Search

The heat transfer process to a non-Newtonian pseudoplastic fluid inside a scraped surface heat exchanger has been experimentally analysed. The scraping device consists of a rod with semicircular pieces mounted on it, which are in contact with the inner surface of the pipe. The whole moves axially and thus, the pieces scrape the inner surface of the pipe, in order to avoid fouling formation and enhance heat transfer. Pressure drop, heat transfer and power consumption measurements, using non-Newtonian pseudoplastic fluids, have been carried out in static and dynamic conditions of the scraper. Four flow regions have been identified: attached laminar, detached laminar, transitional and turbulent flow regions. A generalization method for the fluid viscosity that includes the effects of the non-Newtonian behaviour has been used. Friction factor and Nusselt number have been successfully correlated by employing the generalized viscosity on pressure drop and heat transfer results, both in static and dynamic conditions, for three of the four identified flow regions (it was not possible to get correlations in the transition to turbulent flow region). The study shows that, despite the high power consumption of the scraping movement, the device is suitable for an industrial process using non-Newtonian fluids, since it prevents fouling, increases heat transfer, provides flexibility and enhances the final product quality. Furthermore, the obtained correlations are a valuable tool in the design of heat exchangers.

Heating and cooling processes involving viscous fluids, crystallization processes or with fouling tendency require often the employment of scraped surface heat exchangers to enhance the heat transfer. In these cases, obtaining the heat transfer coefficient is complex due to the difficulty of measuring the wall temperature. The present work introduces an innovative measurement technique to retrieve the scraped wall temperature based on embedded thermocouples, welded directly into the wall plate. The thermocouple wires were introduced into a knockout and welded with a filler material. Once welded, the entire set was calibrated in a cold room at controlled temperature. A total of 26 T-type thermocouples were welded to a stainless steel wall substrate, tested later in a rotating scraped surface heat exchanger employed in the ice slurry production. The thermocouples presented a variance of 0.3 °C and an accuracy after calibration of 0.2 °C. The deviation between the scraped wall temperature and the thermocouple measurement was assessed by 2D numerical simulations of the transient heat conduction across the wall substrate. The influence of the wall substrate thickness, thermocouple location and scraping velocity has been considered.

The flow pattern of a pseudoplastic fluid inside a scraped surface heat exchanger has been obtained by means of Particle Image Velocimetry. The scraping device consists of a rod with semicircular pieces mounted on it, which are in contact with the inner surface of the pipe. The whole moves axially and thus the pieces scrape the inner surface of the pipe, in order to avoid fouling formation and enhance heat transfer. The aim of this work is to obtain the influence on the flow pattern of the significant parameters of the problem: the Reynolds number, the scraping velocity and the non-Newtonian behaviour of the fluid. In order to achieve this, a numerical model has been created. This model provides the velocity profile of non-Newtonian fluids in a concentric annulus, which has been used as start point for the study of the flow in the pipe with the insert device. Finally, PIV experiments have been carried out in the geometry under study, covering the representative ranges of the mentioned variables. The results provide a deeper knowledge of the flow, allowing for a better understanding of the flow structures, as well as of the consequences they can have on linear pressure drop and heat transfer and on their study. Furthermore, the possibility of applying a suitable generalization method for the viscosity in this device has been analysed.

This work presents and experimental study of the generalization method of the Reynolds number and the viscosity of pseudoplastic fluid flow in ducts of non-uniform cross-section. This method will permit to reduce 1 degree of freedom of hydrodynamical and thermal problems in those ducts. A review of the state of the art has been undertaken and the generalization equation proposed for ducts of uniform cross section has been used as a starting point. The results obtained with this equation have not been found satisfactory and a new one has been proposed. Specifically, the procedure has been developed for two models of scraped surface heat exchanger with reciprocating scrapers. For both models, the scraper consists of a concentric rod inserted in each tube of the heat ex- changer, mounting an array of plugs that fit the inner tube wall. The two models studied differ in the design of the plug. The procedure to perform the generalization method out of experimental data is accurately detailed in the present document. The first author thanks Mr. Martínez and Dr. Solano for their invaluable contribution to the project and their advise. He also thanks the Spanish Government, Ministry of Education for the FPU scholarship referenced as AP2007-03429 which covered the expenses of a 4-year research at Universidad Politécnica de Cartagena.

