Difference In Heat Transfer Rate Research Articles

A COMPREHENSIVE REVIEW STUDY ON HEAT TRANSFER IMPROVEMENT TECHNIQUES WITHIN TWISTED TUBES

Heat transfer equipment has been used in many different domestic and industrial applications. There has been a concentrated effort to create a heat exchanger design that will reduce energy requirements while saving materials and other costs. Increasing the effective heat transfer surface area or creating turbulence are two common ways to improve heat transfer and hence lower thermal resistance. The thermal Performance Factor is the ratio of the difference in heat transfer rate to the difference in friction factor and serves as a metric to assess the efficiency of heat transfer enhancement technologies. Different types of twisted tubes are used in many heat transfer improvement devices. geometrical parameters of the twisted tube encompassing the aspect ratio, twist ratio, twist direction, twist length, etc. impact the heat transfer. For Instance, oval pipes with unequal twist pitches have a thermal performance factor (1.75) and equal twist pitches have a thermal performance factor (1.98). furthermore, the thermal performance factor of the twisted tube with oval dimples is equal to 1.19 compared with the twisted tube without dimples. The thermal performance factor of the twisted tube with oval dimples is equal to 1.38 compared with the straight tube, with another improvement to the twisted tube that improves the heat transfer properties by disrupting the thermal boundary layer and destabilizing it. This paper presents a comprehensive investigation of passive heat transfer devices (twisted tubes) and their relative merits in a myriad of commercial applications.

Numerical study on the anisotropy in thermo-fluid behavior of triply periodic minimal surfaces (TPMS)

Porous structures are frequently utilized as thermal conductivity enhancers in the realm of heat transfer enhancement. Triply Periodic Minimal Surface (TPMS) has gained significant attention in recent years due to its favorable performance in many fields including mechanics and thermodynamic. The exceptionally large specific surface area grants it promising performance in heat transfer enhancement. However, the angular effect on thermal-fluid characteristics are not understood and requires further investigation. In this work, Gyroid and Diamond with various rotating angles used as sandwich cores were designed utilizing the implicit function method. Then, the discussions on thermal and hydraulic behaviors in the TPMS-based sandwich panels under an isothermal condition were systematically conducted by means of computational fluid dynamics. After that, the fluid flow mechanisms and heat transfer properties were visually investigated according to the comparative analysis of velocity fields, pressure drops, vortices inducing, and Nusselt number distribution. The results showed that the flow field characteristics and the heat transfer performance exhibited an apparent 45° symmetry in both Gyroid and Diamond. Moreover, the pressure gradient exhibited evident dependence on the rotating angle in both Gyroid and Diamond groups. The 45° rotated Gyroid structure case had the most extensive pressure gradient of 11.4 kPa/m; to the contrary, the 45° rotated Diamond structure had the smallest one of 9.9 kPa/m in their respective group. Nonetheless, the angular difference in heat transfer rate (HTR) is not significant, and the maximum total HTR in Gyroid and Diamond groups was 8.25 W and 9.43 W, respectively. Overall, this work contributes to a better understanding of the angular behavior of TPMS-based sandwich panels and provides valuable information for their potential applications in various industries.

흡수식 냉동기용 유하액막식 증발기의 전열관 형상이 열전달 성능에 미치는 영향

To understand the mechanism and obtain data that can be used for design, an experimental apparatus was constructed to investigate the heat transfer characteristics of a falling film evaporator for an absorption chiller. Evaporators with plain tubes or three enhanced tubes were prepared. The enhanced tubes were designed to improve surface wetting rate with surface protrusions or a floral pattern shape. The performance change of the evaporator was investigated according to the flow rate of chilled water, the inlet temperature of the chilled water, the liquid film Reynolds number, and the evaporation temperature. In the case of using the enhanced tube, the average heat transfer rate was approximately 16.3% higher than that of the plain tube, and the difference in heat transfer rate between the enhanced tubes was as small as approximately 6%. The Nusselt number of end-cross, end-dimple, and end-dimple floral tubes was higher by 13.1%, 26.5%, and 46.9%, respectively, than in the plain tube.

