Bin-Juine Huang

A 1-D analysis of ejector performance

A 1-D analysis for the prediction of ejector performance at critical-mode operation is carried out in the present study. Constant-pressure mixing is assumed to occur inside the constant-area section of the ejector and the entrained flow at choking condition is analyzed. We also carried out an experiment using 11 ejectors and R141b as the working fluid to verify the analytical results. The test results are used to determine the coefficients, h p, h s, f p and f m defined in the 1-D model by matching the test data with the analytical results. It is shown that the1-D analysis using the empirical coefficients can accurately predict the performance of the ejectors. q 1999 Elsevier Science Ltd and IIR. All rights reserved.

Empirical correlation for ejector design

In the present study, two empirical correlations from the test results of 15 ejectors are derived for the performance prediction of ejectors using R141b as the working fluid. The ratio of the hypothetical throat area of the entrained flow to the nozzle throat area Ae/At, the geometric design parameter of the ejector A3/At, and the pressure ratios Pg/Pe and Pc*/Pe are used to correlate the performance of the ejector. The prediction of the entrainment ratio v using the correlations is within ^ 10% error. A method of calculation for the ejector design using the correlations is also developed. R141b is shown in the present study to be a good working fluid for an ejector. The measured v for the ejectors used in the present study can reach as high as 0.54 at Pga 0.465 MPa (848C), Pc*a 0.087 MPa (288C) and Pea 0.040 MPa (88C). For Pga 0.538 MPa (908C), Pc*a 0.101 MPa (328C) and Pea 0.040 MPa (88C), v reaches 0.45. q 1999 Elsevier Science Ltd and IIR. All rights reserved.

Performance analysis of a solar-assisted heat pump water heater

Abstract A modeling and system simulation of an integral-type solar assisted heat pump water heater (ISAHP) was carried out in the present study. The modeling and simulation assumes a quasi-steady process for all the components in the ISAHP except the storage tank. The simulation results for instantaneous performance agreed very well with experiment. The simulation technique was used to analyze the daily performance of an ISAHP for 1 year. It is shown that the daily total COP (COP o ) is around 1.7 to 2.5 year around for the ISAHP, depending on seasons and weather conditions. COP o is higher than 2.0 for most of the time in a year and the daily operating time varies from 4 to 8 h. The online adjustment requirement of the expansion valve was also investigated using the present simulation technique. The analysis shows that the expansion device does not need to be controlled online. Using the 1-year simulation results, a universal daily performance correlation of the ISAHP was derived and shown experimentally to be applicable to another design of ISAHP.

System dynamic model and temperature control of a thermoelectric cooler

A linear dynamic model of the thermoelectric cooler including the heat sink and the cooling-load heat exchanger was derived using small-signal linearization method. It shows that the dynamic model of a thermoelectric cooler has two poles and one zero. The linear dynamic model is shown to vary with operating conditions. A linear feedback system is designed for the cold-end temperature control of a thermoelectric cooler using the average linear dynamic model of the thermoelectric cooler and a PDF controller structure. The step response tests show that the controller has a very satisfactory performance. Some tests under variable cooling load and ambient temperature are also performed to examine the disturbance-rejection property of the controller. Experimental results show that the cold-end temperature can be maintained at the fixed value within a0.1C irrespective of the variations of the cooling load and the ambient conditions. # 2000 Elsevier Science Ltd and IIR. All rights reserved.

Similarity theory of solar water heater with natural circulation

Abstract The similarity theory of solar thermosyphon collector is developed in the present paper. Ten dimension-less groups or system characteristic parameters which uniquely determine the performance of the collector are derived. The solution shows that the mean efficiency generally increases with increasing incident solar radiation and relative height of the tank. For the frictional parameters Ne and Nf higher than 105, the efficiency appears to be independent of the incident radiation and the relative height of the tank. Therefore, for parallel plate absorber, the tank may be designed to sit on the floor without sacrificing the efficiency since the values of Ne and Nf are usually larger than 105 in most designs.

Integral-type solar-assisted heat pump water heater

An integral-type solar-assisted heat pump water heater (ISAHP) is designed and tested in the present study. The storage tank and the Rankine cycle unit are integrated together to make a more compact size. A thermosyphon loop is used to transfer the heat from the condenser to the water storage tank. The highest COP obtained in the tests is 3.83.