The flow pattern inside a scraped surface plate heat exchanger used for ice slurry production is studied both experimentally and numerically. Isothermal planar velocity fields are reported in the range 2.2 · 104⩽Rerot⩽1.7 · 105 using a phase averaged PIV technique. Unsteady RANS modelling of the flow, using the rotating frame methodology is used to obtain a time-averaged description of the flow structure, which was successfully validated against the PIV data. The flow structure is characterized by the presence of a roll-up vortex generated by the scraper blade, which is the main factor for both the radial and vertical displacements of the flow. Increasing the Re rot number leads to a more uniform flow, reducing the presence of stagnant zones. However, the main pattern structure does not change significantly when increasing the scraping velocity.

The flow pattern within an enhanced tubular heat exchanger equipped with a reciprocating scraping device is experimentally analysed. The insert device, specially designed to avoid fouling and to enhance heat transfer, has also been used to produce ice slurry. It consists of several circular perforated scraping discs mounted on a coaxial shaft. The whole is moved alternatively along the axial direction by a hydraulic cylinder. The phase-averaged velocity fields of the turbulent flow have been obtained with PIV technique for both scraping semi-cycles. Special attention has been paid to the effect of the non-dimensional scraping velocity and the Reynolds number in the flow field. CFD simulations provide support for the identification of the flow patterns and the parameter assessment extension. The results show how the scraping parameters affect the turbulence level produced in the flow and therefore the desired heat transfer enhancement.

Background: Levels of bone turnover markers (BTM) might be correlated with outcome in terms of skeletal-related events (SRE), disease progression, and death in patients with bladder cancer (BC) and renal cell carcinoma (RCC) with bone metastases (BM). We try to evaluate this possible correlation in patients who receive treatment with zoledronic acid (ZOL). Methods: This observational, prospective, and multicenter study analysed BTM and clinical outcome in these patients. Serum levels of bone alkaline phosphatase (BALP), procollagen type I amino-terminal propeptide (PINP), and beta-isomer of carboxyterminal telopeptide of type I collagen (beta-CTX) were analysed. Results: Patients with RCC who died or progressed had higher baseline beta-CTX levels and those who experienced SRE during follow-up showed high baseline BALP levels. In BC, a poor rate of survival was related with high baseline beta-CTX and BALP levels, and new SRE with increased PINP levels. Cox univariate analysis showed that beta-CTX levels were associated with higher mortality and disease progression in RCC and higher mortality in BC. Bone alkaline phosphatase was associated with increased risk of premature SRE appearance in RCC and death in BC. Conclusion: Beta-isomer of carboxy-terminal telopeptide of type I collagen and BALP can be considered a complementary tool for prediction of clinical outcomes in patients with BC and RCC with BM treated with ZOL., As this was a multicenter study, Adknoma Health Research (Barcelona, Spain) collected and ordered data throughout the study. We especially thank Margarida Garcia from Adknoma who followed carefully the development of the study. And we thank Novartis Oncology Spain for supporting this study.

