Search Results (16)

The cooling system plays an essential role in regulating the temperature of hybrid vehicle engines. With the contemporary surge in the number of hybrid vehicles, the cooling system’s performance is vital for the safe and stable operation of these cars. The radiator, as the core component of the cooling system, has become central to enhancing thermal efficiency through performance optimization. Improvements to existing radiators are especially important in order to meet increasing performance demands. This paper firstly outlines the development of radiator technology for hybrid vehicles both domestically and internationally; it then analyzes the tube and belt radiator, and selects a louvered finned radiator with highly efficient heat dissipation performance as the object of research. It then carries out the detailed design and assessment of the radiator, formulates an accurate design scheme, and creates a three-dimensional model of the radiator and its main parts using the CATIA V5 software. Finally, the simulation and analysis Fluent software (ANSYS 2023 R1) is used to carry out a comparative analysis of the designed radiator and its important parts. The study focuses on how fin angle, inlet and outlet positioning, radiator orientation, and fan speed affect thermal performance. The findings indicate that a 26° fin angle, a same-side inlet and outlet layout, correct radiator orientation, and higher fan speeds enhance cooling efficiency. These optimizations improve radiator performance, ensuring efficient cooling under various operating conditions. Full article

Pin-fin and flat-tube heat exchangers (PFFTHXs) offer a promising alternative to traditional louvered-fin and flat-tube heat exchangers (LFFTHXs), especially when used as evaporators. The streamlined structure of pin fins helps to effectively remove condensate and defrost water. In this study, we conducted a numerical analysis of 60 different pin-fin configurations across three pin diameters to enhance heat transfer in PFFTHXs. Our investigation focused on how pin pitch affects both airflow and heat transfer efficiency. The results show that a closer pin pitch increases both the heat transfer rate per unit area and the pressure drop for a given airflow velocity. We evaluated the overall performance of these configurations using the heat transfer rate per unit frontal area obtained at equivalent fan power levels. The analysis identified optimal configurations for each pin diameter, with the 0.2 mm diameter configuration demonstrating the highest heat transfer efficiency—this was on par with louvered fins but used fewer resources. This makes it an ideal choice for evaporative applications in PFFTHXs. Full article

Triangles are an ever-present feature in nature, which the building construction industry duly echoes. However, an exact expression intended to supply the radiant field of any triangle in an upright or inclined position has not been identified by previous research. In this case, the author has been able to solve, via direct integration, the canonical expression of radiative transfer. This result alone confers a myriad of possibilities, that had been inconceivable before, for studying in detail the three-dimensional heat-transfer behavior of volumes and figures in which triangles manifest, such as fins, windows, roof-gables and louvers of various kinds. Typically, shading devices, when tilted, give rise in their extremes to rhomboidal shapes which were difficult to take into account or had to be subject to discretization and subsequent Monte Carlo methods in order to perform an approximate calculation of their emissions. This implied a lengthy and inexact procedure that induced many errors and consumed computing time. We can now avoid all these former downsides due to the advances hereby presented. As this novel expression can be converted into an algorithm, it will be advantageously employed for simulation. This significant finding dovetails into the intricate puzzle of radiated heat and we believe that its consequences will greatly affect the conception and design of HVAC devices, aircraft manufacturing and specifically the building or lighting industries, among others. Full article

This research explores the potential of hybrid nanofluids to improve the thermal efficiency of a car’s louvered fin flat-tube radiator. Hybrid nanofluids were prepared by combining distilled water with a 0.1% vol. concentration of Si${\mathrm{O}}_2$ and MWCNT nanoparticles, using different ratios of nanoparticles: 80:20, 50:50, and 20:80. The experimental analysis focused on examining the heat-transfer performance of the radiator. The results clearly demonstrated a significant improvement in the radiator’s thermal performance when using hybrid nanofluids. These nanofluids effectively enhanced the rate and coefficient of heat transfer. Notably, an increase of 15.6% in the Nusselt number was observed with the Si${\mathrm{O}}_2$–MWCNT 20:80 water containing a 0.1% volumetric concentration of nanoparticles. Overall, the findings highlight the promising application of hybrid nanofluids in boosting the thermal efficacy of car radiators. Full article

