查看更多>>摘要：Measurement uncertainty has significant negative impacts on the operation and control of heating， ventilation and air conditioning systems。 It is a big challenge and should be solved urgently。 Existing studies focus on reducing the impacts of measurement uncertainty by developing uncertainty tolerant methods without quantifying the measurement uncertainties themselves。 They therefore fail to fundamentally solve them。 This study aims to directly quantify the measurement uncertainties of water flow meters in multiple water-cooled chiller systems using a Bayesian approach。 A measurement uncertainty quantification strategy is proposed based on Bayesian inference and energy balance models， and the Markov chain Monto Carlo method is used to achieve the strategy。 The site data collected from a chiller system are used to test the strategy。 Four simulation tests with different levels of measurement uncertainty are conducted to further test and systematically validate the strategy。 Test results show that the measurement uncertainties (both systematic and random uncertainties) of the water flow meters in the chiller systems can be quantified effectively and with acceptable accuracy。 The strategy performs very well in quantifying random uncertainties of flow meters， and the relative errors range from 0% to 12。8%。 The performance of the strategy in quantifying systematic uncertainties is also satisfactory， and the relative errors range from 0。1% to 36。57%。 The proposed strategy is able to quantify measurement uncertainties and can be used to optimize the control of chiller systems and improve the reliability of chiller systems。
查看更多>>摘要：Heat transfer deterioration (HTD) of supercritical CO2 heated in a tube influences the efficiency and safe operation of the system due to the occurrence of local high temperature。 To suppress and delay the HTD， the characteristics and mechanisms of self-excited oscillation pulsating flow on HTD of supercritical CO2 are studied by experiment and simulation at pressure 8 MPa， mass fluxes from 350 to 800 kg/m2。s， heat fluxes from 30 to 200 kW/m2。 The Helmholtz oscillator is introduced into the inlet of the vertical tube for generating a pulsating flow of supercritical CO2。 The heat transfer performance is compared with that of without Helmholtz oscillator at the inlet of the tube。 The results show that the self-excited oscillation pulsating flow improve the heat transfer performance significantly。 The heat transfer parameters present oscillations with small amplitude along flow direction before pseudo-critical point (Tpc)。 The average heat transfer coefficient can be up to 3。4 times and the enhancement takes place mainly at the HTD region which is located at the entrance section of the heated tube。 The effect of suppressing HTD is more significant at higher heat flux， and the peak of wall temperature can be reduced by 100 K at a heat flux of 200 kW/m2。 Compared to the steady flow， the mechanism analysis of the selfexcited oscillation pulsating flow based on radial distributions of velocity， turbulent kinetic energy (TKE)， and density reveals that the velocity distribution of "M- shape" appears later and gentler。 The production and diffusion of TKE are improved at log layer (30 < y+ < 0。2r)。 In addition， the period and the amplitude do not show monotonous trends on heat transfer performance。 The effects of pulsating parameters on HTD are optimized that the heat transfer performance with the period of 0。016 s and the amplitude of 100 kg/m2。s is the best in calculated cases。
查看更多>>摘要：Falling film evaporation is a promising technology widely applied in refrigeration， desalination and beyond applications owing to the great advantages。 However， the liquid film hydrodynamics and heat transfer performance are studied insufficiently。 Compered with experiments， numerical simulations are economical and efficient especially in the study of liquid film， through which some microscopic understandings are expected to be extracted。 In this paper， a comprehensive review for a large pool of computational studies about falling liquid film flow and heat transfer on the horizontal tube and tube bundle is presented。 Computational methods of liquid-gas two-phase flow and mass transfer model， as well as relevant researches were first introduced。 Then， the studies on the falling film hydrodynamics， film thickness， sensible heat transfer， flow pattern， evaporation and boiling outside the single tube， tube bundle， special-shaped tube and entire evaporator studied with 2D and 3D models are respectively reviewed in order。 Then， the investigations on the falling film breakout and dryout are reviewed。 And then， the numerical predictions of falling film thickness and heat transfer coefficient are involved。 Afterthat， the benchmark data for falling film numerical simulation are summarized。 Finally， some future needs and recommendation relating to crucial technologies that must be solved are proposed。
