Effects of personal heating on thermal comfort:A review

Personal conditioning system(PCS)is receiving considerable attention due to its energy-saving potential and the ability to satisfy individual comfort requirements.As a part of PCS,personal heating systems can maintain human thermal comfort in cold environments,which leads to their potential role of important heating mode in cold winter,especially in the Hot Summer and Cold Winter regions of China.In order to better promote the development and application of personal heating systems,this paper reviews the published studies.Personal heating systems can be divided into four types based on the mode of heat transfer:conductive,convective,radiative and combinative type.Characteristics of each category and respective devices are introduced.Furthermore,identifying the effects of personal heating on thermal comfort and the models for predicting or evaluating thermal comfort during local heating.This paper would provide users with a guideline for choosing suitable heating equipment during winter.

Active Control of Sound Transmission in Ship Cabins Through Multiple Independently Supported Flexible Subplates

The vibration and noise produced by the powertrain and waves inside ship cabins limit working efficiency and crew and passengers’accommodation quality.This paper simplifies ship cabins as cavities and explores active control techniques to attenuate sound transmission via multiple parallel-supported flexible subplates.The theoretical formulations of the interaction between multiple subplates and cavities were performed and the coupling relationships between them were analyzed.Based on the multiple subplates and the cavity coupling models,numerical simulations were performed using the derived optimal controller to minimize the transmission of sound into the cavities through two and nine parallel-supported subplates.The various control strategies were explored to minimize the coupling system’s acoustic potential energy,and the control performances were compared and discussed.The mechanism of reducing sound transmission through multiple supported subplates into a cavity is revealed.The simulation results showed that the vibration pattern of the controlled subplate is changed after it is regulated,which increases its radiation to subdue the other subplates’radiation,while increasing vibration of the controlled subplate.The more subplates a cavity has,the more kinetic energy the controlled subplate possess.Furthermore,the noise reduction performance of a cavity with fewer subplates is better than that with more subplates.

Finite Element Modeling and Vibration Analysis of Sprag Clutch⁃Flexible Rotor System

To study the overall vibration characteristics of the sprag clutch⁃flexible rotor system(SC⁃FRS)under high⁃speed operating conditions,a finite element model of SC⁃FRS considering rotor flexibility and bearing support stiffness was established based on the proposed calculation method of the stiffness matrix.According to this model,the natural frequency and mode shape of the system are calculated,and the correctness of the model was verified by comparing it with the calculation results of ANSYS software.Under the action of unbalance,the bending⁃torsion coupled vibration and the dynamic load of the inter⁃shaft bearings were analyzed,and it is found that the resonant peak in the torsional direction has the same resonance frequency as that in the bending direction.A test rig for the sprag clutch⁃rotor system was built,and the axis trajectory and critical speed were tested.The test results show that the finite element model of SC⁃FRS can accurately describe the vibration characteristics of the system.The coupling vibration characteristics analysis of the sprag clutch⁃flexible rotor system can provide theoretical guidance for the dynamic design of the sprag clutch components.

Studies on Performance of Distributed Vertical Axis Wind Turbine under Building Turbulence

As a part of the new energy development trend,distributed power generation may fully utilize a variety of decentralized energy sources.Buildings close to the installation location,besides,may have a considerable impact on the wind turbines’operation.Using a combined vertical axis wind turbine with an S-shaped lift outer blade and-shaped drag inner blade,this paper investigates how a novel type of upstream wall interacts with the incident wind at various speeds,the influence region of the turbulent vortex,and performance variation.The results demonstrate that the building’s turbulence affects the wind’s horizontal and vertical direction,as well as its speed,in downstreamplaces.The wall’s effect on wind speed changing in the downstreamarea is thoroughly investigated.It turns out that while choosing an installation location,disturbing flow areas or low disturbing flow zones should be avoided to have the least impact on wind turbine performance.

Model-Free Sliding Mode Control for PMSM Drive System Based on Ultra-Local Model

This paper presents a novel model-free sliding mode control(MFSMC)method to improve the speed response of permanent magnet synchronous machine(PMSM)drive system.The ultra-local model(ULM)is first derived based on the input and the output of the PMSM.Then,the novel MFSMC method is presented,and the controller is designed based on ULM and MFSMC.A sliding mode observer(SMO)is constructed to estimate the unknown part of the ULM.The estimated unknown part is feedbacked to MFSMC controller to performcompensation for parameter perturbations and external disturbances.Compared with the sliding mode control(SMC)method,the results of simulation and experiment demonstrate that the presented MFSMC method improves the dynamic response and robustness of the PMSM drive system.

