Heat transfer using heat sinks

In summary, the conversation discusses a small project on thermoelectric refrigeration and the need to dissipate 98 W of power from one module via a heat sink. The speaker also mentions a heat sink of pin type measuring 96*96 mm with 98 pins of rectangular cross section and the need to find its thermal resistance when coupled with a cooling fan of 12.5W. They also ask for help in choosing a heat sink that can restrict the temperature rise to 20 degrees from the ambient temperature, and discuss the use of formulas and experimentation to find the answers.
  • #1
george varkey
3
0
hello
I need help regarding a small project on thermoelectric refrigerator. I need to cool a 5.4 ltr capacity refrigerating space to maintain it at 10-12 degrees. I have the cooling module in place.I needed to dissipate 98 W of power from one module via a heat sink.

I have a heat sink that is of pin type measuring 96*96 mm with 98 pins of rectangular cross section.I need to find:

a) The thermal resistance of this heat sink when coupled with a cooling fan of 12.5W

b)how to choose a heat sink so that the temperature rise can be restricted to 20 degrees from the ambient temperature.

anyone having any idea in this topic please reply!
 
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  • #2
Welcome to PF!

Temperature rise is a function of the airflow of the fan on the heatsink, so just multiply the heat you are dissipating by the specific heat of air and desired delta-T.

If you already have all your parts, I'd start finding some of the answers by experimentation: calculating the performance of a heatsink from scratch is near impossible.
 
  • #3
george varkey said:
hello
I need help regarding a small project on thermoelectric refrigerator. I need to cool a 5.4 ltr capacity refrigerating space to maintain it at 10-12 degrees. I have the cooling module in place.I needed to dissipate 98 W of power from one module via a heat sink.

I have a heat sink that is of pin type measuring 96*96 mm with 98 pins of rectangular cross section.I need to find:

a) The thermal resistance of this heat sink when coupled with a cooling fan of 12.5W

b)how to choose a heat sink so that the temperature rise can be restricted to 20 degrees from the ambient temperature.

anyone having any idea in this topic please reply!

Generally the datasheet for the heat sink will give you numbers for its "thermal resistance" versus airflow and orientation. Can you find a datasheet for it? If not, you could try some Google Images searching to find similar heat sinks, and look for their datasheets.
 
  • #4
thank you for both the replies!

1) yes i did figure out id have to experiment and find out the temperature rise of the heat sink( coupled with the fan )corresponding to the 90 W dissipation and see if it rises above the 20degrees from ambient.But isn't there any basic formulas behind it??(i did google it...not much help) Can you suggest me where it?

2) Yeah they do have a datasheet, but it has a thermal resistance (without the air flow) of 1.1 K/W which is a lot (because 1.1 *90 =99 degrees rise!...i do believe that is what it means right?) whereas by using the formula:

Th = Tamb + (Qh)*Rt
Th=50
Qh=90
Tamb=30

Rt comes out to be 0.22k/w ,ie to maintain temperature rise within the 20 degrees mark,i need something that is of this thermal resistance.

So i do want to know if the thermal resistance can fall this much,ie from 1.1 to .22 when coupled with a cooling fan.If so if there's any method to evaluate it theoritically?

(though my pin fin heat sink and fan should be sufficient... practically because it was provided by the thermoelectric suppliers corresponding to the particular module i had selected for cooling..so...)

yeah Ill be starting with the experimenting part !
 
  • #5
george varkey said:
2) Yeah they do have a datasheet, but it has a thermal resistance (without the air flow) of 1.1 K/W which is a lot (because 1.1 *90 =99 degrees rise!...i do believe that is what it means right?) whereas by using the formula:

Th = Tamb + (Qh)*Rt
Th=50
Qh=90
Tamb=30

Rt comes out to be 0.22k/w ,ie to maintain temperature rise within the 20 degrees mark,i need something that is of this thermal resistance.

So i do want to know if the thermal resistance can fall this much,ie from 1.1 to .22 when coupled with a cooling fan.If so if there's any method to evaluate it theoritically?

Inproving the cooling by a factor of 5 by using forced convection doesn't seem unreasonable to me.

Almost all the formulas you will find on the web or in heat transfer handbooks are based on experimental correlations. The big problem with using them correctly is knowing what physical situation they apply to. Outside of their proper range they can sometimes be ridiculously wrong - even giving negative heat transfer (from cold to hot).

It may seem counter-intuitive, but it's actually easier to calculate heat transfer "from first principles" for much more extreme situations, like hypersonic flow (e.g. space shuttle re-entry) than for air wafting around at low speed where the flow pattern is strongly affected by the change in air temperature and the resulting changes in density and bouyancy.
 

1. What is a heat sink and how does it work?

A heat sink is a device used to dissipate heat from an object, typically a computer or electronic component. It works by increasing the surface area of the object, allowing more heat to be transferred to the surrounding air. This is achieved through the use of fins or other structures that extend from the object's surface.

2. How does heat transfer occur in a heat sink?

Heat transfer in a heat sink occurs through conduction, convection, and radiation. Conduction is the transfer of heat through direct contact between the heat sink and the object. Convection is the transfer of heat through the movement of air or liquid over the heat sink's surface. Radiation is the transfer of heat through electromagnetic waves.

3. Can heat sinks be used for both cooling and heating?

Yes, heat sinks can be used for both cooling and heating. For cooling, the heat sink dissipates heat from the object. For heating, the heat sink absorbs heat from the surrounding air or liquid and transfers it to the object.

4. What factors affect the effectiveness of a heat sink?

The effectiveness of a heat sink depends on factors such as the material used, the surface area of the heat sink, the temperature difference between the object and the surrounding air, and the airflow or liquid flow rate over the heat sink's surface.

5. How do I choose the right heat sink for my application?

Choosing the right heat sink depends on the specific requirements of your application. Factors to consider include the thermal properties of the object, the size and shape of the object, the operating environment, and the available airflow or liquid flow. It is important to consult with a specialist or conduct thorough research to ensure the best heat sink is selected for your needs.

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