Frontal Air Velocity Research Articles

Aerodynamic analysis and hygrothermal transfer characteristics of cellulose evaporative cooling pads: A case study applied to protected agriculture

Evaporative cooling pads are clean media for cost-effective temperature management. However, the spatially integrated microclimate resulting from heat and mass transfer in the evaporative cooling pad is an uncertain and nonlinear complexity. Therefore, this purpose of this study is to present an innovative prediction model with computational fluid dynamics and evaluate the operating scenarios and geometrical properties of wet pads from quantitative metrics such as saturation efficiency and pressure drop. The reliability of the established numerical model of wet pads was verified by wind tunnel experiments and existing experiments, which predicted the outlet conditions in satisfactory conformity. The results showed that a wet pad with 8 mm ripple height and 19.6 mm ripple distance exhibits the best prospective, with energy consumption and specific water consumption reduced by 45.28 % and 26.26 %, respectively. Meanwhile, the cross strategy of 45_45° corrugation obliquity reduces the pressure drop by 18.95 %, providing uniform supply air distributions. The heat exchange of the wet pad is mainly concentrated within the first 35 mm from the inlet section, while the mass exchange of the wet pad is concentrated within the first 60 mm. The range of frontal air velocity with 0.9–2.5 m/s is recommend for the evaporative cooling system.

An Experimental Investigation on the Performance Analysis of Two-Stage Desert Cooler

The present experimental investigation reports the performance of both the single and two stage direct evaporative cooling systems in composite climatic conditions of Patna, India. A two-stage direct evaporative cooling system has been designed and fabricated. The first stage of the two-stage cooling system utilizes a heat exchanger designed internally to sensibly cool hot and arid ambient air. The effect of varying the frontal air velocity (0.5–9 m/s) and different saline water concentration (5–10%) on the performance of two stage direct evaporative cooler is investigated. The maximum effectiveness of single and two-stage desert cooler is found to be 0.7 and 0.98 at frontal velocity of 2 m/s and 2.5 m/s, respectively. The performance of the two-stage cooler with tap water is found to be 40% higher than the single stage desert cooler. The effectiveness of single and two stage desert coolers with tap water is found to be in the range of 6–11% and 9.3–14% higher compared to the saline water at salt concentrations of 5–10%, respectively. Moreover, increasing salt concentration leads to reduced relative humidity at the cooler exit, with the two-stage cooler exhibiting 28.5% lower relative humidity than single-stage desert cooler.

Heat transfer in flat tube car radiator with CuO-MgO-TiO2 ternary hybrid nanofluid

An investigation of the performance of a car radiator with CuO-MgO-TiO2 aqueous ternary hybrid nanofluid has been presented to elucidate the effect of nanoparticle concentration, flow rate, and frontal air velocity. The volume concentration of nanoparticles ranges from 0.1% to 0.5%. The effect of fluid inlet temperature, the coolant flow rate and the frontal air velocity on a flat tube radiator were investigated. The effectiveness of the radiator increases with increasing volume concentration as well as coolant flow rate. The coolant side heat transfer coefficient of 0.5% hybrid nano-coolant was 46% higher than the base fluid. The overall heat transfer coefficient was 7.65% higher than the base fluid. The friction factor and the pumping power both decrease with increasing fluid inlet temperature. The pumping power required for nano-coolant is 1.71 times the base fluid. A correlation for the overall heat transfer coefficient is also presented.

