Optimal heat sink design, especially for devices with high heat loads such as MOSFETs and IGBTs, is essential for the efficient operation of these devices and to prevent premature part failure. The use of fans in combination with heat sinks is necessary to provide adequate cooling for high performance devices with significant heat dissipation.

A shroud or duct is often used to direct airflow from the fan to the heat sink, as shown in Figure 1, to prevent airflow from being redirected around the heat sink, which would reduce cooling capacity. effective cooling of the fan and heat sink combination.

Figure 1 Heat Sink and Fan without Bypass Flow

A direct calculation of the ideal fin spacing and resulting thermal resistance of the fan and heat sink combination shown in Figure 1 can be made using a few equations that provide a quick estimate of the heat sink size required for your application. .

Note: It is impractical to optimize the fin spacing of a heat sink assuming constant face velocity or flow. The airflow rate between the fins is determined by the fin spacing and the number of fins using Equation 1. This formula states that the volumetric flow rate of air approaching the heatsink is the same as the rate of volumetric flow of air passing through the heat sink because there is no bypass flow around the heat sink.

Figure 2. Fan-cooled heatsink dimensions

1

Wo:

is the air velocity between the ribs

is the flow rate in the heat sink

is the height of the fins

is the distance between the ribs

is the number of fins

The smaller the gap between the blades, the higher the air velocity V_{F}flows between the fins. The higher the air speed, the more effective the cooling of the fins will be. If you were trying to optimize the dimensions of the heat sink, the fin gap would be a very small value, since the air velocity and thus the cooling rate increases as the fin gap decreases. In real applications, the flow is provided by a fan or blower. The flow rate would not be fixed, it would be limited by the increase in pressure drop across the heat sink that would occur as the spacing between the fins decreases, s.

## Heat Sink Design Assumptions

To simplify the analysis without introducing significant calculation errors, the following assumptions are made.

- The area due to the thickness of the fins t and the thickness of the base b are much smaller than the total area of the heatsink.
- The heat source is the same length and width as the heat sink and is centered on the base of the heat sink.
- The heat source is in perfect contact with the base of the heatsink
- All of the flow from the fan or blower passes through the heat sink.
- Radiant heat transfer is small compared to convection and can be neglected.
- The flow through the heat sink is laminar and constant.
- The thickness of the ribs is small compared to the distance s between the ribs.

The assumption of laminar flow through the heat sink applies to the vast majority of commercial fan/heat sink combinations. Fan noise is an important consideration in electronics, as these fan speeds are intentionally kept lower to avoid the significant increase in noise level that can occur when the flow changes from laminar to turbulent.

## Calculate fan current

The first step in designing a heatsink is to determine the operating point of the fan and heatsink combination. When a fan or blower is attached to a heat sink, the performance of the fan depends on the design of the heat sink.

Each fan has a unique pressure/flow performance curve where flow is inversely proportional to the pressure drop across the fan, as shown in Figure 3. Heat sinks also have a pressure/flow performance curve. flow that is proportional to the pressure drop across the fan. The heat sinks are also shown in Figure 3. The resulting flow rate through a fan/heat sink combination is the intersection of the pressure/flow rate curves for the fan and the heat sink.

Figure 3. Pressure versus flow curves for the fan and heat sink

Fan curves are typically provided by the fan manufacturer and are generally not linear. In many cases, only maximum volume flow and maximum pressure drop are provided as ventilator performance data. To simplify the flow calculation and to account for cases where the fan is only given maximum flow and pressure drop, a simple linear approximation of the fan curve can be expressed using Equation 2. This linear approximation The fan curve will in most cases provide a reasonable estimate of the fan performance curve.

2

Wo:

is the maximum pressure drop of the fan

is the maximum flow of the fan

In situations where multiple fans are used side by side (in parallel), the maximum volume flow of the fans, V_{maximum}is the maximum flow of a fan multiplied by the number of fans.

The equation for the pressure drop across the heat sink is given by Equation 3.

3

The air density ρ is calculated at room temperature.

The hydraulic diameter of the passage between the ribs D_{H}can be approximated as 2s. The K-variables_{C}I_{mi}are the coefficients of pressure drop due to the constriction and expansion of the air as the flow enters and leaves the heat sink. The equations for these pressure drop coefficients are a function of frontal area σ=s/(s + t) and are based on the graphs in reference 1.