Microchannel heat exchangers (MCHX) are increasingly being used in refrigeration and heat pumps due to their superior thermal-hydraulic properties. However, when the MCHX surface temperature drops below the freezing point, frost will accumulate on the fin surface, which significantly affects the heat transfer performance. In this study, a modified MCHX with extended windward fins was developed to improve the frosting performance. The thermal-hydraulic performance of the modified MCHX and conventional MCHX were compared and evaluated under frosting conditions. Results show that the extended fins on the windward side capture a large amount of frost and delay the rapid blockage of air flow passage by frost. The modified MCHX structure makes the frost more evenly distributed. During the 60 min frosting cycle, the total heat transfer capacity and the mass of the accumulated frost of the modified MCHX are 9.6–49.7% and 10.3–46.9% higher than the conventional MCHX, respectively. Furthermore, the modified MCHX has greater potential to improve the thermal-hydraulic performance under the condition of more uneven frost layer distribution. The purpose of this work is to provide useful guidance for the optimal design of MCHX under frosting conditions. Full article

Fuel cell electric vehicles offer a short fuel charging time and high mileage, but require precise thermal management technology to ensure the durability and efficiency of the stack. Accordingly, the size and weight of the heat exchanger increase to ensure the performance of the heat exchanger. For this reason, a louver fin type heat exchanger requires optimal size and weight, as well as high performance. This paper optimally designs high-performance heat exchangers with reduced size and weight by applying genetic algorithms to solve this problem. The optimal result value was achieved by optimizing the design variables using concentrated variable modeling and a genetic algorithm, and the dynamic characteristics of the heat exchanger were analyzed by applying the driving cycle of the vehicle. In addition, 3D modeling was conducted to present the weight and practically applicable form. As a result, compared to the existing model, the heat transfer rate and effectiveness were improved by 5% and 1.6%, respectively, and the weight was also reduced by 5.8%. These results exceed the expected performance improvements of low size and weight. Moreover, it is expected that an improved heat exchanger optimization, as well as a design reflecting a drive cycle, could be conducted using the proposed genetic algorithm and be applied not only to a heat exchanger, but also to various components. Full article

Utilizing ultrasonic excitation as an active method for studying the rate of heat transfer has gained considerable attention recently. The present study investigated the effects of ultrasonic excitation on the heat transfer rate in a fin-and-flat tube heat exchanger experimentally. The performance of the heat exchanger was investigated with and without the presence of ultrasonic excitation. A comprehensive parameter study was attempted, so several parameters, including ambient temperature, flow rate, air passing velocity, Reynolds number, and Nusselt number, were studied in a relatively wide range. An adequate uncertainty test, as well as a validation assessment, is provided to certify the credibility of the obtained results and the hired facility. The results revealed that reducing the flow rate, ambient temperature, and air passing velocity on the heat exchanger increased the ultrasonic excitation’s effects. The highest heat transfer enhancement in the present experiment was 70.11%, measured at the lowest air passing velocity and ambient temperature with a Reynolds number 2166. The data presented in this paper will be useful for the optimal design of ultrasonic vibrating fin-and-tube heat exchangers. Full article

The performance of heat exchangers is severely limited by airside thermal resistance. The effect of redirection louvers (RLs) on the airside thermal performance of a compact flat-tube louvered fin heat exchanger was investigated. A steady-state 3D numerical analysis was conducted for different fin configurations by varying the number of RLs (N_RL = 1, 2, 3, and 5). Conjugate heat transfer analysis was performed at the low Re (50–450) for domestic and transport air-conditioning applications. Geometric parameters such as louver pitch, louver angle, fin pitch, and flow depth were set as 1.7 mm, 27°, 1.2 mm, and 20 mm, respectively. The effective heat transfer fin surface areas of different fin configurations were also kept identical for a comparative analysis. The influence of the RLs on the airside thermal–hydraulic performance was analysed by exploring the local and average Nusselt numbers, pressure drop, Colburn j factor, friction factor f, performance evaluation criteria (PEC), and flow efficiency of different fin configurations. The numerical results revealed that the asymmetric fin configuration with two RLs (N_RL = 2) showed the best heat transfer performance for the entire Re range. It resulted in a 33% higher average Nusselt number, causing a 24% higher pressure drop compared to $N_{RL}=5$. At low flow velocities (Re < 75), N_RL = 3 showed better PEC; however, at high flow velocities (Re > 75), N_RL = 1 outperformed other fin configurations. Finally, it was noted that increasing the number of RLs reduced the amplitude of the wavy-shaped flow formed between the neighbouring louvered fin, consequently deteriorating the flow efficiency. Full article

