Heat Loss Characteristics of Pipe Flange Joints: Experiments and Simulations

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
Xiaotao Zheng ◽  
Xiaohai Zhang ◽  
Jiuyang Gao ◽  
Linwei Ma ◽  
Wei Wang ◽  
...  
Keyword(s):  
Wind Speed ◽  
Ambient Temperature ◽  
Heat Loss ◽  
Average Error ◽  
Flange Joint ◽  
Steady Temperature ◽  
Ambient Temperatures ◽  
Wind Speeds ◽  
Sealing Performance ◽  
C 30

Abstract Sealing performance and heat loss are important factors for pipe flange joints (PFJs) subjected to medium or high temperatures. Heat loss is of great interest in practical engineering for uninsulated PFJs. Since an insulation layer may degrade the sealing performance of PFJs, heat loss of PFJs was tested and simulated considering various ambient temperatures of −10 °C, 0 °C, 10 °C, 20 °C, 30 °C, and 40 °C, with wind speeds of 0 m/s and 3 m/s and flange joint target temperatures of 200 °C, 300 °C, and 400 °C. It is worth noting that the experiments were performed during summer for high ambient temperatures and during winter for low ambient temperatures. As expected, the steady temperature slightly increases with the increase of external ambient temperature. For the same flange joint temperature, a 3 m/s wind speed decreases significantly the steady temperature, especially when the higher target temperature is applied. If the external wind speed is 3 m/s and the flange joint target temperatures are 200 °C, 300 °C, and 400 °C, respectively, the heat loss increases by approximately 38.4%, 30.7% and 23.6% when the ambient temperature changes from 30 °C to 10 °C. Moreover, the simulated temperatures agree well with the tested temperatures in most cases, and the average error is approximately 8%. The energy saving efficiency under the windless condition is approximately on average 26% higher than that with a wind speed of 3 m/s.

Hair density, wind speed, and heat loss in mammals

1965 ◽  
Vol 20 (4) ◽  
pp. 796-801 ◽  
Author(s):  
R. T. Tregear
Keyword(s):  
Wind Speed ◽  
Temperature Gradient ◽  
Heat Loss ◽  
Thermal Insulation ◽  
Hair Density ◽  
Wind Speeds

The heat loss from excised pelts of rabbits, horses, and pigs has been measured at various wind speeds. The temperature gradient through the fur was also measured. The thermal insulation of fur is highly dependent on the hair density (i.e., number of hairs/ cm2), and on the wind passing over its surface. If there are less than 1,000 hairs/cm2, an 8-mph wind penetrates deep into the fur, but at higher hair densities an 18-mph wind penetrates only a little way into the fur. fur insulation; obstruction of wind by hair Submitted on September 10, 1964

Thermoregulation of African and European Honeybees during Foraging, Attack, and Hive Exits and Returns

1979 ◽  
Vol 80 (1) ◽  
pp. 217-229 ◽  
Author(s):  
HEINRICH BERND
Keyword(s):  
Metabolic Rate ◽  
Ambient Temperature ◽  
Heat Loss ◽  
Warm Up ◽  
Ambient Temperatures ◽  
Thoracic Temperature

1. While foraging, attacking, or leaving or returning to their hives, both the African and European honeybees maintained their thoracic temperature at 30 °C or above, independent of ambient temperature from 7 to 23 °C (in shade). 2. Thoracic temperatures were not significantly different between African and European bees. 3. Thoracic temperatures were significantly different during different activities. Average thoracic temperatures (at ambient temperatures of 8–23 °C) were lowest (30 °C) in bees turning to the hive. They were 31–32 °C during foraging, and 36–38 °C in bees leaving the hive, and in those attacking. The bees thus warm up above their temperature in the hive (32 °C) before leaving the colony. 4. In the laboratory the bees (European) did not maintain the minimum thoracic temperature for continuous flight (27 °C) at 10 °C. When forced to remain in continuous flight for at least 2 min, thoracic temperature averaged 15 °C above ambient temperature from 15 to 25 °C, and was regulated only at high ambient temperatures (30–40 °C). 5. At ambient temperatures > 25 °C, the bees heated up during return to the hive, attack and foraging above the thoracic temperatures they regulated at low ambient temperatures to near the temperatures they regulated during continuous flight. 6. In both African and European bees, attack behaviour and high thoracic temperature are correlated. 7. The data suggest that the bees regulate thoracic temperature by both behavioural and physiological means. It can be inferred that the African bees have a higher metabolic rate than the European, but their smaller size, which facilitates more rapid heat loss, results in similar thoracic temperatures.

