scholarly journals Axial profiles of heat transfer coefficients in a liquid film evaporator

2017 ◽  
Vol 10 (2) ◽  
pp. 165-169
Author(s):  
Timár Pavel ◽  
Stopka Ján ◽  
Báleš Vladimír
Keyword(s):  
Film Flow ◽  
Tube Wall ◽  
Numerical Study ◽  
Energy Requirement ◽  
Transfer Coefficients ◽  
Calculation Domain ◽  
Heat Transfer Coefficients ◽  
Used Oil ◽  
Differential Element ◽  
Flow Heat

AbstractRegeneration is the most efficient way of managing used oil. It saves money by preventing costly clean-ups and liabilities associated with mismanagement of used oil and it also helps to protect the environment. A numerical study of the flow, heat and mass transfer characteristics of the vertical evaporating tube with the films flowing down on both the inside and the outside tube surfaces has been carried out. Condensation occurs along the outside wall surface and evaporation at the free surface of the inside film. The calculation domain of two film flow regions and tube wall is solved simultaneously. The longitudinal variation of temperature, mass flow rate, and hence the thickness of the films downward the tube can be obtained by applying conservation of the energy requirement to the differential element.

A Numerical and Experimental Investigation of Turbulent Heat Transport Downstream From an Abrupt Pipe Expansion

1983 ◽  
Vol 105 (4) ◽  
pp. 862-869 ◽  
Author(s):  
R. S. Amano ◽  
M. K. Jensen ◽  
P. Goel
Keyword(s):  
Heat Transfer ◽  
Numerical Solutions ◽  
Numerical Study ◽  
Separated Flow ◽  
Flow Region ◽  
Reynolds Numbers ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Pipe Expansion

An experimental and numerical study is reported on heat transfer in the separated flow region created by an abrupt circular pipe expansion. Heat transfer coefficients were measured along the pipe wall downstream from an expansion for three different expansion ratios of d/D = 0.195, 0.391, and 0.586 for Reynolds numbers ranging from 104 to 1.5 × 105. The results are compared with the numerical solutions obtained with the k ∼ ε turbulence model. In this computation a new finite difference scheme is developed which shows several advantages over the ordinary hybrid scheme. The study also covers the derivation of a new wall function model. Generally good agreement between the measured and the computed results is shown.

Experimental and Numerical Study on the Effects of the Relative Position of Film Hole and Orientation Ribs on the Film Cooling With Ribbed Cross-Flow Coolant Channel

2020 ◽  
Author(s):  
Bingran Li ◽  
Cunliang Liu ◽  
Lin Ye ◽  
Huiren Zhu ◽  
Fan Zhang
Keyword(s):  
Heat Transfer ◽  
Relative Position ◽  
Film Cooling ◽  
Numerical Study ◽  
Cross Flow ◽  
Internal Cooling ◽  
Transfer Coefficients ◽  
Cooling Performance ◽  
Heat Transfer Coefficients ◽  
Numerical Studies

Abstract To investigate the application of ribbed cross-flow coolant channels with film hole effusion and the effects of the internal cooling configuration on film cooling, experimental and numerical studies are conducted on the effect of the relative position of the film holes and different orientation ribs on the film cooling performance. Three cases of the relative position of the film holes and different orientation ribs (post-rib, centered, and pre-rib) in two ribbed cross-flow channels (135° and 45° orientation ribs) are investigated. The film cooling performances are measured under three blowing ratios by the transient liquid crystal measurement technique. A RANS simulation with the realizable k-ε turbulence model and enhanced wall treatment is performed. The results show that the cooling effectiveness and the downstream heat transfer coefficient for the 135° rib are basically the same in the three position cases, and the differences between the local effectiveness average values for the three are no more than 0.04. The differences between the heat transfer coefficients are no more than 0.1. The “pre-rib” and “centered” cases are studied for the 45° rib, and the position of the structures has little effect on the film cooling performance. In the different position cases, the outlet velocity distribution of the film holes, the jet pattern and the discharge coefficient are consistent with the variation in the cross flow. The related research previously published by the authors showed that the inclination of the ribs with respect to the holes affects the film cooling performance. This study reveals that the relative positions of the ribs and holes have little effect on the film cooling performance. This paper expands and improves the study of the effect of the internal cooling configuration on film cooling and makes a significant contribution to the design and industrial application of the internal cooling channel of a turbine blade.

