الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
It is well known that the flow over segmental baffles is relevant to my engineering applications such as heat exchanges, corrugated channels and cooling of gas turbine blade . The presence of baffles causes the flow to separate , reattach and thus creates regions of reverse flow and high shearing rate , thus which means an augmenting of heat transfer.
The object of the present work show the behavior of the flow scross the segmental baffles. The research is directed also to study the effect of baffle height inside a rectangular duct on the flow pattern, heat transfer and pressure DROP for fixed baffle space. The baffles are located alternatively at top and bottom walls of the main duct . The duct has a rectangular cross-section areas (300 mm x 60 mm) with an aspect ratio equal to 5.
The tested air stream was heated by means electric coils which wound on the upper and the down surface of the main duct where the two other sides were kept adiabatic .
The total heat librated from the heaters was directed to the air stream while the different losses were eliminated.
The experiment 3 were carried out for different baffle materials of different thermal conductivities. Window cut ratios of 0.7 0.5 and 0 .3 were performed for constant spacing baffle ratio of 1.0. The investigated Reynolds numbers were ranged from 7000 to 22000.
For the periodic cell, the distribution of the mean velocity temperature and the local Nusselt number of both the top and bottom walls were illustrated. The distribution of walls temperature and local heat transfer coefficient on middle centre of each cell along the duct length were also obtained. The overall Nusselt number and the pressure DROP were presented for periodic cell and the influence of Reynolds number window cut and thermal conductivity of the baffle materials on these values were also studied. The heat transfer coefficients were related in terms of the ratio of Nusselt number value in the actual baffle duct to the value of smooth duct for laminar flow.
The given experimental results showed that, after a finite entry length the flow periodic fully developed for thermal boundary layer. It was found that, the flow became periodic after only after only 2-5 cells from the entrance section . The baffles were found to cause the flow to deflect significanctly . However, the associated increase in pressure DROP was an order of magnitude higher than the increase in heat transfer . In addition , conduction in the baffle materials was found to play a highly beneficial role in enhancing heat transfer .
General relations for the effect of window cut and thermal conductivity of the baffle materials on heat transfer coefficient were obtained.
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In the present work an experimental study on the transient pool boiling heat transfer under conditions of pressure rise inside a constant volume vessel is under taken. Also the same study is made under atmospheric pressure conditions.
An experimental apparatus is designed and constructed for this purpose. A vertical stainless steel cylindrical heating surface of known surface roughness is used. Test runs carried on this apparatus using distilled water as the working fluid. Two glass windows are opened in the test vessel to observe the boundary layer development.
The temperature distribution over the heating surface are measured at 14 locations distributed along its length.
At atmospheric pressure conditions the variations of the difference between the mean heating surface temperature and the corresponding saturation temperature are measured at steady state conditions for various heat fluxes.
The increasing pressure and the consequent variable difference between the mean heating surface temperature and the saturation temperature corresponding to the system pressure are measured during each of the test runs where the input heat power is maintained steady. Also both of the boundary layer and the liquid temperatures are measured.
The runs cover an input heat flux of 40 x 103 to 80 x 103 w/m2 over a pressure range from the atmospheric to 5.5 bars.
The heat transfer coefficient is calculated for each atmospheric and transient pressure conditions.
An empirical correlation to relate the heat transfer coefficient and the difference between the mean heating surface temperature and the saturation temperature corresponding to the atmospheric pressure at steady state conditions is obtained in the form :
H = 58.5 (ots)2.08 (w/m2k)
For transient conditions an emperial correlation to relate the heate transfer coefficient to both heat flux and pressure is obtained in the form :
Ht = 7.47 (q)0.67 (p)0.16 (w/m2k)
-Also experiments show that :
- Increasing the system pressure causes an increase in the outer surface temperature at the same heat flux.
- The heat transfer coefficient increases as the system pressure increases at the same heat flux.
- The saturation temperature difference (ots) decreases as the system pressure increases.
-The mean heating surface . liquid bulk temperature difference (otb) decreases as the system pressure increases for the same heat flux.
-The boundary layer during pressurization is always superheated.