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This paper focuses on the issue of flow measurement in automotive heat exchangers. The measurement is complicated due to the limited space in the heat exchanger area and the non-uniform velocity profile. Therefore, only some measuring techniques can be used, which must be adapted to the specific conditions. The paper presents the initial stages of the development of a sensor for measuring the flow in a heat exchanger. These are CFD simulations used to determine the nature of the flow around the sensor and verify its effect on the flow field in its surrounding and on the entire heat exchanger. The results of these initial simulations are presented and discussed. [ABSTRACT FROM AUTHOR]

In the paper, a new construction of a compact plate heat exchanger dedicated to PVT cooling was numerically tested. The efficiency of photovoltaic panels decreases as their temperature increases, but cooling improves efficiency. A model counter-current heat exchanger with rectangular minichannels was presented. A heated wall of the heat exchanger was a photovoltaic cell. There were laminar flows of Fluorinert FC-72 and distilled water in the minichannels. FC-72 was heated by the photovoltaic panel. The CAD model of a minichannel heat exchanger was proposed. CFD calculations were performed using Simcenter STAR-CCM+ software. The fluid temperature and velocity profile in the minichannels were determined to finally obtain the values of the heat transfer coefficient. The main parameters taken into consideration in the computations concerned: meshes, physics, and geometry. Finally, local heat transfer coefficients were determined. [ABSTRACT FROM AUTHOR]

The paper presents a simplified method of determining the thickness of sludge on the walls of the heat exchanger piping in a biogas plant digester. The evaluation of the thickness of a sludge layer is based on the biogas plant operation parameters, including the inlet and outlet temperature of the heat exchanger, mass flow and the geometric characteristics of the heat exchanger and physical parameters of the substrate working inside a fermentation chamber. Measurement of the thickness of the sludge layer on the walls of a heat exchanger is only possible at the time of general cleaning of a digester, which necessitates switching off the biogas plant operation. The paper compares the results of predictions with experimental data of the work of a biogas plant digester located in north-eastern Poland, in Ryboły. The presentation of the obtained numerical results is supplemented by the uncertainty analysis. The significance of undertaking such research lies in its applicational aspects, as during the operation of a biogas plant sludge accumulates on the walls of a digester, which provides additional thermal resistance and reduces the thermal efficiency of the heat exchanger. [ABSTRACT FROM AUTHOR]

The paper proposes the use of Trefftz method to solve the triple coupled heat conduction problem in flow boiling of refrigerant in an asymmetrically heated minichannel. A mathematical model of heat transfer in a rectangular minichannel is suggested. Two sets of Trefftz functions were used to determine 2D temperature fields at a fluid flow in the minichannel tilted at a known angle. The procedure for the calculation of the liquid temperature was coupled with the process of determining temperature fields in two adjacent elements of the experimental stand with the minichannel, i.e. in the glass pane and the heating foil. Heat transfer in the glass, foil and liquid is described using various 2D differential equations with an adequate set of boundary conditions. Solving those equations led to the solving of the triple coupled heat conduction problem made up of one direct and two subsequent inverse problems. The results are presented as: (1) 2D temperature of the glass pane, the heating foil, the flowing liquid, (2) mean square errors between temperature approximations and selected boundary conditions, (3) the heat transfer coefficient versus the distance from the minichannel inlet. [ABSTRACT FROM AUTHOR]

In present paper new approach to study heat transfer at spray cooling, based on the using of high-speed infrared thermography with high spatial resolution is proposed. Also in the paper new data on basic spray parameters, including sizes and velocities of droplets at different pressure at the nozzle inlet were obtained with the use of shadow technique and high-speed video camera. It is found, that heat transfer coefficient is unequally spatially distributed value and essentially depends on flow rate in the stationary irrigation mode. The dependence of heat transfer coefficient on a distance between spray source and heat exchange surface is obtained and an optimal distance corresponding to the maximum heat transfer intensity at present configuration of irrigation points relatively to the heating surface is determined. [ABSTRACT FROM AUTHOR]

