Forced Flow Of Water Research Articles

Intensification of heat exchange in the developed surfaces in flat channels

The paper presents the results of an experimental study of heat transfer during forced water flow from microstructured surfaces in a slotted channel. The investigated micro-structured surfaces were obtained by a resource-saving (waste-free) method of deforming cutting with various constructive shapes and sizes. A description of the experimental setup, methods for conducting and processing experimental data are presented. The maximum increase in heat transfer coefficients in comparison with a smooth surface reaches Nu/Nu0 = 16.2.

Investigation of the critical heat flux in small-diameter channels

The paper describes experimental studies into the hydrodynamics and heat exchange in a forced water flow in small-diameter channels at low pressures. The timeliness of the studies has been defined by the growing interest in small-size heat exchangers. Small-diameter channels are actively used in components of compact heat exchangers for present-day engineering development applications. The major difficulty involved in investigation of heat-transfer processes in small-diameter channels consists in the absence of common methodologies to calculate coefficients of hydraulic resistance and heat transfer in a two-phase flow. The channel size influences the heat exchange and hydrodynamics of a two-phase flow as one of the determining parameters since the existing internal scales (vapor bubble size, liquid droplet diameter, film thickness) may become commensurable with the channel diameter, this leading potentially to different flow conditions. It is evident that one cannot justifiably expect a change in the momentum and energy transfer regularities in single-phase flows as the channel size is reduced for as long as the continuum approximation remains valid. The authors have analyzed the experiments undertaken by Russian scientists to investigate the distribution of thermal-hydraulic parameters in channels with a small cross-section in the entire variation range of the flow parameters in the channel up to the critical heat flux conditions when the wall temperature increases sharply as the thermal load grows slowly. The experimental critical heat flux data obtained by Russian and foreign authors has been compared.

Review of photovoltaic module cooling methods and performance evaluation of the radiative cooling method

This paper reviews the state-of-the-art cooling methods of photovoltaic (PV) modules and evaluates the performance of the radiative cooling method in detail. Higher operating temperatures of PV modules cause degradation of conversion efficiency and long-term reliability. To overcome this drawback, active or passive cooling methods using heat pipe, natural/forced air flow, forced water flow, phase change material, direct liquid immersion/submerging, and passive heat sink have been studied. In this paper, the methodologies and cooling effects of various cooling methods in the literature are summarized to provide a comprehensive overview of the current cooling technologies. Then, the performance of the radiative cooling method, which is simple and passive (zero power consumption) method, is quantitatively evaluated based on a detailed heat transfer model considering sky radiation properties in four typical climate conditions. Daily heat budgets of the PV modules with different surface emissivity spectra are simulated to estimate the solar cell temperature. The results indicate that modification of the surface emissivity spectrum hardly contribute to the radiative cooling enhancement under any climate conditions, as compared to the conventional glass cover. The present findings serve as a guide for future research and development of better cooling methods.

Implications of Molecular Thermal Fluctuations on Fluid Flow in Porous Media and Its Relevance to Absolute Permeability

This paper addresses the challenge related to the understanding of varying absolute permeability when forcing fluid (mostly water is considered) through a porous medium at varying system temperatures. It is assumed that the total energy dissipation splits into two contributions, a viscous part and a thermal part. These two energy dissipation channels will exactly balance the supplied external energy. The thermal part has not been considered previously regarding forced water flow through porous media, and it is substantiated theoretically by comparison with the well-known Ludwig–Soret effect. It is based on a hypothesis that the flowing water is dissipating molecular kinetic energy to heat (thermal dissipation) due to an asymmetric spatial velocity distribution up- and downstream the solid matrix. Based on previous theoretical calculations, an expression can be derived showing that thermal dissipation will increase proportional with the total inner surface area of the porous medium and the square root of a...

THERMAL-HYDRAULIC ANALYSIS OF IRT-4M IN REACTIVITY INSERTION ACCIDENT AT VR-1 REACTOR

The paper deals with thermal-hydraulic analysis during reactivity insertion accident, i.e. a step increase of nuclear system reactivity by 0.7 eff, at VR-1 Reactor. The reactor utilizes IRT-4M type of fuel assemblies, and even though these fuel assemblies are designed for an operation at the high-power research reactors, they might be also used for zero-power reactors. The thermal-hydraulic analyses must take into account several specific assumptions that are derived from VR-1 reactor specifications. The reactor does not require a forced water flow for a fuel cooling, the core is placed in an open vessel with atmospheric pressure, and amount of coolant water in the vessel is sufficient for providing the inlet water at room temperature for the whole event. Coolant circulation is expected to be formed only by natural convection.

