Thermodynamics analysis on a heat exchanger unit during the transient processes based on the second law

Energy ◽  
2018 ◽  
Vol 165 ◽  
pp. 622-633 ◽  
Author(s):  
Chaoyang Wang ◽  
Ming Liu ◽  
Yongliang Zhao ◽  
Zhu Wang ◽  
Junjie Yan
Keyword(s):  
Heat Exchanger ◽  
Transient Processes ◽  
Second Law ◽  
Thermodynamics Analysis

scholarly journals Second Law Analysis for the Experimental Performances of a Cold Heat Exchanger of a Stirling Refrigeration Machine

Entropy ◽  
2020 ◽  
Vol 22 (2) ◽  
pp. 215 ◽  
Author(s):  
Steve Djetel-Gothe ◽  
François Lanzetta ◽  
Sylvie Bégot
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Entropy Generation ◽  
Mass Flow ◽  
Hydraulic Diameter ◽  
Entropy Generation Rate ◽  
Second Law ◽  
Water Mixture ◽  
Fluid Friction ◽  
Refrigeration Machine

The second law of thermodynamics is applied to evaluate the influence of entropy generation on the performances of a cold heat exchanger of an experimental Stirling refrigeration machine by means of three factors: the entropy generation rate N S , the irreversibility distribution ratio ϕ and the Bejan number B e | N S based on a dimensionless entropy ratio that we introduced. These factors are investigated as functions of characteristic dimensions of the heat exchanger (hydraulic diameter and length), coolant mass flow and cold gas temperature. We have demonstrated the role of these factors on the thermal and fluid friction irreversibilities. The conclusions are derived from the behavior of the entropy generation factors concerning the heat transfer and fluid friction characteristics of a double-pipe type heat exchanger crossed by a coolant liquid (55/45 by mass ethylene glycol/water mixture) in the temperature range 240 K < TC < 300 K. The mathematical model of entropy generation includes experimental measurements of pressures, temperatures and coolant mass flow, and the characteristic dimensions of the heat exchanger. A large characteristic length and small hydraulic diameter generate large entropy production, especially at a low mean temperature, because the high value of the coolant liquid viscosity increases the fluid frictions. The model and experiments showed the dominance of heat transfer over viscous friction in the cold heat exchanger and B e | N S → 1 and ϕ → 0 for mass flow rates m ˙ → 0.1 kg.s−1.

A Thermodynamic Efficiency Concept for Heat Exchange Devices

1983 ◽  
Vol 105 (1) ◽  
pp. 199-203 ◽  
Author(s):  
L. C. Witte ◽  
N. Shamsundar
Keyword(s):  
Heat Exchanger ◽  
Heat Exchange ◽  
Energy Use ◽  
Second Law Of Thermodynamics ◽  
Thermodynamic Efficiency ◽  
Second Law ◽  
Two Fluids ◽  
Environment Temperature ◽  
Efficiency And Effectiveness ◽  
The Mean

A thermodynamic efficiency based on the second law of thermodynamics is defined for heat exchange devices. The efficiency can be simply written in terms of the mean absolute temperatures of the two fluids exchanging heat, and the appropriate environment temperature. It is also shown that for a given ratio of hot to cold inlet temperatures, the efficiency and effectiveness for particular heat exchange configurations are related. This efficiency is compared to second-law efficiencies proposed by other authors, and is shown to be superior in its ability to predict the effect of heat exchanger parameter changes upon the efficiency of energy use. The concept is applied to typical heat exchange cases to demonstrate its usefulness and sensitivity.

Second-law analysis of a wet crossflow heat exchanger

Energy ◽  
2000 ◽  
Vol 25 (10) ◽  
pp. 939-955 ◽  
Author(s):  
Jung-Yang San ◽  
Chin-Lon Jan
Keyword(s):  
Heat Exchanger ◽  
Second Law ◽  
Second Law Analysis

The Use of the Second Law of Thermodynamics in Process Design

1995 ◽  
Vol 117 (3) ◽  
pp. 179-185 ◽  
Author(s):  
D. A. Sama
Keyword(s):  
Heat Exchanger ◽  
Design Procedure ◽  
Second Law Of Thermodynamics ◽  
Global Optimum ◽  
Second Law ◽  
Complex Processes ◽  
Cost Of Energy ◽  
Heat Exchanger Networks ◽  
Improved Design ◽  
Optimum Solution

The importance of using the second law of thermodynamics in the design of heat exchangers, heat exchanger networks, and processes in general, is discussed. The optimal ΔT at a refrigerated heat exchanger is considered from a second law viewpoint. It is shown that the use of minimum total annualized cost as the single optimizing factor is unsatisfactory. Total annualized costs are based on predicted costs of fuel, equipment, and capital, which are uncertain at best. Instead of a singular or “global optimum” ΔT, there is a range of optimal ΔTs, over which the total annualized cost is essentially the same, but within which the distribution between cost of capital and cost of energy is significantly different. In selecting a design ΔT, this distribution of costs should also be considered. The possibility of only one singular, or global optimum, solution for complex processes is also considered from a philosophical viewpoint, and is again rejected. The existence and identification of design decisions which unnecessarily waste thermodynamic availability (physical exergy) are discussed and identified as “second law errors.” Elimination of a second law error from a design guarantees an improved design. An optimal design, which may be any one of a numerous set of optimal designs, will result when all second law errors are eliminated. A design procedure to develop optimal process designs, using such thermodynamic insights, is proposed.

