<p>Run-around energy recovery systems are one of the several ways for transferring energy between two air streams. Compared with other air-to-air energy recovery systems, run-around systems are very reliable and flexible, especially in retro-fit applications. Previous research in this area has mainly dealt with sensible run-around heat recovery system. However, an ideal air-to-air energy recovery device should be able to recover moisture as well as sensible heat. It is the objective of this research project to simulate a run-around system that exchanges both moisture and sensible heat, and to do a performance analysis to find the design characteristics of such a system.</p><p>The first step in the study was to develop a numerical model for a run-around system with two sensible heat exchangers and validate the model using data from the published literature. Following this, a mathematical/numerical model of a heat and moisture exchanger and the run-around heat and moisture recovery system was developed using only basic physical and chemical principles, component properties and operating conditions. With this model, the position dependent temperature and moisture content properties of both a single exchanger and a run-around system were simulated for steady state operating conditions. This simulation enables the study of the performance of the exchanger and the run-around system. In the investigation, the method was employed to characterize the performance of a single exchanger and a run-around system and two new independent parameters, the number of mass transfer units and mass flow rate ratio, were introduced.</p><p>The results show that, for the sensible run-around heat recovery system with a specified NTU, the maximum effectiveness occurs approximately at a heat capacity ratio, but for the run-around system with both heat and moisture exchange, the maximum effectiveness occurs approximately at heat capacity ratio for ARI summer and winter test conditions and the maximum effectiveness varies with . The analysis of the run-around system with both heat and moisture exchange with and as independent parameters shows that the maximum effectiveness occurs approximately when . As well, the value of maximum effectiveness was found to be different when different coupling salt solutions were used.

<p>Run-around energy recovery systems are one of the several ways for transferring energy between two air streams. Compared with other air-to-air energy recovery systems, run-around systems are very reliable and flexible, especially in retro-fit applications. Previous research in this area has mainly dealt with sensible run-around heat recovery system. However, an ideal air-to-air energy recovery device should be able to recover moisture as well as sensible heat. It is the objective of this research project to simulate a run-around system that exchanges both moisture and sensible heat, and to do a performance analysis to find the design characteristics of such a system.</p><p>The first step in the study was to develop a numerical model for a run-around system with two sensible heat exchangers and validate the model using data from the published literature. Following this, a mathematical/numerical model of a heat and moisture exchanger and the run-around heat and moisture recovery system was developed using only basic physical and chemical principles, component properties and operating conditions. With this model, the position dependent temperature and moisture content properties of both a single exchanger and a run-around system were simulated for steady state operating conditions. This simulation enables the study of the performance of the exchanger and the run-around system. In the investigation, the method was employed to characterize the performance of a single exchanger and a run-around system and two new independent parameters, the number of mass transfer units and mass flow rate ratio, were introduced.</p><p>The results show that, for the sensible run-around heat recovery system with a specified NTU, the maximum effectiveness occurs approximately at a heat capacity ratio, but for the run-around system with both heat and moisture exchange, the maximum effectiveness occurs approximately at heat capacity ratio for ARI summer and winter test conditions and the maximum effectiveness varies with . The analysis of the run-around system with both heat and moisture exchange with and as independent parameters shows that the maximum effectiveness occurs approximately when . As well, the value of maximum effectiveness was found to be different when different coupling salt solutions were used.

