Heat Transfer Entropy Research Articles

Entropy generation and thermal analysis of nanofluid flow inside the evacuated tube solar collector

In the current investigation, the thermal and thermodynamic behavior of a buoyancy-driven evacuated tube solar collector (ETSC) has undergone precise evaluation, and the efficacy of nanoparticle dispersion in the testing fluid was scrutinized. The natural convection process was analyzed in different vertical sections of the absorber tube. The outputs for water and the utilized nanofluid were compared at various cutting planes along the tube during the simulation time. In this problem, CuO nanoparticles with optimum thermal properties were distributed in the base fluid. According to the surveyed results, the temperature distribution analysis illustrates that the mean wall temperature experiences more enhancement when the nanofluid is used. The comparison of the heat transfer coefficient between the two simulated cases show the competency of utilizing CuO-{mathrm{H}}_{2}mathrm{O} nanofluid and highlight its crucial character in improving the thermal treatment of the operate fluid through the collector pipe. Based on irreversibility assessment, the irreversibility due to fluid friction rises when the nanofluid is applied during the flow time. In contrast, the entropy generation of pure water owing to heat transfer surpasses the case with nanofluid. More specifically, the heat transfer entropy generation experience a reduction of about 6.3% (0.143–0.134 W/K) by utilization of CuO with a volume fraction of 5% after 1 h of flow time, whereas the entropy generation by fluid viscosity enhances up to 23% when the nanofluid is applied in the system. The irreversibility originated from heating and fluid viscosity has significant difference in value, owing to the fluid’s low-velocity range in the natural convection process.

Heat transfer analysis and entropy generation in the nanofluids composed by Aluminum and [formula omitted] Aluminum oxides nanoparticles

A porous rotating disk is used to study the second law of thermodynamics in relation to an electrically conducting, incompressible γ− alumina nanofluid. An external uniform vertical magnetic field. Base fluids are ethylene glycol and water. Alumina nanofluids make use of the experimentally derived viscosity and thermal conductivity models, as well as Brinkman viscosity and Maxwell's thermal conductivity models. Nuclear propulsion space vehicles can use the results of this research in rotating magnetohydrodynamic (MHD) energy generators and also thermal conversion processes. With shooting approach, fourth order Runge–Kutta method is used to solve the governing boundary layer equations numerically. The entropy generation equation can be obtained from the velocity and temperature gradients, respectively. There is a high level of agreement between the current study's findings and those of previously published studies. Using geometric and physical flow field-dependent parameters, this equation is nondimensional. Researchers have discovered that there are three types of velocity profiles that can be obtained: radial (or circumferential) velocity profiles, and tangential velocity profiles (radial velocity profiles). The influence of nanofluid type on fluid velocity, temperature, entropy generation, Bejan number, skin friction coefficient, and Nusselt number has been investigated. The same nanoparticles are expected to behave differently in temperature profiles with water and ethylene glycol. As well as demonstrating the potential of using magnetic rotating disk motors in revolutionary nuclear space propulsion engines, this model is valuable for increasing heat transfer in renewable energy systems and industrial thermal management.

Parametric analysis of entropy generation in turbulent convective forced flow in spiral channels at constant wall temperature

This paper discuses parametric analysis of entropy generation in a forced convective turbulent flow of an incompressible fluid at a constant wall temperature through spiral channel of rectangular cross section of flow path has been carried out in terms of mass flow rates, temperature differences between fluid flow and temperature of the wall of the passage surface, width of the spiral passages and the shape geometry, as well as the types of fluids. Air is used as the working fluid, and in addition, water and oil are used in the parametric study. The competition between heat transfer enhancement and entropy generation has been addressed. Comparison between entropy generation profiles for different passage widths and shapes have been reported. It is found that mass flow rate and inlet fluid temperature have a considerable impact on entropy generation and hence on heat transfer enhancement. The findings show that the narrowing passage consumes more pump power to overcome viscous dissipation. Regarding the channel shape, it was found that the rectangular channel has the highest Bejan number (Be), while the circular spiral channel requires more pump power than the others. The data obtained indicate that the selection of the most suitable configuration and the best flow conditions becomes a critical task. Also, secondary flow due to centrifugal force and curvature has a significant effect on increasing heat transfer and entropy generation.