A novel optimum constructal fork-shaped fin array design for simultaneous heat and mass transfer application in a space-constrained situation

The present study deals with the design and analysis of an array of constructal fork-shaped fins adhered to a circular tube and operating under fully wet conditions. Fork-shaped fin arrays with two and three numbers of branches are considered in the current work. The mass transfer process is calculated by using a cubic relation between the humidity ratio of saturated air and the corresponding fin surface temperature. The governing equations are highly non-linear and hence they are solved by using a semi-analytical technique called Homotopy Perturbation method. The optimisation is done by maximising the net heat transfer rate of the fin array and un-finned surface and by imposing certain constraints. The constraints are taken such that the radial space limitations fin material limitations, as well as the minimum fin gap considerations, are taken into account. As the present problem involves a large number of design parameters as well as the interrelated constraints, a bio-inspired metaheuristic algorithm called the Firefly Algorithm has been employed for obtaining the optimum condition. The analysis has been performed for different operating conditions and the results have been compared with the corresponding rectangular fin array. From the study, it has been seen that the heat transfer rate from the optimum fork-shaped fin array with two branches is higher than that from the optimum rectangular fin array. However, in a few cases, it has been found that there is marginal difference in heat transfer rate between the optimum fork-shaped fin array with two branches and the rectangular fin array but the total length of each fin for the former case is found to be smaller and hence fork-shaped fin array with two branches would be a better selection than the rectangular fin array. However, increasing the number of branches of the fork-shaped fins from two to three does not provide any benefit in terms of either lower fin length or higher heat transfer rate.

A novel optimal constructal fork-shaped fin array design to ascertain thermo-heightened performance under dehumidifying conditions

The current work deals with the design and analysis of an array of constructal fork-shaped fins attached to a circular tube and operating under fully wet condition. For the mass transport process, a linear relation is adopted between the humidity ratio of saturated air and the corresponding fin surface temperature. After obtaining temperature distribution analytically, a metaheuristic optimization technique is adopted to maximize the net heat transfer rate of the fin array and un-finned surface imposing certain constraints. The constraints are taken such that the radial space limitations, fin material limitations as well minimum fin gap considerations are taken into account. As the present problem involves a large number of design parameters as well as the interrelated constraints, Particle Swarm Optimization technique has been employed for determining the optimum condition. The proposed theoretical analysis has been performed for different operating conditions and the results have been compared with the corresponding rectangular fin array. From the analysis, it has been found that optimum fork–shaped fin array with two branches gives higher heat transfer rate than the corresponding optimum rectangular fin array. For a typical situation (fin volume 0.0005 m3, air relative humidity 70%, ambient temperature 30 °C, base temperature 5 °C, convective heat transfer coefficient 20Wm-2 K−1, fin material thermal conductivity 236 Wm-1 K−1 and minimum gap between fins 0.002 m), optimum fork-shaped array with two branches gives 59.58% higher heat transfer rate than that of the optimum rectangular fin array. In certain cases, though the difference in heat transfer rate between optimum fork–shaped fin array with two branches and the corresponding optimum rectangular fin array is small, but the total fin length for the former case is found to be lower and thus fork shaped fin array with two branches is a better option than the rectangular fin array. However, no benefit in terms of either higher optimum heat transfer rate or lower total fin length is obtained by increasing the number of branches of the fork shaped fins beyond two.

