Advantages of the use of Pillow-Plates Heat Exchangers (PPHEs)

Last week, we published our very brief introduction about this innovative heat exchanger, explaining the origin of the name pillow, citing some examples of applications, and explaining the fabrication process of the plates.

The purpose of this article is to describe several advantages the PPHEs offer when related to certain applications. Some of these principal applications are Ice Machines; Heat pumps; Jacketed Tanks; Film falling evaporators; Thermosiphon Reboiler, column reboilers, and heat recovery. These applications are presented in many industries like HVAC, Food, Chemistry, automotive, etc.

Beyond the fact that they have high corrosion resistance, low-pressure drop, high-pressure, and temperature resistance, as pointed in the previous article, the list below describes other advantages of the use of PPHE.

• Good cleanability: The PPHE has a good cleanability that leads also to low costs of maintenance. Differently from other types of heat exchangers, as shell and tube, a mechanical cleaning procedure is not available. The inner channels of the pillow plates can be cleaned exclusively chemically or with the use of a return flow. Is not desirable to use fouling media in the inner channels but only in the outer channels between the plates that can be cleaned both chemically and mechanically.
• High Welding Reliability: Commonly the welding point diameters are chosen as small as possible is that so provide the necessary mechanical stability for the plate the hydroforming process and long-term use of the plates. Reducing the welding point diameter improves heat transfer and decreases pressure loss. Mitrovic and Maletic (2011) reported that the presence of a welding spot in a pillow channel increases the thermal performance compared to other conventional heat exchangers, particularly at a high Reynolds number.
• Excellent Turbulence Design: The wavy aspect of the plates plays is a key factor in the thermo-hydraulic performance of this type of heat exchanger ensuring the turbulent movement of heat carriers inside them. The possibility to use different cross-sectional areas for the cold and hot sides allows the heat transfer surface area in PPHEs to be reduced compared to other types of heat exchangers under the same application conditions. (Arsenyeva et al. 2018)
• High Heat Exchange Coefficient: The medium inside the pillow-plates is being continuously redirected by the welding point pattern. This leads to thin boundary layers and good heat transfer performance, and hence, to lower required heat transfer area and lower investment. (M. Tran et al.2018)
• No gaskets required: As no gaskets are required, it contributes to PPHE to achieve high temperatures and high pressures leaving aside the need for caution on choosing the gasket material to specific operating conditions. Besides the fact that it promotes a low production cost.
• Flexible Design: Due to their flexible design, pillow plates may also be used as heating or cooling jackets for reactors, vessels, tubing of storage tanks, etc. (M. Tran et al.2018))

It is apparent from the list above that there are many benefits when using a PPHE about its thermal performance besides the evidence of low manufacturing costs and low maintenance costs in respect to other types of heat exchangers.  Their manufacturing process is much simpler than the Shell and Tube Heat Exchanger manufacturing process, involving much less physical space, costs with transportation and installation and material.

The high complexity geometry of the pillow-plates makes a very challenging task their design parameters. Generally, a design parameter is evaluated to order to increase the PPHE performance. (M. Tran et al. 2018).

A number of researchers have reported the thermal performance of different types of PPHE comparing numerical and experimental data (Jia et al., 2017; Zhang et al., 2017; Aradag et al., 2017; Arie et al., 2015; Dutta and Rao, 2018; Jin and Hrnjak, 2017; Rao and Das, 2004; Rao et al., 2006, apud Shirzada et al. (2019)).

Piper M. et al. (2015), studied the determination of the geometric design parameters of the PPHE presenting new equations, obtained by simulations, for the accurate determination of the mean hydraulic diameter, mean cross-sectional area, and heat transfer area for the inner channel and the outer channel. The main contribution of their work is that the equations presented allow the calculation of Reynolds and Nusselt numbers as well as the heat transfer area for the PPHE. Shirzada et al. (2019) investigated the effects of geometrical parameters on the PPHE performance through numerical simulations comparing them to experimental data.

Figure 1. a) A Pillow Plate heat exchanger

Figure 1. b) Channels formed by pillow plates;  Arsenyeva et al. (2018)

As can be observed, several studies are being conducted in order to obtain a procedure for an optimal design parameter for PPHEs that are in the growing demand for energy-saving in industries.

Next steps…

In next article we will approach a specific PPHE application. Which one would prefer to read about? Heat Recovery, Film Falling Evaporator, Air Heater or Air Cooler? Let us know!

Milena Vilar França
Dsc degree in Mechanical Engineering
Engineering Dept., Unilab Srl

References

• Piper, A. Olenberg, J.M. Tran, E.Y. Kenig, Determination of the geometric design parameters of pillow-plate heat exchangers, Applied Thermal Engineering (2015), doi: 10.1016/ j.applthermaleng.2015.08.097
• Mitrovic, J., Maletic, B., 2011. Numerical simulation of fluid flow and heat transfer in thermoplates. Eng. Technol. 34, 1439–1448. doi:10.1002/CEAT.201100271
• Shirzada, M., Delavar, M. A., Soheil, S., Ajarostaghi, M., Sedighi, K., Evaluation the effects of geometrical parameters on the performance of pillow plate heat exchanger, Chemical Engineering Research and Design 1 5 0 (2019) 74–83 https://doi.org/10.1016/j.cherd.2019.06.032
• Arsenyeva, J. Tran, M. Piper, E. Kenig, An approach for pillow plate heat exchangers design for single-phase applications, Applied Thermal Engineering (2018), doi:https://doi.org/10.1016/ j.applthermaleng.2018.08.083
• Tran J.M., Piper M., Kenig E.Y., Scholl S. (2018) Pillow-Plate Heat Exchangers: Fundamental Characteristics. In: Bart HJ., Scholl S. (eds) Innovative Heat Exchangers. Springer, Cham. https://doi.org/10.1007/978-3-319-71641-1_7