scholarly journals Gradient heat flux measurement during condensation at the surfaces of pipes

2019 ◽  
Vol 140 ◽  
pp. 06006
Author(s):  
Sergey Sapozhnikov ◽  
Vladimir Mityakov ◽  
Alexander Babich ◽  
Elza Zainullina
Keyword(s):  
Heat Flux ◽  
Local Heat Transfer ◽  
Flux Measurement ◽  
Local Heat ◽  
Steam Condensation ◽  
Transfer Coefficients ◽  
Pipe Length ◽  
Heat Transfer Coefficients ◽  
Heat Flux Measurement ◽  
New Information

Gradient heat flux measurement was used to study steam condensation at the inner and outer surfaces of pipes. Experimental setups were developed, manufactured and tested. The setups were able to incline the pipes for different angles relative to vertical and to rotate them around their main axes. Local heat transfer coefficients (HTC) along the pipe length and perimeter were determined. Formation and motion of condensate film were studied. The results are corresponding to classical ideas and give us some new information.

Investigation of Buoyancy Effects in Asymmetrically Heated Near-Critical Flows of Carbon Dioxide in Horizontal Microchannels Using Infrared Thermography

2021 ◽  
Author(s):  
Lindsey V. Randle ◽  
Brian M. Fronk
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Heat Flux ◽  
Infrared Thermography ◽  
Test Section ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Parallel Microchannels

Abstract In this study, we use infrared thermography to calculate local heat transfer coefficients of top and bottom heated flows of near-critical carbon dioxide in an array of parallel microchannels. These data are used to evaluate the relative importance of buoyancy for different flow arrangements. A Joule heated thin wall made of Inconel 718 applies a uniform heat flux either above or below the horizontal flow. A Torlon PAI test section consists of three parallel microchannels with a hydraulic diameter of 923 μm. The reduced inlet temperature (TR = 1.006) and reduced pressure (PR = 1.03) are held constant. For each heater orientation, the mass flux (520 kgm−2s−2 ≤ G ≤ 800 kgm−2s−2) and heat flux (4.7 Wcm−2 ≤ q″ ≤ 11.1 Wcm−2) are varied. A 2D resistance network analysis method calculates the bulk temperatures and heat transfer coefficients. In this analysis, we divide the test section into approximately 250 segments along the stream-wise direction. We then calculate the bulk temperatures using the enthalpy from the upstream segment, the heat flux in a segment, and the pressure. To isolate the effect of buoyancy, we screen the data to omit conditions where flow acceleration may be important or where relaminarization may occur. In the developed region of the channel, there was a 10 to 15 percent reduction of the local heat transfer coefficients for the upward heating mode compared to downward heating with the same mass and heat fluxes. Thus buoyancy effects should be considered when developing correlations for these types of flow.

Using Gradient Heat Flux Measurement to Experimentally Determine Local Heat Transfer Coefficient on Combustion Chamber Surface in a Diesel Engine

2019 ◽  
pp. 87-96
Author(s):  
V.B. Sapozhnikov ◽  
V.Yu. Mityakov ◽  
A.V. Mityakov ◽  
A.V. Vintsarevich ◽  
D.V. Gerasimov
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Combustion Chamber ◽  
Local Heat Transfer ◽  
Flux Measurement ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Engine Operation ◽  
Heat Transfer Coefficients

We used gradient thermometry to determine local heat transfer coefficients on the fire deck surface. We studied two modes of engine operation, that is, motored and fired. We show that the heat transfer coefficient distribution over the fire deck surface is inhomogeneous. Our investigation results may be used to validate existing models of heat transfer in a combustion chamber.

Local Heat Transfer Coefficients and Pressure Drop During Evaporation in a Smooth Horizontal Tube

2002 ◽  
Author(s):  
C. Aprea ◽  
A. Greco ◽  
G. P. Vanoli
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Mass Flux ◽  
Local Heat Transfer ◽  
Horizontal Tube ◽  
Local Heat ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

R22 is the most widely employed HCFC working fluid in vapour compression plant. HCFCs must be replaced within 2020. Major problems arise with the substitution of the working fluids, related to the decrease in performance of the plant. Therefore, extremely accurate design procedures are needed. The relative sizing of each of the components of the plant is crucial for cycle performance. For this reason, the knowledge of the new fluids heat transfer characteristics in condensers and evaporators is required. The local heat transfer coefficients and pressure drop of pure R22 and of the azeotropic mixture R507 (R125-R143a 50%/50% in weight) have been measured during convective boiling. The test section is a smooth horizontal tube made of a with a 6 mm I.D. stainless steel tube, 6 m length, uniformly heated by Joule effect. The effects of heat flux, mass flux and evaporation pressure on the heat transfer coefficients are investigated. The evaporating pressure varies within the range 3 ÷10 bar, the refrigerant mass flux within the range 200 ÷ 1000 kg/m2s, the heat flux within 0 ÷ 44 kW/m2. A comparison have been carried out between the experimental data and those predicted by means of the most credited literature relationships.

