Showing papers in "Heat Transfer Engineering in 2001"
TL;DR: In this paper, a curve-fitted equation is defined for the relationship between the Lockhart-Martinelli parameter and the liquid viscosity, which is a strong function of the LMC parameter.
Abstract: Pressure drop data measured during adiabatic two-phase flow in a plate-and-frame heat exchanger (PHE) are normalized with respect to the single-phase liquid pressure drop to give two-phase multipliers. A curve-fitted equation defines this relationship, which is a strong function of the Lockhart-Martinelli parameter. C coefficients are shown to be strong functions of both the Lockhart-Martinelli parameter and liquid viscosity, making this correlation unsuited to predictions of pressure drop in PHEs. Interfacial structure, observed during air-water downflow in replica channels (dC = 3 mm), is categorized into five flow patterns. These have a number of similarities with structures reported for circular and rectangular channels of similarly low hydraulic diameter. The transition boundaries between the patterns are shown to be a function of the chevron angle.
58 citations
TL;DR: In this paper, a newly developed methodology for the design of multistream plate-fin heat exchangers in the optimization of heat exchanger networks is described in detail, where the requirements of heat transfer and pressure drop are fulfilled through proper surface selection.
Abstract: A newly developed methodology for the design of multistream plate-fin heat exchangers in the optimization of heat exchanger networks is described in detail. The designed heat exchanger consists of several block sections with intermediate entry and exit points along its length, and these sections are determined by the composite curves in the Pinch technology. The requirements of heat transfer and pressure drop are fulfilled through proper surface selection. The methodology was applied to an industrial case study, and the detailed design parameters are given. The example confirms the validity of the suggested methodology.
45 citations
TL;DR: In this article, the authors used electron microscopy to determine the important mechanisms in the deposition of particles in waste-heat-recovery boilers and found that inertia controlled transport is the dominant transport mechanism of particles.
Abstract: Gas-side fouling of waste-heat-recovery boilers, caused mainly by the deposition of particulate matter, reduces the heat transfer in the boiler. The fouling as observed on the tube bundles in the boiler of a Dutch refuse waste incinerator varied from thin and powdery for the economizer to thick and sintered for the superheater. Analysis of process data showed that both types of layers resulted in a 27% decrease of the heat transfer coefficient of the bundles. To determine the important mechanisms in the deposition of particles, layers taken from the different bundles are analyzed using electron microscopy. The analysis revealed the existence of a melt in the thick deposit. The melt, giving rise to a liquid phase, increases the sticking efficiency of the deposit and leads to larger deposition rates. For the economizer and the superheater the actual deposition rate is calculated from the change in heat transfer. On the basis of a comparison between the calculated deposition rates and deposition rates to be expected in the case of a pure diffusion and thermophoresis process, it is shown that for both types of deposits inertia-controlled transport is the dominant transport mechanism of particles.
38 citations
TL;DR: In this article, an experimental investigation is conducted to study the performance of evaporative condensers/coolers, including development of correlations for the external heat transfer coefficient and the system efficiency.
Abstract: Experimental investigation is conducted to study the performance of evaporative condensers/coolers. The analysis includes development of correlations for the external heat transfer coefficient and the system efficiency. The evaporative condenser includes two finned-tube heat exchangers. The system is designed to allow for operation of a single condenser, two condensers in parallel, and two condensers in series. The analysis is performed as a function of the water-to-air mass flow rate ratio (L/G) and the steam temperature. Also, comparison is made between the performance of the evaporative condenser and same device as an air-cooled condenser. Analysis of the collected data shows that the system efficiency increases at lower L/G ratios and higher steam temperatures. The system efficiency for various configurations for the evaporative condenser varies between 97% and 99%. Lower efficiencies are obtained for the air-cooled condenser, with values between 88% and 92%. The highest efficiency is found for the tw...
