Increasing Heat Load Research Articles

Physiological and Pyhsical Responses of Dairy Cattle to Heat Stress

Herd management and nutrition strategies against increasing negative effects of global warming on farm animals have been the subject of significant debates in recent years. The fact that the changes in the environmental conditions are directly related to the habitats of the animals and the conditions inside the barn can affect the farm animals negatively. Although effects of heat stress differ according to species, especially high-yielding dairy cattle exposed to heat stress, respond with various interactive mechanism such as physiological, biochemical, immunological, anatomical and behavioral. Therefore, with the selection practices that have been going on for many years to improve the yield characteristics of the animals significantly increased. In this respect, the increased heat load in the body of dairy cattle due to the high productivity decreases their tolerance to environmental conditions. This situation adversely affects the productivity of cows with high breeding value. Yield losses, varying according to some factors about heat stress, can be partially explained by decreasing feed intake as a result of a series of hormonal responses affecting appetite center. However, the physiological requirements of cattle must be defined in order to develop appropriate strategies to reduce or eliminate the negative effects of heat stress. In this review, the variations in physiological, biochemical and behavioral mechanisms originating from heat stress in dairy cattle and the care, nutrition and herd management strategies that can be applied to eliminate or reduce the negative effects were discussed.

Enhancement technology of underground water flow field in coal mine to improve energy efficiency of heat pump system in geothermal energy development

In order to solve the problem that the cold/heat released from the underground pipe of coal mine into the soil layer is difficult to dissipate in a short time, the technology of enhancing the underground flow field of coal mine in geothermal energy development to improve the energy efficiency of the heat pump system is proposed. In this paper, based on the ground source heat pump project located in a coal mine, the energy efficiency enhancement technology of the artificial flow field ground source heat pump system is studied and tested. The test results show that when starting work at about 8:00, due to the increase of heating load, the accumulation of cooling capacity around the buried pipe increases gradually, and the return water temperature at the ground source side decreases gradually. At 14:05, the water was pumped for the operation of the artificial groundwater flow field. It can be seen that the temperature of the return water at the ground source side began to rise gradually, indicating that the accumulation of cold water around the buried pipe was relieved to a certain extent. In conclusion, the artificial groundwater flow field can alleviate the accumulation of cold water around the buried pipe heat exchanger to a certain extent, improve the return water temperature of the buried pipe heat exchanger, and improve the energy efficiency of the ground source heat pump system.

High temperature fuel impacts on combustion characteristics of a swirl-stabilized combustor

Future aircraft will require advanced thermal management systems to manage the increased heat loads resulting from the avionics, turbomachinery and other subsystems of higher performance, and high speed flight systems. Fuel is the primary coolant to alleviate these thermal management challenges. Heated fuel entering the combustor is likely to affect combustion performance due to dramatic changes in properties that impact fuel atomization, distribution, vaporization and fuel/air mixing. In this study, the combustion performance, emissions, and flame characteristics of a single-nozzle, swirl-stabilized combustor operating with high temperature fuels were investigated. Four fuels representing a wide range of jet fuel physical and chemical properties were studied at injection temperatures of 32, 121 and 260 °C. The test fuels included a conventional Jet A (A-2), a low cetane number alcohol-to-jet (ATJ) alternative fuel (C-1), n-dodecane (n-C12) and a high viscosity jet fuel blend (C-3A). Tests were conducted at a combustor pressure of 2 atm and inlet air temperature of 121 °C at global equivalence ratios (ϕ) of 0.10–0.24 for most fuel temperatures. Particulate matter (PM) emissions (concentrations and size distributions), and primary gaseous emissions were measured. High frequency pressure measurements and high-speed video were collected to assess fuel temperature impacts on combustion stability and flame characteristics, respectively. Results show that the heated fuel impacts on combustion were highly dependent on fuel type, temperature and ϕ. Qualitative results show that as fuel temperature increased, the flame in the primary zone appeared more compact, and less thermally radiant (lower soot). PM emissions were significantly impacted with reductions exceeding 95 % in particle number density for all fuels, and between 20 and 55 % reductions in mean particle diameters for aromatic-containing fuels. Gaseous emissions show up to ∼ 90 % reduction in unburned hydrocarbons (UHC) and up to 60 % reduction in carbon monoxide (CO), and corresponding moderate increases in NOx and CO2 with the heated fuel. The combustor acoustic response was slightly suppressed in frequencies of interest as fuel temperature increased. In general, the impacts of heated fuel on combustion were mostly beneficial and are primarily attributed to improved fuel atomization and reduced fuel evaporation timescales of the heated fuel. Specific impacts of fuel physical and chemical properties, and potential implications of heated fuel combustion are discussed.

