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Showing papers in "Heat Transfer Engineering in 2002"


Journal ArticleDOI
TL;DR: In this paper, a comprehensive review of literature on evaporation in small-diameter passages along with some results obtained by the author for water evaporating in 1mm-hydraulicdiameter multichannel passages is presented.
Abstract: The small hydraulic diameters employed during flow boiling in compact evaporator passages are becoming more important in diverse applications including electronics cooling and fuel cell evaporators. The high pressure drop characteristics of these passages are particularly important as they alter the flow and heat transfer, especially in parallel multichannel configurations. The pressure drop oscillations often introduce dryout in some passages while their neighboring passages operate under single-phase mode. This article presents a comprehensive review of literature on evaporation in small-diameter passages along with some results obtained by the author for water evaporating in 1-mm-hydraulic-diameter multichannel passages. Critical heat flux is not covered in this article due to space constraints.

141 citations


Journal ArticleDOI
TL;DR: In this article, a review of the conventional and more recent forms of shell-and-tube heat exchangers is presented, and the benefits of global and local intensification are illustrated with examples of a helically baffled heat exchanger (Helixchanger), as a representative of a more recent form of shell and tube exchanger.
Abstract: A variety of different strategies are available to process and equipment designers to improve industrial heat transfer. These range from the use of efficient forms of individual heat exchangers to the optimum utilization of the individual units in a network, generally referred to as "process integration." This article attempts to review these strategies with reference to the conventional and more recent forms of shell-and-tube heat exchangers. In the context of a heat exchanger network, process heat transfer intensification ( global intensification ), i.e., network design for maximum energy recovery, is a first important step. This needs to be then combined with heat transfer intensification in individual units/shells ( local intensification ). The benefits of global and local intensification are illustrated with examples of a helically baffled heat exchanger ( Helixchanger ), as a representative of a more recent form of shell-and-tube exchanger. Some aspects concerning the use of multistream heat exchang...

124 citations


Journal ArticleDOI
TL;DR: In this paper, a study on heat transfer in condensation of pure and mixtures of hydrocarbons in a compact welded plate heat exchanger is presented, where three pure fluids (pentane, butane, and propane) and two mixtures (butane + propane).
Abstract: This article presents a study on heat transfer in condensation of pure and mixtures of hydrocarbons in a compact welded plate heat exchanger. Three pure fluids (pentane, butane, and propane) and two mixtures (butane + propane) have been used. The operating pressure ranges from 1.5 to 18 bar. For pure fluids, two heat transfer mechanisms have been identified. For low Reynolds numbers, the condensation occurs almost filmwise and the heat transfer coefficient decreases with increasing Reynolds number. For higher values of the Reynolds number, the heat transfer coefficient increases gently. The transition between the two regimes is between Re = 100 and 1,000 and depends on the operating conditions. For mixtures, the behavior is different. For low Reynolds numbers, mass transfer affects heat transfer and reduces the heat transfer coefficient by a factor of up to 4. Correlations for filmwise and in-tube condensation do not predict the results accurately, and a specific correlation is proposed for pure fluid condensation. For mixtures, the condensation curve method does not allow mass transfer effects to be taken into account, and more work is required to establish an accurate predictive model.

54 citations


Journal ArticleDOI
TL;DR: In this article, single-phase pressure drops inside the complex headers and parallel circuits of a microchannel heat exchanger were measured systematically, for the purpose of identifying and quantifying internal manufacturing defects.
Abstract: Single-phase pressure drops inside the complex headers and parallel circuits of a microchannel heat exchanger were measured systematically, for the purpose of identifying and quantifying internal manufacturing defects. Results confirmed the Moody chart to be applicable for the submillimeter channel flows. Based on nonintrusive testing followed by destructive evaluation, two types of manufacturing defects were quantified: variation of microchannel port diameters and port blockage by brazing flux. A pressure drop model for the whole heat exchanger was developed, and predicted the pressure and mass flow rate distribution inside the heat exchanger, providing valuable insights for selecting microchannel tube dimensions and heat exchanger circuiting. Most important, simple nitrogen flow tests can now be used to help control the quality of the brazing process, by detecting the presence of blocked or deformed ports in the finished product.

