scholarly journals Heat Transfer in Dragonflies: ‘Fliers’ and ‘Perchers’

1978 ◽  
Vol 74 (1) ◽  
pp. 17-36 ◽  
Author(s):  
BERND HEINRICH ◽  
TIMOTHY M. CASEY
Keyword(s):  
Heat Transfer ◽  
Heat Input ◽  
Blood Circulation ◽  
Behavioural Thermoregulation ◽  
Direct Sunlight ◽  
Experimental Conditions ◽  
Anterior Portion ◽  
Warm Up ◽  
Anax Junius ◽  
Air Temperatures

1. Both ‘perchers’ (Libellula saturata) and ‘fliers’ (Anax junius and Aeshna multicolor) remained active in the field in sunshine at air temperatures from at least 24 °C to 36 °C. 2. The percher basked at low air temperatures and regulated exogenous heat input by postural adjustments. It markedly reduced flight activity at high air temperatures but flew nearly continuously at intermediate temperatures. 3. In direct sunlight, the abdomen of L. saturata heated faster than the thorax, but this percher exhibited little or no capacity to transfer heat between abdomen and thorax. 4. In contrast, the fliers gave no evidence of behavioural thermoregulation, but both showed impressive capacities for heat transfer from thorax to abdomen. 5. When heated exogenously on the thorax the temperature of the entire abdomen of both fliers increased uniformly, but with endogenous heat production during pre-flight warm-up there was only a slight temperature increase near the anterior portion of the abdomen. 6. Removal of abdominal air sacs or immobilizing the abdomen with wax to prevent all abdominal pumping did not significantly alter the capacity to transfer heat from thorax to abdomen. 7. Ligation of the heart anywhere along the length of the abdomen abolished heat transfer. Given sufficient exogenous heat input, fliers that can regulate their thoracic temperature by transferring the excess heat to the abdomen died in about 2 min due to overheating when the heart was occluded. Under our experimental conditions the fliers appeared to thermoregulate exclusively via a control of blood circulation.

scholarly journals Mechanisms of Body-Temperature Regulation in Honeybees, Apis Mellifera: II. Regulation of Thoracic Temperature at High Air Temperatures

1980 ◽  
Vol 85 (1) ◽  
pp. 73-87
Author(s):  
BERND HEINRICH
Keyword(s):  
Heat Transfer ◽  
Body Temperature Regulation ◽  
Free Flight ◽  
Anterior Portion ◽  
Lethal Temperatures ◽  
Primary Mechanism ◽  
Thoracic Temperature ◽  
Air Temperatures ◽  
A Minor ◽  
Production Mechanisms

1. Honeybees could remain in continuous free flight at extremely high air temperatures (up to at least 46 °C). 2. The metabolic rate in free flight, 80–85 ml O2g body weight−1 h−1, was independent of air temperature (TA) over a span of at least 22 °C. 3. The bees' ability to fly at high TA was due to their ability to maintain thoracic temperature (TTh) near TA despite prodigious rates of heat production. Mechanisms of preventing TTh from overheating at high TA were investigated. 4. Bees in flight at high TA regurgitated fluid from their honeycrop and large droplets sometimes spread over the anterior portion of the thorax. 5. Bees without the first two sets of legs, or without a ‘tongue’, maintained as low TH and TTh as intact bees. 6. The abdomen serves only a minor function as a heat exchanger. In tethered bees, heating of the thorax to 45–50 °C resulted in significant, yet relatively little, temperature increase of the abdomen above that of dead or non heat-stressed animals. Similarly, in free flight abdominal temperatures (TAb) were close to TA at all TA. 7. Thoracic heating to near lethal temperatures did not result in droplet extrusion from the mouth nor in significant physiologically facilitated heat transfer to the head. Furthermore, it resulted in no, or in relatively small, changes in pulsation of the aorta and the heart. 8. However, the bees prevented the head from overheating, and the head served as a heat sink for excess heat from the thorax. Keeping TH < TA resulted in keeping TTh near TA. 9. It is concluded that during flight at high TA regulation of TH by evaporative cooling is the primary mechanism of reducing TTh.

