Gas Flow Heat Transfer Research Articles

Heat Transfer of Gas Flow within a Partially Heated or Cooled Square Cavity

Natural convection of gas flow (air) confined within an enclosed square-section cavity is investigated numerically using the lattice Boltzmann method (LBM). The right (left) side of the enclosure is partially heated (cooled) by a hot (cold) chip, while the left (right) one is completely kept at cold (hot) temperature. However, the horizontal walls and vertical parts near the chip are kept adiabatic. The buoyancy effect induced by the gravity acceleration, related to the convection force, is evaluated through the Rayleigh number in the range of 1 0 3 − 1 0 6 (laminar regime). The wall heating-ratio effect on the flow properties such as temperature and velocity profiles was examined. The heat transfer is analyzed through the Nusselt number for different chip lengths. Results show that the wall heat ratio has an interesting effect on the flow behavior. Results show good agreement with those of full natural convection in the literature, experimental, and simulation data.

Variational entropy generation minimization of a channel flow: Convective heat transfer in a gas flow

Variational methods are used to optimize convective heat transfer in a channel gas flow. The minimization of a functional objective combining the rate of total entropy generation in the channel on the one hand and the total viscous dissipation on the other hand results in velocity and temperature fields. A weighting factor allows varying the relative importance of these two terms and a virtual body force field is applied to vary the velocity field pattern via the momentum equation source term. The result is velocity configurations that minimize the objective functional. This study shows that the velocity fields determined by the optimization process effectively lead to a reduction in the entropy generation rate in the flow as well as a reduction in the temperatures of the heated plate. In addition, the value of the weighting factor triggers the transition from slightly to highly perturbed velocity and temperature fields when compared to a non-optimized flow. The heat transfer enhancement is assessed and the increase of the Nusselt number is put in perspective with the reduction of the entropy generation rate and the increase of viscous friction. The results could be used to design passive technologies for enhancing wall-to-fluid heat transfer.

Physical and numerical simulation of the thermal and mechanical characteristics of stationary flows in the gasair paths of piston engines

Thermomechanical perfection of intake and exhaust systems largely determine the efficiency of the working process of reciprocating engines (ICE). The article presents the results of numerical simulation and experimental study of the heat transfer of gas flows in profiled gas- air systems of ICEs. A description of the numerical simulation technique, experimental setup, configurations of the studied hydraulic systems, measuring base and features of the experiments are given. On the basis of numerical modeling, it has been established that the use of profiled sections with cross sections in the shape of a square or a triangle in exhaust systems of an ICEs leads to a decrease in the heat transfer coefficient by 5-11%. It is shown that the use of similar profiled sections in the intake system of reciprocating engines also leads to a decrease in the heat transfer coefficient to 10 % at low air flow rates (up to 40 m/s) and an increase in the heat transfer coefficient to 7% at high speeds. Experimental studies qualitatively confirm the simulation results.

Analysis of heat transfer for gas flow in the multichannel plate heat exchanger depending on the gas Prandtl number

The analysis of an experimental investigation of heat transfer for a gas flow into the multichannel plate heat exchanger depending on the gas Prandtl number is presented. The gas mixture with Prandtl number of 0.23 and 0.7 were used. It is shown that the design procedure by the method a local thermal balance possesses an adequate accuracy for verification design equation for Nusselt number, including definition of the conditions validity of the model of flow regime heat exchanger.

Heat Transfer of Gas Flow through Microchannels using Extended Navier–Stokes Equations

In this paper, the temperature profile of hydrodynamically fully developed, laminar, nonisothermal, and incompressible gas flow through rectangular microchannels is modelled using Extended Navier–Stokes Equation (ENSE). A semianalytic solution is obtained for the proposed model in its total velocity form, using integral transform technique. Further, the relation between Nusselt number, Knudsen number, and Prandtl number under various aspect ratios was analysed. The results obtained show excellent agreement with existing measurements.