50 citations


Journal ArticleDOI
TL;DR: In this paper, the two-phase flow patterns of HFC-134a with lubricant oil mixtures inside a smooth horizontal tube were experimentally elucidated, and the most obvious difference from oil-free cases reported is the presence of froth flow pattern, which is related to the increase of surface tension and viscosity.
Abstract: The two-phase flow patterns of HFC-134a with lubricant oil mixtures inside a smooth horizontal tube were experimentally elucidated. Tests were performed in an inside diameter of 7.8 mm having a lubricating oil concentration of 5%. Tests were made of mass fluxes ranging between 150 and 590 kg/m 2 s. The most obvious difference from oil-free cases reported is the presence of froth flow pattern. Apparently, this flow pattern is related to the increase of surface tension and viscosity. With the presence of lubricant oil, the onset of transition from stratified flow region to annular flow regime shifted to a lower value of superficial gas velocity. In addition, the tearing phenomenon of the refrigerant-oil mixtures may be related to its relevant properties such as wettability and surface tension.

38 citations


Journal ArticleDOI
TL;DR: In this paper, the authors measured the flow field in shell-and-tube heat exchangers with helical baffles using laser Doppler anemometry (LDA), and investigated the influence on the velocity distribution, impulsive velocity by helix inclination angle, and flow rate.
Abstract: The flow field in shell-and-tube heat exchangers with helical baffles was measured using laser Doppler anemometry (LDA). The influence on the velocity distribution, impulsive velocity by helix inclination angle, and flow rate was investigated. The influence on heat exchanging capability and flow resistance on velocity distribution was also investigated. The dimensions of the heat exchanger shell used in these experiments were 200 2 6 2 3,000 mm (inner diameter 2 wall thickness 2 length). The heat exchanger was made of organic glass and the tube bundle consisted of 52 tubes with external diameter of 15 mm. Six different inclination angles were designed in double-helix style: 30°, 35°, 40°, 42°, 45°, and 50°. The working flow medium under normal temperature was service water. Generally, the linear velocity and impulsive velocity will increase with decreasing helix inclination angle, which promotes the heat exchanging capability. With flow volume increasing, the velocity distribution along the diameter incre...

37 citations


Journal ArticleDOI
TL;DR: A semi-empirical fouling model for crude oil fouling developed by Panchal and co-workers allows the effects of fouling to be considered at the design stage for such networks as mentioned in this paper.
Abstract: Fouling in crude oil preheat trains is a significant industrial problem which has restricted the application of process integration techniques such as "pinch technology" in this sector. A semiempirical fouling model for crude oil fouling developed by Panchal and co-workers allows the effects of fouling to be considered at the design stage for such networks. Application of this model at three levels--(1) design of new networks; (2) retrofitting of existing systems; and (3) identification of robust specifications for individual heat exchanger units--is discussed. The design issues are discussed using case studies illustrated by a graphical construction, the temperature field plot. Rigorous optimization of the final designs is not reported. The specification discussion describes how the crude fouling model can be incorporated into existing heat exchanger design software to identify exchanger configurations which are less likely to experience significant fouling over a range of operating conditions. This arti...

33 citations


Journal ArticleDOI
TL;DR: In this paper, the authors describe the development of simple algebraic correlations that can be used to approximate the intermittent overall heat transfer between a fluid flowing in an isolated buried pipe and the surrounding ground.
Abstract: An accurate estimate of the heat transfer from a buried pipe to the surrounding ground is essential for the design of the ground-loop portion of a ground-source heat pump. Exact analytical solutions to this problem are complicated by the fact that heat pump systems rarely operate continuously. Complete numerical simulations of system designs can be carried out, but these are unwieldy and difficult to justify for initial scoping calculations, or for preliminary performance estimates. The purpose of this article is to provide insight into the heat transfer mechanisms and to describe the development of simple algebraic correlations that can be used to approximate the intermittent overall heat transfer between a fluid flowing in an isolated buried pipe and the surrounding ground. The correlations described in this article were drawn from results of a numerical finite-difference analysis of a fluid flowing intermittently in a single round pipe and exchanging heat with the surrounding ground. It is found that t...

26 citations


Journal ArticleDOI
TL;DR: In this paper, the physical and mathematical models describing the free-falling turbulent wavy films with the free surface boundary are presented, and the governing equations are solved numerically in the film waves based on the coordinate transformation of the measured time-dependent film thickness data.
Abstract: The evolution of the surface waves for vertical free-falling films with Reynolds number ranging from 440 to 5,100 was measured using multiple-point conductance sensors and a computer-based data acquisition system. The physical and mathematical models describing the free-falling turbulent wavy films with the free surface boundary are presented. The governing equations are solved numerically in the film waves based on the coordinate transformation of the measured time-dependent film thickness data. The results show that the evolution of the surface waves has a remarkably nonlinear nature. The hydrodynamics and velocity profiles at the wave front, the wave crest, and the wave back for the solitary waves indicate significant effects of the solitary surface waves with interior recirculation flow on heat and mass transfer enhancement. A correlation for an average heat transfer coefficient is proposed as a function of the Reynolds and Prandtl numbers based on the measurements.