Entropy generation analysis of laminar forced convection through uniformly heated helical coils considering effects of high length and heat flux and temperature dependence of thermophysical properties

In this study, combined effects of length and heat flux of the coil as well as the effects of temperature dependence of thermophysical properties on entropy generation rates and optimal operation of uniformly heated helical coils with laminar forced convection have been analyzed analytically. For these purposes, comprehensive analytical formulas, which could be used for any duct shape and flow regime, are derived for thermal, frictional, and total entropy generation rates, and the effects of involved parameters on the entropy generation rates are examined for laminar forced flow of water through uniformly heated helical coils. Then, using the minimal entropy generation principle, the inlet Reynolds number is optimized for various values of the involved parameters, and some correlations are proposed for optimal values of this parameter which extend and modify the existing correlations of water. It is found that the entropy generation rates are highly dependent on the combined effects of length and heat flux of the coil, introduced by the parameter ηC, and temperature dependence of thermophysical properties, such that all of them noticeably augment with increase in ηC and the inlet temperature.

Thermal management of a multiple mini-channel heat sink by the integration of a thermal responsive shape memory material

In this paper, a novel application of a thermo-responsive shape memory polymer (SMP) is proposed to smart-control the forced flow of water in a multi mini-channel heat sink. In particular, it is reported that millimeter-sized cylinders made of SMP could be used to smartly obstruct the fluid flow by adapting the flow cross section to the heat load to be removed. By integrating the sensing, the control and the actuation functions within a unique, millimeter-sized device, these micro-valves, unlike the traditional actuators normally used for flow control, could be easily embedded into small heat sinks, with significant space and energy saving, useful, in particular, in systems where several miniaturized components have to be cooled concurrently, such as the modern mainframes or the concentrated photovoltaic solar cells.Two possible configurations for the SMP were considered in this study: an “open” configuration, without any obstruction of the water flow free and an “obstructed” configuration, with the millimeter-sized cylinder partially occupying the mini-channel. A numerical, steady state analysis was carried out with water in single-phase forced convection, to determine the effect of these two states on the internal fluid flow characteristics under different conditions of heat flux and pressure drop and to evaluate the overall thermal behavior of the smart-controlled multiple mini-channel heat sink in terms of ability to control the temperature of the system and to reduce the energy consumption.

Simplified film model of a heat transfer crisis in tubes

A simplified model is proposed dealing with a heat transfer crisis during forced flow of water in tubes. The formula for the critical heat flow is obtained. The verification showed that this formula with a single empirical coefficient embraces 4745 experimental values of critical heat flows at a mean square error of 0.0691 in a wide range of parametric variations.

Grow-out of northern pike (Esox lucius L.) larvae under uncontrolled conditions

.Background. This study aimed to determine survival rate, extent of cannibalism, and growth rate of northern pike (Esox lucius L.) larvae fed live zooplankton during a grow-out period, i.e., the time prior to when fish become valuable as stocking material. An attempt was also made to assess the food conversion ratio (FCR) with respect to the natural food applied. Materials and Methods. Grow-out operations began with 1-day-old pike larvae and involved experimental in-ground tanks with no artificial aeration, forced water flow, artificial circadian lighting, or temperature control. Differently structured habitats (black polyethylene foil, vascular plants, or plastic netting) were placed in all the tanks to separate larvae and provide cover. Feeding live zooplankton to the larvae began on day 3 and food was administered such that larvae were always surrounded by a zooplankton “cloud.” Results. The survival rate during the first- (days 1–7) and second (days 8–27) stage of culture was 92.3% and 95.7%, respectively. Highest survival rates were associated with tanks with polyethylene foil habitats, while lowest survival rates were associated with tanks containing plastic netting. No cannibalism was observed in any tank. During the growout period, the total length of larvae increased by an average of 20.88 mm. Although the length increase observed in the three experimental treatments was similar; the significantly highest (P < 0.01) mean length (32.66 mm) was associated with larvae raised in tanks containing polyethylene foil. Until day 13, the mean weight of the larvae did not differ between the three treatments (P = 0.21). At and beyond day 20, fish kept in tanks equipped with polyethylene foil exhibited higher weight increments and on termination of the experiment the mean individual weight of larvae was significantly higher (P < 0.05) than those of larvae in tanks with vascular plants and plastic netting. The food conversion ratio, calculated for the entire culture period was 4.9. Conclusion. High survival rate of the cultured pike larvae demonstrated the success of pike larvae grow-out under uncontrolled conditions.

