Najiba Hasan Hamad^1,*, Ranj Sirwan Abdullah², Ahmed Mohammed Adham²

Energy Engineering, Vol.123, No.1, 2026, DOI:10.32604/ee.2025.073377 - 27 December 2025

Abstract Coiled tube heat exchangers are widely preferred in shell structures due to their superior heat transfer performance, driven by favorable flow characteristics. This study investigates the effect of modifying coil and shell configurations on heat transfer efficiency. Two key enhancements were examined: adding fins to the outer coil surface and integrating longitudinal slots within a hollowed shell. These modifications promote turbulence and extend heat transfer duration, thereby improving performance. However, they also introduce challenges, including increased pressure loss and manufacturing complexity. Numerical simulations were conducted using ANSYS Fluent 2024R1 under identical boundary conditions. With a… More > Graphic Abstract

Shuo Wang^1,2,*, Huiming Wang^1,2, Ying Zhang^1,2, Zhiqiang Zhang^1,3, Li Jia^1,2

Frontiers in Heat and Mass Transfer, Vol.23, No.6, pp. 1721-1740, 2025, DOI:10.32604/fhmt.2025.073226 - 31 December 2025

Abstract This experimental investigation was conducted on the flow boiling performance of refrigerant R134a in two types of parallel microchannels: sintered porous microchannels (PP-MCs) and smooth parallel microchannels (SP-MCs). The tests were performed under controlled conditions including an inlet subcooling of 5 ± 0.2°C, saturation temperature of 33°C, mass fluxes of 346 and 485 kg/m²·s, and a range of heat fluxes. Key findings reveal that the sintered porous microstructure significantly enhances bubble nucleation, reducing the wall superheat required for the onset of nucleate boiling (ONB) to only 0.13°C compared to 2.2°C in smooth channels. The porous structure… More >

Noor Moneer Basher¹, Omar Rafae Alomar^1,*, Omar Mohammed Ali², Diyar Abdullah Ahmed³

Frontiers in Heat and Mass Transfer, Vol.23, No.6, pp. 2001-2024, 2025, DOI:10.32604/fhmt.2025.066997 - 31 December 2025

Abstract The energy consumption of a Split air conditioning unit (ACU) inside a building is extremely large, and efforts to decrease this issue are ongoing. The current work aims to experimentally investigate the thermal performance of ACU using an external cooling-water loop for pre-cooling the condenser to improve the efficiency and to reduce energy consumption by reducing refrigerant temperature before entering the condenser, thereby reducing the coefficient of performance. The experiments are performed on ACU with and without using an external cooling-water loop under different climate conditions. By using the experimental data, the systems’ performances for… More >

Ying Zhang^1,2, Chao Dang^1,2,*, Zhiqiang Zhang^1,2

Frontiers in Heat and Mass Transfer, Vol.23, No.4, pp. 1215-1242, 2025, DOI:10.32604/fhmt.2025.067373 - 29 August 2025

Abstract In this study, the flow boiling characteristics of R1234yf in parallel microchannels were experimentally investigated. The experiments were conducted with heat flux from 0 to 550 kW/m², mass flux of 434, 727, and 1015 kg/(m² s), saturation temperatures of 293, 298, and 303 K, and inlet sub-cooling of 5, 10, and 15 K. The analysis of the experimental results provides the following conclusions: a reduced mass flux and lower subcooling correspond to a diminished degree of superheat at the boiling inception wall; conversely, an elevated saturation temperature results in a reduced amount of superheat at the… More >

Zongyu Jie^1,2, Chao Dang^1,2,*, Qingliang Meng ^3,4

Frontiers in Heat and Mass Transfer, Vol.23, No.4, pp. 1053-1089, 2025, DOI:10.32604/fhmt.2025.066792 - 29 August 2025

Abstract With the increasing miniaturization of systems and surging demand for power density, accurate prediction and control of two-phase flow pressure drop have become a core challenge restricting the performance of microchannel heat exchangers. Pressure drop, a critical hydraulic characteristic, serves as both a natural constraint for cooling systems and determines the power required to pump the working fluid through microchannels. This paper reviews the characteristics, prediction models, and optimization measures of two-phase flow pressure drop for low-boiling-point working fluids in microchannels. It systematically analyzes key influencing factors such as fluid physical properties, operating conditions, channel… More >

