scholarly journals Heat Transfer Investigation of Air Flow in Microtubes—Part II: Scale and Axial Conduction Effects

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Ting-Yu Lin ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Scale Effects ◽  
Air Flow ◽  
Tube Length ◽  
Viscous Heating ◽  
Outer Diameter ◽  
Axial Conduction ◽  
Heating Effects ◽  
Nickel Tube ◽  
Inner Diameter

In this paper, the scale effects are specifically addressed by conducting experiments with air flow in different microtubes. Three stainless steel tubes of 962, 308, and 83 μm inner diameter (ID) are investigated for friction factor, and the first two are investigated for heat transfer. Viscous heating effects are studied in the laminar as well as turbulent flow regimes by varying the air flow rate. The axial conduction effects in microtubes are experimentally explored for the first time by comparing the heat transfer in SS304 tube with a 910 μm ID/2005 μm outer diameter nickel tube specifically fabricated using an electrodeposition technique. After carefully accounting for the variable heat losses along the tube length, it is seen that the viscous heating and the axial conduction effects become more important at microscale and the present models are able to predict these effects accurately. It is concluded that neglecting these effects is the main source of discrepancies in the data reported in the earlier literature.

Heat Transfer Investigation of Air Flow in Microtubes—Part I: Effects of Heat Loss, Viscous Heating, and Axial Conduction

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Ting-Yu Lin ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Conduction ◽  
Turbulent Flow ◽  
Heat Loss ◽  
Air Flow ◽  
Heat Losses ◽  
Viscous Heating ◽  
Axial Conduction ◽  
Axial Heat ◽  
Axial Heat Conduction

Experiments were conducted to investigate local heat transfer coefficients and flow characteristics of air flow in a 962 μm inner diameter stainless steel microtube (minichannel). The effects of heat loss, axial heat conduction and viscous heating were systematically analyzed. Heat losses during the experiments with gas flow in small diameter tubes vary considerably along the flow length, causing the uncertainties to be very large in the downstream region. Axial heat conduction was found to have a significant effect on heat transfer at low Re. Viscous heating was negligible at low Re, but the effect was found to be significant at higher Re. After accounting for varying heat losses, viscous heating and axial conduction, Nu was found to agree very well with the predictions from conventional heat transfer correlations both in laminar and turbulent flow regions. No early transition to turbulent flow was found in the present study.

Influence of fully submerged permanent magnets in the evaluation of heat transfer and performance analysis of single slope glass solar still

2021 ◽  
pp. 095765092110310
Author(s):  
Ajay Kumar Kaviti ◽  
Akkala Siva Ram ◽  
Amit Kumar Thakur
Keyword(s):  
Heat Transfer ◽  
Permanent Magnets ◽  
Outer Diameter ◽  
Solar Still ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Inner Diameter ◽  
Evaporative Heat Transfer ◽  
And Performance ◽  
Depth Water

In this experimental study, permanent magnets with three different sizes (M-1: 32 mm inner diameter, 70 mm outer diameter and 15 mm thick, M-2: 25 mm inner diameter, 60 mm outer diameter and 10 mm thick, M-3: 22 mm inner diameter, 45 mm outer diameter and 9 mm thick) are fully submerged in the single-slope glass solar still. The performance of magnetic solar stills (MSS) with three different sizes at 2 cm depth water to ensure that magnets are fully submerged is compared with conventional solar still (CSS) at the location 17.3850°N, 78.4867°E. Tiwari model is adapted to calculate the heat transfer coefficients (HTC), internal and exergy efficiencies. MSS with M-1, M-2 and M-3 significantly enhanced the convective, radiative, and evaporative heat transfer rate for the 2 cm depth of water. This is due to the desired magnetic treatment of water, which reduces the surface tension and increases the hydrogen bonds. The MSS's total internal HTC, instantaneous efficiencies led CSS by 25.52%, 28.8%, respectively, with M-1. Having various magnetic fields due to different magnets sizes increases MSS's exergetic efficiency by 33.61% with M-1, 33.76% with M-2, and 42.25% with M-3. Cumulative yield output for MSS with M-1, M-2, and M-3 is 21.66%, 17.64%, 15.78% higher than CSS. The use of permanent magnets of different sizes in the MSS is a viable, economical and straight forward technique to enhance productivity.

