Begell House Inc.
Heat Transfer Research
HTR
1064-2285
48
16
2017
EFFECTS OF WALL CONJUGATION AND FLUID AXIAL CONDUCTION IN CIRCUMFERENTIALLY PARTLY HEATED PIPES AND MINIPIPES
1433-1458
Ulas
Atmaca
Department of Mechanical Engineering, Selcuk University, 42031 Konya, Turkey
Şefik
Bilir
Department of Mechanical Engineering, Selcuk University, 42031 Konya, Turkey
Ali
Ateş
Department of Mechanical Engineering, Selcuk University, 42031 Konya, Turkey
Transient conjugated heat transfer in circumferentially partly heated thick-walled pipes and minipipes with thermally developing laminar flows is investigated, involving three-dimensional wall conduction and fluid axial conduction. The problem is handled for an initially isothermal, two-regional infinite pipe, for which the upstream region is completely insulated and the downstream region is circumferentially partly insulated by considering an instant increase in the outer wall temperature
of the other circumferential part in the downstream region. Solution is made numerically by a finite-difference method, and a parametric study is conducted to analyze the effects of four defining parameters, namely, the Peclet number, wall-to-fluid thermal conductivity ratio, wall-to-fluid thermal diffusivity ratio, and wall thickness ratio, on heat transfer characteristics. The results show that in both the wall and the fluid sides, besides backward heat transfer due to axial conduction, a large amount of heat is transferred because of angular conduction from the circumferentially heated to the unheated part of the pipe. Wall conjugation highly compensates the effects of partial heating and an important percentage of heat transfer to fluid is realized from the unheated circumferential part of the pipe. The results are also seen to be much affected by the parameter values.
NUMERICAL INVESTIGATION OF CONJUGATE MIXED CONVECTION IN A RECTANGULAR CAVITY WITH HEAT-CONDUCTING WALLS OF FINITE THICKNESS UNDER CONDITIONS OF RADIANT ENERGY SUPPLY
1459-1472
Genii V.
Kuznetsov
National Research Tomsk Polytechnic University, Institute of Power Engineering, Tomsk,
634050, Russia
V. Yu.
Zyubanov
National Research Tomsk Polytechnic University, 30 Lenin Ave., Tomsk, 634050, Russia
Alexander E.
Nee
National Research Tomsk Polytechnic University, 30 Lenin Ave., Tomsk, 634050, Russia
A mathematical modeling of conjugate heat transfer in a semi-open rectangular cavity filled with air and semi-restricted by solid heat-conducting walls of finite thickness is performed under conditions of radiant energy supply in a mixed convection mode. According to the results of numerical modeling, differential (fields of temperature and stream function) and integral (average Nusselt numbers) characteristics of heat exchange have been obtained in a wide range of governing parameters (104 ≤ Ra ≤ 106, 300 ≤ Re ≤ 700). Based on the analysis of temperature and stream functions fields, it was established that the conjugate heat transfer process under study had a significantly unsteady nature. Scale influence of lifting force increasing on isolines of temperature and stream function formation in the air cavity is shown. It was found that an increase in the Rayleigh number leads to a rise in the average Nusselt number in a mixed convection mode.
THERMAL CHARACTERISTICS OF NON-NEWTONIAN POWER-LAW FLUID FLOWS AROUND A CONFINED TRIANGULAR PRISM
1473-1495
Richa
Agarwal
Department of Chemical Engineering, Indian Institute of Technology Roorkee,
Roorkee - 247 667, India
Amit Kumar
Dhiman
Department of Chemical Engineering, Indian Institute of Technology Roorkee,
Roorkee - 247 667, India
The thermal characteristics of non-Newtonian power-law fluid flows in a horizontal channel with a symmetrically built-in
equilateral triangular prism have been examined. Particularly, two-dimensional numerical computations are carried out for Reynolds numbers Re = 1–40, Prandtl numbers Pr = 1–50, blockage ratios β = 0.125–0.5, and power-law indices n = 0.4–1.8. Extensive numerical results on isotherm patterns, average Nusselt number, the Colburn heat transfer factor jh, and the local Nusselt number on the surface of the triangular prism are reported to elucidate the combined effects of Re, Pr, β, and n. The results show that for the fixed Re, Pr, and n, the local and average Nusselt numbers increase with β, except for Re = 1 and Pr = 1, where the opposite trend is observed. Also, the average Nusselt number decreases as the fluid behavior alters from pseudoplastic to Newtonian and finally to dilatant (except for Re = 1, Pr = 1, and β = 0.5 for the range n ≤ 0.6), for the fixed Re, Pr, and β. Further, the jh factor is found to increase with increasing β, for the fixed Re, Pr, and n. The maximum percent enhancements in the average Nusselt number at Pr = 1 with respect to that at Pr = 50 are observed to be approximately 80% for both β = 0.125 and 0.25, and approximately 89% for β = 0.5. Finally, a simple heat transfer correlation is determined for various values of Re, Pr, n, and β.
