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Optimizing flow distribution in a heat sink to accelerate flow to improve heat transfer

IP.com Disclosure Number: IPCOM000189084D
Original Publication Date: 2009-Oct-27
Included in the Prior Art Database: 2009-Oct-27
Document File: 4 page(s) / 65K

Publishing Venue

IBM

Abstract

A method must be devised to lower the overall heat sink impedance while utilizing that bottom airflow more effectively. This article describes using a scoop in the heat sink to collect a larger portion of inlet air and utilize it in the heat sink to improve the heat transfer effectiveness.

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Optimizing flow distribution in a heat sink to accelerate flow to improve heat transfer

The CPU cooling in a blade server relies upon flow through a heat sink. Traditionally, the airflow in that heat sink is divided into two parts, the upper side and the lower side (with reference to the heat sink base). The majority of the flow goes through the top of the heat sink and provides the majority of the cooling for the CPU. Unfortunatley if one was to block off the bottom side flow to put more airflow and cooling to the top side, this greatly increases the impedance (resistance to flow) and reduces the overall thermal performance of the heat sink. A method must be devised to lower the overall heat sink impedance while utilizing that bottom airflow more effectively. This article describes using a scoop in the heat sink to collect a larger portion of inlet air and utilize it in the heat sink to improve the heat transfer effectiveness.

The main idea of this disclosure is to utilize the bottom airflow, while minimizing the impedance increase, and maximizing the thermal performance. The flow is now directed up to the top side of the heat sink to contribute to the majority of the cooling. In doing so, the flow area is larger at the front of the heat sink and narrows as you move in the flow direction. This causes the airflow to accelerate and therefore increases the heat transfer coefficients in the heat sink. This behavior makes the effectiveness of the fin larger and improves the thermal performance of the heat sink without a significant increase in pressure drop.

The new heat sink design better utilizes all of the airflow presented to the heat sink. Previously, the airflow is split in to two paths: flow that goes into the top fins and flow that goes into bottom fins. Figure 1 shows that typical distribution. The majority of the airflow goes to the top fins and thus the majority of the heat transfer occurs in those fins.

Figure 1: Flow Path Through Old Heat Sink (Side View).

AIRFLOW

Bottom Fins

Instead of allowing the airflow to spilt, one could combine the airflow paths to maximize the possible heat transfer. Figure 2 shows the combination of those flow streams.

Figure 2: Flow Path Through New Heat Sink (Side View).

Top Fins

1

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Flow


Acceleration Top Fins

AIRFL

There are several benefits in doing this. First, the airflow is accelerated in the top f...