Transfer Enhancement Effect Research Articles

Thermal Performance of Selected Nanofluids in Combination with Heat Transfer Inserts

Two methods of heat transfer enhancement that have received considerable interest in recent years are nanofluids and heat transfer inserts. Comparatively few studies have evaluated the performance of systems with heat transfer inserts and nanofluids used in combination. In this study, heat transfer enhancement effects of alumina/water (Al2O3/H2O), copper oxide/cetyltrimethyl ammonium bromide/water (CuO/H2O/CTAB), and activated carbon/arabinogalactan/water (C/H2O/ARB) nanofluids both with and without hiTRAN® inserts were investigated using double-pipe heat exchangers in a customized experimental rig. The increase in heat transfer rates due to the nanoparticles (1% by mass of the nanofluids) was comparable in magnitude to the increase observed for the inserts without nanoparticles (i.e. water only), however, the friction factors of the inserts in water were considerably higher than for the nanofluids. The effects of the two heat transfer enhancement methods appeared to be additive when inserts were used in conjunction with nanoparticles. Of the three nanofluids the C/H2O/CTAB nanofluid had the best thermal enhancement assessed using the most commonly applied enhancement index, both with and without inserts. Due to agglomeration of nanoparticles, particularly for the Al2O3/H2O nanofluid that did not have a surfactant, the nanofluids were much less practical to deal with than the inserts.

Enhancing SNR in CEST imaging: A deep learning approach with a denoising convolutional autoencoder.

To develop a SNR enhancement method for CEST imaging using a denoising convolutional autoencoder (DCAE) and compare its performance with state-of-the-art denoising methods. The DCAE-CEST model encompasses an encoder and a decoder network. The encoder learns features from the input CEST Z-spectrum via a series of one-dimensional convolutions, nonlinearity applications, and pooling. Subsequently, the decoder reconstructs an output denoised Z-spectrum using a series of up-sampling and convolution layers. The DCAE-CEST model underwent multistage training in an environment constrained by Kullback-Leibler divergence, while ensuring data adaptability through context learning using Principal Component Analysis-processed Z-spectrum as a reference. The model was trained using simulated Z-spectra, and its performance was evaluated using both simulated data and in vivo data from an animal tumor model. Maps of amide proton transfer (APT) and nuclear Overhauser enhancement (NOE) effects were quantified using the multiple-pool Lorentzian fit, along with an apparent exchange-dependent relaxation metric. In digital phantom experiments, the DCAE-CEST method exhibited superior performance, surpassing existing denoising techniques, as indicated by the peak SNR and Structural Similarity Index. Additionally, in vivo data further confirm the effectiveness of the DCAE-CEST in denoising the APT and NOE maps when compared with other methods. Although no significant difference was observed in APT between tumors and normal tissues, there was a significant difference in NOE, consistent with previous findings. The DCAE-CEST can learn the most important features of the CEST Z-spectrum and provide the most effective denoising solution compared with other methods.

Evaluation of heat transfer enhancement effect at the hot/cold end of a Stirling engine using performance improvement factor

The driving force of a Stirling engine comes from the heating expansion and cooling compression of working medium. The enhancement of heat transfer capacity of the hot/cold end is the key to improve the Stirling engine performance, while how to objectively evaluate the heat transfer enhancement effect is a precondition. Herein, a polytropic model of a Stirling engine thermal cycle process was firstly established. A method for evaluating the heat transfer enhancement performance under oscillating flow was proposed based on the efficiency and power improvement of a Stirling engine. This method was further used to evaluate the heat transfer enhancement effect of a novel four-leaf helical heating tube under oscillating flow, the efficiency and power improvement factor of which was reached 13.5 % and 6.1 %, respectively. The results show that the efficiency and power improvement evaluation criterion was more comprehensive and intuitive in evaluating the heat transfer enhancement performance under oscillating flow compared with the conventional evaluation indictor like performance evaluation criterion and equivalent tube length and tube number criterion.

