Heat Transfer Distribution Research Articles

Heat Transfer Characteristics of a Quiescent Fluid over a Moving Flat Surface

Optimizing thermal control methods and enhancing the efficiency of various engineering processes, such as the cooling of hot moving surfaces, is imperative. Therefore, it is crucial to investigate heat transfer and temperature distributions across moving surfaces in stationary fluids. In this study, the combined effects of viscous dissipation, temperature-dependent viscosity, and a moving surface in a quiescent fluid on the temperature and velocity profiles are investigated. A two-dimensional steady laminar boundary layer flow of an incompressible Newtonian fluid, driven by the movement of the surface where viscosity is an inverse function of temperature, is analyzed. The effects of flow parameters, including Reynolds number, Eckert number, Prandtl number, variable viscosity, and surface velocity on temperature and velocity profiles, are determined. The governing boundary layer partial differential equations are transformed into non-dimensional form and solved using the central finite difference numerical method, implemented in MATLAB software. The numerical results demonstrate that an increase in the Reynolds number and the variable viscosity parameter leads to an increase in the velocity profiles. Additionally, an increase in Reynolds number, Prandtl number, variable viscosity, and surface velocity leads to a decrease in temperature profiles. Finally, an increase in the Eckert number results in higher temperature profiles. Therefore, with suitable flow parameters, the temperature of the fluid can be regulated. These findings are useful in cooling hot sheets or metallic plates drawn over a quiescent fluid to obtain high-quality final products.

COOLING INJECTION EFFECT ON THE SUCTION SIDE NEAR-TIP REGION OF TURBINE BLADE WITH HIGH-SPEED RELATIVE CASING MOTION

Abstract The high-speed relative casing motion between the casing and the turbine blade tip introduces significant complexities to the flow field near the tip, resulting in alterations to the heat transfer distribution on the suction surface of the blade near the tip, and further influence the arrangement of film cooling arrangements. However, due to the challenges associated with measuring heat transfer, the influence of cooling injection on the near-tip region of the suction side under high-speed relative casing motion still remains uncertain. This study aims to address this knowledge gap by conducting experiments on a high-speed disk rotor experimental rig. The heat transfer coefficient and cooling effectiveness are investigated for different cooling hole arrangements. Additionally, based on Computational Fluid Dynamic (CFD) method, the interaction mechanism of cooling injections under high-speed relative casing movement is comprehensively discussed. It is observed that the cooling effect, which would be effective under stationary conditions, is greatly diminished or even rendered ineffective when subjected to high-speed relative casing conditions. Furthermore, arranging the cooling holes at the location where the interaction between the Over-Tip-Leakage flow and the passage flow occurs would be an effective approach to enhance the cooling performance on blade near-tip suction side. The effect of different relative casing speed on suction side near-tip region cooling injection performances are also numerically investigated. These findings contribute to a better understanding of the considerations involved in the film cooling design of turbine blades.

Analytical and numerical analysis of heat transfer and temperature distribution in laser sintering method

Analytical and numerical analysis of heat transfer and temperature distribution in laser sintering method

Theoretical investigation of new composite based on metamaterial able to strongly attenuate heat and noise propagation for civil engineering

New design in civil engineering need reduction of cost of material. Engineers and researcher are focused on material parameter to improve proposed alternatives. In this work we are developed theoretical tool based on finite element method to evaluate transmission noise and heat transfer along composite wall for civil engineering. In this work, composite based metamaterial is used for wall elaboration. At first Time noise level in broad band high frequency level was extracted using frequency acoustic finite element method, and using advection, diffusion model heat transfer distribution was also extracted. Finally, combination of constitutive model with metaheuristic optimization enabled us optimal parameters of the material composite, for specific condition. Constitutive resulted and discussion will have detailed in the paper. Keywords: frequency acoustic analysis, advection diffusion, genetic algorithm, civil engineering, material science, metamaterial

RANS predictions of turbulent non-isothermal viscoplastic fluid in pipe with sudden expansion