Mixed convection in a lid-driven cavity containing triangular block with constant heat flux: Effect of location of block

The present work examines the two-dimensional, steady, laminar mixed convective fluid circulation and heat transfer in a square lid-driven cavity influenced by the change in the location of the triangular block with constant heat flux (CHF) thermal condition. The effect of the changes in the location of block along the vertical centerline (x=0.5,y) of the cavity has been explored. The dependence of various flow governing dimensionless parameters, such as, Reynolds number (Re=1−1000), Richardson number (Ri=0.01,1,10), blockage (B=0.1,0.2,0.3) and location (Ly=0.25,0.5,0.75) of triangular block on the streamline, temperature contours, Nusselt numbers, etc. has been illustrated. A normalized Nusselt number is also calculated for studying the difference in heat transfer rate with that of constant wall temperature condition. The results of the study indicates higher heat transfer rates for centered block position (Ly=0.5) than remaining two (Ly=0.25,0.75). For a given blockage, Nusselt number shows decline with increasing Ri. The summary of research is expressed by using two forms of empirical correlations (Nu¯=f(Ly,Re)),Nu¯=f(B,Re) for possible utilization in engineering design.

Infrared image monitoring of local anesthetic poisoning in rats

To evaluate the thermographic predictive value of local anesthetic poisoning in rats that indicates the early recognition of thermal signs of intoxication and enable the immediate start of advanced life support. Wistar rats underwent intraperitoneal injection of saline and ropivacaine; they were allocated into pairs, and experiments performed at baseline and experimental times. For thermography, central and peripheral compartment were analyzed, checking the maximum and average differences of temperatures between groups. Thermographic and clinical observations were performed for each experiment, and the times in which the signs of intoxication occurred were recorded. In the thermal analysis, the thermograms corresponding to the times of interest were sought and relevant data sheets extracted for statistical analysis. Basal and experimental: the display of the thermal images at times was possible. It was possible to calculate the heat transfer rate in all cases. At baseline it was possible to see the physiology of microcirculation, characterized by thermal distribution in the craniocaudal direction. It was possible to visualize the pathophysiological changes or thermal dysautonomias caused by intoxication before clinical signs occur, characterized by areas of hyper-radiation, translating Autonomic Nervous System pathophysiological disorders. In animals poisoned by ropivacaine, there was no statistically significant difference in heat transfer rate at the experimental time. The maximum temperature, medium temperature, and heat transfer rate were different from the statistical point of view between groups at the experimental time, thus confirming the systemic thermographic predictive value.

Infrared image monitoring of local anesthetic poisoning in rats

Background and objectivesTo evaluate the thermographic predictive value of local anesthetic poisoning in rats that indicates the early recognition of thermal signs of intoxication and enable the immediate start of advanced life support. MethodsWistar rats underwent intraperitoneal injection of saline and ropivacaine; they were allocated into pairs, and experiments performed at baseline and experimental times. For thermography, central and peripheral compartment were analyzed, checking the maximum and average differences of temperatures between groups. Thermographic and clinical observations were performed for each experiment, and the times in which the signs of intoxication occurred were recorded. In the thermal analysis, the thermograms corresponding to the times of interest were sought and relevant data sheets extracted for statistical analysis. ResultsBasal and experimental: the display of the thermal images at times was possible. It was possible to calculate the heat transfer rate in all cases. At baseline it was possible to see the physiology of microcirculation, characterized by thermal distribution in the craniocaudal direction. It was possible to visualize the pathophysiological changes or thermal dysautonomias caused by intoxication before clinical signs occur, characterized by areas of hyper-radiation, translating autonomic nervous system pathophysiological disorders. In animals poisoned by ropivacaine, there was no statistically significant difference in heat transfer rate at the experimental time. ConclusionsThe maximum temperature, medium temperature, and heat transfer rate were different from the statistical point of view between groups at the experimental time, thus confirming the systemic thermographic predictive value.