Experimental and numerical investigations on enhanced and stabilized flow boiling of hydrocarbon fuel in micro-finned channel

Due to the high heat transfer coefficient, flow boiling has applied in various industrial fields. Previous literature mainly focuses on the enhancement methods of flow boiling for water or refrigerants, with few reports on the enhancement of flow boiling for hydrocarbon fuels. Therefore, in this study, we design different types of micro-finned surface with strong capillary force to increases the nucleate sites and keep the wall in a superwetting state during the flow boiling to postpone the appearance of “annular bubble” flow. The influence of fin width, fin height, fin spacing and coolant type on boiling heat transfer through experiments and numerical simulation. The results show that the wider the fin width, the lower the fin height, the smaller the fin spacing, the stronger the heat transfer enhancement effect, and the more stable the flow boiling. The best heat transfer performance of the finned surface is achieved with the average wall temperature 27 °C lower and heat transfer coefficient 1.9 times higher than the smooth surface. Moreover, the heat transfer coefficient of hydrocarbon fuel is 43.3% larger than that of deionized water.

Accelerating gas escape efficiency by parallel alignment of nanosheets arrays for high-current oxygen evolution and urea oxidation

Electrocatalysts play a crucial role in energy production and chemical oxidation. Nonetheless, the efficacy of catalysts in expediting reactions is notably affected by the escape of bubbles and the re-exposure of active sites, particularly under high-current-density conditions. Herein, parallel-aligned Ni(OH)2 nanosheets array is anchored on nickel foam as substrate to verify mass transfer enhancement theory. Compare with disordered and interconnected nanosheets structures, parallel alignment of nanosheets array with superior mass transfer capability, larger exposed surface area, and spatial confinement effects is demonstrated to boost effective removal of in situ generated gas bubbles. Moreover, carbon coating layer with high electrical conductivity and nickel-iron-based composite with high activity is simultaneously anchored on parallel-aligned nanosheets surface (C@FeNi/NF-P). As illustration of application viability, C@FeNi/NF-P exhibits overpotential of 317 mV and potential of 1.45 V at 500 mA cm−2, respectively, for oxygen evolution (OER) and urea oxidation (UOR) with good stability. Moreover, the mass transfer enhancement effect of parallel aligned structure for the high active electrodes is also discussed. This work provides new insight for physical structural modulation of active materials to strengthen electrocatalytic activity with high mass-transfer efficiency, further ensuring high-efficient and stable water splitting and urea oxidation.

The behaviour of ternary hybrid nanofluid: Graphene oxide, Aluminium oxide, Silicon dioxide in heat transfer rate

The miniaturization in the design of the electronic system became inevitable due to the rapid advancement and development of technology. This has imposed challenges to the thermal management capability as the heat flux density has increased tremendously due to a smaller heat transfer surface. Nanofluids adoption in electronic cooling seems to be an alternative way for better heat dissipation. This research explores the feasibility of ternary hybrid nanofluids GO: Al2O3: SiO2 in water with different volume concentrations and mixture ratios in a serpentine cooling plate. In this research, 0.01% GO + Al2O3: SiO2, 0.006% GO + Al2O3: SiO2, and 0.008% GO + Al2O3: SiO2 in mixture ratios of 10:90 and 20:80 (Al2O3: SiO2) were studied. The result showed that 0.01% GO + Al2O3: SiO2 (10:90) nanofluids displayed the highest enhancement of heat transfer coefficient with 1.1 times higher as compared to the base fluid. This was then followed by 0.008% GO + Al2O3: SiO2 (10:90) and 0.006% GO + Al2O3: SiO2 (10:90) with 1.03 times and 0.87 times higher heat transfer coefficient enhancement consecutively as compared to the base fluid. In term of mixture ratios, GO in 10:90 (Al2O3: SiO2) performed better than 20:80. To assess the feasibility of adoption, the advantage ratio (AR) was conducted to measure both heat transfer enhancement and pressure drop effect. The AR analysis showed that at the lower Reynolds, Re number region, the 0.01% GO + Al2O3: SiO2 (10:90) ternary hybrid nanofluids was proven to be the most feasible due to a higher ratio of heat transfer enhancement over the pressure drop penalty.

A Denoising Convolutional Autoencoder for SNR Enhancement in Chemical Exchange Saturation Transfer imaging: (DCAE-CEST).