4

5

The apparent friction factor f_{Application}it is based on a model developed in reference [2].

6

, is the Reynolds number, where ν is the kinematic viscosity.

oThe term in Equation 6 represents the friction factor due to fully developed flow between the cooling fins. Fully developed flow occurs in very long channels or slower flows where the flow velocity profile remains constant.

7

To determine the fan/heat sink operating point (i.e., the intersection of the fan and heat sink pressure/flow rate curves), equate Equations 2 and 3 and the unknown variablecertainly.

8

## Optimize the space between slats

The distance between the fins that gives the maximum rate of heat transfer, s_{choose}is calculated using Equation 9, where μ and α are the viscosity and thermal diffusivity of air, respectively. This equation was modified by Bejan et al. developed in reference 3.

9

The ideal distance between slats, s_{choose}is a function of the pressure drop across the fan, ΔP_{Fan}and therefore the heat sink, ΔP_{hour}. The pressure through the system determines the flow rate through the heat sink,and it is this flow rate that affects the heat transfer rate of the heat sink.

Equation 9 is replaced with the fin spacing s in Equation 8 and then the system flow is determined by solving the resulting equation for.

Note that although ΔP_{Fan}and PA_{hour}are the same when solving Equation 8, only Equation 2, ΔP_{Fan}should be used in Equation 9 when solving for. Equation 3 for ΔP_{hour}depends on the spacing of the ribs, s therefore with ΔP_{hour}in Equation 9 to solve for the flow rate is mathematically unsolvable.

## Calculation of the heatsink thermal resistance

with the flowand the velocity of flow through the ribs, V_{F}Known from the solution of Equation 8, the heat transfer rate and thermal resistance of the heat sink can now be determined.

The average heat transfer coefficient h_{F}of the cooling fins is calculated using Equations 10, 11, 12, 13 and 14 developed in Reference 4.

10

where k is the thermal conductivity of the air.

11

12

Pr is the Prandtl number for air. For the typical temperature ranges in which a heat sink used in cooling electronic components operates, a value of 0.71 can be used.

13

14

The total thermal resistance of the heat sink R_{hour}and then:

15

The wet surface of the heat sink A_{hour}It is the surface that comes into contact with the air that flows over the heatsink.

The first term in Equation 15 is the thermal resistance due to the fins and the term after the plus sign is the thermal resistance due to the base of the heat sink.

sixteen

check our postHeat sink sizing with some simple equationsfor an explanation of the calculations for optimizing and sizing heat sinks cooled by natural convection.

references

[1] W. M. Kays y A. L. London, Compact Heat Exchangers. Nova Iorque:

McGraw-Hill, 1984

[2] Y. S. Muzychka and M. M. Yovanovich, "Friction Factor Modeling in

Non-Circular Conduits for Development of Laminar Flow”, in Proceedings of the 2nd AIAA Fluid Mechanics Theoretical Meeting, Albuquerque, NM, 15-18. June 1998

[3] A. Bejan and E. Sciubba, "The Ideal Separation of Cooled Parallel Plates by Forced Convection," in International Journal of Heat and Mass Transfer, Vol. 35, no. 12 pages 3259-3264, 1992

[4] P. M. Teertstra, M. M. Yovanovich, J. R. Culham and T. F. Lemczyk,

"Analytical modeling of forced convection of plate-finned heat sinks", in Anais do

15th Annual IEEE Semiconductor Thermal Measurement and Management Symposium, San Diego, CA, 9.–11. March 1999, S. 34 bis 41

## FAQs

### How can I improve my heat sink design? ›

A heat sink design can be improved by **adding fans or pins, choosing an alternative material, or adding in forced cooling via convection**. A heat sink works by absorbing thermal energy in the surrounding environment from electrical component inefficiency via the conduction method of heat transfer.

**What is the optimization of vertical heat sink fin spacing for natural convection? ›**

**At 15 fins optimum spacing is 0.00745m**. by this we can conclude that heat sink with 15 finned surfaces will give the good performance for the given geometry. Therefore, 0.00745m is an optimum spacing for given geometry at which maximum natural convection heat transfer from heat sink is occurring.