RETRACTED: Hall effect on the entropy optimization of radiative magnetized Jeffrey nanofluid flow with homogeneous and heterogeneous reaction by rotating stretching disk

Purpose: The goal of this study is to investigate the entropy optimization of Jeffrey nanofluid flow with the homogeneous and heterogeneous reaction by stretching the rotating disk. The impact of Hall current is also being considered. The process of heat transmission is carried out. For heat transfer coefficient, temperature, concentration, velocity, Bejan number, and entropy generation rate and relevant equations are computed. The implications of various characteristics are investigated. The effect of emerging parameters of nanofluid flow is discussed and represented by a graph. To reduce partial differential equations into ordinary differential equations by using effective similarity transformation. The achieved non-linear system is resolved by the Homotopy analysis technique (HAM) to found the convergent solution of the designated flow problem. The impact of various pertinent parameters, i.e thermal radiations parameter, Brinkman number, Reynolds number, magnetic parameter, Hall Effects parameter, Jeffrey nanofluid parameters are discussed and presented by the graph. Engineering quantities such as Nusselt number and skin friction are also taken into account.

Numerical Simulation of Steady and Unsteady Flow and Entropy Generation by Nanofluid Within a Sinusoidal Channel

Heat transfer has always been one of the most important aspects of human life. So far, many sources have been reported on methods of increasing the heat transfer rate. Many of these methods focus on changes in equipment structure. These techniques can hardly cope with the growing demand for heat transfer and compression in equipment. Recent advances in nanoparticle production can be seen as a breakthrough in methods of increasing heat transfer. The purpose of this study is to numerically investigate the flow field and heat transfer of water-aluminium oxide nanofluid in a wavy channel. The channel consists of two parallel plates and is divided into three parts in the longitudinal direction. The beginning and end parts of the channel are insulated and the middle part is sinusoidal and receives a uniform heat flux. The nanofluid enters the channel at a uniform speed and temperature and exits it in an expanded manner. For numerical analyses, the finite difference method based on control volume and simple algorithm is used. In this research, Reynold’s effect was analysed. The results showed that by increasing the Reynolds number, the speed, temperature gradient and heat transfer rate was increased and the thickness of the thermal boundary layer was decreased. With increasing Reynolds number, the amount of heat transfer from the wall to the fluid and also the production of entropy increases. In the unsteady state, with increasing time and flow rate, the amount of heat transfer and total entropy and temperature gradient increase to reach the steady state.

Modeling and optimization of the thermal-hydraulic performance of direct contact heat exchanger using quasi-opposite Jaya algorithm

In this study, the thermal-hydraulic performance of a direct contact heat exchanger (DCHE) was explored and optimized by applying the multi-objective quasi-opposite Jaya (MOQO-Jaya) algorithm. Inlet temperature of the continuous phase, continuous phase flow rate, dispersed phase flow rate, evaporator height, nozzle diameter, and number of jets were considered as the design variables for the optimization. The optimization functions were the volumetric heat transfer coefficient (VHTC), entransy dissipation, and entropy production. Study results indicated that the entransy dissipation and entropy production were negatively correlated with the heat transfer capacity in a DCHE, with a Pearson correlation coefficient above 0.96; that is, the smaller the entransy dissipation and entropy production, the better the heat transfer performance in the DCHE. The sensitivity of design parameters demonstrated that temperature played an important role. The optimization results and performance of the MOQO-Jaya algorithm were compared with those of the non-dominated sorting genetic algorithm (NSGA-II). The convergence of MOQO-Jaya was 2.24 times quicker than that of NSGA-II in DCHE optimization. The correctness of numerical model for optimizing the DCHE was verified through experiments. The errors of the experimental and algorithm optimizations both were within ±10%. Results demonstrated that after multi-objective optimization, the VHTC increased by 33.89% and entransy dissipation reduced by 44%, compared with those of traditional experiments.

