1,355,113 research outputs found
Frank Angelotti, crouching stance
No full textFrank Angelotti, Purdue Tackle (two copies)Athletics - Football Players (A-BA)Intercollegiat
Frank Angelotti, crouching stance
No full textFrank Angelotti, Purdue Tackle (two copies)Athletics - Football Players (A-BA)Intercollegiat
Frank Angelotti, head and shoulders portrait
No full textFrank Angelotti, Purdue Tackle, circa 1952-1954Athletics - Football Players (A-BA)Intercollegiat
On the performance of energy walls by monitoring assessment and numerical modelling: a case in Italy
No full textThermoactive diaphragm walls have proved their efficiency for near-surface geothermal energy use. To get insights into the heat transfer process occurring between the heat exchanger pipes and the surrounding boundaries, an instrumented real case located in Northern Italy was taken as reference. Combining on-site monitoring data with computational simulations, the role of the basement space in governing the heat fluxes in the different seasons, and the energy performance of the diaphragm wall and of the ground source heat pump system, is highlighted. The numerical analysis represents an effective predictive tool, but is also highly sensitive with respect to parameters of uncertain or complex definition, such as the boundary thermal conditions and the thermal input at the pipe inlet. Intermittent operation and idle periods require a refined simulation, discretising the time dependency of the input variables in appropriate short time steps
A laboratory apparatus to study thermal response test in the presence of groundwater flow
No full textThe standard approach to Thermal Response Test, based on conduction heat transfer in the ground, turns out to be unsuccessful under significant groundwater flow. The applicability of the Moving Infinite Line Source model to interpret the TRT in this case still needs to be proved. In order to study the TRT in the presence of a groundwater flow, an original laboratory apparatus has been developed. The Sand Box design is based on a heat transfer similitude between the real scale TRT problem and the laboratory scale one. The Sand Box sizes (1,2 m x 0.6 m x 1.0 m) are then set in order to keep the boundaries unaffected by the heat source during the TRT. The U-pipe heat exchanger is reproduced through a two-cables electrical resistance 1 m long. A hydraulic loop with a peristaltic pump allows to obtain a Darcy velocity across the sandy soil up to 6,7510-5 m/s. The measurement system consists in several thermocouples in the porous medium and in a flow meter. The TRT results at null groundwater velocity allow to derive a reference thermal conductivity. The first tests with groundwater flow show the suitability of the apparatus and allow to derive some preliminary considerations
A numerical model to simulate the dynamic performance of Breathing Walls
No full textA one-dimensional Finite Difference Model for Breathing Wall components under time dependent Dirichlet boundary conditions is presented. The algorithm undergoes a comprehensive validation against a dynamic analytical model, under either sinusoidal and generically periodic boundary conditions, adopting different airflow velocities and in relation to capacitive and resistive materials alternatively. It is found that the accurate prediction of the temperature profile inside the wall is influenced primarily by the timestep, whose optimal value can be identified through a preliminary frequency analysis of the boundary conditions. Moreover, for a better prediction of the surface heat flow density, and especially in insulating materials, refining the space grid below 1 mm is recommended, as well as the adoption of a 3-point numerical scheme. The numerical model is finally tested against experimental data on a porous concrete wall, showing that numerical errors may compare to other sources of uncertainties, regarding materials properties and boundary conditions
Experimental validation of a steady periodic analytical model for Breathing Walls
No full textThe Breathing Wall behaviour under variable boundary conditions is described by an analytical model based on a one-dimensional porous domain crossed by air and subject to third type steady periodic boundary conditions. To the best of the authors’ knowledge, its experimental validation is not provided in literature. In this work, a new model is derived considering Dirichlet steady periodic boundary conditions. The model is experimentally validated testing a 1 m2 no-fines concrete sample in the Dual Air Vented Thermal Box apparatus, specially improved to replicate dynamic thermal conditions. The experiments show that increasing the air flow velocity across the Breathing Wall from 0 to 12 mm/s enhances thermal coupling between the two environments, namely reduces the wall thermal capacity, with a decrease in the penetration time from 4.3 h to 3 h. The model shows a very good agreement with experimental data when predicting temperature distribution across the domain, with error averages and standard deviations within the thermocouple accuracy after calibration, assumed to be 0.15 ∘C. The lesser yet good agreement concerning conduction heat flux density is explained in terms of accuracy in the measurement of the boundary conditions and critical issues in the heat flow measure itself (i.e. probe thermal resistance, thermal contact, emissivity mismatch)
Borehole Heat Exchangers: how flow velocity influence and dispersion influence heat transfer
No full textThe heat pumps coupled to geothermal systems likely to use low enthalpy resources (T<20°C) are gradually spreading, representing one of the most efficient and lower environmental impact technologies for cooling and heating of buildings. Most common geothermal systems are formed by closed loop boreholes (Borehole Heat Exchangers or BHEs) buried into the ground, typically 100 m deep, where a thermal-carrier fluid is circulated into polyethylene U-pipes, extracting heat from the ground in winter and/or injecting heat into the ground in summer.
