Prevent Heat Loss Research Articles

Development of a thermoelectric energy harvester with thermal isolation cavity by standard CMOS process

A micro thermoelectric generator that combines the conventional in-plane and cross-plane designs is developed to harvest effectively the thermal gradient, where heat flux from the top to bottom surface is confined passing through the in-plane thermocouples. A thermal isolation cavity is created underneath the thermocouples to prevent heat loss, maintain temperature gradient, and improve output power. Analysis shows that, with 10 μm cavity depth, the thermocouple's temperature gradient is above 99% of the hot/cold side temperature difference. By comparison, it is only 14% for those without the isolation cavity. Simulation results show that the optimal thermocouple of 71 μm × 4 μm × 0.275/0.18 μm (length × width × thickness for P-/N-thermolegs) has matching electrical/thermal resistance and can achieve the maximum power factor 0.0473 μW/cm 2 K 2 and voltage factor 2.788 V/cm 2 K. The design is validated by standard CMOS process, where the isolation cavity is realized by dry etching post-process. Design verification by TSMC 0.35 μm 2P4M (2-poly and 4-metal) CMOS process shows that the thermocouple 60 μm × 4 μm can provide the power factor 0.0417 μW/cm 2 K 2 and voltage factor 2.417 V/cm 2 K.

Method of water nebulization used to prevent heat loss during laparoscopic surgery matters

Method of water nebulization used to prevent heat loss during laparoscopic surgery matters

Effects of Different Operating Room Temperatures on the Body Temperature Undergoing Live Liver Donor Hepatectomy

Objective We sought to compare the effects of operation room temperature (ORT) at typical ambient environment (19–21°C) and ORT at 24°C on the core temperature of patients undergoing living donor hepatectomy. Methods and Patients Sixty-two patients undergoing living donor hepatectomy were divided into 2 groups. In group I ( n = 31), surgery was performed at typical ambient ORT, and in group II ( n = 31) in ORT at 24°C. Anesthesia and measures to prevent heat loss, except ORT, were all the same. Nasopharyngeal temperature (NT) was recorded after anesthesia induction, then hourly until completion of the operation. Changes in NTs were analyzed as well as patient age, weight, anesthetic duration, blood loss, intravenous fluids, total urine output, and pre- and postoperative hemoglobin and hematocrit values. The Mann-Whitney U test was used for comparisons between groups. Results The patient's characteristics between groups were not statistically different. However, a significantly higher core temperature was noted in group II compared with group I. Increased ORT from 19 to 21°C to 24°C resulted in an increased core temperature of at least 0.5°C during living donor hepatectomy.

Pressureless Rapid Sintering of UO2 Assisted by High‐frequency Induction Heating Process

Heat generation of uranium dioxide (UO2) powder and its pressureless rapid sintering behaviors have been studied using a high‐frequency induction heating apparatus. The porous graphite housing has been used to prevent heat loss and to preheat the uranium oxides, simultaneously. At an elevated temperature, UO2 powder generated extra heat by itself. The synergism of individual heat generation between the graphite and UO2 powder could effectively heat the UO2 to the sintering temperature of 1700°C. Using this process, densification behavior of cylindrical and disk‐type UO2 green pellets according to the heating rate and grain structure of sintered UO2 pellets were investigated. Rapid sintering caused a large crack around the circumference of the sintered pellet. The formation of cracks could be avoided when the heating rate or sample dimension are properly reduced. A dense and crack‐free UO2 pellet with a relative density of up to 96% was produced within 5 min of the process time. The induction heat sintering process can be a potential candidate for the rapid fabrication of ceramics and composites.