A transition of Newtonian turbulent fluid to viscoplastic non-Newtonian fluid by cooling in a pipe with a sudden expansion is numerically studied. A recirculation region with negative velocities appears for fluid velocity profiles corresponding to the zone of flow recirculation. A small corner eddy disappears for a non-Newtonian fluid. Significant anisotropy between axial and radial components of Reynolds stresses is numerically shown. The heat transfer distributions along the pipe surface for turbulent non- and Newtonian fluids are qualitatively similar. The peak of heat transfer is shifted upstream in the Schwedoff-Bingham fluid in comparison with the Newtonian one. Authors’ numerical predictions are compared with numerical simulations by other authors for turbulent Schwedoff-Bingham fluids.

Heat Transfer Through a Heated Rod Placed in Different Arrangements

Abstract The present work experimentally analyses the surface heat transfer from a thermally active copper rod of circular cross-section placed in different arrangement of dummy rods. All the rods are arranged in cross-flow. Wind-tunnel experiments for nine different arrangements of heated rod at a Reynold’s number of 12600 were investigated. Temperature variation, heat transfer and vertical velocity distribution downstream of the cylinder were studied. Higher heat transfer rate was obtained when the heated rod was placed in downstream position due to the rubbing action of vortex shedding phenomena of upstream rod. Maximum heat transfer rate was reported in tandem arrangement of rod with the thermally active cylinder placed in the downstream row. The wall effect becomes dominant near the wall region and affects the flow and heat transfer in the vicinity of wall. Pressure and logarithmic value of temperature has been reported at suitable positions to explain the thermofluid physics.

Thermal performance of teardrop pin fins and zig zag ribs in a wedge channel

Abstract Aviation, marine propulsion, and power generation employ gas turbine engines extensively. The combustion process’s high temperatures make gas turbine engine development difficult. For safe turbine blade operation, internal cooling is essential. Ribs, pin-fins, and impinging jets are just examples of the several different types of structures that are typically included in internal cooling systems. The present study investigates the effect of rib placed in between the pin fins in a wedge channel. Nine rib configurations along with base line model without ribs are employed in this study. The SST k-omega turbulence model was employed to simulate the flow field and heat transfer of each case using the commercial software ANSYS Fluent. The investigation demonstrated that the heat transfer distribution and flow field in pin-fin arrays were substantially influenced by the ribs-induced secondary flows, particularly in the spanwise direction, which resulted in a significant heat transfer variation. In comparison to other configurations, the 4H4L rib configuration exhibits the highest thermal performance factor, surpassing the baseline by approximately 16.6 %.

Thermal behavior of coated powder during directed energy deposition (DED)

In powder-based additive manufacturing (AM), the quality of the feedstock material is critical for obtaining enhanced mechanical properties. Recently, the application of coated powders during directed energy deposition (DED) has been prompted by the goal of fabricating composite and functional materials in-situ. The complex temperature and momentum fields established during DED render direct experimental characterization of coated powder behavior challenging. To address this challenge, this study reports on the thermal behavior of coated powders during interactions with the molten pool by constructing three-dimensional heat transfer and phase distribution models using the finite elements method (FEM). Transient temperature and phase distributions were calculated for coated and uncoated stainless steel 316L and ZnAl powders under various particle size, coating thickness, molten pool temperature, and coating material conditions. Particle residence time values were extracted from the calculations, defined as time spent by the particle before a phase change. The results show large variations in particle residence time (85 μs to 2670 μs for stainless steel 316L particles, and 48 μs to infinity for ZnAl particles) as a function of the variables considered, especially the thermal diffusivity of the coating materials, thereby highlighting the potential value of coatings as an additional design parameter in DED. Significant increases in particle residence time for both stainless steel 316L and ZnAl particles were found when contact angle increases from 0° (submergence regime) to 180° (floating regime).

