scholarly journals Application of the multi-field coupling enhanced heat transfer principle to the engine compartment design of clean gas bus

2020 ◽  
Vol 11 (1) ◽  
pp. 205-220
Author(s):  
Jiajie Ou ◽  
Lifu Li
Keyword(s):  
Heat Transfer ◽  
Temperature Gradient ◽  
Flow Region ◽  
Transfer Principle ◽  
Engine Compartment ◽  
Enhanced Heat Transfer ◽  
Core Flow ◽  
Field Coupling ◽  
The Core ◽  
Block Area

Abstract. Clean gas engines, such as liquefied petroleum gas (LPG) engines, have high thermal loads on parts under equivalent specific combustion. This study examines the multi-field coupling enhanced heat transfer principle and its applications to the engine compartment of a typical LPG city bus. The field synergy enhanced heat transfer principle (FSP) was applied in the radiator assembly area. The FSP model yielded an optimum velocity -temperature gradient matching field that would improve convective heat transfer in this area. To strengthen the convective heat transfer ability of the limited cooling air in the cabin, temperature field homogenization (TFH) in the core flow region of the engine block area was achieved. The TFH optimization model helped minimize the temperature gradient in the core flow region and maximize it at the heat transfer boundary, and the optimum vector field and flow path were obtained. More comprehensive changes to the structural design were made according to the multi-field coupling enhanced heat transfer principles. The simulation results showed that in the comprehensive structure, the heat transfer efficiency of the radiator increased by 14.66 %, the average temperature of the air passages in the engine block area decreased by 22.23 %, and the heat dissipation coefficient of the engine body and engine cover increased by 4.60 times and 3.49 times, respectively.

Boiling Heat Transfer From an Oscillated Water Column Through a Porous Domain: A Simplified Thermodynamic Analysis

2016 ◽  
Author(s):  
Ersin Sayar
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Water Column ◽  
Thermodynamic Analysis ◽  
Bubbly Flow ◽  
Pool Boiling ◽  
Oscillating Flow ◽  
Transition Regime ◽  
Core Flow ◽  
The Core

Heat transfer in an oscillating water column in the transition regime of pool boiling to bubbly flow is investigated experimentally and theoretically. Forced oscillations are applied to water via a frequency controlled dc motor and a piston-cylinder device. Heat transfer is from the electrically heated inner surface to the reciprocating flow. The heat transfer in the oscillating fluid column is altered by using stainless steel scrap metal layers (made off open-cell discrete cells) which produces a porous medium within the system. The effective heat transfer mechanism is enhanced and it is due to the hydrodynamic mixing of the boundary layer and the core flow. In oscillating flow, the hydrodynamic lag between the core flow and the boundary layer flow is somehow significant. At low actuation frequencies and at low heat fluxes, heat transfer is restricted in the single phase flows. The transition regime of pool boiling to bubbly flow is proposed to be a remedy to the stated limitation. The contribution by the pool boiling on heat transfer appears to be the dominant mechanism for the selected low oscillation amplitudes and frequencies. Accordingly the regime is a transition from pool boiling to bubbly flow. Nucleate-bubbly flow boiling in oscillating flow is also investigated using a simplified thermodynamic analysis. According to the experimental results, bubbles induce highly efficient heat transfer mechanisms. Experimental study proved that the heater surface temperature is the dominant parameter affecting heat transfer. At greater actuation frequencies saturated nucleate pool boiling ceases to exist. Actuation frequency becomes important in that circumstances. The present investigation has possible applications in moderate sized wicked heat pipes, boilers, compact heat exchangers and steam generators.

scholarly journals Blockage Development in a Transonic, Axial Compressor Rotor

1997 ◽  
Author(s):  
Kenneth L. Suder
Keyword(s):  
Boundary Layer ◽  
Axial Compressor ◽  
Flow Region ◽  
Tip Clearance ◽  
Surface Boundary ◽  
Core Flow ◽  
The Core ◽  
Compressor Rotor ◽  
Transonic Axial Compressor ◽  
The Impact

A detailed experimental investigation to understand and quantify the development of blockage in the flow field of a transonic, axial flow compressor rotor (NASA Rotor 37) has been undertaken. Detailed laser anemometer measurements were acquired upstream, within, and downstream of a transonic, axial compressor rotor operating at 100%, 85%, 80%, and 60% of design speed which provided inlet relative Mach numbers at the blade tip of 1.48, 1.26, 1.18, and 0.89 respectively. The impact of the shock on the blockage development, pertaining to both the shock / boundary layer interactions and the shock / tip clearance flow interactions, is discussed. The results indicate that for this rotor the blockage in the endwall region is 2–3 times that of the core flow region, and the blockage in the core flow region more than doubles when the shock strength is sufficient to separate the suction surface boundary layer.

