Active Thermal Protection Research Articles

Numerical investigation on transpiration cooling with phase change based on multiphysics coupled finite element method

Transpiration cooling with phase change is an efficient active thermal protection method in aerospace. However, conducting numerical simulation of transpiration cooling with phase change is still a challenge, because porous flow, heat transfer and phase change are coupled with each other, which lead to numerical difficulties. In this article, the previous model is modified and the Zero Thickness Area Model (ZTAM) is proposed, which improves the efficiency and convergence significantly. In addition, the local thermal nonequilibrium effect and latent heat can be considered. To verify this ZTAM model, one-dimensional control equations of mass, momentum, and energy transpiration are solved using finite element method. Furthermore, the position of phase change is determined by fixed point iteration numerical algorithm, which shows good convergence. Finally, the influence on cooling effect by heat flux, coolant mass flow rate, porosity and pore diameter is investigated numerically.

The importance of using active thermal protection following restoration work on old buildings

The paper deals with the issue of humidity and the unhealthy environment of old buildings. Humidity is a very widespread problem not only in historical buildings, but also in newer buildings. This problem can be observed in various parts of the world and thus it can be said that it is a global problem. Humidity in these buildings causes an unhealthy environment, which has a negative effect on individual building constructions, but also on people’s health. Humidity is also associated with the form of disruption of the individual layers of the construction and the disruption of the thermal resistance of these constructions. Buildings such as these subsequently have an unhealthy environment. After a part of the description of the known issue, the contribution follows on from this part by indicating possible remedial interventions and analyses the systems of additional thermal insulation (ETICS, ATP), ensuring the improvement of the internal environment. Finally, the article presents possible connections and extensions of this research and its application directly in practice. The results of the proposed research will significantly contribute to the approach to rehabilitated older buildings and their long-term sustainability from an economic point of view, as well as the possible use of them.

Numerical Study of Plasma Characteristics Under Magnetohydrodynamic Flow Control in Mars Entry

Magnetohydrodynamic flow control is an active thermal protection method for atmospheric entry vehicles. This study examined the plasma characteristics under magnetohydrodynamic flow control and its thermal protection ability at multiple altitudes (20–60 km) on a typical direct Mars entry path using numerical simulation considering the Hall effect. The simulation considered a spherical-conical capsule with an entry velocity of 8 km/s at an altitude of 60 km, equipped with a dipole magnet generating a magnetic field of approximately 0.3 T at the stagnation point of the capsule. The results showed that magnetohydrodynamic flow control can mitigate convective aerodynamic heating at high altitudes (45 km or more), where the high electrical conductivity of the plasma creates strong magnetohydrodynamic interaction. In contrast, at low altitudes (35 km or less), magnetohydrodynamic flow control is ineffective owing to low electrical conductivity. The high electrical conductivity at high altitudes is attributed not only to large flight velocities under low atmospheric pressures but also to the enlargement of the shock layer owing to the strong magnetohydrodynamic interaction, which expands the ionization progression area. Furthermore, the results indicated that considering the Hall effect in the numerical modeling of magnetohydrodynamic flow control in Mars direct entry is essential.

Analysis of the results of studies of the thermal regime of natural and man-made kurums of the cryolithozone

The subject of research is natural and man-made kurums (blocky accumulations of rocks). The purpose of the work was to analyze the main literary sources, in which the results of research on the formation of the thermal regime of rock dumps (kurums) were published. The retrospective period of the research extends for more than 50 years. Domestic and foreign sources of information are considered. The most representative ones have been selected for analysis, in which the results of research with theoretical value and practical significance have been published. The analysis showed that on many important aspects of the formation of the thermal regime of natural and man-made kurums, all the authors of studies conducted in different regions and at different time periods, independently of each other, came to the same conclusions. This indicates the reliability and objectivity of the results obtained. An analytical review of scientific articles was used as a research method, in which research materials on the formation of the thermal regime of both the kurums themselves and their soil bases were published. The kurums of the permafrost and island permafrost zones are considered. An analytical review of literary sources containing theoretical and practical results of research on the formation of the thermal regime of natural and man-made kurums is carried out. The results of the analysis allow us to draw the following main conclusions. 1. Any types of natural and man-made kurums lead to progressive cooling of the base on which they are located. 2. When interacting with the rock base, the technogenic kurum works as an active thermal protection, changing its thermal resistance during the annual cycle. 3. When modeling the process of thermal interaction of technogenic kurum, it is quite acceptable to consider the kurum as a heat-protective layer, the thermal resistance of which depends on the effective coefficient of thermal conductivity, which changes its value when the sign of atmospheric air temperature changes. Based on the analysis of the results of the published works, conclusions are drawn about the possibility of a number of simplifications in the construction of computational models for forecasting and controlling the thermal regime of frozen bases of technogenic kurums.

