Results 1 - 8 of 8
Results 1 - 8 of 8. Search took: 0.012 seconds
|Sort by: date | relevance|
[en] This paper presents the optimization process of evaporator for a vapor compression cooling system for high heat flux CPU. The CPU thermal capacity was given by 300W. Evaporating temperature and mass flow rate were 18 .deg. C and 0.00182kg/s respectively. R134a was used as a working fluid. Channel Width(CW) and Height(CH) were selected as design factors. And thermal resistance, surface temperature of CPU, degree of superheat, and pressure drop were taken as objective responses. Fractional factorial DOE was used in screening phase and RSM(Response Surface Method) was used in optimization phase. As a result, CW of 2.5mm, CH of 2.5mm, and CL of 484mm were taken as an optimum geometry. Surface temperature of CPU and thermal resistance were 33 .deg. C and 0.0502 .deg. C/W respectively. Thermal resistance of evaporator designed in this study was significantly lower than that of other cooling systems such as water cooling system and thermosyphon system. It was found that the evaporator considered in this work can be a excellent candidate for a high heat flux CPU cooling system
[en] Experimental investigations have been carried out to examine the evaporative heat transfer characteristics of R-134a with the channel-bending angle (CBA) in microchannel heat exchangers. In this study, we examined the effects of evaporation temperature and Reynolds number of R-134a on the evaporative heat transfer characteristics of R-134a in microchannel heat exchangers with CBAs of 120 .deg. , 150 .deg. , and 180 .deg. under counterflow conditions. Experimental results show that the evaporative heat transfer rate and evaporative heat transfer coefficient increased with an increase in the Reynolds number of R-134a. Further, the evaporative heat transfer rate corresponding to CBAs of 120 .deg. and 150 .deg. increased to values greater than the evaporative heat transfer rate corresponding to 180 .deg. by approximately 17.1% and 13.3%, respectively, for evaporating temperatures in the range 4.9-14.9 .deg. C. The evaporative heat transfer coefficient was affected by the channel angle with increasing evaporative heat transfer coefficient at small channel bending angle
[en] In this study, experiments were carried out to investigate the convective heat transfer characteristics of rectangular microchannels. The sample used in the experiments contained 20 rectangular microchannels in parallel. The channels had a hydraulic diameter of 700 μm. Distilled water was used as the working fluid. In the experiments, the Reynolds number ranged from 400 to 800, heat flux ranged from 35 to 85 kW/m2, and the inlet fluid temperature was 20 .deg. C. As a result, the convective heat transfer coefficient increased upon increasing the Reynolds number and ranged from 4.6 to 6.4 kW/m2/ .deg. C in the thermally fully developed region. Moreover, the higher the Reynolds number, the longer the thermal entry length in the rectangular microchannels. However, it was observed that a variable heat flux did not affect the thermal entry length. In conclusion, a correlation was proposed to indicate the heat transfer characteristics in a thermally fully developed region
[en] Liquid desiccant systems have been paid attention because of its advantages in energy saving and an environmental friendliness. The use of liquid desiccant systems offers design and performance advantages over the solid desiccant systems, especially when solar energy is used for regeneration. The objective of this paper is to analyze the simultaneous heat and mass transfer characteristics of lithium chloride aqueous solution for the plate type dehumidification system. The effects of process air and solution inlet conditions on the dehumidification performance are studied in this study. It is found that the heat transfer coefficient of the air side gives much more significant effect on the absorption rate and dehumidification effectiveness than those of the solution and the coolant sides while the mass transfer coefficient of the solution side gives more significant effect than that of the air side. It is also found that the solution concentration is the most important factor for absorption performance improvement during the dehumidification process.
[en] An experimental investigation was carried out to examine the evaporative heat transfer characteristics of R-134a in a micro-channel heat exchanger. The micro-channel heat exchanger used in this study was a sort of plate heat exchanger. Micro-channels were fabricated on the SUS304 plate by the photo-etching process: 13 sheets of plates were stacked and bonded by the diffusion bonding process. The effects of the evaporating temperature, mass flux of R-134a, and inlet temperature of water were examined. As the difference between the inlet temperatures of R-134a and water increased, the heat transfer rate increased. The evaporative heat transfer coefficients obtained in this study range from 0.67 to 6.23 kW/m2 · .deg. C. The experimental correlation for the Nusselt number as a function of the Reynold number and θ was suggested for the micro-channel heat exchanger
[en] Experimental investigations have been carried out to examine the evaporative heat transfer characteristics of R-134a in micro-channel heat exchangers with straight and zigzag 15 .deg. and 30 .deg. channel. The micro-channels heat exchangers used in this study is a sort of plate heat exchanger. Micro-channels were fabricated on the SUS304 plate by photo-etching process ; 13 sheets of plate were stacked and bonded by diffusion bonding process. Effects of difference in Reynolds number with R-134a and that of difference in heat transfer areas have been examined under counter flow condition. The heat transfer rate of zigzag 15 .deg. and 30 .deg. has increased about 1.1∼1.2 times compared with the straight, and the pressure drop also increased about 1.1∼1.4 times. The evaporative heat transfer coefficients obtained in this study range from 0.97 kW/m2· .deg. C to 7.85 kW/m2 · .deg. C.
[en] This paper presents a study on the regeneration performance characteristics of an internally heated regenerator applicable to a liquid desiccant system. The internally heated regenerator used in this study was designed and manufactured to provide better regeneration performance. An experimental setup was established to examine the regeneration performance. LiCl aqueous solution was used as working fluid. Variables to evaluate regeneration performance characteristics of the internally heated regenerator were dry bulb temperature, relative humidity and velocity of regeneration air, mass flow rate, temperature and concentration of the LiCl aqueous solution. The experimental conditions were chosen by using a 1/2 fractional factorial DOE. Regeneration rate and regeneration effectiveness were taken as results. From the results, solution concentration and regeneration air relative humidity have strong effects on the regeneration rate. The regeneration effectiveness was affected mostly by regeneration air velocity.
[en] Highlights: • The combined heat and mass transfer characteristics of LiCl solution are analyzed. • The heat and the mass transfer coefficients range from 0.25 to 0.47 kW/m"2K and from 4 to 12 × 10"−"7 m/s, respectively. • The air velocity is the most important factor for performance enhancement. • Nu and Sh correlations are developed with the error bands of ±25%, respectively. - Graphical Abstract: Display Omitted - Abstract: Liquid desiccant systems have been extensively drawn attention due to its benefits of reducing the energy consumption and being environmental friendly technology. The objectives of this study are to analyze the combined heat and mass transfer characteristics of LiCl (lithium chloride) aqueous solution for the liquid desiccant system of plate type dehumidifier and to compare the analytical model with the experimental results. The plate surface is treated with a hydrophilic coating to enhance the wettability of the solution distribution and to decrease the solution scattering on the plate surface. It can be seen that the heat transfer coefficient and the mass transfer coefficient range from 0.25 to 0.47 kW/m"2K and from 4 to 12 × 10"−"7 m/s, respectively. It is concluded that the air velocity is the most significant element for enhancing the performance during the dehumidification process. Finally, Nusselt and Sherwood number correlations are developed with the error bands of ±25%, respectively.