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J. Thermal Sci. Eng. Appl. 2018;10(4):041001-041001-12. doi:10.1115/1.4038737.

This paper explores the use of a self-adaptive multipopulation elitist (SAMPE) Jaya algorithm for the economic optimization of shell-and-tube heat exchanger (STHE) design. Three different optimization problems of STHE are considered in this work. The same problems were earlier attempted by other researchers using genetic algorithm (GA), particle swarm optimization (PSO) algorithm, biogeography-based optimization (BBO), imperialist competitive algorithm (ICA), artificial bee colony (ABC), cuckoo-search algorithm (CSA), intelligence-tuned harmony search (ITHS), and cohort intelligence (CI) algorithm. The Jaya algorithm is a newly developed algorithm and it does not have any algorithmic-specific parameters to be tuned except the common control parameters of number of iterations and population size. The search mechanism of the Jaya algorithm is upgraded in this paper by using the multipopulation search scheme with the elitism. The SAMPE-Jaya algorithm is proposed in this paper to optimize the setup cost and operational cost of STHEs simultaneously. The performance of the proposed SAPME-Jaya algorithm is tested on four well-known constrained, ten unconstrained standard benchmark problems, and three STHE design optimization problems. The results of computational experiments proved the superiority of the proposed method over the latest reported methods used for the optimization of the same problems.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2018;10(4):041002-041002-6. doi:10.1115/1.4038708.

The effect of iron (Fe) nanoparticles additive to biodiesel blend and diesel fuels in terms of engine performance and emission characteristics is experimentally investigated in a stationary diesel engine. A fuel additive INP is suspended in the neat diesel (D) and 20% palm biodiesel (PB) blend with diesel (PB20) using ultra-sonication process and these modified fuels are termed as D + 50Fe and PB20 + 50Fe, respectively. Experiments are conducted on a developed diesel experimental setup to evaluate the engine performance and exhaust emissions for the fuels, namely, D, PB20, D + 50Fe, and PB20 + 50Fe. Results indicate that the density, viscosity, and calorific value of the fuel blends tend to increase with the addition of nanoparticles in the blends. Brake thermal efficiency (BTE) gets enhanced by about 2.06% for PB20 + 50Fe and about 0.36% for D + 50Fe with respect to BTE of PB20 and D, respectively. Similarly, brake-specific fuel consumption (BSFC) is lowered by 2.71% for PB20 + 50Fe and by 1.55% for D + 50Fe. Emission of regulated parameters, i.e., hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxides (NOx) emission, shows a reducing trend. Volumetric reduction in the emissions of HC by 3–6%, CO by 6–12%, and NOx by 4–11.16% is observed.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2018;10(4):041003-041003-7. doi:10.1115/1.4038738.

In the present study, laminar forced convective nanofluid flow over a backward-facing step was numerically investigated. The bottom wall downstream of the step was flexible, and finite element method was used to solve the governing equations. The numerical simulation was performed for a range of Reynolds number (between 25 and 250), elastic modulus of the flexible wall (between 104 and 106), and solid particle volume fraction (between 0 and 0.035). It was observed that the flexibility of the bottom wall results in the variation of the fluid flow and heat transfer characteristics for the backward-facing step problem. As the value of Reynolds number and solid particle volume fraction enhances, local and average heat transfer rates increase. At the highest value of Reynolds number, heat transfer rate is higher for the case with the wall having lowest value of elastic modulus whereas the situation is reversed for other value of Reynolds number. Average Nusselt number reduces by about 9.21% and increases by about 6.1% for the flexible wall with the lowest elastic modulus as compared to a rigid bottom wall for Reynolds number of 25 and 250. Adding nano-additives to the base fluid results in higher heat transfer enhancements. Average heat transfer rates enhance by about 35.72% and 35.32% at the highest solid particle volume fraction as compared to nanofluid with solid volume fraction of 0.01 for the case with wall at the lowest and highest elastic modulus. A polynomial type correlation for the average Nusselt number along the flexible hot wall was proposed, which is dependent on the elastic modulus and solid particle volume fraction. The results of this study are useful for many thermal engineering problems where flow separation and reattachment coupled with heat transfer occur. Control of convective heat transfer for such configurations with wall flexibility and nanoparticle inclusion to the base fluid was aimed in this study to find the effects of various pertinent parameters for heat transfer enhancement.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2018;10(4):041004-041004-11. doi:10.1115/1.4038709.