Simultaneous control of head and thoracic temperature by the green darner dragonfly Anax junius (Odonata: Aeshnidae)

1995 ◽  
Vol 198 (11) ◽  
pp. 2373-2384 ◽  
Author(s):  
M May
Keyword(s):  
Heat Transfer ◽  
Air Temperature ◽  
Temperature Sensitive ◽  
Additional Mechanism ◽  
Warm Up ◽  
Anax Junius ◽  
Thermal Window ◽  
Thoracic Temperature ◽  
Simultaneous Control ◽  
Head Temperature

Anax junius is a large dragonfly that regulates thoracic temperature (Tth) during flight. This species, like several other intermittently endothermic insects, achieves control of Tth at least in part by increasing circulation of hemolymph to the abdomen at high air temperature (Ta), thus facilitating heat loss from the thorax. In this paper, I demonstrate that heat transfer to the head is also under active control, very probably owing to temperature-sensitive alteration of hemolymph circulation. As a result, head temperature (Th) is strikingly elevated above Ta during endothermic warm-up and flight. Furthermore, during unrestrained flight in the field, Th is regulated actively by increasing hemolymph circulation from the warm thorax at low Ta. Concurrent measurements of abdominal temperature (Tab) confirm that the abdomen is used as a 'thermal window' at Ta>30 °C but apparently not at lower Ta; thus, some additional mechanism(s) must exist for regulation of Tth at low Ta.

A Numerical Approach to Determine Some Properties of Cylindrical Pieces of Bananas During Drying

2015 ◽  
Vol 11 (3) ◽  
pp. 335-347 ◽  
Author(s):  
Wilton Pereira da Silva ◽  
Cleide M. D. P. S. e Silva ◽  
Aluizio Freire da Silva Junior ◽  
Alexandre José de Melo Queiroz
Keyword(s):  
Numerical Solution ◽  
Numerical Approach ◽  
Moisture Diffusivity ◽  
Convective Drying ◽  
Chi Square ◽  
Experimental Conditions ◽  
Liquid Diffusion ◽  
Air Temperatures ◽  
C 50 ◽  
Volume Method

Abstract This article uses several liquid diffusion models to describe convective drying of bananas cut into cylindrical pieces. A two-dimensional numerical solution of the diffusion equation with boundary condition of the third kind, obtained through the finite volume method, was used to describe the process. The cylindrical pieces were cut into the following dimensions: length of about 21 mm and average radius of 15 mm. Drying air temperatures were 40°C, 50°C, 60°C and 70°C. In order to determine the process parameters, an optimizer was coupled with the numerical solution. A model that considers the shrinkage and variable effective moisture diffusivity well describes drying for all the experimental conditions, and enables to predict the moisture distributions at any given time. For this model, the determination coefficient has varied from 0.99937 (70°C) to 0.99995 (40°C), while the chi-square ranged from 3.41 × 10−4 (40°C) to 4.15 × 10−3 (70°C).

Skinfolds and resting heat loss in cold air and water: temperature equivalence

1975 ◽  
Vol 39 (1) ◽  
pp. 93-102 ◽  
Author(s):  
R. M. Smith ◽  
J. M. Hanna
Keyword(s):  
Heat Transfer ◽  
Water Temperature ◽  
Heat Loss ◽  
Air Temperature ◽  
Indirect Calorimetry ◽  
Cold Water ◽  
Heat Conductance ◽  
Air Temperatures ◽  
Body Core ◽  
Male Subjects

Fourteen male subjects with unweighted mean skinfolds (MSF) of 10.23 mm underwent several 3-h exposures to cold water and air of similar velocities in order to compare by indirect calorimetry the rate of heat loss in water and air. Measurements of heat loss (excluding the head) at each air temperature (Ta = 25, 20, 10 degrees C) and water temperature (Tw = 29–33 degrees C) were used in a linear approximation of overall heat transfer from body core (Tre) to air or water. We found the lower critical air and water temperatures to fall as a negative linear function of MSF. The slope of these lines was not significantly different in air and water with a mean of minus 0.237 degrees C/mm MSF. Overall heat conductance was 3.34 times greater in water. However, this value was not fixed but varied as an inverse curvilinear function of MSF. Thus, equivalent water-air temperatures also varied as a function of MSF. Between limits of 100–250% of resting heat loss the followingrelationships between MSF and equivalent water-air temperatures were found (see article).

Pin-Fin Heat Sink With Horizontal Base and Blocked Edges

2008 ◽  
Author(s):  
D. Sahray ◽  
H. Shmueli ◽  
N. Segal ◽  
G. Ziskind ◽  
R. Letan
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Contact Resistance ◽  
Cross Section ◽  
Heat Input ◽  
Heat Sink ◽  
Numerical Study ◽  
Heat Sinks ◽  
Transfer Enhancement ◽  
Pin Fin

In the present work, horizontal-base pin fin heat sinks exposed to free convection in air are studied. They are made of aluminum, and there is no contact resistance between the base and the fins. For the same base dimensions the fin height and pitch vary. The fins have a constant square cross-section. The edges of the sink are blocked: the surrounding insulation is flush with the fin tips. The effect of fin height and pitch on the performance of the sink is studied experimentally and numerically. In the experiments, the heat sinks are heated using foil electrical heaters. The heat input is set, and temperatures of the base and fins are measured. In the corresponding numerical study, the sinks and their environment are modeled using the Fluent 6 software. The results show that heat transfer enhancement due to the fins is not monotonic. The differences between sparsely and densely populated sinks are analyzed for various fin heights. Also assessed are effects of the blocked edges as compared to the previously studied cases where the sink edges were exposed to the surroundings.

