Water Flow Rate Measurements Research Articles

Improvement of the Probe for Measuring Water Flow Rate in Intact Plants with the Stem Heat Balance Method

A probe was improved for measuring the rate of water flow in the stem of intact plants with the stem heat balance method. It consists essentially of flexible flat heater for feeding constant heat energy to a plant stem, heat flow sensing element for determining heat loss from the surface of the heater to the surrounding air and thermocouples for detecting stem temperatures. The improved probe can be easily set and removed to/from the stem and hardly arrests the radial growth of the plant stem. The comparison of the transpiration rate measured by a balance and the water flow rate determined by the new probe showed that the new probe was able to determine the water flux in a thin plant stem with acceptable error which was almost the same level attained with the original measuring device.

Experiments with a flat plate solar water heating system in thermosyphonic flow

A typical Israeli water heating system in thermosyphonic-flow was tested. The system consisted of two flat plate collectors painted matt black connected in parallel and a 140 l. storage tank. Total surface area of the collectors, employing the parallel flow pattern, was about 3 m 2 and they were tilted about 35° relative to the horizon. All collector pipes and connecting tubes were made of galvanized steel. The underside collector plate, collector tubes and storage tank were equipped with thermo-couples. A specially designed flow meter was used to measure water flow rate. Results show relatively linear temperature distributions both along the collectors and in the storage tank when no water consumption was allowed. Water flow rate was found to essentially follow solar radiation and reached a maximum of about 950 cm 3/min. This value was found to be about 33 per cent smaller than the one predicted by an analytical model developed by the authors. It was also observed that shutting the system off during the afternoon hours, when losses to the environment are enhanced, might increase system efficiency.

Performance Characteristics of Air Lift Pumps of Short Length and Small Diameter

ABSTRACTPerformance data in the literature on air lift pumps have been based primarily on pumps of long length and large diameter (high lift pumps). Since mariculture operations involve pumps of relatively short length and small diameter, performance data are required for efficient operation.To provide such data, an experimental apparatus was designed and fabricated to test air lift pumps from 1.27 cm to 7.62 cm inside diameter and from 30 cm to 3.7 m in length. Instrumentation was provided to measure water flow rate and air flow rate as well as water temperature, air temperature, and pressure throughout the system.Results from this study correlate well with high lift pump data in that, for a given pump geometry, maximum water flow occurs for a specific air flow rate. Driving the pump with air flows larger or smaller than this optimum flow rate will decrease the pumping rate. The optimum flows are significantly different for low lift pumps compared to high lift pumps. However, the pumping rate for low lift pumps approaches that for high lift pumps with increasing length.

Operation of the thermal flowmeter from a superimposed DC and pulse heat injection

A boundary layer thermal flowmeter having the flow sensor on the downstream side of the heater, is operated in a closed-loop form. The DC heat injection source is initially used for maintaining a temperature difference between the flow and reference sensors and the superimposed pulsed-heat injection source for maintaining this temperature difference constant with flow rate. It is shown that the flowmeter output frequency varies from zero upwards in this form of operation and the relationship between the output frequency sensitivity and the flow rate is considerably improved by choosing a very small flow as the least measurable rate. A description is given of a 1/2 in thermal flowmeter that can measure water flow rates from 50 to 1500 lb h-1 and gives output frequency variations from 0 to 1150 Hz.

Analysis of the thermal flowmeter operating from a pulsed-heat injection source

An analytical relation for the thermal flowmeter, operated in a closed- loop form, is derived in terms of increase in heat injection rate and mass flow rate over the laminar as well as turbulent flow ranges. It is pointed out in the analysis that a thermal flow transducer may be characterized by two easily measurable parameters. A description is given of the 1/4 in thermal flowmeter, operated from a small pulsed-heat source, which can measure water flow rates from 50 lb to h-1 to 1500 lb h-1. The analytical relation is verified against the output of this flowmeter and it is shown that the pulsed-heat source improves the flowmeter output characteristics compared with the DC heat source and provides a signal whose frequency depends upon the flow rate.

An improved soil water flux sensor

The design, construction, and calibration of a sensor which can be used to measure water flow rates through soil of 10 −3 cm/sec is described. The instrument is free of some disadvantages associated with previous soil water flux sensors.

Velocity Distribution and Its Effect on the Accuracy of the Gibson Method of Water Measurement

The author demonstrates that significant basic errors are introduced into the Gibson method of measuring water flow rates, even in uniform straight pipes, by failure to take account of velocity distribution in calculating results. Dr. Thoma’s 1926 analysis of the method is quoted extensively, including his conclusion that long straight lengths of pipe upstream and downstream from straight differential-diagram test sections would eliminate the effects of accessory motions and his recommendations for establishing an experimental installation to determine the effects of various disturbed flow conditions. The need for these correction factors or “meter coefficients” in order to avoid consistent errors of approximately 2 percent is emphasized.

Some Improvement and Measurement of the Thermoelectric Method for Measuring Water Flow Rates in Rice Plants

1. Thermoelectric method is advantageous in that repeated measurements can be made on the same intact plant either in the laboratory or under field conditions. There is no injury to the plant tissues and the normal physiological processes are not disturbed because all measurements are made externally on the stem. 2. This papar presents some of the improvement of the thermoelectric method that have been recently developed and used successfully. The different applications of the method presented here, and such a device can be used for further studies in problems concerned with the soilplant-water system. 3. The measuring circuit consisted of the modified wheatstone-bridge with a measuring thermistor in one arm and a compensatory thermistor in another arm of the bridge. Then measurement could be done even in the condition when the temperature varied quickly. 4. Over a period of time following an irrigation, water uptake and movement rates decrease as soil moisture becomes less available. 5. When the lodged stem was raised up, it was immediately apparent that high tensions existed within the rice crop because of the increased water absorption and movement rates in the stem. As the internal negative or suction pressure of the plant was released, the rates of water absorption and movement within the crop became slower as shown in figure 7.

Some Applications of the Thermoelectric Method for Measuring Water Flow Rates in Plants1

SynopsisMaximum transpiration rates for cotton plants were found to occur when relative humidities varied between 42 and 50%, temperatures from 95 to 100 F., and wind velocities between 1 and 4 miles per hour. Soil moisture tension appeared to control absorption and movement of water in plants.