Condensation regimes inside a vapor chamber with transparent hollow fins of circular, triangular or fluted cross section

A vapor chamber with integrated hollow fins was manufactured and tested, with the aim of identifying the optimal fin geometry to prevent liquid hold-up and flooding at the condenser. In particular, the influence of the transverse cross section was experimentally investigated. Circular, triangular and fluted cross sections were compared, with inscribed diameters ranging from 1.3 to 2.6 mm. The air-cooled fins were made of polymer in order to visualize the condensation regimes. When operating with HFE-7100, three regimes were identified with increasing heat load (up to 95 W): filmwise condensation, plug condensation and flooding, which significantly deteriorates the heat transfer performance. The triangular cross section is the most interesting shape among those tested because flooding occurs at higher heat load and/or smaller diameter than in other shapes thanks to drainage into the corners. Circular fins have the worst performance and fluted ones are in-between. The critical diameter below which flooding occurs even at low heat load is around 2.0 mm for a triangular section and 2.5 mm for a circular one. Consequently, with an optimum fin placement, the total convective surface area at the condenser could be increased by about 15% when using triangles instead of circles.

Melting performance of a composite bio-based phase change material: An experimental evaluation of copper foam pore size

• PCM-based heat sinks were optimized by combining them with copper foam. • The cooling performance of five different PCM-Copper based heat sinks was studied. • Higher copper foam pore densities were found to yield improved cooling performance. • Increased heat loads triggered a faster thermal response from the heat sink. This paper presents an experimental study on the thermal performance of a composite heat sink consisting of a bio-based phase change material and copper foam. The experiments are carried out at three different heat loads (10, 15, and 20 W) using five copper metal foam samples with the same dimensions (10 × 9 × 0.3 cm), porosity (98%), and pore densities of 20, 35, 60, 80, and 95 pores per inch (PPI). The thermal performances are evaluated using the temperature profiles, the time required to reach specific temperatures, and the enhancement ratios of the heat sinks. The results favor the PCM-Copper composite sample with 95 PPI because it took the longest time to achieve a constant temperature when compared to its other pore density counterparts. Also, for the same sample under 20 W power input, the enhancement ratios are 1.29, 1.45, and 1.23 at critical temperatures of 50, 55, and 60 °C, respectively.

Evaluation and Optimization of heat Pump Combined District Heating System: A Case Study of China

The district heating area in China is continuously increasing, which brings an increase in district heating load. In order to solve the shortage of heating power and realize the carbon neutral target, this study proposes two retrofit schemes for district heating system by integrating air source heat pump and water source heat pump, respectively. Mathematical models are established to study the performance of the integrated systems and a bilevel optimization model is proposed to optimize them. The results show that the air source heat pump combined district heating system has better performance compared to the conventional system, which reduces 50% energy consumption, 10.8% carbon emissions and achieves better economy. The dynamic coupling property of the district heating network and power grid are also considered, and the results indicate that the introduction of air source heat pump can effectively improve the efficiency and stability of power grid and reduce the seasonal fluctuation. The potential of large-scale application of air source heat pump combined system in Beijing is evaluated. The results reveal that retrofit scheme of integrating air source heat pumps into district heating system can cover 2930 MW heating load and bring 362 million Chinese Yuan profit by reducing 219,000 tons of carbon emissions and 539,000 tons of standard coal consumption in 2025.

