Hirofumi Arima

An analytical solution for two-dimensional inverse heat conduction problems using Laplace transform

Abstract An analytical method has been developed for two-dimensional inverse heat conduction problems by using the Laplace transform technique. The inverse solutions are obtained under two simple boundary conditions in a finite rectangular body, with one and two unknowns, respectively. The method first approximates the temperature changes measured in the body with a half polynomial power series of time and Fourier series of eigenfunction. The expressions for the surface temperature and heat flux are explicitly obtained in a form of power series of time and Fourier series. The verifications for two representative testing cases have shown that the predicted surface temperature distribution is in good agreement with the prescribed surface condition, as well as the surface heat flux.

Estimation of Surface Temperature and Heat Flux Using Inverse Solution for One-Dimensional Heat Conduction

An analytical method has been developed for the inverse heat conduction problem using the Laplace transform technique when the temperatures are known at two positions within a finite body. On the basis of these known temperatures, a closed form to the inverse solution can be obtained to predict surface conditions. The method first approximates the measured temperatures with a half polynomial power series of time as well as a time lag, which takes for a monitor to sense the temperature change at the point. The expressions for the surface temperature and the surface heat flux are explicitly obtained in the form of the power series of time

Performance Analysis of the Low-Temperature Solar-Boosted Power Generation System—Part I: Comparison Between Kalina Solar System and Rankine Solar System

On the base of the two classical thermodynamic cycles (Kalina cycle and Rankine cycle), solar-boosted Kalina system (Kalina solar system) and solar-boosted Rankine system (Rankine solar system) with traditional nonconcentrating flat plate solar collector (FPSC) and evacuated tube solar collector (ETSC) are investigated in the present paper. The proposed solar systems are considered to be the hybrid of power generation subcycle and solar collector subcycle. Their electricity generating performances are compared under their respective optimal operating conditions to clarify which one is more competitive in solar utilization. Results show that ETSC is the better choice for the both solar systems. Further, the performance comparison shows that the low-temperature solar energy utilized in Kalina cycle is predominant to generate electricity. Meanwhile, the study also find that mass flow rate of the power generation subcycle, mass flow rate of the solar collector subcycle, mass fraction of ammonia and the regenerator performance are important operational parameters for high performance of the Kalina solar system. Finally, with the aid of the weather conditions of Kumejima Island in Japan, the perceptual knowledge for Kalina solar system by using an application case is shown in the paper.

Performance Analysis of the Low Temperature Solar-Boosted Power Generation System—Part II: Thermodynamic Characteristics of the Kalina Solar System

In part I of the current work, by quantitative analysis, Kalina solar system using traditional nonconcentrating evacuated tube solar collector (ETSC) with certain solar heat transfer rate is proposed as an optimal choice for its superior thermodynamic performance to generate electricity from low temperature solar energy. To better understand and utilize solar energy in Kalina cycle more efficiently, a thermodynamic qualitative analysis of the solar system is carried on in this part. Many thermodynamical parameters are investigated. Results show that the system pressure difference is one key factor for evaluating the power generation subcycle thermal efficiency, which is an important performance benchmark. Thus, through the instrumentality of simulation results, its corresponding relational expressions are developed by using fitting method. Further, a generalized estimating equation using to estimate generating capacity of the solar system is built. It is shown that when the Kalina solar system is designed and completed, its generating capacity can be estimated by using this equation. And then, a case study of Kalina solar system with 10,000 m2 ETSC is given with the aid of the weather conditions of Kumejima Island in Japan. In this case, its maximum annual power generation is estimated as 931,124 kW h, which is an ideal goal. Herefrom, the corresponding control strategies are proposed for approaching this target. Finally, thermodynamic characteristics of the low temperature Kalina solar system are clarified.

Visualization of FC-72 Flow Boiling in Parallel- and Counter-Flow Plate Heat Exchangers

This study investigates FC-72 (Perfluorohexane) flow boiling in a plate heat exchanger. A plate heat exchanger which has a transparent cover plate is manufactured to visualize boiling two-phase flow pattern of the working fluid FC-72 heated by hot water. Titanium is used for heat transfer plate, which has micro pin-fin structure on the heat transfer surface to enhance heat transfer. Experiment is conducted for parallel- and counter-flow arrangements to compare thermal and hydraulic performances. Flow boiling is photographed by a digital camera and instantaneous images are processed to classify flow pattern and to measure void fraction in the heat exchanger. Flow rates and temperatures of FC-72 and hot water at inlet and outlet of the heat exchanger are simultaneously measured to obtain overall heat transfer coefficient. Two-phase flow pattern of FC-72 flow boiling and void fraction along flow direction as well as thermal performance are discussed. Experimental results show that bubbly flow, slug flow, and churn flow are observed for the experimental range of this study. Extent of churn flow in the parallel-flow heat exchanger is larger than that of the counter-flow one due to generated bubbles at upstream region in working fluid channel. Void fraction of the parallel-flow plate heat exchanger increases rapidly compared with that of the counter-flow one due to location of onset of nucleate boiling. Overall heat transfer coefficients for the parallel-flow arrangement is larger than that of the counter-flow due to destruction of thermal boundary layer. The experimental results show that flow arrangement of a plate heat exchanger has the potential to improve its thermal performance.Copyright

