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Article

A Prototype and Efficiency Analysis of Indirect Regenerative Evaporative Cooling System for Electronics

by
Dmytro Levchenko
1,*,
Robert Olbrycht
2,
Marcin Kałuża
2,
Mariusz Felczak
2,
Przemysław Kubiak
1 and
Bogusław Więcek
2
1
Institute of Marketing and Sustainable Development, Faculty of Organization and Management, Lodz University of Technology, Al. Politechniki 8, 93-590 Łódź, Poland
2
Institute of Electronics, Lodz University of Technology, Al. Politechniki 8, 93-590 Łódź, Poland
*
Author to whom correspondence should be addressed.
Energies 2025, 18(23), 6288; https://doi.org/10.3390/en18236288 (registering DOI)
Submission received: 31 October 2025 / Revised: 21 November 2025 / Accepted: 26 November 2025 / Published: 29 November 2025
(This article belongs to the Special Issue Advanced Developments and Challenges in Refrigeration and Energy Systems)
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Abstract

This paper presents an innovative solution based on the Indirect Regenerative Evaporative Cooling (IREC) concept for high-power density electronics. The technology relies on forced convective cooling by air that is additionally cooled via evaporation. The system comprises dry and wet channels for the cooled and wet air, respectively; water is delivered through porous membranes in the wet channels. The novelty relative to HVAC-type exchangers (based on IREC technology) is a full flow return configuration, in which the entire stream from the dry channels is redirected into the wet channels. The performance benefits become pronounced at high ambient temperatures, where traditional forced convection may be insufficient; inlet air absolute humidity is a key factor governing efficiency. The authors present a developed prototype, a simplified thermal analysis, measurement results, and a discussion of IREC applicability to electronics cooling. The results indicate feasibility and highlight the potential of the proposed design for the energy-efficient thermal management of sensitive electronic equipment.

