Tag Archives: tribologie

Introduction à la tribologie – Introduction to tribology

Posté le 17 January 2017 by Noël Brunetière - 1,923 views vues

Ce document constitue une introduction à la tribologie.

This document is an introduction to tribology.

Tribologie pdf

Ce document constitue une introduction à la tribologie (version mise à jour 2023):

This document is an introduction to tribology (last version 2023)

Tribologie

Analytical modelling of mechanical face seals: post #1

Posté le 4 July 2011 by Noël Brunetière - 2,447 views vues

Heat transfer in mechanical seals

The first step of the model concerns heat transfer in the mechanical seal rings. As illustrated in the following figure, the mechanism of heat transfer in the vicinity of mechanical seal could be quite complicated.

However it has been shown that the heat generated in the seal interface is mainly transferred by conduction through the rings to the surrounding sealed fluid and then removed by convection. The heat transfer or convection coefficient is $h_c$ . This parameter in mechanical seal can be evaluated using the Becker’s correlation (Becker 1963).

The previous figure shows the temperature distribution in the stationary part (part 1) of the seal when submitted to a heat flux $q_1$ . The average resulting temperature rise of the face is $\Delta T_1$ . Let us introduce the thermal efficiency $E_{t1}$ of the ring 1 defined as the ratio of the thermal power $P_1$ entering the face to the average temperature rise.

$E_{t1} = \frac{P_1}{\Delta T_1}= \pi \left( r_o^2-r_i^2\right)\frac{q_1}{\Delta T_1}$

where $r_o$ and $r_i$ are respectively the outer and inner radii of the seal interface.

For a given seal design, this coefficient is only dependent on the thermal boundary conditions and can easily be calculated with a FEA software. If the seal width $\Delta r=r_o- r_i$ is very small compared to the ring length $e$ , an analytical expression of $E_{t}$ can be found using the fin theory (Buck, 1989):

$E_t = 2 \pi r_oe h_c \frac{\tanh m}{m}$

where $m$ is a heat transfer parameter including $h_c$ and the thermal conductivity of the ring $k$ :

$m = \frac{e}{\Delta r} \sqrt{ \frac{h_c \Delta r }{k} }$

A dimensionless version of the thermal efficiency can be expressed in this way:

$\bar{E_t}=\frac{E_t}{2 \pi r_oeh_c }$

The evolution of the dimensionless thermal efficiency is presented on the next figure as a function of the thermal parameter $m$ (black solid curve). On the same figure, results obtained with FEA are presented when the seal ring length is varied from 1 to 8 and for a radii ratio of 0.88. It can be seen that the analytical solution is a reasonable approximation when the seal length is more than 4 times the seal width.

If the two seal rings are supposed to be at the same temperature $\Delta T= \Delta T_1= \Delta T_2$ , a global thermal efficiency $E_t$ , being the sum of the two individual thermal efficiencies, can be defined. The total thermal power $P$ entering the seal faces is thus:

$P=E_t \Delta T= \left(E_{t1}+ E_{t2}\right)\Delta T$

References

Becker, K. “Measurement of Convective Heat Transfer from a Horizontal Cylinder Rotating in a Tank of Water,” International Journal of Heat and mass Transfer (6), 1963, pp. 1053-1062.

Buck, G. “Heat Transfer in Mechanical Seals”‘Proceedings of the 6th International Pump Users Symposium’, Houston, Texas, USA, 1989, pp. 9-15.

Constitution and phenomenolgy of mechanical seals

Posté le 10 June 2011 by Noël Brunetière - 3,083 views vues

Mechanical seals are sealing components used in rotating machines such as pumps, compressors, agitators, etc. They are used to seal every types of fluid (liquid, gas, paste, etc) in all industrial domains from nuclear to food industry.

Constitution of a mechanical seal

As can be seen, on the first figure, a seal is basically composed of a rotating ring linked to the shaft and of a static ring linked to the housing, one of this link being flexible to allow a good alignment of the faces. The rings are pushed in close contact under the action of elastic elements and the pressurised fluid. A thin fluid film of about one micrometer can build-up and generally separates the seal rings avoiding wear and increasing reliability. This film must, on the other hand, remain sufficiently thin to prevent leakage. The thickness of the lubricating film depends on many interacting physical phenomena as illustrated on the second figure. The central point is lubrication which controls the fluid flow of the fluid, the pressure distribution and the asperity contact. Because of the flexible link, the floating ring can encounter vibrations. Moreover, the geometry of the faces and thus the fluid film thickness is greatly affected by elastic distortions due to the pressure loading and thermal distortions resulting from the heat dissipated by friction in the contact. In some situations, phase change can take place in the contact. Another key parameter which is not illustrated here is the wear of the surfaces.

Phenomenology of mechanical seals

Bonjour, Hello

Posté le 3 June 2011 by Noël Brunetière - 1,297 views vues

Je suis chargé de recherche CNRS à l’Institut Pprime de Poitiers. Ce blog présente certains de mes travaux de recherche sur la tribologie et plus particulièrement sur la lubrification des garnitures mécanique.

I am a CNRS researcher at the Institut Pprime in Poitiers, France. This blog presents some of my research work on tribology and more particularly on the lubrication of mechanical face seals.