Bosch rexroth MBT, Manual

Page: 281 / 422

Coolant Specific heat capacity c in J / kg ⋅ K Density ρ in kg/m³
Water 4,183 998.3
Thermal oil
(example)
1000 887
Air 1007 1188
Tab. 9-6: Substance values of different coolants at 20°C
Reduction of the motor torque with
non-water coolants and identical
flow rate
To determine the reduction in motor torque with a non-water coolant at an
identical flow rate, use the following formula:
k
cred
Motor torque reduction factor referred to water in percent
c
w
Specific heat capacity of water in J / kg ⋅ K
ρ
w
Density of water in kg/m³
c
x
Specific heat capacity of the applied coolant in J / kg ⋅ K
ρ
x
Density of the used coolant in kg/m³
Fig. 9-6: Reduced motor torque with non-water coolant at identical flow rate
Pressure drop
The flow resistance at the pipe walls, deflections and changes in cross sec‐
tion leads to a pressure drop in the flown through component (see fig. 9-4
"Pressure drop via flown through component" on page 268 ).
The pressure drop Δp is increased with an increase in flow rate (see fig. 9-7
"Pressure drop depending on the flow rate; general representation" on page
269 ).
The overall pressure drop of the cooling system is determined by
various partial pressure drops (motor, feeders, connectors, etc.).
This has to be taken into account by using manufacturer-specific
data when the cooling circuit is sized.
1
2
① Pressure drop Δp
② Flow rate Q
Fig. 9-7: Pressure drop depending on the flow rate; general representation
MBT High Synchronous Torque Motors 269/409
Application notes
R911298798_Edition 08 Bosch Rexroth AG