Cheolho Bai

Effect of electronic anti-fouling treatment on fouling mitigation with circulating cooling-tower water

The purpose of the present study was to investigate the effect of electronic anti-fouling (EAF) technology on fouling mitigation in a heat exchanger in an open cooling-tower system. Two tests were performed in a rectangular heat-transfer channel at 5 cycles of concentration: one without the EAF treatment and the other with the EAF treatment. The fouling resistance in the case with the EAF treatment was about 70% less than that in the case without the EAF treatment at the end of 270-hr tests.

Dynamic effect of surface contact angle on liquid transfer in a low speed printing process

In this study, experiments on liquid transfer were performed to observe the change of the surface contact angle with respect to the process speed. The liquid transfer ratio from the experiments was compared with that from numerical simulation for low speed ranges. While the surface contact angle on the lower plate was almost constant in the experiment regardless of operating speed, the surface contact angle on the upper plate was found to be significantly changed during the process at the low speed ranges. This resulted in a reduction of the transfer ratio. By applying the time-dependent values of contact angle to the numerical simulation model, the transfer ratio showed better agreement with the experimental results. The dynamic effect of surface contact angle should be considered as an additional variable, especially for the analysis of liquid transfer in a low speed printing process.

A Study on Control Method of Thermal Storage Tank for Varying Thermal Load in Heat Pump Water Heater

A characteristic behavior of the thermal storage tank for varying thermal load in heat pump water heater was studied. The control method was suggested and applied. By measuring the temperature within the storage tank, the heat pump was ON/OFF controlled. The appropriate measuring position and the size of heat exchanger gives the minimized power consumption of heat pump. As the length of heat exchanger increases, the temperature measuring position goes down of the storage tank and the power consumption increases.

A Study on the Reliability of Cooling Water Systems Using R436B

The alternative refrigerant R436B is applied, to assess the application feasibility for a commercial cooling water system. The characteristic stability was verified by Sealed glass tube test and Autoclave test. R436B is chemically stable with the compressor material. The Oil miscibility test shows the usual compressor oil mixed well with R436B. Through the life acceleration test, the cooling performance is maintained. Though slight changes in oil and capillary tube diameter were found, they were within the permitted range. R436B should be applied to commercial cooling water systems as a simple replacement for the usual refrigerant.

THERMODYNAMIC PROPERTY VARIATION OF NONAZEOTROPIC REFRIGERANT MIXTURES (NARMs) IN THE TEMPERATURE GLIDING ZONE

The relations among enthalpy, temperature and quality of nonazeotropic refrigerant mixtures (NARMs) in the phase change region (temperature gliding region) are investigated to seek a possibility for linear approximations. Using REFPROP, a refrigerant property calculation package developed by NIST, temperature-enthalpy, temperature-quality, quality-enthalpy relations are investigated for 4 binary and 15 ternary NARMs. Those 19 NARMs tested are the most promising alternative refrigerants for conventional CFC and HCFC refrigerants. A normalized enthalpy. which is a pseudo-quality in a sense, is defined based on the dew and bubble point enthalpies to compare with the conventional quality. The results show that the pseudo-quality and the conventional quality are almost identical independent of system pressure for all the NARMs tested while enthalpy-temperature and quality-temperature relations are diverse and highly pressure dependent depending on mixture combinations. The significance of the near-identical relation between the two qualities is that the easy-to-calculate pseudo-quality can replace quality in convective heat transfer coefficient representations.