Both series and parallel cooling channel connections are common practices in production plants. Each method affects pressure loss, cooling efficiency, and the overall thermal performance of the mold differently. Understanding these effects is essential for optimizing the cooling process and ensuring consistent quality in molded parts.
In a series configuration, the cooling medium flows sequentially through each cooling channel. The coolant enters the first channel, exits it, and then enters the next channel, continuing this path through all channels before returning to the cooling system. In contrast, in a parallel configuration, a manifold splits the cooling medium into multiple streams that simultaneously enter each cooling channel. The coolant is then collected back into a single stream before returning to the cooling system.
Effects of Series and Parallel Configurations
- Pressure Losses
- Series Cooling Channels:
In this setup, the coolant flows through each segment of the mold in sequence. This configuration leads to cumulative pressure losses, as the fluid encounters resistance at every bend, turn, or restriction along its path. The total pressure loss in a series system can be described using the Darcy-Weisbach equation.
- Series Cooling Channels:
where:
 | Pressure loss |
 | Friction coeficient |
 | Channel length |
 | Channel diameter |
 | Liquid density |
 | Flow velocity |
Extended Flow Path in Series Cooling and Its Impact on Pressure Loss
In series cooling, the extended flow path of the medium results in greater pressure losses due to increased friction and, possibly, smaller channel and hose diameters. This can lead to higher requirements for the flow rate of the feeding pump.
- Parallel Cooling Channels:
In this configuration, the coolant is split into multiple “branches,” each cooling a specific part of the mold. Since each channel operates independently, the total pressure loss is significantly lower, as the fluid does not need to flow sequentially through all channels.
For each branch, the pressure loss is still governed by the Darcy-Weisbach equation, but the shorter lengths and individual pathways lead to significantly reduced pressure losses. The total pressure drop in a parallel system can be modeled as the sum of pressure drops across all channels, calculated using:
2. Flow Turbulence
- Series-Connected Channels:
The longer the fluid remains in the channel, the greater the likelihood it will transition into turbulent flow, especially if the coolant’s velocity is high or the channel diameter is small. Turbulent flow enhances convective heat transfer but at the cost of higher pressure losses and increased energy needed to pump the medium through the channels. - Parallel-Connected Channels:
In parallel channels, the flow is typically divided into lower-velocity streams that generally remain laminar or only slightly turbulent. This results in a more predictable and controlled flow but may lead to lower heat exchange rates if the flow rate in each branch is not appropriately regulated.
The Reynolds number Re helps determine the flow regime:
where:
 | Dynamic fluid viscosity |
In general, turbulent flow (high Reynolds number, Re>4000Re > 4000Re>4000) enhances heat exchange but also increases pressure losses. In series channels, achieving turbulence may be desirable, whereas in parallel systems, maintaining a more laminar flow can provide better control and efficiency.
3. Heat Exchange Efficiency
- Series-Connected Channels:
The temperature of the cooling medium rises as it absorbs heat from each successive section of the mold. By the time the coolant reaches the final sections, heat removal may be less effective due to a larger temperature differential. This can result in uneven cooling across the mold. - Parallel-Connected Channels:
Each channel has a more consistent coolant temperature since it flows simultaneously into each circuit. This results in more uniform cooling throughout the mold, leading to better heat management and, consequently, higher molded part quality. However, careful channel design is necessary to ensure balanced thermal distribution in the mold to avoid “dead zones” or inefficient heat removal.
The Nusselt number (Nu) is often used to quantify heat exchange efficiency:
where:
- h is the convective heat transfer coefficient,
- k is the thermal conductivity of the fluid.
In series-connected systems, the local Nusselt number will vary along the length of the connected channels and decrease as the coolant warms up. In contrast, parallel systems make it easier to maintain a more consistent Nusselt number across all channels.
4. Impact on Cooling Efficiency
- Series Configuration:
- Temperature Gradient: The coolant passing through multiple channels sequentially absorbs heat, causing its temperature to rise. This creates a temperature gradient within the mold, where the initial channels are cooler, while the later ones become progressively warmer. This uneven cooling can lead to an inconsistent cooling rate across the molded part, potentially resulting in warping or other defects.
- Reduced Flow Rate: The cumulative pressure loss in a series configuration can significantly reduce the overall flow rate, decreasing the coolant’s ability to absorb heat efficiently. This can lead to longer cycle times and lower production efficiency.
- Parallel Configuration:
- Uniform Temperature Distribution: In a parallel configuration, the coolant entering each channel has approximately the same temperature, leading to a more uniform cooling process throughout the mold. This helps maintain consistent part quality and reduces the likelihood of defects associated with uneven cooling.
- Higher Flow Rate: Since pressure losses are minimized in a parallel configuration, a higher flow rate can be maintained, enhancing heat exchange efficiency. This may result in shorter cooling times and improved production efficiency.