• Journal of the Korean Solar Energy Society
• /
• v.27 no.4
• /
• pp.175-182
• /
• 2007

Geothermal-energy has been getting popular as a natural energy source for green buildings these days. As a result Geothermal Source Heat Pump System (GSHPs) was being recognized effective alternative systems to conventional heating and cooling systems owing to their higher energy utilization efficiency. But GSHPs has not been popularized thereby the large amount of initial cost of the system and insufficiency of studies for economic estimation. Therefore GSHPs are being developed to make up for the weak points that are the large amount of initial cost of the system and much annual electricity consumption. In this paper, economic estimation was conducted by payback period method and it shows that the pay back period of Heat Storage Type GSHPs was calculated 6.8 years compared with the absorption Chiller-Heater system and 8.2 years compared with the Ice storage-Boiler system. Heat Storage Type GSHPs also has the lower annual source energy consumption than the conventional heating and cooling systems because of using nighttime electricity.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.20 no.8
• /
• pp.517-525
• /
• 2008

In order to study the heat transfer and pressure drop of an internal heat exchanger for $CO_2$ heat pump under cooling condition, the experiment and numerical analysis were performed. Four kinds of internal heat exchangers with a coaxial tube type and a micro-channel tube type were used. The experimental apparatus consisted of a test section, a power supply, a heater, a chiller, a mass flow meter, a pump and a measurement system. The section-by-section method and Hardy-Cross method were used for the numerical analysis. The effects of the internal heat exchanger refrigerant flow rate, the length of the internal heat exchanger, the operating condition of the gas-cooler, the evaporator and the type of the internal heat exchangers were investigated. With increasing of the flow rate, the heat transfer rate increased about 25%. The heat transfer rate of the micro-channel tube type was higher about 100% than that of the coaxial tube type. With increasing of the length of the internal heat exchanger, the heat transfer rate increased about $20{\sim}50%$. The pressure drop of the low-side tube was larger compared with that of the high-side tube.

• Proceedings of the SAREK Conference
• /
• 2008.06a
• /
• pp.304-308
• /
• 2008

The optimal design of two stage evaporation & absorption system which is related to the large temperature difference system was investigated numerically in the absorption refrigeration system. The concentrations at inlet & oulet of absorber are 62.9% and 56.9%, but in two stage absorption system the values are 62.2% and 56.2%. Therefore strong solution & weak solution became diluted than the standard value. The amount of weak solution circulation can be reduced in absorption refrigeration system, and the sensible heat load is more reduced to enhance the COP of system. As UAR is increased, COP becomes larger, and this means the role of top section is more important than bottom section in two stage evaporation & absorption system. But the increase of COP becomes slower at 0.7 of UAR ratio. The performance of Type2 is higher than Type1 in COP with the flow direction of cooling waters. This phenomena is due to the active absorption of vapor -absorption & lower temp. cooling water is more effective. The pressure at bottom section becomes higher & that at top section becomes lower and therefore the circulation rate can be diminished more.

• Food Science of Animal Resources
• /
• v.24 no.3
• /
• pp.310-318
• /
• 2004

Eating quality is a reflection of consumer satisfaction, while beef quality grade describes carcass characteristics of chiller assessment which are largely influenced by production systems including breeding and feeding schemes. On the other hand, it should be emphasized that high palatability of beef is a function of production and processing components including breed, nutrition, animal handling, post-slaughter intervention and cookery. Numerous efforts have been made by Korean beef industry and research institutes to deliver high quality beef with which domestic beef consumers are satisfied. However, majority of studies have tended to focus on improvement of intramuscular fat content with little attention on its effect on consumer-based eating quality. Furthermore, there is very limited accessible information(if any) on relative importance of eating characteristics (eg, tenderness, juiciness and flavor intensity) to consumer satisfactory rate and palatability grade. On this regard, our recent results indicated, for example, that when m. longissimus was prepared by a thin-slice style BBQ, relative weightings of tenderness, juiciness and flavor intensity for consumer satisfactory rate were 0.4, 0.35 and 0.25, respectively. When eating quality was graded into 4 groups by a sum of tenderness, juiciness and flavor intensity after multiplying these coefficients, consumers responded that the palatability score for high quality beef should be higher than 79 points. Based on our recent experiments, the current report is intended to highlight relative importance of eating quality characteristics on consumer satisfactory rate, and threshold of eating quality grade. In addition, post-slaughter intervention techniques such as electrical stimulation and tenderstretch are given as examples of critical control points of palatability assurance program of Hanwoo beef.

• Food Science of Animal Resources
• /
• v.33 no.4
• /
• pp.508-514
• /
• 2013

Taste-active compounds (e.g., amino acids and nucleotides) play an important role in contribution to the gustatoty sensation of food. The current study aimed to examine the differences in taste-active compounds between different beef muscles, breeds and aging periods. We have chosen the longissimus dorsi and semitendinosus muscles of Hanwoo breed and longissimus dorsi muscle of Angus breed for the investigation of the aforementioned compounds. Hanwoo muscles were aged for 7 or 28 d, and Angus samples were aged for 28 d at $4^{\circ}C$. Results revealed that 8 out of the 18 detected free amino acids (FAA) showed significant (p<0.05) differences between the two Hanwoo muscles. Twelve FAAs showed aging effect (p<0.05) in which the amounts of 8 FAAs significantly increased as aging time increased. Inosine 5-monophosphate (IMP), hypoxanthine (Hx) and inosine showed significant (p<0.05) differences between the Hanwoo muscles, aging resulted in an increase in amounts of these nucleotides. Hanwoo beef had significantly (p<0.05) higher total amount of sweet amino acids than the Angus ones in that 15 amino acids showed differences (p<0.05) between the two breeds. Amounts of guanosine 5-monophosphate (GMP) and Hx were significantly higher (p<0.05) for Angus beef. Current study indicated that muscle type, breed and aging period had large variations in free amino acid and nucleotide contents, which may subsequently affect the taste attributes of cooked beef.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.23 no.4
• /
• pp.243-250
• /
• 2011

