外文资料与中文翻译
外文资料：
Intelligent thermal energy meter controller
Abstract
A microcontroller based, 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.
1 Introduction
Solar water heating systems find wide applications in industry to conserve fossil fuel like oil, coal etc. They employ motor driven pumps for circulating water with on-off
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 essential instruments for monitoring and
evaluating the performance of these 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 these requirements, a microcontroller based instrument was
developed. Shoji Kusui and Tetsuo Nagai [1] developed an electronic heat meter for
measuring thermal energy using thermistors as temperature sensors and turbine flow meter as flow sensor.
2 Instrument details
The block diagram of the microcontroller (Intel 80C31) based thermal energy meter cum controller is shown in Fig. 1. RTD (PT100, 4-wire) sensors are used 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 semiconductor temperature sensor (LM335) is used for ambient temperature measurement. A pyranometer, having an output voltage of 8.33 mV/kW/m2, is used for measuring the incident solar radiation. To monitor the circulating fluid pressure, a sensor with 4–20 mA output is used. This output is converted into voltage using an I-V converter. All these 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 sensor (turbine type) is used 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,
下载翻译器英文翻中文
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 serial
communication port of the microcontroller is fed to the serial 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 serves as a DTC. This has been achieved
by interfacing a relay to the PPI. The system software is developed to accept the
differential temperature set points (ΔT on and ΔT off) from the keyboard. An algorithm
suitable for on-off control having two set-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 sensor
and the error introduced due to temperature drifts in the signal conditioners and the A/D converter. The temperature sensor is immersed in a constant temperature bath (HAAKE B ath-K, German), whose 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 sensor 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 sensor having a maximum flow rate of 1250 l/h is used for flow measurement.
It is calibrated by fixing it in the upstream of a pipeline of length 8 m. The sensor output is connected to a digital frequency counter to monitor the number of pulses generated with
different flow rates. Water collected at the sensor outlet over a period is used for
estimating the flow rate. The K-factor of the sensor is 3975 pulses/l. The uncertainty
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%
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 used for circulating
the water through the collector field. All the pipelines are thermally insulated. The
temperature sensors and the flow sensor 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
is shown in Fig. 3. It is observed 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 losses
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%
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 served as an energy conservation 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.

版权声明：本站内容均来自互联网，仅供演示用，请勿用于商业和其他非法用途。如果侵犯了您的权益请与我们联系QQ:729038198，我们将在24小时内删除。