Cooling towers are evaporative heat transfer devices in which atmospheric air cools warm water, with direct contact between the water and the air by evaporating part of the water. The principle of operation of cooling towers requires spraying or distributing water over a heat transfer surface (packing) across or through which a stream of air is passing. As a result, water droplets are incorporated in the air stream and,depending on the velocity of the air, will be taken away from the unit. This is known as drift. Although cooling tower drift is objectionable for several reasons, the most hazardous problem concerning human health is the emission of chemicals or microorganisms into the atmosphere. Undoubtedly, regarding microorganisms, the most well-known pathogens are the multiple species of bacteria collectively known as legionella. The binomial water distribution system-drift eliminator is identified to be that mainly responsible for cooling tower drift. While water distribution systems affect the mechanics of setting up the drops, drift eliminators work by changing the direction of the airflow and separating droplets from the airstream through inertial impact. The drift eliminator’s performance can be quantified mainly by two factors: droplet collection efficiency and the pressure drop across the eliminator. In contrast, water distribution systems are characterized by the pressure drop across itself and the achieved size of the particle spread. Alongside drift, the binomial water distribution system-drift eliminator affects the cooling tower performance. From the reviewed bibliography, some studies assessing the effect of the drift eliminator on cooling tower performance have been found. Nevertheless, no studies regarding the influence of the water distribution system on the cooling tower’s performance have been detected. In this sense, this paper studies the thermal performance of a forced draft counter-flow wet cooling tower fitted with two water distribution systems (the pressure water distribution system (PWDS) and gravity water distribution system (GWDS)) for six drift eliminators for a wide range of air and water mass flow rates. The data registered in the experimental set-up were employed to obtain correlations of the tower characteristic, which defines the cooling tower’s thermal performance. The outlet water temperature predicted by these correlations was compared with the experimentally registered values, obtaining a maximum averaged difference of ±0.95%. The authors wish to acknowledge the collaboration of the Ministerio de Educación y Ciencia (Spanish Education and Science Ministry) for their support of project PN I+D+I 2008-2011 ENE2010-21679-C02- 02.

The existence of cooling towers arises from the need to evacuate power to the environment from engines, refrigeration equipment and industrial processes. Water drift emitted from cooling towers is objectionable for several reasons, mainly due to human health hazards. It is common practice to fit drift eliminators to cooling towers in order to minimise water loss from the system. The presence of the drift eliminator mainly affects two aspects of cooling towers: their thermal performance and the amount of water drift loss. This paper experimentally studies the drift loss emissions from a cooling tower without drift eliminator and fitted with six different drift eliminators. Chemical Balance is the selected method and Australian Standard methodology is taken as a reference. Some modifications are proposed to reduce uncertainty by increasing the duration of the test and the number of water samples. Installation of a drift eliminator, even in the worst case, reduces the water drift level to less than half of the situation without the eliminator. The water drift losses obtained with the different drift eliminators installed at the pilot plant, from 0.0118% to 0.161%, are within the range generally reflected in the literature. Finally, a criterion for designing drift eliminators in order to optimise both the collection efficiency and the cooling tower's thermal performance is proposed. This research has been partially financed by the project DPI2007-66551-C02-01 grant from the “Dirección General de Industria, M. de Ciencia y Tecnología”, the project 2I05SU0029 grant of the “Secretaría General de la Consejerí de Educación y Cultura de la C.A. de la Región de Murcia” and the HRS Spiratube Company, Murcia (Spain).

This work analyzes the thermal–hydraulic behaviour of three types of enhancement technique based on artificial roughness: corrugated tubes, dimpled tubes and wire coils. The comparison has been performed from the three best specimens selected among the wide range of geometries investigated by the authors in previous works. Heat transfer and pressure drop experimental data in laminar, transition and turbulent regimes are used in this investigation. Results show that the shape of the artificial roughness exerts a greater influence on the pressure drop characteristics than on the heat transfer augmentation. Likewise, this shape strongly affects the advance of the transition to turbulence and its characteristics: smooth or sudden. The study concludes that for Reynolds numbers lower than 200, the use of smooth tubes is recommended. For Reynolds numbers between 200 and 2000, the employment of wire coils is more advantageous, while for Reynolds numbers higher than 2000, the use of corrugated and dimpled tubes is favoured over the wire coils because of the lower pressure drop encountered for similar heat transfer coefficient levels.