ENVIRONOMICAL ANALYSIS AND MATHEMATICAL MODELING OF POTATO CHIPS DRYING IN A MODIFIED SOLAR GREENHOUSE DRYER
1497-1514
Om
Prakash
Department of Mechanical Engineering, Birla Institute of Technology, Mesra Ranchi-835215, India
Anil
Kumar
Energy Technology Research Center, Department of Mechanical Engineering, Faculty of Engineering, Prince of Songkla University, Hat Yai, Songkhla 90110, Thailand; Department of Energy (Energy Center), Maulana Azad National Institute of Technology, Bhopal-462003, India
Perapong
Tekasakul
Energy Technology Research Center, Department of Mechanical Engineering, Faculty of Engineering, Prince of Songkla University, Hat Yai, Songkhla 90110, Thailand
A. M.
Abdel-Ghany
Department of Agricultural Engineering, College of Food and Agriculture Sciences, King Saud
University, P.O. Box 2460, Riyadh 11451, Saudi Arabia
I. M.
Al-Helal
Department of Agricultural Engineering, College of Food and Agriculture Sciences, King Saud
University, P.O. Box 2460, Riyadh 11451, Saudi Arabia
In this communication, potato chips drying has been discussed along with the environomical analysis and mathematical modeling. Drying was done in open-sun drying and a modified greenhouse dryer, which operates in active and passive modes. The potato chips were dried with initial moisture content of 75% w.b. to final moisture content of 13.54% w.b. and 13.10% w.b. for a dryer in an active and a passive mode, respectively. Eight standard mathematical models for thin layer drying were studied. A two-term model is found to be most effective as compared to other models in terms of statistical parameters. Environomical analysis represents environmental and economical analysis of the system. Four environmental protection parameters, which are energy payback time (EPBT), embodied energy, CO2 emission, and earned carbon credit have been analyzed. The dryer in an active mode is found to be more efficient for potato chips drying as compared to passive-mode and open-sun drying. The payback period of the dryer in a passive mode (1.25 years) is found to be less than for a dryer in an active mode (1.9 years). The biochemical nutrient contents of dried potato were also examined. Potato chips
dried in dryers possess superior nutrient content as compared to open-sun dried product. However, between two dryers, potato chips dried in the dryer in an active mode are found to be more nutritious as compared to the other. Experimental internal, external, and total uncertainties are 9.90%, 0.50%, and 10.40% for the passive mode and 9.78%, 0.50%, and 10.28% for the active mode, respectively, which are quite acceptable.
NUMERICAL INVESTIGATION OF MELTING PROCESS IN HORIZONTAL SHELL-AND-TUBE PHASE CHANGE MATERIAL STORAGE CONSIDERING DIFFERENT HTF CHANNEL GEOMETRIES
1515-1529
Seyed Soheil Mousavi
Ajarostaghi
Faculty of Mechanical Engineering, Babol Noshirvani University of Technology, Babol, Iran
Mojtaba Aghajani
Delavar
Faculty of Mechanical Engineering, Babol Noshirvani University of Technology, Babol, Iran
Adel
Dolati
Faculty of Mechanical Engineering, Mazandaran University of Science and Technology, Babol,
Iran
This work studies the effect of channel geometries on melting process (charging) in a phase change material (PCM) cylindrical storage. In order to investigate the melting process, different geometries of HTF channel cross section including circular, rectangular, elliptical, square, and diamond-like are considered. The results show that the melting time of 75% of PCM for all models is very close to each other and there is no significant difference. Thenceforward the main differences appear that depend on the geometry of PCM storage and the impact of the buoyant force. Through this study it is found that PCM cylindrical storage with vertical rectangular cross section has the highest melting rate in comparison with all models, and the melting time decreases to 74% of the circular cross section, while horizontal rectangular and elliptical cross sections
melt slower than other all models.