A simulation method for solar thermosyphon collector

Abstract A simplified simulation method for solar thermosyphon collectors was developed in the present study. The development utilized Hottel-Bliss-Whillier theory for absorber, Closes model for thermally stratified tank, and a newly defined loop resistance relation. It was found that the time step required in numerical computation can be expanded to 15 min with good accuracy, compared to other methods for which the time step is between 1 and 40 s. To verify this, experiments in single-day and long-term scales were made outdoors for different operating conditions. All the experimental results are shown to give very good agreement with the simulation.

Multivariable Robust Control for a Red–Green–Blue LED Lighting System

This paper proposes a novel control structure for a red-green-blue (RGB) LED lighting system, and applies multivariable robust control techniques to regulate the color and luminous intensity outputs. RGB LED is the next-generational illuminant for general lighting or liquid crystal display backlighting. The most important feature for a polychromatic illuminant is color adjustability; however, for lighting applications using RGB LEDs, color is sensitive to temperature variations. Therefore, suitable control techniques are required to stabilize both luminous intensity and chromaticity coordinates. In this paper, a robust control system was proposed for achieving luminous intensity and color consistency for RGB LED lighting in a three-step process. First, a multivariable electrical-thermal model was used to obtain RGB LED luminous intensity, in which a lookup table served as a feedforward compensator for temperature and power variations. Second, robust control algorithms were applied for feedback control design. Finally, the designed robust controllers were implemented to control the luminous and chromatic outputs of the system. From the experimental results, the proposed multivariable robust control was deemed effective in providing steady luminous intensity and color for RGB LED lighting.

PERFORMANCE RATING METHOD OF THERMOSYPHON SOLAR WATER HEATERS

Abstract A rating method for the thermal performance of thermosyphon solar water heaters was developed. Except that the outdoor test procedure still follows the Taiwan Standard CNS B7277, a system characteristic efficiency η s ∗ which is defined as the α0 value corrected at M A c = 75 kg/m 2 , was derived so that η s ∗ is independent of the M A c ratio. Here, η s ∗ can be evaluated by linear regression analysis of the test data. It is found from a series of tests for 31 systems that η s ∗ is independent of M A c indeed, and thus can be used to rate the thermal performance of different thermosyphon solar water heaters during the energy-collecting period. The cooling loss during the no-radiation period is rated by the system cooling time constant τc. The present rating method associated with the Taiwan Standard CNS B7277 has been implemented for more than three years and is accepted by the Taiwan solar industry.

Charaterizing LEDs for Mixture of Colored LED light sources

Because of advantages such as long lifetime, low power consumption, and no mercury containing, LEDs are widely used in a variety of general-purpose illumination applications. There are two different approaches for generating white light with LEDs. The first one is the combination of phosphors excited by blue or UV LED emission, the other one is mixture of multi-color LEDs Without the power loss in the down conversion process of the white LED using phosphors, a higher efficiency and flexible option can be done with the mixture of multi-color LEDs. Questions arise on how the spectra of the mixture of colored LED designed are for good color rendering performance, more output lumens and better luminous efficiency. A lot of papers discuss the different spectrum combinations of multicolored LEDs which yield light with maximum efficacy, luminous flux and CRI, at the desired corrected color temperature, but most of them use the spectral power distribution of a model LED to calculate the luminous efficacy, luminous flux and CRI, and get the best combination as request. But as most people know, the spectral power distribution of a real LED will vary with ambient temperature, forward current and effect of aging, so simulation of the luminous efficacy, luminous flux and CRI will get some problems in practical. On the other hand, the finding of a better luminous efficacy of the mixture of colored LED can provide the best suggestion when the LED manufacturers try to select commercial LED chips to manufacture colored LED light sources. We setup a system with integrating sphere, spectrometer and four independent PC controlled powermeters, which can get the data of luminous flux, CRI and luminous efficiency of light sources automatically with different input power. Using the database from the system and simulations, we can analyze the optical and color characteristics of the mixture of colored LED light source, even the RGB LED (red, green and blue chips in one package). Then the selection of the combination of the LED chips for the mixture of colored LED light source, for generating more luminous flux, better color rendering index and luminous efficiency should be good.