Evidence vs experience in neonatal medicine

Tremendous progress has been made in the field of neonatal–perinatal medicine over the past two decades. However, the incidence of prematurity continues to increase in the United States. Care of infants born prematurely is evolving continuously based on evidence and experience. In 2004, a steering committee (Jatinder Bhatia, Rangasamy Ramanathan, Kris Sekar and Istvan Seri) was established to organize a scientific meeting to present results from randomized controlled trials or when there is no evidence from controlled trials; ‘experts’ in neonatal medicine were invited to discuss their ‘experience’. The 4th Annual Conference in Chicago focused on nutrition of extremely low birth weight (ELBW) infants, necrotizing enterocolitis (NEC), fetal inflammation and lung injury, resuscitation and stabilization of the preterm infant, strategies in protecting the preterm infant's lungs and newer therapeutic options for ELBW infants. National and international experts participated in the meeting to discuss these topics. As program chair, I began the meeting with a brief introduction about the specific aim of the meeting, which is to provide the updated information and take-home messages to clinicians caring for sick newborns based on evidence or experience. Henry Ford, pediatric surgeon from Children's Hospital Los Angeles (CHLA), whose research interest has been to study the role of gut immunity on NEC, elegantly presented data on the role of gut-associated lymphoid tissue, gut epithelial barrier function and pathophysiology of NEC. Following Dr Ford's presentation, Victoria Camerini, also from CHLA, discussed spontaneous intestinal perforation (SIP), which is being increasingly recognized as a different entity from NEC among ELBW infants. She also presented evidence from randomized trials on the medical and surgical management of NEC and SIP and discussed the role of primary peritoneal drainage vs laprotomy. Boris Kramer, from Academisch ziekenhuis Maastricht (the Netherlands), presented on the role of fetal inflammation in initiating lung injury. Use of room air or oxygen during resuscitation of the newborn, especially the preterm infant remains controversial. Professor Ola Saugstad of Oslo, Norway, an internationally known scientist for his work in this area, presented evidence for the optimal resuscitation of infants at birth. Marilyn Escobedo, from Oklahoma University Children's Hospital, a member of the neonatal resuscitation program steering committee, presented revised resuscitation guidelines and practical implications of changes in the guidelines. Bronchopulmonary dysplasia continues to be a major morbidity among preterm infants. Waldemar Carlo, from the University of Alabama, talked about the use of continuous positive airway pressure in the delivery room. I discussed evidence from controlled clinical trials on lung-protective ventilatory strategies in very low birth weight infants requiring positive pressure ventilation. Surfactant therapy is one of the few interventions that has been studied extensively in neonatology. Professor Henry Halliday, from Royal Maternity Hospital in Belfast, Ireland, was our keynote speaker, and he took us through the past, present and future of surfactant therapy. In the final session of our meeting, Roger Soll, from the University of Vermont, reviewed results from the meta-analysis on the prevention of heat loss in preterm infants. Hemodynamically significant patent ductus arteriosus (PDA) frequently complicates the clinical course in ELBW infants. Dr Sekar, from Oklahoma University Children's Hospital, discussed the pros and cons of treatment of PDA with indomethacin vs ibuprofen. Management of infants delivered at the threshold of viability continues to be a major ethical and moral challenge. Dr Seri, from CHLA, discussed the various approaches in the management of micropreemies and provided an algorithm for the management of these tiny infants.

Cold nebulization used to prevent heat loss during laparoscopic surgery: an experimental study in pigs

Prolonged abdominal laparoscopy is responsible for a significant drop in core body temperature. Various modifications of the conditioning for the insufflating carbon dioxide (CO(2)) to prevent the specific hypothermia related to the insufflated gas have been tested. This study aimed to investigate the effects on core temperature of insufflation with unheated humidified CO(2) using the Aeroneb system compared with the use of standard gas and gas made hot and wet using a warming and humidifying system (Pall system). A prospective four-session study was conducted to investigate a homogeneous group of four pigs. After inducation of general anesthesia, all the animals were treated successively with the following protocols in a randomized order at 8-day intervals: control (no pneumoperitoneum), standard (unheated, unhumidified CO(2)), Aeroneb (unheated, humidified CO(2) by cold nebulization), and Pall (heated, humidified CO(2)). The core temperature of the animals was recorded every 10 min. Analysis of variance (ANOVA) confirmed a difference between the insufflation conditions in the evolution of temperature over time (p = 0.004). The method of contrast showed the following results. After 30 min, the core temperature of the Aeroneb group fell significantly less than that of the standard group (p = 0.036). After 100 min, the core temperature of the Pall group fell significantly less than that of the standard group (p = 0.024). After 80 min, the core temperature of the standard group fell significantly more than that of the control group (p = 0.035). In the Aeroneb group, the core temperature dropped less than in the Pall and control groups, but the difference did not reach statistical significance. Cold humidification of insufflating CO(2) prevents heat loss associated with pneumoperitoneal insufflation at least as efficaciously as warmed humidification of the gas.