Multiple-relaxation-time lattice Boltzmann simulation of free convection and irreversibility of nanofluid with variable thermophysical properties

This numerical study demonstrates heat transfer and irreversibility or entropy generation of non-Newtonian power-law Al2O3-H2O (aluminum oxide-water) nanofluids in a square enclosure using multiple-relaxation-time lattice Boltzmann method accelerated by graphics processing unit computing. In this investigation, the effective thermal conductivity and viscosity are variables, and they depend on the fluid temperature and rate of strain, respectively. The enclosure’s left and right walls are uniformly heated with different temperatures, and the upper and lower walls are thermally adiabatic. There is no valid study and results on non-Newtonian fluid using multiple-relaxation-time lattice Boltzmann method for this configuration and hence the novelty of the present results have been ensured. This paper has formulated and appropriately validated the Newtonian and non-Newtonian natural convection problem with the available numerical results. This study includes a set of comprehensive simulations, showing the effects of these fluids’ natural convection by varying three key parameters: the Rayleigh number, the volume fraction of nanoparticles, and the power-law index on the streamlines, isotherms, local and average Nusselt number as well as the local and total entropy generation. The results show that increasing the volume fraction of the nanoparticles from 0% to 2%, the average rate of heat transfer and the total entropy generation increase 6.5% and 7.4%, respectively, while the Rayleigh number, Ra = 105 and the power-law index n = 0.6.

Factorial experimental design for second law analysis of panel radiators as a function of radiator dimension

In this study, the parameters affecting the second law efficiency of panel radiators commonly used in heating systems were investigated. In the experimental system, a total of 6 pc-11 type panel radiators in 2 different heights and 3 different heights were used. In this context, the experiments were carried out by changing the feedwater temperature from 30 °C to 60 °C, with 10 °C increments and the flow rate from 2.5 l/min to 10 l/min, with 2.5 l/min increments. The experimental results obtained were analyzed factorially, and a mathematical model was developed between input parameters (feedwater temperature, flow rate, and radiator dimensions) and output parameters (total heat transfer coefficient and entropy generation). Using the novel model, the heat transfer and irreversibilities that can be obtained from the panel radiator in an operating system with known parameters can be calculated directly. This will provide a design methodology for researchers and engineers to be used for applications in the field. The total heat transfer coefficient and entropy generation from the panel radiator; radiator size increases with increasing flow rate and supply temperature; It has been observed that the total heat transfer coefficient decreases with the radiator size and temperature increase and increases with the increase in flow rate . The results showed an inverse relationship between the feedwater temperature and radiator size and the total heat transfer coefficient. It was also observed that the feedwater temperature was the most significant parameter on the total heat transfer coefficient. The main conclusion is that the most efficient energy utilization is provided by operating the heating systems at low temperatures with high flow rates. Consequently, this will lead to more efficient use of energy and reduced costs and environmental impact. • A factorial experimental study was carried out. • The influence of parameters on model results were analyzed statistically. • A mathematical model was developed. • The parameters exerting the most influence on the total heat transfer coefficient were determined. • The parameters exerting the most influence on entropy generation were determined.

Thermal entropy and exergy efficiency analyses of nanodiamond/water nanofluid flow in a plate heat exchanger

The study is aimed to understand the heat transfer coefficient and thermal entropy generation analyses of plate heat exchanger by using water-based nanodiamond nanofluids. The experiments were conducted in the volume concentration range: 0 ≤ ϕ ≤ 1.0%, the Reynolds number range: 140 ≤ Re ≤ 610, the mass flow rate range: 0.05≤ṁ≤0.183kg/s, and the Peclet number range from 895.78 ≤ Pe ≤ 3882.72, respectively. The effect of Reynolds number, Peclet number and particle volume loadings of nanodiamond nanofluids on heat transfer characteristics and entropy generation has been investigated. Water and nanodiamond nanofluids were considered as hot and cold medium in the plate heat exchanger, respectively, for the experimental study. The study reveals considerable augmentation in heat transfer coefficient and Nusselt number with an increase of nanofluid particle loadings. The study showed 32.50%, 55.47%, 35.11%, 22.80%, and 18.93% enhancements in overall heat transfer coefficient, heat transfer coefficient, Nusselt number, pressure drop and pumping power compared to base fluid at a Reynolds number of 526.37 at ϕ = 1.0%. Improved effectiveness, number of transfer units and exergy efficiency of 14.41%, 32.81% and 19.72% was observed at ϕ = 1.0% and at a Reynolds number of 526.37 against base fluid data. The thermal entropy and friction entropy generation was showed decreasing and increasing trends respectively, in the measured particle volume loadings. The Bejan number and entropy generation number demonstrated the roles of heat transfer and friction factor in the entropy generation. From the experimental results a new Nusselt number and friction factor correlations were proposed.