35 citations
TL;DR: In this article, a study of heat transfer in simultaneously developing flow through rectangular tubes is presented, where three different tube sizes and shapes (D h = 2.21 mm, f = 0.050, D h = 3.02 mm, F = 0,108, and H h = 1.74 mm) were tested to measure the effect of developing flow on the Nusselt number.
Abstract: A study of heat transfer in simultaneously developing flow through rectangular tubes is presented in this article. Heat transfer coefficients were measured for three different tube sizes and shapes (D h = 2.21 mm, f = 0.050; D h = 3.02 mm, f = 0.108; and D h = 1.74 mm, f = 0.029), which correspond to typical dimensions used in automotive heat exchangers. For each of these tubes, several different tube lengths were tested to measure the effect of developing flow on the Nusselt number. The results demonstrate that developing flow enhances Nusselt numbers, especially for short tubes. For the geometry range studied, the effect of aspect ratio was not very significant. Heat transfer correlations that accounted for the effects of Reynolds number (118 < Re < 10,671) Prandtl number (6.48 < Pr < 16.20), and bulk-to-wall property variations (0.243 < w b / w w < 0.630), and geometric features such as tube length, hydraulic diameter, and aspect ratio, were developed from the data.
35 citations
TL;DR: In this article, a comprehensive study of the modified Wilson plot technique has been made and a stepwise methodology has been evolved to determine the condensing-side heat transfer coefficient during condensation of vapor over a horizontal tube.
Abstract: In the present investigation a comprehensive study of the modified Wilson plot technique has been made and a stepwise methodology has been evolved. This technique can be used to determine the condensing-side heat transfer coefficient during condensation of vapor over a horizontal tube. The necessary experimental data have been acquired by conducting experiments for the condensation of steam and R-134a over a plain tube and different finned tubes (CIFTs and SIFTs). The experimental heat transfer coefficient, based on the test-section wall temperature measurement (wall temperature was measured with thermocouples), ho, has been compared with that predicted by the modified Wilson plot technique, hmw. The modified Wilson plot technique underpredicted the condensing-side heat transfer coefficient for the condensation of steam in a range of 7.5-15%. The heat transfer coefficient for the condensation of R-134a is also underpredicted in a range of 13-25% by this technique.
34 citations
TL;DR: In this article, the cooling module consists of a cold plate with microfinned channels and a plate-type integrated condenser, and a separate flow model was employed to predict the mass flux and the pressure drop in the channel of the cold plate.
Abstract: Thermosyphon cooling modules, to cool multichip modules (MCMs), were designed and tested. The cooling module consists of a cold plate with microfinned channels and a plate-type integrated condenser. A separate flow model was employed to predict the mass flux and the pressure drop in the channel of the cold plate. The local and average convective boiling heat transfer coefficients and the corresponding wall superheat were calculated using the Chen's correlation. Experiments were performed to find out how the thermal performance of the cooling module was affected by the condenser size and the amount of charging fluid. Great emphasis was placed on the transient characteristics of the cooling module. For an allowable temperature rise of 58 ° C on the surface of the heater, the cooling module can handle a heat flux of as much as 2.5 W/cm2. No boiling retardation was observed inside the cold plate, which resulted in smooth transition from the transient state to the steady one. It was also found that the appropr...
33 citations
TL;DR: In this article, the authors compared the performance of plate and double-pipe heat exchanger during calcium sulfate crystallization fouling and found that plate heat exchangers fouled significantly less than double-pipes, i.e. 20-25 times less in the presence of particles and around 15 times less when the particles were filtered out.
Abstract: The selection of fouling resistances to design plate-and-frame heat exchangers is usually based on experience or guesswork. The primary aim of this study was to compare fouling resistances for plate heat exchangers with values obtained in a parallel double-pipe heat exchanger under comparable operating conditions. The double-pipe heat exchanger was selected because it represents a shell-and-tube heat exchanger in a simplified form. Correction factors for plate heat exchangers have been obtained by comparing the performance of the two heat exchanger types during calcium sulfate crystallization fouling. Fouling was investigated in both heat exchangers for two conditions: (1) particles present in the process solution were allowed to enhance the crystallization process and (2) particles present in the process solution were removed by an in-line 1-μm filter. For similar flow velocities, the plate heat exchanger was found to foul significantly less than the double-pipe heat exchanger, i.e. 20-25 times less in the presence of particles and around 15 times less when the particles were filtered out. When data for similar overall shear forces are compared, results for both heat exchanger types are much closer, even though the plate heat exchanger still seems to perform somewhat better. Fouling in plate-and-frame heat exchangers was also found to depend significantly on plate design. This will add a further complication in direct comparison with shell-and-tube heat exchangers.