A compact Liquid Lithium Target (LiLiT) has been operating at SARAF for several years with beam power of several kW (1.9-2.5 MeV, up to 2 mA). When bombarding the lithium with low energy protons neutrons are generated. The neutron source, mainly used for nuclear astrophysics research, was decommissioned in 2016 towards an upgraded model - with possible applications to Boron Neutron Capture Therapy (BNCT) and material-science studies. The improved version has been designed to sustain 50 kW proton beam power (2.5 MeV, ~20 mA) to provide sufficient neutron flux required for clinical BNCT application. The new model has a 50 mm wide lithium jet to enable dissipation of the higher beam power and an improved heat exchanger to remove the power to a secondary cooling loop. A new Annular Linear INduction electro-magnetic pump (ALIN) has been designed and built to provide the required lithium flow rate. Other mechanical improvements facilitate the maintenance of the system and the robustness of operation. Radiological risks due to the 7Be produced in the reaction are reduced by using an integrated lead shielding of the lithium reservoir. An integrated neutron moderator is being designed to adjust the neutron energy to the spectrum best suited to BNCT. A low power (6 kW) model of the new design with a narrower nozzle (18 mm wide) and a rotating-magnet electro-magnetic pump is operating at SARAF to support the ongoing astrophysics and nuclear research program [1], [2]. To fulfill clinical BNCT, the upgraded LiLiT model will require an accelerator of appropriate energy and intensity. The design features of the new system are presented in this paper. [ABSTRACT FROM AUTHOR]

In the present paper, results for fluid flow, temperature and air humidity experimental measurements for innovative energy recovery counterflow air-to-air heat exchanger have been shown. For the low outdoor air temperatures case, frost formation is also observed and analysed. Base on the results of analysis the temperature, humidity and total efficiency of the exchanger are presented. The analysis showed that fluid flow rate, humidity and system efficiency significantly drop down under unfavourable conditions in the winter period when the outdoor temperature decrease below -5oC. In the present system, the heat exchanger equipped with a set of opposing air dampers can use intake air to absorb the moisture from the exhaust air. This solution has the advantage to prevent the exchanger frosting as well as melt ice layer if any growth on heat exchanger walls. [ABSTRACT FROM AUTHOR]

The aim of the paper is to estimate effect of the heating surface enhancement on FC-72 flow boiling heat transfer for a vertical minichannel 1.7 mm deep, 24 mm wide and 360 mm long. Two types of enhanced heating surfaces were used: one with minicavities distributed unevenly, and the other with capillary metal fibrous structure. It was to measure temperature field on the plain side of the heating surface by means of the infrared thermography and to observe the two-phase flow patterns on the enhanced foil side. The paper analyses mainly the impact of the microstructured heating surface on the heat transfer coefficient. The results are presented as heat transfer coefficient dependences on the distance along the minichannel length. The data obtained using two types of enhanced heating surfaces in experiments was compared with the data when smooth foil as the heating surface was used. The highest local values of heat transfer coefficient were obtained using enhanced foil with minicavities - in comparison to other cases. Local values of heat transfer coefficient received for capillary fibrous structure were the lowest, even compared with data obtained for smooth foil. Probably this porous structure caused local flow disturbances. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental study of the heat transfer during flow boiling of refrigerant R236fa in a horizontal microchannel heat sink. The experiments were performed using closed loop that re-circulates coolant. Microchannel heat exchanger that contains two microchannels with 2x0.4 mm cross-section was used as the test section. The dependence of average heat flux on wall superheat and critical heat flux were measured in the range of mass fluxes from 600 to 1600 kg/m2s and in the range of heat fluxes from 5 to 120 W/cm2. For heat flux greater than 60 W/cm2, nucleate boiling suppression has significant effect on the flow boiling heat transfer, and this leads to decrease of the heat transfer coefficient with heat flux grows. [ABSTRACT FROM AUTHOR]

The paper presents the measurement of heat transfer coefficient for the refrigerator's condenser in free convection regime. The water was pumped through the steel coils of heat exchanger with a constant flow rate and its temperature was kept at a demanded value by means of ultrathermostat. The research was conducted in stationary conditions which were controlled by a continuous measurement of the water temperature at inflow and outflow to the heat exchanger. The temperature distribution at the external condenser surface was registered by means of an infrared camera. Single elements used to the analysis were selected using the thermogram registered. In free convection regime and in case of small temperature change the heat transfer coefficient value can be calculated by comparing the measured temperature area with analytical solution describing one-dimensional temperature distribution along the rib. The accuracy of the proposed method for measuring the heat transfer coefficient was examined by comparing the heat transferred to the air and the heat lost by water flowing through the spiral of heat exchanger. An error between these two parameters is about 6%. [ABSTRACT FROM AUTHOR]