Phase Change and Heat Transfer Analysis of Different Refrigerants During Condensation in Minichannel Using a Novel Numerical Approach

Abstract This paper analyses the condensation heat transfer phenomena in minichannel using acetone, ammonia, propylene, and R134a as the working fluids used in new-age space applications. A novel numerical model is developed considering the changes in local vapor pressure in the channel established due to shrinking in the flow passage by the gradual formation of the liquid layer. The present developed numerical model is compared with the available numerical and experimental results. The impacts of different inlet mass fluxes (250, 500, and 750 kg/m2 s), channel heights (1, 4, 6, and 8 mm), applied heat loads (10, 100, 250, and 500 W), and channel orientations (0 deg, 30 deg, 45 deg, 60 deg, and 90 deg) on the performance of the condensation heat transfer process are investigated. The formation of the thin liquid film layers and evaluation of the liquid–vapor interface profiles are examined. The study reveals that the channel orientation has a marginal influence on the flow pattern for the considered channel length of 20 mm. The maximum change in pressure loss is found at the channel orientation of 45 deg, and the average heat transfer coefficient is almost the same for all the considered orientations. The flow pattern is affected by the increase in mass flux resulting in the delay of heat transfer coefficient fluctuations. The average heat transfer coefficient decreases with increasing heat load, and the minimum average heat transfer coefficient is obtained for heat load, Q = 500 W.

PSII-B-21 Does Prior Viral Infection Exacerbate the Response to Heat Stress?

Abstract In rodent models, prior immune activation appears to exacerbate the response to heat stress (HS), presumably by compounding an inflammatory response by both insults. Thus, study objectives were to investigate whether prior viral infection aggravates the physiological and feed intake (FI) responses to HS. Crossbred barrows (n=45; 75.5±4.8 kg BW) were enrolled in two experimental periods (P). During P1 (2 d), pigs were fed ad libitum and housed in thermoneutral (20ºC) conditions. During P2 (6 d), pigs were exposed to an increased heat load (28 to 31ºC). Rectal temperature (TR), skin temperature (TS), and respiration rate (RR) were obtained twice daily. FI was measured daily as feed disappearance. Unexpectedly, pigs became sick during the experiment and tested positive for influenza on d 6 of P2. Based on TR obtained during P1, animals were retrospectively categorized into 1 of 2 groups: 1) High-TR (HT; top third of pigs; TR>39.32ºC; x̅=39.38ºC; n=15), or 2) Low-TR (LT; bottom third of pigs; TR< 39.10ºC; x̅=38.95ºC; n=15). Pigs in the middle third tier were excluded from the analysis. This ostensibly categorized pigs into a “sick” and “healthy” status. Data were statistically analyzed using the MIXED procedure in SAS. As expected, HS increased TR in both groups; however, HT had elevated TR during P2 relative to LT pigs (+0.5ºC; P< 0.01). Skin temperature and RR increased during HS but remained similar between HT and LT pigs (P>0.41). During P1, FI was similar between groups (P>0.33). During P2, HS reduced FI in both groups; however, the decrease was more severe in HT than LT pigs (53 vs. 37%, respectively; P=0.01). Altogether, HT pigs, presumably infected before HS exposure, had increased TR and a more drastic reduction in FI during HS than LT pigs. A better understanding of how viral or bacterial infection influences the response to HS would have pragmatic implications for all segments of animal agriculture.

Role of latent heat storage in thermal performance of an axially grooved heat pipe

Heat pipe coupled with phase change material (PCM) based latent heat storage (LHS) is a significant thermal management system that can efficiently control the intermittent high heat loads of electronic devices. Herein, an axially grooved heat pipe-LHS (AGHP&LHS) system has been proposed. The influence of LHS units and their location on dynamic temperature response of AGHP has been investigated both experimentally and theoretically. The effect of filling rates of phase change materials (PCMs) as well as cooling temperature on thermal response of the AGHP has been compared and analyzed. Results indicate that the LHS effectively stabilizes the heat source temperature under the intermittent heating process, enhances the thermostat performance and brings the temperature uniformity in AGHP. In addition, LHS units arranged at the evaporator section are optimal for AGHP under intermittent heat load conditions, reducing the heat source temperature by 27.4% and prolonging the melting time by 81.5%. As the heat load increases, the melting time of AGHP&LHS system becomes shorter, and the overall temperature uniformity is worsened. In particular, the melting time is prolonged by 34.8% for AGHP&LHS system with PCM filling rate of 89% than that of 44% filling rate.

