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.

Second Law Analysis of Spray Evaporation

1990 ◽  
Vol 112 (2) ◽  
pp. 130-135 ◽  
Author(s):  
S. K. Som ◽  
A. K. Mitra ◽  
S. P. Sengupta
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Entropy Generation ◽  
Exergy Analysis ◽  
Droplet Evaporation ◽  
Second Law ◽  
Hot Gas ◽  
Second Law Analysis ◽  
Initial Drop ◽  
Parallel Stream

A second law analysis has been developed for an evaporative atomized spray in a uniform parallel stream of hot gas. Using a discrete droplet evaporation model, an equation for entropy balance of a drop has been formulated to determine numerically the entropy generation histories of the evaporative spray. For the exergy analysis of the process, the rate of heat transfer and that of associated irreversibilities for complete evaporation of the spray have been calculated. A second law efficiency (ηII), defined as the ratio of the total exergy transferred to the sum of the total exergy transferred and exergy destroyed, is finally evaluated for various values of pertinent input parameters, namely, the initial Reynolds number (Rei = 2ρgVixi/μg) and the ratio of ambient to initial drop temperature (Θ∞′/Θi′).

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.

Optimization of Radial Convective Radiating Fin Geometry for Single Cylinder Internal Combustion Engine (ICE): Entropy Generation Minimization

2005 ◽  
Author(s):  
B. N. Taufiq ◽  
T. M. I. Mahlia ◽  
H. H. Masjuki ◽  
M. S. Faizul ◽  
E. Niza Mohamad
Keyword(s):  
Heat Transfer ◽  
Entropy Generation ◽  
Combustion Engine ◽  
Fluid Velocity ◽  
Cross Flow ◽  
Entropy Generation Rate ◽  
Material Surface ◽  
Optimal Geometry ◽  
Entropy Generation Minimization ◽  
Thermodynamic Irreversibility

This study attempts to calculate the optimal geometry of convective-radiating radial of ICEs fin arrays using entropy generation method. The analysis is conducted to achieve the balance between entropy generation due to heat transfer and entropy generation due to fluid friction. In designing of the thermal system, it is important to minimize thermal irreversibilities, because the optimal geometry found while the entropy generation rate is minimized. In this study, the entropy generation minimization (EGM) technique based on fin thickness is applied to study the thermodynamic irreversibility caused by heat transfer and fluid irreversibility in radiating convective radial fin arrays. In addition, the cost parameters of fin optimum thickness is also considered and presented. The entropy generation is found to be strongly influenced by emissivity of fin material surface and increasing the cross flow fluid velocity will enhance the heat transfer rate that will reduce the heat transfer irreversibility.

Second law analysis and heat transfer in a cross-flow heat exchanger with a new winglet-type vortex generator

Energy ◽  
2010 ◽  
Vol 35 (9) ◽  
pp. 3686-3695 ◽  
Author(s):  
Isak Kotcioglu ◽  
Sinan Caliskan ◽  
Ahmet Cansiz ◽  
Senol Baskaya
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Cross Flow ◽  
Vortex Generator ◽  
Second Law ◽  
Second Law Analysis ◽  
Flow Heat

scholarly journals Effect of angle of attack on heat transfer and hydrodynamic characteristics for staggered drop-shaped tubes bundle in cross-flow

2020 ◽  
pp. 21-36
Author(s):  
Rawad Deeb ◽  
◽  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Exchanger ◽  
Power Plants ◽  
Numerical Study ◽  
Angle Of Attack ◽  
Organic Rankine Cycle ◽  
Cross Flow ◽  
Hydrodynamic Characteristics ◽  
Equivalent Diameter

Tube bundles can be used as a separation heat exchanger in the organic Rankine cycle power plants (ORC), while the hot gas passes over the outer surface, and the working substance ORC flows inside the tubes. A numerical study has been conducted to clarify heat transfer and hydrodynamics of a cross-flow heat exchanger with staggered drop-shaped tubes at different flow angles of attack in comparison with circular tubes of the same equivalent diameter. The study was performed for the Reynolds number Re= 1.8  103 ~ 9.4  103, the longitudinal and transverse spacing of the tubes in the bundle are the same and are equal to 37 mm. Four cases of the tube’s arrangement with different angles of attack were investigated: 0, 45, 135, and 180 angles. The article presents a literature review related to the subject of the study. A mathematical and numerical model has been developed to calculate the heat transfer coefficient of the studied staggered drop-shaped tubes bundle using the ANSYS package, taking into account the stress-strain state of the tubes. Correlations of the average Nusselt numbers and the friction coefficient for the considered bundles in terms of the Reynolds number and angle of attack were presented. The results reveal that the thermal–hydraulic performance of the drop-shaped tubes bundle with zero-angle of attack is about 1.6 ~ 1.7 times greater than the circular one.