1. Introduction

Thermal management is critical for electronic devices due to increasing heat fluxes and compact form factors. Efficient heat dissipation prevents performance degradation and premature failure and is central to data centers, HPC, and consumer electronics [1,2,3,4,5,6,7,8]. It plays a crucial role in ensuring the optimal performance and long-time operation of electronic devices. As electronic components are becoming increasingly compact and powerful, the amount of heat generated and to be dissipated continues to rise. Efficient heat dissipation is essential in preventing overheating, which would lead to component performance degradation and failure [4,9,10,11,12,13,14,15]. One of the examples highlighting the significance of cooling in electronics is thermal management strategies, employed in high-performance computing systems. Servers, data centers, and other computational devices rely on sophisticated cooling mechanisms in order to maintain their operational temperatures within safe limits. For instance, liquid cooling solutions, heatsinks, and fans are commonly used in high-end computing systems [1,3,4,5,16,17,18,19] to prevent overheating during intensive tasks like cryptocurrency mining [20], gaming, or video rendering [21]. The impact of inadequate cooling can be observed in electronic devices, such as smartphones and laptops. Insufficient cooling in these devices can result in thermal throttling, whereas the device reduces its performance to lower its temperature, affecting user experience and device efficiency. There are several publications raising the mentioned problems as well as proposing various solutions to them [21,22,23,24,25,26,27].
In the automotive industry, electric vehicles incorporate advanced thermal management systems to ensure optimal battery performance and longevity [28,29,30,31,32]. Effective cooling mechanisms are essential to battery temperature control, to maximize their efficiency and prevent overheating-related safety hazards.
The critical role of cooling in electronics is demonstrated by a diverse range of devices and industries that rely heavily on efficient thermal management. From high-performance computing systems to consumer electronics and electric vehicles, the need for effective cooling solutions is paramount to ensure optimal functionality, reliability, and safety of electronic devices. However, conventional cooling techniques such as fans, heat sinks, and liquid cooling have limited effectiveness in addressing localized hotspots and increasing thermal loads in compact electronic systems. Recent advances in thermal management for high-power electronic devices include a wide range of hotspot mitigation techniques such as microchannel heat sinks, thermoelectric cooling modules, phase change materials, and heat pipes. These methods, while effective in certain applications, often face trade-offs in cost, complexity, energy consumption, or limitations in scalability for large-area cooling. Notably, Lei et al. [33] provide a comprehensive overview of thermoelectric and microchannel-based approaches, highlighting the challenge of simultaneously achieving high cooling power density, rapid transient response, and energy efficiency in hotspot management. As power densities and integration levels continue to rise, there is a clear need for innovative cooling systems that can address both local and system-level thermal bottlenecks. The present study addresses this gap by proposing the IREC system as an energy-efficient (especially at elevated ambient temperature), scalable alternative, capable of overcoming several shortcomings of mainstream thermal management practices.
Evaporative cooling—especially dew-point/indirect regenerative concepts (DPEC/IREC, Maisotsenko cycle)—offers high energy efficiency and robust cooling performance [34,35,36,37,38,39]. However, most implementations are focused on HVAC rather than electronics, which dictates all possible designs of DPEC heat exchangers, as the HVAC system must deliver cooled air to the consumer. The first known design of an IREC device for direct heat removal from a hot surface is similar to the design used for HVAC systems [40]. The literature reports broad advances in the simulation, designs, materials, and climate-specific performance of IREC/DPEC devices [41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60]. Thus, one can mention the most recent publications relevant to the topic: mathematical simulations [45,47,48,49,50], various designs, layouts, and applied materials’ analysis [48,49,51,52,53,54,55,56,57], IREC’s potential for specific climate conditions applications [47,50,53,58,59,60], and future applications and challenges [39,41,42,43,44,45,61]. Heat exchangers operating using DPEC or IREC technology are often referred to as HMX (Heat and Mass exchangers), as their design can include the use of desiccants to ensure operation in different climatic conditions and to increase productivity.
The proposed IREC system addresses a critical need in sustainable energy management by significantly improving the efficiency of electronics cooling—a sector that contributes notably to global electricity demand. By tapping into the high latent heat of evaporation, the IREC concept can deliver effective thermal control with considerably lower energy input than conventional compressor-based systems, potentially saving up to 75% of electrical consumption in suitable environments [62,63]. This reduction translates directly into decreased electricity usage and greenhouse gas emissions, advancing SDG 7 (Affordable and Clean Energy) by supporting target 7.3’s goal to double global energy efficiency by 2030 [64,65]. Beyond reducing operational costs, the modular design and minimal environmental footprint bolster equipment longevity, contributing to more sustainable data-center operations. By weaving together experimental data, theoretical modeling, and sustainability metrics, this work positions the IREC system not only as a technical innovation but also as a strategic contributor to clean energy goals. As such, it offers a compelling case for the adoption of greener thermal management solutions in the electronics industry.
In this article, the authors introduced a new heat exchanger design for electronics and a dedicated test rig to evaluate its operation. The primary goal of this study was to scientifically validate the proposed new concept of heat dissipation in electronics using an innovative heat exchanger design.

2. Materials and Methods

2.1. IREC Heat Exchanger and Test Rig

The developed heat exchanger operated based on the IREC principle. The cooler consists of two aluminum plates enclosing an internal stack forming alternating dry and wet channels, separated by thin membranes (hydrophilic on the wet side, hydrophobic on the dry side). The hydrophilic layer wicks water from a reservoir; the low thermal resistance of the membranes’ material facilitates heat absorption from the dry channels. The hydrophilic layer of the membrane carried water from the side tank. Particular attention was paid to the tightness of the channels to prevent water and vapor ingress into the dry channels.
The construction of the cooler and the principle of operation of the IREC technology are presented in Figure 1 and Figure 2. The basic IREC concept was modified by adding a hot plate (heatsink) equipped with heating electronic components. The heatsink blocks the outlet of the cooled air from the dry channels, forcing a return into the wet channels and reinforcing the IREC process. The authors propose to call the presented innovative concept of an IREC heat exchanger device as the full flow return (FFR) type. The main geometry of the tested counterflow heat exchanger is as follows: the dry and wet channel heights are 2 mm; the dry and wet channel widths are 80 mm; the dry and wet channel lengths are about 300 mm; the turn angle at the inlet for the dry channels and at the outlet for the wet channels is 90 degrees; and the turn angle from the dry to the wet channels is 180 degrees.
The principle of operation of the exchanger single cell is shown in Figure 2 using the Mollier diagram, presenting the changes in air temperature, moisture content, and enthalpy, with the air flowing through the exchanger. The inlet air, possibly warm, is cooled down when passing through the dry channels, and reaches the heatsink, which forces it to return into the wet channels. Due to evaporation in the wet channels, flowing air temperature is lowered, resulting in cooling down the dry channels, at the cost of increased humidity of the outlet air. The heat source is thermally insulated, preventing heat leakage directly to the ambient. Thus, it is possible to assume that almost the entire heat is dissipated through the exchanger. Figure 2 presents the cross-section of a single dry and 2 adjacent wet channels, along with the thermodynamic transitions marked on the Mollier chart, demonstrating the exchanger operation.
The working cooler is shown in Figure 3. Inlet air was supplied to the dry channels through a diffuser equipped with an oversized fan. The heat source consisted of 4 resistors powered by a temperature-stabilizing controller. The entire system was partially insulated, especially at the heat source. In consequence, only a small amount of heat was dissipated through natural convection. The effective area of the heat source exposed to cooling by the IREC exchanger was about 50 × 50 mm2.