Optimization of a boron nitride nanotubes nanofluid-cooled microchannel heat sink at different concentrations

The microchannel heat sink (MCHS) has become the most relevant micro-heat exchanger for a small area in need of an effective high heat removal system. However, heat dissipation from the microchips where the MCHS is utilized—the microprocessor and microcontroller—is getting higher with the sizes getting smaller. A more effective coolant is needed to address the increasing heat load from the microchip and nanofluid, nanosized particles dispersed in a base fluid, is among those explored. This paper reports a new potential use of non-metallic nanofluid, boron nitride nanotube (BNN), that is capable of improving the overall performance of a rectangular MCHS. A heuristic method, multi-objective genetic algorithm (MOGA), is employed to simultaneously minimize the thermal resistance and pressured drop of a boron nitride nanotubes (BNN) nanofluid-cooled MCHS to obtain optimized dimensions at various mass concentrations. The method is capable in achieving conflicting objectives, minimization of the thermal resistance and the pressure drop; an increase in the former decreases the latter and vice versa. In addition, experimental thermophysical properties of the BNN nanofluid are used to provide reliability to the optimization outcomes in identifying the best BNN concentration for cooling of a MCHS at 50 °C. The optimization results showed that as the thermal resistance decreases, the pressure drop decreases. For mass concentrations of 0.001, 0.003, 0.005, 0.01 and 0.03% the thermal resistance is the lowest, 0.0711 K/W at 0.01 mass.%. at 0.0115 W. The thermal resistance is lowered by 5.34% compared to water for the same operating conditions. These results indicate the great potential of BNN nanofluid as a coolant in the electronics cooling system. Optimization with the MOGA provides a fast analysis into the potentials of any coolants for MCHS applications as shown here, reliability being provided by experimentally obtained thermophysical properties.

Energy savings for a junior high school classroom that actively uses daylighting and sensitivity study on the effect of the building envelope thermal performance

AbstractThis paper analyzes the energy‐saving potential of lighting, including its effect on heating and cooling, and analyzes the effect of the thermal performance of a building on the annual energy consumption of a classroom actively using daylighting. The subject of this study is M Junior High School, located in Gifu, Japan. This school has a classroom design with a sloping roof, allowing the installation of large windows from north to south. The window‐to‐wall ratio of 56% for the south wall and 41% for the north wall takes advantage of daylight. Simulation results of illuminance in the classroom were validated through comparison with field measurement data. The result demonstrated that daylight utilization decreases lighting electric power consumption by 66.6% when artificial lighting is controlled in the classroom. The results confirmed that there was no significant heat load increase for heating and cooling even though the window surface area was larger than that of a typical classroom. The sensitivity study showed that the thermal performance of the building envelope mainly affects the heating energy consumption, but it has no significant effect on cooling and lighting energy consumption. In terms of the thermal performance of the building envelope and the amount of energy saving by daylight utilization, it is necessary to consider the appropriate thermal performance to determine cost‐effectiveness.

Effects of High Heat Load Conditions on Blood Constituent Concentrations in Dorper, Katahdin, and St. Croix Sheep from Different Regions of the USA.