Microstructure and ablation behaviour of C/C-SiC-ZrC-Cu composites prepared by reactive melt infiltration

To satisfy the requirements for the new generation solid rocket motors on high ablation-resistant throat materials, an idea that merges passive and active thermal protection together was applied to modify carbon/carbon composites. In this study, SiC and ZrC were used as passive thermal protection materials along with the active thermal protection material Cu to modify C/C composites. C/C-SiC-ZrC-Cu composites were prepared by two-step reactive melt infiltration, which involved the infiltration of Si/Zr followed by Cu/Ti. The Cu content of the C/C-SiC-ZrC composites was controlled by controlling the open porosity of the porous C/C-SiC-ZrC composites. Microstructure, composition and ablation resistance of the C/C-SiC-ZrC-Cu composites were investigated. The results showed that the composites with high Cu content and density exhibited excellent short-term ablation resistance under the 42 kW plasma flame, with a negative linear ablation rate after 20 s of ablation. The active heat dissipation of Cu during the ablation process results in a significant reduction of the thermal response temperature on the composite surface. Moreover, the generated Si-Ti-Zr-O layer could form an effective barrier to protect the matrix.

Numerical Investigation on Transpiration Cooling Performance of Oriented Porous Structure Under Local Block Conditions

With the development of an active thermal protection system (TPS) for hypersonic vehicles, reliability improvement and weight reduction of TPS are key issues to be considered. In this paper, an oriented porous structure (OPS) is proposed to solve the local overheating problem in transpiration cooling. The transpiration cooling performances are investigated in a two-dimensional computational domain using a local thermal nonequilibrium model. The cooling mechanisms of OPS and uniform porous structure (UPS) under local block conditions have been numerically analyzed and compared. The results show that OPS leads to effective cooling of the overheated region by regulating the coolant flow behavior, especially in the case of serious block conditions. The maximum temperature reduction can be up to more than 200 K, and the maximum optimization rate can reach up to 23% compared to UPS. Moreover, OPS consumes less coolant and uses less driving force to deliver coolant when reaching the same peak temperature as OPS. This study shows that OPS has a better thermal protection effect in transpiration cooling, which can improve the reliability of TPSs, and that OPS can also achieve the lightweight of the aircraft.

Numerical study of a composite cooling method for hypersonic aircraft

Thermal protection is a crucial issue for a long-flying hypersonic aircraft. In this work, a composite cooling method is proposed and implemented on a hypersonic blunt cone. The composite cooling method combines impinging and convective cooling at the cone head with transpiration cooling employed downstream to produce an overall cooling effect of the cone. Using computational fluid dynamics, the influences of the cooling gas and different attack angles on the cooling effect are examined. The results indicate that the combined cooling method can effectively reduce the overall outer wall temperature of the cone. In particular, with the combined cooling method, an increase in mass flow rate of the cooling gas has been observed in numerical tests, which results in a decrease in the head temperature. The maximum temperature decrease can reach 77.0% on the wall when the mass flow rate of the cooling stream is 1.1 kg/m2 s. The cooling performance on the leeward side can be better than that on the windward side for a fixed cooling gas mass flow rate. This gap in cooling performance between the two sides can be further amplified by a larger attack angle. Quantitatively, when using the combined cooling method, the temperature difference between the windward and leeward sides increases from 106 to 270 K when the attack angle increases from 4° to 8°. The numerical results in this study could provide theoretical and statistical guidance for the design of novel active thermal protection methods for hypersonic aircraft.

