Economic and Thermodynamic Comparison

The choice of heat transfer technology has a significant impact on capital costs, operational efficiency, and payback period in industrial applications. This study compares pillow-plate heat exchangers (PPHE) with conventional shell-and-tube heat exchangers (STHE) in terms of thermodynamic performance, heat transfer coefficients, pressure drop, capital and operating costs, and payback period. Pillow-plate heat exchangers are characterized by 25–30% higher heat transfer coefficients (1,000–4,000 W/(m²·K)) compared to shell-and-tube systems (150–1,200 W/(m²·K)) ^[1][2]. The compact design reduces material usage by up to 40% and space requirements by one-third ^[2][3]. Despite a 15–25% higher initial investment, PPHE systems pay for themselves within 2–4 years due to lower maintenance costs (25% reduction), higher energy efficiency (10–15% savings), and significantly reduced cleaning effort in the event of fouling ^[3]. Experimental data and CFD simulations demonstrate the superior thermal-hydraulic performance of pillow plates on small and medium scales ^[4].

Heat exchangers play a central role in industrial process heat recovery, chemical processing, food production, and power generation. Inefficient heat transfer systems cause significant industrial energy losses. The selection of the optimal heat exchanger type significantly influences not only thermal efficiency but also capital costs, maintenance requirements, and plant service life ^[5].

Shell-and-tube heat exchangers (STHE) have dominated for decades due to their robustness, pressure resistance, and proven technology in high-temperature and high-pressure applications ^[6]. Pillow-plate heat exchangers (PPHE) represent an innovative alternative that creates complex flow channels through spot and seam welding of two metal sheets followed by pneumatic or hydraulic forming ^[4][7]. This design enables improved heat transfer while simultaneously reducing pressure loss and offering a compact design ^[1][7].

The objective of this work is a systematic comparison of both technologies, taking into account:

• Thermodynamic fundamentals and heat transfer coefficients
• Hydraulic properties and pressure losses
• Design and material requirements
• Investment and operating cost analysis
• Payback calculations for typical industrial applications
• Maintenance and fouling behavior

The analysis integrates experimental data from the literature, in particular the studies by Arsenyeva et al. (2018) on small PPHE systems ^[4], as well as current economic analyses from industrial applications ^[3].

Shell-and-tube heat exchangers consist of a cylindrical shell in which a bundle of parallel tubes is arranged. One fluid flows through the tubes, while the second fluid flows through the shell space ^[6][8].

Design features:

• Tube diameter: typically 15–50 mm
• Tube lengths: 1–12 m depending on the application
• Materials: carbon steel, stainless steel, copper alloys, titanium, aluminum, nickel-based alloys, graphite
• Operating pressures: up to 200 bar
• Operating temperatures: -200 to +600 °C

Advantages:

• High allowable pressure and temperature ^[6][8]
• Proven technology with comprehensive design standards (TEMA, ASME, ISO, API)
• Suitable for contaminated media due to mechanical cleaning capability ^[9]
• Long service life (20–30 years)

Disadvantages:

• Requires a large amount of space and is heavy ^[10][11]
• Lower heat transfer coefficients (150–1,200 W/(m²·K)) ^[2]
• Higher maintenance requirements due to the need for tube cleaning ^[9]
• Uneven temperature distribution with flow maldistribution ^[8]

2.2 Pillow-plate heat exchangers

Pillow-plate heat exchangers are manufactured by spot welding of two metal sheets according to a defined welding pattern and subsequent hydroforming (inflating). This creates pillow-like channels with complex three-dimensional geometry ^[4][7].

Design features:

• Sheet thickness: 0.5–2.0 mm (typically 0.8–1.5 mm)
• Spot weld spacing: 30–60 mm longitudinally, 20–40 mm transversely ^[7]
• Channel expansion (channel height): 2–8 mm
• Materials: Carbon steel, stainless steel, titanium, nickel-based alloys 
• Operating pressures: up to 40 bar (standard), up to 100 bar (special designs)
• Operating temperatures: –273 to +500 °C

Advantages:

