface temperature and heat transfer rate between the sphere surfaces and the cooling fluid. When the Bi<0.1, the temperature variation inside sphere can be neglected and the wildly known lumped capacitance model can be applied to estimate the heat transfer coefficient by measuring the sphere surface temperature. The effect of the different factors such as the inlet Re numbers, surface temperature and water mist rate on heat transfer characteristics are examined. The experimental results showed that the presence of water mist leads to a significant increase in heat transfer rate over the use of air coolant alone. Also, the unsteady thermal behaviors of the water mist impingement on the heated surface and dynamicstate of cooling process changing over the sphere surface were analyzed experimentally based on the unsteady surface temperature measurements. The experimental results of the unsteady heat transfer were compared to the results obtained from steady-state estimation under the corresponding surface temperature of the sphere. Moreover, the new proposed empirical correlation for the Nusselt number based on the present experimental data are given for practical uses. Results reasonably agree well within ±3.8%.

Investigation of air-cooled condenser’s operating parameters in modern thermal power plant

“…Particularly for these reasons, a number of researches have been conducted with a goal to find an optimal direction for further improvement of the air-cooled condenser design, [8][9][10][11][12]. Also, the complex phenomena governing the function of air-cooled condensing devices have also been the field of interest of numerous authors, [13][14][15][16].…”

Water-air aerosol cooling of rows of cylindrical elements under conditions of natural convection

“…The majority of published researches of enhancement of dry cooling methods thermal efficiency considers the variants with forced air movement and humidifying by water micro-drops (aerosol) [7][8][9][10][11][12][13]. This way of cooling increases significantly the efficiency of heat exchange, at the same time reducing the amount of water fed to the cooling air [14][15][16], but it demands the additional expenditure of energy for air-supply blowers' drive.…”

A CFD study on the evaporative cooling of a water droplet located in a duct

“…The problem of multi-phase flow and particularly an air-water interface is seen in a wide variaty of natutal and engineering applications ranging from direct evaporative cooler to spray room to printers to human body (Mahdavi et al, 2020;Abed et al, 2020aAbed et al, , 2020bJia & Qiu, 2003;Betelin et al, 2012;Semenov et al, 2011). More specifically, the presence of a droplet in a surrounding environment with different features is of great importance (Jia & Qiu, 2003;Semenov et al, 201;Norouzi et al, 2019;Fisenko & Khodyko, 2009), The problem can be even more complicated with the existence of heat transfer between two lquids and cooling phenomenon which is somewhat pratical.…”