Energy modeling and optimization of building condenser water systems with all-variable speed pumps and tower fans:A case study

The emergence of building condenser water systems with all-variable speed pumps and tower fans allows for increased efficiency and flexibility of chiller plants in partial load operation but also increases the control complexity of condenser water systems.This study aims to develop an integrated modeling technique for evaluating and optimizing the energy performance of such a condenser water system.The proposed system model is based on the semi-physical semi-empirical chiller,pump,and cooling tower models,with capabilities of fully considering the hydraulic and thermal interactions in the condenser water loop,being solved analytically and much faster than iterative solvers and supporting the explicit optimization of the pump and tower fan frequency.A mathematical approach,based on the system model and constrained optimization technique,is subsequently established to evaluate the energy performance of a typical dual setpoint-based variable speed strategy and find its energy-saving potential and most efficient operation by jointly optimizing pumps and tower fans.An all-variable speed chiller plant from Wuhan,China,is used for a case study to validate the system model’s accuracy and explore its applicability.The results showed that the system model can accurately simulate the condenser water system’s performance under various operating conditions.By optimizing the frequencies of pumps and tower fans,the total system energy consumption can be reduced by 12%–13%compared to the fixed dual setpoint-based strategy with range and approach setpoints of 4℃and 2℃.In contrast,the energy-saving potential of optimizing the cooling tower sequencing is insignificant.A simple joint speed control method for optimizing the pumps and tower fans emerged,i.e.,the optimal pump and fan frequency are linearly correlated(if both are non-extremes)and depend on the chiller part load ratio only,irrespective of the ambient wet-bulb temperature and chilled water supply temperature.It was also found that the oversizing issue has further limited the energy-saving space of the studied system and results in the range and approach setpoints being inaccessible.The study’s findings can serve as references to the operation optimization of all-variable speed condenser water systems in the future.

Using tandem blades to break loading limit of highly loaded axial compressors

It is confirmed that tandem-blade configurations have potential to enlarge the flow turning in two-dimension(2D) studies. However, the potential of tandem blades to enlarge the design space for highly loaded axial compressors was rarely investigated in open literatures. The present work aims to show the capability of tandem blades to break the loading limit of conventional blades for highly loaded compressors. The 2D models of the maximum static pressure rise derived in previous work were validated by a large amount experimental data, which showed a good agreement. An E parameter was defined to evaluate the stall margin of compressor based on the theoretical models, which indicated that the tandem blade was able to increase the loading limit of axial compressors. A single-blade stage with a loading coefficient of 0.46(based on the blade tip rotating speed) was designed as the baseline case under the guidance of the E parameter. A tandem-blade stage was then designed by ensuring that the velocity triangles were similar to the single-blade stage. The performances of both stages were investigated experimentally. The results showed that the maximum efficiency of the tandem-blade stage was 92.8%, 1% higher than the single;the stall margin increased from 16.9% to 22.3%. Besides, the maximum pressure rise of tandem rotors was beyond the loading limit of 2D single-blade cascades, which confirmed the potential of tandem blades to break the loading limit of axial compressors.

The effects of portable cooling systems on thermal comfort and work performance in a hot environment

There are some special spaces in which there is no air conditioning or the people are in move,thus exposing people to a hot environment.In this study,portable cooling systems were proposed and their effects on thermal comfort and work performance were investigated at an air temperature of 32°C.Four conditions were established:cool air towards breathing zone(A),chest and back cooling(B)#combined cooling(C)and no cooling(D).Twenty-eight subjects were exposed to the four conditions in a counterbalanced order.During each exposure they performed tasks and made subjective assessments,while multiple physiological parameters were measured.Compared with no cooling(D),cool air towards breathing zone(A)and chest and back cooling(B)improved work performance by 17.5%and 19.25%,respectively,while decreased the subjects'thermal sensation,skin temperature,and heart rate.When the two cooling systems were combined(C),larger improvements in thermal comfort and work performance were achieved than no cooling(D);the mean thermal sensation rating decreased from 2.4 to 0.7;work performance increased by up to 33%,and physiological parameters including skin temperature,pulse,heart rate and salivary alpha-amylase significantly decreased.The present results suggest that the proposed portable cooling systems could maintain thermal comfort and work performance in a hot environment,while potentially improve air quality for some special spaces.