Simple SummaryHigh heat load (HL) can adversely affect livestock health and cause significant production losses as a result of alterations of many physiological functions including nutrient metabolism, oxidative status, blood constituent levels, and gut dysbiosis. Effects of high HL could vary with breed of hair sheep (i.e., Dorper, Katahdin, and St. Croix) as well as region of the United States of America with different climatic conditions where they originated. Differences among the three sheep breeds in levels of a number of blood constituents were observed. Different HL conditions also altered concentrations of several blood metabolites and constituents, including hemoglobin, oxygen concentration, creatinine, heat shock protein, thyroxine, and cortisol. However, there were no interactions between breed and HL for most blood variables, suggesting similar resilience to high HL. In addition, only a few differences among or interactions involving region suggest that the breeds are highly adapted to diverse climatic conditions.Forty-six Dorper (DOR), 46 Katahdin (KAT), and 43 St. Croix (STC) female sheep (initial body weight of 58, 59, and 46 kg, respectively, SEM = 1.75; 3.3 ± 0.18 years of age, 2.6–3.7), derived from 45 commercial farms in four regions of the USA (Midwest, Northwest, Southeast, and central Texas), were used to evaluate responses in blood constituent concentrations to increasing heat load index (HLI) conditions. There were four sequential 2 weeks periods with target HLI during day/nighttime of 70/70 (thermoneutral zone conditions), 85/70, 90/77, and 95/81 in period 1, 2, 3 and 4, respectively. A 50% concentrate pelletized diet was fed at 53.3 g dry matter/kg body weight0.75. The analysis of most constituents was for samples collected on the last day of the second week of each period at 13:00 h; samples for cortisol, thyroxine, and heat shock protein were collected in week 2 and 8. Previously, it was noted that resilience to high HLI conditions was greatest for STC, lowest for DOR, and intermediate for KAT. There were few effects of region. Other than hemoglobin concentration, there were no interactions between breed and period. Blood oxygen concentration was greatest (p < 0.05) among breeds for STC (5.07, 5.20, and 5.53 mmol/L for DOR, KAT, and STC, respectively; SEM = 0.114) and differed among periods (4.92, 5.26, 5.36, and 5.52 mmol/L for period 1, 2, 3, and 4, respectively; SEM = 0.093). There were breed differences (i.e., main effects; p < 0.05) in glucose (50.0, 52.6, and 52.1 mg/dL; SEM = 0.76), urea nitrogen (17.2, 17.3, and 19.4 mg/dL; SEM = 0.33), creatinine (0.991, 0.862, and 0.802 mg/dL; SEM = 0.0151), total protein (6.50, 6.68, and 6.95 g/l; SEM = 0.017), triglycerides (28.4, 29.1, and 23.5 mg/dL; SEM = 0.87), and cortisol (6.30, 8.79, and 6.22 ng/mL for DOR, KAT, and STC, respectively; SEM = 0.596). Differences among periods (p < 0.05) were observed for lactate (27.9, 25.3, 27.8, and 24.0 mg/dL; SEM = 0.99), creatinine (0.839, 0.913, 0.871, and 0.917 mg/dL; SEM = 0.0128), total protein (6.94, 6.66, 6.60, and 6.65 g/l; SEM = 0.094), and cholesterol (60.2, 56.5, 58.3, and 57.6 mg/dL for period 1, 2, 3, and 4, respectively; SEM = 1.26). In addition, the concentration of cortisol (7.62 and 6.59 ng/mL; SEM = 0.404), thyroxine (5.83 and 5.00 µg/dL; SEM = 0.140), and heat shock protein (136 and 146 ng/mL for week 2 and 8, respectively; SEM = 4.0) differed between weeks (p < 0.05). In conclusion, the lack of interaction between breed and period with different HLI conditions suggests that levels of these blood constituents were not highly related to resilience to high HLI.

Dynamic thermal analysis of startup process for minichannel evaporator

• Start-up regimes of minichannel evaporator are formulated by transfer function. • Evaluation criteria in control theory are proposed to describe start-up behaviors. • Startup performances of minichannel evaporator are quantitatively investigated. • Working fluid with small subcooling degree is beneficial for evaporator start-up. • Evaporator temperature overshoot can be alleviated via increasing heat load. The start-up performance of minichannel evaporator in a mechanically pumped two-phase loop (MPTL) is investigated in terms of the dynamic temperature response. A preliminary start-up regime diagram is identified, where temperature response of start-up process can be recognized as three modes, including the gradual start-up, once-rise overshoot start-up and twice-rise overshoot start-up. Theoretical analysis and model identification are conducted via Laplace-transformation and representative evaluation criterion is proposed to realize the quantitative characterization of specific start-up mode. Time constant and settling time act as the indicators to evaluate temperature response rate, while overshoot is utilized to assess the two-phase flow instability. The results indicate that: for gradual start-up mode, the time to reach quasi-steady state is smaller as heat transfer performance improves via increasing heat load, while temperature response rate is relatively insensitive to flow rate; for once-rise overshoot start-up mode, the two-phase flow instability can be alleviated via increasing the heat load, while the increment of flow rate could intensify the instability; for twice-rise overshoot start-up mode, the temperature overshoot is insensitive to heat load variation. Moreover, preheating the working fluid at evaporator inlet is beneficial to mitigate the instability, indicating that preheater/regenerator can optimize the robustness/stability of start-up.