Numerical study of film cooling at the outlet of gas turbine exhaust

Abstract In order to mitigate the potential operational damage risk caused by traditional cooling methods in engineering applications of heavy-duty gas turbine component testing, the film cooling unit and realizable K-epsilon turbulence model were employed. Numerical simulations were conducted for multiple exhaust film holes with varying curvature and pitch-row under different operating conditions. The heat transfer distribution along the flow direction and radial direction of the high temperature wall was analyzed, as well as the influence of heat transfer under different geometrical parameters. The results indicate that for the integrated configuration of large-diameter cooling units, a blowing ratio of 0.3 yields the most comprehensive cooling effect, primarily due to the extensive spatial coverage by the gas film and the weakening of eddy dissipation mechanisms. Additionally, it was observed that with an increase in hole distance ratio for multiple exhaust film holes, cold air could more stably participate in heat exchange with high-temperature flue gas wake at the outlet of the gas film hole; thus, a hole distance ratio of 3.0 provides optimal comprehensive cooling effects.

Experimental and numerical studies of detailed heat transfer and flow characteristics in the rib turbulated annulus of a double pipe heat exchanger

An enhancement in the overall heat transfer between the fluids in a Double pipe heat exchanger (DPHE) can be achieved through various active or passive techniques. The present study focuses on the passive heat transfer enhancement in the annular region of a DPHE by incorporating circular ribs on the outer surface of the inner pipe. The primary objective is to investigate the influence of the ribs on the local distribution of heat transfer and fluid flow in the annulus of the heat exchanger. The local Nusselt number (Nu) distribution was determined experimentally using a test section specially designed with a provision to measure the wall temperature distribution of the inner pipe with an IR thermal imaging camera. The pressure drop across the channels with the ribs was also measured in the experimental studies. Numerical studies are employed to gain insights into the flow characteristics in the annular region in the presence of ribs. Studies comprise various rib diameters (e/Dh = 0.08, 0.14), rib-to-rib pitches (P/e = 6, 12, 18), and Reynolds number values (Re = 5000, 7500, and 10000). The heat transfer behaviour from the experimental study is discussed based on the flow mechanism observed using numerical techniques. The flow separation and reattachment due to the rib and the induced recirculation zone cause large variations in the Nusselt number distribution between the ribs. The peak Nusselt number value between adjacent ribs is observed at the location of reattachment of the flow to the ribbed wall. Acquired data also shows that the flow and heat transfer characteristics differ significantly with changes in the P/e ratio. The rib configuration with e/Dh = 0.14 and P/e = 12 is identified as optimal, achieving a balanced improvement in heat transfer while showing a relatively lower pressure drop.

Estimation of Surface Temperature and Heat Flux over a Hollow Cylinder and Slab using an Inverse Heat Conduction Approach

A non-iterative approximation of the inverse heat conduction problem has been developed through energy balance between the control volumes. The heat flow domain along the surface normal was divided into three control volumes and studied in three cases, specifically on a heated hollow metallic cylinder cooled in crossflow of air, a heating flat plate in still air, and a heated flat plate when cooled in still air with random air blows. The time derivatives of temperature and heat flux estimates at the surface appearing in derived equations were evaluated by approximate expressions. Both estimates were obtained from the derived equations by simultaneous measurement of temperature-time histories at two locations: one at the inner surface and the other anywhere within the control volume along the surface normal. The deviation was checked by real-time simultaneous measurement of temperature-time history at the outer surface along the normal surface. Comparison between the estimated surface temperature-time history using the derived equations and the real-time measurement showed deviations within 0.5 % for the cylinder, within 0.03 % for the plate in still air and within 0.5 % when air blows were given. Heat fluxes estimated using these time histories were correspondingly arrived at consistent and close approximations for all cases. Estimates from the derived equations were compared with reported equations from the literature, and a wind tunnel experiment for the validation of circumferential distribution of heat transfer was conducted, for which they also showed reasonably good agreements.

