• Tribology and Lubricants
• /
• 제23권1호
• /
• pp.1-8
• /
• 2007

Turbocharger bearings are under the circumstance of high temperature, moreover rotated at high speed. It is necessary to be designed to overcome the high temperature. So the type of oil inlet port, the inlet oil temperature and the sort of engine oil should be designed, controlled and selected carefully in order to reduce the bearing inside temperature. Therefore, in this study, the effects of the type of inlet oil port, inlet temperature and the sort of engine oil on the performance of a turbocharger bearing are to be investigated. It is found that the type of oil inlet ports, the control of inlet oil temperature and the selection of engine oil type play important roles in determining the temperature and pressure, then the friction and load of a turbocharger journal bearing at high speed operation.

• International Journal of Air-Conditioning and Refrigeration
• /
• 제6권
• /
• pp.14-26
• /
• 1998

This paper deals with approximate analytical solutions for the two-region one-dimensional model describing the charging process of stratified thermal storage tanks at variable inlet temperature with momentum-induced mixing. An arbitrarily increasing inlet temperature is decomposed into inherent step changes and intervals of continuous change. Each continuous interval is approximated as a finite number of piecewise linear functions, which admits an analytical solution for perfectly mixed region. Using the Laplace transform, the temperature profiles in plug flow region with both the semi-infinite and adiabatic ends are successfully derived in terms of well-defined functions. The effect of end condition on the solution proves to be negligible under the practical operating conditions. For a Quadratic variation of inlet temperature, the approximate solution employing a moderate number of pieces agrees excellently with the exact solution.

• 설비공학논문집
• /
• 제9권1호
• /
• pp.43-54
• /
• 1997

This paper presents an approximate analytical solution to a two-region one-dimensional model for the charging process of stratified thermal storage tanks with variable inlet temperature in the presence of momentum-induced mixing. Based on the superposition principle, an arbitrary-varying inlet temperature is decomposed into inherent discontinuous steps and continuous intervals approximated as a finite number of piecewise linear functions. This approximation allows the temperature of the upper perfectly-mixed layer to be expressed in terms of constant, linear and exponential functions with respect to time. Applying the Laplace transform technique to the model equation for the lower thermocline layer subject to each of three representative interfacial conditions yields compact-form solutions, a linear combination of which constitutes the final temperature profile. A systematic method for deriving solutions to the plug-flow problem having polynomial-type boundary conditions is also established. The effect of adiabatic exit boundary on solution behaviors proves to be negligible under the actual working conditions, which justifies the assumption of semi-infinite domain introduced in the solution procedure. Finally, the approximate solution is validated by comparing it with an exact solution obtained for a specific variation of inlet temperature. Excellent agreements between them suffice to show the necessity and utility of this work.

• 대한기계학회논문집
• /
• 제14권2호
• /
• pp.422-429
• /
• 1990

The experimental study investigates two aspects of counterflow sensible heat regenerator operation. First, it examines the regenerator performance in periodic steady state operation with spatially nonuniform inlet temperature in one of the fluid stream. Second, the study examines the transient response of a regenerator to a step change in the inlet temperature of one of the fluid streams. The effect of transient inlet temperatures is analyzed in terms of the response of the outlet fluid temperatures to a step change in temperature of one of the inlet fluid streams. The effect of temperature nonuniformities is analyzed in terms of the change of temperature nonuniformities is analyzed in terms of the change in steady state effectiveness due to a circumferential temperature distribution in one of the inlet fluid streams. an experimental analysis has been conducted using a counterflow, parallel passage, and rotary regenerator made from polyethylene film. Efficiencies follow similar trends with increasing matrix to fluid capacity rate ratio for the balanced and symmetric regenerator with nonuniform inlet temperature.

• 설비공학논문집
• /
• 제25권8호
• /
• pp.443-449
• /
• 2013

The purpose of this study is to propose an enhanced variable-speed control method of ground-water circulation pumps using inlet and outlet ground-water temperature difference and analyze its effect for the ground source multi-heat pump system installed in a single-family house. As a result, it has shown to significantly reduce the electricity use of ground-water circulation pump and improve overall system Coefficient of Performance (COP) due to the proposed variable-speed control under partial load conditions after oversized and inefficient single-speed pump retrofit.

