Thermal comfort analysis in a passenger compartment considering the solar radiation effect

Moon, Joo Hyun,Lee, Jin Woon,Jeong, Chan Ho,Lee, Seong Hyuk Elsevier 2016 INTERNATIONAL JOURNAL OF THERMAL SCIENCES Vol.107 No.-

<P><B>Abstract</B></P> <P>The present study numerically investigated thermal comfort in a passenger compartment by considering the spectral solar radiation. With the use of commercial software (ANSYS Fluent V. 13.0) in which the solar load model is embedded, a three-dimensional computational fluid dynamics simulation was conducted to accurately predict thermal and flow fields under the operating conditions of a heating, ventilation, and air conditioning system. This study compared the Fanger model and the equivalent temperature model for thermal comfort analysis, together with the numerical predictions which could be used for estimation of the predicted percentage of dissatisfied, the predicted mean vote, and the equivalent temperature as the important indices in evaluating thermal comfort. From the results, the estimated temperature near the driver and passengers increased by approximately 1–2 °C when considering the spectral solar radiation. This small difference in air temperature caused a substantial variation in thermal comfort level inside the compartment. In addition, it was found that when the spectral solar radiation effect was involved, the predicted mean vote was higher than that of the case without considering the spectral radiation. Through comparison between two thermal comfort models, it was noted that the spectral solar radiation must be considered in evaluating thermal comfort levels, and unlike the Fanger model, the equivalent temperature model could predict the local variations of thermal comfort levels in the compartment.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Thermal comfort is numerically studied in a passenger compartment. </LI> <LI> The spectral solar radiation is considered in this study for HVAC system. </LI> <LI> The Fanger model and the equivalent temperature model are compared. </LI> <LI> With solar radiation model, the maximum temperature difference of 2 °C is observed. </LI> <LI> The spectral solar radiation should be considered for thermal comfort analysis. </LI> </UL> </P>

미세물분무에 의한 열복사 감쇠 효과에 대한 수치해석 연구

고권현 한국화재소방학회 2020 한국화재소방학회논문지 Vol.34 No.4

A numerical study was conducted to investigate the effects of the spray characteristics of water mist on the attenuationof thermal radiation. The attenuation process of the thermal radiation, generated from a hot surface panel, passing throughthe water mist was calculated via Fire Dynamics Simulator (FDS), and the effects of the flow rate, droplet mean diameter,and spray injecting angle of the water mist were analyzed. The results indicated that the increase in flowrate and decreasein droplet size led to an increase in the attenuation of thermal radiation. As the thermal radiation passed through the spraydroplets, the effect of the spatial distribution of spray droplets was verified by calculating the thermal radiation attenuationat different spray injecting angles. The results indicated that the radiation attenuation increases as the spray angle increases. This implies that a wider distribution of spray droplets, irrespective of the droplet size and flowrate, increases theattenuation effect on thermal radiation. 본 연구에서는 미세물분무의 특성이 열복사 감쇠에 미치는 영향을 살펴보기 위한 수치해석 연구를 수행하였다. 고온의 복사 패널로부터 전파되는 열복사가 미세물분무를 통과하여 약화되는 과정을 FDS를 이용하여 해석하였고,미세물분무의 분사유량, 액적평균입경과 분무각에 따른 영향을 분석하였다. 해석 결과로부터 분사유량의 증가와 액적크기의 감소가 열복사 감쇠 효과를 증가시키는 것을 알 수 있었다. 복사열이 통과하는 분무 공간 분포의 영향을살펴보기 위해 분사각을 변화시켜 열복사 특성을 분석하였으며 분사각이 클수록 복사 감쇠 효과가 커지는 것을 확인하였다. 이것은 유사한 액적크기분포와 유량조건에서도 액적들이 공간적으로 더 넓게 퍼져 있는 경우 복사의 감쇠효과가 더 커질 수 있음을 보여준다.

Radiation Effects in Heat Transfer Mechanisms by Dispersive Materials: Numerical Analysis in Diffusive Enclosure Model of Thermal Insulation

Muhd Azi Bin Che Seliman,Yoshio Hirasawa 대한설비공학회 2018 International Journal Of Air-Conditioning and Refr Vol.26 No.4

The current development of global warming and CO2 emission problems cannot be overlooked. Thus, global scale measures of efforts are becoming crucial. Thermal properties of insulation materials need to be considered as high performance thermal insulation systems are crucial for efficient energy saving. The most important parameter as indicator of a thermal insulation material is the effective thermal conductivity, but elements that affect the thermal insulation performance are rather complicated. Generally, conduction and radiation heat transfer are needed to be separately considered in precisely evaluating the thermal insulation performance as they coexist in the heat transfer process inside a multilayer insulation system. In this paper, numerical analysis of a complete diffusive enclosure model as a thermal insulation is observed to investigate the radiation effects by its dispersive heat transfer mechanisms. View factor of each relatively large dispersed material is derived in the enclosure model, where it is applicable to various shapes and any particular arrangements of dispersed materials. As this paper is the first part of a three-part working research paper, numerical analysis in this paper is carried out by assuming that the medium within the space inside the insulation system is taken to be nonparticipating, therefore conduction and convection effects during the heat exchange are negligible. This paper will be continued with application of the numerical analysis in observing radiation heating effects by wall-ceiling integration towards indoor environment and radiation–conduction heat transfer mechanisms in one-dimensional multilayer insulation system.

