Energy recovery | EPFL Graph Search

Energy recovery includes any technique or method of minimizing the input of energy to an overall system by the exchange of energy from one sub-system of the overall system with another. The energy can be in any form in either subsystem, but most energy recovery systems exchange thermal energy in either sensible or latent form. In some circumstances the use of an enabling technology, either daily thermal energy storage or seasonal thermal energy storage (STES, which allows heat or cold storage between opposing seasons), is necessary to make energy recovery practicable. One example is waste heat from air conditioning machinery stored in a buffer tank to aid in night time heating. Principle A common application of this principle is in systems which have an exhaust stream or waste stream which is transferred from the system to its surroundings. Some of the energy in that flow of material (often gaseous or liquid) may be transferred to the make-up or input material flow. This i

Experimental Evaluation and Control of Two-Phase Multi-Microchannel Evaporator Cooling Systems for High Efficiency Data Center

Duan Wu

Thermal designers of data centers and server manufacturers are showing a greater concern regarding the cooling of the new generation data centers, which consume considerably more electricity and dissipate much more waste heat, a situation that is creating a re- thinking about the most effective cooling systems for the future beyond conventional air cooling of the chips/servers. Potentially, a significantly better solution is to make use of on- chip two-phase cooling, which, besides improving the cooling performance at the chip level while also consuming less energy to drive the cooling process, also adds the capability to reuse the waste heat in a convenient manner, since higher evaporating and condensing temperatures of the two-phase cooling system (from 60-95 °C) are possible with such a new “green” cooling technology. In the present thesis, three such two-phase cooling cycles using micro-evaporation technology were experimentally evaluated with specific attention being paid to (i) controllability of the two-phase cooling system, (ii) energy consumption and (iii) overall exergetic efficiency, with the emphasis on (i). The controllers were evaluated by tracking and disturbance rejection tests, which were shown to be efficient and effective. The average temperatures of the chips were maintained below the upper limit of 85 °C of computer CPU’s for all tests evaluated in steady state and transient conditions. In general, simple SISO and SIMO strategies were sufficient to attain the requirements of control. Regarding energy and exergy analyses, the experimental results showed that all these systems can be thermodynamically improved since only about 6% of the exergy supplied is in fact recovered in the condenser in the present setup. Additionally, a series of tests covering a wide range of operating conditions under steady state regime were done. The main idea was to generate a “map of performance” of the different cooling systems in terms of energy consumption, energy recovery at the condenser and heat exchanger performance. A total of 120 tests were done which considered all combinations of the variables involved. Finally, empirical and semi-empirical correlations for overall thermal conductance and performance of all components and piping of all these systems were developed based on the experimental results obtained, which can be used for simulations and validations of potential codes developed to design and/or evaluate performance of cooling systems. An overall energy balance analysis for each system using the correlations developed showed that 99.17% of the experimental data were bounded within ± 10%.

EPFL2012

Polymer spiral film gas-liquid heat exchanger for waste heat recovery in exhaust gases

Antoine Breton

In this master thesis report the development of an innovative spiral heat exchanger based on polymer materials is described. Building prototypes, erection of a test bench and firsts tests of the heat exchanger are presented. The heat exchanger prototype survived all tests especially several days in contact with aggressive gases. A facility integrating a Diesel exhaust gases production has been developed to test this heat exchanger design. Performance results obtained during the tests are analysed. Measurement acquisition software developed with Labview was also used. Challenges have been overcome to run the facility in stable conditions in order to obtain reliable measurement. Heat load recovery achieved with the presented heat exchanger is in the range of 1.5 kW thermic but potential heat recovery about 3.5kW might be achievable. Overall heat transfer coefficient is improved compared to other polymer based heat exchanger design. Pressure drop on gas channel is in the range of several mbar and must be further improved and fouling must be minimized. Such a design based on polymer film technology provides better corrosion and chemical resistance compared to conventional metal heat exchangers. Due to the smooth surface of polymer film fouling is reduced. Series production and usage of such heat exchangers would allow operating low temperature waste heat recovery in gases at affordable costs. One promising application is heat recovery in soiled gases in combination with ORC power generation.

2012

Physico-chemical properties prediction of hydrochar in macroalgae Sargassum horneri hydrothermal carbonisation

Farzaneh Talebkeikhah, Mohsen Talebkeikhah

This study evaluates and compares several machine learning methods on the effects of different parameters in the hydrothermal carbonisation (HTC) process of macroalgae Sargassum horneri. Reaction temperature, residence time, biomass particle size, the amount of catalyst and loaded biomass were considered as inputs and three variables of BET, higher heating value (HHV) and energy recovery were regarded as outputs. For analysing the input parameters, the Taguchi method was used for experimental designs and the obtained results were utilised here as training sets. Various data mining approaches like support vector machine (SVM), group method of data handling, decision tree, random forest, radial basis function, adaptive neuro-fuzzy inference system (ANFIS) and multilayer perceptron (MLP) neural network were implemented to model the problem and two different optimisation techniques named BAT and Grasshopper Optimisation Algorithm (GOA) were employed with MLP and ANFIS model for optimising. By comparing different statistical parameters such as Average Absolute Relative Deviation (AARD), coefficient of determination (R-2), Root Mean Square Error (RMSE) and Standard Deviation (SD), It is found out that SVM method has a considerably better performance relative to other methods for estimating both the BET, HHV and energy recovery parameters. Furthermore, coupling of MLP and ANFIS with GOA increases the accuracy of these models for BET, HHV and energy recovery estimations.

TAYLOR & FRANCIS LTD2019

Experimental Evaluation and Control of Two-Phase Multi-Microchannel Evaporator Cooling Systems for High Efficiency Data Center

Duan Wu

EPFL2012