scholarly journals On the Identification and Decomposition of the Unsteady Losses in a Turbine Cascade

2018 ◽  
Author(s):  
D. Lengani ◽  
D. Simoni ◽  
R. Pichler ◽  
R. Sandberg ◽  
V. Michelassi ◽  
...  
Keyword(s):  
Flow Region ◽  
Suction Side ◽  
Spatial Location ◽  
Flow Coefficient ◽  
Core Flow ◽  
Low Pressure Turbine ◽  
The Core ◽  
Eddy Simulation ◽  
Reduced Frequency ◽  
Proper Orthogonal

The present paper describes the application of Proper Orthogonal Decomposition (POD) to Large Eddy Simulation (LES) of the T106A low-pressure-turbine profile with unsteady incoming wakes at two different flow conditions. Conventional data analysis applied to time averaged or phase-locked averaged flow fields is not always able to identify and quantify the different sources of losses in the unsteady flow field as they are able to isolate only the deterministic contribution. A newly developed procedure allows such identification of the unsteady loss contribution due to the migration of the incoming wakes, as well as to construct reduced order models able to highlight unsteady losses due to larger and/or smaller flow structures carried by the wakes in the different parts of the blade boundary layers. This enables a designer to identify the dominant modes (i.e. phenomena) responsible for loss, the associated generation mechanism, their dynamics and spatial location. The procedure applied to the two cases shows that losses in the fore part of the blade suction side are basically unaffected by the flow unsteadiness, irrespective of the reduced frequency and the flow coefficient. On the other hand, in the rear part of the suction side the unsteadiness contributes to losses prevalently due to the finer scale (higher order POD modes) embedded into the bulk of the incoming wake. The main difference between the two cases has been identified by the losses produced in the core flow region, where both the largest scale structures and the finer ones produces turbulence during migration. The decomposition into POD modes allows the quantification of this latter extra losses generated in the core flow region, providing further inputs to the designers for future optimization strategies.

Multidimensional Analysis of UPTF Upper Plenum Injection Test With MARS-KS Code

2009 ◽  
Author(s):  
Kyung Won Lee ◽  
Yong Jin Cho ◽  
Seung Hoon Ahn
Keyword(s):  
Water Level ◽  
Fluid Model ◽  
Flow Region ◽  
Multidimensional Analysis ◽  
Flow Area ◽  
Core Flow ◽  
Injection Test ◽  
The Core ◽  
Loss Of Coolant Accident ◽  
Calculation Results

This study aims to assess the multi-dimensional fluid model of MARS-KS (KINS standard version of MARS) code. The UPTF upper plenum injection test (UPI Test, Test No. 20) is modeled with the MARS in order to assess the code capability for predicting the multi-dimensional behavior of UPI water in the upper plenum during a reflood phase of large break loss-of-coolant accident. The coolant piping is simulated by one-dimensional components, while the reactor vessel is modeled by the cylindrical multi-dimensional component with five rings in radial direction, eight sectors in azimuthal direction, and fourteen axial levels. The results of MARS calculation are compared with the experimental data of UPTF test, particularly the ECC downflow area in the core flow area, the water carryover rate to hot legs, and the water level distribution in upper plenum. The calculation results indicate that the size of the downflow area is about 16.7% of the core flow area, comparable to the result of 10% in UPTF test. The MARS overestimates the amount of water carryover to the hot legs. As seen in the UPTF UPI test, the collapsed water level formed in the upper plenum is uniform at the entire core flow area, except at the down flow region where more water accumulates. These results demonstrate that MARS can provide a reasonable prediction of multi-dimensional behavior of UPI water in the upper plenum.

scholarly journals The 30 May 1998 Spencer, South Dakota, Storm. Part II: Comparison of Observed Damage and Radar-Derived Winds in the Tornadoes

2005 ◽  
Vol 133 (1) ◽  
pp. 97-119 ◽  
Author(s):  
Joshua Wurman ◽  
Curtis R. Alexander
Keyword(s):  
South Dakota ◽  
Translational Motion ◽  
Flow Region ◽  
Doppler Velocity ◽  
Velocity Data ◽  
Core Flow ◽  
Damage Survey ◽  
The Core ◽  
Time Period ◽  
The Town