• High overall heat transfer coefficients (1,000–4,000 W/(m²·K)) ^[1][2]
• Compact design with up to 30% space savings ^[2][3]
• Low material usage (up to 40% less steel than STHE) ^[12]
• Reduced fouling due to smooth surfaces and turbulent flow ^[7]
• Easy cleaning without disassembly thanks to CIP capability ^[3]
• Flexible adaptation to different flow rates through variable flow guidance and channel spacing ^[4][7]

Disadvantages:

• Limited pressure resistance compared to STHE ^[6]
• Higher initial investment (15–25% above STHE for comparable performance)
• Less established design standards ^[13]
• Limited suitability for very high-viscosity media

The overall heat transfer coefficient U [W/(m²·K)] describes the heat transfer rate:

$\frac{1}{U}=\frac{1}{h_1}+\frac{{\delta }_w}{{\lambda }_w}+\frac{1}{h_2}+R_{f }$

Where h₁ and h₂ are the heat transfer coefficients on both sides [W/(m²·K)], δ_w is the wall thickness [m], λ_w is the thermal conductivity of the wall material [W/(m·K)], and R_f is the fouling resistance [(m²·K)/W] ^[2][14].

Reference values from the literature:

Table 1: Comparison of overall heat transfer coefficients for various heat exchanger types

Pillow plates achieve 25–30% higher heat transfer coefficients than shell-and-tube systems ^[1][7]. 

This results from:

• Turbulence induction: The pillow-like geometry generates artificial turbulence even at low Reynolds numbers (Re < 2300), thereby breaking up the laminar boundary layer ^[4][15].
• Increased surface area: The three-dimensional expansion increases the effective heat transfer area by 15–20% compared to flat plates ^[7].
• Optimized flow guidance: Secondary flows and vortex formation intensify convective heat transfer ^[4][15].

3.2 Experimental Data from Small-Scale PPHE Studies

Arsenyeva et al. (2018) conducted experimental investigations on small pillow plates ^[4]. The main geometric parameters:

Table 2: Geometric parameters of the investigated small pillow plates according to Arsenyeva et al. (2018) ^[4]

Test setup:

• Cooling water (20 °C, 900 kg/h) flows through the internal channels of the pillow plates
• Hot air (325 °C, 40 to 105 kg/h) flows through the outer channel between the pillow plates
• Pressure drop and temperature measurements with an accuracy of ±0.10% (water) and ±0.50% (air) ^[4]

Experimental results:

For the inner pillow channels (water): h₁ = 6.280 W/(m²·K) ^[4]
For the outer channel (air): h₂ = 57 W/(m²·K) ^[4]

Correlation for the outer PPHE channel:

Friction factor for pressure loss:

$\lambda =\mathrm{0,7155}\cdot {\text{Re}}^{-\mathrm{0,361} }$

Nusselt number for heat transfer:

$\text{Nu}=\mathrm{0,0275}\cdot {\text{Re}}^{\mathrm{0,8175}}\cdot {\text{Pr}}^{\mathrm{0,4} }$

Scope of validity: 3.000 < Re < 20.000 (turbulent flow) ^[4].

The deviation between the experimental data and CFD simulations was less than 15%, which represents satisfactory agreement ^[4].

3.3 Comparison of Heat Transfer Efficiency

For a typical application (water-water heat exchange, ΔT = 20 K, Q = 100 kW), the following results:

Required heat transfer area:

$A=\frac{\dot{Q}}{U\cdot \mathrm{\Delta }{T}_{m }}$

where ΔT_m is the mean temperature difference which depends on the flow arrangement.

Comparative calculation:

Table 3: Comparison of the required heat transfer area at thermal performance of 100 kW

PPHE require approximately 60–70% less heat transfer area than STHE for the same thermal thermal performance ^[1][2].

The pressure drop Δp [Pa] in heat exchangers is described by:

$\mathrm{\Delta }p=\lambda \cdot \frac{L}{d_h}\cdot \frac{\rho \cdot v^2}{2 }$

Where λ is the friction factor [-], L is the channel length [m], d_h is the hydraulic diameter [m], ρ is the fluid density [kg/m³], and ν is the mean flow velocity [m/s] ^[14].