Computational study of Staggered and Double Cross Flow Heat Exchanger

2017 ◽  
Vol 67 (4) ◽  
pp. 396
Author(s):  
Annur Srinivasan Krishnan ◽  
Palanivelu Gowtham
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Heat Exchanger ◽  
Transfer Rate ◽  
Cross Flow ◽  
Flow Reynolds Number ◽  
Flow Heat ◽  
Shell And Tube ◽  
Double Cross

The preliminary findings of a comparative study of heat transfer rate and pressure drop between conventional staggered flow and double cross flow heat exchanger is reported. Excepting for the tube arrangements, the shell and tube dimensions, materials and inlet conditions are retained the same for the two configurations. While in the conventional arrangement, adjacent rows of tubes are normal only to the fluid flow in the shell, in the double cross-flow arrangement, they are normal to both fluid flow direction in the shell as well as to each other. Shell dimensions are 100 cm × 20 cm × 20 cm and tube outside and inside diameters are 1 cm and 0.8 cm. The shell and tube materials are steel and copper. Water and air were considered as tube and shell side fluids respectively, with an overall arrangement of parallel flow. The tube flow Reynolds number was fixed at 2200 and the shell flow Reynolds number was varied from 20 to 120 in the laminar regime and 360 to 600 in the turbulent zone. The study reveals that the proposed configuration gives a maximum increase of about 27 per cent in the heat transfer rate per unit pressure drop over the conventional one.

Sensitivity Analysis of a Heat Exchanger Tube Fitted With Cross-Cut Twisted Tape With Alternate Axis

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
M. E. Nakhchi ◽  
J. A. Esfahani
Keyword(s):  
Heat Transfer ◽  
Sensitivity Analysis ◽  
Reynolds Number ◽  
Heat Exchanger ◽  
Thermal Performance ◽  
Diameter Ratio ◽  
Design Parameters ◽  
Twisted Tape ◽  
Heat Exchanger Tube ◽  
Exchanger Tube

Numerical simulations are used to analyze the thermal performance of turbulent flow inside heat exchanger tube fitted with cross-cut twisted tape with alternate axis (CCTA). The design parameters include the Reynolds number (5000<Re<15,000), cross-cut width ratio (0.7<b/D<0.9), cross-cut length ratio (2<s/D<2.5), and twist ratio (2<y/D<4). The objective functions are the Nusselt number ratio (Nu/Nus), the friction factor ratio (f/fs), and the thermal performance (η). Response surface method (RSM) is used to construct second-order polynomial correlations as functions of design parameters. The regression analysis shows that heat transfer ratio decreased with increasing both the Reynolds number and the width to diameter ratio of the twisted tape. This means that the twisted tape has more influence on heat transfer at smaller inlet fluid velocities. Sensitivity analysis reveals that among the effective input parameters, the sensitivity of Nu/Nus to the Reynolds number is the highest. The results reveal that thermal performance enhances with increasing the width to diameter ratio of the twisted tape (b/D). The maximum thermal performance factor of 1.531 is obtained for the case of Re=5000, b/D=0.9, s/D=2.5, and y/D=4.

Industrial Applications of Thermal Devices With Meso-Scale Features

2005 ◽  
Author(s):  
Kevin W. Kelly ◽  
Andrew McCandless ◽  
Christophe Marques ◽  
Ryan A. Turner ◽  
Patrick Luke ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Scaling Laws ◽  
Small Diameter ◽  
Cross Flow ◽  
Experimental Results ◽  
Design Parameters ◽  
Return Flow ◽  
Transfer Coefficients ◽  
High Heat Transfer

Two commercial applications are presented that are based on heat transfer augmentation through the use of micro scale geometries. First, we present a micro-channel cross flow heat exchanger, manufactured by a derivative of the LIGA micromachining process. Both the in-plane and cross-flow passages have characteristic widths which can be as low as 250 micrometers. The manufacturing process of the heat exchanger is described, and the scaling laws capturing various design parameters are discussed. Experimental results which validate these scaling laws are presented. A second product, the Micro Jet Cooling Array (MJCA), consists of an array of small diameter impinging microjets with jet diameters as low as 300 micrometers, and provides extremely high heat transfer coefficients over relatively large target areas. The return flow in the MJCA is based on a patent-pending process that essentially isolates the jets from each other. In this manner a large number of small diameter jets can be placed next to each other without the deleterious effect of (a) cross-washing of neighboring jets, and (b) jet-to-jet flow variations due to variations in the discharge pressure over the target. The manufacturing of the MJCA, the scaling laws, and related experimental results are presented.

