The Prandtl number is correlated with the temperature of the engine oil.
The prandtl number is a dimensionless number defined as below:
Pr = momentum diffusivity / thermal diffusivity = υ/α
‘υ’= momentum diffusivity or kinematic viscosity.
‘α’ = thermal diffusivity.
The prandtl number of engine oil is high which lead to higher convective heat transfer.
As the viscosity of the engine oil decrease with temperature increase the momentum diffusivity over thermal diffusivity which make the engine oil a good choice for heat conduction.
Prandtl Number of Oil Table
| T (C) | T (F) | T (K) | Pr |
|---|---|---|---|
| -0.15 | 31.73 | 273 | 47000 |
| 6.85 | 44.33 | 280 | 27500 |
| 16.85 | 62.33 | 290 | 12900 |
| 26.85 | 80.33 | 300 | 6400 |
| 36.85 | 98.33 | 310 | 3400 |
| 46.85 | 116.33 | 320 | 1965 |
| 56.85 | 134.33 | 330 | 1205 |
| 66.85 | 152.33 | 340 | 793 |
| 76.85 | 170.33 | 350 | 546 |
| 86.85 | 188.33 | 360 | 395 |
| 96.85 | 206.33 | 370 | 300 |
| 106.85 | 224.33 | 380 | 233 |
| 116.85 | 242.33 | 390 | 187 |
| 126.85 | 260.33 | 400 | 152 |
| 136.85 | 278.33 | 410 | 125 |
| 146.85 | 296.33 | 420 | 103 |
| 156.85 | 314.33 | 430 | 88 |
*Property values from Incropera, F. P., and DeWitt, D. P., Fundamentals of Heat and Mass Transfer, 3rd ed., Wiley, New York, 1990. values generated from NIST Database 23: REFPROP Version 7.0 (August 2002).
Prandtl Number of Oil in figure