Flow pattern and thermal-hydraulic characteristics in an innovative tube insert have been experimentally and numerically investigated. The insert device is a concept envisioned for reciprocating scraped surface heat exchangers. It consists of a concentric rod, that mounts an array of semicircular plugs fitted to the inner tube wall. In motionless conditions, the insert works as a turbulence promoter, enhancing heat transfer in laminar regime. Fundamental flow features in the symmetry plane of the tube have been assessed with Particle Image Velocimetry technique. A general model of the flow mechanism has been defined, identifying three regions along a geometrical pitch: recirculation bubbles, flow acceleration and transverse vortex. Results have been complemented with experimental data on pressure drop and heat transfer. The transition onset is clearly identified, and the mechanisms that promote turbulence at low Reynolds number are investigated and discussed. CFD simulations for different Reynolds numbers provide a further insight into the relation of the flow structures with wall shear stress, and their role on the local heat transfer augmentation.

A new coefficient to characterize the global behaviour of adiabatic compressible flow at T-junctions is proposed. The new coefficient is defined according to the conclusions derived from the uncertainty propagation analysis of the total pressure loss coefficient defined by Miller for compressible flow. The numerical results obtained using the new linking between branches coefficient definition, K ∧ , show a logarithmic relationship with mass flow rate ratio between branches, q, and the extrapolated Mach number in the common branch, M 3 ∗ , for all flow types studied in a 90° T-junction. Reliable and practical two parameters or global correlations, K ∧ = K ∧ ( M 3 ∗ , q ) , have been obtained. These correlations can be easily implemented as boundary conditions into 1D global simulation codes.

This paper provides with a set of full-scale experimental data of atrium fires. These data could be used as benchmarks for future numerical validation studies. In particular, the influence of the make-up air velocity as well as the position and area of the vents in an atrium is assessed both experimentally and numerically. Experimentally, the effect of different make-up air supply positions and inlet area on the fire-induced inner conditions and smoke layer descent was studied by means of three full-scale fire tests conducted in a 20 m cubic atrium. Detailed transient measurements of gas and wall temperatures, as well as pressure drop through the exhaust fans and airflow at the inlets were recorded. Later computational fluid dynamics (CFD) simulations of these tests were performed with the code Fire Dynamics Simulator (FDS). Experimentally, the lack of symmetry in make-up air vents and the large inlet area turn the flame and plume into more sensitive to outer effects. However, no significant difference has been observed between the make-up air topologies assessed. Even make-up velocities higher than 1 m/s, with symmetric venting topology, have not induced important flame or plume perturbations. Numerically, the simulations agree well with the experiments for the cases with make-up air velocities lower than 1 m/s. Poor agreement has been found for the case with inlet velocities higher than 1 m/s.

Water drift emitted from cooling towers is objectionable for several reasons, mainly due to human health reasons. A numerical model to study the influence of sychrometric ambient conditions on cooling tower drift deposition was developed. The mathematical model presented, consisting of two coupled sets of conservation equations for the continuous and discrete phases, was incorporated in the general purpose CFD code Fluent. Both experimental plume performance and drift deposition were employed to validate the numerical results. This study shows the influence of variables like ambient dry bulb temperature, ambient absolute humidity and droplet exit temperature from cooling tower on the drift evaporation (and therefore deposition) and on the zone affected by the cooling tower. The stronger effect detected corresponds to the ambient dry bulb temperature. When a higher ambient temperature was present, deposition was lower (evaporation was therefore higher) and the zone affected by the cooling tower was smaller. The influence of the other two variables included in the study was weaker than the one corresponding to the dry bulb ambient temperature. A high level of ambient absolute humidity increased drift deposition and also the size of the zone affected by the cooling tower. Finally, a high level of droplet exit temperature decreased deposition and increased the zone affected by the cooling tower.