2.2. Simplified 2D Simulations

The simulations were carried out using the Energy2D software (version 2.9) [66], which is based on computational physics. The Energy2D is an interactive multiphysics simulation program that models heat transfer by conduction, convection, and radiation. The authors created a simplified model of an exchanger, as shown in Figure 4 and Figure 5, containing one dry and one wet channel, that were surrounded by perfect heat insulators. These channels were separated by two connected layers of materials forming a porous membrane. On the upper left side of the exchanger, there was an air inlet with forced temperature and airflow speed (simulating a heater with fan), separated from an outlet containing another fan located in the wet channel’s outlet. On the right side, there was a heat source with adjustable power density, semi-insulated from the ambient.
The effect of evaporative cooling was modeled as a negative power density in the membrane layer at the wet channel side—due to software limitations, as it was not possible to directly take into account evaporation or air humidity. To keep the model simple, there was only one membrane, but with an increased negative power density to reflect the cooling capacity of the real exchanger containing a structure of membranes forming dry and wet channels. The value of the negative power density in Figure 4 was adjusted to −1.2 MW/m3 in order to obtain the same temperature in the empty space (11.7 °C) as the temperature during real-life measurements, with the heater turned off. The heater’s positive power density in Figure 5 was adjusted to 0.64MW/m3 in order to obtain a heater temperature equal to 45 °C, as in real-life experiments. The thermal conductivity of the walls was set to zero, to avoid the convective cooling effect not resulting from IREC. Only the heater insulating layer had non-zero thermal conductivity to simulate the non-ideal thermal insulation present in real-life measurements. Additionally, the density of the metal heater was decreased to reduce the thermal time constant of the simulations to reduce simulation time.
In the next step, the density of the power dissipated in the membrane was set to zero, simulating the exchanger operation without water. Keeping the heater’s same power density, its temperature increased from 45 °C to 56.6 °C. To reduce this temperature to the previous value of 45 °C, it was necessary to lower the heater’s power density to 0.42MW/m3. Hence, it may be estimated that the power dissipated in the heater increased due to the evaporative cooling by about 52%, compared to the case with convective cooling only.
It is important to emphasize that the Energy2D software employed in this study facilitates rapid, preliminary thermal modeling, but has inherent limitations. Notably, it cannot directly simulate key phenomena such as evaporation, air humidity, or complex fluid flow dynamics that critically affect evaporative cooling performance. To approximate the evaporation effects, we modeled evaporation as a negative power density, which was manually calibrated against experimental temperature measurements to improve qualitative alignment. This approach is not a rigorous, fully coupled simulation, but rather a simplified, pragmatic approximation intended to provide an initial qualitative assessment of the IREC concept’s viability. The authors acknowledge that this methodology may either overestimate or underestimate cooling effectiveness, depending on environmental conditions and interface effects not captured in the model. Realistic modeling of the IREC device requires the incorporation of multiphysics phenomena, including transient mass and heat transfer, flow regimes, and boundary condition variability, which remains a complex and resource-intensive task beyond the scope of this work. Nevertheless, the presented approach, coupled with physical experimentation, establishes a foundation for the ongoing iterative refinement and conceptual validation of this innovative cooling system.

