Unravelling the relationship between stem temperature and air temperature to correct for errors in sap-flow calculations using stem heat balance sensors

2005 ◽  
Vol 32 (7) ◽  
pp. 599 ◽  
Author(s):  
Kathy Steppe ◽  
Raoul Lemeur ◽  
Diego Dierick
Keyword(s):  
Air Temperature ◽  
Flow Rate ◽  
Heat Balance ◽  
Sap Flow ◽  
Heat Storage ◽  
Flow Rates ◽  
Storage Effects ◽  
Stem Temperature ◽  
Oak Tree ◽  
Set Up

Results from measurement of sap flow by heat balance sensors on the stem of a young oak tree (Quercus robur L.) revealed that thermal disequilibrium (i.e. heat storage) within the heated stem segment can introduce considerable errors in the measured sap-flow rates. The magnitude, sign and significance of these errors depend on the sap-flow rate and on the relationship between stem temperature and air temperature. Sap-flow rates were found to be more prone to errors caused by heat storage effects under low flow conditions than at higher rates of sap flow. Furthermore, daytime fluctuations of air temperature and stem temperature inside the heat balance sensor were either in phase when a low, or in opposite phase when a high sap-flow rate was passing through the stem of the young tree. To investigate this relationship, we developed an experimental set-up with cut stem segments through which tap water could be pressed. This set-up allowed the effects of air temperature and sap-flow rates on stem temperatures within heat balance sensors to be clearly separated. Good mathematical relationships were obtained and were successfully used to assess the relative importance of air temperature and sap-flow rate with respect to the fluctuations in stem temperature of the young oak tree. Based on the established relationships, a novel approach was put forward to correct for errors introduced into sap-flow calculations caused by heat storage effects if no measured data on stem temperature are available.

Determination of the water use of two pairs of soybean isolines differing in stomatal frequency using a heat balance stem flow gauge

1995 ◽  
Vol 75 (1) ◽  
pp. 99-103 ◽  
Author(s):  
C. S. Tan ◽  
B. R. Buttery
Keyword(s):  
Soil Moisture ◽  
Water Use ◽  
Heat Balance ◽  
Sap Flow ◽  
Stomatal Frequency ◽  
Flow Rates ◽  
High Soil Moisture ◽  
Stem Flow ◽  
Glycine Max L

Using heat-balance stem flow gauges, we were able to measure directly and continuously the sap flow rates in two pairs of soybean [Glycine max (L.) Merr.] isolines differing in stomatal frequency. Plants with high stomatal frequency transpired significantly more water than the low stomatal frequency plants at high soil moisture levels. Under low soil moisture levels, the water use rate decreased greatly for the high stomatal frequency plants. Plants with low stomatal frequency were able to maintain greater sap flow rates than those with high stomatal frequency. Higher leaf temperatures associated with the low stomatal frequency plants were likely due to lower transpiration rates which reduced evaporative cooling especially under well-watered conditions. Key words:Glycine max (L.) Merr., transpiration, water deficits

Improved heat balance method for determining sap flow rate

1991 ◽  
Vol 56 (1-2) ◽  
pp. 35-48 ◽  
Author(s):  
Tomoyasu Ishida ◽  
Gaylon S. Campbell ◽  
Cornelis Calissendorff
Keyword(s):  
Flow Rate ◽  
Heat Balance ◽  
Sap Flow ◽  
Balance Method

scholarly journals Prediction of Grape Sap Flow in a Greenhouse Based on Random Forest and Partial Least Squares Models

Water ◽  
2021 ◽  
Vol 13 (21) ◽  
pp. 3078
Author(s):  
Xuelian Peng ◽  
Xiaotao Hu ◽  
Dianyu Chen ◽  
Zhenjiang Zhou ◽  
Yinyin Guo ◽  
...  
Keyword(s):  
Random Forest ◽  
Least Squares ◽  
Partial Least Squares ◽  
Flow Rate ◽  
Sap Flow ◽  
Deficit Irrigation ◽  
Coefficient Of Determination ◽  
Growth Stages ◽  
Irrigation Amount ◽  
Flow Rates