プレートフィン熱交換器内沸騰熱伝達に及ぼす加熱媒体の流動方向の影響に関する影響

Effects of flow directions of the heating medium on heat transfer performance of upward evaporating refrigerant flows in a plate-fin heat exchanger with single refrigerant channel were examined using R134a as the refrigerant. The refrigerant channel was sandwiched by two water channels. Hot water flew upward or downward to form a parallel or counter flow heat exchange. To understand the heat flux distribution the temperature distributions on the outside wall of the water channel were visualized by an IR camera. As the results, it was shown that the difference in heat transfer rate between the parallel and counter flow was a little because of the large temperature difference in heat transfer. The pressure loss of the refrigerant flow was larger for the parallel flow than the counter flow. It could be estimated from the wall temperature distribution that the increase in pressure loss might be caused by inhomogeneous phase distribution of refrigerant flow.

On the heat transferred to the air surrounding a semi-infinite inclined hot plate

AbstractAn asymptotic analysis of laminar free convection in a boundary layer over an isothermal semi-infinite flat plate inclined at some angle to the vertical has been performed. Existing analytical solutions show no difference in the heat-transfer rate between the upper and lower surfaces of the plate, contrary to observations. To investigate this, higher-order perturbations of the non-dimensional temperature, velocity and pressure across the boundary layer were computed and found to show only small variations from first-order perturbations previously reported. Unexpectedly, third-order perturbations of all functions were found to be identical to those of the vertical plate, indicating that differences in temperature between both sides of the plate are limited to exceedingly small terms of order ${x}^{- 9/ 4} $ or smaller, $x$ being the distance from the leading edge, non-dimensionalized by the buoyancy length scale. Dominant differences between heat-transfer rates on the upper and lower surfaces were therefore concluded to be due to near-leading-edge effects. In applying an integral form of the conservation equations to the near-leading-edge region, it was found that, up to terms of order unity in $x$, the total heat-exchange rate for the inclined plate is identical to that of the vertical plate, so that the heat-transfer gain on one side balances exactly the loss occurring on the other. This simplification allowed determination of an upper bound for differences in heat-transfer rates between the upper and lower sides, even though complete determination of the differences would require a numerical integration of the full Navier–Stokes equations near the leading edge of the plate.

Experimental study of buoyancy-driven flow in open-cell aluminium foam heat sinks

Air-saturated buoyancy-driven flow in a heat sink with open-cell aluminium foam as extended surface is studied. The experiments were performed in a carefully validated test rig. Influences of the pore density, the foam height and the bonding method are examined in this paper for Rayleigh numbers varying between 4000 and 6500, while maintaining the length-to-width ratio of the substrate on 10. The studied foams have a pore density of 10 and 20 PPI, both with a porosity of 93%. The height of the 10 PPI foam is varied between 6 and 40 mm and for 20 PPI between 6 and 18 mm. The bonding of the foam is done via brazing or by applying a single epoxy.A difference in heat transfer rate is observed between both bonding methods: the brazed samples are superior in all cases. The pore density, has a more pronounced influence. The strongest influence can be attributed to a variation in sample height. A correlation for the Nusselt number is derived, for the studied 10 and 20 PPI foam.

Biomimetic collagen scaffolds with anisotropic pore architecture

Sponge-like matrices with a specific three-dimensional structural design resembling the actual extracellular matrix of a particular tissue show significant potential for the regeneration and repair of a broad range of damaged anisotropic tissues. The manipulation of the structure of collagen scaffolds using a freeze-drying technique was explored in this work as an intrinsically biocompatible way of tailoring the inner architecture of the scaffold. The research focused on the influence of temperature gradients, imposed during the phase of crystallisation of collagen suspensions, upon the degree of anisotropy in the microstructures of the scaffolds produced. Moulding technology was employed to achieve differences in heat transfer rates during the freezing processes. For this purpose various moulds with different configurations were developed with a view to producing uniaxial and multi-directional temperature gradients across the sample during this process. Scanning electron microscopy analysis of different cross-sections (longitudinal and horizontal) of scaffolds revealed that highly aligned matrices with axially directed pore architectures were obtained where single unidirectional temperature gradients were induced. Altering the freezing conditions by the introduction of multiple temperature gradients allowed collagen scaffolds to be produced with complex pore orientations, and anisotropy in pore size and alignment.