Application of Artificial Neural Network for the Heat Transfer Investigation Around a High-Pressure Gas Turbine Rotor Blade

2011 ◽  
Author(s):  
Ibrahim Eryilmaz ◽  
Sinan Inanli ◽  
Baris Gumusel ◽  
Suha Toprak ◽  
Cengiz Camci
Keyword(s):  
Neural Network ◽  
Heat Transfer ◽  
Artificial Neural Network ◽  
High Pressure ◽  
Rotor Blade ◽  
Incidence Angle ◽  
Transfer Coefficients ◽  
Experimental Conditions ◽  
Heat Transfer Coefficients ◽  
Artificial Neural

This paper presents the preliminary results of using artificial neural networks in the prediction of gas side convective heat transfer coefficients on a high pressure turbine blade. The artificial neural network approach which has three hidden layers was developed and trained by nine inputs and it generates one output. Input and output data were taken from an experimental research program performed at the von Karman Institute for Fluid Dynamics by Camci and Arts [5,6] and Camci [7]. Inlet total pressure, inlet total temperature, inlet turbulence intensity, inlet and exit Mach numbers, blade wall temperature, incidence angle, specific location of measurement and suction/pressure side specification of the blade were used as input parameters and calculated heat transfer coefficient around a rotor blade used as output. After the network is trained with experimental data, heat transfer coefficients are interpolated for similar experimental conditions and compared with both experimental measurements and CFD solutions. CFD analysis was carried out to validate the algorithm and to determine heat transfer coefficients for a closely related test case. Good agreement was obtained between CFD results and neural network predictions.

scholarly journals A New Test Facility for Testing of Cooled Gasturbine Components

1998 ◽  
Author(s):  
Ulf R. Rådeklint ◽  
Christer S. Hjalmarsson
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Temperature Fields ◽  
Test Facility ◽  
Operating Point ◽  
Ir Camera ◽  
Turbine Cooling ◽  
Air Temperatures ◽  
Turbine Vanes ◽  
Conventional Instrumentation

A high pressure hot test facility for cooled gas turbine components has been developed for use in turbine cooling research. In this facility, heat transfer tests for a sector of real turbine vanes can be performed under continuous operation. The heat transfer tests are performed at an operating point that is scaled down from the real engine operating point. The compressor can deliver air at the rate of up to 10 kg/s at 20 bars. Air temperatures of up to 1170 K can be achieved by using an oil-fired combustor. Besides conventional instrumentation such as thermocouples and pressure probes, the facility is equipped with an IR-camera to map two-dimensional wall temperature fields. Hot wire anemometry and an LDV system are used to determine mean and fluctuating velocity components. This paper describes design and performance of the test facility as well as the control and measurement equipment. The test and evaluation procedures used for testing of cooled gas turbine vanes are also presented.

Heat Transfer in Reciprocating Planar Curved Tube With Piston Cooling Application

2005 ◽  
Vol 128 (1) ◽  
pp. 219-229 ◽  
Author(s):  
Shyy Woei Chang ◽  
Yao Zheng
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Interactive Effects ◽  
Experimental Conditions ◽  
Nusselt Numbers ◽  
Curved Tube ◽  
The Individual ◽  
Cooling Passage ◽  
Piston Cooling

This paper describes an experimental study of heat transfer in a reciprocating planar curved tube that simulates a cooling passage in piston. The coupled inertial, centrifugal, and reciprocating forces in the reciprocating curved tube interact with buoyancy to exhibit a synergistic effect on heat transfer. For the present experimental conditions, the local Nusselt numbers in the reciprocating curved tube are in the range of 0.6–1.15 times of static tube levels. Without buoyancy interaction, the coupled reciprocating and centrifugal force effect causes the heat transfer to be initially reduced from the static level but recovered when the reciprocating force is further increased. Heat transfer improvement and impediment could be superimposed by the location-dependent buoyancy effect. The empirical heat transfer correlation has been developed to permit the evaluation of the individual and interactive effects of inertial, centrifugal, and reciprocating forces with and without buoyancy interaction on local heat transfer in a reciprocating planar curved tube.

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