Experimental investigation of heat transfer and structure optimization for regenerative cooling channels using n-decane

Regenerative cooling technologies are considered one of the most effective and widely used active thermal protection methods for hypersonic aircraft scramjets. The heat transfer performance of hydrocarbon fuel and the geometric optimization of cooling channels are the key factors to be considered in designing regenerative cooling structures. Therefore, the present study experimentally and numerically investigated the heat transfer characteristics of n-decane in regenerative channels under asymmetric heating conditions and presented a new structure optimization method. The experiment was conducted at 3 MPa and 293 K with a mass flow rate of 0∼2.442 g/s per channel and a heat flux range of 0∼150 kW/m2. Experimental data show that the local Nusselt numbers exhibit a higher sensitivity to changes in mass flow rate compared to heat flux. Compared to symmetric heating, asymmetric heating mainly affects the heat conduction in the solid domain rather than the performance of convective heat transfer. The modified Dittus-Boelter correlation could predict the experimental data with a relative deviation of ±25 %. A rapid temperature prediction method based on heat flux distribution was proposed through heat transfer analysis, and it was utilized with a particle swarm optimization algorithm to conduct structure optimization.

Numerical investigation on the double-layer porous plate of transpiration cooling with phase change under different heat flux

Transpiration cooling is a potential active thermal protection method for aircraft under severe thermal environment. Though it is cooling efficiency that is of concern in most structural designs, the injection pressure is equally critical for transpiration cooling especially when using liquid as coolant. To enhance the cooling performance of transpiration cooling with phase change, double-layer porous plate that upper and lower layers have different porosities is presented and adopted. A new numerical simulation model, modified Two-Phase Mixture Model with Local Thermal Non-Equilibrium is used to investigate two-phase flow and fluid-solid coupled heat transfer under different heat flux. The results reveal that overall pressure drop of the porous plate is mostly dependent on vapor region which has higher flow resistance, so designing larger porosity for the upper layer where is occupied by vapor region can effectively reduce the coolant injection pressure. Besides, since the specific heat of liquid is larger than that of vapor, designing smaller porosity for the lower layer where liquid region is located can lead to lower surface temperature when increasing coolant mass flow. Moreover, designing a thinner lower layer in the region exposed to high heat flux could obtain desired coolant distribution. The double-layer porous plate with unequal thickness can reduce the injection pressure by 20.8 % and improve its relative uniformity by 33.3 % while decreasing the surface temperature at the same time. The new evaluation of cooling performance and the new structure have important guidance and practical significance of transpiration cooling in the actual application of aircraft in severe thermal environment.

Numerical investigation on transpiration cooling performance of turbine blades with non-uniform porosity

As an active thermal protection technology with high cooling efficiency, transpiration cooling can achieve effective thermal protection for turbine blades. However, most of the studies are usually carried out using the flat plate geometry. In this paper, the cooling and flow characteristics of the real C3X blades are investigated numerically. The cooling efficiency and flow field distribution along the blade surface under different coolant mass flow ratios were compared and analyzed. Meanwhile, the total pressure loss and flow distribution of the coolant in the internal channel were studied. The results show that the coolant flow distribution in the leading edge and trailing edge regions has a significant effect on the development of the blade flow boundary layer and the overall cooling performance. In addition, the influence of different porosity on the transpiration cooling performance of the blade was studied. Aiming at the problem that the local region of the blade is prone to mainstream intrusion and the cooling efficiency is reduced, a non-uniform porosity strategy in different regions and a gradient porosity strategy with uniform variation along the path is proposed. By adjusting the permeability of the region along the blade, the optimal flow distribution of coolant in the local area is achieved. The results show that compared with the uniform porosity, reasonable distribution of porosity in different regions of the blade can significantly improve the uniformity of the temperature distribution on the blade surface and obtain the highest cooling efficiency of 13.97 %.

Fundamentals and recent progress of additive manufacturing-assisted porous materials on transpiration cooling

The requirements for new generation vehicles in terms of the flight speed, thrust–weight ratio, and maneuverability necessitate the development of high performance and reliable propulsion systems where active thermal protection technology plays a crucial role. Transpiration cooling based on a microporous structure is considered as one of the most promising techniques for protecting the high heat flux walls from ablation in aerospace applications. Unlike conventional fabrication methods, additive manufacturing (AM) has been applied to fabricate three-dimensional (3D) porous structures with customized geometries that are specific to applications, i.e., in terms of the design of features such as the pore diameter, pore density, porosity, and pore morphology. Three major AM technologies (selective laser melting, inkjet, and stereolithography) followed by a post-printing process have been proposed for the additive manufacture of porous structures. In particular, 3D-printed porous structures have great promise for transpiration cooling applications. In this review, we discuss the detailed steps of porous structure topology design and a general framework is presented for AM. The heat transfer and strength performance are also provided for porous parts fabricated by AM. Furthermore, the applications of 3D-printed porous media in transpiration cooling with different regimes are described. This review concludes by explaining the current challenges and prospects for the next generation of 3D-printed porous structures in transpiration cooling systems.

