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TECHNICAL PAPERS

# A Water Evaporation Based Model for Lubricant Dryoff on Die Surfaces Heated Beyond the Leidenfrost Point

[+] Author and Article Information
Lin Yang

Department of Industrial, Welding and Systems Engineering, Ohio State University, 1971 Neil Avenue, 210 Baker Systems, Columbus, OH 43210

Rajiv Shivpuri1

Department of Industrial, Welding and Systems Engineering, Ohio State University, 1971 Neil Avenue, 210 Baker Systems, Columbus, OH 43210shivpuri.1@osu.edu

1

Corresponding author.

J. Manuf. Sci. Eng 129(4), 717-725 (Mar 05, 2007) (9 pages) doi:10.1115/1.2738126 History: Received August 07, 2006; Revised March 05, 2007

## Abstract

Lubricants in hot forging are applied to the heated die surface by spraying dilute water based graphite suspensions through high-pressure nozzles. To avoid undesirable steam formation, these lubricant droplets need to completely dry before deformation begins. This paper presents an analytical model to estimate evaporation time for the impacting drops at surface temperatures above Leidenfrost, $300–450°C$. It is based on the suspension of deformed droplet on a vapor cushion sustained by a continuous supply of water from the drying droplet. Model predictions are validated by single droplet experiments with different surface temperatures, dilution ratios, and impacting speeds.

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## Figures

Figure 1

Experimental setup for the single droplet experiments (1)

Figure 2

Dryoff times and heat flux at different hot surface temperatures for various lubricant dilution ratios (1)

Figure 3

Schematic of the boiling curve divided into four regimes based on the dominant mechanism of droplet thermodynamics: (I) natural conduction and convection; (II) nucleate boiling; (III) transition boiling; and (IV) film boiling. Surface temperatures are: Tsat (saturation temperature), TCHF (critical heat flux temperature), Tleid (Leidenfrost temperature), and TD (die temperature) (2)

Figure 4

A schematic of the spread and dryoff proess beyond the Leidenfrost point: (a) droplet impact; (b) droplet spread; (c) stabilized spat (deformed droplet or film); and (d) quasi-steady state dryoff

Figure 5

Dryoff time in seconds for a droplet with initial diameter d0=3mm and impact velocity ν0=0.1m∕s

Figure 6

Dryoff time in seconds of a droplet with initial diameter d0=3mm, and impact velocity ν0=1m∕s

Figure 7

Simulation results of lubricant droplet with 1:1 dilution ratio, 4mm diameter, and 10cm∕s impact velocity. Initial grid at the top and the simulation results for droplet deformation at the various time steps.

Figure 8

Configuration of the model for the quasi-steady dryoff of a lubricant droplet on a heated surface

Figure 9

Average thickness of the vapor layer as a function of surface temperature and Weber number

Figure 10

Averaged mass loss rate as a function of temperature and Weber number

Figure 11

Dryoff time for a droplet with initial diameter d0=3mm; analytical and experimental results for 1:1 dilution ratio

Figure 12

Measured surface temperature change on heated surface at initial preheat temperature of 350°C for two droplet impact speeds and three dilution ratios

Figure 13

Measured surface temperature change on the heated surface at initial preheat temperature of 450°C for two droplet impact speeds and three dilution ratios

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