Investigation of entropy generation in a helically coiled tube in flow boiling condition under a constant heat flux

2015 ◽  
Vol 60 ◽  
pp. 217-233 ◽  
Author(s):  
Mohammad Ali Abdous ◽  
Hamid Saffari ◽  
Hasan Barzegar Avval ◽  
Mohsen Khoshzat
Keyword(s):  
Heat Flux ◽  
Entropy Generation ◽  
Flow Boiling ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Coiled Tube ◽  
Helically Coiled Tube

Pressure Drop Characteristics of Nanofluid Flow in a Horizontal Coiled Tube Under Constant Heat Flux

2010 ◽  
Author(s):  
M. A. Akhavan-Behabadi ◽  
S. M. Hashemi
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Mass Velocity ◽  
Constant Heat Flux ◽  
Electrical Heating ◽  
Fluid Temperature ◽  
Constant Heat ◽  
Base Oil ◽  
Coiled Tube ◽  
Helically Coiled Tube

In the present study, an investigation of pressure drop characteristics of CuO-Base oil nanofluid laminar flow inside a horizontal helically coiled tube with constant heat flux boundary condition has been experimentally carried out. The nanofluid is prepared by dispersion of CuO nanoparticles in base oil and stabilized by means of an ultrasonic device. Particle weight fraction is ranging from 0 to 2%. The uniform and constant heat flux produced by an electrical heating coil wrapped around the coiled tube. The required data were acquired for laminar fully developed regime. The effect of different parameters such as fluid temperature, nanofluid particles concentration and mass velocity on the pressure drop characteristics in helically coiled tube for laminar fully developed regime is investigated. The results show that by using the helically coiled tube instead of the straight one, the pressure drop is increased. Also, the pressure drop increasing is happened by using nanofluid instead of base fluid. However, this increase is small compared to the increase resulted by using helically coiled tube. Observations also show that by increasing of mass velocity and concentration of nanoparticles in nanofluid, the pressure drop increasing is more pronounced.

Entropy Generation Minimization of Fully Developed Internal Convective Flows With Constant Heat Flux

2003 ◽  
Author(s):  
Eric B. Ratts ◽  
Atul G. Raut
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
Entropy Generation ◽  
Cross Sections ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Entropy Generation Minimization

This paper addresses the thermodynamic optimum of single-phase convective heat transfer in fully developed flow for uniform and constant heat flux. The optimal Reynolds number is obtained using the entropy generation minimization (EGM) method. Entropy generation due to viscous dissipation and heat transfer dissipation in the flow passage are summed, and then minimized with respect to Reynolds number based on hydraulic diameter. For fixed mass flow rate and fixed total heat transfer rate, and the assumption of uniform heat flux, an optimal Reynolds number for laminar as well as turbulent flow is obtained. In addition, the method quantifies the flow irreversibilities. It was shown that the ratio of heat transfer dissipation to viscous dissipation at minimum entropy generation was 5:1 for laminar flow and 29:9 for turbulent flow. For laminar flow, the study compared non-circular cross-sections to the circular cross-section. The optimal Reynolds number was determined for the following cross-sections: square, equilateral triangle, and rectangle with aspect ratios of two and eight. It was shown that the rectangle with the higher aspect ratio had the smallest optimal Reynolds number, the smallest entropy generation number, and the smallest flow length.

scholarly journals Entropy Generation during Turbulent Flow of Zirconia-water and Other Nanofluids in a Square Cross Section Tube with a Constant Heat Flux

Entropy ◽  
2014 ◽  
Vol 16 (11) ◽  
pp. 6116-6132 ◽  
Author(s):  
Hooman Yarmand ◽  
Goodarz Ahmadi ◽  
Samira Gharehkhani ◽  
Salim Kazi ◽  
Mohammad Safaei ◽  
...  
Keyword(s):  
Heat Flux ◽  
Turbulent Flow ◽  
Cross Section ◽  
Entropy Generation ◽  
Constant Heat Flux ◽  
Constant Heat

Laminar Entropy Generation Over a Flat Plate With Isothermal and Constant Heat Flux Boundary Conditions Using the Von Ka´rma´n Integral Method

Volume 1 ◽  
2004 ◽  
Author(s):  
Eric B. Ratts ◽  
J. Steven Brown
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boundary Conditions ◽  
Flat Plate ◽  
Entropy Generation ◽  
Single Phase ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Fundamental Study ◽  
Flux Boundary Conditions

This paper is a fundamental study on the irreversibility of single-phase laminar convective heat transfer over a flat plate with isothermal and constant heat flux boundary conditions. It quantifies the losses due to viscous momentum transfer losses and heat transfer losses and presents the irreversibility of the convective flow based on the entropy generation (EG) method. This paper determines the entropy generation for incompressible, single phase, laminar flow for large and small Prandtl numbers over a flat plate with isothermal and constant heat flux boundary conditions using von Ka´rma´n’s integral theory.

Experimental study on critical heat flux during flow boiling of R134a in a vertical helically coiled tube

2020 ◽  
Vol 234 (15) ◽  
pp. 3094-3101
Author(s):  
Xiaojuan Niu ◽  
Huaijie Yuan ◽  
Liang Zhao
Keyword(s):  
Experimental Study ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Wall Temperature ◽  
Mass Flux ◽  
Flow Boiling ◽  
Vapor Quality ◽  
Coiled Tube ◽  
Helically Coiled Tube ◽  
System Pressure

This paper carried out an experimental study on the critical heat flux during flow boiling of R134a in a vertical helically coiled tube. The length, inner diameter, coil diameter, and pitch of the test tube were 1.85 m, 8 mm, 205 mm, and 25 mm, respectively. Experiments cover the mass flux range of 190–400 kg·m−2·s−1, heat flux of 15–55 kW·m−2, inlet pressure of 0.8–1.1 MPa, and inlet vapor quality of 0.01–0.35. The effects of critical heat flux identification method, mass flux, system pressure, and inlet vapor quality on critical heat flux were presented. The critical heat flux obtained by the wall temperature rise method was larger than that obtained by the wall temperature oscillation method. The deviation of the critical heat flux corresponding to two methods, including wall temperature rises sharply above 10 ℃ and wall temperature drastic oscillation, was about 20% under the present experimental conditions. The critical heat flux increased with mass flux while it decreased with the inlet vapor quality and pressure. The experiment data were compared with four existing empirical correlations. A new correlation is proposed for critical heat flux prediction in vertical helical tubes.

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