Contribution to Active Thermal Protection Research—Part 2 Verification by Experimental Measurement

This article is closely related to the oldest article titled Contribution to Active Thermal Protection Research—Part 1 Analysis of Energy Functions by Parametric Study. It is a continuation of research that focuses on verifying the energy potential and functions of so-called active thermal protection (ATP). As mentioned in the first part, the amount of thermal energy consumed for heating buildings is one of the main parameters that determine their future design, especially the technical equipment. The issue of reducing the consumption of this energy is implemented in various ways, such as passive thermal protection, i.e., by increasing the thermal insulation parameters of the individual materials of the building envelope or by optimizing the operation of the technical equipment of the buildings. On the other hand, there are also methods of active thermal protection that aim to reduce heat leakage through nontransparent parts of the building envelope. This methodology is based on the validation of the results of a parametric study of the dynamic thermal resistance (DTR) and the heat fluxes to the interior and exterior from the ATP for the investigated envelope of the experimental house EB2020 made of aerated concrete blocks, presented in the article “Contribution to the research on active thermal protection—Part 1, Analysis of energy functions by the parametric study”, by long-term experimental measurements. The novelty of the research lies in the involvement of variant-peak heat/cooling sources in combination with RES and in creating a new, original way of operating energy systems with the possibility of changing and combining the operating modes of the ATP. We have verified the operation of the experimental house in the energy functions of thermal barrier, heating/cooling with RES, and without RES and ATP. The energy saving when using RES and ATP is approximately 37%. Based on the synthesis and induction of analogous forms of the results of previous research into recommendations for the development of building envelopes with energy-active elements, we present further possible outcomes in the field of ATP, as well as already realized and upcoming prototypes of thermal insulation panels.

Contribution to Active Thermal Protection Research—Part 1 Analysis of Energy Functions by Parametric Study

The thermal energy consumption for heating objects is one of the main parameters deciding their technical and structural solution. Reducing energy consumption is realized in various ways. The most used method is passive thermal protection, that is, increasing the thermal insulation parameters of the envelope constructions and optimizing the operation of the technical equipment of the buildings. There are also methods of active thermal protection to reduce heat leakage through non-transparent parts of the building envelope. Active thermal protection (ATP) is a dynamic process that applies primarily to building structures with integrated energetically active elements that fulfill one or more functions in mutually exclusive operating modes of energy systems and heat sources, such as thermal barriers (TB), large-scale heating/cooling, long-term heat/cool storage, capturing solar energy, and energy from the surroundings or even recovering heat in the cold season or cold in the warm season and other combinations. The research area focuses on analyzing active thermal protection’s energy potential. The methodology is based on a parametric study of dynamic thermal resistance (DTR), and heat flows to the interior and exterior from ATP for the investigated envelope of the experimental house EB2020 made of aerated concrete blocks. Such constructions generally show a consistently high DTR of 11.8 to 30.8 ((m2·K)/W) at a low mean heat transfer temperature of 10 to 16 °C, corresponding to the thermal insulation of 300 to 1000 mm. In the case of ATP storage heating with an average temperature of the heat-carrying substance of 30 °C, the heat flow into the interior of the investigated structure would be only 2.31 W/m2. Therefore, they are only suitable for a thermal barrier and heat/cold accumulation. Based on the synthesis and induction of analogical forms of the results of previous research into recommendations for the design of individual energy functions of ATP for perimeter structures of buildings, we present heat flows to the interior/exterior when changing the material of the layers towards the interior from ATP and describe possible variants of the development of building structures with integrated energetically active elements.