A mechanism by which helium increases metabolism in small mammals

1960 ◽  
Vol 199 (2) ◽  
pp. 243-245 ◽  
Author(s):  
H. A. Leon ◽  
S. F. Cook
Keyword(s):  
Thermal Conductivity ◽  
Oxygen Consumption ◽  
Ambient Temperature ◽  
Skin Temperature ◽  
Heat Loss ◽  
Small Mammals ◽  
Thermal Gradient ◽  
Oxygen Mixture ◽  
Ambient Temperatures ◽  
Long Evans

The oxygen consumption of male Long-Evans rats was determined at three different ambient temperatures in air and in an equivalent helium-oxygen mixture. It was found that when the ambient temperature is near the skin temperature of the rat, the effect of helium is insignificant. If the ambient temperature is lowered, helium induces an increased metabolism over air at the same temperature. Since helium has a thermal conductivity about six times greater than nitrogen, it is concluded that the accelerated metabolism is in response to the greater heat loss in the presence of helium and the magnitude of this response is proportional to the thermal gradient between the animal and the environment.

scholarly journals ENDOTHERMY IN THE SOLITARY BEE ANTHOPHORA PLUMIPES: INDEPENDENT MEASURES OF THERMOREGULATORY ABILITY, COSTS OF WARM-UP AND THE ROLE OF BODY SIZE

1993 ◽  
Vol 174 (1) ◽  
pp. 299-320 ◽  
Author(s):  
G. N. Stone
Keyword(s):  
Ambient Temperature ◽  
Heat Loss ◽  
Body Mass ◽  
Thermal Power ◽  
Thermal Conditions ◽  
Energetic Cost ◽  
Solitary Bee ◽  
Warm Up ◽  
Ambient Temperatures ◽  
Thoracic Temperature

1. This study examines variation in thoracic temperatures, rates of pre-flight warm-up and heat loss in the solitary bee Anthophora plumipes (Hymenoptera; Anthophoridae). 2. Thoracic temperatures were measured both during free flight in the field and during tethered flight in the laboratory, over a range of ambient temperatures. These two techniques give independent measures of thermoregulatory ability. In terms of the gradient of thoracic temperature on ambient temperature, thermoregulation by A. plumipes is more effective before flight than during flight. 3. Warm-up rates and body temperatures correlate positively with body mass, while mass-specific rates of heat loss correlate negatively with body mass. Larger bees are significantly more likely to achieve flight temperatures at low ambient temperatures. 4. Simultaneous measurement of thoracic and abdominal temperatures shows that A. plumipes is capable of regulating heat flow between thorax and abdomen. Accelerated thoracic cooling is only demonstrated at high ambient temperatures. 5. Anthophora plumipes is able to fly at low ambient temperatures by tolerating thoracic temperatures as low as 25 sC, reducing the metabolic expense of endothermic activity. 6. Rates of heat generation and loss are used to calculate the thermal power generated by A. plumipes and the total energetic cost of warm-up under different thermal conditions. The power generated increases with thoracic temperature excess and ambient temperature. The total cost of warm-up correlates negatively with ambient temperature.