To develop a SNR enhancement method for chemical exchange saturation transfer (CEST) imaging using a denoising convolutional autoencoder (DCAE), and compare its performance with state-of-the-art denoising methods. The DCAE-CEST model encompasses an encoder and a decoder network. The encoder learns features from the input CEST Z-spectrum via a series of 1D convolutions, nonlinearity applications and pooling. Subsequently, the decoder reconstructs an output denoised Z-spectrum using a series of up-sampling and convolution layers. The DCAE-CEST model underwent multistage training in an environment constrained by Kullback-Leibler divergence, while ensuring data adaptability through context learning using Principal Component Analysis processed Z-spectrum as a reference. The model was trained using simulated Z-spectra, and its performance was evaluated using both simulated data and in-vivo data from an animal tumor model. Maps of amide proton transfer (APT) and nuclear Overhauser enhancement (NOE) effects were quantified using the multiple-pool Lorentzian fit, along with an apparent exchange-dependent relaxation metric. In digital phantom experiments, the DCAE-CEST method exhibited superior performance, surpassing existing denoising techniques, as indicated by the peak SNR and Structural Similarity Index. Additionally, in vivo data further confirms the effectiveness of the DCAE-CEST in denoising the APT and NOE maps when compared to other methods. While no significant difference was observed in APT between tumors and normal tissues, there was a significant difference in NOE, consistent with previous findings. The DCAE-CEST can learn the most important features of the CEST Z-spectrum and provide the most effective denoising solution compared to other methods.

Effects of mechanical vibration on melting characteristics of latent thermal energy storage units using the dynamic mesh method

Phase change materials (PCM) based thermal energy storage technology is an efficient method to overcome the intermittency and instability of energy supply. The heat transfer performance of PCM can be enhanced by the mechanical vibration technique, but the potential mechanisms remain to be revealed. In this study, a dynamic mesh approach was proposed to numerically investigate the effect of mechanical vibrations on the heat transfer performance of PCM. The results indicate that the increase of the vibration frequency leads to the increase of the melting rate, with the vibration frequency increasing from 0 to 3π and 5π, the complete melting time of PCM under vertical vibration can be decreased by 2.21 % and 3.74 %, and complete melting time under horizontal vibration can be decreased by 34.35 %, and 44.39 %, which means that the horizontal vibration exhibits a superior heat transfer enhancement effect. However, it was also found that the energy utilization effect was decreased with the increase of vibration frequency through energy assessment. In addition, the vibration has both promoting and inhibiting effects on the phase transition process, which is related to the melting state and vibration phase. This work provides a novel approach to vibrational simulations and an important guide for practical applications of vibrational heat transfer enhancement.

Numerical study of PCM melting performance in a rectangular container with various longitudinal fin structures

This paper uses the enthalpy-porosity technique to conduct a three-dimensional numerical investigation on the effect of adding longitudinal fins in energy storage units to enhance the melting process, with a specific focus on natural convection. By reducing the extension length of the upper part of the fins and increasing the extension length at the bottom, the work aims to enhance heat transfer while reducing obstruction to convection. The effects of rectangular, trapezoidal, and triangular longitudinal fins with thicknesses of 0.2, 0.25, and 0.3 mm on the melting characteristics were compared while maintaining a constant filling volume of RT42 phase change material (PCM) within the rectangular container. The results indicate that the enhanced heat transfer capacity of fins with different structures increases as the fin length increases. Triangular fins exhibit the most significant heat transfer enhancement effect, with the least hindrance to convection. When the fin thickness is 0.2 mm, the triangular fin decreases the melting completion time by 15.7 %, increases the heat storage rate by 18.7 % compared to the rectangular fin, and exhibits optimal natural convection intensity and temperature distribution in the energy storage unit. Additionally, the maximum flow velocity and average Nusselt number can be increased by 21.2 % and 18.5 %, respectively. It was also found that triangular fins are more suitable for high-temperature working conditions.

Experimental Investigation on Heat Transfer Enhancement of Phase Change Materials by Fractal Fins

The low thermal conductivity of phase change materials restricts their application fields such as thermal storage and electronic equipment cooling. In order to enhance the heat charging capacity of the phase change unit, fractal fins inspired by plant leaves were designed and manufactured. The changes in the solid–liquid interface, temperature distribution and liquid fraction in the phase change units with fractal fins during melting were investigated experimentally and compared units with the conventional rectangular fin. The results show that fractal fins have better heat transfer enhancement effects than rectangular fins because the enhancement of heat conduction exceeds the suppression of natural convection. Increasing the number of fins can also shorten the melting time and make the temperature distribution more uniform. Compared with the one rectangular fin unit, the full melting time of the unit with three fractal fins is reduced by 17.07%, and the bottom surface temperature is reduced by 27.47%. However, increasing the number of fins while using tree-like fractal fins may cause the fins to inhibit natural convection more than enhance heat conduction. The research in this paper will provide a better understanding of the melting process of phase change units with fins and provide data for future numerical simulations.

