High Values Of Heat Transfer Coefficient Research Articles

Flow and thermal transport of supercritical n-decane in square minichannel featuring uniformly spaced tetrakaidecahedron-shaped unit cells

In the current study, a novel cooling channel configuration featuring periodically placed tetrakaidecahedron (TKD) unit cells is proposed and studied computationally. The concept can also be realized through the additive manufacturing process to mitigate the heat transfer deterioration and improve the overall thermal performance of combustor cooling channels with n-decane as the working fuel. The conjugate thermal performance of the TKD channel was investigated and compared with the corresponding smooth channel at 3 MPa operating pressure. Simulations were conducted at a fixed coolant mass flow rate of 2 g/s, wall heat flux of 1.5 MW/m2, and an inlet temperature of 423.15 K. TKD channel provided lower overall wall temperatures and higher heat transfer coefficient values than the smooth channel. Furthermore, the thermal performance of both the smooth and TKD channels were analyzed under accelerated flight conditions by employing accelerations ac=2 g, 4 g, and 6 g in the streamwise direction. For the smooth channel, with increase in the acceleration values, the peak temperature values were reduced, and the location of peak value shifted towards the channel outlet. The thermal performance of TKD channel was, however, not significantly influenced by the accelerated states, which ensures enhanced cooling performance at different operating conditions.

RETRACTED:Numerical study of lozenge, triangular and rectangular arrangements of lithium-ion batteries in their thermal management in a cooled-air cooling system

This paper simulates a battery pack with 45 lithium-ion battery cells. As the coolant in the laminar flow range, the air fluid is responsible for cooling these cylindrical batteries. The battery cells are arranged in three different shapes, lozenge, rectangle and triangle. By changing the Re in the range of 500 to 2000, the temperature values of the battery cells and air, the drop in air pressure in the battery pack, as well as the heat transfer coefficient (HTC) between the battery cells and air have been studied for these three different models of battery cell arrangement. Investigations showed that increasing the Re decreases the maximum and average temperature of battery cells for all three models studied. However, the amount of pressure drop (∆Pa) has increased with increasing the Re for the three layout models. The triangular arrangement of the batteries together makes the maximum and average temperature of the battery cells lower than in other models, while the lozenge arrangement has the opposite effect. The triangular model had the highest ∆Pa and the lozenge arrangement had the lowest air ∆Pa in the battery pack. Triangular, rectangular and rhombic arrangement models have higher HTC values, respectively. Increasing the Re increases this coefficient but decreases the air temperature at the outlet (TOut). The rectangular model has the highest air TOut among the various models.

Modeling Approach of an Air-Based Battery Thermal Management System for an Electric Vehicle

The battery thermal management system is one of the important systems of an electric vehicle with direct effects on its performance. In this regard, this paper proposes a mathematical model that increases the accuracy of data obtained by numerical analysis of the temperature inside battery packs. The activity of the design and development (as accurate as possible) of a battery pack leads to an increase in the life of the battery cells and of the energetic efficiency of the electric vehicle in the specific operating conditions of road traffic. The research methodology of the thermal phenomenon in the battery pack, presented by the authors, is based on an efficient co-simulation concept consisting of steady-state CFD simulations and transient 1D simulations using a new mathematical model for the thermal behavior of a lithium-ion (Li-ion) cylindrical battery and applied in a battery pack’s forced air cooling thermal management system. Comparing the obtained results, it was found that the use of the model provides more accurate calculations of the local thermal performance of the air cooling system, with a direct influence on optimizing its design and construction. It is also highlighted that using the proposed model for higher heat transfer coefficient values (increase in air flow), offers more accurate data compared to other models, with immediate benefits in the proper design and development of the battery’s thermal management system.

Computational Investigation on Natural Convection Heat Transfer in Vertical Plate Fin Arrays

Objectives: To perform computational studies on different combinations of plate fin arrays of different shapes for studying their performance in natural convection heat transfer. To compare the heat transfer performance of uniform notched fins with hybrid notched fins and also performance of normal notched fins with inverted notched fins. Methods: SolidWorks Flow Simulation software is used for the present computational studies. Three types of vertical plate fin arrays viz. plain rectangular fin, rectangular fin with square notch and rectangular fin with semi-circular notch are used with their seven combinations. These fin array combinations are: plain rectangular, rectangular square notched, rectangular semi-circular notched, rectangular inverted square notched, rectangular inverted semi-circular notched, hybrid rectangular square-semi-circular notched and hybrid rectangular inverted square-semi-circular notched. Findings: The highest average heat transfer coefficient of 7.82 W/m2K is found to be for inverted hybrid square-semicircular notched fin array. This value of heat transfer coefficient is about 8% higher than compared to that with plain rectangular plate fin array (7.25 W/m2K) subjected to same operating conditions. Average heat transfer coefficients for inverted plate fin array combinations are high as compared with the non-inverted combinations. Also, hybrid plate fin arrays, whether inverted or not, show higher heat transfer coefficient values as compared with uniform notched fin arrays. Novelty : Seven types of plate fin array combinations are studied computationally. SolidWorks Flow Simulation software is used very effectively for this 3D CFD analysis. The behaviour of fluid i.e. air during natural convection flow is studied using air flow velocity trajectories. Surface contours are effectively used for studying variation in surface temperature and heat transfer coefficient at all locations of fin arrays. Keywords Natural convection, plate fin array, heat transfer coefficient, CFD, heat transfer enhancement

Heat transfer in breaded and non-breaded chicken nuggets baked in a pilot-scale radiant wall oven

A pilot-scale radiant wall oven (RWO) was used for baking chicken nuggets, some breaded with different coatings, and also non-breaded. Overall and radiant heat transfer coefficients were calculated at the surface of nuggets based on the experimental temperature and heat flux measurements. The baking temperatures ranged between 347 °C and 407 °C with different processing times. The non-breaded nuggets had higher heat flux and the radiant heat transfer coefficients, 46897 ± 429 W/m2 and 151.1 W/m2K, than the breaded nuggets. Among the breaded nuggets, the corn flour breaded nuggets had higher heat transfer coefficient values than those of chickpea breaded because the corn flour has greater absorptivity for infrared radiation than that of chickpea flour. A correlation was found between the temperature and heat flux for non-breaded and corn breaded chicken nuggets.

