# Peltier heat conductance concept question (PID)

• Kvm90
In summary, the conversation discusses the use of a Peltier junction for a cooling system and the challenges of maintaining a constant temperature on the hot side. The concept question is whether heat conduction across the bismuth alloy is affected by the temperature difference between the hot and cold sides. The response explains that a Peltier is not an efficient cooling engine and suggests using a different method such as heat pipes or active refrigerant systems. Ultimately, the use of a Peltier should be based on practical reasons rather than simply for its novelty.
Kvm90
Hey,

I am making a cooling system using a peltier junction with a cold finger on one side and a heat sink on the other. For my heat sink, I am depositing the heat into the phase change of a bismuth alloy (about 70 deg C). When the current across the peltier is increased and the hot side increases to large temperatures, it starts to heat up the cold side (which is bad for my project).

My concept question is: Should I install a thermistor on the hot side with a PID loop in order to keep the hot side around 70 C? My concept question is if the rate at which heat is conducted across the bismuth alloy is dependent on the temperature. In other words, if the hot plate is at 100C does that mean the heat sink will disperse the heat faster than if the hot plate is at 70C?

Thanks, quick assistance is appreciated.

The point of the Peltier is that you need to remove the heat. This the basic thermodynamics of it. Dropping the operating current (and thus hot-side temperature) will reduce the cooling. The only "correct" answer is to heat sink the hot side better.

There are two factors: how fast heat and how much heat. A larger temperature differential will increase the these a bit but it's not that simple because it depends on the mode of heat transfer (conduction, convection or radiation) and on the effective resistance of each other these (thermal resistance, flow parameters and albedo & ambient temperature, respectively).

But this is really the whole problem with a Peltier - it's insanely inefficient as a cooling engine (~1-4%) compared to a heat pipe or active refrigerant system which can hit 20-30%. Even a simple minimal latent-heat working fluid (forced water or forced air) will work better than a Peltier in terms of efficiency and flux rate.

The reason for using a Peltier is mostly because there is no other practical alternative to cooling. Usually it's a space problem that has a finite heat source rate and sufficient next-stage transfer like a convected cooling system on the Peltier's sink. If you chose a Peltier cooler because the are "nifty" or equivalent, you selected it for wrong reasons. It's a very niche-y technology in practice.

## 1. What is the Peltier effect and how does it relate to heat conductance?

The Peltier effect is a phenomenon in which a temperature difference is created at the junction of two different conductive materials when an electric current is passed through them. This effect is directly related to heat conductance because it can be used to create a temperature gradient and transfer heat from one material to another.

## 2. How does a Peltier module work?

A Peltier module, also known as a thermoelectric cooler, consists of two different conductive materials with a semiconductor junction in between. When an electric current is passed through the module, one side becomes cold while the other becomes hot due to the Peltier effect. This allows for heat to be transferred from one side to the other.

## 3. What is the role of a PID controller in Peltier heat conductance?

A PID (Proportional-Integral-Derivative) controller is used to regulate the temperature of a Peltier module by adjusting the amount of current passing through it. It continuously monitors the temperature and makes adjustments to maintain a set temperature, making it an essential component in Peltier heat conductance systems.

## 4. Can Peltier modules be used for both heating and cooling?

Yes, Peltier modules can be used for both heating and cooling by simply reversing the direction of the electric current. This allows for precise control of temperature in both heating and cooling applications.

## 5. What are the advantages of using Peltier modules for heat conductance?

Peltier modules offer several advantages for heat conductance, including precise temperature control, compact size, and the ability to heat and cool with one device. They also have no moving parts, making them reliable and low maintenance. Additionally, they can be easily integrated into electronic systems and do not require any external refrigerants or coolants.

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