Fayi Yan^*, Xuejian Pei, He Lu, Shuzhen Zong

Frontiers in Heat and Mass Transfer, Vol.22, No.1, pp. 287-304, 2024, DOI:10.32604/fhmt.2023.045038 - 21 March 2024

Abstract As compact and efficient heat exchange equipment, helically coiled tube-in-tube heat exchangers (HCTT heat exchangers) are widely used in many industrial processes. However, the thermal-hydraulic research of liquefied natural gas (LNG) as the working fluid in HCTT heat exchangers is rarely reported. In this paper, the characteristics of HCTT heat exchangers, in which LNG flows in the inner tube and ethylene glycol-water solution flows in the outer tube, are studied by numerical simulations. The influences of heat transfer characteristics and pressure drops of the HCTT heat transfers are studied by changing the initial flow velocity,… More >

Mainak Bhaumik¹, Anirban Sur^2,*, Kavita Dhanawade³

Frontiers in Heat and Mass Transfer, Vol.21, pp. 467-486, 2023, DOI:10.32604/fhmt.2023.044605 - 30 November 2023

Abstract Pin fins are widely used in applications where effective heat transfer is crucial. Their compact design, high surface area, and efficient heat transfer characteristics make them a practical choice for many thermal management applications. But for a high heat transfer rate and lightweight application, aerofoil shape pin fins are a good option. This work focuses on an experimental model analysis of pin-fins with aerofoil shapes. The results were evaluated between perforation, no perforation, inline, and staggered fin configurations. Aluminum is used to make the pin fins array. The experiment is carried out inside a wind… More >

Shaopeng Liu¹, Guowei Wang^2,3,*, Pengfei Liu¹, Dong Ye¹, Jian Song¹, Xing Liu¹, Yang Cheng^2,3

FDMP-Fluid Dynamics & Materials Processing, Vol.19, No.12, pp. 3045-3058, 2023, DOI:10.32604/fdmp.2023.029810 - 27 October 2023

Abstract Foam drainage is the flow of liquid through the interstitial spaces between bubbles driven by capillarity and gravity and resisted by viscous damping. The so-called foam drainage gas recovery technology is a technique traditionally used to mitigate the serious bottom-hole liquid loading in the middle and late stages of gas well production. In this context, determining the optimal concentration of the bubble drainage agent is generally crucial for the proper application of this method. In this study, a combination of indoor experiments and theoretical analysis have been used to determine the pressure drop related to… More >

Louay Abd Al-Azez Mahdi, Mohammed A. Fayad, Miqdam T. Chaichan^*

FDMP-Fluid Dynamics & Materials Processing, Vol.19, No.9, pp. 2201-2214, 2023, DOI:10.32604/fdmp.2023.027166 - 16 May 2023

Abstract A theoretical study based on the Penalty factor (PF) method by Cavallini et al. is conducted to show that the pressure drop occurring in a wire-on-tube heat exchanger can be converted into a temperature difference for two types of refrigerants R-134a and R-600a typically used for charging refrigerators and freezers. The following conditions are considered: stratified or stratified-wavy flow condensation occurring inside the smooth tube of a wire-on-tube condenser with diameter 3.25, 4.83, and 6.299 mm, condensation temperatures 35°C, 45°C, and 54.4°C and cover refrigerant mass flow rate spanning the interval from 1 to 7 kg/hr.… More > Graphic Abstract

Mohamed Shaimi^* , Rabha Khatyr, Jaafar Khalid Naciri

Frontiers in Heat and Mass Transfer, Vol.20, pp. 1-14, 2023, DOI:10.5098/hmt.20.23

Abstract This paper presents an exact analytical solution to the extended Graetz problem in microchannels and microtubes, including axial heat conduction, viscous dissipation, and rarefaction effects for an imposed constant wall temperature. The flow in the microchannel or microtube is assumed to be hydrodynamically fully developed. At the same time, the first-order slip-velocity and temperature jump models represent the wall boundary conditions. The energy equation is solved analytically, and the solution is obtained in terms of Kummer functions with expansion constants directly determined from explicit expressions. The local and fully developed Nusselt numbers are calculated in… More >