This study investigates the potential of oxygenated additive (ethanol) on adulterated diesel fuel on the performance and exhaust emission characteristics of a single cylinder diesel engine. Based on the engine experimental data, two artificial intelligence (AI) models, viz., artificial neural network (ANN) and adaptive-neuro fuzzy inference system (ANFIS), have been modeled for predicting brake thermal efficiency (Bth), brake specific energy consumption (BSEC), oxides of nitrogen (NOx), unburnt hydrocarbon (UBHC) and carbon monoxide (CO) with engine load (%), kerosene (vol %), and ethanol (vol %) as input parameters. Both the proposed AI models have the capacity for predicting input–output paradigms of diesel–kerosene–ethanol (diesosenol) blends with high accuracy. A (3–9–5) topology with Levenberg–Marquardt feed forward back propagation (trainlm) learning algorithm has been observed to be the ideal model for ANN. The comparative study of the two AI models demonstrated that ANFIS predicted results have higher accuracy than the ANN with a maximum RANFIS/RANN value of 1.000534.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2018;10(4):041005-041005-10. doi:10.1115/1.4038988.

Direct steam generation (DSG) in parabolic trough collector (PTC) is an efficient and feasible option for solar thermal power generation as well as for industrial process heat supply. The two-phase flow inside the absorber tube complicates the thermo-hydraulic modeling of the DSG process. In the present work, a thermo-hydraulic model is developed for the DSG process in the receiver of a solar PTC. The two-phase flow in the evaporating section is analyzed using two empirical correlations of heat transfer and pressure drop, and a flow map integrated heat transfer and pressure drop model. The results of the thermo-hydraulic simulation using different two-phase heat transfer and pressure drop correlations were compared with experimental data from the direct solar steam (DISS) test facility at Plataforma Solar de Almeria (PSA), Spain. The test facility has collectors with aperture width of 5.76 m, focal length of 1.71 m, and absorber tube with inner and outer diameters of 50 mm and 70 mm, respectively. The simulation results using the aforementioned two-phase models were found to be satisfactory and consistent within the experimental uncertainty. The flow map based heat transfer model predicted the mean fluid temperature with root-mean-square error (RMSE) of 0.45% and 1.40%, for the cases considered in the present study. Whereas the flow pattern map based pressure drop model predicts the variation of pressure along the length of the collector with RMSE of 0.5% and 0.14%. Moreover, the flow pattern map based model predicts the different flow regimes paving a better understanding of the two-phase flow and helps in identifying the critical sections along the collector length.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2018;10(4):041006-041006-17. doi:10.1115/1.4038989.

Forced convective flow boiling in a single microchannel with different channel heights was studied through a numerical simulation method to investigate bubble dynamics, two-phase flow patterns, and boiling heat transfer. The momentum and energy equations were solved using a finite volume (FV) numerical method, while the liquid–vapor interface of a bubble is captured using the volume of fluid (VOF) technique. The effects of different constant wall heat fluxes and different channel heights on the boiling mechanisms were investigated. The effects of liquid velocity on the bubble departure diameter were also analyzed. The predicted bubble shapes and distribution profiles together with two-phase flow patterns are also provided.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2018;10(4):041007-041007-9. doi:10.1115/1.4039302.

This paper explores the effects of porosity, pore size, and ligament geometry in metal foams on its fluid flow capability. The motivation to understand this phenomenon stems from exploring the use of metal foams for thermal energy dissipation applications where both thermal convection and fluid flow are desired. The goal of this research is to identify the optimum configuration of metal foam design parameters for maximum flow. To study the impacts of said parameters, an experimental study of air flow through open cell metal foams is performed. Seven foam blocks were used in this partial factorial study, representing varying materials, pore size, and porosity. Wind tunnel tests are performed to measure the velocity of air flowing through the foam as a function of the free stream air velocity. Multinomial logit regression was performed to analyze the effects of the design parameters on velocity loss through the foam. Results indicate that effect of porosity on velocity loss is significant while that of pore size is insignificant. However, one test result did not fit this trend and further investigation revealed that this was due to varying ligament geometry in outlier metal foam. The cross section shape of the ligaments varied from a convex triangular shape to a triangle shape with concave surfaces, increasing the amount of drag in the airflow through the sample.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2018;10(4):041008-041008-10. doi:10.1115/1.4039088.