Abstract A violent supercell tornado passed through the town of Spencer, South Dakota, on the evening of 30 May 1998 producing large gradients in damage severity. The tornado was rated at F4 intensity by damage survey teams. A Doppler On Wheels (DOW) mobile radar followed this tornado and observed the tornado at ranges between 1.7 and 8.0 km during various stages of the tornado's life. The DOW was deployed less than 4.0 km from the town of Spencer between 0134 and 0145 UTC, and during this time period, the tornado passed through Spencer, and peak Doppler velocity measurements exceeded 100 m s−1. Data gathered from the DOW during this time period contained high spatial resolution sample volumes of approximately 34 m × 34 m × 37 m along with frequent volume updates every 45–50 s. The high-resolution Doppler velocity data gathered from low-level elevation scans, when sample volumes are between 20 and 40 m AGL, are compared to extensive ground and aerial damage surveys performed by the National Weather Service (NWS) and the National Institute of Standards and Technology (NIST). Idealized radial profiles of tangential velocity are computed by fitting a model of an axisymmetric translating vortex to the Doppler radar observations, which compensates for velocity components perpendicular to the radar beam as well as the translational motion of the tornado vortex. Both the original single-Doppler velocity data and the interpolated velocity fields are compared with damage survey Fujita scale (F-scale) estimates throughout the town of Spencer. This comparison on a structure-by-structure basis revealed that radar-based estimates of the F-scale intensity usually exceeded the damage-survey-based F-scale both inside and outside the town of Spencer. In the town of Spencer, the radar-based wind field revealed two distinct velocity time series inside and outside the passage of the core-flow region. The center of the core-flow region tracked about 50 m farther north than the damage survey indicated because of the asymmetry induced by the 15 m s−1 translational motion of the tornado. The radar consistently measured the strongest winds in the lowest 200 m AGL with the most extreme Doppler velocities residing within 50 m AGL. Alternate measures of tornado wind field intensity that incorporated the effects of the duration of the extreme winds and debris were explored. It is suggested that damage may not be a simple function of peak wind gust and structural integrity, but that the duration of intense winds, directional changes, accelerations, and upwind debris loading may be critical factors.

Unsteady Flow/Quasi-Steady Heat Transfer Computations on a Turbine Rotor and Comparison With Experiments

2001 ◽  
Vol 124 (1) ◽  
pp. 152-159 ◽  
Author(s):  
T. Korakianitis ◽  
P. Papagiannidis ◽  
N. E. Vlachopoulos
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Unsteady Flow ◽  
Turbine Rotor ◽  
Frequency Parameter ◽  
Unsteady Heat Transfer ◽  
Core Flow ◽  
The Core ◽  
Reduced Frequency ◽  
Steady Heat

The unsteady flow in stator–rotor interactions affects the structural integrity, aerodynamic performance of the stages, and blade-surface heat transfer. Numerous viscous and inviscid computer programs are used for the prediction of unsteady flows in two-dimensional and three-dimensional stator–rotor interactions. The relative effects of the various components of flow unsteadiness on heat transfer are under investigation. In this paper it is shown that for subsonic cases, the reduced frequency parameter for boundary-layer calculations is about two orders of magnitude smaller than the reduced frequency parameter for the core flow. This means that for typical stator–rotor interactions, the unsteady flow terms are needed to resolve the location of disturbances in the core flow, but in many cases the instantaneous disturbances can be input in steady-flow boundary-layer computations to evaluate boundary-layer effects in a quasi-steady approximation. This hypothesis is tested by comparing computations with experimental data on a turbine rotor for which there are extensive experimental heat transfer data available in the open literature. An unsteady compressible inviscid two-dimensional computer program is used to predict the propagation of the upstream stator disturbances into the downstream rotor passages. The viscous wake (velocity defect) and potential flow (pressure fluctuation) perturbations from the upstream stator are modeled at the computational rotor–inlet boundary. The effects of these interactions on the unsteady rotor flow result in computed instantaneous velocity and pressure fields. The period of the rotor unsteadiness is one stator pitch. The instantaneous velocity fields on the rotor surfaces are input in a steady-flow differential boundary-layer program, which is used to compute the instantaneous heat transfer rate on the rotor blades. The results of these quasi-steady heat-transfer computations are compared with the results of unsteady heat transfer experiments and with the results of previous unsteady heat transfer computations. The unsteady flow fields explain the unsteady amplitudes and phases of the increases and decreases in instantaneous heat transfer rate. It is concluded that the present method is accurate for quantitative predictions of unsteady heat transfer in subsonic turbine flows.

scholarly journals On the Identification and Decomposition of the Unsteady Losses in a Turbine Cascade