scholarly journals Thermal Performance in Heat Exchangers by the Irreversibility, Effectiveness, and Efficiency Concepts Using Nanofluids

2020 ◽  
Vol 7 (2) ◽  
pp. F1-F7
Author(s):  
E. Nogueira
Keyword(s):  
Heat Exchanger ◽  
Ethylene Glycol ◽  
Heat Exchangers ◽  
Volume Fraction ◽  
Second Law Of Thermodynamics ◽  
Second Law ◽  
Output Data ◽  
Tube Heat Exchanger ◽  
Shell And Tube ◽  
Effectiveness And Efficiency

The objective of the work is to obtain the outlet temperatures of the fluids in a shell and tube heat exchanger. The second law of thermodynamics is applied through the concepts of efficiency, effectiveness, and irreversibility to analyze the results. Water flows in the shell, and a mixture of water-ethylene glycol is associated with fractions of nanoparticles flows in the tube. Water enters the shell at 27 °C, and the mixture comes to the tube at 90 °C. The mass flow is kept fixed in the shell, equal to 0.23 kg/s, and varies between 0.01 kg/s to 0.50 kg/s. Volume fractions equal to 0.01, 0.10, and 0.25 were considered for analysis, for both nanoparticles from Ag and Al2O3. Results for Reynolds number, heat transfer rate, efficiency, effectiveness, and irreversibility are presented for critique, discussion, and justification of the output data found. It is shown that the flow regime has a significant effect on the performance of the analyzed heat exchanger. Keywords: thermodynamics, second law, ethylene glycol, volume fraction.

scholarly journals Application of Second Law Analysis in Heat Exchanger Systems

Entropy ◽  
2019 ◽  
Vol 21 (6) ◽  
pp. 606 ◽  
Author(s):  
Seyed Ali Ashrafizadeh
Keyword(s):  
Heat Exchanger ◽  
Objective Function ◽  
Entropy Generation ◽  
Heat Exchangers ◽  
Driving Forces ◽  
Minimum Point ◽  
Second Law ◽  
Source Modeling ◽  
Operational Variables ◽  
Exergy Losses

In recent decades, the second law of thermodynamics has been commonly applied in analyzing heat exchangers. Many researchers believe that the minimization of entropy generation or exergy losses can be considered as an objective function in designing heat exchangers. Some other researchers, however, not only reject the entropy generation minimization (EGM) philosophy, but also believe that entropy generation maximization is a real objective function in designing heat exchangers. Using driving forces and irreversibility relations, this study sought to get these two views closer to each other. Exergy loss relations were developed by sink–source modeling along the heat exchangers. In this case, two types of heat exchangers are introduced, known as “process” and “utility” heat exchangers. In order to propose an appropriate procedure, exergy losses were examined based on variables and degrees of freedom, and they were different in each category. The results showed that “EGM” philosophy could be applied only to utility heat exchangers. A mathematical model was also developed to calculate exergy losses and investigate the effects of various parameters. Moreover, the validity of the model was evaluated by some experimental data using a double-pipe heat exchanger. Both the process and utility heat exchangers were simulated during the experiments. After verifying the model, some case studies were conducted. The final results indicated that there was not a real minimum point for exergy losses (or entropy generation) with respect to the operational variables. However, a logic minimum point could be found for utility heat exchangers with regard to the constraints.

The Second Law Analysis of Thermodynamics for the Plate–Fin Surface Performance in a Cross Flow Heat Exchanger

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Mansour Nasiri Khalaji ◽  
Isak Kotcioglu ◽  
Sinan Caliskan ◽  
Ahmet Cansiz
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Exchanger ◽  
Entropy Generation ◽  
Fluid Velocity ◽  
Cross Flow ◽  
Design Parameters ◽  
Second Law ◽  
Transfer Unit ◽  
Pin Fins

In this paper, a particular heat exchanger is designed and analyzed by using second law of thermodynamics. The heat exchanger operates with the cross flow forced convection having cylindrical, square, and hexagonal pin fins (tubular router) placed in the rectangular duct. The pin fins are installed periodically at the top and bottom plates of the duct perpendicular to the flow direction, structured in-line, and staggered sheet layouts. The entropy generation in the flow domain of the channels is calculated to demonstrate the rate of irreversibilities. To obtain the efficiencies, irreversibility, thermal performance factor, and entropy generation number (EGN), the heat exchanger is operated at different temperatures and flow rates by using hot and cold fluids. Optimization of the design parameters and winglet geometry associated with the performance are determined by entropy generation minimization. The variation of the EGN with Reynolds number for various tubular routers is presented. The Reynolds number is determined according to the experimental plan and the performance is analyzed with the method of effectiveness—number of transfer unit (NTU). Based on particular designs, it was determined that the increment in fluid velocity enhances the heat transfer rate, which in turn decreases the heat transfer irreversibility.

Sign in / Sign up

Export Citation Format

Share Document