Enhancement of air conditioning system using direct evaporative cooling: Experimental and theoretical investigation

Abstract Air conditioners (ACs) are more commonly used nowadays in residential and commercial buildings to achieve thermal comfort in the summer season. Due to the high outside temperature, condenser pressure was highest and ultimately resulted in high electricity consumption. One of the ways to reduce the energy consumption of AC systems and increase cooling capacity is by reducing air temperature entering the condenser by using the evaporative cooling principle. This article presents an experimental and theoretical investigation of improving the performance of the conventional air conditioning unit supported by a direct evaporative cooling system to increase the cooling capacity and reduce the consumption of power in hot and dry climates. A window-type AC unit was implemented in the experiment where the AC system is modulated to provide a wide range of various weather conditions. The results show that using evaporative cooling assist enhanced the system to overcome the many challenges by which the refrigeration capacity was increased in the range of 10–20%. Also, the results show a decrease in outlet temperature by 6–10°C, and the power consumption was reduced by about 3%. MATLAB program was used to analyze different data that were obtained. The input parameters for this program are the inlet conditions such as the weather conditions of the located city, namely the outdoor dry temperature and the outdoor relative humidity. The effectiveness and cooling capacity were calculated based on the frontal air velocity and the inlet air temperature. A comparison between the experimental and theoretical work showed a good agreement, as the relative difference is less than 9%.

Preheating Effects on Compression Ignition Engine Through Waste Heat Recovery Using THNF-Based Radiator Coolant: An Experimental Study

Abstract The present paper focuses on the thermohydraulic performance of a car radiator using Al2O3, CuO, and TiO2 nanoparticles disseminated in an equal fraction in the range of 0.06–0.12% called Ternary hybrid nanofluid (THNF), in water-based fluid, operated at coolant flowrate (CFR) range of 3–8 lpm and fan air velocity of 0.25–1.25 m/s). Moreover, a detailed accentuation has been given on the extensive nanofluid characterization mainly thermophysical properties and its stability, to justify nanofluid durability for the long run (scanning electron microscope, Zeta potential). Performance evaluation criteria (PEC) and friction factors were analyzed to evaluate the penalty in pressure drop for the heat transfer enhancement achieved. The experimental analysis revealed a maximum heat transfer enhancement in the coolant of 14.2% at CFR of 6lpm using 0.12% vol. fraction of THNF. The PEC value found within the limit of 1.0045–1.098 indicates a remarkable heat transfer enhancement on nanoparticle addition. Concurrently fuel elevated temperature improved thermal efficiency by 13.6% at 0.25 m/s of frontal air velocity during a maximum fuel-saving of 14.28% at 50% load on the engine. Hence, the preheating of fuel through the radiator waste heat improves the thermal efficiency, lowers the brake-specific fuel consumption, and saves fuel consumption successfully.

Experimental investigation of heat transfer and pressure drop of fin and tube heat exchanger under dry and wet conditions

The heat transfer and pressure drop characteristics of nine flat plate finned tube heat exchangers have been experimentally investigated under dry and wet conditions. The effect of five parameters is evaluated for wet conditions: number of tube row (2, 4, 6), fin pitch (2, 3, 4 mm), frontal air velocity (1, 2, 3 m/s), temperature (25, 30, 35 °C), and relative humidity (60, 70, 80). The Box-Behnken Design (BBD) is used to determine minimum candidate test points of the experimental studies, and more experiments have been carried out to determine the effects more sensitively. For nine heat exchangers, the effect of frontal air velocity (1, 2, 3 m/s) is evaluated for dry conditions. (The Reynolds number ranged from 300 to 2150 for both conditions.) Response Surface Model (RSM) has been used to evaluate the Colburn j factor and Fanning friction f factor for dry and wet conditions. The results show that the j factor decreases with increasing front air velocity and number of tube rows, while the j factor increases with increasing fin pitch, air temperature, and relative humidity for wet conditions. In addition, the f factor decreases with increasing front air velocity, number of tube rows and fin pitch, while the f factor increases with increasing air temperature and relative humidity. For dry conditions, the j factor decreases with increasing front air velocity and number of tube rows, while the j factor increases with increasing fin pitch. In addition, the f factor decreases with increasing front air velocity, number of tube rows, while the f factor increases with increasing fin pitch. The j factor and f factor values are higher under wet conditions than dry conditions.Three correlations are proposed for the j and f factors under dry and wet conditions. For wet conditions, the best mean deviation for the j factor is 8.3%, whereas the best mean deviation for the f factor is 10.9%. For dry conditions, the best mean deviation for the j factor is 8.3%, whereas the best mean deviation for the f factor is 8.2%. The experimental results are compared with the proposed and literature correlations.Compared to the correlations obtained in literature studies using similar geometric parameters in the study, the proposed correlation has gave better results. Even at the values of geometric parameters which literature correlations are failed, the proposed correlations has gave good results.