Understanding variations in sap flow rates and the environmental factors that influence sap flow is important for exploring grape water consumption patterns and developing reasonable greenhouse irrigation schedules. Three irrigation levels were established in this study: adequate irrigation (W1), moderate deficit irrigation (W2) and deficit irrigation (W3). Grape sap flow estimation models were constructed using partial least squares (PLS) and random forest (RF) algorithms, and the simulation accuracy and stability of these models were evaluated. The results showed that the daily mean sap flow rates in the W2 and W3 treatments were 14.65 and 46.94% lower, respectively, than those in the W1 treatment, indicating that the average daily sap flow rate increased gradually with an increase in the irrigation amount within a certain range. Based on model error and uncertainty analyses, the RF model had better simulation results in the different grape growth stages than the PLS model did. The coefficient of determination and Willmott’s index of agreement for RF model exceeded 0.78 and 0.90, respectively, and this model had smaller root mean square error and d-factor (evaluation index of model uncertainty) values than the PLS model did, indicating that the RF model had higher prediction accuracy and was more stable. The relative importance of the model predictors was determined. Moreover, the RF model more comprehensively reflected the influence of meteorological factors and the moisture content in different soil layers on the sap flow rate than the PLS model did. In summary, the RF model accurately simulated sap flow rates, which is important for greenhouse grape irrigation.

scholarly journals Substantial Errors in Estimates of Sap Flow Using the Heat Balance Technique on Woody Stems under Field Conditions

1992 ◽  
Vol 117 (2) ◽  
pp. 351-356 ◽  
Author(s):  
Kenneth A. Shackel ◽  
R. Scott Johnson ◽  
Charles K. Medawar ◽  
Claude J. Phene
Keyword(s):  
Heat Balance ◽  
Sap Flow ◽  
Prunus Persica ◽  
Negative Temperature ◽  
Rate Of Change ◽  
Field Conditions ◽  
Balance Model ◽  
Ambient Conditions ◽  
Stem Temperature ◽  
The Heat Balance

The heat balance method was used to estimate transpirational sap flow through 60- to 75-mm-diameter stems (trunks) of 3-year-old peach [Prunus persica (L.) Batsch. cv. O'Henry] trees under field conditions. On rare occasions, heat balance estimates agreed well with independent lysimetric measurements, but on most occasions, heat balance estimates of sap flow were unrealistic in both direction and magnitude. In some cases, the errors in sap flow approached two orders of magnitude and were always the result of a calculation involving division by a very small and sometimes negative temperature differential between the stem surface temperature above and below the gauge heater. The occurrence of negative temperature differentials under positive transpiration conditions may be inconsistent with a fundamental assumption in the heat balance model, namely that temperature differentials are solely a consequence of the dissipation of energy supplied to the gauge heater. In the absence of heating power applied to the gauge, temperature differentials exceeding - 1C were correlated with the rate of change in stem temperature, indicating that ambient conditions themselves can impose a bias in gauge signals and, hence, influence gauge accuracy. Our results suggest that the effect of ambient conditions on gauge signals should be critically evaluated before considering heat balance estimates of sap flow as reliable under any given conditions.

Liquid Transport Properties in Sub-Micron Channel Flows

2001 ◽  
Author(s):  
K. Johan A. Westin ◽  
Kenneth S. Breuer ◽  
Chang-Hwan Choi ◽  
Peter Huang ◽  
Zhiqiang Cao ◽  
...  
Keyword(s):  
Flow Rate ◽  
Low Flow ◽  
Slip Boundary Conditions ◽  
Liquid Transport ◽  
Flow Rates ◽  
Slip Boundary ◽  
Laminar Channel Flow ◽  
Flow Through ◽  
Set Up ◽  
Good Agreement

Abstract An experimental set-up for pressure driven liquid flow through microchannels have been designed and tested. The flow rate is determined by tracking the free liquid surface in a precision bore hole using a laser distance meter. Measurements of the flow rate through silicon microchannels with a height of less than 0.9 μm show good results for Newtonian fluids (silicon oil, ethanol) at flow rates as low as 0.2 nl/s. The experimental results are also in very good agreement with predictions based on laminar channel flow using no-slip boundary conditions, indicating that standard macroscopic assumptions are still valid for these fluids under these conditions. However, experiments with aqueous solutions show anomalies in the form of unexpectedly low flow rates and time dependent variations. Possible explanations to these observations are discussed.

