scholarly journals Effects of Heat Transfer in Divergent Section of Laval Nozzle on Exhaust Velocity and Area Ratio

2011 ◽  
Vol 54 (185/186) ◽  
pp. 212-220
Author(s):  
Yuki IWAKI ◽  
Tsuyoshi TOTANI ◽  
Masashi WAKITA ◽  
Harunori NAGATA
Keyword(s):  
Heat Transfer ◽  
Laval Nozzle ◽  
Area Ratio

Heat transfer enhancement of round impinging jet by orifice nozzle (Effects of contraction area ratio)

2008 ◽  
Vol 37 (8) ◽  
pp. 445-459
Author(s):  
Mizuki Kito ◽  
Toshihiko Shakouchi ◽  
Tatsuji Sakamoto ◽  
Koichi Tsujimoto ◽  
Toshitake Ando
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Impinging Jet ◽  
Area Ratio ◽  
Transfer Enhancement

scholarly journals Numerical Investigation of a two-inlet PVT air collector

2019 ◽  
Vol 136 ◽  
pp. 05014
Author(s):  
Zhangyang Kang ◽  
Zhaoyang Lu ◽  
Xin Deng ◽  
Qiongqiong Yao
Keyword(s):  
Heat Transfer ◽  
Single Channel ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Thermal Characteristics ◽  
Area Ratio ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Cross Sectional ◽  
Maximum Heat

A numerical study of heat and mass transfer characteristics of a two-inlet PV/T air collector is performed. The influence of thermal characteristics and efficiency is investigated as the area ratios of inlet and outlet of the single channel with two inlets are changed. The design of the two-inlet PV/T air collector can avoid the poor heat transfer conditions of the single inlet PV/T air collector and improve the total photo-thermal efficiency. When the inlet/outlet cross-sectional area ratio is reduced, the inlet air from the second inlet enhances the convection heat transfer in the second duct and the temperature distribution is more uniform. As the cross-sectional area of the second inlet increase, the maximum heat exchange amount of the two-inlet PV/T air collector occurs between the inlet and outlet cross-sectional area ratio L=0.645 and L=0.562.

Nodal Topology in Compact Thermal Models

2007 ◽  
Author(s):  
D. H. Greisen ◽  
V. P. Manno
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Boundary Conditions ◽  
Transfer Coefficient ◽  
Area Ratio ◽  
System Level ◽  
Thermal Models ◽  
Single Boundary

Compact Thermal Models (CTMs) utilize a few connected thermal nodes to represent the thermal characteristics of electronic packages. These models are preferable to highly discretized models in preliminary design and system level analysis because of their computational efficiency. Surface heat flux non-uniformities often make it necessary to subdivide the package surfaces into multiple CTM nodes. This division is often quantified as the surface area ratio. This work assesses CTM performance sensitivity to area ratio changes and variation in heat transfer coefficient boundary conditions. CTMs for benchmark TQFP and BGA packages are developed using an admittance matrix approach. While optimum area ratios are identified, a direct correlation between these optimal values and the heat flux distributions computed from fully-discretized models was not obtained. CTM performance was found to be sensitive to changes in the heat transfer coefficient used to generate the CTM parameter values. A critical generating heat transfer coefficient was determined such that the resulting CTM, when optimized for a single boundary condition, was relatively accurate over the whole set of boundary conditions considered. This single boundary condition also provided an upper bound for error. This finding could be significant in future CTM development procedures.

Film Cooling Performance of Converging-Slot Holes With Different Exit-Entry Area Ratios

2009 ◽  
Author(s):  
Cun-liang Liu ◽  
Hui-ren Zhu ◽  
Jiang-tao Bai ◽  
Du-chun Xu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Thermal Protection ◽  
Area Ratio ◽  
Cooling Effectiveness ◽  
Momentum Ratio ◽  
Film Cooling Effectiveness ◽  
Distribution Features

Film cooling performances of two kinds of converging slot-hole (console) with different exit-entry area ratios have been measured using a new transient liquid crystal measurement technique which can process the nonuniform initial wall temperature. Four momentum ratios are tested. The film cooling effectiveness distribution features are similar for the two consoles under all the momentum ratios. Consoles with smaller exit-entry area ratio produce higher cooling effectiveness. And the laterally averaged cooling effectiveness results show that the best momentum ratio for both consoles’ film cooling effectiveness distribution is around 2. For both consoles, the heat transfer in the midspan region is stronger than that in the hole centerline region in the upstream, but gradually becomes weaker as flowing downstream. With the momentum ratio increasing, the normalized heat transfer coefficient h/ho of both consoles increases. In the upstream, heat transfer coefficient of console with small exit-entry area ratio is higher. But in the downstream, the jets’ turbulence and the couple vortices play notable elevating effect on the heat transfer coefficient for large exit-entry area ratio case, especially under small momentum ratios. Consoles with smaller exit-entry area ratio provide better thermal protection because of higher cooling effectiveness. And the distributions of heat flux ratio are similar with those of cooling effectiveness because the influence of η on q/q0 is larger. For the consoles, smaller exit-entry area ratios produce lower discharge coefficients when the pressure variation caused by the hole shaped is regarded as flow resistant.