The paper presents the influence of flow modification on the operation of an accumulative heat exchanger. This device can be used as a regenerator in ventilation and air supply systems. A heat exchanger uses ceresine (a mixture of paraffins) as a phase change material (PCM). The aim of this research was to determine the effect of flow modification on temperature distribution and pressure drops in the device. The introduction contains a short description of the test stand used, including the accumulative heat exchanger, the guide vanes, and the locations of measurement and control equipment. We found that additional objects limited vortex structures, increased the inside temperature, and dropped the pressure along the heat exchanger. Guidelines for further research are proposed and briefly discussed. [ABSTRACT FROM AUTHOR]

This paper presents an experimental evaluation of moisture transfer of a novel membrane which is used in enthalpy heat exchanger. The moister transfer through a membrane was investigated in a model of counter flow heat exchanger and the effectiveness of moister transfer was evaluated for various flow velocities. It was found that the measuring error, i.e. difference between moister absorbed and released is quite high. Therefore, measuring uncertainty analyses were performed. The resulting uncertainty of effectiveness of moister transfer was derived using partial derivatives of all influencing quantities and considering both random and systematic uncertainties. It was found that measuring of mass flow rate has the biggest influence on resulting uncertainty of moister transfer effectiveness. Therefore, accuracy of measured air flow rates measuring must be improved to reach lower resulting uncertainty. [ABSTRACT FROM AUTHOR]

The phenomenon of phase change is one of the most important contemporary issues of thermal engineering. In particular, this applies to all kinds of heat exchanger systems, which should achieve the highest possible efficiency while reducing investment and operating costs. Some of these systems are heat pipes or thermosyphons, which, among others, are used for the heat transfer, temperature stabilization and the regulation of heat flux density. Additionally, they are passive systems, and therefore do not require an external power supply. Heat pipes can be used to stabilize the surface temperature of roads and driveways. Large heat tubes can be applied for heating the surface of bridges and overpasses, which become icy in unfavorable climatic conditions. The paper presents research on the test facility, whose main component is a long vertical copper fin. The temperature at the base of the fin was kept constant for a given series of measurements. Heat receiving fluid was ethanol at atmospheric pressure. The measurement methodology and the results of investigations were discussed. The surface temperature distribution was measured with the infrared camera, and on this basis the local values of heat flow and the heat transfer coefficient were determined. The results were presented as boiling curves for both the fin with the smooth surface and the one covered with a metal capillary-porous structure. The results obtained are useful in the design of heat exchangers, including passive heating of the ground. [ABSTRACT FROM AUTHOR]

The paper contains a comparison of a numerical simulation with a real experiment. In the measured and simulated device is located a heat exchanger with a centrifugal fan. Due to the fan and the geometrical arrangement the flow is relative uneven and so the heat transfer hard to predict. The simulation should be time and cost affordable, so a standard k-ϵ turbulence model and a relative simple mesh was used for the computations. [ABSTRACT FROM AUTHOR]

This paper deals with study of the pressure losses of the new heat convectors product line. For all devices connected to the heating circuit of the building, it's required to declare a tabulated values of pressure drops. The heat exchangers are manufactured in a lot of different dimensions and atypical shapes. An individual assessment of the pressure losses for each type is very time consuming. Therefore based on the resulting data of the experiments and numerical models, an electronic database was created that can be used for calculating the total values of the pressure losses in the optionally assembled exchanger. The measurements are standardly performed by the manufacturer Licon heat hydrodynamic laboratory and the numerical models are carried out in COMSOL Multiphysics. Different variations of the convectors geometry cause non-linear process of energy losses, which is proportionately about 30% larger for the smaller exchanger than for the larger types. The results of the experiments and the numerical simulations were in a very good conjuncture. Considerable influence of the water temperature onto the total size of incurred energy losses has been proven. This is mainly caused by the different ranges of the Reynolds number depending on the viscosity of the used liquid. Concerning to the tested method of superposition, it is not possible to easily find the characteristic values appropriate for the each individual components of the heat exchanger. Every of the components behaves differently, depend on the complexity of the exchanger. However, the correction coefficient, depended on the matrix of the exchanger, that is suitable for the entire range of the developed product line has been found. [ABSTRACT FROM AUTHOR]