4.2 Comparative Data on Pressure Drop

Tube bundle heat exchanger:

• Tube side: Pressure drop 10–50 kPa (typical)
• Shell side: Pressure drop 20–100 kPa depending on baffle arrangement ^[8]
• Flow maldistribution can lead to dead zone formation ^[6]

Pillow-plate heat exchanger:

• Inner channel: Pressure drop 15–60 kPa
• Outer channel: Pressure drop 5 to 30 kPa ^[4][7]
• Flat, parallel channels reduce pressure loss in the shell space ^[3][12]

Experimental data from Arsenyeva et al. (2018) ^[4]:

For the outer channel at Re = 5.173 (turbulent flow), the following was obtained:

• CFD-simulated heat transfer coefficient: 47 W/(m²·K)
• Experimental value: 56.81 W/(m²·K)
• Deviation: 17%, explainable by inlet effects ^[4]

PPHE units exhibit up to 30% lower pressure drop on the product side compared to STHE units with comparable thermal performance ^[3][12].

Fouling reduces the heat transfer coefficient and increases pressure drop. The fouling resistance R_f [(m²·K)/W] is determined empirically ^[14].

Typical fouling resistances:

Table 4: Comparison of typical fouling resistances [(m²·K)/W]

PPHE exhibit 30–50% less fouling than STHE ^[7] due to:

• Smoother surfaces (welded stainless steel vs. tubes with baffles)
• Higher wall shear stresses due to turbulence ^[4]
• Self-cleaning effect due to pulsating flow in pillow-like channels ^[15]

5.2 Maintenance requirements

Shell-and-tube heat exchangers:

• Mechanical cleaning with tube brushes required (1–2 times per year or more frequently, depending on fouling) ^[9]
• Removal of end caps is time-consuming (4–8 hours) ^[9]
• Gaskets replacement every 2–5 years ^[6]
• Annual maintenance costs: approx. 3–5% of the investment costs ^[3]

Pillow-plate heat exchanger:

• CIP (Cleaning in Place) possible without disassembly ^[3]
• Chemical cleaning with acid/alkali solutions is sufficient
• No gaskets in the welded areas – reduced risk of leakage ^[7]
• Maintenance costs: approx. 1.5–3% of the capital costs per year ^[3]

PPHE reduce maintenance costs by up to 25% compared to STHE ^[3].

The investment costs consist of:

• Material costs (stainless steel, gaskets, fittings)
• Manufacturing costs (welding, pneumatic inflation, quality control)
• Transportation costs
• Installation costs

Comparative calculation for 100 kW thermal performance (water-water, ΔT = 20 K):

Table 5: Investment cost comparison for 100 kW thermal performance

Note: Despite higher equipment costs (+20%), PPHE compensates for this with lower installation and peripheral costs due to a more compact design ^[3].

6.2 Operating Costs

Annual operating costs consist of:

• Energy costs (pump power to overcome pressure loss)
• Maintenance costs (cleaning, inspection, repairs)
• Downtime costs (production stoppage during maintenance)

Assumptions:

• Operating hours: 6,000 h/year
• Electricity price: 0.15 EUR/kWh
• Pump efficiency: 70%
• Product value during downtime: 500 EUR/h

Energy costs (pump electricity):

$P_{\text{pump}}=\frac{\mathrm{\Delta }p\cdot \dot{V}}{{\eta }_{\text{pump} }}$

For V = 10 m³/h and Δp = 50 kPa (STHE) or 35 kPa (PPHE):

Table 6: Energy cost comparison at 6,000 operating hours/year

Maintenance costs:

Table 7: Annual maintenance costs

Downtime costs:

• STHE: 2 maintenance downtimes of 8 hours each = 16 h/year → 8,000 EUR
• PPHE: 1 maintenance period of 4 hours = 4 h/year → 2,000 EUR
• Savings: 6,000 EUR/year

Total annual operating costs:

Table 8: Total annual operating costs

Annual operating cost savings for PPHE: 7,654 EUR/year

6.3 Payback Analysis

Method: Static payback analysis (payback method) ^[23]:

$t_{\text{Payback period}}=\frac{\text{Additional investment}}{\text{Annual savings} }$

Case 1: Same investment costs (40,000 EUR)

$t_{\text{Payback period}}=\frac{0}{7.654}=0$

Case 2: PPHE 20% more expensive (48,000 EUR vs. 40,000 EUR)

$t_{\text{Payback period}}=\frac{8.000}{7.654}=\mathrm{1,05}$

Case 3: PPHE 25% more expensive (50,000 EUR vs. 40,000 EUR)

$t_{\text{Payback period}}=\frac{10.000}{7.654}=\mathrm{1,31}$

Result: PPHE systems pay for themselves within 1–2 years, even with a 25% higher initial investment ^[3].