A commercial fan coil has been experimentally studied in this work in order to assess its behaviour when ice slurry is used as secondary refrigerant. Experimentally obtained results have been compared to theoretical prediction obtained using the correlations proposed in previous papers in order to verify them. Several reasons have been reported to explain the deviation of fan coil behaviour from that expected and which make the direct application of ice slurry inappropriate in the fan coil studied. In order to avoid those problems and to establish a comparison between two secondary refrigerants with similar cold storage capacity, ice slurry direct application has been compared to ice slurry indirect application – only carrier fluid, without ice particles, flowing through the fan coil. The most remarkable conclusion obtained is that indirect application improves the behaviour of the fan coil studied for all the cases analysed, overcoming the problems reported for direct application.

Research paper published in the peer-reviewed journal Building and Environment. Atria and large spaces are common architectonical features in modern buildings such as high rises, auditoria, warehouses, airports and mass transport stations among others. There is currently an international trend towards the performance-based design for fire safety of these building elements. This design process relies heavily on fire modelling but the knowledge in fire dynamics and the movement of smoke in atria and large spaces still presents some gaps. This paper aims at contributing to close these gaps and reports the three Murcia Atrium Fire Tests conducted in a 20 m cubic enclosure using pools of 1.3 and 2.3 MW. Detailed transient measurements of gas and wall temperatures, as well as pressure drop through the exhaust fans and airflow at the inlets were recorded. The study also includes the effect of the mechanical exhaust ventilation. Results have been compared with those predicted by the computational fluid dynamics (CFD) model Fire Dynamics Simulator FDSv4. In general terms, the comparisons between experiments and simulations show good agreement, especially in the far field of the plume, but the accuracy is poor at the lower plume region and near the flame.

Ice slurry performance in a concentric corrugated tube heat exchanger is experimentally studied in this work in order to compare experimental results to theoretical prediction obtained using the correlations proposed in previous papers. Once the validity of those correlations is verified, the behaviour of the studied heat exchanger is analyzed for different ice slurry flow conditions and compared to the results obtained when a heterogeneous storage is used and only carrier fluid flows through the heat exchanger. According to the performance evaluation criterion used – variation in heat transfer rate for equal pressure drop and surface area – the most remarkable conclusion obtained is that slurry improves the behaviour of the heat exchanger studied for all the cases analyzed, although the increase in heat transfer rate is always lower than 15%, being in most cases lower than 5%.

The rheological behaviour of the ice slurry made from 9% NaCl brine has been experimentally studied in this work. Starting from the dimensional analysis of pressure drop and heat transfer processes, the minimum numbers of non-dimensional parameters present in these processes have been determined. Rheological behaviour has been adjusted to the experimental data on ice slurry pressure drop. Two different behaviours were observed depending on the shear rate values, with a clear yield stress recognizable in the low shear rate region and a shear thickening behaviour for high shear rate values. A modified Herschel–Bulkley rheological model has been proposed, which is able to predict ice slurry behaviour in both, low and high shear rate region. The influence of the parameters involved has been determined and an analytical equation for the Darcy friction factor has been obtained from the model proposed and compared to experimental results. The comparison showed a very good agreement between these data.

Ice slurry flow through horizontal pipes is studied experimentally in order to find out its heat transfer and isothermal friction properties. Using 9% NaCl brine as the carrier fluid, different flow conditions are discussed with a view to analyse each involved variable. In this Part I, experimental data are directly correlated and easy-to-use expressions for the Darcy friction factor and the Nusselt number were obtained as functions of non-dimensional parameters expressing flow and geometrical properties. The most remarkable conclusion obtained is a clear influence of the ice particle–pipe diameter ratio in the pressure drop parameters, not previously taken into account, which must be confirmed in heat transfer process. The thermal and hydraulic performance of ice slurry flowing through corrugated pipes is also analysed showing, with regard to smooth pipe, the same behaviour in pressure drop and opposite behaviour in heat transfer.