An experimental study of the air-side performance of a novel louver spiral fin-and-tube heat exchanger

We studied the effect of fin patterns on the air-side performance of a novel type of heat exchanger, namely louver spiral fin-and-tube heat exchangers (LSFTHXs). We investigated three types of fin patterns—radial, curved, and mixed-louver spiral fins—and compared their characteristics with plain spiral fin. We fabricated heat exchangers with a crimped aluminum fin base, two rows of steel tubes, and a fin pitch of 8.45 mm. All heat exchangers had both multipass parallel and counter cross-flow arrangements. The average heat transfer rate (Qave), heat transfer coefficient (ho), and pressure drop (ΔP) increased along with frontal air velocity. The louver-spiral fin provided greater Qave and ho than plain-spiral fin by about 9.7–15.6% and 13.4–27.1%, respectively. The j factors (Colburn factors) of louver-spiral fins were greater by approximately 10.4–13.1% (for mixed LSFTHX), 7.7–8.8% (for radial LSFTHX), and 2.1–5.1% (for curved LSFTHX) compared with the plain SFTHXs. Additionally, we found no significant difference in ΔP or f factor (friction factor) between louver-spiral and plain-spiral fins. LSFTHX configurations increased ho and j.

Numerical investigation of heat transfer and pressure drop characteristics in an offset strip fin heat exchanger

This paper presents a numerical simulation to determine the air-side heat transfer and the pressure drop characteristics of a flat tube heat exchanger with offset strip fin. The effects of the fin bending ratio such as 29%, 36%, 44%, 50%, and the fin spacing such as 2.10 mm, 2.35 mm, 2.60 mm on the performance of the heat exchanger are studied by using a commercial CFD software. The air having constant viscosity, thermal conductivity, and density enters the heat exchanger at 298 K and the wall temperature of the strip fins is considered as constant at 314 K. Variations of the heat transfer coefficient and the pressure drop in the airside are presented with respect to the frontal air velocity while Colburn j-factor and the friction factor f are presented with respect to the airside Reynolds number ranging from 200 to 1200. Finally, the thermal-hydraulic performance of all investigated cases is compared by using the volume goodness factor, j/f 1/3. The results show that the air-side heat transfer coefficient and the pressure drop increase when the frontal air velocity ascends. The air-side heat transfer coefficient decreases with the increase of fin spacing. The fin bending ratio does not have a significant effect on the pressure drop in the considered fin spacing. Both the Colburn j-factor and friction factor reduce with the increment of Reynolds number and fin spacing.

Design and performance optimization of microchannel condensers for electric vehicles

Conventional air conditioning systems for electric vehicle have insufficient performance. Therefore, the structures on both sides of microchannel condensers must be optimized to improve their thermal hydraulic performance and enhance the COP of the air-conditioning system in electric vehicles. Through numerical calculations and experiments, the thermal hydraulic performance of microchannel condensers were evaluated to determine the optimal values of the microchannels number, flat-tube hole aspect ratio, flow passes, and fin pitch. The results obtained using established numerical calculation models have certain reliability with errors within ±5.6%. The results reveal that the heat exchange performance of the microchannel condensers could be enhanced by appropriately reducing the fin pitch at certain frontal air velocities. Additionally, this causes a rapid increase in air flow resistance. When the flat-tube hole aspect ratio is 1.15 and the number of flat-tube channels is 10, the microchannel heat exchanger demonstrates optimum thermal hydraulic performance. Experimental results show that the heat exchange capacity of the three- and four-pass microchannel condenser are very close which is 36.5% greater than that of the two-pass microchannel condenser. Meanwhile, the three-pass condenser refrigerant flow resistance is 8.3% lower than that of the four-pass condenser. Therefore, the microchannel condenser with three passes demonstrates the best thermal hydraulic performance.