Melanin-based color variation in the Bearded Vulture suggests a thermoregulatory function

We document a case of intraspecific variation in plumage colouration in Bearded Vultures that may have arisen as a functional response to climate conditions. Two subspecies, Gypaetus barbatus barbatus (Eurasia and North Africa populations) and Gypaetus barbatus meridionalis (Eastern and Southern Africa), have been described on the basis of plumage colour differences. The plumage of G. b. barbatus tends to be darker in comparison with that of G. b. meridionalis. The plumage of the two subspecies differ in the feathering of the tarsi (more abundant in G. b. barbatus) and presence/absence of dark ear tufts (only present in G. b. barbatus, and this being the most useful character to distinguish adult specimens of both subspecies). When exposing skins under the sun or to electric bulbs in a cold room, temperature increases were significantly higher in the black ear tufts than in the frontal region of the head, suggesting that the melanized ear patch of G. b. barbatus serves, at least, to heat up the air entering the ear channel and perhaps also the underlying skin. In addition, G. b. barbatus, which inhabits mountainous regions with harsh and long winters, would benefit more from feathered tarsi to prevent heat loss through the legs.

Focused Ion Beam in Thermal Science and Engineering

Laboratory of Thermodynamics, ETH Zurich CH-8092 Switzerland In this paper, utilizing a focused ion beam source for applications in thermal science is demonstrated. Focused-ion-beam (FIB) nanolithography has been used to make electrical contacts on nanometer-sized materials. However, a foreseeable damage occurring in these materials by highly energetic ion bombardment during metal deposition restrains its use. The appearance of the dual beam (conventional FIB with a scanning electron microscope) has facilitated the use of dual-beam FIB nanolithography owing to the possibility of acquiring electron beam images in situ and dissociating metalorganic compounds, giving rise to electron-beam-induced metal deposition [1]. Because interaction between electrons and the sample is less destructive than using ions, performing an electron-assisted deposition on the nanostructure can minimize undesired surface damage and structure modification of the nanostructure. The thermal properties of individual multi-walled carbon nanotubes was measured by utilizing the 4-point-probe 3-ω method, based on the fact that the third harmonic amplitude and phase as a response to applied alternate current at fundamental frequency, ω, can be expressed in terms of thermal conductivity and diffusivity. To this end, a microfabricated device composed of four metal electrodes was modified to manufacture nanometer-sized wires by using a focused ion beam source as shown in Fig. 1a. A carbon nanotube could then be suspended over a deep trench milled by the focused ion beam, preventing heat loss to the substrate (Fig. 1b). To deposit individual carbon nanotubes, we utilized the principle of dielectrophoresis (DEP). The dielectrophoresis has been considered as an excellent method for CNT manipulation. Herein, we applied a high-frequency (5 MHz) ac field combined with dc offset between the pads, 1 and 4. When a CNT touches the electrodes, it will stick to them and stays there by Van der Waals force [2]. Finally, to minimize the electrical contact resistance between carbon nanotubes and the metal electrodes, electron beam “soldering” was performed. The pads 1 and 4 have round shapes on the tip, which aids carbon nanotube deposition. Fig. 2 shows three different measurements of 3-ω signals for carbon nanotubes submerged in vacuum, air and deionized water. To this end, the 4-wire configuration (Fig. 1c) was utilized for measuring the 3

An improved model of heat transfer through penguin feathers and down

Penguins, mostly live in the extremely cold Antarctic, are known to have feathers and down, which are light weight, compact and extremely efficient in preventing heat loss. Nevertheless, the mechanisms of heat transfer through the penguin feathers and down, and how the unique characteristics of penguin feathers and down make them such good thermal insulators are not fully understood. In this paper, an integrated model of heat transfer through the penguin feathers and down is developed and computed using finite volume method, with the geometrical structure of the barbules being considered. Monte-Carlo method is adopted to determine the radiative absorption and emission constant in the integrated model. The effective thermal conductance of penguin feathers and down computed from our model compared well with the experimentally measured value reported in the literature. Three models (penguin model, random fibre model (fibre radius=3 μm) and random fibre model (fibre radius=10 μm)) are further simulated and compared. Results showed that the relative small radius of the barbules of penguin feather and their geometrical structure are responsible for the reduction of heat loss in cold environment.

