BIZOMAT MAKEOS · Hydraulics
Coolant Flow for a Heat Load
What flow of water or oil removes this heat load for the allowed temperature rise?
Liquid flow needed to carry away a heat load at a given temperature rise, or the temperature rise for a given flow, for water, glycol mixtures or oil.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Calculate | choice | Find the flow, or the temperature rise. |
| Heat load | kW | Heat to be removed (machine losses, hydraulic power loss, process heat). |
| Allowed temperature rise | K | Outlet minus inlet temperature you can accept. |
| Flow (rise mode) | L/min | Available flow (rise mode). |
| Specific heat of fluid | kJ/(kg·K) | Specific heat (water 4.18, 30% glycol about 3.7, mineral oil about 1.9 kJ/kg·K). |
| Fluid density | kg/m³ | Fluid density (water 998, 30% glycol about 1040, oil about 870 kg/m³). |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Calculate
- What it is
- Whether to find the coolant flow needed for an allowed temperature rise, or the temperature rise that a given flow will produce.
- Units and format
- Choose one of 2 options from the list: Flow for a temperature rise; Temperature rise for a flow.
- Example
- The form opens with “Flow for a temperature rise” selected as a worked example. Choose the option that matches your case.
- Get it right
- Only the input for the chosen direction is used: allowed rise in the first case, flow in the second.
What this means: Heat load
- What it is
- The heat the coolant must carry away, such as machine losses, hydraulic power losses or process heat.
- Units and format
- Enter a number in kW: kilowatts. The form accepts 0.000001 kW to 1000000 kW. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 15 kW as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Flow needed, or temperature rise, increases in direct proportion to the heat load.
- Get it right
- Enter kilowatts of heat, not the motor’s rated power; only the part turned into heat counts.
What this means: Allowed temperature rise
- What it is
- The outlet temperature minus the inlet temperature of the coolant that you can accept; used when finding the flow.
- Units and format
- Enter a number in K: kelvin (a difference of 1 K equals 1 °C). The form accepts 0.000001 K to 500 K. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5 K as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The flow needed falls in inverse proportion to the allowed rise.
- Get it right
- A difference in kelvin equals the same difference in degrees Celsius.
What this means: Flow (rise mode)
- What it is
- The coolant flow available from the pump or supply; used when finding the temperature rise.
- Units and format
- Enter a number in L/min: litres per minute. The form accepts 0.000001 L/min to 10000000 L/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 40 L/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The temperature rise falls in inverse proportion to flow.
- Get it right
- Enter litres per minute, not cubic metres per hour.
What this means: Specific heat of fluid
- What it is
- The specific heat capacity of the coolant: the energy needed to warm one kilogram by one kelvin, from fluid data.
- Units and format
- Enter a number in kJ/(kg·K): kilojoules per kilogram per kelvin. The form accepts 0.000001 kJ/(kg·K) to 10 kJ/(kg·K). Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 4.18 kJ/(kg·K) as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A higher specific heat means less flow, or a smaller rise, for the same heat.
- Get it right
- Glycol mixtures and oils have a lower specific heat than water; use the value for your actual mixture.
What this means: Fluid density
- What it is
- The density of the coolant at its working temperature, used to turn volume flow into mass flow.
- Units and format
- Enter a number in kg/m³: kilograms per cubic metre. The form accepts 0.000001 kg/m³ to 25000 kg/m³. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 998 kg/m³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A denser fluid needs less volume flow for the same heat.
- Get it right
- Enter kilograms per cubic metre.
Method and formulas
- Heat Q = ṁ cp ΔT.
- Volume flow = heat ÷ (ρ cp ΔT), converted to L/min.
- Temperature rise = heat ÷ (ρ cp × flow).
- Example: 15 kW with a 5 K rise needs 43.148 L/min of water.
Limitations
- Steady state; fluid properties taken at the mean temperature.
- Heat exchanger size is a separate calculation (see the LMTD tool).
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size cooling water for a machine, mould or oil cooler
- Check temperature rise in a hydraulic return line
- Size a chiller circuit
Who it is for
- Process engineers
- Maintenance engineers
- Design engineers
What you get
- Flow or temperature rise
- Mass flow
Interpreting the result
- A smaller allowed temperature rise needs proportionally more flow.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 371–374. Topic reference; no source tables or recommended settings are reproduced.
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