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Temperature rise in centrifugal pumps
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| Section summary |
|---|
| 1. Definition |
| 2. Calculation |
| 3. Use |
1. Definition
When liquid is going through a centrifugal pump, most of the energy is transferred as a pressure - head - increase, but a small part of it is dissipated and heats up the fluid. It is usually not a problem at the pump design through since the flow through the pump is high, but the temperature increase can be higher at low flow and will definitively create problem at no flow. The temperature increase at no / low flow will also allow to calculate the minimal flow required to avoid thermal problems with a centrifugal pump.2. Calculation
How to calculate the rate of temperature rise in a centrifugal pump ?
2.1 Temperature rise in centrifugal pump at no flow
In US units [1]
With :
ΔTr = temperature increase in pump (°F/min)
Pso = pump power at no flow (BHP)
W1 = weight of liquid in the pump (lb)
Cp = specific heat of the liquid in the pump (BTU/lb/°F)
In SI units - adapted from [1]
With :
ΔTr = temperature increase in pump (°c/min)
Pso = pump power at no flow (kW)
W1 = weight of liquid in the pump (kg)
Cp = specific heat of the liquid in the pump (kJ/kg/°c)
2.2 Temperature rise in centrifugal pump at low flow
In US units [1]
With :
ΔTr = temperature increase in pump (°F/min)
H = pump head at no flow, low flow at the corresponding efficiency η
(ft)
Cp = specific heat of the liquid in the pump (BTU/lb/°F)
η = efficiency of the pump at low flow- decimal value
In SI units - adapted from [1]
With :
ΔTr = temperature increase in pump (°c/min)
H = pump head at no flow, low flow at the corresponding efficiency η
(m)
Cp = specific heat of the liquid in the pump (kJ/kg/°c)
η = efficiency of the pump at low flow- decimal value
2.3 Temperature rise of the liquid in centrifugal pump in normal operation
In normal operation, part of the energy transferred from the shaft
is lost in heat, the other behind converted as pressure for the
liquid. The formula below is proposed to estimate by how much the
liquid is heated up when passing through the pump.
With :
ΔTliquid = temperature increase of the liquid through the
pump (°c)
Qshaft = shaft power at the corresponding efficiency η (kW)
m = throughput of liquid through the pump (kg/s)
Cp = specific heat of the liquid in the pump (kJ/kg/°c)
η = efficiency of the pump at low flow- decimal value
3. Use of temperature rise in pumps
The calculation of the temperature increase at low flow should be used to calculate the minimal flow that needs to be ensured through a centrifugal pump, often thanks to a bypass line, in order to make sure the heat is not damaging the pump.
Source
Applied process design volume 1, Ludwig, Gulf Professional, page 207