32 citations
TL;DR: In this article, the authors measured the pressure drop in a single channel of a plate-and-frame heat exchanger with chevron angle configurations of 30°/30°, 30° /60°, and 60°/60° and channel gaps of 2 and 3 mm.
Abstract: Pressure drop is measured during steady-state adiabatic gas/liquid flow in a single channel of a plate-and-frame heat exchanger. Channels with chevron angle configurations of 30°/30°, 30°/60°, and 60°/60° and channel gaps of 2 and 3 mm are investigated. The two-phase mixture consists of air and either tap water or an aqueous solution of carboxymethylcellulose. Flow qualities range from 0 to 1 at a mass flux of 50 kg/m2s and from 0 to 0.05 at the highest mass flux of 600 kg/m2s. In addition to the measurement of the pressure difference between inlet and outlet (port to port), pressure taps located inside the channel enable the measurement of the pressure drop across the corrugated section only, allowing for a clear description of the influence of corrugation geometry on pressure drop. Pressure drop is shown to be greatly influenced by channel geometry. For flow of constant mass flux, frictional pressure drop is observed to increase linearly with flow quality. It is independent of flow direction at mass flu...
28 citations
TL;DR: In this article, the effect of radiation on mixed-convection flow of optically dense viscous fluids about an isothermal wedge embedded in a saturated porous medium is investigated.
Abstract: Numerical solutions are presented for the effect of radiation on mixed-convection flow of optically dense viscous fluids about an isothermal wedge embedded in a saturated porous medium. The partial differential equations are transformed into the nonsimilar boundary-layer equations, which are solved by the Keller box method. Numerical results for the dimensionless temperature profiles and the local Nusselt number parameter are presented for the combined convection parameter X, the wedge angle parameter A, the radiation-conduction parameter R d , and the surface temperature parameter H. The entire regime of the mixed convection is included, when X varies from 0 (pure free convection) to 1 (pure forced convection). As X varies from 0 to 1, the variation of the local Nusselt number parameter has the phenomenon of minimum. As the wedge angle parameter λ increases, the local Nusselt number parameter increases. When the radiation effect becomes significant (for the case of large values of R d and H), the local Nusselt number parameter is also greatly increased
TL;DR: In this article, the optimal design of single longitudinal fin with constant thickness, considering different uniform heat transfer coefficients on the fin faces and on the tip, has been approached by means of an accurate mathematical method yielding the solution of constrained minimization (maximization) problems.
Abstract: The optimum design of single longitudinal fins with constant thickness, considering different uniform heat transfer coefficients on the fin faces and on the tip, has been approached by means of an accurate mathematical method yielding the solution of constrained minimization (maximization) problems. Starting from the classical one-dimensional (1-D) model of the fin, the optimum design problem is reduced to a constrained optimization one by considering the limitations of the fin thermal convenience criterion, of the 1-D accuracy criterion, or of the geometric constraint on the primary surface of the fin array. The analysis, developed in dimensionless form, shows that the existence and the uniqueness of the solution are not ensured in any case, and the condition of the solution existence is often a consequence of the imposed constraints. A comparison between the results obtained and those achieved by applying to the fin optimization the half-thickness rule (HTR), based on the Harper and Brown approximation,...
TL;DR: In this article, the optimal spacing for inclined single channels, in terms of thermal performance, is obtained from composite correlations between average Nusselt and Rayleigh numbers as functions of the angle.