2.3. Investigations and Selection of Porous Membranes

One of the key elements of the heat exchanger was the membrane separating the wet channels from the dry channels. One required the membrane to be hydrophobic from the dry channel side and hydrophilic from the wet channel side. Because of the quick availability and ease of laser cutting, when building the exchanger, two different laminates composed of a watertight polyester (PES) film and a polypropylene (PP) non-woven layer were considered: laminate no 1 (53 g/m2 weight with 18 g/m2 for the PES layer and 35 g/m2 for the PP layer) and laminate no 2 (73 g/m2 weight with 18 g/m2 for the PES layer and 55 g/m2 for the PP layer).
To evaluate both laminates, they were tested for vertical wicking height using an approach based on the American Association of Textile Chemists and Colorists (AATCC) Technical Manual: Test Method for Vertical Wicking of Textiles (TM-197) [67]. First, for both materials, samples 25 cm × 3 cm were cut and, using dedicated clips, they were hung from a laboratory stand, as shown in Figure 6a. Next, a recipient containing demineralized water was prepared and the free end of the specimens, freely hanging, were dipped into the water. Based on [68,69], the capillary water rise process was observed and recorded using a FLIR X6901 (USA) cooled in a thermographic camera. After preliminary tests, to achieve better control of sample position during measurements, a small paper clip was attached to each of them at the free end.
Because of the evaporative cooling of water-soaked samples, thermography allowed for good visualization of capillary water rise phenomena in the samples, even in a situation where it was difficult to assess it visually, either using the naked eye or a visible light camera. For an easier wicking height measurement, a metal ruler was added to the setup and immersed into the water. The emissivity difference between the reflective metal surface and the black painted scale provided adequate contrast and height readability on the thermograms. At first, both laminate samples demonstrated hydrophobic behavior of the PP layer (Figure 6b); thus, they were both treated using a softening liquid solution, and the test was repeated, this time clearly demonstrating the hydrophilic behavior of the PP layer (Figure 6c). For the 53 g/m2 laminate, a 40 mm wicking height was obtained, whereas, for the 73 g/m2 specimen, a 60 mm wicking height was obtained. Because both results were considered adequate, the 73 g/m2 laminate was chosen for building the IREC heat exchanger because of its higher mechanical rigidity compared to the 53 g/m2 one.

3. Results and Discussion

3.1. Simulation Results

The results of the performed simulations are listed in Table 1. While their accuracy could be affected by the coarse 100 × 100 mesh of the model, which is due to software limitations, one can clearly see the temperature distributions in the structure. The dissipated power was recalculated from the heater’s power density (0.64 MW/m3) by taking the heater element size (5.39 × 0.52 cm2) and a unit depth of 5 cm, as it was in the developed prototype.