Numerical Study of Boiling Heat Transfer Around Horizontal and Inclined Cylinders

2021 ◽  
Author(s):  
Avik Saha ◽  
Arup Kumar Das
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Horizontal Cylinder ◽  
Uniform Heat Flux ◽  
Cylinder Surface ◽  
Transfer Coefficients ◽  
Heated Cylinder ◽  
Heat Transfer Coefficients ◽  
Stages Of Growth ◽  
Saturated Water

Abstract Pool boiling around a heated cylinder having a diameter larger than the departure diameter of bubbles has been simulated numerically. Thermally uniform heat flux condition has been maintained at the outer surface of the cylinder, submerged at saturated water at atmospheric pressure. Using the Volume of Fluid type framework of liquid phase fraction in the domain, bubble life cycle around the horizontal cylinder has been analyzed to understand different stages of growth, sliding, merging prior to departure. An effort has also been made to characterize the bubble population, emerging from different sites over the cylindrical surface. The influence of cylinder inclination along its axis on these interfacial features has also been discussed using representative numerical simulation. Temperature profiles of the cylinder surface have been portrayed for both horizontal and inclined situations before presenting respective heat transfer coefficients.

scholarly journals Performance Evaluation of Photovoltaic/Thermal (PV/T) System Using Different Design Configurations

2020 ◽  
Vol 12 (22) ◽  
pp. 9520
Author(s):  
M. Imtiaz Hussain ◽  
Jun-Tae Kim
Keyword(s):  
Heat Exchanger ◽  
Numerical Study ◽  
Balance Equations ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Pv Panel ◽  
Exchange Area ◽  
Energy And Exergy ◽  
Overall Efficiency ◽  
T System

This study summarizes the performance of a photovoltaic/thermal (PV/T) system integrated with a glass-to-PV backsheet (PVF film-based backsheet) and glass-to-glass photovoltaic (PV) cells protections. A dual-fluid heat exchanger is used to cool the PV cells in which water and air are operated simultaneously. The proposed PV/T design brings about a higher electric output while producing sufficient thermal energy. A detailed numerical study was performed by calculating real-time heat transfer coefficients. Energy balance equations across the dual-fluid PV/T system were solved using an ordinary differential equation (ODE) solver in MATLAB software. The hourly and annual energy and exergy variations for both configurations were evaluated for Cheonan City, Korea. In the case of a PV/T system with a glass-to-glass configuration, a larger heat exchange area causes the extraction of extra solar heat from the PV cells and thus improving the overall efficiency of the energy transfer. Results depict that the annual electrical and total thermal efficiencies with a glass-to-glass configuration were found to be 14.31% and 52.22%, respectively, and with a glass-to-PV backsheet configuration, the aforementioned values reduced to 13.92% and 48.25%, respectively. It is also observed that, with the application of a dual-fluid heat exchanger, the temperature gradient across the PV panel is surprisingly reduced.

HEAT TRANSFER OF HC290-OIL MIXTURES IN A HORIZONTAL CONDENSING MICRO-FIN TUBE

2005 ◽  
Vol 19 (01n03) ◽  
pp. 639-641
Author(s):  
M. W. TONG ◽  
M. L. DONG ◽  
Y. LI
Keyword(s):  
Heat Transfer ◽  
Condensation Temperature ◽  
Vapor Quality ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Used Oil ◽  
Enhanced Tube ◽  
Oil Mixtures ◽  
Fin Tube ◽  
Spiral Angle

Heat transfer coefficients was experimentally determined for a horizontal micro-fin tube (2m in length, 11.44mm ID) with HC290-oil mixtures. The oil is Suniso 3GS, which is a widely used oil in refrigerant systems. The micro-fin tube is a internally enhanced tube, which has 60 fins with a height of 0.25mm and 20° spiral angle. The condensation temperatures varied from 40° to 45° and the refrigerant mass flux was varied from 40kg/(m2s) to 220kg/(m2s). The results showed that the mean condensation heat transfer coefficients on the test section (inlet vapor quality 1, outlet vapor quality 0.1~0.25) decreased as the oil concentrations were increased and the condensation temperature had negligible effect on the heat transfer coefficients.