The Effect of Fill Volume on Heat Transfer From Air-Cooled Thermosyphons

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Christina A. Pappas ◽  
Paul M. De Cecchis ◽  
Donald A. Jordan ◽  
Pamela M. Norris
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Air Flow ◽  
Condenser Section ◽  
Evaporator Temperature ◽  
Evaporator Section ◽  
Fill Volume ◽  
Inner Diameter ◽  
Cooling Air Flow

The effect of fill volume on the heat transfer performance of a cylindrical thermosyphon with an aspect ratio (ratio of the length of the evaporator section to the inner diameter) of 2.33 immersed in a cooling air flow is investigated. The fill volume was systematically varied from 0% to 70.3% of the volume of the evaporator section in a copper-water thermosyphon having an inner diameter of 19 mm. The condenser section was immersed in a uniform air flow in the test section of an open return wind tunnel. The heat transfer rate was measured as a function of evaporator temperature and fill volume, and these results were characterized by three distinct regions. From 0% to roughly 16% fill volume (Region I), the low rate of heat transfer, which is insensitive to fill volume, suggests that dry out may be occurring. In Region II (extending to approximately 58% fill volume), the heat transfer rate increases approximately linearly with fill volume, and increasing evaporator temperature results in decreased rate of heat transfer. Finally, in Region III (from roughly 58–70.3%), the rate of heat transfer increases more rapidly, though still linearly, with fill volume, and increasing evaporator temperature results in increased rate of heat transfer. The thermosyphon rate of heat transfer is greatest at 70.3% fill volume for every evaporator temperature.

Experimental Investigation to Enhance the Heat Transfer in Heat Exchanger by Made Groove in Outer Surface of the Inner Tube

2017 ◽  
Vol 5 (1) ◽  
pp. 1-15
Author(s):  
Zena K. Kadhim ◽  
Safaa Abed Mohammad
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Flow Rate ◽  
Outer Surface ◽  
Hot Water ◽  
Outer Tube ◽  
Copper Tube ◽  
Working Fluid ◽  
Outer Diameter ◽  
Inner Diameter

This study deals with experimental work implementing to recover the benefit by changing the shape of the tube in heat exchanger (HE) and improving the heat transfer using water as the working fluid. The experimental tests were carried out in build and design a complete test system for counter flow heat exchanger. The tested system consisting of a copper tube with (1m) length (17.05) mm inner diameter (19.05) mm outer diameter, fixed concentric within the outer tube was made of a material PVC. With an “inner diameter (ID) (43 mm) and outer diameter (OD) (50 mm)” isolated from the outside by using insulating material to reduce heat loss. The modify tube was manufacture containing transverse grooves with the depth equivalent to the half thickness of the copper tube. The distance between the grooves on the outer surface of the copper tube is take as a ratio between (0.5, 1) from the outer tube diameter. The laboratory experiment use the hot water at a flow rate ranging between (1-5) LPM, passes in the inner copper tube. As well as the cooling water with the mass flow rate ranging between (3-7) LPM. Three temperatures were the hot fluid are the adoption of (40, 50 and 60) oC and (25) oC the cold fluid. The experiment result showed that the improvement for temperature difference ranging from (14.94 % to 43.2 %) for both corrugated tubes with respect to smooth tube.

Experimental Study on Heat Transfer and Fluid Flow in Vertical Rifled

2012 ◽  
Vol 505 ◽  
pp. 524-533 ◽  
Author(s):  
Abdulati Muftah Mohamed Ibrahim ◽  
Bashir Rahuma Elhub ◽  
H. Abas A. Wahab
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Fluid Flow ◽  
Pressure Drop ◽  
Flow Rate ◽  
Smooth Tube ◽  
Enhancement Effect ◽  
Outer Diameter ◽  
Flow Monitoring ◽  
Inner Diameter

