# Mold Cooling Channel Reynolds Number, Flow and Heat Removal Calculator

> Source: https://netray.co/tools/mold-cooling-channel-reynolds-flow-and-heat-removal-calculator
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Free Tools

## Short answer

Enter coolant flow, channel diameter, water temperature, temperature rise and circuit length to get velocity, Reynolds number, minimum flow for turbulence, heat removed and pressure drop.

## Category

engineering-plm

## Industry

Plastics and Injection Molding

## Audience

- Mold designer
- Process engineer
- Tooling engineer
- Maintenance technician

## Tool

**Kind:** calculator

**Currency:** $

**Inputs:**

#### Flow per circuit

**Key:** flow_lpm

**Type:** number

**Default:** 8

**Min:** 0

**Step:** 0.5

**Unit:** L/min

**Help:** Measured with a flow meter on the circuit. 1 US gpm = 3.785 L/min.

#### Channel diameter

**Key:** dia_mm

**Type:** number

**Default:** 11

**Min:** 3

**Step:** 0.5

**Unit:** mm

**Help:** Typical mold channels are 8 to 14 mm. A 7/16 in channel is 11.1 mm.

#### Coolant temperature

**Key:** visc

**Type:** select

**Default:** 1.002

**Options:**

##### 10 deg C (50 F), viscosity 1.31 mPa s

**Value:** 1.307

##### 20 deg C (68 F), viscosity 1.00 mPa s

**Value:** 1.002

##### 30 deg C (86 F), viscosity 0.80 mPa s

**Value:** 0.797

##### 40 deg C (104 F), viscosity 0.65 mPa s

**Value:** 0.653

##### 60 deg C (140 F), viscosity 0.47 mPa s

**Value:** 0.467

**Help:** Water viscosity falls as it warms, which raises Reynolds number for the same flow.

#### Coolant temperature rise

**Key:** delta_t

**Type:** number

**Default:** 3

**Min:** 0

**Step:** 0.5

**Unit:** deg C

**Help:** Outlet minus inlet. Good practice keeps this at 2 to 3 deg C.

#### Circuit length

**Key:** length_m

**Type:** number

**Default:** 1.5

**Min:** 0.1

**Step:** 0.1

**Unit:** m

#### Target Reynolds number

**Key:** target_re

**Type:** select

**Default:** 5000

**Options:**

##### 4,000 (start of turbulence)

**Value:** 4000

##### 5,000 (common design goal)

**Value:** 5000

##### 10,000 (aggressive)

**Value:** 10000

**Outputs:**

#### Channel cross section

**Key:** area_m2

**Expr:** pi * pow(dia_mm / 1000, 2) / 4

**Format:** decimal

**Description:** Area in square meters.

#### Coolant velocity (m/s)

**Key:** vel

**Expr:** flow_lpm / 60000 / area_m2

**Format:** decimal

#### Reynolds number

**Key:** re

**Expr:** 997 * vel * (dia_mm / 1000) / (visc / 1000)

**Format:** integer

**Primary:** true

**Description:** Re = density x velocity x diameter / viscosity. Above about 4,000 the flow is turbulent and removes heat well.

#### Minimum flow for target Reynolds (L/min)

**Key:** q_min

**Expr:** target_re * pi * (dia_mm / 1000) * (visc / 1000) / (4 * 997) * 60000

**Format:** decimal

**Primary:** true

**Description:** Flow needed at this diameter and temperature to reach the target Reynolds number.

#### Actual flow vs minimum

**Key:** flow_ratio

**Expr:** if(gt(q_min, 0), flow_lpm / q_min * 100, 0)

**Format:** percent

**Description:** Below 100 percent means the circuit is under the target.

#### Heat removed at this temperature rise

**Key:** heat_kw

**Expr:** flow_lpm / 60 * 0.997 * 4.18 * delta_t

**Format:** decimal

**Description:** kW = mass flow (kg/s) x 4.18 kJ/kg K x temperature rise. Water properties assumed.

#### Friction factor

**Key:** fric

**Expr:** if(gte(re, 4000), 0.316 * pow(max(re, 1), -0.25), 64 / max(re, 1))

**Format:** decimal

**Description:** Blasius smooth pipe for turbulent flow, 64/Re for laminar.

#### Pressure drop over the circuit (kPa)

**Key:** dp_kpa

**Expr:** fric * (length_m / (dia_mm / 1000)) * 997 * pow(vel, 2) / 2 / 1000

**Format:** decimal

**Description:** Straight channel only. Bends, baffles and fittings add to it, so treat as a lower bound.

**Chart:**

#### Reynolds number vs flow per circuit

**Type:** line

**X:** flow_lpm

**From:** 1

**To:** 30

**Steps:** 30

**Series:**

- re

**Disclaimer:** Engineering estimate for straight round channels with water. Real circuits have bends, baffles, bubblers and fittings that change pressure drop and turbulence. Glycol mixtures have higher viscosity. Verify with a flow meter and mold temperature measurements.

