BIZOMAT MAKEOS · Hydraulics
Tank Heating or Cooling Coil Plan (Area, Tube Length, Turns, Pressure Drop)
How many turns of tube does my tank heating or cooling coil need for the duty, how long is the tube, and what pressure drop will the water see through it?
Plan for a helical tube coil in a tank: heat-transfer area needed for the duty from the overall coefficient and mean temperature difference, the tube length and turns that give it, the developed length of the coil you choose with its straight ends (as the helix length tool), the area it provides, and the velocity, friction factor and pressure drop of the fluid through the tube (as the pipe friction tool), checked against the duty and your pressure-drop limit.
Open the calculatorRuns in your browser. No account needed.
How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Heat duty | kW | Heat to transfer. |
| Overall heat-transfer coefficient | W/(m²·K) | Overall coefficient for the coil, tube and fluids (from your heat-transfer data). |
| Mean temperature difference | K | Log-mean (or mean) temperature difference between the fluid in the tube and the tank. |
| Coil | ||
| Mean coil diameter | mm | Mean diameter of the coil. |
| Coil pitch | mm | Axial pitch of the coil. |
| Turns | turns | Number of turns you plan. |
| Straight ends (total) | mm | Total length of the straight inlet and outlet legs. |
| Tube outside diameter | mm | Outside diameter of the tube. |
| Tube wall | mm | Wall thickness of the tube. |
| Fluid in the tube | ||
| Flow | L/min | Flow of the heating or cooling fluid through the tube. |
| Kinematic viscosity | cSt | Kinematic viscosity of that fluid. |
| Density | kg/m³ | Density of that fluid. |
| Tube roughness | mm | Roughness of the tube bore. |
| Sum of fitting loss coefficients | Loss coefficients for the entry, exit and fittings. | |
| Largest pressure drop | bar | Largest pressure drop you accept across the coil. |
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: Heat duty
- What it is
- The rate of heat the coil must put into or take out of the tank contents, from your heating or cooling load calculation.
- Units and format
- Enter a number in kW: kilowatts. The form accepts 0.000001 kW to 100000 kW. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 kW as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The area and tube length needed rise in direct proportion to the duty.
- Get it right
- This is a rate (kilowatts), not an energy; convert a heat-up energy to a rate by dividing by the time allowed.
What this means: Overall heat-transfer coefficient
- What it is
- The overall heat-transfer coefficient from the fluid in the tube, through the wall, to the tank contents, from your heat-transfer data or calculation.
- Units and format
- Enter a number in W/(m²·K): watts per square metre per kelvin. The form accepts 0.000001 W/(m²·K) to 100000 W/(m²·K). Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 500 W/(m²·K) as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The area needed falls in inverse proportion to the coefficient.
- Get it right
- Enter watts, not kilowatts, per square metre per kelvin, based on the tube outside area, which is the area this tool uses.
What this means: Mean temperature difference
- What it is
- The mean temperature difference between the fluid in the tube and the tank contents, ideally the log-mean value over the coil.
- Units and format
- Enter a number in K: kelvin (a difference of 1 K equals 1 °C). The form accepts 0.000001 K to 1000 K. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 40 K as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The area needed falls in inverse proportion to the mean temperature difference.
- Get it right
- Enter a temperature difference, not a temperature; a 1 °C difference equals 1 K.
Coil
What this means: Mean coil diameter
- What it is
- The mean diameter of the helical coil, measured to the centre line of the tube on opposite sides of the coil.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 300 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger coil diameter gives more tube length per turn, so fewer turns are needed.
- Get it right
- Use the centre-line diameter, not the outside of the coil; it must fit inside the tank with clearance to the wall and any stirrer.
What this means: Coil pitch
- What it is
- The axial distance between the centre lines of adjacent turns of the coil.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 50 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Pitch adds only slightly to the length per turn but sets the height of the coil.
- Get it right
- Turns × pitch gives the coil height; check it fits below the lowest liquid level.
What this means: Turns
- What it is
- The number of complete turns you plan for the coil; the tool also reports how many turns the duty needs.
- Units and format
- Enter a number in turns: a number of turns. The form accepts 0.000001 turns to 10000 turns. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 14 turns as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- More turns add tube length, increasing both the area provided and the pressure drop.
- Get it right
- Turns need not be whole, but round up so the coil provides at least the area needed.
