Effect of Surface Roughness on Heat Transfer from Horizontal Immersed Tubes in a Fluidized Bed

1979 ◽  
Vol 101 (3) ◽  
pp. 397-403 ◽  
Author(s):  
N. S. Grewal ◽  
S. C. Saxena
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Fluidized Bed ◽  
Total Heat ◽  
Smooth Tube ◽  
Total Heat Transfer ◽  
Maximum Heat ◽  
The Heat Transfer Coefficient ◽  
Outside Diameter

Experimental results of the total heat transfer coefficient between 12.7 mm dia copper tubes with four different rough surfaces and glass beads of three different sizes as taken in a 0.305 m × 0.305 m square fluidized bed as a function of fluidizing velocity are reported. The comparison of results for the rough and technically smooth tubes suggests that the heat transfer coefficient strongly depends on the ratio of pitch (Pf) to the average particle diameter (dp), where Pf is the distance between the two corresponding points on consecutive threads or knurls. By the proper choice of (Pf/dp) ratio, the maximum total heat transfer coefficient for V-thread tubes (hwfb) can be increased by as much as 40 percent over the value for a smooth tube with the same outside diameter. However, for values of (Pf/dp) less than 0.95, the maximum heat transfer coefficient for the V-thread rough tubes is smaller than the smooth tube having the same outside diameter. The qualitative variation of the heat transfer coefficient for rough tubes with (Pf/dp) is explained on the basis of the combined effect of contact geometry between the solid particles and the heat transfer surface, and the solids renewal rate at the surface. The present findings are critically compared with somewhat similar investigations from the literature on the heat transfer from horizontal or vertical rough tubes and tubes with small fins.

scholarly journals Enhancement of Temperature Distribution and Heat Transfer Coefficient of Ribbed Tube by Simulation

2021 ◽  
Vol 7 (1) ◽  
pp. 21-28
Author(s):  
Rahul Kunar ◽  
Dr Sukul Lomash
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Temperature Distribution ◽  
Transfer Coefficient ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Flow Analysis ◽  
Total Heat ◽  
Total Heat Transfer ◽  
The Heat Transfer Coefficient

The heat transfer from surface may in general be enhanced by increasing the heat transfer coefficient between a surface and its surrounding or by increasing heat transfer area of the surface or by both. The main objective of the study and calculate the total heat transfer coefficient. Improve the heat transfer rate by using ANSYS CFD. During the CFD calculations of the flow in internally ribbed tubes. And calculated the temperature distribution and pressure inside the tube by using ansys. The model was created using CatiaV5 and meshed with Ansys, and the flow analysis is done with Ansys 19.2. The results showing that the heat transfer is increased. The enthalpy and temperature increase with flow is advancing when compare with normal boiler tube. In this study the total heat transfer rate of the pipe increase with the increase the rib height. Total heat transfer rate increase up to 7.7kw. The study show that the improvement in furnace heat transfer can be achieved by changing the internal rib design.

Heat Transfer and Fouling Performance During Falling Film Evaporation in Vertical Porous Tubes

2020 ◽  
Author(s):  
Lei Wang ◽  
Weiyu Tang ◽  
Limin Zhao ◽  
Wei Li
Keyword(s):  
Heat Transfer ◽  
Stainless Steel ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Smooth Tube ◽  
Outer Diameter ◽  
Falling Film ◽  
Film Evaporation ◽  
Falling Film Evaporation ◽  
The Heat Transfer Coefficient

Abstract An experimental investigation was conducted on falling film evaporation along two porous tubes, which were sintered by stainless-steel powder with a diameter of 0.45 and 1 um, respectively. The test section is a 2 m long sintered tube with an outer diameter of 25 mm and a wall thickness of 2 mm. During the experiment, the pressure inside the tube was maintained at 1 atm, the inlet temperature was 373 K, and mass flux ranged from 0.51 to 1.36 kg/ (m s). Conditions of the steam outside the pipe, which was the heat source, were fixed, while the fouling tests were carried out at a constant mass flow of 0.74 kg/ (m s) using high-concentration brine as work fluid. The overall heat transfer coefficient under different working conditions was tested and compared with the stainless steel smooth tube of the same dimensions. The heat transfer coefficient of the two porous stainless tubes are about 35% and 20% lower than that of the smooth one, showing an inferior effect because the steam in the pores of the pipe wall during the infiltration process will reduce the heat conductivity. The heat transfer coefficient of the smooth tube deteriorated severely due to the deposition of calcium carbonate, which had little effect on the sintered tubes. Besides, the fouling weight of porous tubes is 2.01 g and 0 g compared with 5.52 g of the smooth tube.