The Determination of the Thermal Characteristics of the Microchannel Heat Exchangers for Single-Phase R600a Flow

Bu çalışmada, özellikle iklimlendirme sistemlerinde ön ısıtma/soğutma, aşırı kızdırma/soğutma gibi tek fazlı soğutkan akışının olduğu uygulamalar için mikrokanal eşanjörlerin matematiksel modellemesi deneysel doğrulamalı olarak ele alınmıştır. Çalışma akışkanının R600a olduğu panjurlu kanatlı mikrokanal eşanjörler için R600a’nın çıkış sıcaklığını, toplam ısı transfer kapasitesini ve entropi üretimini tahmin eden bir matematiksel benzetim modeli geliştirilmiştir. Modelin doğruluk hassasiyetini arttırmak için geçişlerdeki farklı kütle hızları ve uniform olmayan hava hızı modelde dikkate alınmıştır. Bu etkileri dikkate almak için literatürde yer alan diğer modellerden farklı olarak iki seviye ayrıklaştırma ile oluşturulan bir hesaplama sistemi modelde uygulanmıştır. Modelde mikrokanal ısı eşanjörünün ön yüzü hava akış bölgelerine bölünerek uniform olmayan hava hızları dikkate alınmıştır. Model sonuçlarını doğrulamak için deneysel çalışma yapılmıştır. Deneysel doğrulama sonucunda modelin, incelenen tüm test koşulları için çıkış sıcaklığını ±%10 aralığında bir ortalama mutlak sapma ile öngördüğü sonucuna varılmıştır. Mikrokanal ısı eşanjörünün, ısı transfer performansını tahmin etme kabiliyeti, deneylerle değerlendirilmiş, uniform olmayan hava hızının modele dahil etmenin, modelin doğruluk hassasiyetini arttırdığı görülmüştür. Mikrokanal ısı eşanjöründeki entropi üretim mekanizmaları incelenmiş ve akışkan akımı tersinmezliklerinin entropi oluşumuna katkısının, ısı transfer tersinmezliklerine kıyasla oldukça düşük olduğu tespit edilmiştir.

Heat transfer characteristics and entropy generation analysis in a plate heat exchanger using ethylene glycol and water mixture‐based Al2O3nanofluid

AbstractThe present study aims to study the heat transfer and entropy generation analysis in a plate heat exchanger by dispersing Al2O3nanoparticles into a water and ethylene glycol mixture (base fluid) of a 65:35 volume ratio. The study was carried out by varying the nanofluid concentration from 0.2 to 2 wt%. The effects of Peclet number and weight concentration of water:ethylene glycol–Al2O3nanofluid on heat transfer characteristics and entropy generation were investigated. The nanofluid and distilled water were considered as a cold medium and hot medium on the plate heat exchanger, respectively, for the experimental study. The study showed considerable improvement in convective heat transfer coefficient and Nusselt number with the increase in nanofluid concentration. The study showed a 19.32% enhancement in overall heat transfer coefficient compared with base fluid at identical Peclet number. Pressure drop and pumping power were increased due to the addition of nanoparticles. Improved effectiveness was observed with the increase in concentration at higher Peclet numbers. Thermal entropy generation and friction entropy generation showed descending and ascending trends, respectively, for the considered weight concentration of nanofluid for the increased Peclet number. The Bejan number and entropy generation number demonstrated the roles of heat and friction in the entropy generation. A correlation was developed to predict the Nusselt number considering the experimental data. The prediction of the Nusselt number obtained from the present study showed good agreement with the experimental results.

MHD convective process due to rotation of cylinders and movement of a wavy wall of two-sided wavy enclosures with radiation

PurposeThis paper aims to study the mixed convective process due to various dynamics, namely, inner rotating cylinders and upper-wavy wall movement for the first time.Design/methodology/approachThe Galerkin finite element method together with the characteristic-based split scheme is applied to solve the governing system.FindingsThe main outcomes revealed that the direction of the rotation of the cylinders, radius and locations of the rotating shapes are beneficial controlling elements for the enhancement of heat transfer. Also, for all the considered cases, values of the Bejan number indicate that the fluid friction irreversibility is dominance compared to the heat transfer irreversibility. Further, average values of the heat transfer entropy, fluid friction entropy and total entropy are minimized in the case of fixed cylinders regardless of the cylinder radius.Originality/valueThe authors are interested in the mixed convection case due to regular boundaries and hence this simulation purposes a first attempt to examine the mixed convective flow due to irregular wavy boundaries. This study considered various dynamics, namely, inner rotating cylinders and wavy-lid driven wall which makes it more attractive to the readers. Various cases based on radius of the cylinder and direction of the rotations together with several locations of the rotating shapes are taken into account which makes the current simulation is comprehensive. Various studies presented in this field are made by commercial software and these treatments need special conditions (having limitation) but the current solution methodology is based on a finite element method home-code. Various important impacts, are, also, examined, namely, inclined geometry, inclined magnetic field, thermal radiation and heat generation/absorption. The entropy of the current complex system is analyzed based on the second law of thermodynamics.