Thermoregulation and Heat Loss Prevention After Birth and During Neonatal Intensive‐Care Unit Stabilization of Extremely Low‐Birthweight Infants

Extremely low-birthweight infants have inefficient thermoregulation due to immaturity and may exhibit cold body temperatures after birth and during their first 12 hours of life. Hypothermia in these infants can lead to increased morbidity and mortality. Anecdotal notes made during our recent study revealed extremely low-birthweight infants' temperatures decreased with caregiver procedures such as umbilical line insertion, intubations, obtaining chest x-rays, manipulating intravenous lines, repositioning, suctioning, and taking vital signs during the first 12 hours of life. Therefore, nursing interventions should be undertaken to prevent heat loss during these caregiver procedures. Nurses can improve the thermal environment for extremely low-birthweight infants by prewarming the delivery room and placing the infant in a plastic bag up to the neck during delivery room stabilization to prevent heat loss.

Evidence-Based Practices for the Fetal to Newborn Transition

Many common care practices during labor, birth, and the immediate postpartum period impact the fetal to neonatal transition, including medication used during labor, suctioning protocols, strategies to prevent heat loss, umbilical cord clamping, and use of 100% oxygen for resuscitation. Many of the care practices used to assess and manage a newborn immediately after birth have not proven efficacious. No definitive outcomes have been obtained from studies on maternal analgesia effects on the newborn. Although immediate cord clamping is common practice, recent evidence from large randomized, controlled trials suggests that delayed cord clamping may protect the infant against anemia. Skin-to-skin care of the newborn after birth is recommended as the mainstay of newborn thermoregulation and care. Routine suctioning of infants at birth was not been found to be beneficial. Neither amnioinfusion, suctioning of meconium-stained babies after the birth of the head, nor intubation and suctioning of vigorous infants prevents meconium aspiration syndrome. The use of 100% oxygen at birth to resuscitate a newborn causes increased oxidative stress and does not appear to offer benefits over room air. This review of evidence on newborn care practices reveals that more often than not, less intervention is better. The recommendations support a gentle, physiologic birth and family-centered care of the newborn.

Vinyl bags prevent hypothermia at birth in preterm infants

To compare the effect of standard care vs. the use of vinyl bags (Vi-Drape (R) isolation bag) on admission temperature in extremely premature infants < or = 28 weeks gestational age at birth. Twenty seven premature infants with similar baseline characteristics were assigned and placed in vinyl bags (n=14) immediately following delivery without drying or received standard care (controls, n=13), including drying and placement under a radiant warmer. Axillary temperature was recorded on admission to the neonatal unit. The average temperature in the vinyl bag group was significantly higher (35.9 +/- 0.13 vs 34.9 +/- 0.24 degrees C, p=0.002). Although the cord blood pH was similar between the two groups (7.33+0.02 in the vinyl bag group and 7.33 +/- 0.01 in the control group), the worst pH in the first 6 hours of life was significantly lower in the control group (7.32 +/- 0.02 vs 7.22 +/- 0.04, p=0.03). There was a significant increase in maximal oxygen requirement during the first 24 h in the control group (82.9 vs 43.3% in the vinyl bag group, p=0.0004). Vinyl bags prevent heat loss and are a simple and effective intervention in preventing hypothermia in the delivery room and early acidosis in premature infants.

