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Cooling or heating an agitated liquid is a very common operation in many industrial processes. A classic approach is to transfer the necessary heat through the vessel jacket. Another option, frequently used in the chemical and biochemical industries is to use the heat transfer area of vertical tube baffles. In large equipment, e.g. fermentor, the jacket surface is often not sufficient for large heat transfer requirements and tube baffles can help in such cases. It is then important to know the values of the heat transfer coefficients between the baffles and the agitated liquid. This paper presents the results of heat transfer measurements using the transient method when the agitated liquid is periodically heated and cooled by hot and cold water running through tube baffles. Solving the unsteady enthalpy balance, it is possible to determine the heat transfer coefficient. Our results are summarized by the Nusselt number correlations, which describe the dependency on the Reynolds number, and they are compared with other measurements obtained by a steady-state method.

Proceedings of: 14th International Conference on Fluidization: From Fundamentals to Products. Noordwijkerhout, Netherlands, 26-31 may 2013. ; This work presents an experimental study to determine the capacity of a Phase Change Material (PCM) in granular form to be used in a bubbling fluidized bed for thermal energy storage. The experimental measurements are focused on the determination of the heat transfer coefficient between a heated surface and the granular PCM in fluidized state. The results obtained indicates that the heat transfer coefficient notably increases (up to values three times higher) when the granular PCM is in solid form because it changes its phase when touches the heated surface ; This work was partially founded by the Spanish Government (Project ENE2010-15403), the regional Government of Castilla-La Mancha (Project PPIC10-0055-4054) and Castilla-La Mancha University (Project GE20101662). ; publicado

International audience ; The performance gap between the design and the as-built energy performance of buildings is considered a significant risk that may compromise the efforts on meeting the carbon reduction targets set by governments in Europe. The relative importance of irregularities or defects within building walls is more prominent when the thermal insulation level increases. It is thus necessary to quantify the global thermal insulation level of building walls (i.e., including thermal bridges). Classical contact measurement methods only allow local measurements and would thus require the use of a high number of sensors which would limit their applicability. Besides, the presence of thermal bridges prevents the use of contact heat flux measurements because of the 2D or 3D nature of the associated heat transfers through the building walls. To overcome these limitations, the present study proposes an alternative approach consisting in measuring the heat flux on one location and extrapolating its value on the whole building wall through the measurement of the total heat transfer coefficient. Therefore, we developed and/or further improved five different in situ measurement methods of the total heat transfer coefficient on building walls. The measurement methods were thoroughly tested indoor thanks to lab-scale experiments carried out both in steady-state and transient regimes. The results obtained demonstrated the accuracy and the robustness of the proposed methods, as well as their intrinsic limitations. These in situ methods can be used to assess the heat losses on a whole building wall, including the contribution of thermal bridges.

International audience ; The performance gap between the design and the as-built energy performance of buildings is considered a significant risk that may compromise the efforts on meeting the carbon reduction targets set by governments in Europe. The relative importance of irregularities or defects within building walls is more prominent when the thermal insulation level increases. It is thus necessary to quantify the global thermal insulation level of building walls (i.e., including thermal bridges). Classical contact measurement methods only allow local measurements and would thus require the use of a high number of sensors which would limit their applicability. Besides, the presence of thermal bridges prevents the use of contact heat flux measurements because of the 2D or 3D nature of the associated heat transfers through the building walls. To overcome these limitations, the present study proposes an alternative approach consisting in measuring the heat flux on one location and extrapolating its value on the whole building wall through the measurement of the total heat transfer coefficient. Therefore, we developed and/or further improved five different in situ measurement methods of the total heat transfer coefficient on building walls. The measurement methods were thoroughly tested indoor thanks to lab-scale experiments carried out both in steady-state and transient regimes. The results obtained demonstrated the accuracy and the robustness of the proposed methods, as well as their intrinsic limitations. These in situ methods can be used to assess the heat losses on a whole building wall, including the contribution of thermal bridges.

This article deals with the derivation of the temperature response of the finite thickness wall, which is heated by heat flow, as a possibility to measure the local values of the heat transfer coefficient with a very high spatial resolution. In addition to its own experimental measurement technique, it is also possible to use this derivation to describe the gradual heating of the wall while using the temperature oscillation (TOIRT) method for the heat transfer measurement. The system of the partial differential equations and the boundary and initial conditions is solved by a transformation into Laplace's space, where the task is easier to solve. At the end of the article, the results of the analytical solution are compared with a numerical solution of this problem.

Rocket nozzles are often cooled by passing liquid propellants through channels in the nozzle walls. Estimating heat transfer to the wall from the hot gases in the nozzle is essential in deciding on the coolant flow requirements. The present work examines the computational estimation of convection heat transfer to the nozzle walls for compressible turbulent flows. Computations were performed using the rhoPimpleFoam solver in OpenFOAM® with two different turbulence models. We simulate the supersonic flow over a flat plate and validate the heat flux calculation method and turbulence model characteristics. We compare two methods of calculating convection heat transfer in the context of the nozzle flow case presented by Back & Massier. We find that the realizablek-ε turbulence model works well in estimating the heat transfer coefficient.