Heat transfer enhancement and entropy generation analysis of a tube with perforated conical inserts

ABSTRACT The present study examines the flow and thermal characteristics of a tube containing perforated conical inserts by varying the Reynolds number in the range of 4000–20000. The perforated conical insert having (d/D) ratio of 0.3, (p/D) ratio of 2, (x/L) ratio of 0.25, and N = 6 showed the minimum entropy generation. Second law analysis showed that the solid inserts of a lower pitch to diameter ratio are suitable to transfer high energy transfer at lower Reynold’s number, whereas the perforated conical inserts are found to be effective at higher Reynolds numbers. Empirical correlations are developed for solid and perforated conical inserts.

MHD nanofluid free convection inside the wavy triangular cavity considering periodic temperature boundary condition and velocity slip mechanisms

Recent studies have shown that the two-phase modeling of nanofluid in natural convection is more compatible with the experimental results. This numerical study is applied to Buongiorno's model for solving the volume fraction of iron oxide nanoparticles inside a triangular chamber with a hot wavy wall using the finite volume method. Also, a uniform magnetic field is used to improve the heat transfer rate and entropy generation. The periodic temperature boundary condition is considered for the wavy side of the chamber while the other side is at the constant temperature. Hartmann number (Ha), Rayleigh number (Ra), undulation number (n), and inclination angle of magnetic field (ξ) variations are investigated. The results show that n has significant effects on heat transfer. Also, the Nusselt number is inversely related to the undulation number and is directly associated with the Rayleigh number. Moreover, the heat transfer rate is inversely related to the total entropy generation. Due to the magnetic field in high Ra, entropy generation first increases and then remains constant with increasing Ha.

Analysis of thermo-hydraulic and entropy generation characteristics for flow through ribbed-wavy channel

PurposeThe purpose of this study is to analyze the thermal, hydraulic and entropy generation characteristics for laminar flow of water through a ribbed-wavy channel with the top wall as wavy and bottom wall as flat with ribs of three different geometries, namely, triangular, rectangular and semi-circular.Design/methodology/approachThe finite element method-based numerical solver has been adopted to solve the governing transport equations.FindingsA critical value of Reynolds number (Recri) is found beyond which, the average Nusselt number for the wavy or ribbed-wavy channel is more than that for a parallel plate channel and the value of Recri decreases with the increase in a number of ribs and for any given number of ribs, it is minimum for rectangular ribs. The performance factor (PF) sharply decreases with Reynolds number (Re) up to Re = 50 for all types of ribbed-wavy channels. For Re > 50, the change in PF with Re is gradual and decreases for all the ribbed cases and for the sinusoidal channel, it increases beyond Re = 100. The magnitude of PF strongly depends on the shape and number of ribs and Re. The relative magnitude of total entropy generation for different ribbed channels varies with Re and the number of ribs.Practical implicationsThe findings of the present study are useful to design the economic heat exchanging devices.Originality/valueThe effects of shape and the number of ribs on the heat transfer performance and entropy generation have been investigated for the first time for the laminar flow regime. Also, the effects of shape and number of ribs on the flow and temperature fields and entropy generation have been investigated in detail.

Effects of CuO nano powder on performance improvement and entropy production of double-pipe heat exchanger with innovative perforated turbulators

The objective of the present numerical study is to investigate the heat transfer enhancement, entropy generation, and thermal performance of turbulent nanofluids inside double-pipe heat exchangers equipped with novel perforated cylindrical turbulators. Effects of inflow velocity, CuO nanoparticles volume fraction and perforated index are evaluated on the Nusselt number, friction loss, thermal performance factor (η), and viscous irreversibilities of the double-pipe heat exchangers. The newly proposed perforated turbulators with CuO nanopowder with ϕ = 1.5% provide the thermal performance of η = 1.931, which is considerably higher than the other previous studies. The results show that raising PI reduces the turbulent kinetic energy, especially in outer regions of the cylindrical turbulator. The jet formation near the walls and the perforations is the primary physical reason for this. The viscous entropy generation is increased up to 153.0% by increasing the Re number from 6,000 to 17,000 for PI = 8% and DR = 0.7. Thermal boundary layer disruption is the primary physical reason for heat transfer enhancement.