scholarly journals Comparison of heat transfer performance of ZnO-PG, α-Al2O3-PG, and γ-Al2O3-PG nanofluids in car radiator

2019 ◽  
Vol 9 ◽  
pp. 184798041987646 ◽  
Author(s):  
XiaoRong Zhou ◽  
Yi Wang ◽  
Kai Zheng ◽  
Haozhong Huang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Propylene Glycol ◽  
Flow Rate ◽  
Volume Concentration ◽  
Maximum Heat ◽  
Cooling Performance ◽  
Maximum Heat Transfer ◽  
The Heat Transfer Coefficient

In this study, the cooling performance of nanofluids in car radiators was investigated. A car radiator, temperature measuring instrument, and other components were used to set up the experimental device, and the temperature of nanofluids passing through the radiator was measured by this device. Three kinds of nanoparticles, γ-Al2O3, α-Al2O3, and ZnO, were added to propylene glycol to prepared nanofluids, and the effects of nanoparticle size and type, volume concentration, initial temperature, and flow rate were tested. The results indicated that the heat transfer coefficients of all nanofluids first increased and then decreased with an increase in volume concentration. The ZnO-propylene glycol nanofluid reached a maximum heat transfer coefficient at 0.3 vol%, and the coefficient decreased by 25.6% with an increase in volume concentration from 0.3 vol% to 0.5 vol%. Smaller particles provided a better cooling performance, and the 0.1 vol% γ-Al2O3-propylene glycol nanofluid had a 19.9% increase in heat transfer coefficient compared with that of α-Al2O3-propylene glycol. An increase in flow rate resulted in a 10.5% increase in the heat transfer coefficient of the 0.5 vol% α-Al2O3-propylene glycol nanofluid. In addition, the experimental temperature range of 40–60°C improved the heat transfer coefficient of the 0.2 vol% ZnO-propylene glycol nanofluid by 46.4%.

Effect of Liquid Properties on Phase-Change Heat Transfer in Porous Wick Structures

2015 ◽  
Vol 138 (3) ◽  
Author(s):  
Steve Q. Cai ◽  
Avijit Bhunia
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Phase Change ◽  
Transfer Coefficient ◽  
Mode Transition ◽  
Maximum Heat ◽  
Maximum Heat Flux ◽  
Phase Change Heat Transfer ◽  
The Heat Transfer Coefficient

In a heat pipe, operating fluid saturates wick structures system and establishes a capillary-driven circulation loop for heat transfer. Thus, the thermophysical properties of the operating fluid inevitably impact the transitions of phase-change mode and the capability of heat transfer, which determine both the design and development of the associated heat pipe systems. This article investigates the effect of liquid properties on phase-change heat transfer. Two different copper wick structures, cubic and cylindrical in cross section, 340 μm in height and 150 μm in diameter or width, are fabricated using an electroplating technique. The phase-change phenomena inside these wick structures are observed at various heat fluxes. The corresponding heat transfer characteristics are measured for three different working liquids: water, ethanol, and Novec 7200. Three distinct modes of the phase-change process are identified: (1) evaporation on liquid–vapor interface, (2) nucleate boiling with interfacial evaporation, and (3) boiling enhanced interface evaporation. Transitions between the three modes depend on heat flux and liquid properties. In addition to the mode transition, liquid properties also dictate the maximum heat flux and the heat transfer coefficient. A quantitative characterization shows that the maximum heat flux scales with Merit number, a dimensionless number connecting liquid density, surface tension, latent heat of vaporization, and viscosity. The heat transfer coefficient, on the other hand, is dictated by the thermal conductivity of the liquid. A complex interaction between the mode transition and liquid properties is reflected in Novec 7200. In spite of having the lowest thermal conductivity among the three liquids, an early transition to the mode of the boiling enhanced interface evaporation leads to a higher heat transfer coefficient at low heat flux.

scholarly journals Heat transfer in the vortex zone of a cyclone-bed chamber of furnace unit with fluidized bed