Abstract: Dimensional charts for the design of inclined single channels in air natural convection with symmetrical and asymmetrical uniform wall heat flux are proposed on the basis of correlations between the significant dimensionless process parameters derived from previous articles. The radiative contribution to heat transfer is taken into account. The design charts are obtained for two values of surface emissivity, 0.05 and 0.8, and the thermophysical properties are evaluated at the reference temperature equal to 40 ° C. The optimal spacing value for inclined single channels, in terms of thermal performance, is obtained from composite correlations between average Nusselt and Rayleigh numbers as functions of the angle. The estimated values of optimal spacing for vertical single channels correspond well with the results obtained by Bar-Cohen and Rohsenow [14]. A simple estimation procedure is proposed to evaluate the error in the relevant geometric and thermal parameters due to a different value of the reference t...
TL;DR: The difference between heat losses in percentage and in absolute measures is elucidated in this paper, where good conditions for making experimental heat loss determination are outlined, i.e., to avoid varying temperatures in the ground surrounding the district heating (DH) pipes and in the pipe fluid.
Abstract: The difference between heat losses in percentage and in absolute measures is elucidated. Good conditions for making experimental heat loss determination are outlined, i.e., to avoid varying temperatures in the ground surrounding the district heating (DH) pipes and in the pipe fluid. An overview of in-situ methods is given, and methods working on the DH pipe casing are described. Recent developments regarding quantitative thermography are also described. A comparison of the methods on an operating preinsulated transmission line is presented.
TL;DR: In this article, the effects of the tube spacing, the positions of tubes, and the saltwater concentration on bundle boiling heat transfer of salt water in the restricted space of the compact tube bundle evaporator under atmospheric pressure were investigated.
Abstract: In desalinization devices and some heat exchangers making use of low-quality heat energy, both the wall temperature and the heat flux of the heated tubes are generally quite low, hence cannot cause boiling in flooded-type tube bundle evaporators with a large tube spacing. But when the tube spacing is quite small, incipient boiling can occur in the restricted space and results in higher heat transfer than that in a falling-film evaporator or during pool boiling at the same heat flux. This study experimentally investigates the effects of the tube spacing, the positions of tubes, and the salt-water concentration on bundle boiling heat transfer of salt water in the restricted space of the compact tube bundle evaporator under atmospheric pressure. The experimental results provide a restricted space boiling database for salt water in the compact tube bundle. Of particular importance is information concerning the influences of the tube spacing of the tube bundle and the concentration of salt water in desalinatio...
TL;DR: In this article, a nonlinear optimization algorithm is applied to the design of air-cooled heat exchangers, subject to certain geometric and thermohydraulic constraints, and the objective function is the minimum cost of the unit (investment and operation).
Abstract: A nonlinear optimization algorithm is applied to the design of air-cooled heat exchangers. In such equipment, the cold fluid (air) is impelled across banks of finned tubes by means of fans in forced or induced draft. The hot stream flows inside the tubes in one or more passes, and the process that takes place may be cooling of either a gas or a liquid, or condensation of either a pure vapor or a mixture. The objective function is the minimum cost of the unit (investment and operation), subject to certain geometric and thermohydraulic constraints. The optimization algorithm used is that developed by Biegler and Cuthrell [1], and programmed by them in the OPT package. The problem posed in this case is made of 10 optimization variables, subject to five constraints related to geometric and operational parameters of the heat exchanger.
TL;DR: In this paper, a model was developed which describes the phase change process (evaporation) of fuel droplets in a gas turbine engine combustor, where the droplet density was considered to be a function of temperature, and the thermal expansivity α = -ρ p -1 (dρ p /dT p ) was introduced.