3.2. Experimental Results of the FFR Prototype

The first measurements were carried out for two operating modes of the cooling system: without heating and with all four heating resistors operating. In both cases, temperature and relative humidity were measured at control points, as shown in Figure 2. During heating, the temperature of the heatsink stabilized at 45 °C. For the tested FFR prototype, the relevant pressure drops Δp were measured: in dry channels 80 Pa, in wet channels 360 Pa, inlet–outlet 440 Pa. It should be noted that these values are likely exaggerated due to the excess fan power on the test rig. The exact measured values of temperature and humidity are presented in Table 2, whereas the calculated enthalpies are shown in Table 3.
The processes occurring in the heat exchanger when the heat source is turned on are shown in Figure 7 and described in Table 4 below. The evaluation of the energy efficiency of heat exchangers of the IREC type, especially for the FFR design, is not an easy task and requires careful consideration of all flows of matter and energy involved in all working processes. As a first approximate analysis of the energy efficiency of a heat exchanger for cooling electronics, the cycle method [70] can be applied, which is quite widely used for various cooling systems. However, the processes for indirect regenerative evaporative cooling devices can be more conveniently represented in a psychrometric diagram, where one can clearly see the processes with changes in the humidity and thermal characteristics of the air (Figure 7).
The environmental parameters have a decisive influence on the efficiency of heat exchangers operating based on the IREC principle. Thus, with a high absolute humidity of the air at the inlet to the device, it is impossible to achieve high performance and significant cooling effects. In addition, the specifics of the cooling process of electronic devices forces us to evaluate the performance, efficiency, and expediency of the proposed system in comparison with the most accessible cooling systems, for example, a fan and a radiator. Thus, at a sufficiently low ambient temperature at the heat exchanger inlet, the contribution of evaporative cooling to the overall cooling capacity of the cooling system will be small. The specific amount of heat that can be removed at the existing temperature difference between the heated surface of the electronic device and the environment due to convection is the enthalpy difference between states of air 1 and HS at the same absolute humidity. It is the so-called potential of ambient air cooling capacity Δ H H S − 1 .
It is important to note that the efficient cooling process of electronic devices depends not only on the cooling capacity Δ H 2 − 3 generated in the heat exchanger, but also on the ability of the heat-loaded surface to transfer heat to the moving air flow in the process Δ H 3 − 4 . In other words, the intensity of the heat transfer process from the heat-loaded surface plays a very important role in organizing an effective cooling process. In the limit (with the flow rate of the blowing air tending to zero), this process should occur until the air temperature equalizes with the temperature of the heated surface, i.e., Δ H 3 − H S . The processes occurring in the IREC apparatus are characterized by a significant degree of mutual influence, and the specifics of the following:
  • The considered design (FFR) of the apparatus.
  • The efficiency of organizing the process of heat transfer from the heat-loaded surface.
As a result, it is proposed to consider separately two given energy efficiency coefficients of an IREC heat exchanger and the efficiency coefficient COP.
The reduced energy efficiency/cooling capacity coefficient of the IREC unit is as follows:
η 0 = Δ H H S − 1 − Δ H 2 − 3 Δ H H S − 1 − Δ H 2 − T d p
Here, provided that Δ H H S − 1 − Δ H 2 − T d p ≠ 0 , the coefficient can take values as negative, positive, or be equal to zero. This allows us to evaluate the efficiency of the heat exchanger and the feasibility of its use, and also to consider potential ways to improve efficiency (see Table 5).
The reduced coefficient of heat transfer efficiency from a heat-loaded surface is as follows:
η α = Δ H 3 − 4 Δ H 3 − H S
where Δ H 3 − 4 , Δ H 3 − H S represent real and theoretical heat transfer processes to cooled dry air from the surface of a heating source without changing the absolute moisture content in the cold end of the FFR heat exchanger.
This coefficient can take values up to 1, with values closer to 1 characterizing effective heat removal from the heated surface of a flat wall of the heat source and high volumetric air flow. This coefficient takes minimum values and increases with the use of measures to intensify heat exchange from the heated surface to the air flow. Such measures may include increasing the heat transfer surface of the heat source due to finning and/or wetting the heated surface with an evaporating layer of liquid (water).
The performance coefficient considering the electronics cooling effect is as follows:
C O P I R E C = P h P f a n
where P h —power dissipated from the source of heat and P f a n —electric power of the fan, expressed in watts.
During the experiment, a fan with a power significantly exceeding the needs of the heat exchanger with the possibility of smooth regulation of volumetric performance was used. However, for obvious reasons, such a fan operation mode cannot be considered optimal. Therefore, after the tests presented in Table 2, it is possible to select a fan with a performance corresponding to the operating conditions of the device. For this type of fan, the power consumption is from 0.6 to 1 W, which will allow us to obtain high C O P I R E C indicators. However, another feature of the operation of IREC devices is relatively high hydraulic losses, so the actual values C O P I R E C of the performance coefficient will be lower and should be clarified during further research. Table 6 shows the values of the above coefficients for prototypes of FFR heat exchangers based on IREC technology.
A more detailed assessment of the energy efficiency of the IREC apparatus with a FFR design for electronic device cooling purposes can be made based on the latest developments in advanced exergy analysis [72]. An advanced exergetic analysis includes splitting the exergy destruction within each component into endogenous and exogenous parts, as well as into avoidable and unavoidable parts. A combination and an extension of these two splitting approaches provides the designer and operator of an energy conversion system with additional, unambiguous, valuable, and detailed information with respect to options for improving overall efficiency. This splitting of exergy destruction overcomes the limitations of a conventional exergetic analysis, and therefore assists engineers in better understanding how thermodynamic inefficiencies are formed [72].