Experimental study of saving energy and improving Stirling water dispenser performance using the waste heat of both pistons friction

Water dispensers are considered essential. So, water dispensers that use vapor-compression urgently need more energy-saving and environmentally friendly alternatives. Stirling water dispensers are a suitable option. However, the waste heat generated via friction between the pistons and their cylinders decreases the cooling load and power consumption. The present work uses the waste heat of both piston friction via water jackets to save energy and improve Stirling water dispenser performance. The result indicates that the heating and cooling loads of the present water dispenser are increased by about 2952 W and 834 W using the waste heat of both pistons at 1200 rpm. The increase of water flow rate within water jackets increases the heating and cooling loads due to the increased absorption of frictional heat. The comparison shows that the current water dispenser reveals an average increase in cooling load of up to 400 percent at low speeds and 61 percent at high speeds, and an increase in heating load of up to 390 percent at low speeds and 28 percent at high speeds.

Visualization study of a flat confined loop heat pipe for electronic devices cooling

Aiming to alleviate the ‘dry-out’ phenomenon of evaporators with microchannels and cater to the thermal management requirements of electronic devices, a novel flat confined loop heat pipe (FCLHP) was proposed, making its first attempt to provide an open flow space over the microchannel top surface of the evaporator. The internal flow to be confined in only one direction and the bubble to expand freely in the open space was allowed. Meanwhile, the evaporator and condenser were visualized to investigate the operation performance and mechanism of the FCLHP under different heat loads and cooling capacity. The intermittent boiling mechanism of the FCLHP was revealed. The results indicated that the regular rewetting of the heated surface was allowed by the open flow space over the microchannels. The proposed FCLHP could work most effectively as the cooling water temperature was 23 °C and cooling water flow rate was 135 mL/min, under which the FCLHP could start up most quickly; the operating temperature was reduced by 10% at most, and the minimum thermal resistance was just 0.12 K/W. The temperature fluctuation was related to intermittent boiling, and with the increase of heat load, the period of intermittent boiling decreased and then stayed constant. This can be explained as the fact that when the boiling was fully developed, the occurrence of intermittent boiling was attributed to the evaporator outlet restriction. Compared with the conventional MCFLHP in the literature, the proposed FCLHP can successfully start up at a lower heat load, i.e., 30 W; the temperature fluctuation of Teo was greatly reduced to less than 1 °C, and the thermal resistance was reduced by 29%. This research will be useful for the engineers and researchers in the application fields of heat pipes.

Solar Radiation in Architectural Projects as a Key Design Factor for the Well-Being of Persons with Alzheimer’s Disease