Nonstationary gas-dynamics and local heat transfer in the output channel of the turbocharger compressor

Thermomechanical characteristics of the gas flow at the turbocharger compressor outlet largely determine the quality of the intake process in piston engines with boost. The article presents the results of an experimental study of gas-dynamics and heat transfer of gas flows after compression in a turbocharger centrifugal compressor. A brief description of the experimental setup, the configuration of pipes under investigation, the measuring system and the experimental features are given. The studies were carried out on a free compressor, i.e. without considering the piston part. Different conditions in the compressor outlet channel were created by installing special nozzles with different hydraulic resistances. It has been established that the local heat transfer increases from 23 to 46 % with an increase in the turbocharger rotor speed, depending on the outlet channel configuration. It should be noted that an increase in rotor speed is also accompanied by an increase in air flow through the channel. The increase in flow rate was from 10 to 42 %.

Numerical and physical modeling of heat transfer in the exhaust system of a piston engine in stationary conditions

Thermomechanical perfection of exhaust systems largely determines the efficiency of the engine boost system. The article presents the results of numerical simulation and experimental study of heat transfer of gas flows in profiled exhaust systems of ICE. The description of the numerical simulation technique, the experimental setup, the configurations of the hydraulic systems under investigation, the instrumentation and the experimental features are given in the article. On the basis of numerical simulation, it has been established that the use of profiled sections with a cross-section in the form of a square in the exhaust system of an ICE leads to a decrease in the heat transfer rate to 5 %. The use of profiled sections in the form of a triangle in the system under consideration causes a more significant decrease in heat transfer, which reaches 11 %. Experimental studies qualitatively confirm the results of simulation.

Numerical investigation on gas flow heat transfer and pressure drop in the shell side of spiral-wound heat exchangers

As a critical facility, spiral-wound heat exchanger (SWHE) has been widely used in many industrial applications. A computational fluid dynamics (CFD) model was employed with the smallest periodic element and periodic boundary conditions to examine the characteristics of the shell side of SWHE. Numerical simulation results show that the heat transfer coefficients around the tube initially increase and subsequently decrease with radial angle because of the influence of backflow and turbulent separation. The mean absolute deviation between simulated heat transfer coefficients and measured values for methane, ethane, nitrogen and a mixture (methane/ethane) is within 5% when Reynolds number is over 30000. For the pressure drop, the simulated values are smaller than the measured values, and the mean absolute deviation is within 9%. Numerical simulation results also indicate that the pressure drop and heat transfer coefficients on the shell side of SWHE decrease as the winding angle of the tubes increases. Considering the effect of winding angle on pressure drops and heat transfer coefficients, the modified correlations of Nusselt number N u = 0.308 R e 0.64 P r 0.36 ( 1 + sin θ ) − 1.38 and friction factor f = 0.435 R e − 0.133 ( sin θ ) − 0.36 , are proposed. Comparing with the experimental data, the maximum deviations for heat transfer coefficients and pressure drops are less than 5% and 11% respectively.

A study on heat transfer enhancement in the radial direction of gas flow for thermoelectric power generation

The performance of thermoelectric generation (TEG) systems is significantly dependent on the hot side temperature of thermoelectric legs and the temperature difference between the hot side and cold side of the legs. To keep the TEG module working at an optimal condition, a high heat flux over 10W/cm2 through the TEG needs to be maintained. Due to the low heat transfer coefficient of the gas flow to the exhaust pipe wall surface, typically at a high temperature ranging from 400°C to 800°C, the actual heat flux into the TEG heat exchanger is limited significantly, resulting in relatively low efficiency of the TEG conversion. In the present study, an effective solution for enhancing the heat transfer of gas flow in the radial direction to the TEG is proposed by means of immersing high temperature heat pipes perpendicularly into the exhaust flow. Similarly, conventional heat pipes are radially inserted into a concentric coolant jacket in order to enhance heat transfer performance at the cold side of TEG modules. Overall, the TEG assembly is configured as a compact and scalable heat pipe heat exchanger. The simulation results show that the hot side temperature of the TEG can reach and be maintained as high as 300°C while the cold side temperature of the TEG can be maintained at approximately 85°C for a normal engine coolant loop. The results also show that the closer to the heat source in the pipeline the TEG system is located, the better the power generation that is expected. Moreover, better thermoelectric generation can be expected at a higher engine speed. By installing the TEG heat exchanger between catalytic converter and muffler, the best power output in the thermoelectric heat exchanger can be achieved at 450W and 5000rpm. If the TEG heat exchanger is adjacent to the outlet of a catalytic converter, the best-simulated performance at 6000rpm is 705W for a single sub pipeline. Therefore, a total power generation of 1410W is achievable since the existing exhaust pipe is a dual pipeline system.