Experimental Investigation of Area Ratio on Microjet Array Heat Transfer

2009 ◽  
Author(s):  
Gregory J. Michna ◽  
Eric A. Browne ◽  
Yoav Peles ◽  
Michael K. Jensen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Electronics Cooling ◽  
Jet Impingement ◽  
Area Ratio ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Transfer Performance ◽  
Transfer Coefficients ◽  
High Heat Transfer

Electronics cooling is becoming increasingly difficult due to increasing power consumption and decreasing size of processor chips. Heat fluxes in processors and power electronics are quickly approaching levels that cannot be easily addressed by forced air convection over finned heat sinks. Jet impingement cooling offers high heat transfer coefficients and has been used effectively in conventional-scale applications such as turbine blade cooling and the quenching of metals. However, literature in the area of microjet arrays is scarce and has not studied arrays of large area ratios. Hence, the objective of this study is to experimentally assess the heat transfer performance of arrays of microjets. The microjet arrays were fabricated using MEMS processes in a clean room environment. The heat transfer performance of several arrays using deionized water as the working fluid was investigated. Inline and staggered array arrangements were investigated, and the area ratio (total area of the jets divided by the surface area) was varied between 0.036 and 0.35. Reynolds numbers defined by the jet diameter were in the range of 50 to 3,500. Heat fluxes greater than 1,000 W/cm2 were obtained at fluid inlet-to-surface temperature differences of less than 30 °C. Heat transfer performance improved as the area ratio was increased.

S1904-2-2 Improvement of thrust and specific impulse by convective heat transfer in Laval nozzle

2009 ◽  
Vol 2009.5 (0) ◽  
pp. 297-298
Author(s):  
Yuuki IWAKI ◽  
Tetsushi NAGANUMA ◽  
Syunya SATO ◽  
Tsuyoshi TOTANI ◽  
Masashi WAKITA ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Laval Nozzle ◽  
Specific Impulse

Study of Supersonic Micro-Channel for Cooling Electronic Devices

2013 ◽  
Author(s):  
Yuya Takahashi ◽  
Junnosuke Okajima ◽  
Yuka Iga ◽  
Atsuki Komiya ◽  
Wu-Shung Fu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Gas Flow ◽  
Single Phase ◽  
Laval Nozzle ◽  
Cooling System ◽  
Supersonic Nozzle ◽  
Cooling Performance ◽  
Micro Scale ◽  
Mean Temperature

In this study, we focus on a micro-scale cooling device using a supersonic single phase gas flow. The single phase gas cooling system has advantages for cooling electronics device in a micro-scale. Generally, the forced convective heat transfer by single phase gas flow has a lower heat transfer coefficient than other heat transfer mechanisms. However, the heat transfer rate can be largely improved with a low temperature flow that is generated by isentropic expansion in supersonic nozzle. The objective of this study is to conduct a numerical evaluation of the possibility of this cooling system with a supersonic air flow through a heated micro-fin array. In order to calculate the supersonic flow inside the nozzle and evaluate the effect of the nozzle shape on the heat transfer, two types of nozzles are designed. One nozzle is a typical supersonic nozzle called Laval nozzle. The other is named Bump nozzle which has a simple arc shape at the throat. The channel size of both nozzles are about 200 μm in width and 2743.1 μm in length. In order to estimate the cooling performance, the numerical simulations were conducted by using ANSYS FLUENT 12.1 with the density-based Roe-FDS method. The inlet pressure, outlet pressure, and total pressure were set to 290 kPa, 100 kPa, and 367.1 kPa, respectively. The stagnation temperature and wall temperature were assumed 300 K and 350 K, respectively. The values of bulk mean temperature and Nusselt number were estimated. In both nozzles, the calculated bulk mean temperature was about 230 K and the Nusselt number was 7.54, which is the theoretical value of laminar forced convection between the parallel plates. The results showed that the Bump nozzle had almost the same cooling performance as the Laval nozzle in spite of its simple geometry in the each single channel. In addition, the Bump nozzle can have 4 times the number of channels the Laval nozzle configuration can occupy the same area because of its shape. This indicates that cooling performance of a device that includes the Bump nozzle geometry is higher than that of the Laval nozzle.

The effect of area ratio on microjet array heat transfer

2011 ◽  
Vol 54 (9-10) ◽  
pp. 1782-1790 ◽  
Author(s):  
Gregory J. Michna ◽  
Eric A. Browne ◽  
Yoav Peles ◽  
Michael K. Jensen
Keyword(s):  
Heat Transfer ◽  
Area Ratio
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