Laminar Natural Convection in Isosceles Triangular Enclosures Heated From Below and Symmetrically Cooled From Above

2000 ◽  
Vol 122 (3) ◽  
pp. 485-491 ◽  
Author(s):  
G. A. Holtzman ◽  
R. W. Hill ◽  
K. S. Ball
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Study ◽  
Pitchfork Bifurcation ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Aspect Ratios ◽  
Triangular Enclosure ◽  
Laminar Natural Convection ◽  
Flow Symmetry

A numerical study of natural convection in an isosceles triangular enclosure with a heated horizontal base and cooled upper walls is presented. Nearly every previous study conducted on this subject to date has assumed that the geometric plane of symmetry is also a plane of symmetry for the flow. This problem is re-examined over aspect ratios ranging from 0.2 to 1.0 and Grashof numbers from 103 to 105. It is found that a pitchfork bifurcation occurs at a critical Grashof number for each of the aspect ratios considered, above which the symmetric solutions are unstable to finite perturbations and asymmetric solutions are instead obtained. Results are presented detailing the occurrence of the pitchfork bifurcation in each of the aspect ratios considered, and the resulting flow patterns are described. A flow visualization study is used to validate the numerical observations. Computed local and mean heat transfer coefficients are also presented and compared with results obtained when flow symmetry is assumed. Differences in local values of the Nusselt number between asymmetric and symmetric solutions are found to be more than 500 percent due to the shifting of the buoyancy-driven cells. [S0022-1481(00)02503-2]

Uneven Wall Temperature Effect on Local Heat Transfer in a Rotating Two-Pass Square Channel With Smooth Walls

1993 ◽  
Vol 115 (4) ◽  
pp. 912-920 ◽  
Author(s):  
J.-C. Han ◽  
Y.-M. Zhang ◽  
Kathrin Kalkuehler
Keyword(s):  
Heat Transfer ◽  
Wall Temperature ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Diameter Ratio ◽  
Transfer Coefficients ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
Buoyancy Forces ◽  
Flow Heat

The influence of uneven wall temperature on the local heat transfer coefficient in a rotating, two-pass, square channel with smooth walls is investigated for rotation numbers from 0.0352 to 0.352 by varying Reynolds numbers from 25,000 to 2500. The two-pass square channel, composed of 12 isolated copper sections, has a length-to-hydraulic diameter ratio of 12. The mean rotating radius to the channel hydraulic diameter ratio is kept at a constant value of 30. Three cases of thermal boundary conditions are studied: (A) four walls at the same temperature, (B) four walls at the same heat flux, and (C) trailing wall hotter than leading with side walls unheated and insulated. The results for case A of four walls at the same temperature show that the first channel (radial outward flow) heat transfer coefficients on the leading surface are much lower than that of the trailing surface due to the combined effect of Coriolis and buoyancy forces. The second channel (radial inward flow) heat transfer coefficients on the leading surface are higher than that of the trailing surface. The difference between the heat transfer coefficients for the leading and trailing surface in the second channel is smaller than that in the first channel due to the opposite effect of Coriolis and buoyancy forces in the second channel. However, the heat transfer coefficients on each wall in each channel for cases B and C are higher than case A because of interactions between rotation-induced secondary flows and uneven wall temperatures in cases B and C. The results suggest that the effect of uneven wall temperatures on local heat transfer coefficients in the second channel is greater than that in the first channel.