Energy-saving of air-cooling heat exchangers operating under wet conditions with the help of superhydrophobic coating

The condensate retention and bridging on the airside of the heat exchanger, such as the evaporator of the heat pump and air-conditioning system, can adversely increase the pressure drop penalty and energy consumption of the heat transfer systems. The objective of this study is to minimize the airside pressure drop of the rectangular plain heat exchangers using superhydrophobic coating which promotes continuous condensate shedding through coalescence induced droplet jumping. The experiments are carried out for different inlet air temperatures (23 °C and 27 °C), relative humidities (50%, 70%, and 90%) and the fin base temperature is fixed to be 7 °C. While the frontal air velocity is varied from 0.5 to 2.5 m/s, and the fin spacing ranges from 1 mm to 4 mm. The results showed that the heat transfer rate between untreated and superhydrophobic heat exchanger is almost similar; whereas a 30–55% increase in heat transfer is observed when inlet air temperature increased from 23 °C to 27 °C and an increase of 20–50% and 60–100% in heat transfer is noticed when relative humidity increased from 50% to 70% and 90%, respectively. Due to the effective condensate removal and the early arrival of steady state, the airside pressure drop for the superhydrophobic heat exchanger is almost two times lower than that of the untreated one. The reduction in airside pressure drop led to appreciable energy saving of the heat transfer system, and it is found that 30–60% saving can be achieved especially at higher relative humidities (70% or 90%) and frontal air velocities (more than 1 m/s).

Thermal-hydraulic experimental study of louvered fin-and-flat-tube heat exchanger under wet conditions with variation of inlet humidity ratio

An experimental study for air-side thermal-hydraulic performance of louvered fin-and-flat-tube heat exchanger under dehumidifying conditions has been performed. The louvered fin studied, used for an automotive evaporator, is geometrically defined by a flow depth of 47 mm, a high louver angle of 50° and a louver pitch of 1.1 mm. The test was conducted for frontal air velocity ranging from 1.1 to 4.5 m/s. The heat exchanger was tested first in dry condition, working as a heater. In wet conditions, the cooling coil was tested for three air inlet temperatures, Ta, and for various inlet relative humidity, RH, organized as follows: Ta = 30 °C (RH = 40 to 70%), Ta = 35 °C (RH = 30 to 60%), and Ta = 40 °C (RH = 20 to 60%); which correspond to a variation of the inlet humidity ratio from 9.2 to 27.7 gwater/kgdry-air. It was found that, for all inlet conditions, the wet friction factor is higher than that for dry surface (up to 43%). Concerning the heat transfer performance, at low Reynolds number, the sensible Colburn ‘j’ factor is insensitive to the surface conditions. However, as Re number increases, the sensible wet j factor decreases (up to 23%) compared to the dry one. This degradation is more and more pronounced as the inlet humidity ratio increases.

Thermo-hydraulic characteristics of radiator with various shape nanoparticle-based ternary hybrid nanofluid