Cooling towers are equipment devices commonly used to dissipate heat from power generation units, water-cooled refrigeration, air conditioning and industrial processes. Water drift emitted from cooling towers is objectionable for several reasons, mainly due to human health hazards. It is common practice to fit drift eliminators to cooling towers in order to minimize water loss from the system. It is foreseeable that the characteristics of the installed drift eliminators, like their pressure drop, affect the thermal performance of the cooling tower. However, no references regarding this fact have been found in the reviewed bibliography. This paper studies the thermal performance of a forced draft counter-flow wet cooling tower fitted with different drift eliminators for a wide range of air and water mass flow rates. The data registered in the experimental set-up were employed to obtain correlations of the tower characteristic, which defines the cooling tower’s thermal performance. The outlet water temperature predicted by these correlations was compared with the experimentally registered values obtaining a maximum difference of ±3%.

New experimental correlations to characterize energy losses in adiabatic compressible flow at 90-degree T-junctions and their expanded uncertainties are presented. These new correlations are based on a new linking between branches coefficient definition, K ˆ , and show a logarithmic relationship with mass flow rate ratio between branches, q, and the extrapolated Mach number in the common branch, M 3 ∗ , for all the different flow types studied. The extrapolated properties up to the junction are calculated, from measurement sections, subtracting the frictional losses using the Fanno fluid flow model. These two parameters or global correlations, K ˆ = K ˆ ( M 3 ∗ , q ) , can be easily implemented as boundary conditions into 1-D global simulation codes.

Environmental effects are one of the main concerns of massive desalination facilities. To reach the objective of no brine discharge the salt from seawater must be completely separated and obtained as a secondary and valuable product. If no CO 2 emission increase is desired, the power source must be a combination of renewable energy systems (RES). This paper presents an analysis of an integrated desalination scheme consisting of two sequential systems: a multi-effect distillation (MED) plant and a mechanical vapour compression (MVC) system based on evaporator equipment. The energy is obtained by several wind turbines (WT) and a thermal solar collector (TSC) field. Separation of salt and water is achieved in a coupled multi-effect distillation-mechanical vapour compression (MED+MVC) two step process. The MED stage is driven by thermal solar collectors, whereas the energy consuming mechanical compression of the vapour (MVC) is fuelled by wind-powered turbines. Interestingly, the final products of this process are dry salt and fresh water. Such a system has been designed and dimensioned for a throughput of 100 m 3 /h of desalted water A preliminary study of the investment, amortization and exploitation costs of a combined MED+MVC+WT+TSC installation with these dimensions has been done. The price of desalted water, after considering the profits due to the sale of salt and electricity has been estimated at 0.59 Є/m 3 . If the initial investment has a 35% subsidy, a final price of 0.41 Є/m 3 could be ensured, which is near the price associated to conventional energy sources. An outline of the solar collector system and the technical requirements of the wind turbines in needed to meet the energy demand of the MED+MVC system are also included.

Water drift emitted from cooling towers is objectionable for several reasons, mainly due to human health reasons. These objections make the installation of the cooling towers difficult and penalize the COP of the cooling plants. The dry and adiabatic fluid cooler works as a standard fluid dry cooler enhancing the dry cooler's capacity with adiabatic pre-cooling of the air intake. The objectives of this work were twofold: the first one was to review the available drift test methods usually used on cooling towers, and the second one was to carry out drift measurements on a dry and adiabatic fluid cooler and on a cooling tower of similar capacity working in real facilities. No drift was registered on the dry and adiabatic fluid cooler when using the sensitive paper drift test method, while a drift of 0.0023% was measured in the cooling tower.

This research has been supported by The Direccion General de Investigacion of Ministerio de Educacion y Ciencia of Spanish Goverment, through DPI 2003-02719 Project.

This work presents an extensive experimental study on three wire coils of different pitch inserted in a smooth tube in laminar and transition regimes. Isothermal pressure drop tests and heat transfer experiments under uniform heat flux conditions have been carried out. The friction factor increases lie between 5% and 40% in the fully laminar region. The transition from laminar flow to turbulent flow is continuous, without the instabilities and the pressure drop fluctuations that a smooth tube presents. Heat transfer experiments have been performed in the flow ranges: Re = 10 – 2500 , Pr = 200 – 700 and Ra = 3 × 10 6 – 10 8 . At Reynolds numbers below 200, wire coils do not enhance heat transfer with respect to a smooth tube. For Reynolds numbers between 200 and 1000, wire coils remarkably increase heat transfer. At Reynolds numbers above Re ≈ 1000 – 1300 , transition from laminar to turbulent flow takes place. At Reynolds number around 1000, wire inserts increase the heat transfer coefficient up to eight times with respect to the smooth tube. A performance comparison between wire coils and twisted tape inserts has shown that wire inserts perform better than twisted tapes in the low Reynolds number range: Re = 700 – 2500 .