Effect of Channel Geometry on Ammonia Boiling Heat Transfer of a Plate-Type Evaporator

The ocean thermal energy conversion (OTEC) is attracted attention as one of the promising renewable energy. OTEC uses small temperature difference between surface and deep sea water. Plate-type heat exchangers, or evaporators, are usually used for OTEC to obtain vapor for electric generator. Ammonia is used for OTEC as a working fluid. It is important to improve thermal performance of an evaporator for the OTEC. Channel dimension is one of the important factors to improve heat transfer performance of an evaporator. In this study, the measurement and comparison of local heat transfer coefficient for three channels are experimentally performed. The experiments are conducted for a range of mass flux (5 and 7.5 kg/m2s), heat flux (10 to 25 kW/m2), and pressure (0.7 and 0.9 MPa). The results show that the heat transfer coefficient increases as decreases channel height. The modified emprical correlation for a plate-type evaporator is proposed.Copyright

Availability of a high polymer resin coating aluminum to the plate heat exchanger for ocean thermal energy conversion plant using ammonia as working fluid

Ocean thermal energy conversion(OTEC)has attracted attention as a technique to obtain renewable energy. OTEC systems usually use a plate heat exchanger and ammonia as a working fluid. The materials used for manufacturing the heat exchanger are generally “titanium” or “stainless steel” of which contact surface should not be corroded with ammonia. However, the thermal conductivity of these materials is very low. Consequently, the heat transfer performance of the heat exchanger deteriorates. Therefore, the author proposed an advanced plate heat exchanger material with high thermal conductivity for OTEC systems. This plate is made of an aluminum alloy and the surface is coated with a special high polymer material(PEEKTM polymer), which has high ammonia resistance. In this study, two tolerance experiments were performed using the advanced plate at different coating thicknesses of 300 and 20 μm for approximately one month. These experiments were(1)immersion of the plate in a pressure tank containing liquid ammonia and(2)exposure of the plate in the path of a forced convective flow of liquid ammonia. As a result, although the PEEK coating aluminum plate surface deteriorated slightly, it is found that the base of the plate has not influenced by the ammonia. (Received August 24, 2012 Accepted January 18, 2013)

Convective Boiling Heat Transfer Enhancement by Microgrooves in Plate Evaporator

In this experimental study, we investigate the enhancement of heat transfer in ammonia on a new plate evaporator whose surface is configured with microgrooves. The microgrooves have a depth of 30 μm and a width of 200 μm. The local boiling heat transfer coefficients were measured on the evaporator. To compare the heat transfer characteristics of the evaporator, the local boiling heat transfer coefficient on a flat surface and on two microgrooved surfaces—one vertical and one horizontal to the direction of the ammonia flow—were measured at different ranges of mass flux (2–7.5 kg/m2 s), heat flux (10–20 kW/m2 ), and saturation pressure (0.7–0.9 MPa). The results show that the local boiling heat transfer coefficient of the horizontal and vertical microgrooved surfaces was larger than that of a flat surface. In particular, the horizontal microgrooved surface had the best heat transfer coefficient.© 2011 ASME

Experiments on Flow Boiling Heat Transfer of Ammonia/Water Mixture Inside an Internally Spirally Grooved Horizontal Tube

Experiments were performed on the flow boiling of the zeotropic mixture of water-ammonia inside an internally spirally grooved horizontal steel tube with a 12mm average inner diameter. The experimental conditions were the mass fraction of ammonia: 0.95, 1.0 kg/kg, the mass velocity: 40 to 80 kg/(m2 s), the heat flux: 0 to 20 kW/m2 and the pressure: 0.7 MPa. The measured heat transfer coefficient reached its maximum as the quality approached about 0.6 but decreased abruptly as the quality increased. This sharp decrease as the quality increased beyond 0.6 may have been caused by mass diffusion resistance that increased the temperature locally at the vapor-liquid interface. The temperature increase at the vapor-liquid interface is discussed by analyzing the phase equilibrium characteristics and is explained in terms of the relationship between the bulk temperature and vapor quality. The heat transfer coefficients are also compared with those for pure ammonia.Copyright