In order to investigate the effects of PAG oil concentration on heat transfer performance and pressure drop during gas cooling process of $CO_2$, the experiments on fin-tube heat exchanger of $CO_2$ heat pump were performed. The experimental apparatus consists of a gas cooler, a heater, a chiller, a mass flow meter, a pump and measurement system. Experiments were conducted in various experimental conditions, which were inlet temperature($110^{\circ}C$), mass flow rates (50, 55, 60, 65, 70 g/s) and PAG oil concentration(0 to 2.6 wt%). Heat transfer rate decreased with the increase of the oil concentration and the decrease of inlet pressure. And pressure drop increased with the increase of the oil concentration and mass flow rate of refrigerant. The COP reduction by deterioration of gas cooler performance with oil concentration was analyzed. When inlet pressure of gas cooler is 100 bar, the COP reduction was estimated by 6% under 1 wt% of oil concentration.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.23 no.3
• /
• pp.208-215
• /
• 2011

In this work, pool boiling heat transfer coefficients(HTCs) of R22, R123, R134a, and R245fa are measured on both horizontal plain and 26 fpi low fin tubes. The pool boiling temperature is maintained at $7^{\circ}C$ and heat flux is varied from 80 $kW/m^2$ to 10 $kW/m^2$ with an interval of 10 $kW/m^2$. Wall temperatures are measured directly by thermocouples inserted through holes of 0.5 mm diameter. Test results show that HTCs of high vapor pressure refrigerants are usually higher than those of low pressure fluids in both plain and low fin tubes. On a plain tube, HTCs of R245fa are 23.3% higher than those of R123 while on a 26 fpi low fin tube, HTCs of R245fa are 46.3% higher than those of R123. The fin effect is more prominent with low vapor pressure refrigerants than with high vapor pressure ones due to a sweeping effect.

• Proceedings of the SAREK Conference
• /
• 2008.11a
• /
• pp.203-211
• /
• 2008

The optimal design of two stage evaporation & absorption system which is related to the large temperature difference system was investigated numerically in the absorption refrigeration system. The concentrations at inlet & oulet of absorber are 62.9% and 56.9%, but in two stage absorption system the values are 62.2% and 56.2%. Therefore strong solution & weak solution became diluted than the standard value. The amount of weak solution circulation can be reduced in absorption refrigeration system, and the sensible heat load is more reduced to enhance the COP of system. As UAR is increased, COP becomes larger, and this means the role of top section is more important than bottom section in two stage evaporation & absorption system. But the increase of COP becomes slower at 0.7 of UAR ratio. The performance of Type2 is higher than Type1 in COP with the flow direction of cooling waters. This phenomena is due to the active absorption of vapor -absorption & lower temp. cooling water is more effective. The pressure at bottom section becomes higher & that at top section becomes lower and therefore the circulation rate can be diminished more.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.29 no.5
• /
• pp.239-248
• /
• 2017

At the $21^{st}$ Conference of the Parties (COP) of the United Nations Climate change Conference, representatives of the 195 member countries reached an agreement requiring all participating countries, including Korea, to establish proactive measures to fight climate change. Under this vision, energy network technologies are deemed as a key site of research towards meeting this goal. Herein, the headquarters of the Korea Institute of Energy Research (KIER) is a worthy site for carrying out energy network technology research insofar as it contains various heat sources. To prepare for this research, a study was conducted analyzing the heat sources at KIER based on measured data. The study also consisted of developeding simulation models to predict the amount of energy savings that could be derived by replacing an absorption chiller/heater with an absorption heat pump during winter seasons. In our simulation results, we observed a primary energy saving ratio of 65~72% based on the water temperature from the heat source of a coal power plant.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.19 no.9
• /
• pp.615-621
• /
• 2007

Experimental study on the heat transfer characteristics of $CO_2$ in a horizontal smooth tube was carried out to investigate the heat transfer coefficient and pressure drop during evaporation of $CO_2$. The experiment apparatus consisted of a test section, a DC power supply, a heater, a chiller, a mass flow meter, a pump and a measurement system. Experiment was conducted for various mass fluxes ($200{\sim}1200kg/m^2s$), heat flukes ($10{\sim}100kW/m^2$) and saturation temperatures (-5, 0, $5^{\circ}C$). With increasing the heat flux, the evaporation heat transfer coefficient increased. But the variation of the heat transfer coefficient on the increase of the mass flux was not large. And the significantly drops of the heat transfer coefficient was observed at any heat flux and mass flux because of the change of the flow pattern in the tube. With increasing the saturation temperature, the heat transfer coefficient increased due to the promotion of a nucleate boiling. The measured pressure drop during evaporation increased with increasing the mass flux and decreasing the saturation temperature.