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
D. Lengani ◽  
D. Simoni ◽  
R. Pichler ◽  
R. D. Sandberg ◽  
V. Michelassi ◽  
...  
Keyword(s):  
Flow Region ◽  
Suction Side ◽  
Spatial Location ◽  
Flow Coefficient ◽  
Core Flow ◽  
Low Pressure Turbine ◽  
The Core ◽  
Eddy Simulation ◽  
Reduced Frequency ◽  
Proper Orthogonal

The present paper describes the application of proper orthogonal decomposition (POD) to large eddy simulation (LES) of the T106A low-pressure-turbine profile with unsteady incoming wakes at two different flow conditions. Conventional data analysis applied to time averaged or phase-locked averaged flow fields is not always able to identify and quantify the different sources of losses in the unsteady flow field as they are able to isolate only the deterministic contribution. A newly developed procedure allows such identification of the unsteady loss contribution due to the migration of the incoming wakes, as well as to construct reduced order models that are able to highlight unsteady losses due to larger and/or smaller flow structures carried by the wakes in the different parts of the blade boundary layers. This enables a designer to identify the dominant modes (i.e., phenomena) responsible for loss, the associated generation mechanism, their dynamics, and spatial location. The procedure applied to the two cases shows that losses in the fore part of the blade suction side are basically unaffected by the flow unsteadiness, irrespective of the reduced frequency and the flow coefficient. On the other hand, in the rear part of the suction side, the unsteadiness contributes to losses prevalently due to the finer scale (higher order POD modes) embedded into the bulk of the incoming wake. The main difference between the two cases has been identified by the losses produced in the core flow region, where both the largest scale structures and the finer ones produces turbulence during migration. The decomposition into POD modes allows the quantification of this latter extra losses generated in the core flow region, providing further inputs to the designers for future optimization strategies.

Blockage Development in a Transonic, Axial Compressor Rotor

1998 ◽  
Vol 120 (3) ◽  
pp. 465-476 ◽  
Author(s):  
K. L. Suder
Keyword(s):  
Boundary Layer ◽  
Axial Compressor ◽  
Flow Region ◽  
Tip Clearance ◽  
Surface Boundary ◽  
Core Flow ◽  
The Core ◽  
Compressor Rotor ◽  
Transonic Axial Compressor ◽  
The Impact

A detailed experimental investigation to understand and quantify the development of blockage in the flow field of a transonic, axial flow compressor rotor (NASA Rotor 37) has been undertaken. Detailed laser anemometer measurements were acquired upstream, within, and downstream of a transonic, axial compressor rotor operating at 100, 85, 80, and 60 percent of design speed, which provided inlet relative Mach numbers at the blade tip of 1.48, 1.26, 1.18, and 0.89, respectively. The impact of the shock on the blockage development, pertaining to both the shock/boundary layer interactions and the shock/tip clearance flow interactions, is discussed. The results indicate that for this rotor the blockage in the endwall region is 2–3 times that of the core flow region, and the blockage in the core flow region more than doubles when the shock strength is sufficient to separate the suction surface boundary layer.

scholarly journals Effect of core flow heat transfer enhancement on power generation characteristics of thermoelectric generators with different performances

2021 ◽  
pp. 184-184
Author(s):  
Yanzhe Li ◽  
Shixue Wang ◽  
Yunchi Fu ◽  
Yulong Zhao ◽  
Like Yue
Keyword(s):  
Heat Transfer ◽  
Power Generation ◽  
Figure Of Merit ◽  
Thermoelectric Generator ◽  
Metal Foam ◽  
Maximum Output ◽  
Thermoelectric Generators ◽  
Core Flow ◽  
Gas Channel ◽  
The Core

In this study, the effect of enhancing the core flow heat transfer with metal foam on the performance of thermoelectric generators with different power generation characteristics is studied experimentally. Filling the core flow area of the gas channel in a thermoelectric generator with metal foam can greatly improve the heat transfer capacity of the gas channel with a small pressure loss, thereby improving the power generation efficiency. The results show that, first, the heat transfer enhancement achieved by partially filling the core area of the gas channel with metal foam can significantly improve the performance of thermoelectric generators, the maximum output power is about 1.5 times higher than that of the unfilled channel. Second, for a thermoelectric generator with different modules, the friction coefficient for different filling ratios increases by about 16 times at most, while the Nu value increases by only three times at most, and according to the PEC of the gas channel, metal foam with high filling rate and low pore density is more suitable for the thermoelectric generator. Third, it is more appropriate to use the thermoelectric module with a high figure of merit as the selection criterion for deciding whether to adopt the technique of enhancing heat exchange through the gas channel. The maximum output power and efficiency of the thermoelectric generator using the high figure of merit module are 300% and 160% higher than those of the thermoelectric generator using the low figure of merit module, respectively.

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