Abstract: A model is developed which describes the phase-change process (evaporation) of fuel droplets in a gas turbine engine combustor. To develop this model we have employed the conservation laws (droplet momentum, heat and mass transfer). Specifically, we used Newton's second law of motion in conjunction with the thermal expansion of the droplet. In this study the droplet density is considered to be a function of temperature, ρ p = ρ p (T p ). As a consequence, the thermal expansivity α = -ρ p -1 (dρ p /dT p ) is introduced, which has a significant effect on the evaporation process. Furthermore, the conditions on the droplet's surface are determined by taking into account the effect of surface tension on the fuel vapor pressure. The droplet characteristics such as position, velocity, temperature, and diameter are described by a system of six ordinary differential equations, which are solved numerically using a variable step Runge-Kutta algorithm of order 5(4). Due to the above conditions, our results differ from those reported in the literature [1-5J.
TL;DR: In this paper, the authors used computational fluid dynamics (CFD) analysis to compute effective nozzle discharge coefficients for subscale sharp-edged converging/diverging nozzles, with a variety of convergence half-angles, motor operating conditions, and two propellants with different ballistics.
Abstract: Computational fluid dynamics (CFD) analysis was used to compute effective nozzle discharge coefficients for subscale sharp-edged converging/diverging nozzles, with a variety of convergence half-angles, motor operating conditions, and two propellants with different ballistics. Convergence half-angles ranged from 10° to 90°. Analysis was conducted at total temperatures from 2,946 K (5303°R) to 3,346 K (6023°R) and total pressures ranging from 2.72 MPa (395 psia) to 20.68 MPa (3,000 psia). Area ratios (A e /A*) ranged from 7.43 to 9.39. Ratio of specific heats ( n ) ranged from 1.13 to 1.18. The maximum throat and exit Reynolds' numbers based on axial diameter ranged from 6.73 2 105 to 3.61 2 106 and 3.26 2 105 to 1.99 2 106, respectively. Present results of nozzle discharge coefficients are reported and correlated as a function of nozzle convergence half-angle ( / c ), area ratios (A e /A*), and pressure ratio (P o /P X ) for a constant divergence half-angle ( / d ) of 15°. Computed discharge coefficients r...
TL;DR: In this paper, an analytical model of heat transfer and pressure drop is worked out, which accounts for components of the heat flux density in the boundary sublayer due to convection, interaction of heat sinks, and turbulence effects.
Abstract: The article describes results of investigations of heat transfer and pressure drop during saturated bubbly boiling of new environment-friendly refrigerating media. Taking advantage of the experimental results, an analytical model of heat transfer and pressure drop is worked out. An essential feature of the model is that it accounts for components of the heat flux density in the boundary sublayer due to convection, interaction of heat sinks, and turbulence effects. The comparison of computational results and experimental data, from the present study and from other investigations, shows that the proposed method of determination of heat transfer coefficients and pressure drop can be applied to a number of refrigerating media with a wide range of heat and flow parameters, assuring accuracy to - 20%. Therefore, the method can be used in design of heat exchangers for refrigeration units as well as complete refrigeration units.
TL;DR: In this article, the optimum dimensions of rectangular longitudinal radiating fins with radiant interaction between the fin and its base are determined by means of dimensionless variables and solved using a variable-step Runge-Kutta algorithm, with local extrapolation, in order to carry out the required minimization procedure.
Abstract: The optimum dimensions of rectangular longitudinal radiating fins with radiant interaction between the fin and its base are determined. The basic assumptions are one-dimensional heat conduction and ideal black-surface radiation. The governing differential equation is formulated by means of dimensionless variables and is solved using a variable-step Runge-Kutta [1, 2] algorithm, with local extrapolation [3], in order to carry out the required minimization procedure. The optimum thickness, height, and percent contribution of the fin heat dissipation are presented in dimensionless form in several diagrams that give insight into the operational characteristics of the heat rejection mechanism. It has been found that the results are strongly affected by the surface Biot number Br = hrR/k. Several examples that highlight design criteria with regard to the selection of the material, amount of heat rejected, and tube and fin base temperature are given. A comparison of our results with those existing in the literat...
TL;DR: In this article, the effect of phase-lag in the wave theory of heat conduction on the thermal behavior of systems that exhibit phase-change processes such as melting and solidification is investigated.