Transition of the flow type in the supersonic cavity controlled by the wall temperature

The wall temperature of the high-speed aircraft increases quickly under hypersonic/supersonic incoming flow, which will cause a significant change in the flow structure. To study the transition of the flow type in the supersonic cavity controlled by the wall temperature, numerical simulations are conducted. The cavity length-to-depth ratio (L/D) is varied from 10 to 15, and the wall temperature ranges from 300 K to 1300 K. The results indicate that the type of cavity flow with an L/D ratio of 13 transforms from a closed cavity flow to a transitional cavity flow, when the temperature reaches approximately 775 K. And the transitional temperature rises with the elevated total temperature of the incoming flow. Furthermore, the mechanism of the cavity flow change with wall temperature could be the competition between the recirculation zone and the shear layer in the cavity. The rising pressure with higher wall temperature in the recirculation zone weakens the downward development of the cavity shear layer, preventing it from hitting the cavity floor. As a result, the mass exchange of cavity lip surface, pressure distribution, total pressure recovery coefficient, and heat transfer distribution in the supersonic cavity change dramatically. The critical wall temperature also affected by the sidewall effects and the inflow Mach number.

Investigation on the Flow and Heat Transfer Characteristics in a Multi-Pass Channel Using Magnetic Resonance Velocimetry and Transient Thermochromic Liquid Crystal

Abstract The three-dimensional flow field in multi-pass channels with and without ribs was measured by magnetic resonance velocimetry (MRV), while heat transfer performance on the endwall of channels in the same geometry was investigated using transient thermochromic liquid crystal (TLC) technique. The evolution of comprehensive three-dimensional flow field and their correlation with local heat transfer enhancement on end wall of multi-pass channels with and without ribs were revealed as a whole picture. Results show that the flow characteristics in the right-angle bend as well as the second pass are dramatically different for the smooth and ribbed channels, resulting in totally different features of heat transfer distribution on the end wall in those two channels. For the smooth channel, strong dean vortices form around the bend region near the outer wall where heat transfer is enhanced substantially. For the ribbed channel, no dean vortex but complex three-dimensional flow presents around bends. Heat transfer downstream of ribs close to the reattachment regions is strengthened noticeably. Comparison between velocity and heat transfer results suggest that one of the principle mechanisms driving heat transfer enhancement is both endwall directed velocity for smooth and ribbed channels, even though they are induced by different flow structures.

Research on heat transfer and flow distribution of parallel-configured microchannel heat sinks for arrayed chip heat dissipation

The heat dissipation ability and compact structure of microchannel flow boiling show great promise for high-efficiency heat dissipation in the field of chip cooling. In arrayed chip cooling scenarios, multiple microchannel heat sinks are typically arranged in parallel. Random fluctuations in the heat load of each chip can lead to non-uniform flow distribution and even thermal failure of the chip. However, there are still limited studies on the non-uniform flow distribution in the parallel use of multiple microchannel heat sinks. This study presents an experimental and theoretical study on the boiling heat transfer and flow distribution characteristics of two heat sinks in parallel using HFE-7100. The steady-state test results indicated that the flow distribution characteristics in parallel-configured heat sinks were closely correlated with the flow pattern. In the single-phase region, flow distribution in both heat sinks was primarily influenced by the physical properties of the fluid. The effect of heat flux on non-uniform flow distribution was within 7 %. When one of the heat sinks entered the two-phase region, microchannel resistance characteristics changed significantly, leading to a dramatic increase in non-uniform flow distribution, up to 26.0 %. The critical heat flux (CHF) was triggered prematurely, with a decrease of up to 31.4 %. In dynamic characteristics testing, when both heat sinks were in the two-phase region simultaneously, the increase in heat flux led to greater non-uniformity in the flow distribution of the parallel-configured heat sinks compared to the single-phase region. Furthermore, considering the transition boundary of two-phase flow patterns in microchannels, a prediction model for flow distribution in parallel-configured microchannel heat sinks was proposed, demonstrating good predictive capability. The research provides a reference for the design and optimization of two-phase cooling systems for arrayed chip configurations.