In this paper, heat transfer and fluid flow monitoring experiments for pressure drop and efficiency were performed to investigate the fluid flow characteristics of rifled tubes in comparison with a smooth tube. The rifled tube has an outer diameter of 25mm, maximum inner diameter of 18.8 mm; minimum inner diameter of 17.50mm, rib height of 0.6835, rib width of 9.25, helix angles 60 o and the number of starts is four. The smooth tube has an outer diameter of 26.7mm and an inner diameter of 18.88 mm, with a wall thickness of 3.91mm. The experiments were conducted on a vertical orientation of the steel tubes (rifled and smooth) under varying flow rate of 15, 30, 40, 50, 60 and 70. The fluid used is 131.64 litres of water and the initial temperature is 25oC. The fluid is raised to an average temperature of 33oC during the experimental study. During the experiment, it was found that at 360 mins for the smooth tube, an increase in flow rate does not affect the time for the fluid (water) to attain a temperature of 33oC. For the rifled tube, as the flow rate increases, the time for the fluid (water) to attain a temperature of 33oC also increases. This is as a result of the effect of ribbing the tube. The time taken to attain the optimum temperature of 33oC is shorter using the rifled tube than the smooth tube. The rifled tube has heat transfer efficiency higher than the smooth tube. The pressure drop and the energy consumed by using the rifled tube were also found to be less than that of the smooth tube. The pressure drop increase factor was found to be 0.85 in the spirally rifled tube as compared to the smooth tube at the different flow rates. The enhancement effect of ribbing the tube is apparent.

scholarly journals UNSTEADY HEAT TRANSFER IN AN ANNULAR PIPE. PART II: SWIRLING LAMINAR FLOW

2012 ◽  
Vol 12 (6) ◽  
Author(s):  
Kelvin Ho Choon Seng
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Dimensional Analysis ◽  
Transfer Problem ◽  
Axial Flow ◽  
Outer Diameter ◽  
Unsteady Heat Transfer ◽  
Ansys Cfx ◽  
Inner Diameter ◽  
Annular Pipe

The   heat  transfer   problem  in   magnetocaloric regenerators  during  magnetization  has  been  described  and investigated for convective heat transfer by means of axial flow in part I of this series.   This work will focus on enhancing the unsteady heat  transfer using swirling laminar flow generated using axial vanes.   The governing parameters for this  studyare,  the  D*  ratio  (Inner  diameter/Outer  diameter)  and  the swirl number, S.   The study is conducted  using  dimensional analysis and commercial CFD codes provided by ANSYS CFX. The  hydrodynamics and the  heat transfer of the  model are compared with data from similar cases found in literature and is found to be in the vicinity of good agreement.Keywords-  Annular ducts; unsteady heat transfer;  magnetic refrigeration/cooling;   swirling   laminar    flow;    dimensional analysis.

scholarly journals Numerical Investigation of Forced Convection Heat Transfer on a Circular Finned tube with AL2O3-Water Nano Fluid

2018 ◽  
Vol 6 (06) ◽  
Author(s):  
Khudheyer Ahmed F. ◽  
Hameed, .Raghad A.
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Volume Concentration ◽  
Convection Heat Transfer ◽  
Nano Particles ◽  
Outer Diameter ◽  
Convection Heat ◽  
Forced Convection Heat Transfer ◽  
Nano Fluid ◽  
Inner Diameter

This paper presents a three-dimensional numerical analysis to study the laminar forced convection heat transfer and flow characteristics of AL2O3–water Nano fluid with Solid particles less than 100 nm through a tube with 1m Length and 25 mm inner diameter and 30mm outer diameter contains circular fins with 30mm inner diameter and 50mm outer diameter with thickness of 2mm , investigated numerically by using finite volume method, models using ANSYS 14.5 Based on the single-phase approach, The flow of fluid is assumed to be incompressible, steady and laminar with various thermo physical properties according to volume concentration of Nano particles The Navies Stokes equations along with the energy equation have been solved by using SIMPLE algorithm Technique. The effects of different parameters such as nanoparticle volume concentration (1%, 3% and 5%), and Reynolds number are varied from (500 - 2100) for various axial locations of tube with AL2O3–water fluids and the effect of different values of velocity at the tube inlet will be studied during this paper. Where the results showed that the coefficient of heat transfer increases when the concentration of Nano fluid increase.

NUMERICAL STUDY OF HEAT TRANSFER AND AIR FLOW IN HEATED GREENHOUSES

2008 ◽  
Author(s):  
Nadia Dihmani ◽  
Ahmed Mezrhab ◽  
Larbi Elfarh ◽  
Hicham Bouali ◽  
Hassan Naji
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Air Flow
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