This contribution deals with H-modes with significant heat exchange between electrons and ions, but which can still show large differences between electron and ion-temperatures especially inside half minor radius. These conditions are referred to as moderately collisional. A systematic study shows that an increasing fraction of electron heating increases the transport in the ion channel mainly due to the dependence of the ITG dominated ion transport on the ratio Te/Ti in agreement with modeling. The rotational shear in the plasmas under study was so small that it hardly influences ITG stability, such that variations of the rotation profile due to a change of the heating method were of minor importance. These findings connect to studies of advanced tokamak scenarios using ECCD as a tool to modify the q-profile. The electron heating connected to the ECCD tends to increase the transport in the ion channel quite in contrast to the goal to operate at reduced current but with increased confinement. The confinement only increases as the fraction of ion heating is increased by adding more NBI. An ITER case was modeled as well. Due to the larger value of vei ⋅ τE the ratio Te/Ti is only moderately reduced even with strong electron heating and the confinement reduction is small even for the hypothetic case of using only ECRH as additional heating. Finally the paper discusses the ongoing upgrade of the AUG ECRH-system. [ABSTRACT FROM AUTHOR]

The paper deals with the possibilities of measurement and evaluation of the heat transfer coefficient in circular minichannels. Evaluation procedure is demonstrated on real data and the results obtained are compared with the expected values of the heat transfer coefficient. Possible reasons for the difference are discussed. [ABSTRACT FROM AUTHOR]

A conference paper about the development of textile processes for silicon carbide (SiC)/SiC materials that are used in nuclear reactors is presented. It cites studies which explored the use of SiC, Hexagonal Tube (HT) for pin assembling, control rods, heat exchangers or thermal barriers for the hot gas duct as alternatives to zircaloy fuel claddings that can withstand core overheating accidents. A flexible ceramic porous bond with a textile structure is proposed to strengthened materials.

While thermal structures such as greenhouses are complex to model under transient conditions because of coupled heat and mass (H2O and CO2) exchanges between their different parts, systems theory allows a simple analysis of the input/output behaviour of the model. In particular, parameters of the reduced dynamic models can be derived from in-situ measurements on these systems. This paper describes an application of the systems approach to a greenhouse climate model which incorporates CO2 balance, crop transpiration and photosynthesis and the effects of heating, CO2 enrichment, natural ventilation and evaporative cooling. In a first stage, system parameters such as the equivalent thermal mass, the wind dependent coefficient of natural ventilation and the various heat exchange coefficients were identified in situ from sequences of input-output data concerning the heat and water vapour balance, recorded over the crop production period from December to July. Good agreement between measured and computed values of air temperature, air humidity was observed. In a second stage, we have considered simultaneously the sensible heat, water vapour and CO2 exchanges and tested the model against experimental data measured using a commercial greenhouse climate control computer. The identified values of the physical and physiological parameters are close the theoretical values and the accuracy of temperature, humidity and CO2 content is rather good. [ABSTRACT FROM AUTHOR]

The article presents high-order simulations of heat transfer in fluid flow. Heat induced changes in material properties (density, viscosity and heat conductivity) substantially influence flow structures. The change of fluid density implies naturally the thermal expansion what results in non-homogeneous divergence of velocity and the model of evolutionary Navier-Stokes-Fourier equations is not strictly incompressible in this case. Proposed algorithm treats the model as a fully coupled system of equations. Applied method of operator splitting is promissing to become a more general concept for numerical modelling of active quantities advected by incompressible fluids. This work follows the 2D results presented during EFM 2019 and extends to 3D together with advances of the code reimplementation to current version of the Nektar++ library (open-source framework for spectral/hp finite elements). Results for various settings for both the forced/mixed and natural convection are shown. [ABSTRACT FROM AUTHOR]

The University of West Bohemia in Pilsen (Department of Power System Engineering) is working on the selection of effective heat exchangers. Conventional shell and tube heat exchangers use simple segmental baffles. It can be replaced by helical baffles, which increase the heat transfer efficiency and reduce pressure losses. Their usage is demonstrated in the primary circuit of IV. generation MSR (Molten Salt Reactors). For high-temperature reactors we consider the use of compact desk heat exchangers, which are small, which allows the integral configuration of reactor. We design them from graphite composites, which allow up to 1000°C and are usable as exchangers: salt-salt or salt-acid (e.g. for the hydrogen production). In the paper there are shown thermo-physical properties of salts, material properties and principles of calculations. [ABSTRACT FROM AUTHOR]

The paper describes new results for an experimental heat exchanger equipped with a single corrugated capillary tube, basic information about the measurements and the experimental setup. Some of the results were compared with numerical simulations. [ABSTRACT FROM AUTHOR]