In this study, a numerical model is developed for determining coupled heat and moisture transfer in a run-around membrane energy exchanger (RAMEE) using two counter/cross flow exchangers and with a salt solution of MgCl2 as the coupling fluid. The counter/cross flow exchanger is a counter-flow exchanger with cross-flow inlet and outlet headers. The model is two-dimensional, steady-state and based on the physical principles of conservation of momentum, energy, and mass. The finite difference method is used in this model to discretize the governing equations.<p> The heat transfer model is validated with effectiveness correlations in the literature. It is shown that the difference between the numerical model and correlations is less than ¡À2% and ¡À2.5% for heat exchangers and run around heat exchangers (RAHE), respectively. The simultaneous heat and moisture transfer model is validated with data from another model and experiments. The inter-model comparison shows a difference of less than 1%. The experimental validation shows an average discrepancy of 1% to 17% between the experimental and numerical data for overall total effectiveness. At lower NTUs the numerical and experimental results show better agreement (e.g. within 1-4% at NTU=4).<p> The model for RAHE is used to develop new effectiveness correlations for the geometrically more complex counter/cross flow heat exchangers and RAHE systems. The correlations are developed to predict the response of the exchangers and overall system to the change of different design characteristics as it is determined by the model. Discrepancies between the simulated and correlated results are within ¡À2% for both the heat exchangers and the RAHE systems.<p> It is revealed by the model that the overall effectiveness of the counter/cross flow RAMEE depends on the entrance ratio (the ratio of the length of the inlet and outlet headers to the length of the exchanger, xi/x0), aspect ratio (the ratio of the height to the length of the exchanger, y0/x0), number of heat transfer units (NTU), heat capacity rate ratio (Cr*), number of mass transfer units (NTUm), and the mass flow rate ratio of pure salt in desiccant solution to dry air (m*). Beside these dimensionless parameters, the performance of the RAMEE system is affected by the liquid-air flow configuration and the operating inlet temperature and humidity.<p> This study concludes that the maximum effectiveness of the RAMEE system with two counter/cross flow exchangers occurs when NTU and NTUm are large (e.g. greater than 10). At any NTU, the overall effectiveness of the RAMEE system increases with Cr* until it reaches a maximum value when Cr*= . Increasing Cr* above causes the overall effectiveness to decrease slightly. Therefore, to achieve the maximum overall effectiveness of the system, Cr* must be close to . is a function of NTU and operating conditions e.g., with NTU=10, and under AHRI summer and winter operating conditions, respectively. The exchangers in the RAMEE system are needed to have a small aspect ratio (e.g. y0/x0<0.2) and small entrance ratio (e.g. xi/x0<0.1) to get the maximum overall effectiveness of a RAMEE system using two counter/cross flow exchangers. Such a RAMEE system has a total effectiveness 6% higher and 1.5% lower compared to the same cross-flow and counter-flow RAMEE, respectively (at NTU=10, Cr*¡Ö3, y0/x0=0.2 and xi/x0=0.1).

In this thesis, a numerical model for coupled heat and moisture transfer in a run around membrane energy exchanger (RAMEE) with a liquid desiccant as a coupling fluid is developed. The numerical model is two dimensional, transient and is formulated using the finite difference method with an implicit time discretization. The model for the case of only heat transfer for a single heat exchanger is compared to an available analytical solution and good agreement is obtained. It is shown that the discrepancy between the numerical and theoretical dimensionless bulk outlet temperature of the fluids is less than 4% during the transient period. The model is also validated for the case of simultaneous heat and moisture transfer using experimental data measured during the laboratory testing of a RAMEE system. The results for both sensible and latent effectiveness showed satisfactory agreement at different operating conditions. However, there are some discrepancies between the simulation and the experimental data during the transient times. It is proposed that these discrepancies may be due to experimental flow distribution problems within the exchanger. The maximum average absolute differences between the measured and simulated transient effectivenesses were 7.5% and 10.3% for summer and winter operating conditions, respectively.<p> The transient response of the RAMEE system for step changes in the inlet supply air temperature and humidity ratio is presented using the numerical model. In addition, the system quasi steady state operating conditions are predicted as the system approaches its steady state operating condition. The effect of various dimensionless parameters on the transient response is predicted separately. These included: the number of heat transfer units, thermal capacity ratio, heat loss/gain ratio, storage volume ratio and the normalized initial salt solution concentration. It is shown that the initial salt solution concentration and the storage volume of the salt solution have significant impacts on the transient response of the system and the heat loss/gain rates from/to the circulated fluid flow can change the system quasi steady effectiveness substantially. The detailed study of the transient performance of the RAMEE is useful to determine the transient response time of the system under different practical situations.

