Cemil Yamalı

Influence of sweeping on dropwise condensation with varying body force and surface subcooling

Abstract An experimental work is conducted to study the effect of body forces on dropwise condensation heat flux under controlled subcooling. For this purpose a centrifuge is designed. A gold plated condenser surface, which is placed horizontally on the centrifuge so that horizontal centrifugal force becomes parallel to the condenser surface, is used to obtain dropwise condensation. Experimental data is obtained at various acceleration levels while the coolant temperature is kept constant. To determine the noncondensable effect, data is collected with and without surface suction. Results of the experiments showed an increase in dropwise condensation heat transfer coefficient with an increase in body force. Some noncondensable effect is observed at low acceleration levels (1 and 5 × g ). No definite effect of subcooling on heat transfer coefficient is observed. Variations in heat transfer coefficient with different subcoolings are believed to be due to the variation in nucleation site density.

Magnetically geared direct drive wind generator thermal analysis

This paper considers Dual Stator Spoke Array Vernier Permanent Magnet (DSSA-VPM) generator for the direct drive wind-electric energy conversion. The structure of the generator is described. Although how this design is optimized is not discussed, dimensions of the designed generator are given. In electrical machine design thermal performance is naturally of utmost importance. In this paper thermal performance of the design and how its temperature can be kept within the temperature limit imposed by its insulation class and the permanent magnets used is investigated. It is found that when air flow within the generator is not permitted, at rated load condition the generator temperature reaches very high levels. To lower the operating temperature, ventilation holes are introduced to the end plates of the frame. Also some blades are placed on the rotor to help flow of air over the end windings. A model is introduced to calculate the air speed in the region where air flows. Using the calculated air speed a new heat transfer coefficient is determined for the region where air flows. It is found out that with the mentioned modifications to the structure of the generator the designed generator temperature rise can be kept within the value permitted for its insulation class. Therefore, the power density of the design can be safely compared with the power density of other types of designs for direct drive turbines. It is found that DSSA-VPM generator topology offers a clear advantage over other types of generators considered in the literature.

Technical Analysis of a Hybrid Desiccant Cooling in a Mediterranean Climate

This chapter presents a performance analysis of a hybrid liquid desiccant cooling system (DCS) with lithium chloride as the desiccant material in a Mediterranean climate. Mathematical models of desiccant contactors are adopted from the literature. The complete system is modeled in the TRNSYS platform and is simulated using Typical Meteorological Year data. The building model was developed in accordance with the building’s construction material and usage style. Simulations are performed over the summer period of a typical year and the results of the system are compared with the results of a conventional vapor compression cooling system (VCCS) from viewpoint of system characteristics and energy savings. One of the important contributions is the conclusion that a transient cycle analysis is necessary to understand the DCS cycle’s performance. The results also indicate that the consumed energy in both systems is approximately equal in magnitudes but different in type; DCS shifts the energy required for the operation of the system from electrical energy to thermal energy. It is also observed that for large supply-airflow rate applications, DCS would be more beneficial than VCCS.

Experiments on condensation over in-line and staggered condenser tubes in the presence of non-condensable gases

The problem of the forced film condensation heat transfer of pure steam and steam-air mixture flowing downward a tier of horizontal cylinders is investigated experimentally. An experimental setup was manufactured and mounted at Middle East Technical University workshop. A set of experiments were conducted to observe the condensation heat transfer phenomenon and to verify the theoretical results. The results of the experimental investigation are presented to show the effect of different parameters on the film condensation heat transfer phenomenon over bundle of tubes. These parameters include; free stream velocity, free stream non-condensable gas (air) mass fractions, free stream temperature to wall temperature difference, the angle of inclination. heat transfer coefficients are evaluated at different working conditions for both inline and staggered arrangements. Results show that; a remarked reduction in the vapor side heat transfer coefficient is noticed when very small amounts of air mass fractions pres...

Film condensation of steam flowing downward on a tier of horizontal cylinders at different inclination angles in the presence of a non-condensable gas

The problem of forced laminar film condensation of steam flowing downward a tier of horizontal cylinders is investigated numerically. The effects of free stream non-condensable gas, air concentration (m1,∞), free stream velocity (Reynolds number), cylinder diameter, and angle of inclination on the condensation heat transfer are analyzed. Two flow arrangements, inline and staggered, are analyzed and investigated. The mathematical model takes into account the effect of staggering of the cylinders and how condensation is affected at the lower cylinders when condensate does not fall on to the center line of the cylinders. Condensation heat transfer results are available in ranges from (U∞ = 1 − 30 m/s) for free stream velocity, (m1,∞ = 0.01 −0.8) for free stream air mass fraction and (D = 12.7 −50.8 mm) for cylinder diameter. Results show that; a remarked reduction in the vapor side heat transfer coefficient is noticed. This results from the presence of small amounts of free stream air mass fractions in the s...