4. Conclusions

In this article, an innovative heat exchanger design for cooling electronic devices through IREC technology was presented and experimentally tested. The proposed full flow return (FFR) heat exchanger design allowed for heat dissipation from the heat-loaded surfaces of electronic devices. A hot flat metal surface of a heat source was cooled by cold air flowing from the dry channels of the heat exchanger, which operated based on the IREC technology, helping to reduce the influence of ambient temperature on electronics cooling efficiency.
Based on the presented research results, several conclusions can be drawn for the tested device configuration.
  • In the unloaded mode, the heat exchanger showed sufficiently high efficiency, confirming the effectiveness of the IREC technology for the proposed device design.
  • During the tests of the current heat exchanger design, several features having a significant impact on the cooling process efficiency and the overall cooling system operation were identified:
    • High hydraulic resistance due to low channel height and the 180º air flow turn. This resulted in significant pressure losses, especially in wet channels, and led to the fan operating outside its design zone, energy overconsumption, and increased flow rate measurement errors. Means of pressure loss reduction should be considered, such as HMX channels’ geometry changes. To enhance experimental accuracy, it is recommended to proportionally increase the dimensions of the cooled surface and heat exchanger. Also, for the next prototype, a more precise selection of fans and their performance characteristics should be made.
    • Heat input occurs at the flow turn in the device and has a decisive impact on the cooling system’s efficiency. The warm dry air leaving the dry channels heats up, absorbing heat from the hot plate surface and enters the wet channels. As a result, the warm dry air entering the wet channels intensifies the evaporation process from the hydrophilic membrane’s surface, while also transferring heat back to the dry channels, pushing the heat exchanger beyond its effective operation zone. This likely occurs due to the low height of the wet channels and relatively low air flow velocities, leading to the rapid saturation of water vapor near the heat source and weakened evaporation in the main part of the wet channels. Consequently, the air’s relative and absolute humidity at the wet channels outlet are low, which is caused by non-characteristic temperature distribution fields in the device (for setups operating based on IREC technology), as well as the aforementioned channel geometry limitations and airflow organization methods.
  • Taking into account the operating features of the IREC device with the FFR design, three efficiency coefficients were proposed, their possible values were analyzed from the point of view of the technology application feasibility for electronic devices cooling, and recommendations were developed aiming to increase the cooling the efficiency of systems using IREC devices.
  • Further research is required on the device, considering the influence of the identified factors:
    • Testing of a device with an increased height of wet channels. This solution would significantly reduce hydraulic losses and intensify the evaporation process in the wet channels.
    • Testing of a device with an increased gap between the heat exchanger membranes and the cooled surface.
  • Further research on the membrane materials separating wet channels from dry channels is required.
  • Future developments of the setup can include configurations where the heat source has a hydrophilic porous layer with water running through it, along with various heat exchange intensification methods, such as finning or surface treatment.
In conclusion, the IREC prototype not only achieves robust thermal performance, but also has the potential to deliver meaningful energy savings, offering a promising pathway toward SDG 7.3 by reducing electricity consumption and associated emissions in electronics cooling. Future research will broaden this impact through life-cycle assessments that quantify the full environmental footprint—tracking global warming potential, water usage, and resource demands from cradle to grave. Also, such essential aspects, such as moisture ingress, condensation risks, water quality requirements (including scaling, fouling, and bio-growth), and long-term reliability, should be considered. In addition, it must be recognized that the quantitative results obtained are still insufficient for practical implementation and require a comparative study of energy characteristics to create a truly practical solution. Comparative energy performance and life-cycle analysis against traditional refrigerant-based systems will also strengthen the case for IREC’s deployment in sustainable techno-industrial ecosystems [73].
In this article, we focused on fundamental experimental studies for the proposed IREC heat exchanger innovative design and developed an adapted methodology for evaluating its performance by introducing new efficiency metrics regarding electronics cooling peculiarities. Ultimately, this work lays the foundation for scalable, energy-efficient cooling solutions that align both with environmental targets and the global quest for affordable, clean energy.

Author Contributions

Conceptualization, D.L. and B.W., methodology, R.O. and D.L.; software, R.O.; validation, D.L., M.K., B.W., and M.F.; formal analysis, D.L., R.O., M.F., and B.W.; investigation, D.L., R.O., M.F., M.K., and P.K.; resources, D.L. and M.K.; data curation, D.L. and B.W.; writing—original draft preparation, D.L., R.O., M.F., M.K., P.K., and B.W.; writing—review and editing, B.W.; visualization, D.L., R.O., M.F., M.K., and B.W.; supervision, D.L. and B.W.; project administration, B.W.; funding acquisition D.L., R.O., M.F., M.K., and B.W. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Polish National Science Centre project OPUS no. 2022/45/B/ST7/02820.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Abbreviations

The following abbreviations are used in this manuscript:
IRECIndirect Regenerative Evaporative Cooling
DPECDew Point Evaporative Cooling
M-cycleMaisotsenko Cycle
SDG Sustainable Development Goals
FFRFull Flow Return
HMXHeat and Mass Exchanger