The effects of Propiscin (etomidate) on the behaviour, heart rate, and ventilation of common carp, Cyprinus carpio L.

Background. The use of anaesthetics in aquaculture requires conducting specific studies of their effects on fish. The objective of this study was to evaluate the effects of Propiscin (Polish agent containing etomidate) on common carp behaviour, heart rate, and ventilation. Material and methods. Carp were anaesthetised with Propiscin at the concentrations of 1 and 2 ml·l-1. An electrocardiograph was used to record the heart rate and the amplitude and rate of the opercular movements. The effects of atropine and forced water flow over the gill system on the anaesthetised carp’s heart rate were also studied. Results. At either concentration, Propiscin caused general anaesthesia manifesting itself in: a loss of equilibrium, faded responses to external stimuli, gradual ventilation failure, and bradycardia. A high correlation between respiration rate and heart rate was found in the anaesthetised fish. Conclusion. The hypoxia was the direct cause of bradycardia, and the regularity and amplitude of breathing were the most important indicators of the level of Propiscinevoked anaesthesia.

Prediction of Critical Heat Flux in Annular Flow Using a Film Flow Model

A new set of correlations for the film flow analysis was developed to predict the critical heat flux in annular flow regime accurately. All the correlations adopted here were based on experimental data or considerations of the processes in annular flow; the resulting model required no parameters that should be adjusted from the measured data of critical heat flux. The 4,375 data of critical heat flux in forced flow of water in vertical uniformly heated round tubes were used to test the basic performance of the model. The comparisons between the calculated and measured critical heat fluxes showed that the predicted results by the present model agree with the experimental data fairly well if the flow pattern at the onset of critical heat flux condition is considered annular flow. The predictive capability was not deteriorated even in the cases of small diameter tube, short length tube as well as low vapor quality. Good agreements were also achieved in the preliminary tests against the critical heat flux data for Freon 12 and Freon 21. It is expected from these results that the present model satisfactorily expresses the important phenomena to predict the critical heat flux in annular flow regime.

Prediction of Critical Heat Flux in Annular Flow Using a Film Flow Model

A new set of correlations for the film flow analysis was developed to predict the critical heat flux in annular flow regime accurately. All the correlations adopted here were based on experimental data or considerations of the processes in annular flow; the resulting model required no parameters that should be adjusted from the measured data of critical heat flux. The 4,375 data of critical heat flux in forced flow of water in vertical uniformly heated round tubes were used to test the basic performance of the model. The comparisons between the calculated and measured critical heat fluxes showed that the predicted results by the present model agree with the experimental data fairly well if the flow pattern at the onset of critical heat flux condition is considered annular flow. The predictive capability was not deteriorated even in the cases of small diameter tube, short length tube as well as low vapor quality. Good agreements were also achieved in the preliminary tests against the critical heat flux data for Freon 12 and Freon 21. It is expected from these results that the present model satisfactorily expresses the important phenomena to predict the critical heat flux in annular flow regime.

Flow Film Boiling Heat Transfer in Water and Freon-113.

Experimental apparatus and method for film boiling heat transfer measurement on a horizontal cylinder in forced flow of water and Freon-113 under pressurized and subcooled conditions were developed. The experiments of film boiling heat transfer from single horizontal cylinders with diameters ranging from 0.7 to 5 mm in saturated and subcooled water and Freon-113 flowing upward perpendicular to the cylinders were carried out for the flow velocities ranging from 0 to 1 m/s under system pressures ranging from 100 to 500 kPa. Liquid subcoolings ranged from 0 to 50 K, and the cylinder surface superheats were raised up to 800 K for water and 400 K for Freon-113. The film boiling heat transfer coefficients obtained were depended on surface superheats, flow velocities, liquid subcoolings, system pressures and cylinder diameters. The effects of these parameters were systematically investigated under wider ranges of experimental conditions. It was found that the heat transfer coefficients are higher for higher flow velocities, subcoolings, system pressures, and for smaller cylinder diameters. The observation results of film boiling phenomena were obtained by a high-speed video camera. A new correlation for subcooled flow film boiling heat transfer was derived by modifying authors' correlation for saturated flow film boiling heat transfer with authors' experimental data under wide subcooled conditions.

