Hyung-Yong Cho

CHARACTERISTICS OF HEAT TRANSFER IN IMPINGING JETS BY CONTROL OF VORTEX PAIRING

The present study is conducted experimentally to obtain heat transfer characteristics on the impingement surface for controlled jets. Counterflowing or coflowing stream around the jet periphery is used to control the jet at the nozzle lip. The characteristics of flow and heat transfer are studied on two different jet nozzle exit flow conditions, including a fully developed turbulent tube flow and an uniform velocity distribution flow. The experiments are carried out for nozzle-to-plate distances of 2 to 8 nozzle diameters, jet Reynolds numbers in the range of 10,000 to 70,000, and main and secondary flow velocity ratios, R = ΔU/2U, of 0.45 to 1.86. The secondary counter- and co-flows change the flow instability conditions in the shear layers resulting in changes of heat transfer on the impingement surface. For secondary counterflows, heat transfer on the impingement surface is changed little for the small nozzle-to-plate distance of H/D = 2, but is enhanced on the stagnation region with reduction on the secondary peak region for H/D = 4. Augmentation of heat transfer on the stagnation region increases with increasing jet Reynolds numbers. For secondary coflows, the jet potential core extends far downstream due to inhibited development of the vortices, but the heat transfer is reduced significantly and the secondary peak appears downstream with increasing blowing rates.Copyright

A Study of Sodium Reduction Effect in Foods Using Fermented Soy Sauce

Salt (NaCl) is one of the most important main source of sodium in our diet. However, health concerns related to salt overconsumption have led to an increased demand for salt-reduced food. The objective of this study was to investigate the possibility of the use of fermented soy sauce to reduce the level of salt in foods. The contents of sodium in bean sprout soup and chicken rice porridge prepared with salt were 1.59±0.05 and 1.89±0.03 g/L, respectively. Whereas, the sodium content range of the same samples prepared with soy sauce were 0.38±0.01-1.54±0.02 and 0.37±0.00-1.44±0.01 g/L, respectively. Paired difference test between control and various soy sauce samples was used to provide the amount of soy sauce needed to replace salt without changing the overall taste and intensity. The results showed that sodium reduction (22.0-69.3%) could be achieved in tested foods with the fermented soy sauce.

Prediction of Kinetic Parameters for Food Quality Changes Using Equivalent Time at Standard Temperature

The effectiveness of three different numerical methods has been assessed for the estimation of kinetic parameters from literatural and experimental data. Generalized one step procedure using equivalent time, which provides a method for converting any variable temperature history to equivalent time at specified reference temperature, gave the smallest sum of squares for error and 6∼15 times faster computing rate than those estimated by the conventional one step method.

Hydrolysis of Isolate Soybean Protein Using Subcritical Water

Hydrolysis of isolate soybean protein (ISP) using subcritical water (SCW) was conducted to study the feasibility for producing protein hydrolyzate. SCW hydrolysis of SPI suspension (5-15%) was conducted in an electrically heated batch reactor (2 L). The effects of temperature (230 to 270 o C) and holding time (10 to 50 min) on the degree of hydrolysis (DH) and the production of amino acids were studied by surface response method. The DH was determined by derivatizing the hydrolyzates with ortho-phthalaldehyde (OPA) solution. It was confirmed that reaction temperature and holding time affected the hydrothermolysis of soybean protein. However, the holding time was less effective on amino acid yield when the temperature was higher than 230 o C. In order to achieve optimal yields of amino acids exceeding 43%, the temperature should be within the range between 256 and 268 o C with holding time from 29 to 41 min, respectively. A maximum estimated amino acid yield of 43.5% was obtained at 268 o C for 35 min.