Water-based ternary hybrid nanofluid with various shape nanoparticles, i.e., spherical (Al2O3), cylindrical (CNT), and platelet (Graphene) as a new radiator coolant has been investigated in the present analysis. Effect of thermo-hydraulic (pressure drop and heat transfer rate) performance along with exergetic analysis (irreversibility, entropy generation, exergy loss) on ternary hybrid nanofluid vol. concentrations, coolant flow rate, and frontal air velocity has been considered. Furthermore, the XRD and SEM morphology analysis have been conducted for 1% vol. fraction of ternary hybrid nanofluid. The comparative theoretical analysis revealed that the change in ternary hybrid concentrations play an important role in thermal performance due to its shape configuration and 18.45%, 6.3% increment in the heat transfer rate, the second law of efficiency respectively, are observed for 1%–3% vol. fractions range. The irreversibility of the system increases with the application of ternary hybrid nanofluid on coolant flow rate and frontal air velocity. However, a 42.45% increase in irreversibility is observed for a change in ternary hybrid concentrations within the range of 1%–3%. Change in entropy for air is higher compared to the coolant entropy change and results in an increment of 27.27% in entropy change for ternary hybrid nanofluid. Similarly, an increase in air velocity also has the least effect on fan power. Thus, the particle shape in ternary hybrid nanofluids has a significant impact, and its application is more effective in enhancing the thermo-hydraulic performance for an automotive cooling system.

Experimental study on the heat and mass transfer characteristics of air-water two-phase flow in an evaporative condenser with a horizontal elliptical tube bundle

In this paper, the heat and mass transfer performance of an evaporative condenser with a horizontal elliptical tube bundlewasexperimentally studied. The effects of important parameters, such as the spray density, frontal air velocity, ambient temperature and humidity, on the heat and mass transfer performance were discussed in detail. Among all parameters studied, it was found that the wet bulb temperature has greater effects on the heat transfer performance than the relative humidity. Thedifference between the steamtemperature and tube wall temperature, the inlet steam flow rate and the steam saturation temperature all affect the mean within-tube condensation heat transfer coefficient. Themeanwithin-tube condensation heat transfer coefficientincreases greatly when the latter two increase, while the increase in the difference between steam and tube wall temperature hinders the mean within-tube condensation heat transfer coefficient. The empirical correlations of the mean within-tube condensation heat transfer coefficient, wall-film convective heat transfer coefficient and the film-air convective mass transfer coefficient were finally obtained by regression fitting the experimental data using the least square method and all empirical correlations have enough precision in engineering calculation.

Combined evaporative air cooler and refrigeration unit for water purification and performance enhancement of air cooling system

Experimental and theoretical studies of hybrid system combined an evaporative air cooler and refrigeration unit are presented. The aim of the current study is to enhance performance of the evaporative air cooler and reduce moisture content in the outlet air as well as to produce fresh water. Heat and mass transfer for wetted pad in the air cooler and the evaporator of the refrigeration unit are formulated and simulated under Basra climate conditions in (May, June, July, and August). Different controlling parameters like (inlet temperature, relative humidity, evaporator coil temperature, frontal air velocity and thickness of the wetted pad are studied). The evaporative air cooler used in the experimental rig. was of (2061) cfm volumetric flow rate with dimension (0.72m, 0.72m, 0.85m). It has a selector of two air velocities (low and high) the minimum and maximum frontal air velocities are (0.5 m/s - 4 m/s) respectively. The refrigeration unit consist of a Compressor of 1/3hp capacity (AC 220 volts, R134a refrigerant). The evaporator coil has one row, 18 tube of 24.5 cm length, and outside diameter of 0.9 cm. The experimental results show a decrease in outlet temperature by (1-3 ) and the fresh water production increases with increasing, humidity ratio, relative humidity, and decreasing of the coil temperature. A comparison between the experimental and theoretical work shows a good agreement[

Airside thermal-hydraulic characteristics for tube bank heat exchangers used to cool compressor bleed air in an aero engine

A numerical study has been carried out to investigate the airside heat transfer and pressure drop characteristics of bare tube bank and plain finned tube heat exchangers used to cool the compressor bleed air in an aero turbine engine. The exchangers use small diameter tubes (3.0 mm) with compact staggered tube layout and operate in high temperature circumstances with large temperature differences. Calculations are performed using the Realizable k-ɛ turbulence model with consideration of the air property variations caused by the air temperature and pressure changes. Calculations are implemented for 5–20 m/s frontal air velocities, 561–690 K and 0.5–1.0 MPa frontal air temperatures and pressures, which correspond to 15–30 compressor compression ratios, and 298 and 350 K tube wall temperatures. The airside thermal-hydraulic performance is evaluated using the heat transfer coefficient and pressure drop as well as their dimensionless forms - j and f factors. The results suggest that the heat transfer coefficient and pressure drop are strongly affected by the frontal air state whereas the j and f factors are less dependent on it. The effect of air property variability on j factor is limited while that on f factor is more notable.