## Content

**Intro:** Cooling time is usually the largest part of the molding cycle, and it only works if coolant flow in the channels is turbulent. A laminar circuit can carry a fraction of the heat. This calculator checks Reynolds number for your flow and diameter and tells you the minimum flow to get turbulence.

**Sections:**

#### How to use it

**Body:** Measure flow in each circuit with a flow meter, or take it from the temperature controller specification divided across the circuits in parallel. Enter the channel diameter, the coolant temperature and the temperature rise you see between inlet and outlet. The primary results are the Reynolds number and the minimum flow needed to hit your target. If actual flow is below the minimum, check for serial circuits, undersized hoses and quick disconnects before touching process settings.

#### The engineering behind it

**Body:** Reynolds number is density times velocity times diameter over dynamic viscosity. Flow in a round pipe is laminar below about 2,300 and turbulent above about 4,000, with a transition region between. Mold designers commonly target 5,000 or more for a margin. Heat removed is mass flow times the specific heat of water, 4.18 kJ per kg K, times the coolant temperature rise. Pressure drop uses the Darcy equation with the Blasius friction factor for smooth turbulent flow, or 64 over Re for laminar flow.

**Bullets:**

- Re = 997 x v x d / viscosity (water near room temperature)
- Laminar below 2,300, turbulent above 4,000
- Heat (kW) = kg/s x 4.18 x delta T

#### Reading the result

**Body:** With the defaults, 8 L/min in an 11 mm channel at 20 deg C gives about 1.4 m/s and a Reynolds number above 15,000, well into turbulence, and removes about 1.7 kW at a 3 deg C rise. The chart shows how Reynolds number scales linearly with flow, so a circuit at 2 L/min would be near 3,800 and transitional. A large temperature rise with low flow is the field symptom of a circuit that is carrying too little heat.

#### Common mistakes

**Body:** Putting cooling channels in series so the last one gets warm coolant, using small hose barbs that choke flow, running chilled water at 10 deg C where viscosity is highest, and assuming the controller's rated flow reaches the mold. Scale and rust reduce effective diameter over time, so flow checks belong on the preventive maintenance plan.

**Bullets:**

- Prefer parallel circuits of equal length
- Keep the inlet to outlet rise within 2 to 3 deg C
- Descale or flush cooling lines on a schedule

**Cta:** Netray can help tie mold flow checks and cycle time data from your MES into your ERP maintenance records, so a cooling restriction shows up as a work order before it shows up as scrap.

**Faq:**

#### What Reynolds number do I need for mold cooling?

**Answer:** Flow is fully turbulent above roughly 4,000, and designers typically aim for 5,000 to 10,000. Between 2,300 and 4,000 the flow is transitional and heat transfer is unreliable. Turbulence matters because heat transfer can be several times higher than in laminar flow.

#### Does this work for water and glycol?

**Answer:** It assumes plain water near room temperature. Glycol mixtures are more viscous, which lowers the Reynolds number for the same flow. For a mix, increase the viscosity and density to match the supplier's data. The select list offers water only.

#### How do I convert gallons per minute?

**Answer:** One US gallon per minute equals 3.785 liters per minute. A common 3 gpm flow through a mold circuit is therefore about 11.4 L/min. Enter liters per minute in this calculator.

#### Why is pressure drop a lower bound?

**Answer:** The formula covers only a straight smooth round channel. Real circuits have bends, baffles, bubblers, O-ring steps and quick couplings that add losses, often doubling the total. Use it to compare options rather than to size a pump exactly.

## Search terms

mold cooling channel Reynolds number, turbulent flow mold cooling, injection mold cooling flow rate, mold water flow calculator, cooling channel diameter flow rate, mold cooling heat removal calculation, conformal cooling flow check, mold temperature controller flow

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