Begell House Inc.
Heat Transfer Research
HTR
1064-2285
50
1
2019
ANALYSES OF ENTRANSY DISSIPATION RATIO AND ENTROPY GENERATION RATIO FOR GAS POWER CYCLES UNDER VARIOUS CONDITIONS: EDEG SOFTWARE
1-16
Ankur
Geete
Mechanical Engineering Department, Sushila Devi Bansal College of Technology, Indore, Madhya
Pradesh, 453331, India
Gas power plants are based on a gas power cycle with two constant pressure processes and two isentropic processes. In this paper, a thermodynamic analysis of a gas power plant is made. Entransy dissipation analysis and entropy generation analysis are made under various operating conditions, that is: at different specific heats of fluids, different numbers of transfer units, and different isentropic efficiencies for the turbine and compressor. In this work, the entransy dissipation-entropy generation (EDEG) software has been developed which is used to analyze the effectiveness, entransy dissipation, entropy generation, entransy dissipation ratio, and entropy generation ratio for the cycle under different operating conditions. The EDEG software is also used to generate different performance characteristic curves of various parameters. These curves help to identify that optimum conditions at which both entropy generation and entransy dissipation are minimum. The conclusions of this research work are: (a) when Cp is 0.5 kJ/kg K, the effectiveness for hot and cold fluids is maximum and equal to 0.973 and 0.970, respectively, and the entransy dissipation ratio is 1.836 which is also maximum; (b) when Ch and Cc are 5.0 and 4.0 kJ/kg K, respectively, the effectiveness for hot and cold fluids is maximum and equal to 0.967 and 0.962, respectively, but EGr and EDr are minimum — 0.84 and 0.961, respectively; (c) when NTUs for hot and cold fluids are 5, the effectiveness for hot and cold fluids is maximum and equal to 0.982 and 0.976, respectively, and (d) when ηcom and ηtur are 75% and 85%, respectively, the EGr and EDr are maximum and equal to 1.217 and 1.817, respectively.
EXPERIMENTAL INVESTIGATION OF THE EFFECT OF FLOW BLOCKAGES ON HEAT TRANSFER AND FLUID FRICTION IN A ROUND TUBE USING WALL-ATTACHED CIRCULAR RINGS
17-32
Adhikrao
Patil
Research Scholar,Department of Mechanical Engineering, Sinhgad College of Engineering, Savitribai Phule Pune University, Pune
Sandeep S.
Kore
Sinhgad Academy of Engineering, Pune, India, 411048 Savitribai Phule Pune University, Pune, India
Narayan K.
Sane
Department of Mechanical Engineering Walchand College of Engineering Vishrambag, SANGLI - 416 415 (Maharashtra), INDIA
This paper studies the flow blockage effect on thermal performance in a round tube. The experiments were carried on a heat exchanging tube which is fitted with wall-attached circular rings (with no gap between the ring and inner wall of the tube) as a flow blockage device. The aim of this investigation is to introduce a flow blockage area (FBA) as a new parameter to evaluate the performance of different turbulators (turbulator is a passive device which induces secondary/reverse flow within the flow field). The wall-attached circular rings were selected as flow blockage geometry and configured with different inner diameters to achieve flow blockage area of 30%, 40%, and 50%. The parameters varied during the tests were FBA, the pitch-to-diameter ratio (PDR), and the Reynolds number. Air with ambient temperature was used as a working fluid in a test tube in which the inner wall is maintained at a uniform heat flux. The Reynolds number and pitch-to-diameter ratio were varied from 6000 to 24,000 and from 2 to 4, respectively. Significant enhancement in heat transfer rate up to 3.04 times that of the smooth tube was observed with inserts of 50% FBA and a smaller pitch-to-diameter ratio, i.e., 2 at a higher Reynolds number. An insert, i.e., a circular ring which offers flow blockage area of 30% and pitch-to-diameter ratio 2, gives the highest overall performance factor (1.26) at a lower Reynolds number.
COUPLED HEAT TRANSFER ANALYSES OF MOLTEN SALT WITH VARIATION OF THERMOPHYSICAL PROPERTIES
33-56
Ziming
Cheng
Harbin Institute of Technology at Weihai, Harbin Institute of Technology, 2 West Wenhua Road,
Weihai 264209, P.R. China
Ruitian
Yu
School of Power and Energy Engineering, Harbin Engineering University, Harbin 150000, Heilongjiang, China
Fuqiang
Wang
Harbin Institute of Technology at Weihai, Harbin Institute of Technology, 2 West Wenhua Road,
Weihai 264209, P.R. China
Huaxu
Liang
Harbin Institute of Technology at Weihai, Harbin Institute of Technology, 2 West Wenhua Road,
Weihai 264209, P.R. China
Ming
Xie
School of Energy Science and Engineering, Harbin Institute of Technology, 92 West Dazhi Street,
Harbin 150001, P.R. China
Dong
Li
School of Architecture and Civil Engineering, Northeast Petroleum University, Fazhan Lu Street,
Daqing 163318, China
Jianyu
Tan
Harbin Institute of Technology at Weihai, Harbin Institute of Technology, 2 West Wenhua Road,
Weihai 264209, P.R. China
In this study, coupled heat transfer analysis of molten salt with variation of thermophysical properties was made. Radiative transfer and energy equations were solved by FEM using the codes compiled by the authors, while the mass and momentum conservation equations were solved by Fluent soft ware. Thereafter, the temperature distribution of the molten salt flowing in a tube receiver with/without considering radiative transfer was presented. The effects of scattering albedo, refractive index, and convective heat-transfer coefficient on the temperature distribution of the molten salt were investigated. The numerical results showed that the maximum deviations in the elevated temperature of the molten salt at the cross section x = 0.5 and fluid outlet surface are 39.8% and 50.7%, respectively, when the radiative heat transfer is neglected.