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Figure 1. Developed FFR heat exchanger for power-electronics cooling: (a) design; (b) implementation.
Figure 1. Developed FFR heat exchanger for power-electronics cooling: (a) design; (b) implementation.
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Figure 2. Cross-section of dry/wet channels with measurement points (a) and corresponding psychrometric transitions on the Mollier psychrometric chart (b).
Figure 2. Cross-section of dry/wet channels with measurement points (a) and corresponding psychrometric transitions on the Mollier psychrometric chart (b).
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Figure 3. Operating FFR heat exchanger with hot-plate temperature 45 °C at ≈9 W: (a) visual; (b) infrared image.
Figure 3. Operating FFR heat exchanger with hot-plate temperature 45 °C at ≈9 W: (a) visual; (b) infrared image.
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Figure 4. Simulation with heater off.
Figure 4. Simulation with heater off.
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Figure 5. Simulation with heater on.
Figure 5. Simulation with heater on.
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Figure 6. (a) Measurement setup for vertical wicking height testing; (b) thermogram of a 53 g/m2 (left side) and a 73 g/m2 (right side) polyester–polypropylene laminate, demonstrating hydrophobic properties; (c) thermogram of a 53 g/m2 (left side) and a 73 g/m2 (right side) polyester–polypropylene laminate after chemical treatment, demonstrating hydrophilic properties.
Figure 6. (a) Measurement setup for vertical wicking height testing; (b) thermogram of a 53 g/m2 (left side) and a 73 g/m2 (right side) polyester–polypropylene laminate, demonstrating hydrophobic properties; (c) thermogram of a 53 g/m2 (left side) and a 73 g/m2 (right side) polyester–polypropylene laminate after chemical treatment, demonstrating hydrophilic properties.
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Figure 7. Psychrometric representation of FFR HMX processes [71].
Figure 7. Psychrometric representation of FFR HMX processes [71].
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Table 1. Simulation results with/without heating.
Table 1. Simulation results with/without heating.
HeatingThermocoupleAmbientInputEmpty SpaceOutputDry ChannelDissipated Power
modeTth, °CTa, °CTDB, °CTH, °CTout, °CTDC, °CP, W
Off13.222.623.411.720.910.40
On4522.623.432.420.318.79.09
Table 2. Measurement results with and without heating.
Table 2. Measurement results with and without heating.
HeatingThermocoupleAmbientInputEmpty SpaceOutputDry ChannelDissipated Power
modeTth, °CTa, °CRH, %TDB, °CRHDB, %DP, °CWB, °CTH, °CRHH, %Tout, °CRHout, %TDC, °CRHDC, %P, W
Off15.422.629.423.827.03.613.411.658.720.248,77.677.80
On45.022.928.424.325.13.113.031.617.222.141,418.038.39
Table 3. Enthalpy data for HMX operation modes.
Table 3. Enthalpy data for HMX operation modes.
Heating is OnHeating is Off
Points/ProcessH, kJ/kgH, kJ/kg
Heat Source (HS)57.5no
135.135.3
236.536.5
330.120.1
443.924.1
539.738.6
at (Tdp)15.0
(3.12 °C)		16.1
(3.7 °C)
Table 4. Enthalpy differences and interpretation of key processes.
Table 4. Enthalpy differences and interpretation of key processes.
ProcessValue, kJ/kgComments
Δ H 1 − 2 1.4heat supply during the process of air injection into the heat exchanger (with an increase in temperature of approximately 1 °C)
Δ H 2 − 3 −6.3real cooling process of the supplied air in dry channels of the heat exchanger
Δ H 3 − 4 13.8real process of heat transfer to cooled dry air from the surface of a heating source without changing the absolute moisture content in real FFR HMX
Δ H 3 − H S 27.3“ideal”/theoretical process of heat transfer to cooled dry air from the surface of a heating source without changing the absolute moisture content in real FFR HMX
Δ H 4 − 5 −4.2real cooling process of heated air in the wet channels of a heat exchanger due to the evaporation process
Δ H 4 − 5 s 0adiabatic cooling of heated air in wet channels of a heat exchanger due to the evaporation process (actual process is not shown)
Δ H H S − 6 s 0adiabatic cooling of heated air in wet channels of a heat exchanger due to the evaporation process (“ideal process” is not shown)
Δ H 2 − T d p −21.4“ideal”/theoretical process of the supplied air cooling in the dry channels of the heat exchanger
Δ H H S − 1 −22.4cooling capacity potential of the ambient air
Δ H T d p − H S 42.4“ideal”/theoretical process of heat transfer to cooled dry air from the surface of a heating source without changing the absolute moisture content in theoretical FFR HMX
Table 5. Ranges of the reduced efficiency/productivity coefficient values and their meaning.
Table 5. Ranges of the reduced efficiency/productivity coefficient values and their meaning.
