The use of heat transfer improvement methods is crucial for enhancing energy efficiency, minimizing system sizes, lowering costs, and promoting environmental sustainability. In this context, passive (fins, nanoparticles, etc.) and active (ultrasonic, magnetic field) heat transfer improvement methods are applied to the thermal systems. However, relatively few studies have examined the combination of nanofluid and ultrasonic enhancement. Taking advantage of this gap in the literature, this study presents the first systematic experimental investigation of a CuO/water nanofluid in laminar flow regime combined with low-power (Pus = 5 W) ultrasound (US), focusing on the synergistic effects on thermohydraulic performance. For this purpose, a heat flux of q″ = 2250 W·m−2 was applied to the surface of a smooth tube made of copper, and two different volumetric concentrations (φ = 0.01% and 0.05%) of CuO/water nanofluid were passed through it at four different Reynolds numbers (Re) of 500, 825, 1500, and 1780. In addition, US was applied at a frequency of f = 25.7 kHz at the entry section. The average Nusselt number (Nu) was found to increase with both the increase in Re and the application of US. With the application of US, the average Nu values of the systems containing water, φ = 0.01% and 0.05% CuO/water nanofluids were increased by 11.0 %, 2.0 %, and 4.0 %, respectively. However, when the nanofluid concentration was increased to φ = 0.05%, the average Nu decreased compared to φ = 0.01%, which was considered to be due to increased viscosity and particle agglomeration. The average friction coefficient (ff) increased with both nanofluid use and US. In experiments with water, an average of 20% increase was obtained with the US application, while increases of 15% and 10% were observed with φ = 0.01% and 0.05%, respectively. In measurements performed under NUS (non-ultrasonic) conditions, it was determined that φ = 0.01% and 0.05 % CuO/water nanofluids increased the friction in the system by 11.0% and 15.7 %, respectively. In terms of Performance Evaluation Criteria (PEC) analyses, the use of φ = 0.01% CuO/water nanofluid was more favorable than φ = 0.05%. Although PEC was higher in US conditions at low Re, NUS conditions were found to be more advantageous, as the average PEC values obtained under NUS conditions were 3.0% higher compared to US conditions. These findings demonstrate that the use of low-concentration nanofluid and optimal US application is critical to efficiency in heat transfer systems.

Heat Transfer Enhancement with Low-Concentration CuO/Water Nanofluid and Ultrasonic Energy: An Experimental Study

期刊论文
发表日期：

2025年12月18日

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Alper Ergün,
Emrehan Gürsoy,
Abdulmajeed Alenezi,
Amarnath Periyakaruppan,
Abdallah Y. M. Ali,
Ehab Mina,
Patrick Phelan

摘要

The use of heat transfer improvement methods is crucial for enhancing energy efficiency, minimizing system sizes, lowering costs, and promoting environmental sustainability. In this context, passive (fins, nanoparticles, etc.) and active (ultrasonic, magnetic field) heat transfer improvement methods are applied to the thermal systems. However, relatively few studies have examined the combination of nanofluid and ultrasonic enhancement. Taking advantage of this gap in the literature, this study presents the first systematic experimental investigation of a CuO/water nanofluid in laminar flow regime combined with low-power (P_us = 5 W) ultrasound (US), focusing on the synergistic effects on thermohydraulic performance. For this purpose, a heat flux of q″ = 2250 W·m⁻² was applied to the surface of a smooth tube made of copper, and two different volumetric concentrations (φ = 0.01% and 0.05%) of CuO/water nanofluid were passed through it at four different Reynolds numbers (Re) of 500, 825, 1500, and 1780. In addition, US was applied at a frequency of f = 25.7 kHz at the entry section. The average Nusselt number (Nu) was found to increase with both the increase in Re and the application of US. With the application of US, the average Nu values of the systems containing water, φ = 0.01% and 0.05% CuO/water nanofluids were increased by 11.0 %, 2.0 %, and 4.0 %, respectively. However, when the nanofluid concentration was increased to φ = 0.05%, the average Nu decreased compared to φ = 0.01%, which was considered to be due to increased viscosity and particle agglomeration. The average friction coefficient (ff) increased with both nanofluid use and US. In experiments with water, an average of 20% increase was obtained with the US application, while increases of 15% and 10% were observed with φ = 0.01% and 0.05%, respectively. In measurements performed under NUS (non-ultrasonic) conditions, it was determined that φ = 0.01% and 0.05 % CuO/water nanofluids increased the friction in the system by 11.0% and 15.7 %, respectively. In terms of Performance Evaluation Criteria (PEC) analyses, the use of φ = 0.01% CuO/water nanofluid was more favorable than φ = 0.05%. Although PEC was higher in US conditions at low Re, NUS conditions were found to be more advantageous, as the average PEC values obtained under NUS conditions were 3.0% higher compared to US conditions. These findings demonstrate that the use of low-concentration nanofluid and optimal US application is critical to efficiency in heat transfer systems.