Optimization of Pin-Fins for a Heat Exchanger by Entropy Generation Minimization and Constructal Law

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Gongnan Xie ◽  
Yidan Song ◽  
Masoud Asadi ◽  
Giulio Lorenzini
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Entropy Generation ◽  
Thermal Energy ◽  
Pin Fin ◽  
Entropy Generation Minimization ◽  
Flow And Heat Transfer ◽  
Constructal Law ◽  
Pin Fins ◽  
Computational Fluid Dynamics Cfd

Pin-fins are considered as one of the best elements for heat transfer enhancement in heat exchangers. In this study, the topology of pin-fins (length, diameter, and shape) is optimized based on the entropy generation minimization (EGM) theory coupled with the constructal law (CL). Such pin-fins are employed in a heat exchanger in a sensible thermal energy storage (TES) system so as to enhance the rate of heat transfer. First, the EGM method is used to obtain the optimal length of pin-fins, and then the CL is applied to get the optimal diameter and shape of pin-fins. Reliable computational fluid dynamics (CFD) simulations of various constructal pin-fin models are performed, and detailed flow and heat transfer characteristics are presented. The results show that by using the proposed system with optimized pin-fin heat exchanger the stored thermal energy can be increased by 10.2%.

Experimental Study on Air Cooling via a Multiport Mesochannel Cross-Flow Heat Exchanger

2011 ◽  
Author(s):  
Sarbadaman Dasgupta ◽  
Faisal A. Siddiqui ◽  
Md. Abdul Quaiyum ◽  
Serena A. Al-Obaidi ◽  
Amir Fartaj
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Exchanger ◽  
Thermal Resistance ◽  
Heat Exchangers ◽  
Cross Flow ◽  
Uniform Temperature ◽  
Flow Channels ◽  
Flow Heat

Researchers are moving forward to provide energy efficient, compact and inexpensive heat exchangers. Main focus is being deployed to the heat exchangers comprising narrow size flow channels such as mesochannels and microchannels for their augmented heat transfer characteristics, compactness and energy efficiency compared to conventional heat exchangers with the same heat exchange duty. Air to water cross-flow heat exchangers are encountered in many engineering applications. While numerous investigations were performed to characterize the heat transfer and fluid flow in mesochannels and microchannels, the literatures examining the air side heat transfer and flow behaviors in the cross-flow mesochannel heat exchangers are inadequate. In the current study air side heat transfer and flow characteristics of cross-flow cooling of air through a multiport slab mesochannel heat exchanger were investigated experimentally. The major components of experimental setup are the closed loop integrated thermal wind tunnel, liquid circulation network with heat add or removal system arrangement, sets of measuring instruments, data acquisition system, and multiport slab mesochannel heat exchanger as the test specimen. The multiport slab mesochannel heat exchanger consists of 15 finned aluminum slabs with 304 mm × 304 mm size frontal area and 100 mm flow length across the direction of air flow. Each slab contains 68 flow channels of 1mm circular diameter. Cold deionized (DI) water at a constant mass flow rate (0.0196 kg/s) was forced to flow through the mesochannels whereas the hot air at different velocities was allowed to pass through the finned passages of the heat exchanger core in cross-flow orientation. The inlet air temperature was changed in three levels (28°C, 33°C and 38°C) while maintaining a constant inlet water temperature of 8° C. The air velocity was varied in four steps (3.5m/s, 5.5m/s, 7.5m/s, and 9.5 m/s) at each temperature level. In the present study heat transfer and fluid flow key parameters such as heat transfer rate (Q˙), number of transfer units (NTU), effectiveness (ε), overall thermal resistance (Rtotal), and the air side Nusselt number (Nua) as well as Reynolds number (Rea) were examined in the region of the air side Reynolds number at the range of 972–2758, with a constant water side Reynolds number of 135. Heat balance performance of the experiment was found to be 4% for all operating conditions. The air side thermal resistance was found to be dominating over the overall thermal resistance ranging from 85% to 91% of the overall thermal resistance. The effect of air side Reynolds number on air side Nusselt number was examined and a general correlation of Nusselt number with Reynolds number was obtained as Nua = 0.3972(Rea)0.3766. The Nusselt number value was found to be higher in comparison with other research works for the corresponding Reynolds number range. The multiport mesochannel flat slab has offered uniform temperature distribution into the core. This uniform temperature distribution leads to higher heat transfer over standalone inline flow tube bank.

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