Influence of High-Frequency Gas-Dynamic Unsteadiness on Heat Transfer in Gas Flows of Internal Combustion Engines

The results of experimental research of the influence of high-frequency gas-dynamical nonstationarity on the intensity of heat transfer in the intake and exhaust tract of piston engines are presented in the article. Experimental setup and methods of the experiments are described in the article. Dependences of instantaneous values of flow velocity and the local heat transfer coefficient in the intake and exhaust tract of the engine from the crankshaft rotation angle are presented in the article.

J081044 運転条件とセパレーター特性が固体高分子形燃料電池単セル内熱・物質移動現象と発電性能に及ぼす影響([J08104]燃料電池(4))

The aim of this study is pointing out the dominant factors of transfer phenomena and the main reason for distribution about heat and mass in single cell of Polymer Electrolyte Fuel Cell. In-plane temperature distribution in the single cell under power generation was measured by thermograph. The local in-plane temperature distribution under various experimental conditions was analyzed by dividing the images of in-plane temperature distribution. As a result, according to the analysis of the areas which are turned edges of gas channels in observation area, a temperature rise ratio is decreased with narrowing gas channel pitch irrespective of analyzed area and gas flow rate at inlet. In addition, the temperature rise ratio in the latter half in observation area is higher than that in the first half in observation area since the unreacted gas in gas channel was heated by convection heat transfer. Furthermore, the temperature rise ratio in the analyzed area near the gas inlet is decreased by increasing gas flow rate at inlet due to cooling effect by convection heat transfer of gas flow.

Heat Transfer Investigation of Intake Port Engine Based on Steady-State and Transient Simulation

This research is presents the gas flow heat transfer investigation in the intake port of four stroke direct injection compression ignition engine using GT-Suite software for steady-state and transient simulation. To investigate and simulate the intake port gas flow heat transfer profile of compression ignition engine is using GT-Power engine model were developed in this research. GT-Power is sub-system menu from GT-Suite. The engine model is developed from the real compression ignition engine data and input to software library. In this research, the simulation of engine model is running in variations engine speeds. The simulation output data is collected from the GT-Post results plots and casesRLT in post processing. The simulation results of the intake port engine model are shown the characters in intake port heat transfer profile of engine in variations engine speeds. The detail performance intake port gas flow heat transfer is shown that in 3500 rpm engine speed is the best

Numerical Study of Film and Regenerative Cooling in a Thrust Chamber at High Pressure

Numerical study of coupled heat transfer of gas flow with film cooling, chamber wall conduction, and regeneration coolant cooling in the thrust chamber of a liquid rocket engine was performed. A one-dimensional model was adopted for regeneration cooling to couple two-dimensional model simulation in the thrust camber. Numerical results show that the method adopted can simulate the gas flow field well, and can calculate the heat flux through the wall, the wall temperature, and the temperature increase of the coolant quickly. In addition, liquid film cooling can reduce the wall temperature greatly, and decrease the heat flux transferred from the hot gas to the chamber wall.

Heat transfer of gas flow through a packed bed

This paper reports an experimental study of both the transient and steady-state heat transfer behaviour of a gas flowing through a packed bed under the constant wall temperature conditions. Effective thermal conductivities and convective heat transfer coefficient are derived based on the steady-state measurements and the two-dimensional axial dispersion plug flow (2DADPF) model. The results reveal a large temperature drop at the wall region and the temperature drop depends on the axial distance from the inlet. The 2DADPF model predicts the axial temperature distribution fairly well, but the prediction is poor for the radial temperature distribution. Length-dependent behaviour of the effective heat transfer parameters and non-uniform flow behaviour are proposed to be responsible. A comparison with previously published correlations and data in the literature shows that the relationships proposed by Bunnell et al. and Demirel et al. agree well with the measured effective radial thermal conductivity, whereas the wall–fluid heat transfer coefficient is better represented by the Li–Finlayson correlation.