A novel heat exchanger for automotive applications developed by the Heat Transfer and Fluid Flow Laboratory at the Brno University of Technology, Czech Republic, is compared with a conventional commercially available metal radiator. The heat transfer surface of this heat exchanger is composed of polymeric hollow fibers made from polyamide 612 by DuPont (Zytel LC6159). The cross-section of the polymeric radiator is identical to the aluminum radiator (louvered fins on flat tubes) in a Skoda Octavia and measures 720 × 480 mm. The goal of the study is to compare the functionality and performance parameters of both radiators based on the results of tests in a calibrated air wind tunnel. During testing, both heat exchangers were tested in conventional conditions used for car radiators with different air flow and coolant (50% ethylene glycol) rates. The polymeric hollow fiber heat exchanger demonstrated about 20% higher thermal performance for the same air flow. The efficiency of the polymeric radiator was in the range 80–93% and the efficiency of the aluminum radiator was in the range 64–84%. The polymeric radiator is 30% lighter than its conventional metal competitor. Both tested radiators had very similar pressure loss on the liquid side, but the polymeric radiator featured higher air pressure loss. Full article

Although the research on potential use of nanofluids in automotive vehicles is in its embryonic stage, a number of studies have suggested the strong prospect of nanofluids for the efficient thermal management of automotive vehicles. Nevertheless, the pinnacle of nanofluid-based systems awaits stable nanoparticle suspension. The present work studies the heat transfer performance of an aluminum tube automotive radiator with 31 flattened tubes and louvered fins using water and different concentrations (0.04, 0.08, and 0.12 vol.%)-based SiO₂/water nanofluids as the engine coolant. Inlet temperature and flowrate of the fluid were varied from 60 to 70 °C and 12 to 18 LPM, respectively. The topmost increment in heat transfer rate of 36.92% and Nusselt number of 45.53% were observed in the upper range of tested operational parameters, however, the relative heat transfer increment percentage dropped from 5% (between 0.04 and 0.08 vol.%) to 3.5% (between 0.08 and 0.12 vol.%) due to agglomeration and cluster formation caused by the presence of a greater number of nanoparticles. Precise evaluation of the experimental results was also carried out by reperforming the tests after three days of initial experimentations. A mere deviation of less than 1% was observed between the initial and repeated tests, however, the decline was caused due to the synergistic effects of clustering and fouling. Full article

According to the temperature regulations and high energy consumption of air conditioning (AC) system in data centers (DCs), natural cold energy becomes the focus of energy saving in data center in winter and transition season. A new type of air–water heat exchanger (AWHE) for the indoor side of DCs was designed to use natural cold energy in order to reduce the power consumption of AC. The AWHE applied micro-heat pipe arrays (MHPAs) with serrated fins on its surface to enhance heat transfer. The performance of MHPA-AWHE for different inlet water temperatures, water and air flow rates was investigated, respectively. The results showed that the maximum efficiency of the heat exchanger was 81.4% by using the effectiveness number of transfer units (ε-NTU) method. When the max air flow rate was 3000 m³/h and the water inlet temperature was 5 °C, the maximum heat transfer rate was 9.29 kW. The maximum pressure drop of the air side and water side were 339.8 Pa and 8.86 kPa, respectively. The comprehensive evaluation index j/f^1/2 of the MHPA-AWHE increased by 10.8% compared to the plate–fin heat exchanger with louvered fins. The energy saving characteristics of an example DCs in Beijing was analyzed, and when the air flow rate was 2500 m³/h and the number of MHPA-AWHE modules was five, the minimum payback period of the MHPA-AWHE system was 2.3 years, which was the shortest and the most economical recorded. The maximum comprehensive energy efficiency ratio (EER) of the system after the transformation was 21.8, the electric power reduced by 28.3% compared to the system before the transformation, and the control strategy was carried out. The comprehensive performance provides a reference for MHPA-AWHE application in data centers. Full article