Modeling of multi-phase flow in plasma transferred arc cladding of NiCrBSi/WC metal matrix composite

In this paper, a 3D multiphase flow model has been established for the plasma transferred arc (PTA) cladding of composite powder (NiCrBSi/50 wt% WC) on a 40CrNi2MoA substrate. The multiphase flow model simulates both the discrete phase (WC particles) and continuous phase in the melt pool, including the behaviors of heat transfer and particle distribution. The buoyancy, arc pressure, surface tension, and electromagnetic force are calculated. The model is then used to predict the influences of welding currents and preheating temperatures on the depth of heat-affected zone (HAZ), the temperature field, and the dimensions of the cladding layers. To validate this model, the dimensions and the HAZ depth are analyzed and compared to experimental data. The results show that the dimensions and HAZ depth obtained by the model simulation are in good agreement with the experiment. The HAZ depth, the melt pool length, and the dimensions of cladding layer would increase with the increasing welding current or preheating temperature. Driven by the inward convection in the melt pool, WC particles tend to distribute around the center line of cladding layers. This is the first work of modeling 3D multiphase flow in PTA cladding process of particle-reinforced metal matrix composite (MMCs). The work can provide theoretical guidance for adjusting process parameters to control HAZ depth and cladding quality in actual production.

An Experimental Investigation Of Local Thermo-Fluidic Heat Transfer In A U-Shaped Mini-Channel Sink

This study investigates experimentally a heated U-shaped mini-channel heat sink using Infrared Thermography and Particle Image Velocimetry for a water coolant flow of Reynolds numbers of 280, 650, and 1350 (based on the hydraulic channel diameter). The choice of this cell geometry is based on its role as a simplified unit of a serpentine heat exchanger, which is proved to be one of the most promising for cooling processes. The use of the infrared camera allows the detection of temperature fields on top of the external surface of the cell. Therefore, aiming to derive the temperature distribution on the channel roof, a dedicated transfer function is implemented. Moreover, we employed the lumped capacitance model for thermal analysis on both infrared measurements and thermocouple data. The latter are recorded to capture the cooling process of the aluminium base and water temperature at the end of the outlet tube. As a result, thermal transient rate, cooling magnitude and equilibrium temperature are obtained. These parameters indicate that higher Reynolds numbers correspond to increased thermal transient rates, enhanced cooling effects, and lower equilibrium temperatures. A non-uniform distribution of heat transfer along the channel is reported, with the most efficient cooling area localized close to the first 90-degree corner. These findings are consistent with numerical simulations and previous experimental observations. PIV results reveal the presence of two fluid acceleration zones following both 90-degree corners, which contribute to improve the water cooling ability in their respective regions. Additionally, the formation of two recirculating bubbles is reported at the inner wall from corners vertices, whose intensity is dependent on Reynolds number, pushing the main flow towards the outer channel wall and reducing the local heat transfer. Turbulent kinetic energy distributions are also investigated, pointing out the presence of intense areas that better match with regions of minimum equilibrium temperature than maximum velocity zones. This suggests the presence of local turbulent unsteadiness and three-dimensional phenomena, which contributes significantly to cooling enhancement.

Enhancing thermal efficiency of double-pass solar air collectors: A comparative study on the role of V-angled perforated fins

This study investigates the enhancement of thermal efficiency in double-pass solar air collectors (DPSACs) by incorporating V-angled perforated fins. It compares the performance of a finned model (FDPSAC) with a conventional smooth model, aiming to optimize thermal efficiency through improved heat transfer and air distribution. The experiments were conducted under three airflow rates: 0.00864 kg/s (Case I), 0.01143 kg/s (Case II), and 0.01317 kg/s (Case III). The findings indicated that the FDPSAC significantly outperformed the DPSAC, achieving higher outlet temperatures and demonstrating superior heat gain. The daily efficiency for the FDPSAC was 51.6 %, 54.7 %, and 59.2 %, exceeding the DPSAC, which were 49.4 %, 50.5 %, and 53.9 % for cases I, II, and III, respectively. The daily collector efficiency of the FDPSAC improved by approximately 4.45 %, 8.32 %, and 9.83 % relative to the DPSAC for the same case order. The results also showed that the FDPSAC maintained lower temperatures of the absorber plate, suggesting more effective heat dissipation and overall system efficiency. This study highlights the critical role of innovative fin design and optimal airflow management in enhancing solar collector performance. These improvements highlight the potential of the proposed fins to enhance solar air collector efficiency, providing key insights for optimizing thermal systems in sustainable energy.