The beneficial effects of solar radiation on human health are well documented. One necessary mechanism triggers the production of vitamin D, whose insufficiency has been linked to a variety of disorders such as diabetes; hypertension; and, more recently, amyloidosis and Alzheimer’s disease. However, there are few architectural designs capable of ensuring the adequate provision of solar radiation inside buildings. Conventional fenestration is not sufficient to provide for significant doses of sunlight, even to prevent seasonal affective disorder (SAD). In this paper, we discuss the effect of new design alternatives for skylights, especially in the refurbishment of obsolete facilities. Based on the authors’ previous studies, we defined a theoretical model that was subsequently adapted to a real building that was to be retrofitted in an area near Sevilla. After such complex refurbishment was executed, we analyzed the performance of buildings in warm and sunny climates, as is the case of southern Spain, where cloudiness is very scarce and available simulation models are not useful. The study of the factors that relate to sunlight; UV reception and energy; and, to a certain extent, other aspects such as ventilation and insulation has been considered a priority. Many architectural designs are presented as correct if the thermal requirements alone are met, even at the risk of later energy waste in lighting devices and visual or physical discomfort. On the other hand, large glazed areas allow for more daylight and UV radiation into a space if properly treated, but they may also produce excessive heat gains or losses, which increase the air-conditioning cooling or heating load, respectively. The uncontrolled increase in temperature can have negative effects on the well-being of a person with Alzheimer’s dementia. To avoid these problems, we have considered the combined effect of daylight and energy from the beginning of the skylight design-process. Daylighting software, based on configuration factors that we have applied in studies of the complex problem of there being direct sunlight over architectural structures, has been used. This question cannot be treated adequately with conventional programs for overcast skies. The skylights have already been constructed, with special UV increasing glazing and on-site measurements in the offices to complement the computer simulation data. The results show that it is possible to achieve energy saving and high radiation levels in winter without increasing heat loads during the summer. Ventilation is also improved through the aerodynamic design of the clerestories. All this is considered beneficial to improve the condition of users with cognitive diseases as Alzheimer’s disease, by virtue of adapted spaces.

High Repetition Rate, TEM00 Mode, Compact Sub-Nanosecond 532 nm Laser

As a critical transmitter, compact 532 nm lasers operating on high repetition and short pulse widths have been used widely for airborne or space-borne laser active remote sensing. We developed a free space pumped TEM00 mode sub-nanosecond 532 nm laser that occupied a volume of less than 125 mm × 50 mm × 40 mm (0.25 L). The fundamental 1064 nm laser consists of a passively Q-switched composite crystal microchip laser and an off-axis, two-pass power amplifier. The pump sources were two single-emitter semiconductor laser diodes (LD) with 808 nm wavelengths and a maximum continuous wave (CW) power of 10 W each. The average power of the fundamental 1064 nm laser was 1.26 W, with the laser operating at 16 kHz repetition rates and 857 ps pulse widths. Since the beam distortion would be severe in microchip lasers due to the increase in heat load, in order to obtain a high beam quality of 532 nm, the beam distortion in our experiment amplifying the fundamental laser was compensated by adjusting the distribution of the pumping beam. Furthermore, in the critical phase matching (CPM) regime for the second harmonic generation (SHG), a Type I LiB3O5 (LBO) crystal obtained 770 ps, a beam quality of M2 &lt; 1.2, and a 16 kHz pulse output at 532 nm, which was better than 0.6 W average power.

Elliptical and linear relationships with rumen temperature support a homeorhetic trajectory for DMI during recovery of feedlot cattle exposed to moderate heat load.

Most feedlot animals in Australia experience 2 to 3 moderate heat waves during summer. This study aimed to gain understanding of the physiological drivers in response to and during recovery from such events with a view to designing strategies to ensure rapid and safe recovery. Two hypotheses were tested during thermal challenge and recovery in climate-controlled rooms (CCR): firstly, the feedlot steer on a grain-based diet mounts appropriate physiological responses during moderate heat load and in recovery so that its performance and physiology state after recovery is not different to the feed restricted thermoneutral (FRTN) steer. Secondly, commonly used indicators of increased heat load, e.g., respiration rate (RR), panting score (PS), body surface temperatures (ST), and water consumption (WC), reflect rumen temperature (RT) during thermal challenge and recovery at the level of daily means. In this study, 36 Angus steers (live weight (LW) 451.5 ± 22.6 kg) made up 3 cohorts of 12 animals that sequentially underwent the CCR phase. For this 18-d phase, the steers were allocated to either a moderate heat load treatment (thermally challenged, TC, n = 18) or a FRTN treatment (n = 18). The TC group underwent 3 periods, Pre-Challenge (4 d, temperature humidity index (THI) range of 68 to 71), Challenge (7 d, THI 73 to 84 with diurnal cycling), and Recovery (7 d, THI 68 to 71). The FRTN group were held at thermoneutral conditions in the CCR (THI 66.9 ± 0.3), and each animal was offered an amount of feed was based on the feed intake of its LW matched TC pair. Thus, as DMI fell in the TC group during Challenge, feed restriction was imposed on the FRTN group. The data were collected by trained observers were DMI, RT, RR, PS, body STs (forehead, shoulder, leg, rump), and WC. Challenge induced a heat stress response in the TC group with reduced DMI and LW, and elevated RT, RR, PS, body STs, and WC (P < 0.001). These measures were unchanged or reduced in the FRTN group (P < 0.001). At the end of Recovery, the TC and FRTN groups had converged on most measures including LW. Daily mean RT of both groups showed strong linear relationships with THI, RR, PS, head ST, and WC (P ≤ 0.0022) but opposing elliptical relationships with DMI; that is, as DMI fell with increasing RT for the TC group, DMI increased with rising RT for the FRTN group. In all, the feedlot steers in this study demonstrated sufficient homeorhetic capacity to adjust to moderate heat load and recover from it.