Recent developments in the designing of the thermohydraulic systems have heightened the need for special software tools. Possibility of incorporating the measured data, easy and quick rearrangement of the system and short simulation time play a key role in successful progress in designing of the thermohydraulic systems. Commercial software sometimes does not fit to our special tasks or it lacks some utilities. This paper attempts to show usefulness of MATLAB and Simulink in the development of the "drag and drop" software. In the Simulink it is possible to develop specialized libraries containing graphical blocks representing parts of the real systems. Easy cooling circuit was designed using developed graphical blocks. The main parts of the circuit consist of the heat source and heat exchanger/cooler. Another parts such as pumps, pipes and properties of the cooling medium etc. are taken into account in the investigated system. These results obtained by the developed software are presented for similar circuits with different heat exchangers/coolers. Simulations for different heat exchangers were solved with different initial conditions. These results are consequently compared. Characteristic properties (heating/cooling power and pressure drop according to flow rate) of the heat exchangers/coolers were obtained experimentally in our laboratory and by the numerical CFD simulation in ANSYS/FLUENT software. [ABSTRACT FROM AUTHOR]

Recent compact heat exchangers are very often assembled from numerous parts joined together to separate heat transfer fluids and to form the required heat exchanger arrangement. Therefore, the leak tightness is very important property of the compact heat exchangers. Although, the compact heat exchangers have been produced for many years, there are still technological problems associated with manufacturing of the ideal connection between the individual parts, mainly encountered with special purpose heat exchangers, e.g. gas turbine recuperators. This paper describes a procedure used to identify the leakage location inside the prime surface gas turbine recuperator. For this purpose, an analytical model of the leaky gas turbine recuperator was created to assess its performance. The results obtained are compared with the experimental data which were acquired during the recuperator thermal performance analysis. The differences between these two data sets are used to indicate possible leakage areas. [ABSTRACT FROM AUTHOR]

New Technologies Research Centre at the University of West Bohemia in Pilsen uses middle-sized wind tunnel experimental facility. The tunnel equipment is extended in order to let us measure also heat transfer: the main wind tunnel duct itself forms the opened cooling air circuit, one closed circuit is there for water based coolant flow and one more closed circuit forms the hot compressed air loop. In this article, the typical measurement of the thermal characteristics of the common water-air heat exchanger is presented. [ABSTRACT FROM AUTHOR]

This article surveys a so far little known approach to two simultaneously requested but mutually opposed requirements on internal conditions in buildings. It is the growing demand of better internal comfort while the other is decrease of costs and energy consumption. The internal conditions is ensured by terminal units located and adjusted at the points of conditioned air delivery into rooms. Author's terminal units achieve the goal by having no moving parts. Advantages are low cost, robustness and long operating life without maintenance. Capability to switch the air flows at a high frequency without wear opens new ways to control, such as the flow pulse width modulation. The fast switching also makes possible small regenerative heat exchangers, keeping inside the building the heat extracted from the removed contaminated air. [ABSTRACT FROM AUTHOR]

Considerable amount of heat produced during composting of organic matter is usually lost to the surrounding environment. In order to utilize this potential heat source, biomass is composted in mounds or vessels and excess thermal energy is captured via heat exchangers and transported to the site for space heating, preparation of utility water and other applications. The aim of this experimental research is to measure the temperature profiles in a pilot-scale composting bioreactor and assess its performance. [ABSTRACT FROM AUTHOR]

The article presents the results of experimental and computer simulations studies of the high temperature heat receiver working in the concentrated solar radiation system. In order to study the radiation absorption process and heat exchange, the two types of computer simulations were carried out. The first one was used to find the best location for absorber in the concentrating installation. Ray Tracing Monte Carlo (RTMC) method in Trace Pro software was used to perform the optical simulations. The results of these simulations were presented in the form of the solar radiation distribution map and chart. The data obtained in RTMC simulations were used as a second type boundary conditions for Computational Fluid Dynamics (CFD) simulations. These studies were used to optimize the internal geometry of the receiver and also to select the most effective flow parameters of the working medium. In order to validate the computer simulations, high temperature heat receiver was tested in experimental conditions. The article presents the results of experimental measurements in the form of temperature, radiation intensity and power graphs. The tests were performed for varied flow rate and receiver location. The experimental and computer simulation studies presented in this article allowed to optimize the configuration of concentrating and heat receiving system. [ABSTRACT FROM AUTHOR]

Is numerically investigated the process of convective heat transfer in the reservoirs of liquefied natural gas (LNG). The regimes of natural convection in a closed rectangular region with different intensity of heat exchange at the external borders are investigated. Is solved the time-dependent system of energy and Navier-Stokes equations in the dimensionless variables "vorticity -- the stream function". Are obtained distributions of the hydrodynamic parameters and temperatures, that characterize basic regularities of the processes. The special features of the formation of circulation flows are isolated and the analysis of the temperature distribution in the solution region is carried out. Is shown the influence of geometric characteristics and intensity of heat exchange on the outer boundaries of reservoir on the temperature field in the LNG storage. [ABSTRACT FROM AUTHOR]