查看更多>>摘要：COVID-19 (Coronavirus Disease 2019) pandemic highlighted the importance of air biosecurity because SARS-CoV-2 is mainly transmitted from person to person via airborne droplets。 Preventing infectious droplets from entering the body is one of the best ways to protect against infection。 This paper reviews the transmission patterns of airborne pathogens and air disinfection methods。 A particular emphasis is put on studies devoted to the thermal inactivation of viruses。 These reviews reveal that air heat treatment has not been seriously considered as a possible air disinfection approach。 Simple calculations show that the energy input required for thermal disinfection of human's air daily consumption is almost the same as for daily water consumption (by heat treatment from room temperature to 100 degrees C)。 Moreover， it is possible to organize a continuous heat recovery from the air already heated during disinfection to the inlet air， thus significantly increasing the energy efficiency。 Therefore， I propose a solution for the thermal inactivation of airborne pathogens based on air heating and its subsequent cooling in a heat exchanger with heat recovery。 Such a solution could be used to create mobile personal and stationary indoor air disinfectors， as well as heating， ventilation， and air conditioning systems。 Thermal disinfection of air to breathe might one day be part of people's daily life like thermal disinfection of drinking water。 Aside from limiting infectious disease transmission， thermal inactivation might be the basis for developing inhaled vaccines using thermally inactivated whole pathogens。
查看更多>>摘要：Adsorption cooling is a sustainable technology， since it can utilize solar energy or waste heat， while employing substances without ozone depletion and global warming potential。 The adsorption reactor design is determinant for the system performance。 An underexplored geometry hitherto - the hexagonal honeycomb adsorption reactor - was numerically investigated。 An in-house， validated， three-dimensional computational model based on unstructured meshes was employed。 The Specific Cooling Power (SCP) and Coefficient of Performance (COP) were quantified for several geometrical and operational parameters。 The cell inradius creates a dichotomy between SCP and COP， being 218。9 W/kg(s) and 0。356 for 1 mm， while being 80。4 W/kg(s) and 0。606 for 6 mm。 The cell height influences prominently the SCP， being 159。5 W/kg(s) and 86。1 W/kg(s) for 5 mm and 30mm， respectively。 The fin thickness impacts mostly the COP， being 0。599 and 0。364 for 0。5 mm and 3 mm， respectively。 Higher COP is achieved for higher evaporator， lower adsorption and lower condenser temperatures。 Higher SCP is achieved for lower adsorption and condenser， and higher evaporator and desorption temperatures。 Shorter cycles result in high SCP and low COP， whereas the inverse occurs for longer cycles。 Aluminum heat exchanger yields 7。7% higher COP than copper。 The results are discussed from a physical， as well as， an engineering perspective。
查看更多>>摘要：Based on the electro-osmotic regeneration of solid desiccants， this paper proposes an improved dehumidification fin with a silica gel-based composite and internal cooling fins to investigate the potential for the application of air dehumidification。 In order to solve the problems existed in the current literature， such as the poor structural stability of the hygroscopic sheet， the effect of Joule heat and the operation modes， series tests were present in this study to provide foundation for the reasonable design of the dehumidifying fins and the determination of the suitable working conditions。 This paper first introduced the fabrication method and basic performance tests， including adsorption and stability tests。 Based on the behavior of adsorption and the stability of the structure， the types of composites and relevant contents were optimally selected to fabricate a hygroscopic sheet and dehumidification fin。 Subsequently， electro-osmotic tests were applied to the hygroscopic sheet to investigate the main factors that affect the electro-osmotic procedures in the sample sheet。 The results indicated the hygroscopic sheet with particle sizes of 0。1-0。2 mm and a voidage of 60。75% exhibited the best performance when an electric field with an intensity of 3。92 V/mm。 Dehumidification tests were further applied to the optimal selected sample fin installed in the air duct for the effects of dehumidification rate， Joule heat effect， operation modes， and energy consumption。 Results show that under the two different conditions set， the dehumidification rate of the dehumidification fin with the above structure can reach 974。19 and 950。24 g/m(2)。h， respectively， and the corresponding energy consumption is 770。35 and 726。93 kg/m(2)。kWh， respectively。 The theoretical specific moisture extraction rate (SMER) of the proposed fin could be more than twice that of other dehumidification methods。
查看更多>>摘要：Phase change material (PCM) has great potential in thermal control of aircraft electronic components because of their excellent latent heat capacity。 In the current work， a finned copper foam phase change energy storage unit (PCESU) was fabricated using n-eicosane， 97。2% porosity copper foam and 0。8 mm fins。 The effects of four different heating power i。e。 40 W， 45 W， 50 W， 55 W corresponding to heat flux of 0。4 W/cm(2 ) 0。45 W/cm(2 ) 0。5 W/cm(2)， 0。55 W/cm(2) at four different centrifugal acceleration magnitudes， i。e。 0 g， 5 g， 9 g， 13 g with three different acceleration directions on the thermal performance of PCESU were experimentally studied in a systematic manner。 Experimental results indicated that: (1) the acceleration direction has a significant effect on the thermal performance of PCESU which can be improved for the cases of vertical and opposite directions， whereas restrained for the case of same direction。 Under acceleration condition， the average melting time for the cases of opposite and same direction are 15。19% and 37。10% longer than that for the case of vertical direction， respectively。 The temperature difference of PCESU while the melting is completed is 95。12% higher than that for the case of vertical direction on average。 (2) the effect of acceleration magnitude on the heat transfer performance can be determined significantly when the acceleration direction is applied。 The melting time decreases with the increase of the acceleration magnitude along vertical direction and increases along same direction。 The temperature difference decreases with the increase of the acceleration magnitude along vertical direction， whereas increases along opposite or same direction。 Moreover， the melting time and temperature difference for acceleration magnitude changing from 0 g to 5 g have an obvious larger change rate than that from 5 g to 9 g and 9 g to13 g。 (3) the melting time is negatively correlated to the heating power， whereas the temperature difference is positively correlated to the heating power。 The proposed two-dimensional (2D) simplified model can be helpful to reveal the physical mechanism of the thermal performance of PCESU。
