Performance Study of a Bi-Directional Thermodiode Designed for Energy-Efficient Buildings

2002 ◽  
Vol 124 (3) ◽  
pp. 291-299 ◽  
Author(s):  
Wongee Chun ◽  
Kuan Chen ◽  
Hyung Taek Kim
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Energy Efficient ◽  
Onset Time ◽  
Incident Radiation ◽  
Maximum Temperature ◽  
Performance Study ◽  
Energy Efficient Buildings ◽  
Diode System ◽  
Shading Device

A new, bi-directional thermodiode designed for energy-efficient buildings was constructed and tested. Experimental results are presented and discussed for solar-heating applications. The thermodiode system consisted of a number of rectangular loops filled with water. The tilting angle of the loops can be altered to reverse the direction of natural convection within the loops for bi-directional operations. The horizontal segments of the loops were attached to metallic panels facing indoors or outdoors. The amount of thermal radiation incident on the outdoor-facing surfaces can be adjusted by rotating the panels or by installing a removable shading device in front of the surfaces. Results of the indoor tests for winter use of the diode showed an onset time between 7 to 20 min for natural convection to be induced throughout the loops in the thermodiode. Before the throughflow started, the fluid in the heated copper tubes reached its maximum temperature. A sudden drop and rebound in this temperature was observed immediately after the onset of throughflow. After that, temperatures at different locations on the thermodiode rose at approximately the same rate until a steady state was reached. During the cool-down phase, the temperatures decreased at the same rate without humps, indicating only conduction took place in the rectangular loops when the thermodiode was reverse-biased. A simple analytical model was developed to estimate the temperature variations and heat transfer rates in the diode system. The diode under forward-biased condition increases the heat transfer rate by nearly 100 times for an incident radiation of 600 W/m2.

Effect of Periodic Imposed Heat Flux on Three-Dimensional Natural Convection in a Partially Heated Cubical Enclosure

2016 ◽  
Vol 831 ◽  
pp. 83-91
Author(s):  
Lahoucine Belarche ◽  
Btissam Abourida
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Study ◽  
Control Volume ◽  
Vertical Wall ◽  
Three Dimensional ◽  
Maximum Temperature ◽  
Cubical Enclosure ◽  
Simplec Algorithm ◽  
Volume Method

The three-dimensional numerical study of natural convection in a cubical enclosure, discretely heated, was carried out in this study. Two heating square sections, similar to the integrated electronic components, are placed on the vertical wall of the enclosure. The imposed heating fluxes vary sinusoidally with time, in phase and in opposition of phase. The temperature of the opposite vertical wall is maintained at a cold uniform temperature and the other walls are adiabatic. The governing equations are solved using Control volume method by SIMPLEC algorithm. The sections dimension ε = D / H and the Rayleigh number Ra were fixed respectively at 0,35 and 106. The average heat transfer and the maximum temperature on the active portions will be examined for a given set of the governing parameters, namely the amplitude of the variable temperatures a and their period τp. The obtained results show significant changes in terms of heat transfer, by proper choice of the heating mode and the governing parameters.

Thermal Model of a Solar Thermochemical Reactor for Metal Oxide Reduction

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Bo Wang ◽  
Lifeng Li ◽  
Johannes J. Pottas ◽  
Roman Bader ◽  
Peter B. Kreider ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Metal Oxide ◽  
Reduction Rate ◽  
Incident Radiation ◽  
Maximum Temperature ◽  
Transfer Model ◽  
Oxide Reduction ◽  
Solar Simulator ◽  
Metal Oxide Reduction ◽  
Solar Thermochemical

Abstract A transient heat transfer model is developed to study the thermal performance of a high-temperature solar thermochemical reactor for metal oxide reduction. The solar reactor consists of an indirectly irradiated tubular fluidized bed contained in a solar cavity receiver. Radiative heat transfer in the cavity, modeled with the Monte Carlo ray-tracing method, is coupled to conduction in the tube and cavity walls. Incident radiation distributions from a diffuse radiative source and a high-flux solar simulator are implemented separately in the model to study the influence of incident radiation directionality on the performance of the reactor. Maximum temperature, maximum thermal stress, start-up time, energy balance, and particle reduction rate for the proposed reactor concept are calculated to inform the design and optimization of a prototype reactor.