Abstract: The aim of the present work is to investigate the effect of the phase-lag concept in the wave theory of heat conduction on the thermal behavior of systems that exhibit phase-change processes such as melting and solidification. The general analysis is carried out and then two examples are given to describe the thermal behavior of systems involving phase-change processes under the effect of the hyperbolic heat conduction model. The first example describes the ablation process and the second example describes the solidification of a supercooled liquid confined in a half-space.
TL;DR: In this article, a contact resistance between two dissimilar materials of finite thickness is formulated as two cylinders in contact over an area at their centers, and the noncontact gap between the two cylinders is assumed to be filled with a thermally conducting fluid.
Abstract: Contact resistance between two dissimilar materials of finite thickness is formulated as two cylinders in contact over an area at their centers. The noncontact gap between the two cylinders is assumed to be filled with a thermally conducting fluid. The lateral surfaces are insulated, while the top and bottom surfaces are kept at constant temperatures. Heat diffusion equations in the cylinders are transformed to two integral equations for the heat flux through the contact and noncontact areas with the interstitial fluid conductance as a parameter. The integral equations are solved numerically. Therefore, no assumption on the heat flux distribution on the contact and noncontact surfaces is made. An expression for the dimensionless overall resistance is developed using the rate of heat transfer through the contact and noncontact areas. The effects of the length of the cylinders and the gap conductance on the overall and contact resistances were evaluated. Radial heat flux and temperature distributions over t...
TL;DR: In this article, a computer program, HaGuo Start-up Simulation Program (HGSSP), for thermal-hydraulic analysis is developed for simulation of start-up behavior of a once-through boiler equipped with various integral separator startup systems.
Abstract: In this study a computer program, HaGuo Start-up Simulation Program (HGSSP), for thermal-hydraulic analysis is developed for simulation of start-up behavior of a once-through boiler equipped with various integral separator start-up systems With the simulation results, design principles for optimizing a start-up system for design and optimization of start-up procedures for operation, which will result in minimum start-up losses by reducing the start-up time as much as possible, can be obtained On the basis of Dolezal's model, an improved analytical-numerical method is proposed to solve the coupled energy equations for flue gas and working fluid describing the transient heat transfer occurring in individual heating surfaces In order to verify the program presented here, the cold start of a 600-MW supercritical once-through boiler located in China on July 6, 1993, is simulated and a comparison with measured data made This comparison indicates reasonable agreement between the computational main steam pres
TL;DR: The use of two-fluid thermosyphons is especially advantageous for high-temperature applications as mentioned in this paper, in which Dowtherm A-water shows a 15-99% increase in heat transfer performance relative to DowTherm A alone in the range of 375°C > T hi > 350°C.
Abstract: In this study, the concept of introducing two-fluid thermosyphons is examined. Calculations were performed for both low and high temperature ranges with parallel and counter-flow arrangements. For lower-temperature application, 125°C > T hi > 75°C, use of ammonia in some rows and water in the rest of the thermosyphon can slightly improve the associated heat transfer performance for balanced counter-flow arrangement. However, for balanced parallel-flow arrangement in both low-and high-temperature applications, the concept of using two-fluid thermosyphons may not be feasible. The use of two-fluid thermosyphons is especially advantageous for high-temperature applications. For instance, in the range of 375°C > T hi > 350°C, the two-fluid thermosyphons (Dowtherm A-water) shows a 15-99% increase of heat transfer performance relative to Dowtherm A alone.
TL;DR: In this article, the dynamic behavior of a horizontal boiling channel with a surge tank is investigated through a nonlinear analysis and the qualitative features of the response can be understood in terms of the underlying model.
Abstract: The dynamic behavior of a horizontal boiling channel with a surge tank is investigated through a nonlinear analysis. The surge tank is subject to a constant inlet flow rate and the outlet pressure-flow rate relation of the downstream boiling regime is described by a constitutive model containing a cubic nonlinearity. Within certain operating regimes, the model exhibits self-excited periodic oscillations which can be identified with pressure-drop oscillations. In this study, these oscillations are described as relaxation oscillation and the qualitative features of the response can be understood in terms of the underlying model. Finally, the present model is compared with the experimental data available in literature.