On influence of selected parameters on the spatial distribution of the heat transfer coefficient for an array of air jets

The paper deals with the reconstruction of the spatial distribution of the heat transfer coefficient (HTC). Jet impingement heat exchange is pursued by a hot air that flows through set of nozzles. High velocity gas is directed toward targeted surface and produces very high values of HTC. Due to limited operation range of a single jet an array of jets is analyzed. Retrieval of the heat transfer coefficient is pursued in two steps. The procedure starts with assuming of the functional form of temperature and heat flux at fluid–solid interface. Then the functional is parameterized. In second step the definition of the convective boundary condition is used to force the temporal invariability of HTC. The approximation coefficients are determined from a least square fit of the measured and computed temperatures. The study assesses the impact of the geometrical and flow parameters on the heat transfer coefficient produced by an array of jets.

Nanoparticle layer detachment and its influence on the heat transfer characteristics in saturated pool boiling of nanofluids

In nucleate pool boiling of nanofluid, nanoparticles suspended in liquid are deposited to form nanoparticle layer on the heated surface. As a result, surface properties are changed and the critical heat flux (CHF) is usually enhanced. However, since adhesion of the nanoparticle layer to the heated surface is not necessarily strong, partial detachment of the nanoparticle layer frequently occurs during nucleate boiling. In this study, peeling test was conducted for the nanoparticle layer formed during nucleate boiling of the water-based nanofluids to measure the adhesion force. The material of the heated surface was copper, and TiO2, Al2O3 and SiO2 were used as the nanoparticle material. It was found that the adhesion force is highly dependent on the nanoparticle material; it was greatest for SiO2 and weakest for TiO2 in the present experiments. Then, saturated pool boiling curves were obtained using the damaged heated surfaces after the peeling. For the nanoparticle-layer coated surfaces without peeling, the heat transfer coefficient (HTC) was lower and CHF was higher than those for the bare surface. It was shown that with an increase in the mass of the nanoparticles removed by peeling, the decrease of HTC and the increase of CHF were mitigated. Even higher HTC values and a lower CHF value than those for the bare heated surface were measured for significantly damaged surfaces.

Experimental and Numerical Study of the Flow Through Helical Passage Heat Exchanger Used for Solar Air Refrigeration System

Producing compact and high effective heat exchanger system is always a challenge. These heat exchanger systems can effectively be used in many application starting from cooling electrical circuits, absorbing and storing heat from say solar ducts/panels, etc. It has been seen that the heat transfer will be more for the turbulent flows or flows where mixing dominates with higher heat transfer coefficient values. In this paper, we have developed such a small concentric annulus heat exchanger having a helical flow passage. This compact heat exchanger is utilized to replace electric heat source supplied to the Electrolux refrigerator. The helical flow is produced by providing a helical rubber baffle between the two concentric annulus pipes. Presently only one helix is studied. The flow through helical passage concentric annulus heat exchanger is simulated for various Reynolds numbers. The pressure drop, local and average heat transfer coefficient is studied and presented here. Due to the helix, the flow is very complex as well as interesting. The mushroom-shaped temperature contours are observed. At the last, the simulated results are validated with experimental values and their matching is found good.

Numerical Studies on Heat Transfer over a Flat Plate with Triangular Rib-Groove Geometry at Laminar Flow Conditions

In this present study, periodically positioned triangular shaped ribs having a round top corner at the bottom with groove positioned on the top side of the plate is analyzed at laminar flow conditions. The numerical results obtained for the heated plate with rib-groove geometry are compared with that of the flat plate kept under similar conditions. At lower air flow velocity, the Nusselt number of the flat plate improved from 400 to 1407 with the provision of triangular ribs-groove arrangement in it. Similarly, it improved from 850 to 6420 at higher air flow velocity with triangular ribs-groove arrangement. Higher Nusselt number values leads to a higher heat transfer coefficient values. Therefore, the triangular ribs-groove geometry gives an enhanced rate of heat transfer with minimum pressure drop. The study shows that irrespective of geometry, the rate of heat transfer is relying on fluid (air in this present case) flow velocity over heated plate, fluid flow contact with the heated plate and surface area of the heated plate.

Gravity controlled condensation of an ethanol and water mixture on a horizontal tube.

The experimental results for gravity-controlled condensation of ethanol and water vapor mixtures on a horizontal tube are presented. Dropwise, drop and streak, and ring wise condensations are observed for the ranges of ethanol vapor mass fraction W<1∞&gt;=0.20.5, 0.50.7 and 0.750.8, respectively, while smooth-film condensation takes place for the ranges of W1∞=00.2 and W1∞=0.81. Previous theoritical results for the heat transfer coefficent by the present authors based on the two-phase boundary layer theory are valid for the case of smooth-film condensation, while 20 to 60% higher heat transfer coefficient values are obtained for the other cases.