Huiming Zou

INTEGRATED STEADY-STATE AND DYNAMIC SIMULATION OF MULTI-UNIT AIR CONDITIONERS BASED ON TWO-PHASE FLUID NETWORK MODEL

An integrated simulation model is developed to investigate the steady-state and dynamic performance of multi-unit air conditioners (MUACs). It is built as two-phase fluid network which is able to describe different systems by incidence matrixes. And the submodels are embedded in the system framework, where the submodels can be either steady-state or dynamic model, distributed parameter or lumped parameter model. For this case, the numerical submodels are employed with moving-boundary models of condenser and evaporator, steady-state models of compressor and electronic expansion valve. The comparison with experimental data shows that it cannot only predict the steady-state performance, but also catch dynamic trends with high accuracy, for example, the differences of evaporating pressure < ± 4%, condensing pressure < ± 3%, compressor discharge temperature < ± 4°C, superheating degree < ± 2°C and subcooling degree < ± 1°C. Therefore, the simulation model is confirmed as an effective tool to analyze the steady and transient characteristics and optimize the design and control algorithm of MUACs.

Stroke and natural frequency estimation for linear compressor using phasor algorithm

The stroke and natural frequency are key controlling quantities for linear compressor controller. This paper proposes a phasor algorithm for the linear compress stroke and natural frequency calculation. The phasor algorithm employs vectors to express the voltage, current and velocity respectively for the calculation in frequency domain. A test bench has been installed, and the feasibility of phasor algorithm is verified with the linear compressor load changing. The relative deviation of the calculated stroke can be achieved within ± 3% compared to the experimental results at 0.4 MPa, 0.5 MPa and 0.6 MPa discharge pressure respectively. The calculated results shows that the computation time of phasor algorithm is one-third shorter than that of time domain algorithm, which means it is possible to employ relatively low energy consumption and low cost hard ware. The calculation natural frequency decreases with the stroke increases at 0.4 MPa, 0.5 MPa and 0.6 MPa discharge pressure respectively, and the tested motor efficiency reaches a maximum when the calculated natural frequency equals to the operating frequency.

Efficiency measurement of linear oscillation motor with gas load

Linear oscillation motor (LOM) is the key assembly for a linear compressor, and its efficiency has great impact on the integral compressor performance. This paper presents a novel gas load method to measure the efficiency of LOM, analyses the effects of some main factors on the LOM efficiency in theory, and shows the efficiency test results. Different load conditions can be simulated by adjusting the discharge pressure of the gas and the load force presents nonlinear periodical curve. In the experiment, we changed the syntonic springs of the tested LOM to measure the LOM efficiency on different work conditions. The results of both theoretical analysis and experiment show that the LOM efficiency is the highest when the phase angle between current and displacement is 90◦. While the springs stiffness coefficient is 54.44N/mm, the highest efficiency of the tested LOM is 85.97% on the condition that the discharge pressure is 0.25MPa. While the springs stiffness coefficient is 44.64N/mm the highest efficiency of the tested LOM is 84.67% on the condition that the discharge pressure is 0.4MPa. While the springs stiffness coefficient is 38.4N/mm the highest efficiency of the tested LOM is 78.35% on the condition that the discharge pressure is 0.5MPa.

Experimental investigation on electromagnetic transduction characteristic of linear oscillation electrical machine

The electromagnetic transduction coefficient has a strong influence on efficiency as well as the sensorless control of linear oscillation electrical machine (LOEM). This paper presents a reciprocal LOEM method for measurement of the electromagnetic transduction coefficient, to investigate the effect of the magnet length on the characteristics of the transduction coefficient. The result shows that the transduction coefficient has two regimes, a constant regime and a nonlinear regime. As the harmonic distortion begins to appear in the induced electromotive force, the electromagnetic transduction coefficient passes from the constant regime to the nonlinear regime, and the corresponding stroke is defined as critical stroke. The range of constant regime equals the observed critical stroke, and the critical stroke is 8.81 mm and 10.78 mm when the length of the permanent magnet is 11 mm and 13 mm respectively. The relationship among the geometrical dimension of yoke and permanent magnet, the critical stroke and the stroke of the LOEM are carefully investigated. Then optimal lengths for both the yoke and the permanent magnet are suggested for the LOEM design with the rated stroke, to achieve the highest efficiency and least material cost simultaneously.

Investigation on the Jump Phenomenon of Linear Compressor

According to the experiments on the linear compressor operating in the refrigeration system, the occurrence conditions and regularity of jump phenomenon is investigated on different working conditions. When jump phenomenon happens, the current, input power, as well as piston stroke jumps upward abruptly. Under the same discharge pressure condition, the higher the power frequency is, the earlier the jump phenomenon will happen. When the power frequency decreases under a certain value, the jump phenomenon will disappear. The lower the discharge pressure is, the wider the power frequency range of jump phenomenon occurrence will be. Through the phase angle analysis, it is discovered that the jump phenomenon occurs not only on the status of mechanical resonance but also on the status of electromagnetic oscillation.