Fluorescent columnar liquid crystals based on BTD hexacatenars with salicylaldimine and benzaldimine core: Self-assembly and multifunctional properties

Two series of hexacatenars SB/n and BB/n containing a benzothiadiazole (BTD) central core with triple alkyl chains at both ends via salicylaldehyde or benzaldehyde derivated Schiff base links, respectively, were prepared. Different Schiff base links lead to different self-assembly and photophysical behaviors. Both series can self-assemble into columnar liquid crystal (LC) phases but with different lattices (p6mm for SB/n, p4mm for BB/n) in bulk states, and SB/n can additionally form gels in organic solution. Interestingly, SB/n series were characterized with excited state intramolecular proton transfer (ESIPT) and aggregation-induced emission enhancement (AIEE) effects, and displayed high fluorescence in their solid, LC and gel states with large Stokes shifts and environmental sensitive unique spectra patterns. The effect of photoisomerization driven by ESIPT process on LC state of SB/n was observed. The applications of SB/n as fingerprint imaging device, Al3+ fluorescence chemosensor, white light emitting diodes (WLED) as well as light-emitting liquid crystal displays (LE-LCD) have been successfully realized.

Heat transfer enhancement and long-term test of non-ionic Triton surfactant with different hydrophilic chain lengths

Surfactant aids boiling enhancement, but the related mechanism is not yet comprehensively understood. For mechanism investigation on surfactant molecule, most of existing studies focused on its hydrophobic part, while research on hydrophilic part is scarce. In this paper, a group of non-ionic Triton surfactants with same functional group but different hydrophilic chain lengths were experimentally tested for pool boiling on flat copper. At critical micelle concentration (CMC), long-chain Tx-405 exhibited higher heat transfer coefficient (97.4 kW/(m2·K)) than Tx-100 (77.1 kW/(m2·K)) and Tx-114 (77.4 kW/(m2·K)). Long-term test indicated a gradually deteriorating trend of heat transfer performance from days on. Solution properties and bubble dynamics were measured. At low concentration, surfactant with shorter hydrophilic chain has better heat transfer performance due to greater surface tension reduction. The increase of hydrophilic chain length improves water affinity of surfactant and thus leads to higher CMC. If there is no restriction for surfactant concentration, a longer hydrophilic chain is favorable for higher heat transfer coefficient at CMC. The results in this paper provide insights for mechanism investigation on surfactant, promote further design of new surfactant, and contribute to the prediction of heat transfer enhancement effect.

Effects of viscosity on hydrodynamics and mass transfer under a wire mesh-coupled solid particles method

Many practical industrial processes require gas–liquid mass transfer in highly viscous liquids, and liquid viscosity affects bubble characteristics and gas–liquid mass transfer. The current study investigated the effects of liquid viscosity on bubble dynamics and gas–liquid mass transfer via shadow imaging and dynamic oxygen dissolution methods, and the influence of fluid viscosity on the hydrodynamic effect when using a wire mesh-coupled solid particles method. The coupling strategy was associated with a bubble size regulation effect, with greater viscosity increasing the gas–liquid interface area by 27%–55% compared with unreinforced gas–liquid flow, which was superior to embedded wire mesh and added solid particles methods. Increased viscosity weakened the mass transfer enhancement effect of the coupling method, but the coupling method still effectively enhanced the gas–liquid mass transfer process, increasing the volumetric mass transfer coefficient (KLa) by 80%–130% compared to non-enhanced gas–liquid flow. Novel empirical KLa correlation equations were developed to predict the effects of the coupling method on gas–liquid mass transfer processes, and those equations exhibited good reliability and predictive capacity.