6.4 Life Cycle Cost Analysis (15 years)

Total costs over 15 years:

Table 9: Life-cycle cost comparison over 15 years

Over a 15-year lifespan, PPHE saves approximately 53% of total costs ^[3].

• High operating pressures (> 40 bar)
• Extreme temperatures (> 300 °C or < -50 °C)
• Highly contaminating media requiring mechanical cleaning
• Chemical processes involving aggressive media (acids, alkalis)
• Petrochemical industry ^[6][8]

7.2 Preferred applications for PPHE

• Food and beverage industry (pasteurization, fermentation, cooling)
• Pharmaceutical industry (aseptic processes) ^[7]
• Chemical process engineering (moderate pressures and temperatures) ^[7]
• Energy recovery in buildings and ventilation systems
• Dairies and milk processing
• Space-constrained applications ^[2][10]

7.3 Decision Matrix

Table 10: Qualitative evaluation matrix (⭐ = low/poor, ⭐⭐⭐⭐⭐ = high/very good)

The experimental and CFD-based studies by Arsenyeva et al. (2018) ^[4] clearly demonstrate the higher heat transfer coefficients of pillow-plate heat exchangers ^[4]. The pillow-like geometry generates artificial turbulence, intensifies secondary flows, and increases the effective heat transfer area ^[7][15]. This results in heat transfer coefficients that are 25–30% higher compared to conventional shell-and-tube systems ^[1][7].

The CFD analysis also shows an uneven distribution of wall shear stress and heat flux across the pillow plate surface ^[4]. While weld points exhibit lower heat fluxes, convex areas reach maximum values. This inhomogeneity helps prevent fouling, as high local shear stresses inhibit deposits ^[15].

8.2 Economic Advantages Despite Higher Initial Investment

Despite 15–25% higher acquisition costs, PPHE systems pay for themselves within 1–2 years due to ^[3]:

• Reduced maintenance costs (25% savings due to CIP capability)
• Lower energy costs (10–15% due to lower pressure loss)
• Minimized downtime costs (shorter downtime)
• Space savings (up to 30% reduction in footprint)

Over a service life of 15–20 years, total cost savings of 20–40% result compared to STHE ^[3]. These results are consistent with industrial case studies from the food, pharmaceutical, and chemical industries.

8.3 Limitations of PPHE Technology

Despite the thermohydraulic advantages, PPHE remains limited in the following areas:

• Pressure resistance: Standard designs up to 40 bar, special designs up to 100 bar ^[7]. STHE can also be used at pressures >200 bar ^[6].
• Temperature range: PPHE, typically for austenitic stainless steels, -273 to + 500 °C . STHE: -273 to +600 °C .
• Design standards: STHE have established standards (TEMA, ASME) [8]. PPHE design is based on empirical correlations with limited scope of validity ^[4][13].
• Mechanical cleaning: For highly contaminating media (e.g., crude oil, slurries), mechanical tube cleaning is more advantageous for STHE ^[9].

8.4 Future Developments

PPHE technology is becoming increasingly important due to:

• Growing demand for compact, energy-efficient heat exchangers
• Stricter hygiene regulations in the food and pharmaceutical industries
• Advances in laser welding technology and cold forming ^[7]
• Development of CFD-based design tools ^[4][15]

The global PPHE market is estimated to reach $2.4 billion by 2033, with an annual growth rate of 7–9% ^[17].

Pillow-plate heat exchangers (PPHE) significantly outperform shell-and-tube heat exchangers (STHE) in terms of heat transfer efficiency (25–30% higher heat transfer coefficients), compactness (30% space savings), ease of maintenance (25% cost reduction), and life-cycle cost efficiency (20–40% total savings) ^[1][3][7]. Despite a 15–25% higher initial investment, PPHE systems pay for themselves within 1–2 years due to lower operating and maintenance costs ^[3].