ValueMeaningRecommendations
η 0 < 0 The IREC unit’s cooling capacity is low compared to the ambient air’s cooling potential.
The heat exchanger is either not operating efficiently under the current ambient inlet conditions, or the temperature of the heated surface is too high, or the ambient air temperature is too low.		There are several potential reasons that could have caused this. First of all, one should evaluate the temperature level of the heat source and the environment. Perhaps the temperature level of the heat source is too high or the ambient temperature is too low. A similar situation is also possible with a low or moderate temperature of the heat source and high temperature and relative humidity of the environment. If there is no critical need to supply low-temperature cooled air to the heated surface, the feasibility of using a heat exchanger should be considered. The geometry of the device is incorrectly selected. First of all, it is necessary to consider changing (increasing) the length and number of cells of the heat exchanger.
η 0 = 0 The cooling capacity of the IREC unit is equal to the cooling potential of the surrounding air. Depending on the temperature level of the heated surface and the surrounding environment, its value can be quite significant. This is the lower limit of efficiency for the rational use of the IREC unit in the current design.It is recommended to conduct a technical and economic analysis of this device in comparison with the use of classic cooling systems based on forced convection (fan + radiator). Since the positive effect of using the IREC device increases with increasing ambient temperature, it is recommended to optimize the design and geometry of the device for conditions with higher temperatures.
η 0 > 0 The IREC unit’s cooling capacity exceeds the cooling potential of the environment. The use of the device is justified!Further increase in the productivity and efficiency of the heat exchanger may consist of the following:
  • optimal selection of fans at the inlet and/or outlet of the IREC device;
  • reduction in hydraulic resistance in the device;
  • drying the air before entering the IREC device.
Table 6. Values of the reduced efficiency coefficients for the tested prototype.
Table 6. Values of the reduced efficiency coefficients for the tested prototype.
CoefficientsValueComments
η 0 η 0 < 0 In the case when this coefficient takes values below zero, the numerical negative values are difficult to analyze for an accurate quantitative assessment, considering all possible reasons for it.
In general, it means that the cooling capacity potential of the ambient air is significant comparing to the IREC HMX cooling capacity increment. Its application is preferable at high ambient temperatures and/or lower humidity of ambient air.
η α 0.5Heat removal from the heated surface should be improved
C O P I R E C 0.09 ÷ 0.15 (15)At this stage of the investigation, the actual value C O P I R E C is senseless, since the FFR was tested with an extremely overpowered fan, VKM 150, with a peak power of 100 W, a volumetric flowrate about 580 m3/h, and a pressure 350 Pa. This fan was dedicated for test rig operation in a wide range of volumetric flowrates and pressures to define the limits of the tested prototypes. Therefore, even with smooth fan control, its power consumption greatly exceeds the power of the fan selected for the required flow and pressure parameters. The estimated value in brackets, provided that the fan is selected for a given volumetric flow rate for the FFR prototype.
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Levchenko, D.; Olbrycht, R.; Kałuża, M.; Felczak, M.; Kubiak, P.; Więcek, B. A Prototype and Efficiency Analysis of Indirect Regenerative Evaporative Cooling System for Electronics. Energies 2025, 18, 6288. https://doi.org/10.3390/en18236288

AMA Style

Levchenko D, Olbrycht R, Kałuża M, Felczak M, Kubiak P, Więcek B. A Prototype and Efficiency Analysis of Indirect Regenerative Evaporative Cooling System for Electronics. Energies. 2025; 18(23):6288. https://doi.org/10.3390/en18236288

Chicago/Turabian Style

Levchenko, Dmytro, Robert Olbrycht, Marcin Kałuża, Mariusz Felczak, Przemysław Kubiak, and Bogusław Więcek. 2025. "A Prototype and Efficiency Analysis of Indirect Regenerative Evaporative Cooling System for Electronics" Energies 18, no. 23: 6288. https://doi.org/10.3390/en18236288

APA Style

Levchenko, D., Olbrycht, R., Kałuża, M., Felczak, M., Kubiak, P., & Więcek, B. (2025). A Prototype and Efficiency Analysis of Indirect Regenerative Evaporative Cooling System for Electronics. Energies, 18(23), 6288. https://doi.org/10.3390/en18236288

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