22 citations


Journal ArticleDOI
TL;DR: In this article, the numerical simulation of reactive turbulent flow and heat transfer in a regenerative gas-fired furnace has been carried out to investigate its performance, and the effects of geometric and operating conditions on the performance of the furnace have also been studied.
Abstract: In the present study, the numerical simulation of reactive turbulent flow and heat transfer in a regenerative gas-fired furnace has been carried out to investigate its performance. The effects of geometric and operating conditions on the performance of the furnace have also been studied. A moment closure method with an assumed g probability density function for mixture fraction is used in the present work to model the turbulent nonpremixed combustion process in the furnace. A comparison is made between the predicted results and the experimental data.

18 citations


Journal ArticleDOI
TL;DR: In this article, the theoretical fin efficiency of serrated fin was analyzed and an analytical solution of the fin efficiency was derived in the form of a function of modified Bessel functions.
Abstract: Fin efficiency of serrated fins was analyzed and an analytical solution of the theoretical fin efficiency was derived in the form of a function of modified Bessel functions. Furthermore, an approximate equation has been given which enables one to calculate the theoretical fin efficiency with a pocket calculator with an accuracy of - 1.5%. In the analysis of the theoretical fin efficiency, however, two assumptions were employed, i.e., uniform heat transfer coefficient over the fin surface and thermal insulation at the end surface of the segmented sections. To compensate for these assumptions, a correction factor was introduced and determined experimentally. Using this correction factor, together with the theoretical fin efficiency, the actual fin efficiency can be estimated for serrated fins of various fin geometries, including plain fins.

Journal ArticleDOI
TL;DR: In this paper, the analytical time constants of temperatures transient response along a countercurrent heat exchanger when a mass flow-rate step change is applied on hot fluid flowing through the inner duct are investigated.
Abstract: This article investigates the analytical time constants of temperatures transient response along a countercurrent heat exchanger when a mass flow-rate step change is applied on hot fluid flowing through the inner duct. The time constants of the hot and cold fluids are spatially linear and the fluid not submitted to step change shows two types of transient response. The first corresponds to a linear spatial decreasing of the time constant, while the second presents a uniform time constant along the heat exchanger. For each case, the analytical expressions of time constants are derived taking the conditions of the transient response on the boundaries of the heat exchanger. The condition which enables distinguishing the two cases is also proposed in this article. The comparison between theoretical and experimental results allows us to validate the analytical expressions, which depend on the initial and final steady states. The influence of the magnitude of flow-rate step change on the transient behavior is s...

Journal ArticleDOI
TL;DR: In this paper, a new steady-state formulation of temperatures along a double-pipe heat exchanger in counterflow configuration when the mass flow rate is submitted to step change is presented.
Abstract: This article deals with a new steady-state formulation of temperatures along a double-pipe heat exchanger in counterflow configuration when the mass flow rate is submitted to step change. The steady-state method is based on estimation of the exponential factor of temperature profile. This method, compared to results obtained from correlations, gives an alternative approach to the well-known procedures for sizing and rating heat exchangers in industrial applications, such as the k -NTU and LMTD methods. It is based on the average convective heat transfer coefficients of the hot and cold sides, while the other methods are based on the overall heat transfer coefficient.

Journal ArticleDOI
TL;DR: In this paper, a preliminary method to estimate the plume chimney height for a still ambient condition is presented, where the authors predict a negligible effect of the chimney's height on the performance of a laboratory-size test exchanger.
Abstract: A preliminary method to estimate the plume chimney height for a still ambient condition is presented here. The method predicts a negligible plume chimney effect on the laboratory-size test exchanger. Measurements from an industrial-size heat exchanger (2.4 2 6.0 m 2 ) in forced-draft mode have been compared with simulations incorporating the new method. The simulated heat loads agree with the 11 measurements to within +25/-40%, compared to an average of +70% if calculated by an existing formula and -75% by assuming negligible effective plume chimney height. Agreement between the new method and the measured exchanger performance did not appear to be affected by wind speeds in the range 2-6 m/s.