**What is optimization of thermal design of heat sinks? ›**

The thermal design optimization of the heat sinks **leads to minimize the size and weight of the heat sink, and then improve the heat removal in consequently increasing the speed of electronic devices**. Electronic devices are increasingly miniaturized and the operating power of CPU increases.

**What are three factors you should consider when choosing a heatsink? ›**

**What exactly makes a good heat sink?**

- The operating temperature of the machine.
- Heat dissipation characteristics.
- Maximum operational limits for the key components.

**Which fin shape is best for heat sink? ›**

Wiriyasart and Naphon [22] presented a numerical study of a plate heat sink with different fins shapes (**circular, conical and rectangular**). The results showed that the circular fins enhanced the thermal performance of the heat sink and lower the thermal resistance by 25% and 12% than the other two shapes respectively.

**Is higher or lower thermal resistance better for heat sink? ›**

A material's thermal conductivity is the number of Watts conducted per metre thickness of the material, per degree of temperature difference between one side and the other (W/mK). As a rule of thumb, the lower the thermal conductivity the better, because the material conducts less heat energy.

**What heat sink is best for natural convection? ›**

We recommended the use of an **anodized finish** under natural convection. Since an anodized surface offers higher emissivity than bare aluminum, the thermal performance will be better.

**What is optimal fin spacing? ›**

These results indicate that the optimum fin spacing is **between 6.1 and 11.9 mm**, for the fin arrays employed in the earlier and present work.

**Which heat exchanger design is the most efficient? ›**

**Plate exchanger** is the most efficient due to turbulent flow on both sides. High heat-transfer coefficient and high turbulence due to even flow distribution are important. However, a plate heat exchanger regenerator is restricted to low viscosities.

**What are the guidelines recommended for the selection of heat sinks? ›**

When selecting a heat sink, it is necessary to **classify the air flow as natural, low flow mixed, or high flow forced convection**. Natural convection occurs when there is no externally induced flow and heat transfer relies solely on the free buoyant flow of air surrounding the heat sink.

### How do you optimize the thermal performance of building components? ›

**Installing floor insulation** can improve thermal performance and comfort. Cold floors absorb heat, and wooden floorboards can let cold air enter a room from below. A warm floor significantly improves thermal comfort for occupants.

**What is thermodynamic optimization? ›**

Thermodynamic optimization is **a response to requirements on energy production and its efficient use**.

**Does a bigger heatsink mean better cooling? ›**

Top Things to Look For in a CPU Cooler

**The larger the heatsink, the more readily it can dissipate heat**. On this note, a larger base plate surface area means better transfer of heat from the CPU to the pipes and more room for mounting error.

**Does the color of a heatsink matter? ›**

**In natural convection a black or dark colored heatsink will perform 3% to 8% better than an aluminum heatsink in its natural silverish color**. This is due to the fact that dark colors radiate heat more efficiently.

**Does size of heatsink matter? ›**

The most important factor in the effectiveness of a heatsink is the surface area of the fins or pins – **the greater the surface area, the more effective the heatsink**. This can be achieved by having either a larger plan area or taller fins.

**What is the most efficient fin shape? ›**

The **rectangular fin with single-step change** has been found to be the most efficient fin profile in terms of maximum heat loss and fin efficiency.

**Which shape of fin is most effective? ›**

Why is the **Elliptical Fin** the Best Shape? The reason the elliptical fin shape is best is that it produces the least amount of “induced drag.” Induced drag is a fancy aeronautical engineer- ing term that means that the drag force produced is actually a result of something else happening.

**Can a heat sink be too big? ›**

It's irrelevant how long it takes for the sink to heat up, as long it is giving the source's heat a place to go and an easy path to get there. **A bigger-than-needed heat sink is fine, as long as the thermal impedance between the source and sink is low enough**.

**What variables affect the performance of a heat sink? ›**

Heat sink performance is known to be affected by a number of factors including: **fin shapes, fin dimensions, fin gap space, number of fins, fin array arrangements, position of heat surfaces and type of cooling liquid used in heat sink**.

**Does lower resistance produce more heat? ›**

The heating effect of an electric current depends on three factors: The resistance, R of the conductor. **A higher resistance produces more heat**.

