Jeongil Kim

In pots heated above gas stoves, heat transfer occurs through both the bottom and side surfaces, with significant differences between the two. In this paper, we propose a new measurement method to separately measure the heat transferred to the bottom and side of a pot. Several aluminum pots of different diameters and heights were used. We showed that it is possible to determine the radial distribution of the heat transfer rate and the heat flux in the bottom of the pot, as well as the distribution of the heat transfer rate and the heat flux along the side of the pot. In addition, our results show that the heat transfer rate in the bottom of the pot can be approximated with a quadratic function of the bottom area, and the heat flux decreases in proportion to the bottom area. Moreover, the results indicate that the heat transfer rate to the side can be approximated with a quadratic function of the lateral area of the pot, and the heat flux decreases in proportion to the lateral area of the pot. The results of the validation experiment based on this measurement were in good agreement with previously reported values using the same pot.

This study aims to investigate the heat transfer mechanism of a pot heated on a commercial cooking gas stove. The process involves the premixed flame of natural gas and air from the gas burner colliding with the pot's bottom, where it continues to burn while drawing in surrounding air and spreading radially outward. As the combustion gas reaches the outer edge of the pot's bottom, buoyancy causes it to change direction vertically upwards, flowing along the pot's side. This process results in heating of both the bottom and sides of the pot. Given the significant difference in heating patterns between the bottom and sides of the pot, understanding the heat transfer characteristics for each area is crucial. In this study, convective heat transfer between the combustion gas and the outer surface of the pot was experimentally examined to better understand heat transfer characteristics on the pot's side. To estimate the convective heat transfer coefficient, temperature distributions of the combustion gas near the pot's side were measured. The combustion gas temperature on the pot's side was measured in four directions, considering the non-uniform flow of premixed gas from the burner flame port. Subsequently, the convective heat transfer coefficient was evaluated using heat flux and reference fluid temperature. The heat flux through the pot's side was determined by measuring temperature distributions near the pot. In the experiment, the gas stove burner's heating power was adjusted to 9.2 kW based on the lower calorific value standard. The pot material used was aluminum, with a height of 0.185 m and outer diameter of 0.303 m. The convective heat transfer coefficient for the pot was approximately 23 W/(m²·K).

This study is based on the concept of dynamic steady-state concentration applied to an air recirculating system that treats the exhaust and return air and supplies it back into the room. We aimed to develop a tracer gas experimental method to determine the ventilation efficiency of the air supplied to the target room. In this report (Part 3), we show the procedure for age of air measurement using dynamic steady-state concentration. We confirmed in laboratory experiments that the dynamic steady-state concentration obtained when data collection is performed at an appropriate timing is equivalent to the age of air of the corresponding open-air system. Furthermore, a method for calculating the age of air distribution for multiple air recirculation systems is presented. Experimental verification and CFD analysis of the age of air distribution of the air supplied from two multi-split building air conditioners were performed in a real space where multiple multi-split building air conditioners are in operation. As a result, we confirmed that accurate age of air measurement is possible if data are collected at a timing of 1.0 to 1.5 times the nominal time constant associated to recirculating air flow rate. Furthermore, accurate age of air measurement is possible by manipulating the observed age of air distribution of each air recirculation system when performing age of air measurement for multiple air recirculating systems in real spaces.

This study applies the concept of dynamic steady-state concentration to air recirculating system in order to develop a tracer gas method to experimentally determine ventilation efficiency. The air recirculating system treats exhaust and return air from a room before resupplying it. To build on the previous paper (part 1), this paper (part 2) presents a method for calculating the age of air distribution using the dynamic steady-state concentration in the air recirculating system. Additionally, we confirmed the principle of age of air measurement and performed CFD analysis to investigate the appropriate timing for sampling. Results indicate that the age of air distribution determined by the dynamic steady-state concentration in an air recirculating system coincides with the age of air distribution in an open-air system. As time passes from the start of measurement, the age of air in open-air systems, which are influenced by the spatial uniform generation of the passive scalar, tend to deviate from the distribution of air recirculating systems. This is especially true if there is an air infiltration port in the vicinity. Results show it is possible to measure the age of air with high accuracy if concentration data sampling is performed at the correct time. Sampling should occur at 1.0-1.5 times the nominal time constant, which considers recirculating airflow rate and room volume without immediate vicinity of an air infiltration port. To determine age of air in interior spaces, concentration data sampling is permitted at several times the nominal time constant from the start of measurement.

In an open air system where outside air is supplied and room air is exhausted, methods to measure the age of air distribution using tracer gas have been established. However, in air recirculating systems where exhausted air is re-supplied back into the room, no tracer gas technique for evaluating fresh air distribution effectiveness and contaminated air removal efficiency has been developed. Here, we carried out a theoretical study on the tracer gas experimental method for measuring the age of air distribution in an air recirculating system by applying the concept of dynamic steady-state concentration. Furthermore, in order to determine key issues faced when applying this theoretical method to perform accurate measurements of the ventilation efficiency of air recirculating systems, case studies were carried out using CFD. In this paper, we theoretically considered the relationship between the concept of dynamic steady-state concentration in the air recirculation system and the age of air distribution and studied the effect of leakage when measuring the age of air distribution in an actual space. When the source was located in contact with the supply outlet, the concentration increase rate at each point in the air recirculation system without air leakage was constant, which was consistent with the increase rate of the average concentration. On the other hand, the ratio of the concentration increase rate at each point to the average concentration increase rate when there was air leakage became constant after 2 to 3 times the nominal time constant of the recirculating ventilation rate to the room volume. The results confirmed that the smaller the leakage is, the closer the value of the rate at each point is to 1.

The purpose of this study is to examine the feasibility of radiant heating & cooling system by means of field measurements and computational fluid dynamics (CFD) simulations coupled with convection and radiation. Radiant panels can be operated below the dewpoint temperature and can remove humidity from the air by condensation. It is necessary to model the radiant panel in the shape of actual use to understand the thermal characteristics of the radiant panel. In the first step of this study, the indoor thermal environment of the real scale space, which is air-conditioned by radiant heating system, is analyzed by field measurement and CFD. With comparing the both results, the validity of the CFD method is examined from the practical point of view. In case of the multi panel model, the influence of convection is greater. The radiant panel of actual use is not real “Radiant Panel” because ASHRAE named it which radiant heat transfer rate of the overall heat transfer rate is more than 50%.