Swirl development and enhanced heat transfer analysis of ferrofluid in elliptical ducts under thermal-magnetic-flow fields coupling

It is a new practical method to apply external magnetic field in magnetic working fluid to enhance heat transfer. In this paper, the swirl flow and heat transfer characteristics of ferrofluid in elliptical tubes under thermal-magnetic-flow fields coupling have been studied by using the finite volume method. The flow structure and secondary vortices evolution process of magnetic nanofluid in elliptical ducts under the action of the magnetic fields have been obtained. The effects of magnetic induction intensity and the ratio of major axis to minor axis of elliptical pipe on the flow and heat transfer performances have been main investigated. The results show that there is obvious secondary flow (with four vortices or eight vortices) on the cross section and the swirling flow is gradually formed due to the coupling of thermal-magnetic-velocity fields. With the increase of the ratio of major axis to minor axis, the heat transfer enhancement effect with the application of external magnetic field is weakened. The comprehensive performance of flow and heat transfer are better at lower Reynolds number and higher magnetic induction intensity.

Flow and heat transfer characteristics of microencapsulated phase change material slurry in bonded triangular tubes for thermal energy storage systems

Three nanoscale metal oxides composed of nano TiO2, nano Al2O3, and nano MgO were added to the phase change microcapsule slurry for optimising the heat transfer behaviour. The thermal and rheological properties of the resulting microencapsulated phase change materials (MPCMs) and microencapsulated phase change material slurries (MPCSs) were characterized to determine the effects of added metal oxides in optimising the performance of MPCSs. The impacts of factors like metal oxides, concentrations, and flow rates on the heat transfer behaviour of MPCSs were investigated by forced convective heat transfer experiment with various working conditions. Compared to 6 wt% MPCSs, the heat transfer coefficients (hx) of 6 wt% slurries containing 1 wt% TiO2, 1 wt% Al2O3, and 1 wt% MgO increased by 4.0 %, 2.5 %, and 7.13 %, respectively. Nano-MgO showed the most significant heat transfer enhancement effect on MPCSs. Moreover, the heat transfer performance gradually enhanced as a function of the concentration for nano MgO. Overall, the addition of metal oxides enhanced heat transfer by increasing the thermal conductivity of the slurry, as well as improved the micro-convection effect. The proposed MPCSs are promising for applications in solar photovoltaic/thermal (PV/T) systems, chip cooling, thermal management, buildings, and automotive cooling.

Study on the heat transfer enhancement characteristics by flow-induced vibration of inserting polyethylene membrane inside the channel

With the development of science and technology, the heat dissipation problem of high-density electronic products has gradually emerged in engineering practice. In this paper, the enhanced heat dissipation process of fluid induced oscillation through flexible membrane is proposed, which belongs to the multi-field synergistic bidirectional coupling effect of thermal-fluid-solid coupling. Through the comparative numerical analysis of the flow induced oscillation of the flexible membrane and the fixed rigid fin in the flow channel, the mechanism of the fluid induced oscillation of the flexible polyethylene membrane is revealed. Based on the two-way fluid-solid coupling method, a numerical model for the heat transfer process of polyethylene membrane with thickness of 0.02 mm in the fluid channel was established. The temperature field, Nu (Nusselt number) and PEC (Performance comparison index) number of the rigid fin and polyethylene membrane installed in the channel under different Reynolds numbers were calculated respectively. The ratio of the length of the membrane to the height of the channel was adjusted for multiple groups of calculations to verify the positive effect of the polyethylene membrane installed in the channel on the heat exchange effect. The results show that in the fully developed area of heat transfer, the channel with polyethylene membrane is better than that with rigid fins in terms of turbulence and vortex shedding; at Re = 4400, the comprehensive enhanced heat transfer factor of heat exchange is the largest, up to 1.27; as the ratio of the height of the new flexible membrane to the height of the channel is 1, the heat transfer enhancement effect is best. In the next step, the correlation theory between oscillation characterization parameters and heat transfer enhancement effect under pulsating fluid excitation will be investigated.

The effect of dimple/protrusion arrangements on the comprehensive thermal performance of variable cross-section rotating channels for gas turbine blades

The cooling structure design of turbine blades plays a vital role in ensuring the safety and reliability of the entire gas turbine set. Our team's previous research revealed the influence of the rotating and variable cross-section effect on the aerothermal characteristics of the channel. In order to further enhance the cooling performance, four types of dimple/protrusion arrangement schemes are applied to five channels with different height ratios in this research. The detailed flow-heat transfer-friction characteristics and comprehensive thermal performance of each channel are obtained. The results show that the introduction of heat transfer enhancement element produces obvious heat transfer enhancement effect. Compared with the smooth reduced cross-section channel, the Nu/Nu0 is increased by 10.9 % (height ratio = 4:1, both of two passes are arranged by protrusions). For the rough expand cross-section channel, the Nu/Nu0 is increased by 8.9 % (height ratio = 1:2, the first pass is arranged by protrusions and the second pass is arranged by dimples). Within the scope of this paper, the arrangement scheme of both of two passes are arranged by dimples has the best comprehensive thermal performance. The arrangement scheme of both of two passes are arranged by protrusions has the highest Nu/Nu0, but also the highest f/f0.