Natural convection and entropy generation of a nanoliquid in a crown wavy cavity: Effect of thermo-physical parameters and cavity shape

Natural convection (NC) of nanoliquids specifically in enclosures is of use in diverse fields such as solar collectors, HVAC, and medical treatment. Recent research shows that suspension of nano-materials within the base fluid enhanced the heat transfer performance. NC heat transfer of Al2O3–H2O nanoliquid within a crown cavity with a circular cylinder inside it is studied in this paper. The flow is considered buoyancy-driven which is under thermal radiation (Rd) and constant magnetic field within the porous media. Dimensionless modes of Navier-Stokes equations are considered as governing equations, and FEM is used to discrete the equations. Two scenarios are considered in the present paper. In the first scenario, the effect of parameters namely; Rayleigh number (103-105), Darcy number (0.001–0.1), Hartmann number (0–20), Radiation parameter (0.1–0.3), angle of magnetic field (0∘−90∘), and nanoparticle concentration (0.01–0.04) on heat transfer performance and entropy generation (Sgen) is studied. In the second scenario, the effect of geometry on Nusselt number (Nu) and Sgen is investigated. Da, Rd, and nanoparticle concentration have a positive impact on Nuavg and enhance heat transfer. Besides, the geometry with the best heat transfer performance is the one with the base wavy wall and the cylinder at the left side.

Numerical Investigation on heat transfer enhancement and entropy generation in a triangular ribbed-channel using nanofluid

Numerical Investigation on heat transfer enhancement and entropy generation in a triangular ribbed-channel using nanofluid

Heat transfer and entropy generation in a MHD Couette–Poiseuille flow through a microchannel with slip, suction–injection and radiation

Flow, heat transfer and entropy generation in a vertical microchannel made of two parallel porous plates (the injection plate kept at rest while the suction plate is moving in upward/downward direction) under the combined action of buoyancy force and transverse magnetic field are studied. Variable pressure gradient (favorable/adverse) due to Couette–Poiseuille (C–P) flow is considered here. This is one of the fundamental problems of applied science and engineering. Slip conditions for the velocity at plates are implemented for both moving-plate directions and pressure gradients with the help of classical C–P flow. The basic equations are solved numerically by using Runge–Kutta–Fehlberg method along with shooting technique. Numerical results are in concordance with previously published results for specific cases. The present results are frequently compared with those of the classical C–P flow. Influence of operational parameters (plate movement, pressure gradient, injection–suction rate, slip length, Grashof Number, temperature ratio (between hotter to colder side) and viscous dissipation effect) on the flow and heat transfer characteristics (velocity, temperature, Nusselt number (Nu) distribution, entropy generation and Bejan Number) are investigated here. An effort is made to search singularity in the variation of Nu with some parameters, and find the parameters’ values at which the global entropy is minimally generated in the channel. Finally, a critical analysis is conducted on the individual contribution of irreversibilities due to heat flow, fluid friction and Joule heating to the total entropy generation.

Thermo-entropic evaluation of the effect of air injection into horizontal helical tube

In the present paper, the influence of two-phase stream on the thermal and entropic properties of horizontal helical tube was probed. Furthermore, the flow structures were analyzed too. The flow patterns were created and recorded in a glass made tube. The tube had same geometrical dimensions as like to that used in thermal tests. With the aim of probing the heat transfer coefficient constant heat flux was applied to an aluminum made tube. The range of volume fraction investigated in the present study was 0.07 to 0.75. The flow visualization results revealed that four flow patterns of stratified, slug, slug-wavy and plug flow were created at the mentioned range of volume fraction. The results presented that the variation of volume fraction has significant effect on the flow pattern, heat transfer coefficient and entropy generation of air/water two-phase stream. Up to 20% augmentation was observed in the heat transfer coefficient due to the use of two-phase flow. The maximum rise in the entropy generation was about 33% and was occurred at the VF 0.55 and gas superficial Dean number of 230.8. Besides, the best value of Whitte-Shamsunder efficiency factor was found to be about 0.984 which was observed at Desl=1175.45 and Desg= 230.8.