A global methodology has been developed and validated to obtain the total pressure loss coefficient in internal compressible flow in T-type junctions. This methodology is based on the calculation of the thermo-fluid properties extrapolated to the branch axes intersection, once the straight pipe friction losses numerically calculated have been subtracted from the total energy losses. For this purpose, a steady adiabatic compressible one-dimensional flow with friction mathematical model has been applied to the results obtained by numerical simulation using the commercial finite volume code Fluent to solve the steady state Navier–Stokes equations. A 90° T-type junction has been studied and the predicted loss coefficient has been related to the extrapolated Mach number in the common branch and to the mass flow rate ratio between branches at different flow configurations, in both combining and dividing flows. The numerical results have been compared with experimental results and published data in open literature. In general, a good agreement is obtained and the correlations obtained will be applied as boundary condition in one-dimensional global simulation models of fluid systems in which these components are present.

An environmentally friendly alternative device, called Hydrosolar Roof, designed for heat dissipation in buildings has been necessary to include all the elements in a global model. Then, three main subsystems have been considered: Cooling Machine, Hydraulic Network and Hydrosolar Roof. A description of the three subsystem is done and the mathematical model is presented.The Cooling machine thermodynamic model has been carried out using EES (Engineering Equation Solver). The Hydraulic network model has piping, pump and nozzle information. The Hydrosolar Roof direct contact heat and mass transfer simulation has been development with a CFD code. Special attention has been paid on the cooling efficiency. The global model has been applied to a real prototype facility experimentally tested. All the energy consumptions have been calculated for different pumping heads. A global coefficient of performance (COP) has been defined and the optimum value obtained. The authors wish to acknowledge the collaboration in the calculations of A. Navarro, as well as José María Galán, Energy, Comfort and Enviroment S.L. Manager, as the proporser of the original idea.

Operation temperature of solar heating systems makes the use of a radiant floor to transfer heat into the conditioned spaces suitable. Performance data related to solar heating systems are scarce. Knowledge of these data is important to establish control strategies that lead to an optimal operation of these systems. The objectives of this study were to acquire and analyse the performance data of a residential solar heating system in Murcia (Spain), and to compare the recorded data with the performance estimate provided by the f-chart method used for sizing the system. The solar fractions registered in the system during the months of January and February 2004 were 20% lower than those predicted by the f-chart method. This lack of coincidence was assumed as inherent to the f-chart method.

A numerical model for studying the evaporative cooling processes that take place in a new type of cooling tower has been developed. In contrast to conventional cooling towers, this new device called Hydrosolar Roof presents lower droplet fall and uses renewable energy instead of fans to generate the air mass flow within the tower. The numerical model developed to analyse its performance is based on computational flow dynamics for the two-phase flow of humid air and water droplets. The Eulerian approach is used for the gas flow phase and the Lagrangian approach for the water droplet flow phase, with two-way coupling between both phases. Experimental results from a full-scale prototype in real conditions have been used for validation. The main results of this study show the strong influence of the average water drop size on efficiency of the system and reveal the effect of other variables like wet bulb temperature, water mass flow to air mass flow ratio and temperature gap between water inlet temperature and wet bulb temperature. Nondimensional numerical correlation of efficiency as a function of these significant parameters has been calculated.