CFD-Assisted Optimization of Chimneylike Flows to Cool an Electronic Device

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Varghese Panthalookaran
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Energy Efficient ◽  
Electronic Device ◽  
Cooling System ◽  
Electronic Devices ◽  
Cost Effective ◽  
Transfer Rates ◽  
Slot Opening ◽  
Convection Cooling

Natural convection cooling provides a reliable, cost-effective, energy-efficient and noise-free method to cool electronic equipment. However, the heat transfer coefficient associated with natural convection mode is usually insufficient for electronic cooling and it requires enhancement. Chimneylike flows developed within the cabinets of electronic devices can provide better mass flow and heat transfer rates and can lead to greater cooling efficiency. Constraints in the design of natural convection cooling systems include efficiency of packing, aesthetics, and concerns of material reduction. In this paper, methods based on computational fluid dynamics are used to study the effects of parameters such as (1) vertical alignment of the slots, (2) horizontal alignment of slots, (3) area of slots, (4) differential slot opening, and (5) zonal variation in heat generation on natural convection cooling within such design constraints. Insights thus derived are found useful for designing an energy-efficient and ecofriendly cooling system for electronic devices.

scholarly journals Numerical Study of Heat Transfer and Optimum Design for Trench Laying Cables with Ceramic Plates

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Chen-Zhao Fu ◽  
Wen-Rong Si ◽  
Duo Yang ◽  
Jian Yang
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Taguchi Method ◽  
Heat Transfer Performance ◽  
Numerical Study ◽  
Lower Layer ◽  
Maximum Temperature ◽  
Ceramic Plate ◽  
Transfer Performance ◽  
Electromagnetic Loss

Trench laying cables are often used at inlet and outlet regions of a power distribution cabinet. In order to improve the heat transfer performance and extend service life of a trench laying cable, the heat transfer and cable ampacity of the trench laying cable with a ceramic plate were numerically studied in the present paper and the results were compared with those of a traditional trench laying cable. The variations of conductor loss and eddy current loss of different loop cables were discussed in the trench with a ceramic plate, and the effects of ceramic plate parameters on heat transfer performance of the trench laying cable were optimized using the Taguchi method. It is found that for the trench with ceramic plates, although the ceramic plate restrains the natural convection in the trench, the total heat transfer for natural convection and thermal radiation are enhanced for the cables and the cable ampacity can be improved. The difference of electromagnetic loss between the upper- and lower-layer cables in the trench with ceramic plate is quite small. When the cable core current (I) increases from 700 A to 1100 A, the maximum difference of averaged electromagnetic loss between the upper- and lower-layer cables is 1.22%. With the Taguchi method, an optimum parameter combination is obtained. When the length, thickness, and surface emissivity of the ceramic plate are equal to 0.48 m, 0.0734 m, and 0.8, respectively, at I = 900 A, the cable maximum temperature in the trench is the lowest.

Development of a Computer Model for Solar Simulation and Shaded Fenestration Design

2001 ◽  
Author(s):  
John Kie-Whan Oh ◽  
Jeffrey S. Haberl ◽  
Larry O. Degelman
Keyword(s):  
Heat Transfer ◽  
Solar Radiation ◽  
Computer Model ◽  
Thermal Performance ◽  
Energy Efficient ◽  
Design System ◽  
The Sun ◽  
Physical Test ◽  
Shading Device ◽  
Solar Simulation