Nursing and medical staff knowledge regarding the monitoring and management of accidental or exposure hypothermia in adult major trauma patients

Recording a patient's vital signs is a basic requirement that in part informs clinical decision-making. Practice suggests that recording a trauma patient's temperature is occasionally overlooked in the emergency department. A staff survey was undertaken to gain an appreciation of knowledge and understanding of the issues that surround accidental or exposure hypothermia in trauma patients. Results demonstrate that nurses and doctors are unsure of how to define hypothermia and are not conversant with simple ways to prevent heat loss or rewarm patients. Complications from hypothermia such as coagulopathy and metabolic acidosis were seldom identified. Issues that limit staff recording temperature include patient access and acuity, lack of knowledge and confidence and access to temperature-measuring devices. These results emphasize the need for regular education. Implications for clinical practice were considered; an algorithm to guide staff on ways to improve the monitoring and management of temperature in trauma patients was developed. Opportunities for ongoing and further research were identified.

Optimization of a flow reversal reactor for the catalytic combustion of lean methane mixtures

This paper describes a parametric study of a catalytic flow reversal reactor used for the combustion of lean methane in air mixtures. The effects of cycle time, velocity, reactor diameter, insulation thickness, thermal mass and thermal conductivity of the inert sections are studied using a computer model of the system. The effects on the transient behaviour of the reactor are shown. Emphasis is placed on the effects of geometry from a scale-up perspective. The most stable system is obtained when the thermal mass of the inert sections is highest, while thermal conductivity has only a minor effect on reactor temperature. For a given operation, the stationary state depends on the combination of velocity and switch time. Provided that complete conversion is achieved, highest reactor temperature is achieved with the highest switch time. The role of the insulation is not only to prevent heat loss to the environment, but also to provide additional thermal mass. During operation heat is transfer to and from the insulation. The insulation effect leads to higher reactor temperature up to a maximum thickness. The insulation effect diminishes as the reactor diameter increases, and results in higher temperatures at the centreline.

Measurement of the Thermal Conductivity of Individual Carbon Nanotubes by the Four-Point Three-ω Method

The thermal conductivity of individual multiwalled carbon nanotubes was measured by utilizing the four-point-probe third-harmonic method, based on the fact that the third harmonic amplitude and phase as a response to applied alternate current at fundamental frequency, omega, can be expressed in terms of thermal conductivity and diffusivity. To this end, a microfabricated device composed of four metal electrodes was modified to manufacture nanometer-sized wires by using a focused ion beam source. A carbon nanotube could then be suspended over a deep trench milled by the focused ion beam, preventing heat loss to the substrate. Compared with the two-point-probe technique, a significant improvement in accuracy is assured by using four probes, because the contact contribution to the determination of the thermal conductivity is eliminated, making it possible to measure the correct signals of first and third harmonics. The multiwalled carbon nanotube was modeled as a one-dimensional diffusive energy transporter and its thermal conductivity was measured at room temperature under vacuum to be 300 +/- 20 W/mK.

Numerical Study on Mould Powder Entrapment Caused by Vortexing in a Continuous Casting Process

Unsteady three‐dimensional turbulent flow phenomena are seen to have a major impact on steel quality in the continuous casting process. Usually steel mould powder is placed on top of the mould in order to use it as a lubricant between the solidifying steel and the mould and to prevent heat losses from the molten steel. It is well known that mould powder entrapment into the molten steel lowers the quality of the final steel products significantly. This can be caused by a vortexing flow at the interface between mould powder and molten steel near the submerged entry nozzle (SEN).The paper describes a study which was performed to analyse if commercial Computational Fluid Dynamics (CFD) software is capable of predicting the transient build‐up of vertical structures in the casting mould. Two‐phase‐flow phenomena have been modelled by using the Volume Of Fluid (VOF) method. The influence of different turbulence models, mesh densities and initial as well as boundary conditions on the resulting flow field was investigated. Due to the size and complexity of the problems the simulations partially had to be performed in parallel mode on a Linux‐cluster computing environment.