2019 ◽  
Vol 64 (1) ◽  
pp. 87-97
Author(s):  
E. A. Pitsuha ◽  
E. K. Buchilko ◽  
Yu. S. Teplitskii ◽  
D. S. Slizhuk
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Fluidized Bed ◽  
Flow Rate ◽  
Radial Direction ◽  
Air Flow ◽  
Air Flow Rate ◽  
Outlet Hole ◽  
The Heat Transfer Coefficient

An experimental investigation of the heat-transfer coefficient to a spherical probe in a cyclone-bed chamber with fluidized bed in the “cold” and “hot” regimes has been carried out. The heat-transfer coefficient was determined by the regular thermal regime. The dependences of the heat-transfer coefficient in the vortex-bed furnace on the various parameters: the diameter of the outlet hole, the air flow rate, the share of the bottom blast and the location of the probe were determined. It is revealed that in the “cold” regime the heat-transfer coefficient has practically constant value in the radial direction, it almost does not depend on the diameter of the outlet hole and the share of the bottom blast and depends significantly on the position of the probe along the height of the furnace and the air flow rate. The effect of flow swirling on the heat-transfer coefficient in a cyclone-bed chamber with fluidized bed is determined. When the fuel burns (“hot” regime), the heat-transfer coefficient is not constant in the radial direction and accept the maximum values in the central area of the chamber. At the same time, the part of conductive-convective component in the total heat-transfer coefficient to the spherical probe, depending on its radial position, is estimated at 40–70 %. The results can be used in the design and creation of modern high-efficiency furnaces for burning local solid biofuels.

scholarly journals Experimental Research and Simulation of Fin and Tube Heat Exchanger

2017 ◽  
Vol 9 (4) ◽  
pp. 451-461
Author(s):  
Artur Rubcov ◽  
Sabina Paulauskaitė ◽  
Violeta Misevičiūtė
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Heat Exchangers ◽  
Ventilation System ◽  
Experimental Tests ◽  
Maximum Heat ◽  
Tube Heat Exchanger ◽  
The Heat Transfer Coefficient

The paper provides the results of experimental and theoretical test of a wavy fin and tube heat exchanger used to cool air in a ventilation system when the wavy fin of the heat exchanger is dry and wet. The experimental tests, performed in the range of 1000<Re<4500 of the Reynolds number applying LMTD-LMED methodology, determined the dependency of the heat transfer coefficient on the supplied air flow rate with the varying geometry of the heat exchanger (the number of tube rows, the distance between fins, the thickness of the fin and the diameter of the tube). The experimental tests were performed on 9 heat exchangers in heating and 6 heat exchangers in cooling mode. After processing the results of the experimental tests, empirical equation defining the characteristics of the heat transfer coefficient of all heat exchangers were derived. The maximum heat transfer coefficient deviation is 11.6 percent. The correction factor of the wet fin (Lewis number) depending on the number of Reynolds, which ranges from 0.75 to 1.1 also is determined. Maximum capacity deviation equals 3.7 percent. The obtained equations can only be applied to a certain group of heat exchangers (with the same shape of fins or the distance between the tubes). The results of the experimental test and simulation with ANSYS program are compared and the heat transfer coefficients vary from 6.5 to 11.4 percent.

Effects of Pitch and Depth on the Condensation Heat Transfer of R-134a Flowing Through Corrugated Tubes

2011 ◽  
Author(s):  
Suriyan Laohalertdecha ◽  
Somchai Wongwises
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Condensation Heat Transfer ◽  
Smooth Tube ◽  
Maximum Heat ◽  
Frictional Pressure Drop ◽  
R 134A

The effects of pitch and depth on the condensation heat transfer of R-134a flowing inside corrugated tubes are experimentally investigated. The test section is a horizontal tube-in-tube heat exchanger. The refrigerant flows in the inner tube and the water flows in the annulus. The length of heat exchanger is 2 m. A smooth tube and corrugated tubes having inner diameters of 8.7 mm are used as an inner tube. The corrugation pitches used in this study are 5.08, 6.35, and 8.46 mm. Similarly, the corrugation depths are 1, 1.25, and 1.5 mm. The effects of corrugation pitch and depth on tube wall temperature, heat transfer coefficient and frictional pressure drop are discussed. The results illustrate that the maximum heat transfer coefficient and frictional pressure drop obtained from the corrugated tube are up to 50% and 70% higher than those obtained from the smooth tube, respectively.

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