Begell House Inc.
Heat Transfer Research
HTR
1064-2285
40
5
2009
PREFASE
379-380
Experimental Investigation of Opposing Turbulent Mixed Convection Heat Transfer in an Inclined Flat Channel for Unstable Density Stratification.1. Method and Results for an Inclination Angle φ = 60°
381-390
Donatas
Sabanskis
Lithuanian Energy Institute, Branduolinës inzinerijos problemø laboratorija, Breslaujos str. 3, LT-44403 Kaunas, Lithuania
Robertas
Poskas
Lithuanian Energy institute; Kaunas Univerity of Technology, Kaunas, Lithuania
An experimental investigation of heat transfer in an inclined (φ = 60° from the horizontal position) flat channel with bottom wall heating (unstable density stratification) for turbulent mixed convection opposing flow conditions has been performed in the region of Re = 4·103−6.5·104 and Grq = 4.4·107−7.6·1010. Data and results presented in the article complement the research in the case of mixed convection published earlier in this journal. The obtained results are compared to the previous results in the inclined flat channel, when the upper wall is heated.
Experimental Investigation of Opposing Turbulent Mixed Convection Heat Transfer in an Inclined Flat Channel for Unstable Density Stratification. 2. Inclination Angle Effect on Heat Transfer
391-398
Robertas
Poskas
Lithuanian Energy institute; Kaunas Univerity of Technology, Kaunas, Lithuania
Donatas
Sabanskis
Lithuanian Energy Institute, Branduolinës inzinerijos problemø laboratorija, Breslaujos str. 3, LT-44403 Kaunas, Lithuania
Experimental investigations of heat transfer for an inclination angle φ = 30° (from the horizontal position) and analysis of the effect of flat channel inclination on heat transfer in a flat channel with bottom wall heating (unstable density stratification) for turbulent mixed convection opposing flow conditions have been performed in the regions of Re = 4·103−6.6·1044 and Grq = 4.4·107−7.6·1010. The presented data and results supplement the data previously given in this journal for the case of mixed convection. These experimental data are compared to the previously obtained experimental data in an inclined flat channel (φ = 60° from the horizontal position), when the bottom channel wall is heated.
Heat Transfer in the Arc Discharge Channel
399-413
Vilma
Snapkauskiene
Lithuanian Energy Institute, Plazminiø technologijø sektorius, Breslaujos str. 3, LT-44403 Kaunas, Lithuania
Vitas
Valincius
Lithuanian Energy Institute, Plasma Processing Laboratory, Breslaujos 3, 44403 Kaunas, Lithuania
Pranas
Valatkevicius
Lithuanian Energy Institute, Breslaujos 3, LT-4440, Kaunas, Lithuania
An experimental approach is presented for the analysis of thermal characteristics of a linear plasma torch with a hot cathode and a step-shaped anode. The experiment is performed in air at atmospheric pressure for discharge currents of 175−245 A and voltage of 200−250 V. The fed gas flow rate varied in the range of (2.5−8.5)·10−3 kg·sec−1 , and the Reynolds number was (4−13)·103. The place of gas injection, flow distribution, and rate affect the heat-transfer characteristics of the plasma source, which were generalized employing the similarity theory.
Heat Transfer by a High-Temperature Gas Flow in the Cooled Units of Heat Exchangers
415-430
Algimantas
Ambrazevicius
Lietuvos karo akademija, Silo g. 5A, LT-07104 Vilnius, Lithuania
Pranas
Valatkevicius
Lithuanian Energy Institute, Breslaujos 3, LT-4440, Kaunas, Lithuania
This article presents the results of local heat-transfer research in high-temperature turbulent flows of two-atomic gases (air or nitrogen) in channels of three different geometries: stable and entrance regions of a circular tube, an annular tube, and complicated fibroids and rectangular inned banks. Specific features of the dynamics and heat transfer of a high-temperature gas flow in the entrance region of annular tubes (x/d < 15) with and without interference and in separation and attachment zones have been determined. The obtained original correlations can be widely applied in practice.
Numerical Simulation of Turbulent Mixed Convection Heat Transfer in a Vertical Flat Channel for Aiding Flows
431-441
Rimantas
Makarevicius
Lithuanian Energy Institute, Kaunas, Lithuania
Renoldas
Zujus
Lithuanian Energy Institute, 3 Breslaujos str., LT-3035 Kaunas, Lithuania
Povilas
Poskas
Lithuanian Energy Institute, Branduolines inzinerijos problemas laboratorija, Breslaujos str. 3, LT-44403 Kaunas, Lithuania
Numerical simulation of heat transfer and velocity-temperature profiles for a two-sided symmetrically heated vertical flat channel was performed using the low-Reynolds number Chen-Kim and Lam-Bremhorst k−ε turbulence models in a wide range of buoyancy parameters. Modeling results are in good agreement with experimental data on heat transfer for high values of the buoyancy parameter Bo = Grq/(Re3.425Pr0.8). When the effect of buoyancy is small, the Lam-Bremhorst model gives better results than the Chen-Kim model, but in both cases the disagreement with experimental data is rather big. Tendencies in the dynamics of temperature profiles with increasing the buoyancy parameter Bo are the same as in experiments, but the dynamics of velocity profiles is different.