Laminar and Transitional Boundary Layer Structures in Accelerating Flow With Heat Transfer

1986 ◽  
Vol 108 (1) ◽  
pp. 116-123 ◽  
Author(s):  
K. Rued ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Gas Turbine ◽  
Turbine Blades ◽  
Pressure Gradients ◽  
Transfer Coefficients ◽  
Gas Turbine Blades ◽  
Heat Transfer Coefficients ◽  
Layer Structures ◽  
Flow Heat

The accurate prediction of heat transfer coefficients on cooled gas turbine blades requires consideration of various influence parameters. The present study continues previous work with special efforts to determine the separate effects of each of several parameters important in turbine flow. Heat transfer and boundary layer measurements were performed along a cooled flat plate with various freestream turbulence levels (Tu = 1.6−11 percent), pressure gradients (k = 0−6 × 10−6), and cooling intensities (Tw/T∞ = 1.0−0.53). Whereas the majority of previously available results were obtained from adiabatic or only slightly heated surfaces, the present study is directed mainly toward application on highly cooled surfaces as found in gas turbine engines.

Local Two-Phase Flow Heat Transfer in Plate Heat Exchangers

2007 ◽  
Author(s):  
Stephan Kabelac ◽  
Sebastian W. Freund
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Local Heat ◽  
Theoretical Development ◽  
Condensation Process ◽  
Vapor Quality ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Evaporation And Condensation ◽  
Flow Heat

Experimental results on quasi-local heat transfer coefficients for evaporation and condensation in PHEs related to vapor quality, mass flow rate and heat flux are presented in this paper. The data is obtained from a refrigeration cycle involving a PHE evaporator and a PHE condenser with a secondary fluid loop. The considered refrigerants are ammonia and R-134a. Evaporator and condenser are equipped with multiple thermocouples along the plates, which allow for the deduction of local heat flux and heat transfer coefficients on seven subsections of the plates. The data resolves for the first time the complete evaporation and condensation process along a plate channel and thus may contribute to the understanding of flow distribution and heat transfer mechanisms. The results show an increase of heat transfer coefficients with the vapor quality and the effects of mass flux and heat flux. The results conclude that parallel flow arrangement is advantageous for evaporation while counter flow enhances condensation heat transfer. Plates with low pitch angle chevron corrugations increase the evaporation. Comparisons with the limited available data from literature and various correlations indicate the need for further theoretical development. The data may be suitable for developing correlations of the thermo-hydraulic performance of plate evaporators and condensers as a function of flow, heat flux and plate parameters, which are not established in literature.

Multi-Jet Impingement Heat Transfer With a Dimple-Pimple Patterned Jet Plate

2020 ◽  
Author(s):  
Husam Zawati ◽  
Gaurav Gupta ◽  
Yakym Khlyapov ◽  
Erik Fernandez ◽  
Jayanta Kapat ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Turbulence Models ◽  
Jet Impingement ◽  
Underlying Mechanism ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Air Jets ◽  
Impingement Heat Transfer ◽  
Definition Of

Abstract The objective of the present study is the evaluation of the heat transfer difference between a novel jet plate configuration and a conventional flat jet orifice plate. Physical mechanisms that lead to a change in Nusselt number when comparing both configurations are discussed in two regions: impingement and crossflow. In the presented work, both plates with identical inline arrays of (20 × 26) circular air jets impinging orthogonally on a flat target comprised of 20 segments parallel to the jet orifice plates, are studied. The first is a staggered configuration of a pimple-dimple (convex-concave) plate. This plate features two jet diameters: (a) 4.63 mm emanating from negative sphere of 14.63 mm in radius inward imprint; (b) 2.19 mm emanating from a positive sphere of 17.07 mm in radius, protruding from the base of the plate. The second jet plate is flat, which serves as a baseline for the heat transfer study. This plate has a constant jet orifice diameters of 3.49 mm, found based on the definition of total average open area of the first plate (NPR configuration). Heat transfer characteristics and turbulent flow structures are investigated over jet-averaged Reynolds numbers (Reav,j) of 5,000, 7,000, and 9,000. Jet-to-plate distance (Z/Dj) is varied between (2.4 – 6.0) jet diameters. A numerical study is carried out to compare various turbulence models (κε-EB, κε-Lag EB, κε-v2f, κω-SST, RST). Numerical simulations are analyzed in detail to explain the underlying mechanism of heat transfer enhancement, related to such geometries. The convex-concaved plate yields lower globally-averaged heat transfer coefficients when compared to a flat jet plate in the impingement region. However, enhancement up to 23% is seen in the crossflow region, where the crossflow effects are dominant in a maximum-crossflow configuration.

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