Abstract The goal of this study was to develop a computer model for solar radiation calculation and display and a shaded fenestration design system that can be used by architectural and engineering designers. This computerized model calculates the amount of insolation and transmitted solar radiation through a shaded window as well as the heat transfer through it. The computer model, called Shaded Fenestration Design (SFD), contains various functions relating to solar simulation such as: display of the sunpath diagrams and the accompanying shading mask protractor, display of the hourly intensity of solar radiation onto the path of the sun for horizontal and vertical surfaces at varying off-south azimuths, and simulating the thermal performance of a shaded fenestration. The model also provides graphical aids for energy-efficient shading device design with use of various kinds of sunpath diagrams and solar radiation diagrams. The model performs solar radiation simulation using the methods developed in the ASHRAE Handbook, Duffie and Beckman, and Kreider and Rabl. An anisotrophic sky model was applied for the calculation of solar radiation on a titled surface and the transmitted solar radiation through a single-glazed window. A part of the model was validated experimentally using a physical test box and was also compared to simulated results from the DOE-2 program; however, the validation is not included in this paper.

scholarly journals Study of Natural Convection of Lithium-Ion Battery Module Employing Phase Change Material

Processes ◽  
2021 ◽  
Vol 9 (11) ◽  
pp. 2023
Author(s):  
Horng-Wen Wu ◽  
Yi-Chen Ciou ◽  
Jun-Kuan Wu ◽  
De-An Huang
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Phase Change ◽  
Lithium Ion Battery ◽  
Phase Change Material ◽  
Short Circuit ◽  
Lithium Ion ◽  
Peak Temperature ◽  
Maximum Temperature ◽  
Change Material

When the Lithium-ion battery operates at high temperature, it would bring about short circuit; if it reaches a critical temperature, it will explode. It is important to reduce its maximum temperature by appropriate heat transfer technique. When it operates without an external force for cooling, it needs natural convection technique to take away heat dissipation. Therefore, this study numerically examines three-dimensional transient natural convection of cylindrical lithium-ion batteries inside a rectangular pack with air between cylinders. The heat transfer technique in this study applies PCM (phase change material) between cylinders without or with fin array on top changing distance between cells. The results indicated that for no fin array, the package adopting the PCM could achieve the peak temperature 14.2 °C smaller than the package adopting the air. However, the package adopting the PCM with fin array vertical to the top of the package can best enhance average Nusselt number by 120% compared with using air and no fin array. Replacing the air by the PCM can keep the peak temperature of the batteries within the desirable operation range.

Natural Convection Heat Transfer in Horizontal Rod-Bundle Enclosures

1996 ◽  
Vol 118 (3) ◽  
pp. 598-605 ◽  
Author(s):  
M. Keyhani ◽  
T. Dalton
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Convection Heat Transfer ◽  
Diameter Ratio ◽  
Array Size ◽  
Maximum Temperature ◽  
Natural Convection Heat Transfer ◽  
Convection Heat

Natural convection heat transfer in enclosed horizontal N × N arrays (N = 3, 5, and 7) of electrically heated rods with a pitch-to-diameter ratio (P/d) of 1.35 has been experimentally investigated. Each array was positioned in an isothermal square enclosure with a width-to-diameter ratio (W/d) of 20.6. Pressurized air or helium was used as the working fluid. It was observed that the bottom-tow rods were relatively insensitive to increases in the array size, as they exhibit only slight temperature variations, but the top-row rods demonstrated substantial temperature increases. Natural convection correlations in the form of Nusselt number (Nud) as a function of modified Rayleigh number (Rad*) were obtained for each rod in each array. The correlations cover three flow regimes of conduction, transition, and convection in the range of 6.45 < Rad* < 3.08 × 105. A generalized enclosure Nusselt number was correlated as a function of enclosure modified Rayleigh number and the array size (N). Comparison of the data with previous numerical prediction showed that this correlation may be readily used to obtain a conservative estimate of the maximum temperature in the arrays with N = 3, 5, 7, and 9.