Setting the “Furnace” during Anesthesia

Setting the “Furnace” during Anesthesia

A Survey of Delivery Room Resuscitation Practices in the United States

To determine current resuscitation practices of neonatologists in the United States. A 15-question survey was developed and mailed to neonatal directors in May 2004. Of the total of 797 surveys mailed, 84 were returned undeliverable or unanswered and 450 were returned completed (63% response rate). Respondents were mainly (70%) from level III NICUs. Most programs resuscitate newborns in the delivery room (83%), rather than in a separate room. The number and background of individuals attending deliveries vary greatly, with 31% of programs having <3 individuals attending deliveries. Flow-inflating bags are most commonly used (51%), followed by self-inflating bags (40%) and T-piece resuscitators (14%). Pulse oximeters are used during resuscitation by 52% of programs, and 23% of respondents indicated that there was a useful signal within 1 minute after application. Blenders are available for 42% of programs, of which 77% use pure oxygen for the initial resuscitation and 68% use oximeters to alter the fraction of inspired oxygen. Thirty-two percent of programs use carbon dioxide detectors to confirm intubation, 48% routinely and 43% when there is difficulty confirming intubation. Preterm infants are wrapped with plastic wrap to prevent heat loss in 29% of programs, of which 77% dry the infant before wrap application. A majority of programs (76%) attempt to provide continuous positive airway pressure or positive end expiratory pressure (PEEP) during resuscitation, most commonly with a flow-inflating bag (58%), followed by a self-inflating bag with PEEP valve (19%) and T-piece resuscitator (16%). A level of 5 cm H2O is used by 55% of programs. Substantial variations exist in neonatal resuscitation practices, some of which are not addressed in standard guidelines. Future guidelines should include recommendations regarding the use of blenders, oximeters, continuous positive airway pressure/PEEP, and plastic wrap during resuscitation.

Heating capabilities of the Hotline® and Autoline® at low flow rates

At low flow rates, fluid warmers using coaxial warming tubes are superior in preventing heat loss. This laboratory investigation was performed in order to compare the heating capabilities of two coaxial fluid warmers. The Hotline and the Autoline were investigated by using normal saline at various flow rates (10-99 ml x h(-1)). Final infusion temperatures were measured six times in a row at the end of the tubing by using a rapid-response thermometer. Final temperatures were compared with those of infusions, which passed through disposable i.v. tubing covered and warmed using an 'off label' convective air warming system (WarmTouch). Measurements were performed at two different room temperatures (20 and 24 degrees C). Each group was analyzed with respect to differences between various flow rates as well as differences between the groups at comparable flow rates by using a three-way anova with multiple comparisons according to Tukey's procedure. Significance was defined at P < 0.05. Both devices heat infusions at low flow rates efficiently above 34 degrees C, with the Hotline being more effective than the Autoline (P < 0.0001). Except for the lowest flow rate (10 ml x h(-1)), the Hotline delivered infusion temperatures between 38 and 39 degrees C, while the Autoline warmed the infusions upto 36 degrees C. While heating capability of the Hotline was improved with elevated room temperatures at low flow rates (10-60 and 80 ml x h(-1)), the Autoline demonstrated lower infusion temperatures throughout elevated room temperature at flow rates between 20 and 90 ml x h(-1). Both devices heated infusions more efficiently compared with 'off label used' convective air warmer (each with P < 0.0001). Both the Hotline and the Autoline heated infusions sufficiently at low flow rates. However, the heating capability of the Hotline was superior and can further be increased at low flow rates by increasing the room temperature.

Heat Loss Prevention: A Systematic Review of Occlusive Skin Wrap for Premature Neonates

To systematically identify and synthesize investigations of the effectiveness of occlusive skin wrap for reducing heat loss in premature infants born at less than 36 weeks gestations. Systematic review. Three randomized controlled trials (RCT) and five historical controlled trials (HCT) were included. Meta-analysis shows wrapped infants had significantly higher admission temperatures than unwrapped infants (RCTs WMD 0.63 degrees C, 95% confidence interval (CI) 0.38, 0.87; HCTs WMD 0.96 degrees C, 95% CI 0.66, 1.27). A statistically significant difference in mortality was not found between wrapped and unwrapped infants in the RCTs (RR 0.72, 95% CI 0.36, 1.45) or the HCTs (RR 0.76, 95% CI 0.51, 1.13). The findings suggest that occlusive skin wrap prevents heat loss in premature infants. The meta-analysis lacked the power to provide definitive results regarding the effect of wrap on mortality.