Feeding System of Aerostatic Bearings With Porous Media

2006 ◽  
Author(s):  
G. Belforte ◽  
T. Raparelli ◽  
V. Viktorov ◽  
A. Trivella
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Darcy’S Law ◽  
Darcy's Law ◽  
Flow Rates ◽  
Gas Bearings ◽  
Mass Flow Rates ◽  
Set Up ◽  
Forchheimer’S Law

In porous resistances, Darcy’s law provides a good approximation of mass flow rate when the differences between upstream and downstream pressures are sufficiently small. In this range, the mass flow rates are proportional to the porous resistance’s permeability. For gas bearings, the pressure difference is normally higher, and it is known experimentally that the mass flow rates are lower than would result from Darcy’s law. Forchheimer’s law adds an inertial term to Darcy’s law and, when an appropriate coefficient is selected for this term, provides a good approximation of flow rates for the same applications even with the highest pressure differences. This paper presents an experimental and theoretical investigation of porous resistances used in gas bearing supply systems. Cylindrical sintered bronze inserts featuring lengths, diameters and particle sizes commonly used in gas bearings and thrust pads were examined. The paper describes the test set-up and experimental results obtained for: a) Mass flow rate through single porous resistances at different upstream and downstream pressures; and b) Mass flow rate and pressure distribution on a pneumatic pad featuring the same porous resistances. The theoretical permeability of the chosen porous resistances was calculated, and the results from set-up a) were then used to obtain experimental permeability and to determine the inertial coefficients. The results, which are expressed as a function of the Reynolds number, confirmed the validity of using Forchheimer’s law. The mass flow rates from set-up b) were compared with those from set-up a) at the same pressure differentials across the insert.

Simulation of chemical processes with uncertain parameters

1983 ◽  
Vol 48 (6) ◽  
pp. 1588-1596 ◽  
Author(s):  
Mirko Dohnal ◽  
Marie Ulmanová
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Method ◽  
Flow Rate ◽  
Chemical Processes ◽  
Uncertain Parameters ◽  
Flow Rates ◽  
The Monte Carlo Method ◽  
Sensitivity Studies ◽  
Set Up ◽  
Simulation Problem

An integral part of the simulation problem are numerical values of parameters or constants of industrial units. Either these quantities need not be known accurately or it is not possible to control them at the set up value. The result of simulation cannot be then accurate. It is necessary to determine the region in which the flow rates of components through branches could change when the parameters and constants change. For these purposes is applicable the Monte Carlo method. But it is very time-consuming. Here, algorithms are proposed which with the use of the algebraic norm approximately determine the looked-for set of flow rate uncertainty. These algorithms can be applied for solution of a number of practical problems related with optimum sizing of units, sensitivity studies etc. An example is given of a cooling cascade cycle.

scholarly journals Thermal Stratification Performance of a Packed Bed Latent Heat Storage System during Charging

2018 ◽  
Vol 64 ◽  
pp. 03001
Author(s):  
Mawire Ashmore ◽  
Lentswe Katlego ◽  
Lugolole Robert ◽  
Okello Denis ◽  
Nyeinga Karidewa
Keyword(s):  
Latent Heat ◽  
Flow Rate ◽  
Thermal Stratification ◽  
Heat Storage ◽  
Storage System ◽  
Packed Bed ◽  
Heat Transfer Fluid ◽  
Latent Heat Storage ◽  
Flow Rates ◽  
Peak Value

Experimental thermal stratification evaluation of a packed bed latent heat storage is done during charging cycles. The packed bed latent heat storage system consists of adipic acid encapsulated in aluminum spheres. Sunflower oil is used as the heat transfer fluid during charging cycles. Stratification number profiles are used to evaluate thermal stratification in the storage system. Charging experiments are carried out with three different flow-rates (4 ml/s, 8 ml/s and 12 ml/s). Charging experiments are also done using the same flow-rate (8 ml/s) with three different set heater temperatures (220 °C, 240 °C and 260 °C). The lowest charging flow-rate (4 ml/s) shows the best variation of the stratification number profile since it shows the least drop from the peak value and the shortest charging interval. Different set heater temperatures show almost identical stratification number profiles. The effect of the charging flow-rate is more significant than the effect of the charging set heater temperature when evaluating thermal stratification for this particular system.

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