外文资料与中文翻译
外文资料：
Intelligent thermal energy meter controller
Abstract
A microcontroller bad, thermal energy meter cum controller (TEMC) suitable for solar thermal systems has been developed. It monitors solar radiation, ambient temperature,
fluid flow rate, and temperature of fluid at various locations of the system and computes the energy transfer rate. It also controls the operation of the fluid-circulating pump
depending on the temperature difference across the solar collector field. The accuracy
of energy measurement is ±1.5%. The instrument has been tested in a solar water heating
system. Its operation became automatic with savings in electrical energy consumption of
pump by 30% on cloudy days.
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1 Introduction
Solar water heating systems find wide applications in industry to conrve fossil fuel like oil, coal etc. They employ motor driven pumps for circulating water with on-off
卡通歌曲controllers and calls for automatic operation. Reliability and performance of the system depend on the instrumentation and controls employed. Multi-channel temperature recorders, flow meters, thermal energy meters are the esntial instruments for monitoring and
evaluating the performance of the systems. A differential temperature controller (DTC) is required in a solar water heating system for an automatic and efficient operation of
the system. To meet all the requirements, a microcontroller bad instrument was
developed. Shoji Kusui and Tetsuo Nagai [1] developed an electronic heat meter for
measuring thermal energy using thermistors as temperature nsors and turbine flow meter as flow nsor.
2 Instrument details
The block diagram of the microcontroller (Intel 80C31) bad thermal energy meter cum controller is shown in Fig. 1. RTD (PT100, 4-wire) nsors are ud for the temperature
measurement of water at the collector field inlet, outlet and in the tank with appropriate signal conditioners designed with low-drift operational amplifiers. A precision miconductor temperature nsor (LM335) is ud for ambient temperature measurement. A pyranometer, having an output voltage of 8.33 mV/kW/m2, is ud for measuring the incident solar radiation. To monitor the circulating fluid pressure, a nsor with 4–20 mA output is ud. This output is converted into voltage using an I-V converter. All the output
signals are fed to an 8-channel analog multiplexer (CD4051). Its output is fed to a
dual-slope 12-bit A/D converter (ICL7109). It is controlled by the microcontroller through the Programmable Peripheral Interface (PPI-82C55).
Fig. 1. Block diagram of thermal energy meter cum controller.
A flow nsor (turbine type) is ud with a signal conditioner to measure the flow
rate. Its output is fed to the counter input of the microcontroller. It is programmed to
monitor all the multiplexed signals every minute, compute the temperature difference,
energy transfer rate and integrated energy. A real-time clock with MM58167 is interfaced
to the microcontroller to time-stamp the logged data. An analog output (0–2 V) is provided using D/A converter (DAC-08) to plot both the measured and computed parameters. A 4×4 matrix keyboard is interfaced to the microcontroller to enter the parameters like specific
heat of liquid, data log rate etc. An alphanumeric LCD display (24-character) is also
interfaced with the microcontroller to display the measured variables. The rial
communication port of the microcontroller is fed to the rial line driver and receiver
(MAX232). It enables the instrument to interface with the computer for down-loading the
logged data. A battery-backed static memory of 56K bytes is provided to store the measured parameters. Besides data logging, the instrument rves as a DTC. This has been achieved
by interfacing a relay to the PPI. The system software is developed to accept the
differential temperature t points (ΔT on and ΔT off) from the keyboard. An algorithm
suitable for on-off control having two t-points is implemented to control the relays.
3 Instrument calibration
The amount of energy transferred (Q) is :
Where = mass flows rate of liquid kg/s ; V = volumetric flow rate (l/h) ; ρ= density of water (kg/l) ; Cp = specific heat (kJ/kg°C); and ΔT = temperature difference between hot and cold (°C).
The accuracy in energy measurement depends on the measurement accuracy of individual parameters. Temperature measurement accuracy depends on the initial error in the nsor
and the error introduced due to temperature drifts in the signal conditioners and the A/D converter. The temperature nsor is immerd in a constant temperature bath (HAAKE B ath-K, German), who temperature can be var ied in steps of 0.1°C. A mercury glass thermometer (ARNO A MARELL, Germany) with a resolution of 0.05°C is also placed along with PT100 nsor in the bath. This is compared with the instrument readings. The accuracy of the instrument in temperature measurem ent is ±0.1°C. Hence, the accuracy in differential temperature measurement is ±0.2°C.
The flow nsor having a maximum flow rate of 1250 l/h is ud for flow measurement.
It is calibrated by fixing it in the upstream of a pipeline of length 8 m. The nsor output is connected to a digital frequency counter to monitor the number of puls generated with
different flow rates. Water collected at the nsor outlet over a period is ud for
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estimating the flow rate. The K-factor of the nsor is 3975 puls/l. The uncertainty麻辣毛豆
in flow measurement is ±0.25% at 675 l/h. Uncertainties in density and specific heat of
water are ±0.006 kg/l and ±0.011 kJ/kg°C respectively.
Maximum amount of energy collection (Q) = 675×0.98×4.184×15/3600 = 11.53kW. Uncertainty in energy measurement
ωq/Q = [(ωv/V)2 + (ωρ/ρ)2 + (ωcp/Cp)2+(ωt/T )2]1/2.
Inaccuracy in electronic circuitry is ±0.03 kW.
The net inaccuracy in energy measurement is ±1.5%承包经营协议
4 Field test
The instrument is incorporated in a solar water heating system as shown in Fig. 2.
It consists of five solar flat plate collectors having an absorber area of 1.6 m2 each. The absorber is a fin and tube extruded from aluminium and painted with matt black paint. The collectors are mounted on a rigid frame facing south at an angle equal to the latitude of Bangalore (13°N). They are arranged in parallel configuration and connected to a
thermally insulated 500 l capacity storage tank. A 0.25 hp pump is ud for circulating
the water through the collector field. All the pipelines are thermally insulated. The
temperature nsors and the flow nsor are incorporated in the system as shown in Fig.
2. The data on solar radiation, ambient temperature, water flow rate, solar collector inlet and outlet temperatures and the system heat output are monitored at regular intervals.
Fig. 2. Solar water heating system with thermal energy meter cum controller.
The performance of the solar water heating system with TEMC on a partial cloudy day
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is shown in Fig. 3. It is obrved that DTC switched OFF the pump around 14:40 h as there
is no further energy gain by the collector field. This in turn reduced the heat loss苹果怎么看是不是国行
from the collector to ambient. Experiments are conducted with and without DTC o n both sunny and cloudy days. The DTC operated system shows the savings in electrical energy by 30%简笔画彩色
on a partial cloudy day and 8% on a sunny day. The variation in system output with and
without DTC i s around 3%. Thus the controller has not only rved as an energy conrvation device, but also switches ON/OFF the system automatically depending on the availability
of solar radiation. The collector field output (shown in Fig. 3) is calculated by measuring the fluid flow rate using volumetric method and the temperature difference with another
pair of standard thermometers. It is 16.86 kWh. It is compared with the instrument reading 17.18 kWh. Thus, the deviation is 1.9%. Fig. 3 shows that the solar collector field
efficiency is 54% when the incident solar irradiation is 31.75 kWh.