TL;DR: In this paper, a new technique for prediction and measurement of compact heat exchanger surfaces has been established, which utilizes an analogy between heat transfer and fluid friction proposed by a French scientist in 1928.
Abstract: A new technique for prediction and measurement of compact heat exchanger surfaces has been established. The method utilizes an analogy between heat transfer and fluid friction proposed by a French scientist in 1928. The applicability of this analogy to plate heat exchanger surfaces was examined recently. The present work proposes to use the same analogy for crossed rod bundles used in regenerators. For this purpose, the analogy equation has been modified to include a geometric factor which takes care of the fraction of the pressure drop arising out of skin friction. The proposed form of equation is found to be more general, applicable to crossed rod structures of any geometric configuration. The proposition was formulated based on standard data from the literature and also by conducting independent experiments. The result of the transient experiment indicate excellent adherence to the proposed analogical equation. The experimental evidence clearly indicates the possibility of predicting heat transfer char...
TL;DR: In this paper, the surface heat transfer on the quenched part of a gear blank in agitated and stagnant oil is calculated using a straightforward minimization of an appropriate norm and the time history of temperature is determined with a whole-domain optimizer technique inverse solution method.
Abstract: This article presents experimental and numerical results for the quench of a gear blank in agitated and stagnant oil. The time history of temperature is determined with a whole-domain optimizer technique inverse solution method. This article offers a procedure to calculate the surface heat transfer on the quenched part by utilizing a straightforward minimization of an appropriate norm. The article presents 10 variations in setting up this inverse problem. The results indicate that dividing the boundary of the gear blank into four zones and assigning a fixed heat transfer coefficient or heat flux to each zone yields an average error of 40 K. This error can be reduced by either increasing the number of zones or by allowing the heat transfer coefficient or heat flux to vary within the zones. Of these possibilities, variation of heat transfer within the zones results in a greater reduction of the average error for the required level of computational effort.
TL;DR: The thermal aspects of manufacturing are a very important activity that can have profound effects on the optimization of process parameters, the quality and reliability of the parts produced, and the economics of the process itself as discussed by the authors.
Abstract: It is a welcome opportunity and an honor to prepare this guest editorial on the Thermal Aspects of Manufacturing, a topic of great personal interest and of signi cant importance to the global economy and to share it with our distinguished heat transfer colleagues around the world. Various manufacturing processes used in the production of a wide range of products and tribology (friction, lubrication, and wear)applications account for a signi cant fraction of GNP. Several hundred billion dollars per year are consumed in the U.S. alone for these activities. The plastic deformation and/or frictional energy involved in the above operations manifest as heat energy generating high temperatures, as well as high temperature gradients that can have detrimental effects on the nished parts and on the cutting and forming tools. Consequently, thermal aspects of manufacturing are a very important activity that can have profound in uence on the optimization of process parameters, the quality and reliability of the parts produced, and nally the economics of the process itself. Jaeger, in his classical paper on “Moving Sources of Heat and the Temperature at Sliding Contacts,” [1] commences his article with the following statement: “Problems involving moving sources of heat arise frequently in practice in the calculation of temperatures at sliding or cutting contacts, but despite their importance they have not been studied systematically.” Similarly, Schneider in his book on conduction heat transfer [2] points out that the subject of transient heat ow originating from a moving source of heat has extensive application in sliding friction, internal ballistics, machining, and numerous metal treatment operations such as welding, casting, quenching, and ame-hardening. It is clear from the above, the importance of thermal aspects of manufacturing as a research and a teaching endeavor. Exact mathematical analysis of moving heat sources using the Fourier’s partial differential equation of heat conduction was developed by Rosenthal in the U.S. from the mid-1930’s to the mid-1940’s [3]. For addressing welding problems, Rosenthal introduced the moving coordinate system and considered quasi-steady state conditions . Around the same time, Herman Blok of the Netherlands introduced