What this means: Straight ends (total)
- What it is
- The total length of the straight inlet and outlet legs that connect the coil to the tank nozzles, added to the coil’s developed length.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 1000000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 500 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Add both legs together; only legs that sit in the tank liquid really transfer heat, but all of them add pressure drop.
What this means: Tube outside diameter
- What it is
- The outside diameter of the coil tube, which sets the heat-transfer area and, with the wall, the bore the fluid flows through.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 25 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger tube gives more area per metre and a larger bore, so less length and lower pressure drop.
- Get it right
- Use the actual tube outside diameter from the tube standard, not the nominal pipe size.
What this means: Tube wall
- What it is
- The wall thickness of the coil tube; the bore is the outside diameter less twice this wall.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A thicker wall narrows the bore, raising fluid velocity and pressure drop.
- Get it right
- Twice the wall must be less than the outside diameter.
Fluid in the tube
What this means: Flow
- What it is
- The volume flow of steam condensate, hot water, thermal oil or coolant through the coil tube.
- Units and format
- Enter a number in L/min: litres per minute. The form accepts 0.000001 L/min to 1000000 L/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 L/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Pressure drop rises roughly with the square of flow in turbulent flow.
- Get it right
- Enter litres per minute; convert from m³/h by multiplying by 1000 and dividing by 60.
What this means: Kinematic viscosity
- What it is
- The kinematic viscosity of the fluid in the tube at its working temperature, from the fluid data sheet.
- Units and format
- Enter a number in cSt: centistokes (kinematic viscosity, 1 cSt = 1 mm²/s). The form accepts 0.000001 cSt to 100000 cSt. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 cSt as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Higher viscosity lowers the Reynolds number and raises the friction factor and pressure drop.
- Get it right
- Centistokes equal mm²/s. If you only have dynamic viscosity in centipoise, divide it by the density in g/cm³.
What this means: Density
- What it is
- The density of the fluid flowing in the tube at its working temperature, from the fluid data sheet.
- Units and format
- Enter a number in kg/m³: kilograms per cubic metre. The form accepts 0.000001 kg/m³ to 3000 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
- Pressure drop rises in direct proportion to density for the same velocity.
- Get it right
- Use the density of the tube fluid, not the tank contents.
What this means: Tube roughness
- What it is
- The absolute roughness of the tube bore, a measure of the height of its surface irregularities, from pipe-friction data for the tube material.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 10 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.0015 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Enter the absolute roughness in millimetres, not a relative roughness ratio.
What this means: Sum of fitting loss coefficients
- What it is
- The total of the minor loss coefficients for the coil’s entry, exit, bends at the ends and any fittings, each from pipe-fitting loss data.
- Units and format
- Enter a plain number with no unit. The form accepts 0 to 10000. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.5 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Each extra unit of K adds one velocity head of pressure drop.
- Get it right
- Add the coefficients for every fitting in the coil circuit; the coil’s own length is covered by the friction factor.
What this means: Largest pressure drop
- What it is
- The largest pressure drop across the coil that your pump, steam trap or supply pressure allows.
- Units and format
- Enter a number in bar: bar (1 bar = 100 kPa). The form accepts 0.000001 bar to 1000 bar. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.5 bar as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Enter bar (1 bar = 100 kPa), as a difference between inlet and outlet.
Method and formulas
- Area needed = Q ÷ (U ΔT_m); tube length needed = area ÷ (π × tube OD).
- Developed length = turns × √[(π D_c)² + p²] + ends (as the helix length tool); area provided = π × OD × length.
- Pressure drop = (f L ÷ d + ΣK) ρ v² ÷ 2 with the Colebrook friction factor for the tube bore (as the pipe friction tool).
- Example: 20 kW needs 1 m², about 12.961 turns; 14 turns give 1.077 m² of 13.713 m tube with 0.085323 bar drop.
Limitations
- Straight-tube friction factor; coil curvature raises the pressure drop somewhat.
- Overall coefficient must allow for fouling and the tank side agitation.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a heating or cooling coil for a tank or bath
- Check an existing coil for a new duty
- Find the pressure drop through a coil
Who it is for
- Plant engineers
- Process engineers
- Maintenance engineers
What you get
- Area and tube length needed, turns needed
- Developed length and area provided
- Velocity and pressure drop
Interpreting the result
- If the drop is too high, split the coil into parallel circuits rather than shortening it.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2060–2062, 3024–3027, 371–378. Topic reference; no source tables or recommended settings are reproduced.
BIZOMAT tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Tank Heating or Cooling Coil Plan (Area, Tube Length, Turns, Pressure Drop) calculator