Electric vehicles use positive temperature coefficient (PTC) heaters and heat pumps to warm the vehicle cabin. High-capacity PTC heaters are needed because heat pump performance decreases sharply in the winter months due to low outdoor temperatures. The weight of PTC heaters is an important heater design factor for improving the single-charge travel distance of electric vehicles. A fin shape is necessary to improve the heater’s heat transfer performance in comparison to its weight. To develop a 6 kW class high-capacity PTC heater for electric vehicles, this study presents a numerical analysis of heat flow according to a modified louver fin’s geometric shape variables and evaluates heating performance. Based on the geometric shape of an initial plate-shaped fin prototype, a numerical analysis was performed on the width, position, height, and angle to develop a modified louver fin while considering heat transfer performance and ease of manufacturing. An improved prototype was built using the developed modified louver fin, and its heating performance under standard conditions was evaluated. The improved prototype had a heating performance of 6.05 kW, an efficiency of 98.0%, a pressure drop of 18.3 Pa, and a heating density of 3.81 kW/kg. Compared to the initial prototype, its heating performance and heating density were improved by approximately 15.7%. Full article

This study performs a 3D turbulent flow numerical simulation to improve heat transfer characteristics of wavy fin-and-tube heat exchangers. A compound design encompassing louver, flat, and vortex generator onto wavy fins can significantly enhance the heat transfer performance of wavy fin-and-tube heat exchangers. Replacement of wavy fins around tubes with flat fins is not effective as far as the reduction of thermal resistance is concerned, although an appreciable pressure drop reduction can be achieved. Adding two louvers with a width of 8 mm to the flat portion can reduce thermal resistance up to 6% in comparison with the reference wavy fin. Increasing the louver number and width can further decrease the thermal resistance. Also, it is found that the optimum louver angle is equal to the wavy angle for offering the lowest thermal resistance. Therefore, compound geometry with three louvers, a width of 12 mm, and the louver angle being equal to wavy angle with waffle height to be the same as fin pitch of the reference wavy fin has the most reduction in thermal resistance of 16% for a pumping power of 0.001 W. Adding punching longitudinal vortex generators on this compound geometry can further decrease thermal resistance up to 18%. Full article

Enhancing the heat transfer surface by usage of cellular metal structures, such as foams or wire structures, might allow enlarging the surface area, increasing the heat transfer coefficients, decreasing the material utilization, and enabling the flexibility of different geometrical dimensions. However their manufacturing and assembling in a large heat exchanger for performance testing and optimizing can be costly. Therefore a test rig was constructed for experimental characterization of heat transfer surface area enhancements. Heat exchanger samples with dimensions in the centimeter range can be measured. The fluid flow and heat transfer features of a micro pin fin wire structure made from copper by soft-soldering were experimentally characterized under steady-state forced air convection. The results are compared to performance characteristics of louvered fins. Heat transfer coefficients of the pin fins are twice as high as for the louvered fins. The relative expanded uncertainty of the Nusselt number is ±7%. Full article

The air-side thermal-hydraulic performance of multi-louvered aluminium fin heat exchangers is investigated. A systematic numerical study has been performed to analyze the air-sde thermal hydraulic characteristics over a wide range of Reynolds number i.e., from 30 to 500. Air-side heat transfer coefficient and pressure drop were calculated and validated over the mentioned band of Reynolds numbers. The critical Reynolds number was determined numerically; and also the variation of flow pattern along with the air-side heat transfer coefficient and pressure drop in a multi-louvered heat exchanger associated with $R{e}_{cri}$ has been reported. Moreover, a parametric study of the multi-louvered aluminium fin heat exchangers was also performed for 36 heat exchanger configurations with the louver angles (19–31°); fin pitches (1.0, 1.2, 1.4 mm) and flow depths (16, 20, 24 mm); and the geometric configuration exhibiting the highest air-side heat transfer coefficient was reported. The air-side heat transfer coefficient and pressure drop results for different geometrical configurations were presented in terms of Colburn j factor and Fanning friction factor f; as a function of Reynolds number based on louver pitch. Full article