Journal ArticleDOI
TL;DR: In this paper, the authors focused on the computational analysis of evaporative film cooling, in connection with an experimental campaign carried out at the University of Pisa by the EFFE facility.
Abstract: The present work is focused on the computational analysis of evaporative film cooling, in connection with an experimental campaign carried out at the University of Pisa by the EFFE facility ( E xperiments on F alling F ilm E vaporation). The aim of the study is to contribute to the understanding of the heat and mass transfer mechanisms involved in the problem and to check the possibility of making use of a multipurpose commercial computational fluid dynamics (CFD) code for simulating mass transfer phenomena of interest in the nuclear field. After a description of the assumptions adopted in the mathematical formulation of the problem, the governing equations and the boundary conditions implemented in the code are briefly reported. In particular, the method used to evaluate the mass transfer through the interface is described. Then, the calculated results are analyzed and a comparison with experimental data is made. The improvement in the cooling capabilities of the heated plate due to evaporation with resp...

Journal ArticleDOI
TL;DR: In this paper, a network model of a fin-wall assembly, whose admittance is identical to the thermal admittance of the system, has been designed for the whole system.
Abstract: The classical performance indicators for extended surfaces, efficiency and effectiveness, cannot be used for the proper design of finned systems subject to time-dependent processes, such as heat exchangers or electric devices. Based on the network simulation method, a network model of a fin-wall assembly, whose admittance is identical to the thermal admittance of the system, has been designed for the whole system. A new fin performance indicator, output admittance, is proposed, and frequency analysis of the system is carried out. The simulated numerical response is rapidly obtained by running the network in the appropriate circuit resolution software. This method is especially useful for studying complex thermal transmission functions such as admittance, evaluating modulus, phase, and real and imaginary components of the thermal signal.

Journal ArticleDOI
TL;DR: In this paper, teaching desalination - a multidiscipline engineering science is discussed, with a focus on teaching Desalination in the context of heat transfer engineering, and a review of the literature.
Abstract: (2002). Teaching Desalination - A Multidiscipline Engineering Science. Heat Transfer Engineering: Vol. 23, No. 5, pp. 1-3.

Journal ArticleDOI
TL;DR: In this article, the authors derived the governing equations from ice melting with specified heat fluxes on the boundary of complete removal of melt, and the approximation solutions were obtained, from the integral boundary-layer analysis, to estimate the thickness of ice melted and the thermal penetration distance in the ice-layer region.
Abstract: A more efficient device in energy transfer for a cool thermal discharge system has been designed. The governing equations have been derived from ice melting with specified heat fluxes on the boundary of complete removal of melt, and the approximation solutions were obtained, from the integral boundary-layer analysis, to estimate the thickness of ice melted and the thermal penetration distance in the ice-layer region. Considerable improvement in performance of cool thermal discharge can be achieved if the operation is conducted with complete removal of melt, rather than without removal of melt.

Journal ArticleDOI
TL;DR: In this article, a probe to monitor gas-side fouling in cross flow has been developed and tested in laboratory experiments, which is suitable for monitoring both the heat flux and the mass accumulated on the front and rear side of a cylinder in cross-flow.
Abstract: A probe to monitor gas-side fouling in cross flow has been developed and tested in laboratory experiments. The probe is suitable for monitoring both the heat flux and the mass accumulated on the front and rear side of a cylinder in cross flow. A procedure for converting the mass accumulation measurements to thermal resistance is developed. Experimental results obtained using the mass accumulation method are compared to data obtained by heat flux measurements, and show good agreement in terms of the thermal fouling factor. It is also shown that the test results are in good agreement with other experimental results found in the literature. The probe is well suited for distinguishing the thermal effect (thermophoresis) from the other forces contributing to fouling. It is also useful for nonfouling heat transfer studies, providing average heat transfer coefficients on the front and rear sides of a cylinder.

Journal ArticleDOI
TL;DR: In this paper, the identical-fin concept and the Z-Y graph are used to determine the optimal heat transfer conditions for each stream and the network configuration simultaneously to promote the use of compact heat exchangers.
Abstract: Industries are starting to replace shell-and-tube heat exchangers with compact heat exchangers in several applications. Benefits have been reported when using compact heat exchangers at the equipment level. However, greater economic benefits can be realized when applying compact heat exchangers in the context of the overall heat transfer system. This is not an easy task for both industries and designers who are new to compact heat exchangers. This is because the data for heat transfer conditions for each stream are not available in the early design stage to guide the overall network design. Hence, a method which can determine the optimal heat transfer conditions for each stream and the network configuration simultaneously is essential in promoting the use of compact heat exchangers. Here a novel method is developed which can achieve this objective. The new method utilizes the advantages of two new physical insights into heat transfer surface selection, i.e., the identical-fin concept and the Z - Y graph. ...