The experimental studies by Arsenyeva et al. (2018) on small pillow plates demonstrate superior thermal-hydraulic performance with heat transfer coefficients of up to 6,280 W/(m²·K) in the inner channel ^[4]. CFD simulations confirm the intensified turbulence and optimized heat flux distribution on the pillow plate surface ^[4][15].

For applications in the food, pharmaceutical, and chemical industries with moderate pressures (< 40 bar) and temperatures (< 500 °C), PPHE represent the economically and thermodynamically superior technology ^[7]. STHE remain the preferred choice for high-pressure, high-temperature, and heavily fouling applications in petrochemicals and power generation ^[6][8].

Future developments in PPHE design standards, advanced manufacturing technologies, and CFD-based optimization tools will further accelerate the market penetration of this innovative heat exchanger technology ^[17].

^[1] HTT-AG. (2025). Dimple Plate.
https://www.htt-ag.com/de/dimple-plate/

^[2] HTT-AG. (2025). Pillow Plate Heat Exchangers: Efficient Solutions for Industry.
https://www.htt-ag.com/pillow-plate/

^[3] Raystone. (2025). The Advantages of Pillow Plate Heat Exchangers for Enhanced Efficiency in Chemical Processing.
https://www.sdraystone.com/news_details/37.html

^[4] Arsenyeva, O. P., Piper, M., Zibart, A., Olenberg, A., & Kenig, E. Y. (2018). Heat Transfer and Pressure Loss in Small-Scale Pillow-Plate Heat Exchangers. Chemical Engineering Transactions, 70, 799-804.
DOI:10.3303/CET1870134

^[5] Joybari, M. M., et al. (2022). Potentials and challenges for pillow-plate heat exchangers. ScienceDirect.
https://www.sciencedirect.com/science/article/pii/S1359431122006834

^[6] Varalka. (2024). Plate Type vs. Shell & Tube Heat Exchangers: A Comprehensive Comparison.
https://www.varalka.com/plate-type-vs-shell-tube-heat-exchangers-a-comprehensive-comparison

^[7] MBS Apparatebau. (n.d.). Pillow-Plate Condenser vs. Shell.
https://www.mbs-apparatebau.de/bilder/galerie/CaseStudy.pdf

^[8] Chemat. (2024). Shell-and-tube heat exchangers: Applications, advantages, and disadvantages.
https://chemat.de/rohrbundelwarmetauscher-anwendung-vor-und-nachteile/

^[9] EJ Bowman. (n.d.). Difference Between Plate Heat Exchangers and Shell-and-Tube Heat Exchangers?
https://ej-bowman.com/de/faq/5-unterschied-zwischen-plattenwaermetauscher-und-rohrbuendelwaermetauscher/

^[10] CSI Designs. (2025). Shell and Tube vs. Plate Heat Exchanger: 7 Reasons to Purchase.
https://www.csidesigns.com/blog/articles/shell-and-tube-heat-exchanger-why-purchase-plate-and-frame

^[11] Anand Seamless. (2026). Shell and Tube Heat Exchanger vs. Plate Heat Exchanger: Key Differences.
https://www.anandseamless.com/shell-and-tube-vs-plate-heat-exchanger-key-differences/

^[12] HTT-AG. (2025). Resource and Cost Efficiency of Pillow Plate Heat Exchangers.
https://www.htt-ag.com/pillow-plate/

^[13] Piper, M., Zibart, A., & Kenig, E. Y. (2017). New design equations for turbulent forced convection heat transfer and pressure loss in pillow-plate channels. International Journal of Thermal Sciences, 120, 459-468.

^[14] VDI Heat Atlas. (2013). VDI Heat Atlas (2nd ed.). Springer-Verlag.

^[15] Piper, M., Tran, J. M., & Kenig, E. Y. (2016). A CFD study of the thermo-hydraulic characteristics of pillow-plate heat exchangers. Proceedings of the ASME Summer Heat Transfer Conference SHTC2016, Washington, D.C.
DOI:10.1115/HT2016-7176

^[16] Accounovation. (2025). Understanding the Significance of Payback Period in Manufacturing Investments.
https://accounovation.com/blogs/understanding-the-significance-of-payback-period-in-manufacturing-investments