Mixed Convection Transport From an Isolated Heat Source Module on a Horizontal Plate

1990 ◽  
Vol 112 (3) ◽  
pp. 653-661 ◽  
Author(s):  
B. H. Kang ◽  
Y. Jaluria ◽  
S. S. Tewari
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Mixed Convection ◽  
Forced Convection ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Finite Thickness ◽  
Forced Flow ◽  
Maximum Temperature ◽  
Convection Dominated

An experimental study of the mixed convective heat transfer from an isolated source of finite thickness, located on a horizontal surface in an externally induced forced flow, has been carried out. This problem is of particular interest in the cooling of electronic components and also in the thermal transport associated with various manufacturing systems, such as ovens and furnaces. The temperature distribution in the flow as well as the surface temperature variation are studied in detail. The dependence of the heat transfer rate on the mixed convection parameter and on the thickness of the heated element or source, particularly in the vicinity of the source, is investigated. The results obtained indicate that the heat transfer rate and fluid flow characteristics vary strongly with the mixed convection variables. The transition from a natural convection dominated flow to a forced convection dominated flow is studied experimentally and the basic characteristics of the two regimes determined. This transition has a strong influence on the temperature of the surface and on the heat transfer rate. As expected, the forced convection dominated flow is seen to be significantly more effective in the cooling of a heat dissipating component than a natural convection dominated flow. The location of the maximum temperature on the module surface, which corresponds to the minimum local heat transfer coefficient, is determined and discussed in terms of the underlying physical mechanisms. The results obtained are also compared with these for an element of negligible thickness and the effect of a significant module thickness on the transport is determined. Several other important aspects of fundamental and applied interest are studied in this investigation.

scholarly journals Experimental and Numerical Study for a Novel Arrangement of a SuperCapacitors Stack to Improve Heat Transfer

2022 ◽  
Vol 12 (2) ◽  
pp. 662
Author(s):  
Ionut Victor Voicu ◽  
Florin Bode ◽  
Wassim Abboud ◽  
Hasna Louahlia ◽  
Hamid Gualous ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Energy Storage ◽  
Forced Convection ◽  
Electrical Energy ◽  
Maximum Temperature ◽  
Temperature Deviation ◽  
Electrical Energy Storage ◽  
Improve Heat Transfer ◽  
The Impact

Supercapacitors (SCs) are electrical energy storage devices which have the peculiarity of storing more electrical energy than capacitors and supply it at higher power outputs than batteries. This, together with the fact that the SCs have high cyclability and long-term stability, make them very attractive devices for electrical energy storage. Thermal transfer around a novel arrangement of a module of five rows of SCs is approached in this paper. A mixed aligned/staggered configuration is studied, aiming to explore a new possibility that can improve heat transfer more than other configurations studied before in the literature. The maximum SC current rate current is 84 A and the maximum temperature is 65 °C. The module undergoes charge and discharge cycles. The current tests are performed up to 50 A for natural convection and up to 70 A in forced convection. For the natural convection case, the SC located in the center of module is the most critical from the temperature point of view and the temperature evolution shows the necessity of a cooling system. The relative temperature reaches 27 °C for 50 A and the permanent regime cannot be reached with a current greater than 50 A. Thereafter, the impact of position and current on the temperature of SCs in forced convection is examined. The airflow mean air velocity is 0.69 m/s. The temperature of the SCs located on the third and fourth row are very close. However, the last row is the least cooled. This low temperature rise can be explained by the change from an aligned to a staggered arrangement between these rows. Compared to the natural convection case, a significant decrease is observed for the relative temperatures. The difference between the highest and lowest temperature augmentation also decrease but remain high. The temperature difference becomes greater than 5 °C if continuous current exceeds 39 A. CFD numerical simulation is performed for steady state at maximum experimental current rate in order to better understand the thermal and flow behavior. Numerical and experimental results are in good agreement, with a temperature deviation of less than 10%.

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