Integrated fluid-thermal-structural numerical analysis for the quenching of metallic components

The quenching of a metal component with a channel section in a water tank is numerically simulated. Computational fluid dynamics (CFD) is used to model the multiphase flow and the heat transfer in film boiling, nucleate boiling and convective cooling processes to calculate the difference in heat transfer rate around the component and then combining with the thermal simulation and structure analysis of the component to study the effect of heat transfer rate on the distortion of the U-channel component. A model is also established to calculate the residual stress produced by quenching. The coupling fluid-thermal-structural simulation provides an insight into the deformation of the component and can be used to perform parameter analysis to reduce the distortion of the component.

Performance and optimization analysis of SRC profile fins subject to simultaneous heat and mass transfer

Fin material near the tip of a uniform cross sectional (UC) fin does not participate actively in transferring heat. This effect may seem to have progressed much with the increase in fin length. A uniform cross sectional fin with a step reduction in local cross section (SRC) not only increases the effective utilization of fin material near the tip but also it promotes the ease of fabrication. In this study, an effort has been devoted to determine analytically the overall fin performance of both longitudinal and pin fins of SRC profile under fully dry, partially wet and fully wet conditions. The effect of various design and psychometric parameters on the fin performance of SRC fins has been investigated and compared it is with the corresponding UC fin. A scheme for optimizing SRC fins has also been demonstrated in the present work. From the result, it can be highlighted that the optimum values of Biot number and aspect ratio of SRC fins increase with the increase in relative humidity for the same fin volume. In comparison with the UC fin for the identical fin volume, the SRC fin transfers more rate of heat and consequently, this difference in heat transfer rate increases slowly with the relative humidity.

Temperature Distribution in a Standard 1-Basket Water-Cascade Retort

Temperature distribution studies were carried out in a standard 1-basket horizontal retort (Barriquand Steriflow) operated on water spray heat transfer principle. Time-temperature data were gathered from 24 thermocouples (Type-T) located throughout the retort to measure medium temperature, and from 24 Lexan™ transducers, with centrally located thermocouple tips, placed either on the top, middle or bottom tray of the loading car. The retort was fully loaded with Lexan bricks and temperatures were recorded at fifteen second intervals for up to 35 minutes. Retort temperature data were analyzed for means and standard deviations in temperature at each recorded time (temperature stability), maximum temperature difference between test locations (temperature deviation) and means and standard deviation for each location (temperature uniformity) during the cook period (excluding come-up). The study indicated the maximum overall standard deviation in retort temperature during the cook period to be 0.71C° while the maximum temperature difference within the retort at any time was 3.5C°. The study indicated differences in heat transfer rates of bricks at different tray levels, but these differences did not contribute to large variations in process lethality.

Experimental Investigation of Multilayer Insulation With Room Temperature Outside and Liquid Helium Temperature Inside

Experiments on multilayer insulation were conducted with the conditions of room temperature outside and liquid helium temperature (4.2K) inside. By varying the total number of radiation shields, heat trans fer rate and transverse layer-by-layer temperature distribution were measured. Experimental data with liquid nitrogen (77K) were also ob tained and the difference in heat transfer rate between from room tempera ture to liquid helium temperature and from room temperature to liquid nitrogen temperature was demonstrated. Prior to the experiment, preliminary consideration was made as to the determination of each radiation shield temperature in multi-shield system. A single parameter A, which represents the conductive to radiative heat transfer ratio, was introduced, and it is shown that in the case of constant emissivity, the temperature distribution may be computed with the simple method introduced in this investigation. From the temperature distribution thus obtained, it is possible to calculate the total heat transfer rate and the radiative to total heat transfer ratio at each radiation shield with various boundary temperature conditions and the number of radiation shields.