Study on transpiration cooling performance of SiC porous ceramics

Ceramic matrix composites are desirable for applications in the thermal protection system of hypersonic flight vehicles due to their excellent oxidation resistance. However, the service temperature exceeds the melting point of the components with a small curvature radius. Among the active cooling techniques, transpiration cooling has been proven to be a promising thermal protection method for hypersonic vehicles. In this study, SiC porous ceramics with different geometrical shapes and open porosities are fabricated using the polymer infiltration and pyrolysis route and sacrificial template method. Theoretical analysis and experimental investigation are performed to explore the feasibility of transpiration cooling with various coolants for SiC porous ceramics. The results confirm that the specific heat capacity is a key parameter that affects the cooling efficiency when a gas is used as the coolant. The effects of the material’s porosity, the attack angle, and the heat flux on the transpiration cooling performance with nitrogen are experimentally tested, and the highest cooling efficiency exceeded 80%. Meanwhile, the SiC porous ceramics displayed superior adaptive and self-pumping transpiration cooling performance when in a quartz lamp heating environment for about 10 min. The cooling mechanisms with a water phase change are also analyzed in detail. This study offers the possibility of developing thermal protection materials that could be used in active thermal protection techniques.

Design and optimization study of discrete inclined ribs enhanced bend tube based on “Diamond” active cooling thermal protection systems of hypersonic aircraft

When the hypersonic aircraft cruises, the surface will generate huge aerodynamic heating. Aiming at the thermal protection of hypersonic aircraft, this paper presented a study on the thermal–hydraulic and thermodynamic performance of discrete inclined ribs enhanced bend tube based on the designed “Diamond” channel. Meanwhile, a comprehensive numerical investigation was carried out for different models. The fluid velocity was found to vary in the range of 0.1–3.5 m·s−1, with the corresponding Reynolds number ranging from 3600 to 127000. The inlet temperature of heat transfer fluid was set to 253 K. It was visible that double–symmetrical longitudinal swirl was generated under a single upper and lower arrangement (Model D), which led to the best cooling performance on the inner wall. The performance evaluation criteria (PEC) and efficiency evaluation criterion (EEC) reached 0.99–1.18 and 0.66–1.00, respectively. The effect of four geometrical parameters (height–width ratio(H/d), length–width ratio (L/d), group number of ribs (n), and tilt angle (α)) of which the ranges are 0.5–2.5, 1.0–4.0,6–15 and 0°–90°, separately, was explored. The results showed that the inner wall temperature decreased up to 4.4 K when the Reynolds number was 72000. The Nusselt number and friction factor increased about 9.9 %–28.8 % and 16.5 %–111.5 %. Efficiency evaluation criterion reached 0.43–0.96. It was found that the combination of parameters would significantly affect the distribution of longitudinal swirls under the influence of secondary circulation in the bend tube. Moreover, many pairs of small vortices near the wall could improve active thermal protection performance. After obtaining the fitting function through the artificial neural network (ANN), the genetic algorithm (GA) was applied to obtain the Pareto front. The design variable for the L/d = 3.19, n = 11, and α = 14.3° was selected as the optimal solution by the TOPSIS method. When Reynolds number is 72000, the corresponding Tin and ΔP were 261.86 K and 2471.2 Pa. The performance evaluation criteria and efficiency evaluation criterion reached 1.02 and 1.09, respectively. Furthermore, a design variable for the L/d = 3.0, n = 11, and α = 15° was given for ease of engineering. The present work verified the feasibility of realizing heat transfer enhancement by combining the secondary circulation with longitudinal swirls formed by bend tube and discrete inclined ribs and proposed a new design scheme of active cooling thermal protection systems (ACTPS).

Cover Picture: Application of Carbon Fiber‐Reinforced Ceramic Composites in Active Thermal Protection of Advanced Propulsion Systems: A Review (Chem. Rec. 4/2023)

Cover Picture: Application of Carbon Fiber‐Reinforced Ceramic Composites in Active Thermal Protection of Advanced Propulsion Systems: A Review (Chem. Rec. 4/2023)

Numerical Investigation on the Thermal Protection Characteristics of a New Active Jet Design Parameter for Hypersonic Flight Vehicle

This study investigated the thermal protection performance of an active jet thermal protection system (PRsAJ-TPS) based on a new jet design parameter PRs for hypersonic flight vehicles (HFVs). The new parameter PRs is defined as the relationship between the jet flow total pressure and the free flow total pressure behind the outer bow shock. A 20° tilted nozzle design is employed together with the PRs to form the PRsAJ-TPS. Theoretical and numerical analysis is performed to prove the advantages of using the PRs. A conventional in-house CFD solver with the k ‐ ω SST turbulence model is utilized to perform the calculation. The influence of different PRs (working in the short penetration mode) and flight angles of attack on the performance of the PRsAJ-TPS is also studied. The simulation results confirmed that with a constant PRs, the Mach disk location stays the same and the normalized heat flux reduction is similar at different flight conditions. Nearly linear relationships exist between the new design parameter PRs and thermal protection performance indicators. The PRsAJ-TPS also exhibits good protection when flight angle of attack (AoA) varies between 0° and 40°, with the best results achieved at AoA = 0 ° . This study provides valuable information for the engineering application of the jet-based TPS to future HFVs.