A microchannel heat sink with convergent-divergent (CD) shape and bifurcation is presented, and flow and heat transfer characteristics are analyzed for Re ranging from 120 to 900. The three-dimensional governing equations for the conjugate heat transfer with temperature-dependent solid and fluid properties are solved using the finite volume method. Comparisons are carried out for four cases, namely, rectangular shape with and without bifurcation and CD shape with and without bifurcation. The pressure drop, flow structure, and average Nusselt number are analyzed in detail, and the thermal resistance and overall performance are compared. It is shown that the CD shape with bifurcation has more uniform and lower temperature at the bottom wall and better heat transfer performance compared to other geometries. The heat transfer augmentation in the CD shaped microchannel with bifurcation can be attributed not only to the accelerated and redirected flow toward the constant cross section segment but also to periodically interrupted and redeveloped thermal boundary-layers due to bifurcation. It is also shown that increasing Re leads to thinning of thermal boundary-layers resulting in an enhanced heat transfer in terms of an increased average Nusselt number from 38% to 74%. However, there is an increased pressure drop due to channel shape and obstacle in fluid flow. Further, due to a high pressure drop penalty at high Re, CD shaped microchannel with bifurcation loses its heat transfer effectiveness.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2018;10(4):041009-041009-13. doi:10.1115/1.4039055.

The flame behavior and the thermal structure of gaseous fuel jets issued from rectangular nozzles of high and low aspect ratios with co-flowing air were experimentally studied. Two rectangular nozzles with aspect ratios AR = 36 and 3.27 and with side channels for co-flowing air were examined. Flame behaviors were studied by photography techniques. Flame temperatures were measured using a fine-wire thermocouple. The AR = 36 burner exhibited three characteristic flame modes: attached flame, transitional flame, and lifted flame. The AR = 3.27 burner presented three characteristic flame modes: diffusion flame, transitional flame, and triple-layered flame. High AR jets promoted entrainment and mixing in the region around the flame base, whereas low AR jets enhanced mixing in the regions along the flame edges. At low co-flows, at Rec < 1200, the low AR burner flames were shorter, but at Rec > 1200, the high AR burner flames became shorter and wider. At Rec > 950, the high AR burner recorded higher flame temperatures, compared to the low AR burner by over 100 °C. At high fuel jet Reynolds numbers and moderate co-flow, high AR burner flames presented better combustion performances when compared to low AR jet flames. The good combustion performance of the high AR jet flames was due to enhanced entrainment and mixing, which were induced by flame lifting. However, at low Rec and high co-flow, the low AR jet flames exhibited desirable flame characteristics due to improved entrainment and turbulence at the jet interfaces.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2018;10(4):041010-041010-10. doi:10.1115/1.4039304.

Exhaust gas heat recovery is one of the interesting thermal management strategies that aim to improve the cold start of the engine and thus reduce its fuel consumption. In this work, an overview of the heat exchanger used as well as the experimental setup and the different tests will be presented first. Then numerical simulations were run to assess and valorize the exhaust gas heat recovery strategy. The application was divided into three parts: an indirect heating of the oil with the coolant as a medium fluid, a direct heating of the oil, and direct heating of the oil and the coolant. Different ideas were tested over five different driving cycles: New European driving cycle (NEDC), worldwide harmonized light duty driving test cycle (WLTC), common Artemis driving cycle (CADC) (urban and highway), and one in-house developed cycle. The simulations were performed over two ambient temperatures. Different configurations were proposed to control the engine's lubricant maximum temperature. Results concerning the temperature profiles as well as the assessment of fuel consumption were stated for each case.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Thermal Sci. Eng. Appl. 2018;10(4):044501-044501-6. doi:10.1115/1.4038703.

Analysis of entropy generation in mixed convection flow over a vertically stretching sheet has been carried out in the presence of variable thermal conductivity and energy dissipation. Governing equations are reduced to self-similar ordinary differential equations via similarity transformations and are solved numerically by applying shooting and fourth-order Runge–Kutta techniques. The expressions for entropy generation number and Bejan number are also obtained by using similarity transformations. The influence of embedding physical parameters on quantities of interest is discussed through graphical illustrations. The results reveal that entropy generation number increases significantly in the vicinity of stretching surface and gradually dies out as one move away from the sheet. Also, the entropy generation number decreases with an increase in temperature difference parameter. Moreover, entropy generation number enhances with an enhancement in the Eckert number, Prandtl number, and variable thermal conductivity parameter.

Commentary by Dr. Valentin Fuster

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