• Nuclear Engineering and Technology
• /
• 제55권8호
• /
• pp.2812-2822
• /
• 2023

The supercritical carbon dioxide (sCO₂) Brayton power cycle is more effective than the conventional power cycle and is more widely applicable to heat sources. The inlet working conditions of the compressor have a higher influence on their operating performance because the thermophysical properties of the CO₂ vary dramatically close to the critical point. The flow in the sCO₂ compressor is simulated and the compressor performance is analyzed. The results show that the sCO₂ centrifugal compressor operates outside of its intended parameters due to the change in inlet temperature. The sCO₂ compressor requires more power as the inlet temperature increases. The compressor power is 582 kW when the inlet temperature is at 304 K. But the power is doubled when the inlet temperature increases to 314 K, and the change in the isentropic efficiency is within 5%. The increase in the inlet temperature significantly reduces the risk of condensation in centrifugal compressors. When the heat load of the sCO₂ power system changes, the inlet pressure to the turbine can be kept constant by regulating the rotational speed of compressors. With the increase in rotational speed, the incidence loss and condensation risk increase.

• 태양에너지
• /
• 제15권2호
• /
• pp.25-37
• /
• 1995

유입관성에 의한 유체혼합뿐 아니라 입구온도의 변화까지 고려된 성층축열조의 충전과정 모델에 대하여 해석적 근사해를 제시하였다. 해석모델은 깊이가 일정한 완전혼합 및 압출유동영역으로 구성되며, 입구온도의 변화는 중첩의 원리에 근거하여 계단함수로 근사화하였다. 완전혼합영역의 과도온도를 구한 후 함수형태에 따라 구분하고, 각각을 경계조건으로 하는 압출유동영역의 온도분포를 잘 정의된 함수의 항으로 유도하였다. 결과적으로 이들의 일차결합이 압출유동영역에 대한 최종해이다. 근사해의 타당성 및 결과의 유용성은 입구온도가 선형적으로 증가하는 경우에 대한 엄밀해와의 비교를 통하여 검증하였다. 계단수의 증가에 따라 근사해는 엄밀해로 급속히 접근하며, 유한한 수의 계단에 의한 근사해도 광범위한 혼합깊이에 대하여 엄밀해와 잘 일치한다. 또한, 혼합깊이가 클수록 소수의 계단에 의한 근사해로도 의미있는 예측결과를 얻을 수 있었다.

• 유체기계공업학회:학술대회논문집
• /
• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
• /
• pp.80-87
• /
• 2003

Micro gas turbines are designed with low turbine inlet temperature and pressure ratio. To overcome the efficiency defect of the simple cycle, adoption of the recuperator is an inevitable choice. In addition to the design performance, we should also pay attention to the off-design performance of gas turbines since they usually operate at part-load conditions for a considerable amount of the time. This study aims at analyzing off-design performance characteristics of micro gas turbines and addressing the importance of the recuperator in the part load operation. Comparative analyses have been performed to evaluate the part load performance differences among various design and operating options : simple vs recuperative cycles, single vs two shaft configurations, various operating strategies for the single shaft configuration (fuel only control, variable speed operation, variable inlet guide vane control), and current vs advanced engines. Major finding is that maintaining turbine at high level is crucial in efficient operation of micro gas turbines.

• 오토저널
• /
• 제7권1호
• /
• pp.24-34
• /
• 1985

The study of unsteady gas exchange processes in the inlet and exhaust systems of the single-cylinder 4-stroke cycle spark ignition engine is presented in this paper. The generalized method of characteristics including friction, heat transfer, change of flow area and entropy gradients was used for solving the equations defining the gas exchange process. The path line calculation was also conducted to allow for calculation of the gas composition and entropy change along the path lines, and of the variable specific heat due to the change of temperature and composition. As the result of the simulation, the properties at each point in the inlet and exhaust pipe, pressure and temperature in the cylinder, and charging efficiency were obtained. Pumping loss and residual gas fraction were also computed. The effect of engine speed, exhaust and inlet pipe length on the pumping loss and charging efficiency were studied showing that the results were in agreement with what has been known from experiments.

• 동력기계공학회지
• /
• 제6권4호
• /
• pp.16-22
• /
• 2002

This study was conducted to find performance evaluation method for automobile air conditioner. Experimental facilities were constructed to simulate wide range of operating condition for the automobile air conditioner. Compressor speed was controled by variable speed electric motor and the power was measured through torque transducer and tachometer was used to measure compressor speed. Parametric studies were conducted in this study, to figure out effect of environment variables on the performance of the automobile air conditioner. The environmental variables are inlet air temperature, relative humidity and air flow rate for the evaporator and inlet air temperature and air flow rate for the condenser. Compressor speed is also changed. The results of this study shows that air flow rate of the evaporator is more sensitive to the performance of the automobile air conditioner than the other variables. However relative humidity of the inlet air of the evaporator strongly affects capacity rather that COP.