Heat transfer agent magnetic fluids based on aqueous solutions of hydrogen peroxide or a mixture of ethylene glycol with the powders of lanthanum manganite and the toner cartridge are considered. Experimental data on the effect produced by an external magnetic field on the characteristics of magnetic fluids and heat exchanger efficiency were analyzed. As the heat exchanger is considered flat-plate solar collector. The conclusion about the possibility of using the above technologies to improve the efficiency of heat exchangers. [ABSTRACT FROM AUTHOR]

Measurements of heat transfer rates performed with an experimental condensation heat exchanger are reported for a corrugated minichannel tube and for a straight minichannel tube. The two cases were compared at same flow regimes. The corrugation appears advantageous for relatively low steam pressures and flow rates where much higher heat transfer rates were observed close to the steam entrance, thus allowing shortening the heat exchanger with the associated advantages of costs lowering and smaller built-up space. At high steam pressures and high flow rates both tubes performed similarly. [ABSTRACT FROM AUTHOR]

Experiments have been carried out in order to investigate the stabilization of water temperature with a water-PCM heat exchanger. The water-PCM heat exchanger was of a rather simple design. It was a round tube, through which the water flowed, surrounded with an annular layer of PCM. The heat exchanger was divided into one meter long segments (modules) and the water temperature was monitored at the outlet of each of the segments. A paraffin-based PCM with the melting temperature of 42 °C was used in the experiments. The experimental set-up consisted of two water reservoirs kept at different temperatures, the water-PCM heat exchanger, PC controlled valves and a data acquisition system. As the first step a response to a step change in the water temperature at the inlet of the heat exchanger was investigated. Subsequently, a series of experiments with a square wave change of temperature at the inlet of the exchanger were carried out. The square wave temperature profile was achieved by periodic switching between the two water reservoirs. Several amplitudes and periods of temperature square wave were used. The results of experiments show that a water-PCM heat exchanger can effectively be used to stabilize the flowing water temperature when the inlet temperature changes are around the melting range of the PCM. [ABSTRACT FROM AUTHOR]

The theoretical and experimental aspects concerning the typical bubble shape at the flow line of a standard domestic central heating system are investigated. This is done in support of the on-going research on two-phase flows in domestic central heating systems. Bubble nucleation and detachment at the primary heat exchanger wall of a domestic central heating boiler results in a bubbly two-phase flow in the system pipe work. Bubbly flow results in undesired cold spots at higher points in the system, consequently diminishing system performance. An experimental analysis was done on the bubble shape at the exit of the boiler through the application of photographic techniques. The results are presented in terms of the measured bubble aspect ratios at some principal system operating conditions. The dimensionless Eotvos and bubble Reynolds number were calculated and tabulated with the measured mean diameters. The data was subsequently correlated to the bubble shape regime diagram. Results suggest that most bubbles are quasi-spherical in shape with a noticeable elongation at lower bulk fluid Reynolds numbers. [ABSTRACT FROM AUTHOR]

The theoretical and experimental aspects of bubble distribution in bubbly two-phase flow are reviewed in the context of the micro bubbles present in a domestic gas fired wet central heating system. The latter systems are mostly operated through the circulation of heated standard tap water through a closed loop circuit which often results in water supersaturated with dissolved air. This leads to micro bubble nucleation at the primary heat exchanger wall, followed by detachment along the flow. Consequently, a bubbly two-phase flow characterises the flow line of such systems. The two-phase distribution across the vertical and horizontal pipes was measured through a consideration of the volumetric void fraction, quantified through photographic techniques. The bubble distribution in the vertical pipe in down flow conditions was measured to be quasi homogenous across the pipe section with a negligible reduction in the void fraction at close proximity to the pipe wall. Such a reduction was more evident at lower bulk fluid velocities. [ABSTRACT FROM AUTHOR]

Due to the optimization of geometrical parameters of the heat exchanger in indirect heated water heaters created a mathematical model of heating hot water, by which I have subsequently made the simulation of the device to change its geometrical parameters. Based on these results, the impacts of the geometrical parameters affect the performance of the heat exchanger. The results of the optimization to create a CFD model which watched at the behavior of optimized heat exchanger for indirect heated water heaters. [ABSTRACT FROM AUTHOR]