Numerical Simulation of Turbulent Mixed Convection Heat Transfer Variation along a Vertical Flat Channel for Aiding Flows
443-454
Renoldas
Zujus
Lithuanian Energy Institute, 3 Breslaujos str., LT-3035 Kaunas, Lithuania
Rimantas
Makarevicius
Lithuanian Energy Institute, Kaunas, Lithuania
Povilas
Poskas
Lithuanian Energy Institute, Branduolines inzinerijos problemas laboratorija, Breslaujos str. 3, LT-44403 Kaunas, Lithuania
Numerical modelling results on variation of turbulent mixed convection heat transfer along a vertical flat channel, when forced and natural convection directions coincide (aiding flows), are presented in this paper. Investigations with two-side symmetrical heating (qW1 = qW2 = const) were performed in a wide range of buoyancy parameters Bo = Grq/(Re3.425·Pr0.8) — from forced convection to natural convection. The computer code PHOENICS, which allows solving the system of mean flow equations of momentum, energy, and continuity, has been used for numerical simulation. Low Reynolds number Chen-Kim (CK) and Lam-Bremhorst (LB) k-ε turbulence models were used for closing the system of equations. The results obtained for numerical heat transfer simulation (for a two-dimensional case) were compared to the data from the experiments carried out at the Lithuanian Energy Institute (LEI). It was shown, that under a small effect of buoyancy [when buoyancy parameters are less than a critical value (Bo ≤ Bocr)] the Chen-Kim turbulence model simulates the heat transfer results in vertical short (x/de ≤ 20) channels better than the Lam-Bremhorst model. It was also demonstrated that the Lam-Bremhorst turbulence model could be used for heat transfer simulation with uncertainties less than 15% in the quasi-stabilized region (x/de ≥ 30) for a wide range of variation of buoyancy parameters.
Experimental Research of Heat Transfer from an In-Line Tube Bundle to a Vertical Foam Flow
455-472
Jonas
Gylys
Department of Thermal and Nuclear Energy, Kaunas University of Technology, K.Donelaièio str. 20, LT-44239 Kaunas, Lithuania
Tadas
Zdankus
Energy Technology Institute, Kaunas University of Technology, K. Donelaicio 20-212 LK, LT-44239 Kaunas, Lithuania
Irena
Gabrielaitiene
Energy Technology Institute, Kaunas University of Technology, Lithuania
Stasys
Sinkunas
Department of Thermal and Nuclear Energy, Kaunas University of Technology, Donelaicio 20, LT-44239 Kaunas, Lithuania
Development of heat exchangers with low consumption of primary energy resources and the enhanced heat transfer rates is the aim of our investigation. There are some ways of heat exchangers development. Usage of advanced coolants with the most suitable characteristics is one of the best and promising ways. We estimated that usage of aqueous foam as a coolant results in a relatively large heat transfer rate due to a small mass flow rate of such coolant. The main task of this work was to experimentally investigate the intensity of heat transfer from an in-line tube bundle to vertical upward and downward (after a 180-deg turning) foam flows. The influence of the foam flow parameters, such as flow velocity, direction of flow, volumetric void fraction of foam, and liquid drainage from foam, on the in-line tube bundle heat transfer intensity was determined. The influence of the tube position in the bundle on heat transfer intensity was investigated as well. The results of our experimental investigation are presented and analyzed in this paper. The results of investigation could enable one to create a modern and economic heat exchanger with simple and safe operation using a two-phase foam flow. It must be a compact, light heat exchanger with a relatively large intensity of heat transfer.
Interaction of the Transient Heat and Mass Transfer Processes through Evaporation of Sprayed Liquid Droplets
473-483
Gintautas U.
Miliauskas
Department of Thermal and Nuclear Energy, Kaunas University of Technology, Donelaicio 20, LT-44239 Kaunas, Lithuania
Stasys
Sinkunas
Department of Thermal and Nuclear Energy, Kaunas University of Technology, Donelaicio 20, LT-44239 Kaunas, Lithuania
Methods of combined analytical-numerical solution of the droplet problem, which includes internal heat exchange processes in semi-transparent droplet liquid and heat and mass transfer in the surrounding gas medium, are applied to modeling of combined transient heat and mass transfer of liquid droplets. Characteristic curves are obtained for conductive heating, that describe the variation of the thermal state of droplets and of phase change parameters with the help of the Fourier criterion. Departure from these characteristic curves allows evaluation of the influence exerted by boundary conditions of heat and mass transfer on heating and evaporation intensity under the conditions of combined heat supply. The results of numerical investigation are compared with the experimental results obtained by other authors.
Self-Similarity of Differential Equations and Heat Transfer Patterns of a Turbulent Near-Wall Layer
485-504
Vytautas Vincentas
Makarevicius
Lithuanian Energy Institute, Breslaujos str. 3, LT-44403 Kuanas, Lithuania
After looking at the works performed it becomes obvious that one of the most significant things is recast of a turbulent near-wall layer into locally self-similar one (depending on one coordinate). To solve this task, a number of steps were undertaken, such as determination of a new generalized coordinate, selection of constants and their determination. It should be noted that such recast of near-wall layer equations was carried out for the first time. The recast of equations of this type into locally self-similar ones enables one to ensure high accuracy of the iteration solution, however, powerful means are required — up-to-date computers and software. Such means had not been available previously, thus iteration solutions of quadratures were not performed. Application of the concurrent iteration solution method together with total solution of differential equations may be used with the objective of higher accuracy. Another important task is the determination of boundary heat transfer patterns in cases of variable physical properties. These patterns enable one to choose generalized heat transfer expressions. It was revealed that at high flow temperature turbulence and heat transfer decrease the velocity and temperature profiles change. This phenomenon has a practical value. At high flow temperatures there is no need to install turbulizers for intensification of heat transfer processes since no positive results will be obtained. The latter pattern comprises discovery elements.