Rotary Compressor Performance at Low Ambient Temperatures

2020 ◽  
Vol 28 (04) ◽  
pp. 2050037
Author(s):  
S. Lowrey ◽  
G. Reboux
Keyword(s):  
Ambient Temperature ◽  
Heat Loss ◽  
Heat Pump ◽  
Simulated Data ◽  
Performance Testing ◽  
Rotary Compressor ◽  
Ambient Conditions ◽  
Ambient Temperatures ◽  
Compressor Performance ◽  
Performance Envelope

Small rotary compressors are used in domestic heat pump appliances, for example, in domestic dehumidifiers and heat pump clothes dryers. Compressor performance curves provided by the manufacturer can be based on testing at relatively high ambient temperatures, in some cases as high as 35∘C. This can be much higher compared with the ambient temperature in which the compressor operates when, for example, it is installed in a domestic dehumidifier which can operate in ambient temperatures as low as 10∘C. We have developed a compressor calorimeter to test a small R134a rotary compressor extracted from a commercial domestic dehumidifier and use this to measure compressor performance parameters including the isentropic and volumetric efficiencies and the compressor heat loss fraction. The performance testing has been carried out at ambient temperatures 10∘C, 15∘C, 20∘C and 25∘C for a fixed relative humidity of 70% to compare how the compressor performance varies with the ambient temperature, and to determine how well the compressor performs outside of the performance envelope provided by the manufacturer. The results show that isentropic and volumetric efficiency of these small compressors is relatively insensitive to variation in ambient temperature, even outside of the performance envelope provided by the manufacturer. However, the compressor heat loss fraction can, on average, double from 15% to 30%, between operation at ambient 25∘C and ambient 10∘C. The data obtained in this work is used to construct compressor sub-models for certain ambient temperatures. We show how these sub-models can be used to improve a domestic dehumidifier model for operation at low ambient conditions within the evaporator frosting regime and good agreement is obtained between experimental and simulated data. The authors are not aware of a domestic dehumidifier model designed to work at ambient temperatures within the frosting regime.

scholarly journals Thermal Effects on Photovoltaic Array Performance: Experimentation, Modeling, and Simulation

2021 ◽  
Vol 11 (4) ◽  
pp. 1460
Author(s):  
Levon Ghabuzyan ◽  
Kevin Pan ◽  
Arianna Fatahi ◽  
Jim Kuo ◽  
Christopher Baldus-Jeursen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Wind Speed ◽  
Ambient Temperature ◽  
Wind Direction ◽  
Loss Factor ◽  
Thermal Loss ◽  
Cfd Simulations ◽  
Wind Speeds ◽  
Pv Array

The performance of photovoltaic (PV) arrays are affected by the operating temperature, which is influenced by thermal losses to the ambient environment. The factors affecting thermal losses include wind speed, wind direction, and ambient temperature. The purpose of this work is to analyze how the aforementioned factors affect array efficiency, temperature, and heat transfer coefficient/thermal loss factor. Data on ambient and array temperatures, wind speed and direction, solar irradiance, and electrical output were collected from a PV array mounted on a CanmetENERGY facility in Varennes, Canada, and analyzed. The results were compared with computational fluid dynamics (CFD) simulations and existing results from PVsyst. The findings can be summarized into three points. First, ambient temperature and wind speed are important factors in determining PV performance, while wind direction seems to play a minor role. Second, CFD simulations found that temperature variation on the PV array surface is greater at lower wind speeds, and decreases at higher wind speeds. Lastly, an empirical correlation of heat transfer coefficient/thermal loss factor has been developed.

Thermoregulatory effects of methoxamine and isoprenaline following injections into the cerebral ventricles of conscious rabbits

1977 ◽  
Vol 55 (4) ◽  
pp. 821-827 ◽  
Author(s):  
D. L. Jones ◽  
W. L. Veale ◽  
K. E. Cooper
Keyword(s):  
Body Temperature ◽  
Ambient Temperature ◽  
Heat Loss ◽  
Heat Production ◽  
Adrenergic Receptors ◽  
Cerebral Ventricles ◽  
Inhibitory Neurotransmitter ◽  
Ambient Temperatures ◽  
Hypothalamic Preoptic Area ◽  
Dose Dependent