Application of Carbon Fiber-Reinforced Ceramic Composites in Active Thermal Protection of Advanced Propulsion Systems: A Review.

Thermal protection is one of the crucial issues for the advanced propulsion systems of Reusable Launch Vehicles. New service requirements for materials, such as high strength, low density, low thermal expansion, high thermal stability, etc., are raised for the thermal structure with the increasing demand of flight Mach numbers and thrust-to-weight ratio. Carbon fiber-reinforced ceramic composites, which generally meet the aforementioned requirements, show great potential for various applications and they have been widely applied in the thermal protection for hypersonic vehicles. This paper gives a comprehensive and systematic review of current research status for carbon fiber-reinforced ceramic composites applied in the thermal structure of advanced propulsion systems. Three aspects are presented and discussed: the ceramic composites fabrication and the property characterization, the thermal performance of composite thermal structure used in practical engines, and the numerical methods for predicting mechanical and thermal properties of composites as well as the physicochemical phenomenon in the cooling channels. Firstly, the main manufacturing processes for the carbon-reinforced ceramic composites are presented and the corresponding advantages and disadvantages are analyzed. The high-temperature oxidation and ablation behaviors of composites are demonstrated and the improvement of oxidation and ablation resistance by introducing the ultra-high-temperature ceramics into C/C composites is discussed in detail. Then, several typical applications of carbon fiber-reinforced ceramic composites (mainly C/SiC), including the work of RCI, JAXA and NASA, have been reviewed and analyzed. After that, the current research status of macroscale equivalent and multiscale numerical methods for predicting the mechanical and thermal properties of composites as well as the complex physicochemical phenomenon occurring in hydrocarbon fuels are sorted out. Finally, several potential prospects are pointed out for the future research on the thermal protection of advanced propulsion systems based on the carbon fiber-reinforced ceramic composites.

Experimental Study on the Ethanol-Assisted Catalytic Steam Reforming of Endothermic Hydrocarbon Fuel.

Thermal protection is a critical problem in the development of hypersonic aircraft. To enhance the thermal protection capability of hydrocarbon fuel, the ethanol-assisted catalytic steam reforming of endothermic hydrocarbon fuel was proposed. The result shows that the total heat sink can be significantly improved by the endothermic reactions of ethanol. A higher water/ethanol ratio can promote the steam reforming of ethanol and further increase the chemical heat sink. The addition of 10 wt % ethanol at 30 wt % water content can improve the total heat sink by 8-17% at 300-550 °C, which is caused by the heat absorption by phase transition and chemical reactions of ethanol. The reaction region of thermal cracking moves backward, resulting in the suppression of thermal cracking. Meanwhile, the addition of ethanol can inhibit the coke deposition and increase the working temperature upper limit of the active thermal protection.

Experimental Study on Active Thermal Protection for Electronic Devices Used in Deep−Downhole−Environment Exploration

Electronic devices are commonly used for exploiting and extracting shale oil in deep downhole environments. However, high−temperature−and−pressure downhole environments jeopardize the safe operation of electronic components due to their severe thermal conditions. In the present study, an active thermal−insulation system is proposed, which consists of a spiral annular cooling plate (ACP), a thermal storage container with phase−change material (PCM) and an aerogel mat (AM). The effect of the ACP’s structure, layout and working−medium flowrate on the heat−protection performance were experimentally measured; temperature−control capability and system−operating time were used as the criteria. The results show that the AM layer is necessary and that the inner−ACP case displays better thermal−protection performance. Next, a dimensionless temperature−control factor (TCF) was proposed to evaluate the trade−off between temperature control and the system’s operating time. Note that the TCF of the spiral ACP can be improved by 1.62 times compared to the spiral−ACP case. Since the lower flowrate allows better TCF and longer operating times, intermittent control of the flowrate with a 1−minute startup and 2−minute stopping time at 200 mL/min can further extend the system’s operating time to 5 h, and the TCF is 3.3 times higher than with a constant flowrate of vm = 200 mL/min.