Journal ArticleDOI
TL;DR: In this paper, the authors defined a thermo-fluid dynamic efficiency for a mechanical draft water-cooling tower, which allows evaluating the heat transfer related to the pressure drop, and showed that this efficiency is not a function of the height of the fill.
Abstract: A thermo-fluid dynamic efficiency is defined for a mechanical draft water-cooling tower. It allows evaluating the heat transfer related to the pressure drop. It could also be used in isolated fills in different types of water-cooling towers. Thermo-fluid dynamic efficiency values obtained with available experimental results acquired from commercial fills are shown, and it can be concluded that this efficiency is not a function of the height of the fill.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the effect of buoyancy forces on heat transfer from a straight isothermal elliptic tube at different angles of attack (u), placed in a convective environment with fluctuations in the free-stream velocity, and found that the time average of the Nusselt number increases with increasing amplitude of fluctuations and with decreasing Strouhal number.
Abstract: The problem of mixed-convection heat transfer from a straight isothermal elliptic tube at different angles of attack ( u ), placed in a convective environment with fluctuations in the free-stream velocity, is investigated numerically, including the effect of buoyancy forces. The free-stream direction is horizontal and normal to the tube axis, and the flow field is essentially two-dimensional. The investigation is based on a numerical solution of the conservation equations of mass, momentum, and energy. The parameters involved are fluctuations amplitude g , Strouhal number S, Reynold number Re, Grashof number Gr, Prandtl number Pr, the tube geometry, and its orientation presented by its angle of attack u . The study focuses on the effect of S, Re, Gr, and u on the heat transfer process. The time average of the Nusselt number is found to increase with increasing amplitude of fluctuations and with decreasing Strouhal number. The response of the total rate of heat transfer to changes in inclination angle is f...

Journal ArticleDOI
TL;DR: In this paper, the Peltier effect is used to measure the thermal diffusivity of a material by monitoring the propagation of the temperature cycles along the optically accessible surface of the material, adjacent to the thermal input surface area.
Abstract: A new test method is presented for the on-field nondestructive measurement of the thermal diffusivity of solid materials. A periodic thermal disturbance is supplied to the inspected material by a thermoelectric source based on the Peltier effect. This can alternate heating and cooling stages and provide, if properly controlled, a harmonic disturbance with null net heat flux. A steady-periodic temperature field can thus be induced within the specimen. The diffusivity of the material is then estimated by monitoring the propagation of the temperature cycles along the optically accessible surface of the specimen, adjacent to the thermal input surface area. A camera for infrared thermography is used for nonintrusive surface temperature measurement. At the current stage of development, the focus is on the accurate reproduction of the theoretical model on which the method is based. Ease of operation and portability of the test equipment are also pursued. However, tests on thin specimens of materials with known p...

Journal ArticleDOI
TL;DR: In this paper, the thermal behavior of a thin layer carrying pulsating signals under the effect of the dual-phase-lag heat conduction model is investigated and the deviation between the predictions of the classical diffusion and the dual phase-lag models is investigated.
Abstract: The thermal behavior of a thin layer carrying pulsating signals under the effect of the dual-phase-lag heat conduction model is investigated Two types of pulsating signals are considered, a pulsating heat source and a pulsating imposed temperature at the boundary The deviation between the predictions of the classical diffusion and the dual-phase-lag models is investigated

Journal ArticleDOI
TL;DR: In this paper, a new approach to correlate the frictional performance of fin-and-tube heat exchangers in "completely wet" and "partially wet" conditions by using "completely dry" data was presented.
Abstract: This study presents a new approach to correlate the frictional performance of fin-and-tube heat exchangers in "completely wet" and "partially wet" conditions by using "completely dry" data. A total of 22 samples of uncoated plain fin-and-tube heat exchangers are used to develop the associated frictional correlation. The developed correlation is capable of predicting the frictional performance of "completely wet" and "partially wet" conditions with a mean deviation of 7.2%.

