scholarly journals Predictable Modelling of Heat Transfer Coefficient between Spraying Water and a Hot Surface above the Leidenfrost Temperature.

1997 ◽  
Vol 37 (5) ◽  
pp. 492-497 ◽  
Author(s):  
Hitoshi Fujimoto ◽  
Natsuo Hatta ◽  
Hiroyoshi Asakawa ◽  
Toshie Hashimoto
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Leidenfrost Temperature ◽  
Hot Surface

scholarly journals Leidenfrost evaporation of water droplet

2018 ◽  
Vol 240 ◽  
pp. 01029
Author(s):  
Tadeusz Orzechowski
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Order Differential Equation ◽  
Water Drop ◽  
Heating Surface ◽  
Lower Surface ◽  
First Order ◽  
Hot Surface ◽  
The Heat Transfer Coefficient

The present paper examines the behaviour of a single large droplet levitating over a hot surface, unsteady mass of the droplet, and heat transfer. It was assumed that the evaporation from the upper surface of the droplet is negligibly small compared with the amount discharged from its lower surface, and the heat transfer coefficient is the power function of droplet orthogonal projection onto the heating surface. Based on the photographic documentation, the dependence of the droplet projection on time was approximated. A heat balance was written in the form of a non-linear first order differential equation. The solution to the equation was included. The analytical function of droplet mass change in time was used to determine the exponent of the power dependence of the heat transfer coefficient on the orthogonal droplet projection onto the heating surface. The comparison showed the method proposed in the study could be applied to analyse the behaviour of a water drop levitating above a surface at the temperature higher than the Leidenfrost point.

scholarly journals Spray Cooling Heat Transfer above Leidenfrost Temperature

Metals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1270
Author(s):  
Martin Chabicovsky ◽  
Petr Kotrbacek ◽  
Hana Bellerova ◽  
Jan Kominek ◽  
Miroslav Raudensky
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Correlation Functions ◽  
Spray Cooling ◽  
Impact Pressure ◽  
Good Prediction ◽  
Spray Parameters ◽  
Cooling Intensity ◽  
Leidenfrost Temperature

This study considers spray cooling starting at surface temperatures of about 1200 °C and finishing at the Leidenfrost temperature. Cooling is in the film boiling regime. The paper uses experimental techniques for the study of which spray parameters are necessary for good prediction of spray cooling intensity. The research is based on experiments with water and air-mist nozzles. The following spray parameters were measured together with a heat transfer coefficient: water flowrate, water impingement density, impact pressure, droplet size and velocity. Derived parameters as droplet kinetic energy, droplet momentum and droplet Reynolds number are used in the tested correlations as well. Ten combinations of spray parameters used for correlation functions for the heat transfer coefficient (HTC) are studied and discussed. Correlation functions for prediction of HTC are presented and it is shown which spray parameters are necessary for reliable computation of HTC. The best results were obtained when the parameters impact pressure and water impingement density were used together. It was proven that the correlations based only on water impingement density, which are the most frequent in literature, can not provide reliable results.

Evaporation of lignin-lean black liquor

TAPPI Journal ◽  
2015 ◽  
Vol 14 (7) ◽  
pp. 441-450
Author(s):  
HENRIK WALLMO, ◽  
ULF ANDERSSON ◽  
MATHIAS GOURDON ◽  
MARTIN WIMBY
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Black Liquor ◽  
Salt Content ◽  
Solubility Limit ◽  
Lignin Removal ◽  
Kraft Black Liquor ◽  
Black Liquors ◽  
The Heat Transfer Coefficient

Many of the pulp mill biorefinery concepts recently presented include removal of lignin from black liquor. In this work, the aim was to study how the change in liquor chemistry affected the evaporation of kraft black liquor when lignin was removed using the LignoBoost process. Lignin was removed from a softwood kraft black liquor and four different black liquors were studied: one reference black liquor (with no lignin extracted); two ligninlean black liquors with a lignin removal rate of 5.5% and 21%, respectively; and one liquor with maximum lignin removal of 60%. Evaporation tests were carried out at the research evaporator in Chalmers University of Technology. Studied parameters were liquor viscosity, boiling point rise, heat transfer coefficient, scaling propensity, changes in liquor chemical composition, and tube incrustation. It was found that the solubility limit for incrustation changed towards lower dry solids for the lignin-lean black liquors due to an increased salt content. The scaling obtained on the tubes was easily cleaned with thin liquor at 105°C. It was also shown that the liquor viscosity decreased exponentially with increased lignin outtake and hence, the heat transfer coefficient increased with increased lignin outtake. Long term tests, operated about 6 percentage dry solids units above the solubility limit for incrustation for all liquors, showed that the heat transfer coefficient increased from 650 W/m2K for the reference liquor to 1500 W/m2K for the liquor with highest lignin separation degree, 60%.

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