### What is typical heatsink thermal resistance? ›

A heat sink will be required with a Thermal Resistance of less than or equal to **5.76°C/W**.

**What are the design parameters of heat sink? ›**

Some of the key factors that should be considered in heat sink design include **thermal resistance, material, fin configuration, fin size and shape, fin efficiency, heat sink attachment method, and thermal interface material**.

**Which is better natural or forced convection? ›**

The big positive attribute of **forced convection** versus natural convection is the increased amount of heat transfer. By being able to move more fluid through a system in the same period of time, more heat absorbed by the fluid can be forced away from your heat source.

**Is forced convection better than natural? ›**

**Forced convection increases the rate of heat transfer compared to natural convection**. The rate of heat transfer in forced convection depends on the velocity of air. The higher the air velocity, the higher will be the rate of heat transfer. Forced convection involves fluid motion as well as conductive heat transfer.

**How do you maximize fin efficiency? ›**

Since the fin efficiency is inversely proportional to Λ, it can be improved either by **increasing k and B, or by decreasing 〈h〉 and L**. If the average heat transfer coefficient, 〈h〉, is increased due to an increase in the air velocity past the fin, the fin efficiency decreases.

**Why are thin and closely spaced fins always preferred? ›**

For highest fin effectiveness, the perimeter of fin should be large and cross- sectional area should be low. It means, for a large value of perimeter, fins should be closely spaced (**to increase the total number of fins** ) and for lower value of cross-sectional area, it should be thin.

**Does fin shape matter? ›**

FIN SHAPE. **The shape of the fin also affects the way the board behaves in different conditions**. A fin with a more upright shape (with less rake) is designed for more vertical surfing and offer less hold/more release.

**How do you maximize a heat exchanger? ›**

**Consider the following techniques, as applicable, to optimize heat exchanger efficiency:**

- Changing from series to parallel exchanger operation. ...
- Checking and correcting exchanger tube velocities. ...
- Increasing air flow to air-cooled exchangers. ...
- Adding more heat exchanger surface.

**Which flow pattern is more efficient for heat transfer? ›**

“The **counter flow pattern** in shell and tube heat exchangers is the most efficient.” The counter flow pattern is the most common in shell and tube heat exchangers, primarily because it's the most efficient. This flow pattern allows for the greatest temperature change between fluids.

**Which two standards are generally used for heat exchanger design? ›**

There are various standards, codes and quality control guidelines that apply to the design and manufacture of heat exchangers. These include industry codes such as **ASME, PD500 and EN13445**, manufacturing standards like TEMA and API, plus standards such as ISOs.

### What is design and selection criteria for heat exchanger? ›

Main Criteria for Heat Exchanger Sizing and Selection

For a gasketed plate heat exchanger, **the gaskets must be compatible with the fluids in the unit**. Thermal fluid characteristics and product mix. If the heating or cooling fluid is susceptible to fouling, a corrosion resistant material may be needed. Location.

**Which of the following combinations of properties would be most desirable for a heat sink in a machine? ›**

**High specific heat and low conductivity**.

**What factors should be considered by the designers to ensure thermal comfort of a building? ›**

From an indoor environmental point of view, as well as air temperature, we also need to take into account parameters such as **radiant temperature, humidity and air velocity**.

**How do you achieve optimum thermal comfort in buildings? ›**

**4 ways thermal comfort can be achieved through good design, construction, and maintenance**

- Use a HVAC system that regulates MRT. ...
- Minimise leakage. ...
- Design and build for some occupant control. ...
- Maintain the thermal environment, and make changes as necessary.

**What is the most efficient thermodynamic cycle? ›**

Classical thermodynamics indicates that the most efficient thermodynamic cycle operating between two heat reservoirs is the **Carnot engine** [1] , and a basic theorem expresses that any reversible cycle working between two constant temperature levels should have the same efficiency as a Carnot cycle [2].

**What are the 4 thermodynamic processes? ›**

**There are four types of thermodynamic processes, they are,**

- Isothermal process.
- Isobaric process.
- Isochoric process.
- Adiabatic process.