지구 저궤도에서 운용되는 영상센서를 위한 열설계 및 열해석

신소민(Somin Shin),오현웅(Hyun-Ung Oh) 한국항공우주학회 2011 韓國航空宇宙學會誌 Vol.39 No.5

지구의 저궤도에서 운용되는 영상센서는 극저온 환경에서 태양 복사 뿐 아니라 지구의 적외선 및 알베도(Albedo)의 영향을 받는다. 극한 환경에 노출되는 영상센서는 작동/비작동시 허용 온도를 벗어나지 않도록 열설계가 필요하며, 정상상태 에너지 평형식을 통해 필요한 방열판 면적 및 히터 예비 설계 값을 설정한다. 일반적으로 위성체 패널에 주기를 갖는 발열장비가 장착되어, 패널의 일부를 방열판 면적으로 설계한다. 본 논문에서는 위성체와 분리하여 설계하는 영상센서의 열제어를 위하여, 내부에서 항상 발열하는 장비의 열을 히트파이프를 이용하여 패널에 장착된 방열판으로 효과적으로 전달하도록 설계하였다. 예비 설계값을 기준으로 수치해석에 기반을 두는 SINDA를 이용하여 궤도 열해석을 실시하여, 방열 면적 및 히터 설계는 쉽고 빠르게 계산되어졌다. 또한, 방열 성능을 유지하면서 질량을 줄이도록 방열판을 립형상(Rib-type)으로 설계하였으며, 궤도 열해석 결과, 영상센서의 열적 요구사항을 만족함을 검증하였다. Space Imaging Sensor operated on LEO is affected from the Earth IR and Albedo as well as the Sun Radiation. The Imaging Sensor exposed to extreme environment needs thermal control subsystem to be maintained in operating/non-operating allowable temperature. Generally, units are periodically dissipated on spacecraft panel, which is designed as radiator. Because thermal design of the imaging sensor inside a spacecraft is isolated, heat pipes connected to radiators on the panel efficiently transfer dissipation of the units. First of all, preliminary thermal design of radiating area and heater power is performed through steady energy balance equation. Based on preliminary thermal design, on-orbit thermal analysis is calculated by SINDA, so calculation for thermal design could be easy and rapid. Radiators are designed to rib-type in order to maintain radiating performance and reduce mass. After on-orbit thermal analysis, thermal requirements for Space Imaging Sensor are verified.

Effect of thermal radiation on convection heat transfer in cooling channel of photovoltaic thermal system

Shuang-Ying Wu,Ying-Ying Wu,Lan Xiao 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.8

The effect of thermal radiation on convection heat transfer in flat-box type cooling channel of photovoltaic thermal system with tilt angleof 30 degree was studied by 3D numerical simulation under constant heat flux boundary condition. The temperature contours andvelocity fields of fluid near the outlet were obtained. The variations of wall temperature and convection Nusselt number along flow directionfor all the separate walls composing the cooling channel were compared and analyzed. The results show that due to thermal radiation,the deflection of the maximum velocity region to heated top wall, together with the asymmetry of temperature field is weakened. Fornatural convection, radiation promotes the formation of multi-vortices. For mixed convection, heat transfer on all the cooling channelwalls is enhanced under the condition of lower heat flux while heat transfer on heated top wall is deteriorated when the heat flux is relativehigh. Also, pressure re-rising is promoted by thermal radiation.

Finite Size Effect of One-dimensional Thermal Radiation

김희태,윤석주,유순재 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.2

The size effect of one-dimensional thermal radiation is investigated as a function of length and temperature. When the length of the body becomes small, the maximum wavelength of the thermal radiation is on the order of the size, so the spectrum of the thermal radiation becomes different from that of one-dimensional blackbody radiation. We calculate the energy density by considering the dimension of the length. The thermal radiation can be approximated by Wien’s law in highfrequency range when the size becomes small. The energy density is shown to be a function of length at constant temperature. The energy density is also shown to be a function of temperature at constant length.

Optical Tunneling Mediated Sub-Skin-Depth High Emissivity Tungsten Radiators

Cho, Jin-Woo,Lee, Kyung-Jun,Lee, Tae-Il,Kim, Young-Bin,Choi, Dae-Geun,Nam, Youngsuk,Kim, Sun-Kyung American Chemical Society 2019 NANO LETTERS Vol.19 No.10