An experimental, computational and flow visualization study on the air-side thermal and hydraulic performance of louvered fin and round tube heat exchangers

The aim of this study is to determine heat transfer and pressure drop characteristics in different louvered fin geometries for manufacturing of commercial louvered fin and round tube heat exchangers. Numerical simulations were carried out for various louver angles, louver lengths (pitches), fin pitches and frontal air velocities. The heat transfer and pressure drop characteristics of the louvered fin and round tube heat exchangers, Colburn and friction factors, were respectively normalized with Colburn and friction factors of the flat plate fin and round tube heat exchangers operating under the same conditions and they were presented as the relative Colburn factor j∗ and the relative friction factor f∗. Thermal & hydraulic performance was presented as JF∗. Temperature and local Nusselt number contours, and streamline patterns were provided to reveal the mechanisms behind the heat transfer enhancement. Among different heat exchangers for which heat transfer and pressure drop characteristics were obtained, one was chosen to manufacture a real size heat exchanger. Flow visualization studies were also conducted with a PIV system in an open water channel to determine whether the flow structure is louvered directed or not. The louvered fin heat exchanger tested in the PIV system was a five times scaled up model of the real size louvered fin heat exchanger and made from a transparent plexiglas material. PIV results were presented and evaluated based on streamlines and velocity vectors. Furthermore, a numerical analysis was performed using exactly the same dimensions and conditions of the model tested in the PIV system. The comparison between numerical and experimental results was done to validate the numerical model. Consequently, the performance of the fabricated real size heat exchanger was tested at different air velocities in a wind tunnel in a conditioned room. The experimental results were compared with numerical analyses and found to be compatible with each other. Finally, thermal and hydraulic performance of the louvered fin and round tube heat exchanger was compared with a wavy fin and round tube heat exchanger with identical size and specifications. It was found that the thermal and hydraulic performance of the louvered fin and round tube heat exchanger is higher than that of the wavy fin and round tube heat exchanger. The Colburn factor j, friction factor f and JF of the louvered fin and round tube heat exchanger are higher about 16.8–7%, 19.9–8.2% and 10–4.3% than that of the wavy fin and round tube heat exchanger depending on the Reynolds number, respectively.

Performance improvements evaluation of an automobile air conditioning system using CO2-propane mixture as a refrigerant

The main purpose of this work is to enhance the energy efficiency of CO2 automobile air conditioning system. Theoretical analysis demonstrated that the mixture of CO2 and propane can improve its performance, thus, experiments have been carried out to see effects of various CO2-propane mass fractions of 100/0, 90/10, 80/20, 70/30, 60/40, 50/50 on the system performance at different ambient temperatures and gas cooler frontal air velocities. Experimental results show similar trends with those from the theoretical results. It has been shown that under the same compressor speed, system COP reaches highest at 60% of CO2 mass fraction, which is 29.4% higher than pure CO2 system and even achieves equal level of the R134a system, the optimum pressure and discharge temperature are reduced up to a maximum of 40% and 47 °C during the research range. Furthermore, comparison was carried out under the same cooling capacity by adjusting compressor speed for different mass fraction of CO2, results demonstrate that the use of CO2-propane mixtures yields a maximum COP rise of 22%even when cooling capacity is kept constant. A new optimum high pressure control algorithm for the transcritical CO2-propane mixture cycle has been developed based on the experimental data within a deviation of 5%.