**What are the 3 thermodynamic processes? ›**

In Thermodynamics, types of processes include: Isobaric process in which the pressure (P) is kept constant (ΔP =0). Isochoric process in which the volume (V) is kept constant (ΔV =0). Isothermal process in which the temperature (T) is kept constant (ΔT =0).

**Are thicker heatsinks better? ›**

All else being equal, yes. **A larger heat sink will have more surface area than a smaller one of the same geometry**. The rate of heat transfer across a surface is proportional to both the temperature differential and the surface area, so more surface area means a proportionately higher rate of transfer.

**Does the orientation of the heatsink matter? ›**

**Heat sink attachment/orientation plays a significant role under natural convection**. It is recommended that the heat sink be installed to orient the fins in a direction that will not block air movement under natural convection.

**What color deflects heat best? ›**

1. **Wear White**. A white object is white because it reflects white light, and white light is a combination of all the visible colors. This means that a white shirt (or pants) will reflect most of the light and not get hot.

### Does painting a heatsink affect performance? ›

**Do not paint heat sinks**. The layer of paint will act as an insulator between the metal and the air, reducing its ability to dissipate heat.

**How can I improve my heatsink performance? ›**

A really effective way of improving the spreading capability of a heat sink base is to **embed heat pipes**. Heat Spreading Heat Pipe Assemblies leverage the rapid heat transport capabilities of two-phase cooling, which helps increase how well a heat sink base can spread heat to each of the fins.

**Is higher thermal resistance better for heat sink? ›**

Thermal resistance : Heat sinks are rated by their thermal resistance and measured in Kelvin per watt (K/W). **The lower the thermal resistance is, the better the heat sink will transfer heat**. Thermal Resistance = Temperature/Power Dissipation.

**How can I improve the heatsink on my laptop? ›**

**Here are some simple ways to do that.**

- Avoid carpeted or padded surfaces. ...
- Elevate your laptop at a comfortable angle. ...
- Keep your laptop and workspace clean. ...
- Understand your laptop's typical performance and settings. ...
- Cleaning and security software. ...
- Cooling mats. ...
- Heat sinks.

**Can you stack heatsinks? ›**

Without gluing them, I did test and confirm that **all heatsinks can be stacked on top of each other and fit inside the case**. With the heatsink pile so high, the cooling fan was blowing right through them (that shouldn't be a problem once they are properly glued in with thermal glue).

**What are four factors that affect heat distribution? ›**

**The altitude of the place**. **Distance from the sea**. **The air- mass circulation**. **The presence of warm and cold ocean currents**.

**What metal is best for heat sink? ›**

Aluminum is the most common material for heat sinks. In particular, **extruded aluminum** heat sinks fit the needs of most projects. The metal is lightweight and has relatively good thermal conductivity.

**How tight should a CPU heatsink be? ›**

You don't have to screw it down all the way (though I tend to) when it has springs on the screws but so long as there's enough pressure to keep the cooler flat against the CPU then it is **tight enough to function fine**.

**Why do laptops use a heat spreader instead of heatsinks in their cooling system? ›**

Heat spreaders are **ideal for systems that expect to operate under extreme shock and vibration**, or systems that need to be completely sealed inside a container to protect it from the environment.

**How many degrees does a laptop cooling pad help? ›**

First, laptop cooling pads do offer varying degrees of effective cooling. Both internal and external temperatures were effectively lowered, with internal heat levels dropping by **as much as 30 degrees Fahrenheit** when added up across multiple tests and averaged across our three laptops.

### What characteristics does a heat sink have that improves its ability to get rid of heat energy? ›

The materials for heat sink applications should have **high heat capacity and thermal conductivity** in order to absorb more heat energy without shifting towards a very high temperature and transmit it to the environment for efficient cooling.

**What are the physical principles behind the action of the heat sinks? ›**

Heat sinks work by **redirecting heat flow away from a hot device**. They do this by increasing the device's surface area. In order for heat sinks to properly work, they must have a temperature higher than the surroundings to transfer heat.

**In what direction do the hottest materials move during convection? ›**

Convection works when a liquid or gas is unevenly heated. Hot liquids (and gases) are less dense and rise, causing. **The warmer section of the material will rise** while the cooler part sinks. This creates a current of warmer material going up and a current of cooler material going down.