an ingenious principle of heat partition between a stationary and moving heat source for the case of sliding friction by matching the temperature of the two bodies at the interface [4]. He also brought into focus the importance of ash temperatures in sliding contacts. Jaeger from Tasmania, Australia, developed the mathematical analysis of moving heat sources and the temperature at sliding contacts using the heat source method in 1942 [1] that became the basis for much of the analytical work that followed for addressing various manufacturing processes and tribological problems. Many other researchers extended this work for various applications. Even though Heat Transfer is an important part of the mechanical engineering curriculum (often with three courses—Conduction, Convection, and Radiation), its application to manufacturing and tribology is generally not addressed in the undergraduate curriculum. Similarly, many Heat Transfer books, including those that limit the scope to Heat Conduction, either cover this topic very brie y or not at all; instead the emphasis is on the traditional issues in stationary conduction bodies. This by no means is a criticism either of the course content or the contents of the textbooks but merely a re ection of certain preferences that were made years ago by the mechanical engineering community-at-large . The main problem, in an ever growing scienti c and engineering knowledge-base in manufacturing and limited available time due to tight course schedule, the question arises at to which topics should be included and which should face sun set. Or, in other words, the problem is one of establishing the priorities. For example, electronic cooling, a very important topic, is now included in the course curriculum. Similarly, it is our hope that thermal aspects of manufacturing and tribology will also be considered by our distinguished colleagues for inclusion as part of the course curriculum, at a minimum, if not as a new elective course. At Oklahoma State University (OSU) we have been actively engaged in research on the thermal aspects of manufacturing and have been investigating a range of manufacturing processes and tribological applications , including, welding [5, 6], laser transformation hardening of gears [7], high-speed machining [8], temperature distribution due to shear plane heat source and the frictional heat at the chip-tool interface in cutting [9–11], polishing [12–14], general solutions [15], and
TL;DR: In this paper, the authors studied the internal corrosion of tubes used in a thermosyphon heat exchanger for waste heat recovery and found that the average corrosion rate was inversely proportional to time and depended on the temperature.
Abstract: The purpose of this article is to study the internal corrosion of tubes used in a thermosyphon heat exchanger for waste heat recovery. The thermosyphons used were made of aluminum, copper, iron, copper with internal spiral grooving, and stainless steel with internal spiral grooving. Different corrosion-protection methods were used, including tube burning and the addition of inhibitors. The thermosyphons were installed in the heat exchangers and tested over a period of 4,000 hrs at working temperatures of 150, 250, and 350 °C. The Arrhenius and fouling models of Kern and Seaton were employed to analyze the data. It was found from experiments that the average corrosion rate was inversely proportional to time and depended on the temperature. The results were then compared with those taken in standard untreated tubes. Results showed that the most appropriate material for thermosyphons in waste heat recovery systems is copper tubing with a grooved internal surface. The most appropriate corrosion protection for...
TL;DR: In this article, a method for evaluation of the critical velocity in the case of two (vapor?liquid)-phase mixtures transported in pipelines was developed. This method is based on a theoretical background of complex hydrocarbon mixture thermodynamics with respect to application in the petrochemical industry.
Abstract: A method for evaluation of the critical velocity in the case of two (vapor?liquid)-phase mixtures transported in pipelines was developed. This method is based on a theoretical background of complex hydrocarbon mixture thermodynamics with respect to application in the petrochemical industry. Methods published so far have focused on applications in the power industry, where the water?steam two-phase system is considered. The method presented allows one to calculate pressure drop, velocity, and temperature profiles for two-phase complex hydrocarbon systems and to identify the critical flow presence. In this method the critical condition means a singular discontinuity where the finite pressure and/or velocity change corresponds to an infinitesimal change in space coordinate. An example of applying the method in the case of a furnace-to-distillation column transfer line is shown. It can be observed that using this method can be considered a contribution to solving practical industrial cases. This method was ve...