Physiological and Behavioral Reactions of Simmental Dairy Cows to Increasing Heat Load on Pasture

Climate change is accompanied by temperatures exceeding the thermal comfort zone of dairy cows, resulting in numerous consequences for production and welfare. Early detection of heat load enables taking countermeasures and can be realized using monitoring systems. We aimed at investigating heat load-induced changes in the behavior and physiology of grazing Simmental cows. Data were collected on five (round 1; r1) and eight (round 2; r2) consecutive days on a dairy farm combining a freestall barn with permanent access to pasture. Weather data, respiration rate, milk yield, milk composition, and fecal cortisol of eleven (r1) and thirteen (r2) cows were collected. The behavior of five animals was recorded with collar-based monitoring systems. Previously reported thresholds of different weather indices were exceeded on two days in r1 and on four days in r2. Under heat load, respiration rate and somatic cell count increased. Fecal cortisol did not change in r1 but increased steadily in r2. Grazing time decreased in r1. Rumination mainly occurred at night in both rounds, and its synchrony decreased in r2. Although limited by sample size, our results give a first impression on heat load induced physiological and behavioral reactions of Simmental dairy cows on pasture.

Visualized-experimental investigation on a mini-diameter loop thermosyphon with a wide range of filling ratios

The mini-diameter loop thermosyphon, which has an excellent heat transfer performance with simple, compact structure and pump-free advantages, can effectively solve the problem of heat transfer under high heat load in a confined space. The mini-diameter loop thermosyphon exhibits different gas-liquid transport and heat transfer patterns than the conventional-diameter one due to various gas-liquid phase transformation properties and a strong friction force in the mini-diameter channel. Furthermore, data on the visual analysis of gas-liquid transport and heat transfer properties of the mini-diameter loop thermosyphon under various filling ratios is still lacking. In this paper, a visible experimental research on a mini-diameter loop thermosyphon (3 mm) in a wide filling ratio range(44% -97%) is undertaken. The maximal heat transfer capacity increases initially and subsequently falls with the filling ratio, according to the testing data. At a low filling ratio, the flow pattern changes as slug flow - churn flow - annular flow with the heat load increase, leading to a low loop thermal resistance, and dry out occurs at 185 W heat load under 50% filling ratio. The gas-liquid flow shifts to slug flow-geyser boiling-bubble flow at high filling ratios (73% and 82%), and the bubble departure diameter steadily decreases with increasing heat load. Consequently, the heat transfer performance (thermal resistance) has been enhanced, and the maximum heat transfer capacity has been increased to 280 W. Single-phase flow is plainly seen in the loop when the filling ratio reaches 91% or even 97%, thus reduced heat transfer capacity. Therefore, the high-filling-ratio mini-diameter loop thermosyphon is better for high-load heat dissipation. However, a low thermal resistance shows at the low filling ratio, but the heat load is also low. As a result, a loop thermosyphon with a low filling ratio should be selected for the low heat load situation.