There is evidence to suggest that within the hypothalamus noradrenaline (NA) is an inhibitory neurotransmitter acting on both the heat production and heat loss pathways in the rabbit. Further, it has been proposed that the inhibition of the heat loss pathway which results in hyperthermia is mediated primarily through α-adrenergic receptors within the anterior hypothalamic–preoptic area. We have investigated the effects of the α-receptor agonist methoxamine, administered directly into the cerebral ventricles, on body temperature at various ambient temperatures in both the shorn and unshorn rabbit. At all ambient temperatures tested, administration of methoxamine into a lateral cerebral ventricle produced a gradual dose-dependent hyperthermia. The magnitude of the hyperthermic response diminished with decreasing ambient temperatures. It is already known that the β-adrenergic agonist isoprenaline produces little or no effect on body temperature following intracranial application at ambient temperatures above 18 °C. In our experiments conducted at the lower ambient temperature, it produced a pronounced dose-dependent fall in body temperature in the shorn rabbit. The results of this work support the suggestion that NA can act as an inhibitory substance on the heat production or heat loss pathway in the rabbit. Which pathway is inhibited at any one time is dependent on the ambient temperature. Further, it would appear that inhibition of the heat loss pathway is largely mediated through α-adrenergic receptors, whilst the inhibition of the heat production pathway is mediated to a large extent through β-adrenergic receptors.

scholarly journals Heat loss from humans measured with a direct calorimeter and heat-flow meters

1980 ◽  
Vol 43 (1) ◽  
pp. 87-93 ◽  
Author(s):  
W. H. Close ◽  
M. J. Dauncey ◽  
D. L. Ingram
Keyword(s):  
Heat Flow ◽  
Ambient Temperature ◽  
Heat Loss ◽  
Skin Surface ◽  
Total Heat Loss ◽  
Flow Meters ◽  
Ambient Temperatures ◽  
External Insulation ◽  
The Subject ◽  
The Difference

1. Heat loss from three men and three women was measured in a direct calorimeter over 2 or 3 h periods and compared with that determined simultaneously from heat-flow meters attached to the skin surface at the waist. The comparisons were made at each of four ambient temperatures, 15, 20, 25 and 30°. Each subject wore a cotton boiler-suit and minimal underwear.2. Oral temperatures and skin and clothing temperatures on both trunk and forearm were determined, thus enabling the subjects' internal and external insulation to be calculated.3. Heat loss determined by the meters was lower than that determined by the calorimeter. The difference increased with increase in ambient temperature. ‘Meter’ heat loss decreased linearly as ambient temperature was raised.4. It was concluded that heat-flow meters could provide a useful estimate of total heat loss when the evaporative component is low. The estimate might be improved if the subject is calibrated while wearing the meters in a calorimeter over several short periods. Heat-flow meters could therefore be of particular value in sedentary individuals, when the heart-rate method for estimating energy expenditure can be inappropriate.

Effect of ambient temperature on heat production and heat loss in burn patients

1975 ◽  
Vol 38 (4) ◽  
pp. 593-597 ◽  
Author(s):  
D. W. Wilmore ◽  
A. D. Mason ◽  
D. W. Johnson ◽  
B. A. Pruitt
Keyword(s):  
Metabolic Rate ◽  
Ambient Temperature ◽  
Heat Loss ◽  
Environmental Temperature ◽  
Burn Patients ◽  
Evaporative Water ◽  
Ambient Temperatures ◽  
Wet Heat ◽  
Total Body ◽  
Normal Men

Four controls and eight burned patients with thermal injury ranging from 7 to 84% total body surface were studied in an environmental chamber at 25 and 33 degrees C ambient temperature and a constant vapor pressure during two consecutive 24-h periods. Hypermetabolism was present in the burn patients in both ambient temperatures and core and skin temperatures were consistently higher than in the normal men despite increased evaporative water loss. The higher environmental temperature decreased metabolic rate in patients with large thermal injuries in whom the decrement in dry heat loss produced by higher ambient temperature exceeded the increase of wet heat loss. In patients with burns smaller than 60%, these changes equaled one another and higher environmental temperature exerted no effect on metabolic rate. Core-skin heat conductivity increased with burn size; patients with large burns were characterized by inadequate core-skin insulation when exposed to the cooler environment, necessitating the compensatory increase of metabolic rate. This increase, however, was small and of the order of 5–8 kcal times m-2 times h-1.

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