Sinan Caliskan

Bio: Sinan Caliskan is an academic researcher from Hittite University. The author has contributed to research in topics: Heat transfer & Nusselt number. The author has an hindex of 10, co-authored 39 publications receiving 404 citations. Previous affiliations of Sinan Caliskan include Zonguldak Karaelmas University.

Choroidal Thickness in Patients with Graves’ Ophthalmopathy

Abstract: Purpose: The purpose of the study is to compare choroidal thickness (CT) in patients with active and inactive Graves’ ophthalmopathy (GO) and that in healthy subjects by using spectral domain optical coherence tomography (SD-OCT).Methods: We conducted an observational, cross-sectional study of 28, 48, and 74 eyes of 14 patients with active GO (group 1), 24 patients with inactive GO (group 2), and 37 age-matched healthy subjects (group 3), respectively. Activity of GO was assessed by using initial clinical activity score (CAS). CT was measured by using SD-OCT. The differences in CT among the groups were compared, and the factors affecting subfoveal CT were analyzed.Results: The mean subfoveal CT was significantly greater in group 1 (395.84 ± 9.68 µm) than that in group 2 and group 3 (319.76 ± 7.07 µm and 314.22 ± 5.74 µm, respectively; p < 0.001) after adjusting for age, axial length, and intraocular pressure (IOP). Subfoveal CT was positively correlated with CAS (p < 0.001; r = 0.567). In multivar...

Enhanced Depth Imaging Optical Coherence Tomography of the Choroid in Normal Eyes

Abstract: PURPOSE To measure macular choroidal thickness in normal eyes at different points using enhanced depth imaging (EDI) optical coherence tomography (OCT) and to evaluate the association of choroidal thickness and age. DESIGN Retrospective, observational case series. METHODS EDI OCT images were obtained in patients without significant retinal or choroidal pathologic features. The images were obtained by positioning a spectral-domain OCT device close enough to the eye to acquire an inverted image. Seven sections were obtained within a 5 x 30-degree area centered at the fovea, with 100 scans averaged for each section. The choroid was measured from the outer border of the retinal pigment epithelium to the inner scleral border at 500-microm intervals of a horizontal section from 3 mm temporal to the fovea to 3 mm nasal to the fovea. Statistical analysis was performed to evaluate variations of choroidal thickness at each location and to correlate choroidal thickness and patient age. RESULTS The mean age of the 30 patients (54 eyes) was 50.4 years (range, 19 to 85 years), and 14 patients (46.7%) were female. The choroid was thickest underneath the fovea (mean, 287 microm; standard deviation, +/- 76 microm). Choroidal thickness decreased rapidly in the nasal direction and averaged 145 microm (+/- 57 microm) at 3 mm nasal to the fovea. Increasing age was correlated significantly with decreasing choroidal thickness at all points measured. Regression analysis suggested that the subfoveal choroidal thickness decreased by 15.6 microm for each decade of life. CONCLUSIONS Choroidal thickness seems to vary topographically within the posterior pole. The thickness of the choroid showed a negative correlation with age. The decrease in the thickness of the choroid may play a role in the pathophysiologic features of various age-related ocular conditions.

Review of heat transfer enhancement methods: Focus on passive methods using swirl flow devices

Abstract: Economic reasons (material and energy saving) leads to make efforts for making more efficient heat exchange. The heat transfer enhancement techniques are widely used in many applications in the heating process to make possible reduction in weight and size or enhance the performance of heat exchangers. These techniques are classified as active and passive techniques. The active technique required external power while the passive technique does not need any external power. The passive techniques are valuable compared with the active techniques because the swirl inserts manufacturing process is simple and can be easily employed in an existing heat exchanger. Insertion of swirl flow devices enhance the convective heat transfer by making swirl into the bulk flow and disrupting the boundary layer at the tube surface due to repeated changes in the surface geometry. An effort has been made in this paper to carry out an extensive literature review of various turbulators (coiled tubes, extended surfaces (fin, louvered strip, winglet), rough surfaces (Corrugated tube, Rib) and swirl flow devices such as twisted tape, conical ring, snail entry turbulator, vortex rings, coiled wire) for enhancing heat transfer in heat exchangers. It can be concluded that wire coil gives better overall performance if the pressure drop penalty is considered. The use of coiled square wire turbulators leads to a considerable increase in heat transfer and friction loss over those of a smooth wall tube.

A comprehensive review on single phase heat transfer enhancement techniques in heat exchanger applications

Abstract: The objective of this paper is to review the different techniques, which have been used to enhance the heat transfer rate in heat exchanger devices such as solar air heater, cooling blades of turbine and so on using single phase heat transfer fluids. The results of recent published articles with the development of new technologies such as Electrohydrodynamic (EHD) and Magnetohydrodynamics (MHD) are also included. Enhancement of heat transfer in heat exchanger can achieved by means of several techniques. These techniques are grouped into the active and passive method. In the active methods, system need some external power, however, passive method utilize surface modification either on heated surface or insertion of swirl devices in the flow field. Active methods are very complex because of external power supply, although these methods have great potential and can control thermally. Passive methods include artificial roughness, extended surface, winglets, insertion of swirl devices in the flow which alters the flow pattern causes to disturb the thermal boundary layer, and consequently high heat transfer. Passive methods are dominant over active methods because its can easily employed in existing heat exchangers. In this paper, an effort has been made to categorize the active and passive methods and review the various heat transfer techniques applied in heat exchangers. Important results have been listed for ready reference. It has been concluded that either active or passive methods have been employed alone. Based on literature, a combined method have also been recommended which include both active and passive methods.