Evaporating Temperature Uniformity of the Pulsating Heat Pipe with Surfactant Solutions at Different Concentrations

The evaporating section of the pulsating heat pipe(PHP)is in direct contact with the electronics when it is used for heat dissipation,and thus the evaporating temperature uniformity has an important effect on the safe and reliable operation of electronic equipment.On the basis of these conditions,an experimental study on the evaporating temperature uniformity of the PHP with surfactant solutions at different concentrations was conducted at the heat fluxes of(1911–19427)W/m^(2).Sodium stearate was utilized for the solute;the surfactant solutions were prepared with the concentrations of 0.001 wt%,0.002 wt%,and 0.004 wt%,respectively,and the filling ratios of the PHP were 0.31,0.44 and 0.57,respectively.The experimental results revealed that under all tested working conditions,the highest temperature always appeared in the intermediate zone of the evaporating section.As the heat flux increased,the temperature differences among different zones rose initially and then reduced due to the change of the flow motion and the flow pattern.The evaporating temperature uniformity of the sodium stearate solutions-PHP was better than that of the deionized water-PHP,which suggested that the evaporating temperature uniformity might be improved through decreasing the surface tension.Furthermore,combined with the effect of surface tension and viscosity,for different filling ratios,the required concentration was different when the best evaporating temperature uniformity was achieved.To be specific,when the filling ratio were 0.31 and 0.44,the best evaporating temperature uniformity was achieved at the concentration of 0.004 wt%,while at the filling ratio of 0.57,the best evaporating temperature uniformity was attained at the concentration of 0.002 wt%.

Risk Evaluation of Ammonia Leakage based on Modified Probability Calculation Formulas

Due to its flammable,explosive,and corrosive characteristics,fire,and explosion accidents caused by ammonia leakage occur from time to time.In this work,the concentration distribution of the model was calculated according to the existing formula of probabilistic risk assessment.Using the revised formulas,the leakage of the ammonia room was quantitatively analyzed,and different state parameters were analyzed to find out the dangerous leakage points of the ammonia refrigeration system.The results of the calculation are that the existence of obstacles in the space will increase the probability of leakage risk.And the greater the leakage time to the lower flammability limit accounts for the total leakage time,the greater the risk probability.Dangerous leakage in ammonia systems mainly occurs in storage tanks and condensers.The data show that the dynamic mass flow of ammonia leakage decreases with time,and the leakage diameter increases with the increase of leakage pressure.At the same time,the leakage mass increases gradually with the leakage aperture near circular.

Simulation of thermal and humid environment of rural residence envelope inner surface during the plum rains season in Changsha China

The Plum Rains Season(PRS)has the typical characteristics of outdoor air temperature dramatic changes and high air humidity in the hot summer and cold winter region in China.Even if the indoor heat source and moisture production is constant,when the outdoor air temperature rises rapidly during high air humidity PRS,the build-ing envelope temperature heats up much more slower than the indoor air temperature and therefore the wall surface temperature is lower than the indoor air dewpoint which leads to condensation phenomenon,resulting in deterioration of insulation performance,mouldy walls,deterioration of indoor air quality.At present,there is a lack of research on the factors affecting condensation in rural residence during PRS.This paper evaluates the impact of occupants’habit of window opening modes and building construction parameters on the building envelope surface condensation in Changsha during PRS.Using Designer’Simulation Toolkit(DeST)simulated and analysed the impact of key parameters such as window-to-wall ratio,exterior wall reflectivity,window opening mode(open/close),and external wall insulation on the building indoor thermal and humid environment.The condensation risk X is proposed to evaluate the condensation possibility on the building envelope’s inner sur-face.The results show that from the perspective of anti-condensation:The rural residential building in Changsha should balance the window-wall ratio against better natural lighting;Keeping windows closed during PRS can effectively alleviate the condensation problem while the insulation in the external wall layer could aggravate the condensation.