Eiji Hihara / Professor / Division of Environmental Studies
Department of Human and Engineered Environmental Studies / / Energy Environment

Career Summary
1982: Lecturer, University of Tokyo
1983: Associate Professor, University of Tokyo
1993-1994: Visiting Scholar, University of California, Berkeley
1999-Present: Professor, University of Tokyo
Educational Activities
Graduate School: Advanced Lecture on Environmental Energy Systems
Undergraduate School: Thermal Engineering Level 1, Environmental Energy Systems, Environmental and Energy Strategy
Research Activities
Human beings consume considerable resources to maintain a comfortable lifestyle. As a result, we currently face serious environmental problems that affect us all, including a diminishing ozone layer, increasingly widespread environmental endocrine disruptors, and global warming, all of which are approaching crisis levels. To resolve these problems, our society must replace its cycle of mass production, mass consumption, and mass disposal with a form of resource utilization that is more environmentally benign. Sustainable development can be achieved by cultivating a society that employs recycling and incorporates efficient use of energy and resources into its daily activities. Our research focuses on the apparent compromise between environmental impact and maintenance of a comfortable lifestyle.
(a) Low-GWP refrigerants for heat pump applications
A quarter of Japanfs primary energy is consumed in the residential and commercial sectors. About half of this energy is consumed for heating and cooling. HFCs, which have been used as working fluids for heating and cooling equipment, are regulated as greenhouse gases. Demand for protection against global warming has resulted in development of new low-GWP refrigerants. However, their spread is limited by the fact that low-GWP refrigerants are chemically unstable and have mildly flammable properties. We are conducting research into the following topics regarding safe use of mildly flammable refrigerants:
- Thermophysical properties of low-GWP refrigerants
- Thermal stability of mildly flammable refrigerants
- Diesel combustion of refrigerant and lubricating oil mixtures
(b) Effective use of solar energy
Solar energy, including solar power and solar thermal utilization, is a highly promising form of renewable energy. However, further cost reduction is required for self-reliant spread. We are developing a new solar power system that produces electricity and heat at the same time, and an air conditioning system that uses solar heat.
- Solar heating, cooking and power combination systems
- Solar cooling systems
(c) Air conditioning systems with separately processed latent and sensible heat
The purpose of an air conditioner is to adjust room temperature and humidity to comfortable levels. Because current air conditioners control both temperature and humidity at the same time, there is a limit to their adjustment capability, which results in low energy efficiency. In this study, we are investigating new air conditioning methods by separating the adjustment processes for temperature and humidity.
- Adsorption and desorption performance of desiccant material
- Hybrid heat pump/desiccant air conditioning systems
(d) Compact heat exchangers with mini- and microchannels
An effective method for developing highly efficient and small-sized heat exchangers is reduction of the heat transfer tubesf diameter. Microchannel heat exchangers offer good heat transfer performance and low pressure drop characteristics. The optimum design for microchannel heat exchangers is investigated through experimentation and CFD simulation.
- Cooling heat transfer of carbon dioxide in small diameter tubes
- Boiling and Condensation heat transfer of low-GWP refrigerants in mini-channels
- Flow boiling heat transfer coefficient and pressure drop in multiport extruded tubes

Solar heating, cooking and power combination system
Solar heating, cooking and power combination system

1) Tanaka, Dang, Hihara: Characteristics of flow boiling heat transfer in rectangular minichannels, 2014 Internal Heat Transfer Conference, Kyoto, (2014).
2) Kamiaka, Dang, Hihara: Vapor-liquid equilibrium measurements for binary mixtures of R1234yf with R32, R125 and R134a, Int. J. Refrigeration, 36-3, (2013), 965-971.
3) Wang, Dang, Hihara: Experimental study on condensation heat transfer of low GWP refrigerant HFO-1234yf in a horizontal tube, Int. J. Refrigeration, 35-5, (2012), 1418-1429.
4) Zhang, Hihara, Matsuoka, Dang: Experimental analysis of mass transfer in adiabatic structured packing dehumidifier/regenerator with liquid desiccant, Int. J. Heat Mass Transfer, 53, (2010), 2856-2863.
5) Dang, Haraguchi, Hihara: Flow boiling heat transfer of carbon dioxide inside a small-sized microfin tube, Int. J. Refrigeration, 33-4, (2010), 655-663.

Other Activities
Japan Society of Mechanical Engineers (JSME)
Heat Transfer Society of Japan (HTSJ)
Society of Heating, Air-Conditioning and Sanitary Engineers of Japan (SHASE)
Japan Society of Refrigerating and Air Conditioning Engineers (JSRAE)
American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)
Future Plan
To combat global warming, reduction of energy consumption in the consumer sector is vital. It is important to introduce the optimal-mixed-energy systems to the consumer sector and to encourage the spread of highly efficient air-conditioning systems. We would like to resolve environmental and energy problems through the establishment of energy systems that are optimally mixed and the development of fundamental technologies for use in innovative air conditioning systems.
Messages to Students
We conduct extensive research on technologies for reasonable supply and efficient use of energy. It is important to create a comfortable living environment using technologies with a small environmental impact. We hope to conduct the research that society needs, using a variety of research methods and collaborating with students from diverse backgrounds.