<P>Tailoring the spectrum of thermal radiation at high temperatures is a central issue in the study of thermal radiation harnessed energy resources. Although bulk metals with periodic cavities incorporated into their surfaces provide high emissivity, they require a complicated micron metal etch, thereby precluding reliable, continuous operation. Here, we report thermally stable, highly emissive, ultrathin (<20 nm) tungsten (W) radiators that were prepared in a scalable and cost-effective route. Alumina/W/alumina multiwalled, submicron cavity arrays were fabricated sequentially using nanoimprinting lithography, thin film deposition, and calcination processes. To highlight the practical importance of high-temperature radiators, we developed a thermophotovoltaic (TPV) system equipped with fabricated W radiators and low-bandgap GaSb photovoltaic cells. The TPV system produced electric power reliably during repeated temperature cycling between 500 and 1200 K; the power density at 1200 K was fixed to be approximately 1.0 W/cm<SUP>2</SUP>. The temperature-dependent electric power was quantitatively reproduced using a one-dimensional energy conversion model. The symmetric configuration of alumina/W/alumina multiwall together with the presence of a void inside each cavity alleviated thermal stress, which was responsible for the stable TPV performance. The short-current-density (<I>J</I><SUB>SC</SUB>) of developed TPV system was augmented significantly by decreasing the W thickness below its skin depth. A 17 nm thick W radiator yielded a 32% enhancement in <I>J</I><SUB>SC</SUB> compared to a 123 nm thick W radiator. Electromagnetic analysis indicated that subskin-depth W cavity arrays led to suppressed surface reflection due to the mitigated screening effect of free electrons, thereby enhancing the absorption of light within each W wall. Such optical tunneling-mediated absorption or radiation was valid for any metal material and morphology (e.g., planar or patterned).</P> [FIG OMISSION]</BR>

Development and testing of a simple heat gauge for the measurement of high-intensity thermal radiation

Chen, K.,Parker, N.,Chun, W.,Oh, S.J.,Lim, S.H. Pergamon Press ; Elsevier Science Ltd 2013 International Communications in Heat and Mass Tran Vol.46 No.-

A simple and inexpensive radiation heat gauge was developed and tested for high-intensity thermal radiation measurements. The gauge used a thermal image camera to record the temperature variation of a metallic bar painted in black and heated at one end by thermal radiation. The average flux of the irradiation was determined from the rate of temperature change at a selected point on the bar. The aperture of the gauge can be easily varied by changing the diameter of the washer in front of the metallic bar. Numerical solutions were obtained for the transient heat conduction process in the metallic bar, and casted into dimensionless forms which can be conveniently used for bars of different sizes and materials, and/or subjected to different radiation fluxes. The gauge was employed to measure the radiation beams produced by a commercial IR (Infrared) heater and the results were in good agreement with the heater manufacturer's data.

Effect of variable viscosity on thermal boundary layer over a permeable flat plate with radiation and a convective surface boundary condition

Oluwole Daniel Makinde 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.5

"In this paper, the combined effects of radiation, temperature dependent viscosity, suction and injection on thermal boundary layer over a permeable flat plate with a convective heat exchange at the surface are investigated. By taking suitable similarity variables, the governing boundary layer equations are transformed into a boundary value problem of coupled nonlinear ordinary differential equations and solved numerically using the shooting technique with sixth-order Runge-Kutta integration scheme. The solutions for the velocity and temperature distributions together with the skin friction coefficient and Nusselt number depend on six parameters; Prandtl number Pr,Brinkmann number Br, the radiation parameter Ra, the viscosity variation parameter a, suction/injection parameter fw and convection Biot number Bi. Numerical results are presented both in tabular and graphical forms illustrating the effects of these parameters on thermal boundary layer. The thermal boundary layer thickens with a rise in the local temperature as the viscous dissipation, wall injection, and convective heating each intensifies, but decreases with increasing suction and thermal radiation. For fixed Pr, Ra, Br and Bi, both the skin friction coefficient and the Nusselt number increase with a decrease in fluid viscosity and an increase in suction. A comparison with previously published results on special case of the problem shows excellent agreement."

사각튜브부착형 흡열판을 적용한 Unglazed PVT 복합모듈의 열적 전기적 성능분석

정선옥(Jeong, Seon-Ok),천진아(Chun, Jin-Aha),김진희(Kim, Jin-Hee),김준태(Kim, Jun-Tae),조인수(Cho, In-Soo),남승백(Nam, Seung-Baeg) 한국태양에너지학회 2011 한국태양에너지학회 학술대회논문집 Vol.2011 No.11

The heat from PV modules should be removed for better electrical performance, and can be converted into useful thermal energy. A photovoltaic-thermal(PVT)module is a combination of PV module with a solar thermal collector which forms one device that converts solar radiation into electricity and heat simultaneously. The performance of the PV/Thermal combined collector module is directly influenced by solar radiation that also has an effect on PV module temperature. It is also has believe that the energy performance of PV/T collector is related to absorber design as well as PV module temperature. The existing study has been paid to the PV/Thermal combined collector module with circle tube absorbers. The aim ofthis study is to analyze the experimentalperformance ofthe PV/Thermalcombined collector rectangular tube absorbers according to solar radiation. The experimental result show that the average thermal and electrical efficiencies o fthePVT collector were 43% and14.81% respectively. Solar radiation is one of the most influential factors to determine the energy performance of PVT collector, but from a certain level of solar radiation the PVT collector receives on, its efficiencies began to decrease.