Journal ArticleDOI
TL;DR: In this paper, the authors performed boiling experiments on new, chemically cleaned, and fouled steam generator tubes to determine the heat transfer performance of each, and found that the fouled tube was the best, followed by the chemically cleaned tube.
Abstract: Boiling experiments were performed on new, chemically cleaned, and fouled steam generator tubes to determine the heat transfer performance of each. It was found that the heat transfer performance of the fouled tube was the best, followed by the chemically cleaned tube. The performance of the new tube was the worst. Scanning electron microscope (SEM) photographs of the boiling surfaces were taken to identify differences in surface characteristics. Results revealed the presence of significant amounts of porous deposits on the surface of the fouled tube that provided ample nucleation sites for boiling. Chemical cleaning removed most of the deposits such that the boiling performance of the cleaned surface was degraded. The new tube was very smooth and there were relatively fewer nucleation sites as evidenced in the SEM photographs. Available correlations were used to predict the heat flux for a given wall superheat and were compared with the experimental data.

Journal ArticleDOI
TL;DR: In this paper, the authors deal with the time histories of the air flow rate required and the temperature of chilled air produced during cooling of air by melting ice with specified heat flux at the free liquid surface.
Abstract: This article deals with the time histories of the air flow rate required and the temperature of chilled air produced during cooling of air by melting ice with specified heat flux at the free liquid surface. The equations for estimating the required mass flow rate of air to maintain a specified heat flux removal of cool thermal discharge by direct contact of air with melting ice to produce chilled air were derived from an analysis of the heat transfer coupled with the moving boundary. Numerical examples are illustrated in which the inlet air temperatures were either specified or varied with time to simulate practical systems.

Journal ArticleDOI
TL;DR: In this article, the authors classified liquid crystals into three types: smectic, nematic, and cholestric, and used them for convective heat transfer measurements.
Abstract: Although liquid crystals have been used as temperaturesensing devices for quite some time, only for the past several decades they have been used for convective heat transfer measurements. As an intermediate phase between liquid and solid phase, liquid crystals were discovered in 1888. They have the structure of a crystalline solid and at the same time acquire the  uidity of a liquid. Depending on the molecular arrangements, liquid crystals are categorized in three ways: smectic, nematic, and cholestric. The smectic phase includes a series of layers and molecules that are located either in order or in random in each layer, and the layers are free to slide over one another. In the nematic phase, molecules are oriented parallel with respect to each other along their long axes such that their molecular centers of gravities are disordered. In the cholesteric phase, which is a special case of the nematic phase, the layers of the molecules produce a screw axis normal to the molecular direction in each layer. Because of their speciŽ c molecular arrangements, cholesteric liquid crystals are optically active, and it is this property that makes them attractive for applications such as temperature and heat transfer measurements. Heat transfer measurements using cholesteric liquid crystals have been mainly conducted by one of the two techniques: steady-state or transient. In steady-state technique,

Journal ArticleDOI
TL;DR: In this article, the authors review the similarity law of conventional fossil fuel-fired boilers and show that the surface heat flux limit is dominated mainly by the critical heat flux (CHF) inside the water wall tubes of the boiler furnace.
Abstract: This article begins with a brief review of the similarity law of conventional fossil fuel-fired boilers. The concept is based on the fact that the heat release due to combustion in the furnace is restricted by the furnace volume but the heat absorption is restricted by the heat transfer surface area. This means that a small-capacity boiler has relatively high specific furnace heat release rate, about 10 MW/m 3 , and on the contrary, a large-capacity boiler has a lower value. The surface heat flux limit is dominated mainly by the critical heat flux (CHF) inside the water wall tubes of the boiler furnace. This heat flux limit is almost the same order, independent of the capacity of the boiler. For the safety of water walls, it is essential to retain a good amount of water circulation, i.e., the circulation ratio and velocity of the water must be high enough above the respective critical values. This principle is common knowledge in boiler designer, but the actual situation is not the case. Newly designed bo...

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the relationship between heat transfer ratios of the Nusselt number for single-phase flow and pressure drop for flow boiling in channels with corrugated walls.
Abstract: The problem of heat transfer for flows in channels with corrugated walls is very complicated. Previously most investigators have focused their attention on studies of forced-convection, single-phase flow, and condensation of pure vapors and vapor gas mixtures. The results of new experimental investigations into heat transfer and pressure drop, for flow boiling in channels with corrugated walls, are discussed. The experimental section was a part of a pack of an industrial plate exchanger, which contained several pressed plates with longitude corrugations located under an angle to flow direction and had many contact points on the heat transfer area. The condensation method was used for the investigations. The relationship between the heat transfer ratios of the Nusselt number for single-phase flow was obtained. This correlation compares very favorably with the similar relationship obtained for flow bubble boiling in tubes proposed by Sterman [11]. For correlation of the pressure drop data, the Martinelli-Lo...