Heat transfer during drop impingement onto a hot wall: The influence of wall superheat, impact velocity, and drop diameter

A fundamental understanding of droplet dynamics is important for the prediction and optimization of technical systems involving drops and sprays. The Collaborative Research Center (CRC) SFB-TRR 75 was established in January 2010 to focus on the dynamics of basic drop processes, and in particular on processes involving extreme ambient conditions, for example near thermodynamic critical conditions, at very low temperatures, under the influence of strong electric fields, or in situations involving extreme gradients of the boundary conditions. The goal of the CRC was to gain a profound physical understanding of the essential processes, which is the basis for new analytical and numerical descriptions as well as for improved predictive capabilities. This joint initiative involved scientists at the University of Stuttgart, the TU Darmstadt, the TU Berlin, and the German Aerospace Center (DLR) in Lampoldshausen. This first chapter provides a brief overview of the overall structure of this CRC as well as a summary of some selected scientific achievements of the subprojects involved. For further details the reader is referred to the subsequent chapters of this book related to the individual subprojects.

Section: Droplet and Spray Interactions With Hot Wallsmentioning

confidence: 99%

Collaborative Research on Droplet Dynamics Under Extreme Ambient Conditions

Schulte

Dreizler

Munz

et al. 2022

“…A thermal boundary layer in the vapour region close to the wall is initialised prior to the simulation. Dimensions of the domain are chosen such that boundary conditions do not influence the drop impingement process [1] It is shown in associated experiments in [6,7] that no three-dimensional effects (like splash) are observed for the investigated parameter range. Hence, a static, structured 2D axis-symmetric grid with local grid refinement at the solid-fluid interface is chosen.…”

Section: Model Descriptionmentioning

confidence: 99%

“…12). The experimental setup and procedure are described in [6,7]. After the impact and coalescence of two drops, the combined drop spreads.…”

Section: Vertical Coalescencementioning

confidence: 99%

Numerical Simulation of Heat Transfer and Evaporation During Impingement of Drops onto a Heated Wall

Sontheimer

Schlawitschek

Batzdorf

et al. 2022

In this study, hydrodynamics and heat transport during the impact of single and multiple drops onto a hot wall are studied numerically. The heat transfer in the vicinity of the three-phase contact line, where solid, liquid and vapour meet, contributes significantly to the global heat transfer. The microscale processes in the region of the three-phase contact line are analysed using a lubrication approximation. The results in the form of correlations are integrated into an overall model. The impingement of drops on a macro scale is simulated using a numerical model developed within the OpenFOAM library. The influence of dimensionless parameters, i.e., the Reynolds, Weber, Bond, Prandtl and Jakob numbers, as well as the influence of pressure, on the transport phenomena is discussed. The analysis of the influence of drop frequency and substrate thickness during the vertical coalescence and the influence of the drop spacing during the horizontal coalescence of drops on the hot surface complete the study. The results contribute to a better understanding of the complex mechanisms of spray cooling.

“…The heat conduction equation is solved using the finite volume method. The details of the above procedure for determination of heat flux distribution and its accuracy are discussed in [8,22].…”

Section: Data Reductionmentioning

confidence: 99%

“…Numerical simulations [11,12,21] and experimental studies [8,11] reveal that, if the drop impinges an impermeable and rigid substrate in drop deposition (in the absence of splashing and bouncing phenomena) and film evaporation regimes, its evolution can be subdivided into three subsequent phases: (i) the drop spreading phase, in which the contact line advances radially outwards due to action of inertia; (ii) the drop receding phase, in which the contact line moves inwards due to surface tension; and (iii) the phase of sessile drop evaporation, in which the drop is at a state of mechanical equilibrium. During all three phases, heat is transferred by conduction, convection, and evaporation.…”

Section: Introductionmentioning

confidence: 99%

High Resolution Measurements of Heat Transfer During Drop Impingement onto a Heated Wall

Gholijani

Fischer

Gambaryan‐Roisman

et al. 2022

Drop impact on a hot surface heated above the saturation temperature of the fluid plays an important role in spray cooling. The heat transferred from the wall to the fluid is closely interrelated with drop hydrodynamics. If the surface temperature is below the Leidenfrost temperature, the heat transport strongly depends on the transport phenomena in the vicinity of the three-phase contact line. Due to extremely high local heat flux, a significant fraction of the total heat flow is transported through this region. The local transport processes near the three-phase contact line, and, therefore, the total heat transport, are determined by the wall superheat, contact line velocity, system pressure, fluid composition, surface structure and physical properties on the wall. The effect of the aforementioned influencing parameters on fluid dynamics and heat transport during evaporation of a single meniscus in a capillary slot are studied in a generic experimental setup. The hydrodynamics and evolution of wall heat flux distribution during the impact of a single drop onto a hot wall are also studied experimentally by varying the impact parameters, wall superheat, system pressure, and wall topography. In addition, the fluid dynamics and heat transport behavior during vertical and horizontal coalescence of multiple drops on a heated surface are studied experimentally.