Modeling Bubble Growth in Micro-Channel Cooling Systems

2007 ◽  
Author(s):  
Joshua L. Nickerson ◽  
Martin Cerza ◽  
Sonia M. F. Garcia
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Conduction Equation ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

The solution of the heat conduction equation in the liquid layer beneath a moving bubble’s base and the resulting local heat transfer coefficient are presented. An analytical model was constructed using separation of variables to solve the heat conduction equation for the thermal profile in the liquid film beneath the base of a bubble moving through a microchannel at a given velocity. Differentiating the resulting liquid thermal profile and applying the standard definition for the local heat transfer coefficient resulted in a solution for local heat transfer coefficient as a function of bubble length. Analysis included varying pertinent parameters such as film thickness beneath the bubble base, wall heat flux, and superheated temperature in the microchannel. Water and FC-72 were analyzed as prospective coolant fluids. Analytical data revealed that as the superheated temperature in the microchannel increases, local heat transfer coefficients increase and arrive at a higher steady-state value. Increasing wall heat flux achieved the same result, while increasing film thickness resulted in lower heat transfer coefficients. The model indicated that water had superior performance as a coolant, provided the dielectric fluid (FC-72) is not mandated.

scholarly journals Investigation of flow and heat transfer at the circular fins

2018 ◽  
Vol 245 ◽  
pp. 06001 ◽  
Author(s):  
Vladimir Mityakov ◽  
Andrey Gusakov ◽  
Vladimir Seroshtanov ◽  
Michail Grekov
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Thermal Imaging ◽  
Flux Measurement ◽  
Transfer Coefficients ◽  
Water Steam ◽  
Heat Transfer Coefficients ◽  
Heat Flux Measurement ◽  
Comprehensive Method ◽  
Flow And Heat Transfer

For simultaneous investigation of heat transfer and hydraulic parameters of finned circular tube is proposed to connect PIV (Particle Image Velocimetry) method and thermal imaging with gradient heat flux measurement. In the first series of experiments, the hollow fin was investigated. The hollow fin was heated with saturated water steam and its isothermal surface simulated the ideal (isothermal) fin. The solid fin made of titanium alloy was investigated in similar regimes for comparison. In the second series, the influence of distance between fins on the heat transfer coefficients (HTC) at the circular fin, mounted on a circular cylinder was studied. The unique Gradient Heat Flux Sensors (GHFSs) were installed at different places of the fin surface. Comprehensive method including heat flux measurement, PIV and thermal imaging allows to study flow and heat transfer at the surface of the fin in real time. Possibility of complex study of flow and heat transfer for non-isothermal fins is shown.

scholarly journals Study of condensation at the surfaces of tube with gradient heat flux measurement

2018 ◽  
Vol 245 ◽  
pp. 06010 ◽  
Author(s):  
Sergey Sapozhnikov ◽  
Vladimir Mityakov ◽  
Alexandr Babich ◽  
Elza Zainullina
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Cooling Water ◽  
Flux Measurement ◽  
Transfer Coefficients ◽  
Water Steam ◽  
Condensate Film ◽  
Heat Transfer Coefficients ◽  
Heat Flux Measurement ◽  
Minimal Distortion

Gradient heat flux measurement is used for study of heat transfer during condensation of water steam at inner and outer surfaces of tube. Experimental setups allow producing experiments with minimal distortion of condensate film flow. Experiments were carried out for different directions of steam and cooling water flows and for different angles of tube inclination relative to the vertical. Heat transfer coefficients and their change along the length and perimeter of tube were measured. The obtained data allow to study formation of condensate film and parameters of film motion. The results are corresponding to classical ideas.

Local Friction and Heat Transfer Behavior of Water in a Turbulent Pipe Flow With a Large Heat Flux at the Wall

1995 ◽  
Vol 117 (2) ◽  
pp. 283-288 ◽  
Author(s):  
E. Choi ◽  
Y. I. Cho
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Turbulent Pipe Flow ◽  
Turbulent Heat Transfer ◽  
Transfer Coefficients ◽  
Viscosity Change ◽  
Heat Transfer Coefficients ◽  
Large Heat

The present study investigated the behavior of friction and heat transfer coefficients of water flowing turbulently in a relatively long (i.e., 950 diameter long) circular pipe. When a large heat flux was applied at the wall, the viscosity of water significantly decreased along the axial direction due to the increasing temperature of water. A concept of a “redeveloping region” was introduced, where the local heat transfer coefficient increased while the local friction coefficient decreased due to the above-mentioned viscosity change. The present study proposed the use of local bulk-mean temperature to determine local Nusselt numbers by using local Reynolds (ReLB) and Prandtl numbers (PrLB), a method that automatically took into account the effect of axial viscosity change on the evaluation of local heat transfer coefficients. A new turbulent heat transfer correlation for the prediction of the local Nusselt number is given as Nux=0.00425ReLB0.979PrLB0.4(μw/μb)−0.11.

The Effect of Regulating Elements on Convective Heat Transfer along Shaped Heat Exchange Surfaces

2013 ◽  
Vol 34 (1) ◽  
pp. 5-16 ◽  
Author(s):  
Jozef Cernecky ◽  
Jan Koniar ◽  
Zuzana Brodnianska
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Cfd Simulation ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Temperature Fields ◽  
Transfer Coefficients ◽  
Heat Transfer Intensification ◽  
Heat Transfer Coefficients ◽  
Forced Air

Abstract The paper deals with a study of the effect of regulating elements on local values of heat transfer coefficients along shaped heat exchange surfaces with forced air convection. The use of combined methods of heat transfer intensification, i.e. a combination of regulating elements with appropriately shaped heat exchange areas seems to be highly effective. The study focused on the analysis of local values of heat transfer coefficients in indicated cuts, in distances expressed as a ratio x/s for 0; 0.33; 0.66 and 1. As can be seen from our findings, in given conditions the regulating elements can increase the values of local heat transfer coefficients along shaped heat exchange surfaces. An optical method of holographic interferometry was used for the experimental research into temperature fields in the vicinity of heat exchange surfaces. The obtained values correspond very well with those of local heat transfer coefficients αx, recorded in a CFD simulation.

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