The energy performance of these systems depends on the heat transfer process between the BHEs and the ground. In many applications the ground can be considered as a purely conductive medium: in fact this hypothesis is at the base of the most commercially availabele tools used to design BHEs, such as GHLEPRO or EED (Hellstrom 2001). Therefore some efforts have recently been carried out to include the effects of the presence of a groundwater flow into the BHEs modeling (Diao 2004). In this case the heat is transported not only by conduction but also by advection. To consider this extended problem could change both the correct prediction of the energy performance of the BHEs and their design and also the investigation of the thermal impact, in other words the temperature perturbation produced by the BHEs operation in surrounding aquifer. The aim of this work is the evaluation of these two aspects, varying the rate of groundwater flow velocity and dispersion coefficient using a numerical model realized through Modflow/MT3D (Angelotti 2014), already validated respect to the Moving Line Source (Molina-Giraldo 2011), demonstrating that both advection and dispersion play an important role in the heat transfer
Measuring a Breathing Wall's effectiveness and dynamic behaviour
No full textBreathing Walls are building structures based on porous materials crossed by an airflow, which act both as building envelopes and ventilation system components. In climates where both heating and cooling are needed, a pro-flux configuration (heat and air mass both flowing in the same direction) might be alternated with a contra-flux configuration (heat and air mass flowing in opposite directions) during the year or even on a day. Understanding and modelling the Breathing Walls' stationary and dynamic behaviour is thus fundamental, in order to optimize their design and to fully exploit their energy-saving potential. In this experimental study, a small-scale no-fines concrete Breathing Wall was investigated. The steady-state contra-flux tests performed in a Dual Air-Vented Thermal Box laboratory apparatus were used to derive the heat recovery efficiency of the sample as a function of the cross airflow velocity. The effectiveness of this technology was then evaluated in a virtual case study. An optimal airflow velocity across the Breathing Wall was found, leading to energy savings between 9% and 14%. Dynamic tests were performed assuming a sinusoidal variation of the operative temperature on one side of the sample. They showed how airflow velocity affected the Breathing Wall inertia and dynamic behaviour
Numerical validation of a simplified design procedure for calculating the heating load in buildings with Breathing Wall components
No full textBreathing Walls (BWs) can provide significant building energy saving in winter conditions, but the present standard methodology for heating load calculation fails to consider this technology, thus limiting its application. In this paper, a procedure to include BWs in the EN 12831-1:2017 is then proposed. The methodology is tested against a numerical calculation of the heating load based on the coupling between the Building Energy Simulation (BES) engine TRNSYS and a Matlab Finite Difference Model (FDM) addressing heat and mass transfer across the BW. The very good agreement demonstrates that the BW can be syntethized by two key parameters, namely the effective thermal transmittance at the interior surface and the thermal recovery efficiency
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