A numerical study of natural convective flows in a vertical converging channel for different angles of convergence has been carried out, taking into account the lacks reported in the literature on some aspects of this configuration. Two-dimensional laminar simulations were obtained by solving the fully elliptic governing equations using two different general purpose codes: Fluent and Phoenics. Special emphasis is made on the systematic comparisons of computational results with experimental and numerical data taken from literature. A generalized correlation for the average Nusselt number has been obtained from numerical results in a channel with isothermal heated plates, for symmetric and asymmetric heating conditions. This correlation has been obtained for wide and not yet covered ranges of the modified Rayleigh number varying from 1 to 106 and the angle of convergence from 1° to 30°. Good agreement has been obtained with respect to the available experimental asymptotes of the bibliography for fully developed and boundary layer regimes.

We present an experimental investigation carried out in corrugated tubes for laminar and transitional flow. Employing water and ethylene glycol as test fluids, a wide range of flow conditions was covered in order to use these results under the typical flow conditions of the chemical and food industry. Laminar flow heat transfer through horizontal corrugated tubes is produced by mixed convection where the Nusselt number depends on both natural convection and the entry region. Heat transfer results are presented in the form Nu = f(Ra,x*) and showed that at high Rayleigh numbers, enhancement produced by corrugated tubes can be up to 30%. Pressure drop results showed that friction factors in corrugated tubes are between 5 and 25% higher than the smooth tube ones. Moreover, it was observed that roughness accelerates transition to critical Reynolds numbers below 1300

Corrugated tubes have been experimentally studied in order to obtain their heat transfer and isothermal friction characteristics. The use of water and ethylene glycol as test fluids has allowed to cover a wide range of turbulent fluid flow conditions: Reynolds number from 2000 to 90 000 and Prandtl number from 2.5 to 100. The paper presents a comprehensive experimental study on a family of 10 corrugated tubes which were manufactured by cold rolling. Artificial roughness is characterised by rib height h / d ranging from 0.02 to 0.06 and spiral pitch p / d from 0.6 to 1.2. The results show that a unique dimensionless parameter named severity index ( φ = h 2 / pd ) can be used to establish roughness influence on flow. The large amount of experimental data has been correlated in order to obtain easy to use expressions for Fanning friction factors and Nusselt numbers as functions of flow and geometry dimensionless parameters. The real benefits which are offered by corrugated tubes have been assessed by calculating one of the performance evaluation criteria commonly used in the enhanced heat transfer literature. Finally an optimisation study shows the guidelines to choose which roughness geometry offers the best performance for specific flow conditions.

An improved heat dissipation system for buildings’ air conditioning, based on a previous prototype, has been developed and tested. It acts as an extended solar driven cooling tower, reducing service water temperature. The paper presents the physical basis of the system, the geometrical modifications of the new prototype, the mathematical model and the performed tests. Experimental results obtained during summer 2000 in a full-scale prototype showed that the cooling power capacity of this model is about 50% greater than that of the preliminary model. For each square meter of Hydrosolar Roof, more than 400 W of heat released can be reached under common operating conditions. Correlations of the system thermal performance have been obtained as functions of solar radiation, wind velocity and ambient conditions, allowing the design of system for actual buildings’ applications.

A new system based on the harnessing of solar and wind power is presented for heat dissipation in air conditioning facilities. The innovation offered by the new system is the integration of two well-known subsystems: a cooling tower and a solar chimney which increases the air flow without the use of electric power. The system is described and presented together with a model for its study. The field data acquired from the prototype built in southern Spain establishes the actual potential of the system, which provides a new approach to a sustainable technological development.

A detailed flow field analysis is carried out downstream of a Bjork-Shiley prosthetic aortic valve, placed in a Great Circulation simulator. Mean periodic velocity and turbulence are obtained by means of selective sampling through enabling windows. Flow mapping includes three different heights and three meridional planes (i.e. nine diameters). Some effort is devoted to study cycle-to-cycle variations, and to remove them for determining true turbulence values. A lagrangian interpretation, based upon the convection of vorticity produced at the aortic prosthesis, is needed to understand the flow pattern behaviour.