Airside heat transfer and pressure loss characteristics of bare and finned tube heat exchangers used for aero engine cooling considering variable air properties

Numerical studies have been conducted to investigate the airside thermal-hydraulic characteristics of bare tube bank and plain finned tube heat exchangers intended for use in aero-engine cooling. The exchangers use small diameter tubes (3.0mm) with compact tube layout and operate at high temperatures with large temperature changes over the exchanger depth. Calculations are performed for frontal air velocities between 5 and 20m/s, yielding tube diameter based Reynolds numbers from 4898 to 19,592. Calculations are implemented using the Realizable k-ɛ turbulence model with consideration of the air physical property variations caused by the air temperature changes. The results show that ignorance of the air property variability leads to overestimations of both heat transfer and pressure loss, with a smaller air velocity yielding a more serious overestimation. The numerical fin efficiency agrees with the Schmidt fin efficiency within 7.0%. The plain finned tube heat exchanger is superior to the bare tube bank heat exchanger if the exchanger performance is evaluated using the heat transfer rate to pressure drop ratio.

INVESTIGATION ON HEAT TRANSFER ENHANCEMENT IN A CORRUGATED FIN-AND-TUBE COMPACT HEAT EXCHANGER

Heat transfer augmentation and pressure loss penalty in the fin-and-tube compact heat exchangers (FTCHEs) with the corrugated shape as a special form of the fin are numerically investigated to improve heat transfer performance criteria in low Reynolds numbers. The corrugated fin as the newly design of fin pattern is presented in this study. The influence of applying corrugated design adjustments on the thermal and hydraulic characteristics of air flow are analyzed on the in-line tube arrangements. The performance of air-side heat transfer and fluid flow is investigated by numerical simulation for Reynolds number ranging from Re = 400 to 800 based on the tube collar diameter, with the corresponding frontal air velocity ranging from 0.35 to 0.72 m/s. The outcomes of simulation revealed that the corrugated fin could significantly improve the heat transfer augmentation of the FTCHEs with a moderate pressure loss penalty. The computational results indicated that some eddies were developed behind the fluted domain of corrugated finwhich produce some disruptions to fluid flow and enhance heat transfer compared with plain fin. The corrugated form of fins could enhance the thermal mixing of the fluid, delay the boundary layer separation, and reduce the size of the wake and the recirculation region behind tubes compared with the conventional form of the fin at the range of Reynolds number used in this study. In addition, the results showed that the average Nusselt number for the FTCHE with corrugated fin increased by 7.05–10.0% over the baseline case and the corresponding pressure loss decreased by 5.0–6.2%.

Cooling Performance Characteristics of the Stack Thermal Management System for Fuel Cell Electric Vehicles under Actual Driving Conditions

The cooling performance of the stack radiator of a fuel cell electric vehicle was evaluated under various actual road driving conditions, such as highway and uphill travel. The thermal stability was then optimized, thereby ensuring stable operation of the stack thermal management system. The coolant inlet temperature of the radiator in the highway mode was lower than that associated with the uphill mode because the corresponding frontal air velocity was higher than obtained in the uphill mode. In both the highway and uphill modes, the coolant temperatures of the radiator, operated under actual road driving conditions, were lower than the allowable limit (80 °C); this is the maximum temperature at which stable operation of the stack thermal management system of the fuel cell electric vehicle could be maintained. Furthermore, under actual road driving conditions in uphill mode, the initial temperature difference (ITD) between the coolant temperature and air temperature of the system was higher than that associated with the highway mode; this higher ITD occurred even though the thermal load of the system in uphill mode was greater than that corresponding to the highway mode. Since the coolant inlet temperature is expected to exceed the allowable limit (80 °C) in uphill mode under higher ambient temperature with air conditioning system operation, the FEM design layout should be modified to improve the heat capacity. In addition, the overall volume of the stack cooling radiator is 52.2% higher than that of the present model and the coolant inlet temperature of the improved radiator is 22.7% lower than that of the present model.