Mini-channel cooling system for solar PV Panels with hybrid magnetic nanofluid and magnetic field

This study delves into the interplay between magnetic fields, heat transfer, and fluid behavior within a 3D mini-channel. Exploring the effects of a magnetic field on a hybrid nanofluid (Fe3O4–TiO2) under varying intensities (1000–2000 Gauss) and positions. Using numerical simulations (finite volume method), key parameters like Nusselt number (Nu), Friction factor (f), and Thermal Enhancement Factor (TEF) have been analyzed to uncover how magnetic fields and nanofluids interact in complex geometries. Results showed that the application of a magnetic field significantly enhanced heat transfer performance, with a maximum Nusselt number enhancement of 230%. Moreover, it was shown that greater magnetic field intensities were associated with elevated friction factors, whereas friction factors exhibited a declining trend as Reynolds numbers increased. The thermal enhancement factor initially increased with Reynolds numbers, but declined after reaching a peak. However, higher magnetic field strengths mitigated this decline, intensifying heat transfer enhancement effects reaching a maximum of 2.18 at 2000G magnetic field. These findings provide quantitative insights into the effectiveness of magnetic fields in enhancing heat transfer in Fe3O4–TiO2 hybrid nanofluids.

Secondary vortex drag reduction and heat transfer enhancement of nanofluids in hierarchical microchannels applied to thermal management of electronic components

In order to improve the heat dissipation performance of electronic components, two hierarchical microchannel structures with curve and straight corners are proposed, and semi-circular and trapezoidal secondary flow structures are introduced into the structure with the best performance. The effects of coolant (Fe3O4-water nanofluid), layered structure and secondary flow structure on the comprehensive performance of MCHS were studied by numerical simulation. Results showed that deionized water is more suitable for the heat dissipation of microchannels at this scale. The hierarchical structure has the effect of enhancing heat transfer, and Nu can be increased by up to 67.32 %. The introduction of secondary flow structure has drag reduction effect in a certain Reynolds number range. The hierarchical MCHS with semi-circular secondary flow structure has drag reduction effect in the Reynolds number range of Re = 200–400, and the pressure drop can be reduced by up to 1.89 %. The hierarchical MCHS with trapezoidal secondary flow structure always has a drag reduction effect in the range of Reynolds number Re = 200–600, and the maximum pressure drop can be reduced by 2.46 %, showing excellent drag reduction ability. In addition, the introduction of trapezoidal secondary flow in MCHS increases the Nusselt number by 9.70 %, the comprehensive performance index reaches 1.10, and the cooling performance and comprehensive performance are optimal. The combination of hierarchical structure and secondary flow structure has excellent drag reduction and heat transfer enhancement effects, and has broad application prospects in the field of thermal management of electronic devices.

The heat transfer enhancement of the converging-diverging tube in the latent heat thermal energy storage unit: Melting performance and evaluation

Latent heat thermal energy storage (LHTES) has emerged as a promising approach to settle the intermittent and fluctuant of renewable energy but heat transfer enhancement is necessary due to the low thermal conductivity of the phase change material (PCM). This study numerically investigated the heat transfer enhancement effect of the typically converging-diverging tubes (CDTs) inside a shell-and-tube LHTES unit. The evolution of melting behavior was analyzed to describe the heat transfer enhancement mechanism of the CDT. Based on the enhancement effect and pump power consumption associated with the CDT, a modified performance evaluation criterion (PEC) was established to evaluate the feasibility of current designs. The arrangement of CDTs was found to significantly improve the heat transfer performance of LHTES. The triangle CDT exhibited the maximum melting time reduction of 20.77%. The heat transfer enhancement effect of CDT was attributed to the enhanced natural convection of PCM and forced convection of heat transfer fluid. The analysis of the evaluation ensures the feasibility of the new criterion and its specific application field. Moreover, it was worth to note that the triangle CDT achieved the best cost performance of 0.363 ω, where ω represented the return factor.