What is the Difference Between Pool Boiling and Flow Boiling

The key difference between pool boiling and flow boiling is that pool boiling occurs in the absence of bulk fluid flow, whereas flow boiling occurs in the presence of bulk fluid flow.

Pool boiling is a heat transfer mechanism in which a phase transition occurs from liquid to vapor. Flow boiling, on the other hand, is a heat transfer mechanism that occurs when a fluid circulates over a heated surface due to external causes such as a pump or due to the natural buoyancy effect.

CONTENTS

1. Overview and Key Difference
2. What is Pool Boiling 
3. What is Flow Boiling
4. Pool Boiling vs Flow Boiling in Tabular Form
5. Summary – Pool Boiling vs Flow Boiling 

What is Pool Boiling?

Pool boiling is a heat transfer mechanism in which a phase transition occurs from liquid to vapor. This can happen in the presence of any motion of the fluid occurring due to natural convection currents and the motion of the bubbles under the influence of buoyancy.

The rate of heat transfer in the pool boiling process greatly depends on the number of active nucleation sites on the surface and also the rate of bubble formation at each site. Therefore, we can modify and enhance nucleation on the heating surface to enhance the heat transfer in nucleate boiling. Besides, uneven heating surface such as roughness and dirt can serve as an additional nucleation site for boiling.

What is Flow Boiling?

Flow boiling is a heat transfer mechanism that occurs when a fluid circulates over a heated surface due to external causes such as a pump or due to the natural buoyancy effect. In other words, in the process of flow boiling, the fluid is forced to move in a heated pipe or over a surface by external means.

This is also known as external forced convection boiling. Here, the fluid undergoes phase change upon moving through an external source such as a pump. In this case, the boiling tends to exhibit combined effects of convection and pool boiling. We can classify flow boiling as either external or internal flow boiling. In external flow boiling, the higher the velocity, the higher the nucleate boiling heat flux and the critical heat flux. There are different flow regimes related to flow boiling, which include:

What is the Difference Between Pool Boiling and Flow Boiling?

Pool boiling is a heat transfer mechanism in which a phase transition occurs from liquid to vapor. Flow boiling, on the other hand, is a heat transfer mechanism that occurs when a fluid circulates over a heated surface due to external causes such as a pump or due to the natural buoyancy effect. Pool boiling and flow boiling are important boiling techniques. The key difference between pool boiling and flow boiling is that pool boiling occurs in the absence of bulk fluid flow, whereas flow boiling occurs in the presence of bulk fluid flow.

Below is a summary of the difference between pool boiling and flow boiling in tabular form for side by side comparison.

Summary – Pool Boiling vs Flow Boiling

Pool boiling is a heat transfer mechanism in which a phase transition occurs from liquid to vapor. Flow boiling, on the other hand, is a heat transfer mechanism that occurs when a fluid circulates over a heated surface due to external causes such as a pump or due to the natural buoyancy effect. The key difference between pool boiling and flow boiling is that pool boiling occurs in the absence of bulk fluid flow, whereas flow boiling occurs in the presence of bulk fluid flow.

Reference:

1. Roh, Heui-Seol. “Heat Transfer Mechanisms in Pool Boiling.” International Journal of Heat and Mass Transfer, Pergamon, 12 Oct. 2013.

Image Courtesy:

1. “Boiling, water, hot, pool, spring, water” (CC0) via Pixabay

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