Flow boiling heat transfer characteristics and mechanism analysis of high-pressure water in parallel twin narrow rectangular channels

Experimental investigations on the flow boiling heat transfer characteristics of high-pressure water are carried out in parallel twin narrow rectangular channels. An integrated structure was utilized to define the geometry of the test section in this study. The cross-sectional size of a single channel measures 60 × 2 mm, with an effective heating and flow length of 1450 mm. Experiments encompass a range of pressures 10–16 MPa, mass flux 500–1500 kg m−2·s−1 and heat flux 100–300 kW m−2. First, the heat transfer characteristics in the parallel twin channels are determined. Results show the heat transfer and flow distribution between the twin channels are generally balanced, with only a slight fluctuation observed near the saturation point. Besides, for one narrow rectangular channel, the boiling heat transfer coefficient is found to be essentially affected by the system parameters. The increases in mass flux, heat flux, and pressure will all exert the promotion of boiling enhancement. Among these factors, pressure and heat flux have a relatively more pronounced impact. In addition, heat transfer mechanisms in narrow rectangular channel with a large aspect ratio under high-pressure conditions are analyzed in detail. The transverse buoyancy effect has been identified as a significant factor in the regions of single-phase forced convection and partial subcooled boiling. Once the heat transfer reaches the stage dominated by nucleate boiling, the bubble nucleation and motion behaviors constitute the primary factors of heat transfer enhancement, under the coupling effects of channel structure and high-pressure conditions.

Heat transfer and rock-soil temperature distribution characteristics in whole life cycle for different structure sizes of medium-deep U-shaped butted well

Medium-deep U-shaped butted well (MUBW) is one of the most potential geothermal-heating way. However, the thermal interference may happen during long-term geothermal extraction period, which results in a heating performance attenuation. In this work, the heat transfer performance and surrounding rock-soil temperature distribution characteristics of MUBW in whole life cycle were investigated. The three-dimension full-size heat transfer model for long-term thermal extraction was proposed and the different structure sizes were considered. The results showed that the thermal interference is more likely to happen in a high heating load condition for the conventional structure size. By increasing horizontal length from 200 m to 600 m, the average specific heating load could increase by 26.1 %. When vertical depth increases to 3000 m, the heating load increases by 47.0 % at least. It is noted that the annual average inlet and outlet temperatures decrease by 5.1 °C in the whole life cycle, which should be considered in design on system operation. Additionally, the horizontal length of 600 m is large enough to avoid thermal interference in whole life cycle for MUBW with depth of 2000∼3000 m. This study has a practical meaning for ensuring a sustainable thermal extraction of MUBW.

Numerical simulation of single-phase flow and heat transfer characteristics of three-petal shaped fuel assembly

Petal-shaped fuel rods are an important means to realize reactor miniaturization and high power density. This paper establishes a numerical analysis model of a triangularly arranged 7-rod bundle with three-petal shaped fuel assembly, analyzes the single-phase flow and heat transfer characteristics under cosine heating conditions, and compares it with a four-petal shaped fuel assembly. The results show that the helical structure of the petal-shaped fuel rods can induce lateral fluid flow, generate secondary flow, and enhance the churning ability between fluids. Its unique structure makes the circumferential heat flow density, temperature, and Nussle number (Nu) on the fuel surface periodically non-uniformly distributed. Compared with the four-petal rod, the three-petal rod performs better in the circumferential direction in terms of heat transfer and temperature distribution uniformity. The related research results provide a theoretical basis for the application of petal-shaped fuel elements in reactors.