Changes in Water Relations of Cornus stolonifera During Cold Acclimation1

Abstract Stomatal resistance of leaves, water absorption through roots, and water content of stem internodes was evaluated during cold acclimation of red-osier dogwood (Cornus stolonifera Michx.). Four weeks of short-days at 20/15°C resulted in a significant reduction in stem water content. This reduction was related to water lost from pith cells as this tissue senesced sequentially in successively younger internodes from the stem base to its apex at autumn growth cessation. A 1.5 fold decrease in relative stomatal resistance of leaves and a 3.5 fold increase in resistance to water flow though roots at 0.15 bars tension occurred prior to hardening to -12°C. Additional hardening to -40°C resulted in a 28 fold increase in resistance to forced water flow through roots and equalization of water content in all internodes. Thereafter, water content remained constant but stems continued to harden to temperatures below -65°C. Comparison of resistance to forced water flow through living and dead roots from hardy and tender plants suggested there was a decrease in the permeability of root cells to water during the initial (-12°C) stage of acclimation. Root surfaces became suberized, as acclimation progressed, giving rise to an additional barrier to water uptake in roots of very hardy plants (-45°C). It seems likely that the decrease in hydration of overwintering stems during cold acclimation results from a decreased stomatal resistance and increased root resistance to water movement.

Effects of Cold Hardening and CCC Treatment on Hydration and Frost and Desiccation Hardiness of Plant Tissues

Treatment at 5 C or with CCC (2-chloroethyl-trimethylammonium chloride) has enhanced resistance to frost injury in the leaves of winter rape, Brassica napus L. var. oleifera cv. Górczański, grown in water culture in temperature-controlled rooms. The leaves of the treated plants were also more resistant to desiccation injury caused by a highly effective desiccant. They were able to lose water at a faster rate in the presence of the desiccant. This was coincident with a lower impedance of those leaves. On the other hand, the leaves of the treated plants have shown a smaller water saturation deficit (WSD) under prevailing culture conditions. The WSD changes were not accompanied by changes in the number of stomata, and only cold-hardened leaves had their stomata closed. Both treatments caused a decrease in permeability of root systems to forced water flow. The possible reasons for the described phenomena and a possible role of these phenomena in frost hardiness of plants are discussed.

Ocean Surface Reverberation Mechanisms and Their Laboratory Simulation

Ocean surface roughness is generated by a combination of gravity and wind driven waves. These water/air interface perturbations are directly related to water motion just below this interface. This circular motion of the water may extend down to a depth of up to approximately two times the trough to crest measure of such waves. The ocean reverberation analyses to date have employed an interface description in the form of wave height measurements taken at a point and/or its associated spectrum, with very reasonable results. The experimental reverberation data has not been fully exploited to determine the significance of the said underlying water motion as the major contributor to the acoustic signal intensity scattered into the water body. It is this aspect that is investigated both theoretically with a model of the moving surface as well as the water mass underneath it, and experimentally in a laboratory tank with controlled and repeatable conditions using 1 Mc/sec carrier pulse of widths 4–6 μsec. The water motion was simulated by forced flow of water just underneath the air/water intersurface. The position of a small specular reflecting test plate was varied vertically between the transmit-receive transducer and the air/water interface in order to identify and separate subsurface volume and water/air interface reverberations. Various mechanisms generating the frequency spread of the acoustic signal incident on the surface are also discussed. [This work is sponsored by the Office of Naval Research, under Contract.]

The correlation of the experimental data on critical heat loads in forced flow of water heated below the boiling temperature

At low pressures, theory predicts a simplification of the similarity-parameter equation proposed by the writer [2] on the basis of a correlation of the experimental data on critical thermal loads in forced flow of water not heated to boiling, in the pressure range 100–210 atmos.

Critical heat loadings in forced flow of water heated below boiling

Critical heat loadings in forced flow of water heated below boiling