This paper is closed access until it is published. ; This paper aims to identify the impact of traditionally unmonitored energy sources and sinks on assessment of the as-built thermal performance of occupied homes. The analysis aims to demonstrate the potential scale of uncertainties introduced in a heat balance estimation of the heat transfer coefficient (HTC) when using in-use monitored data. Energy flows for two UK homes—one a 1930s dwelling with high heat loss, the second a higher-performing 2014-built home—are predicted using the UK Government's Standard Assessment Procedure (SAP) and visualised using Sankey diagrams. Selected modelled energy flows are used as inputs in a quasi-steady state heat balance to calculate in-use HTCs as if from measured datasets gathered in occupied homes. The estimated in-use HTCs are compared against SAP-calculated values to illustrate the impact of including or omitting various heat sources and sinks. The results demonstrate that for well-insulated dwellings with low heat loss, a heat balance estimation of the HTC is likely to be more sensitive to inclusion or omission of traditionally un-metered energy flows; in the presented case studies, this increased sensitivity is a consequence of a higher proportion of heating demand being met by internal and solar gains. While simple quasi-steady state heat balance methods may be appropriate for dwellings with very high heat loss, alternative approaches are likely to be required for those with lower heat loss. There is a need to understand the impacts of unmetered heat flows on the accuracy with which a building's thermal performance may be inferred from in-use monitored data: this paper illustrates the scale of these impacts for two homes at opposite ends of the energy performance scale.

<p>Accurate prediction of surface temperature of high speed aerospace vehicle is very necessary for the selection of material and determination of wall thickness. For aerothermal characterisation of any high speed vehicle in its full trajectory, it requires number of detailed computational fluid dynamics (CFD) calculations with different isothermal calculations. From the detailed CFD calculations for different flow conditions and geometries, it is observed that heat transfer coefficients scale with the difference of adiabatic wall temperature and skin temperature. A simple 'isothermal method', is proposed to calculate heat flux data with only two CFD simulations one on adiabatic condition and other on isothermal condition. The proposed methodology is validated for number of high speed test cases involving external aerodynamic heating as well as high speed combusting flow. The computed heat fluxes and surface temperatures matches well with experimental and flight measured values.</p>

This work presents an experimental study to determine the capacity of a phase change material (PCM) in granular form to be used in fixed and bubbling fluidized beds for thermal energy storage. The experimental measurements are focused on determination of the heat transfer coefficient between a heated surface immersed in the bed and the granular PCM. The flow rate is varied to quantify its influence on the heat transfer coefficient. The PCM used is Rubitherm GR50 with a phase change temperature of approximately 50° C. The PCM is available in two different particle sizes, 0.54 mm and 1.64 mm, of which the finer is used in the fluidized bed and the coarser is used in the fixed bed. In addition, the results obtained for the PCM are compared with the heat transfer coefficients measured for sand, a material commonly used for thermal storage. In comparing the heat transfer coefficients for fixed and fluidized beds, the heat transfer coefficients in the fluidized bed with PCM are nearly three times higher than those for the fixed bed at the same gas flow rate. This increase in the heat transfer is a result of two main factors: first, the continuous renewal of PCM particles from the heated surface when they are fluidized, and second, the large quantities of energy in latent form absorbed by the PCM. In the fixed bed there is no renovation of particles, consequently only a small percentage of particles are able to change its phase. Hence, there is no increase in the heat transfer coefficient due to this fact. ; This work was partially funded by the Spanish Government (Project ENE2010-15403), theRegional Government of Castilla-La Mancha (Project PPIC10-0055-4054) and Castilla-La Mancha University (Project GE20101662). ; Publicado

Intensification of heat and mass transfer processes in industrial drop cooling towers is one of the main areas of research in modern heating engineering. Increasing the efficiency of transfer processes during the direct interaction of water and air in cooling tower sprinklers is possible when moving from creating a contact surface in the form of a flowing liquid film to sprinklers creating drop-film surfaces. One of the possible devices that create such surfaces are devices with vertical contact grids, which make it possible to obtain significant drop surfaces at low energy costs. A mathematical description of mass and heat transfer processes in devices with vertical grids is impossible without the presence of functional dependencies of mass and heat transfer coefficients depending on the hydrodynamic parameters of the process. Obtaining analytical expressions convenient for engineering modeling is difficult due to the complexity of the mathematical description, therefore in some cases it is more convenient to use experimental dependences of the coefficients on the process parameters. The experiments carried out on mass and heat transfer in devices with vertical grids made it possible to confirm the possibility of using the Lewis relation, based on the similarity between the processes of heat and mass transfer under conditions of water cooling in cooling towers equipped with devices with vertical grids. This made it possible to use only one experimental dependence in the mathematical description of transfer processes. An experimental dependence of the volumetric heat transfer coefficient on the hydrodynamic parameters of the interaction of water and air on the contact grids was also obtained.