Computational Modeling of the Structure of a High-Current Discharge in a Magnetogasdynamic Channel

A two-dimensional computational model is proposed to calculate radiative-convective heat transfer in gas flows with large gradients of physical properties. The model is based on the numerical solution of the unsteady dynamic equations for a compressible inviscid gas and the radiative transfer equations. Flow calculations for the magnetogasdynamic channel of a rail accelerator show that the dynamics of the process is substantially affected by the flow in the discharge region and hydrodynamic instability, resulting in the nonstationarity and nonuniformity of the flow and discharge structure. During the process, the discharge can exist both in the form of several current-carrying channels and in the form of a unified plasma formation. Results of the numerical calculations agree qualitative with experimental data.

“Deterioration” criteria for convective heat transfer in gas flow through non-circular ducts

The reduction in turbulent, convective heat transfer parameters observed in some supercritical data and in experiments with common gases can be due to radial property variation, acceleration, buoyancy or combinations of these phenomena, depending on the conditions of the applications. To date criteria for the onsets of these effects have been developed for vertical circular tubes. This note presents extensions of these criteria to non-circular ducts with constant cross-sections as in the cooling channels of some advanced nuclear reactors.

Turbulent gas flow heat transfer and friction in channels of different cross-sections

Consideration is given to gas flow in channels of circular, annular and plane cross-sections. A mathematical model is suggested which uses an integral approach for describing momentum and energy transfer in a turbulent boundary layer. It is assumed that dynamic and thermal boundary layers start to develop on the channel walls simultaneously and subsequently converge.

Finite element solution of heat transfer for gas flow through a tube

An analysis was performed of the axial temperature distribution along the wall of a circular tube. A transparent gas in forced convection enters a tube with variable heat-transfer coefficient, internal radiation exchange, and axial wall heat conduction. The nonlinear integro-differential equation describing the process of energy exchange was solved using the Galerkin finite element technique with isoparametric, quadratic elements. An arbitrary heat generation distribution in the tube wall as a function of axial position can be taken into this model, depending on the particular physical problem; however, only the uniform and the sinusoidal heat generation cases have been considered here. The tube interior surface was assumed to be black, and the gas was considered transparent. This type of problem is of practical interest for the high-temperature, gas-cooled reactor (HTGR) core flow and for tubular heat-exchanger flow. In an HTGR the coolant is helium and can be well approximated as a transparent gas. Similar problems also arise for flow of a gas through electrically heated tubes and coils. Results for only the uniform heat generation case are available from other numerical techniques, and the results using the finite element method were found to be in good agreement. Nomenclature Cp = specific heat at constant pressure, J/kg°C D = tube diameter, m h = convective heat-transfer coefficient, W/m2 °C h^ = fully developed convective heat-transfer coefficient, .' W/m2°C k = thermal conductivity, W/m °C L = tube length, m q = heat added at wall per unit inside area and time, W/m2 R = tube radius, m T = temperature, °C u = mean gas velocity, m/s X,Z = axial length coordinates measured from the tube entrance, m p = density of gas, kg/m3 a . = Stefan-Boltzmann constant, W/m2K4

Variable properties laminar gas flow heat transfer in the entry region of parallel porous plates

The principal effect of property variation is to slightly increase the Nusselt number in the thermal entry region. Previous investigations have given solutions to the flow and heat transfer problems over the entire range of wall Reynolds and Péclét numbers for a model of laminar, incompressible, steady, constant property flow. This note gives the designer an indication of the limitations of such a model. Specifically, for injection, eventually the Mach number and Reynolds number of the main channel flow will exceed the limits of the incompressible and laminar flow assumptions. For suction, the heat-transfer predictions cease to be valid near the point of complete mass extraction since the axial heat conduction now becomes important and cannot be assumed to be negligible.

Convective heat transfer in transverse gas flow over a cylinder

A method is described for studying convective heat transfer in transverse flow over a wire, from the temperature dependence of the heat transfer coefficients. A formula has been obtained for calculating convective heat transfer in gas flow over a. wire, for temperature differences up to 1000°C and Re values from 0.14 to 2.