BUBBLE ENERGY AND LATENT HEAT FLUX ESTIMATION
57-64
Jure
Voglar
Faculty of Mechanical Engineering, University of Ljubljana, Askerceva 6, 1000 Ljubljana,
Slovenia
This paper investigates the latent heat flux during saturated pool boiling. The local latent heat flux is considered on a single nucleation site and has a decreasing trend if the empirical relation between the bubble departure diameter and the departure frequency has an exponent on the bubble diameter equal to or larger than one. If the exponent is smaller than one, the local latent heat flux starts to increase with increasing bubble departure radius. Empirical relations between the bubble departure diameter and frequency, which enable the local latent heat flux to decrease with increasing bubble radius, were proposed.
But some researchers of empirical relations suggest, and we take it to be possible, that this trend could also have an opposite nature. Besides this, an equation for estimation of the of latent heat flux was proposed to be used in experimental observations of boiling process.
NUMERICAL STUDY OF THE MOMENTUM AND CONJUGATE HEAT TRANSFER BETWEEN A SPHERE AND A MICROPOLAR FLUID FLOW
65-87
Gheorghe
Juncu
Department of Chemical and Biochemical Engineering, Politehnica University Bucharest, 1 Polizu, Bucharest, 011061, Romania
The flow of a micropolar fluid past a rigid sphere and the conjugate heat transfer from the sphere to the micropolar fluid are investigated numerically for moderate Reynolds numbers. The results indicate that the flow field is governed by the parameter that characterizes the interaction between the fluid and the sphere's surface, α. For α = 1 the flow is similar to that of a Newtonian fluid. The influence of the non-Newtonian effects increases when 0 ≤ α < 1. The effects of non-Newtonian fluid parameters on the heat transfer rate depend on the thermal wake phenomenon.
THERMOHYDRAULIC CHARACTERISTICS OF MICROCHANNEL HEAT SINKS COMBINED WITH RIBS AND CAVITIES: EFFECTS OF GEOMETRIC PARAMETERS AND HEAT FLUX
89-105
Cong
Li
Department of Process Equipment and Control Engineering, School of Mechanical
Engineering, Xiangtan University, Xiangtan 411105, People's Republic of China
Hong-Ju
Guo
Department of Process Equipment and Control Engineering, School of Mechanical
Engineering, Xiangtan University, Xiangtan 411105, People's Republic of China
Wei-Biao
Ye
Department of Process Equipment and Control Engineering, School of Mechanical
Engineering, Xiangtan University, Xiangtan 411105, People's Republic of China
Yuxiang
Hong
Department of Chemistry and Chemical Engineering, Lishui University, Lishui 323000,
People's Republic of China
Si-Min
Huang
Key Laboratory of Distributed Energy Systems of Guangdong Province, Department of Energy
and Chemical Engineering, Dongguan University of Technology, Dongguan 523808, People's
Republic of China
The effects of the geometric parameters and heat flux on the thermohydraulic characteristics of microchannel heat sinks
combined with ribs and cavities are investigated numerically. The numerical study is performed under conditions of laminar flow with conjugate heat transfer between silicon and water. In order to find the optimum substrate thickness, ratios of substrate thickness to microchannel height (Hs/Hc = 0, 0.25, 0.50, 0.75, 1.00, 1.25, and 1.50) are investigated. It is found that the temperature of the substrate surface firstly decreases and then gradually increases, the minimum temperature of the substrate surface occurs with Hs/Hc = 0.25. Furthermore, the microchannel heat sinks are studied at rib width to the spacing ratios (Lr/Sr = 0.25, 0.50, 0.75, and 1.0), rib heights to parallel sidewalls width ratios (Hr/Wc = 0.10, 0.15, 0.20, and 0.25), spacing to the parallel sidewalls width ratios (Sr/Wc = 4, 8, 12, and 16) and heat fluxes (qw = 50, 100, 150, 200, 250, and 300 W cm–2). The results show that the Performance Evaluation Criterion (PEC) is continued to slowly decrease with increase of qw. For all cases of qw, the maximum value of PEC occurs in model 2 with Lr/Sr = 0.50, Hr/Wc = 0.20, and Sr/Wc = 4. For Re > 320, the wall temperature of model 1 is slightly smaller than that of model 2.