查看更多>>摘要：In this study， state-of-the art deep neural networks to train and predict the heat transfer in building structures were proposed。 Today， many of studies analyze thermal energy performance of buildings by analytical or numerical methods。 Although building energy performance can be predicted effectively by finite element method， it is still time-consuming to calculate and solve the heat transfer problem。 Moreover， expert engineer is required and complicate process to set simulation model is essential。 In this work， a novel deep-learning method， which was pre-trained by the thermal simulation data， was developed to predict the thermal behavior of building structures in a fast time without complicated process。 Heat transfer simulations of the slab wall building structure depending on its thermal properties and geometries were carried out to get training datasets for deep learning。 The database of thermal simulation results was used for deep learning training。 The image of temperature and heat flow distribution was trained by convolutional encoding-decoding network and the value of total heat loss through building and thermal bridge coefficient was trained by multi-layer perceptron。 After train completed， the thermal behavior could be predicted in a second by just feeding information such as blueprint image and thermal properties of constructions into deep-learning architecture。 There was no need to set a new simulation model at each time which consumes time and effort for modeling， meshing and calculating。 With the developed network， the prediction of thermal behavior with high accuracy was possible in a super-fast time。
Elawady, NahedBekheit, MaherSultan, Ahmed A.Radwan, Ali...
19页
查看更多>>摘要：Achieving the concept of energy efficient building (EEB) is a promising direction for global energy saving。 The incorporation of phase change materials (PCM) in the building structure is one of the new techniques recently applied in EEB。 However， many recent investigations used short-term analysis of roof integrated PCM。 Therefore， long-term thermal behavior of building roof containing PCM layer is investigated in this study。 The roof with and without PCM layer are compared at variable outside weather conditions。 Enthalpy-porosity model along with a simplified thermal model are developed and simulated using ANSYS-Fluent。 The enthalpy-porosity model is essential to capture the melting behavior inside the PCM layer， while the simplified model is the appropriate model for long-term simulation。 The two models are compared and validated with the experiments conducted in this study and with data in the literature。 Roof with three different PCMs and three thicknesses are evaluated。 Long term simulation is conducted for both roof with and without PCM in hot summer season of Aswan city， Egypt。 The results showed that using PCM in the roof structure decreases the indoor heat flux and attains an indoor wall temperature closer to the indoor air temperature requirements。 Further， the larger thickness of the PCM， the better performance。 Based on four months' simulation， the average predicted indoor wall temperature reached 32。5 C and 29。4 C for the roof without and with PCM respectively。 Furthermore， around 40% decrease in the total energy gain in four summer months is attained due to the use of 40 mm of RT31-PCM in the roof structure。
查看更多>>摘要：Free piston engine generator (FPEG) is a new energy conversion plant to substitute for conventional combustion engine。 However， the fluctuation of gas exchange is a key problem to induce the FPEG to run unsteadily and restrict its engineering application。 This paper presents a study to explore the multi-field coupling effect of fuel injection duration on the gas exchange stability of a diesel compression-ignition， direct-injection， looped scavenging FPEG。 A full-cycle gas exchange model of the FPEG is carried out by coupling the zero-dimensional dynamics， multi-dimensional combustion model and scavenging model， and an iterative calculation method is proposed for numerical simulation of the model。 Meanwhile， the effect of injection duration schedule lasting from 0。50 ms to 0。80 ms on the scavenging and gas exchange is analyzed。 The results show that the shorter injection duration brings about higher fresh trapping efficiency due to its faster reciprocating frequency which reduces the available time for fresh gas to flow out of the cylinder during gas exchange process， and the trapping efficiency is 41。3 % and the operating frequency achieves 36。6 Hz in the injection duration of 0。5 ms condition。 However， the influence of injection duration on exhaust gas cleaning is opposite， and the scavenging efficiency varies in positive correlation with the injection duration， because the long injection leads to low motion velocity and causes the exhaust port to be opened and closed slowly， which provides long exhaust time of the residual burned gas in the cylinder。 The maximum scavenging efficiency occurs in the injection duration of 0。8 ms condition and features with 97。9%。 Suggesting， relatively high scavenging efficiency and trapping efficiency can be obtained at the same time under appropriate injection duration condition。
NSTL
Elsevier