In this thesis, a numerical model for coupled heat and moisture transfer in a run around membrane energy exchanger (RAMEE) with a liquid desiccant as a coupling fluid is developed. The numerical model is two dimensional, transient and is formulated using the finite difference method with an implicit time discretization. The model for the case of only heat transfer for a single heat exchanger is compared to an available analytical solution and good agreement is obtained. It is shown that the discrepancy between the numerical and theoretical dimensionless bulk outlet temperature of the fluids is less than 4% during the transient period. The model is also validated for the case of simultaneous heat and moisture transfer using experimental data measured during the laboratory testing of a RAMEE system. The results for both sensible and latent effectiveness showed satisfactory agreement at different operating conditions. However, there are some discrepancies between the simulation and the experimental data during the transient times. It is proposed that these discrepancies may be due to experimental flow distribution problems within the exchanger. The maximum average absolute differences between the measured and simulated transient effectivenesses were 7.5% and 10.3% for summer and winter operating conditions, respectively.<p> The transient response of the RAMEE system for step changes in the inlet supply air temperature and humidity ratio is presented using the numerical model. In addition, the system quasi steady state operating conditions are predicted as the system approaches its steady state operating condition. The effect of various dimensionless parameters on the transient response is predicted separately. These included: the number of heat transfer units, thermal capacity ratio, heat loss/gain ratio, storage volume ratio and the normalized initial salt solution concentration. It is shown that the initial salt solution concentration and the storage volume of the salt solution have significant impacts on the transient response of the system and the heat loss/gain rates from/to the circulated fluid flow can change the system quasi steady effectiveness substantially. The detailed study of the transient performance of the RAMEE is useful to determine the transient response time of the system under different practical situations.

In this study, a numerical model is developed for determining coupled heat and moisture transfer in a run-around membrane energy exchanger (RAMEE) using two counter/cross flow exchangers and with a salt solution of MgCl2 as the coupling fluid. The counter/cross flow exchanger is a counter-flow exchanger with cross-flow inlet and outlet headers. The model is two-dimensional, steady-state and based on the physical principles of conservation of momentum, energy, and mass. The finite difference method is used in this model to discretize the governing equations.<p> The heat transfer model is validated with effectiveness correlations in the literature. It is shown that the difference between the numerical model and correlations is less than ¡À2% and ¡À2.5% for heat exchangers and run around heat exchangers (RAHE), respectively. The simultaneous heat and moisture transfer model is validated with data from another model and experiments. The inter-model comparison shows a difference of less than 1%. The experimental validation shows an average discrepancy of 1% to 17% between the experimental and numerical data for overall total effectiveness. At lower NTUs the numerical and experimental results show better agreement (e.g. within 1-4% at NTU=4).<p> The model for RAHE is used to develop new effectiveness correlations for the geometrically more complex counter/cross flow heat exchangers and RAHE systems. The correlations are developed to predict the response of the exchangers and overall system to the change of different design characteristics as it is determined by the model. Discrepancies between the simulated and correlated results are within ¡À2% for both the heat exchangers and the RAHE systems.<p> It is revealed by the model that the overall effectiveness of the counter/cross flow RAMEE depends on the entrance ratio (the ratio of the length of the inlet and outlet headers to the length of the exchanger, xi/x0), aspect ratio (the ratio of the height to the length of the exchanger, y0/x0), number of heat transfer units (NTU), heat capacity rate ratio (Cr*), number of mass transfer units (NTUm), and the mass flow rate ratio of pure salt in desiccant solution to dry air (m*). Beside these dimensionless parameters, the performance of the RAMEE system is affected by the liquid-air flow configuration and the operating inlet temperature and humidity.<p> This study concludes that the maximum effectiveness of the RAMEE system with two counter/cross flow exchangers occurs when NTU and NTUm are large (e.g. greater than 10). At any NTU, the overall effectiveness of the RAMEE system increases with Cr* until it reaches a maximum value when Cr*= . Increasing Cr* above causes the overall effectiveness to decrease slightly. Therefore, to achieve the maximum overall effectiveness of the system, Cr* must be close to . is a function of NTU and operating conditions e.g., with NTU=10, and under AHRI summer and winter operating conditions, respectively. The exchangers in the RAMEE system are needed to have a small aspect ratio (e.g. y0/x0<0.2) and small entrance ratio (e.g. xi/x0<0.1) to get the maximum overall effectiveness of a RAMEE system using two counter/cross flow exchangers. Such a RAMEE system has a total effectiveness 6% higher and 1.5% lower compared to the same cross-flow and counter-flow RAMEE, respectively (at NTU=10, Cr*¡Ö3, y0/x0=0.2 and xi/x0=0.1).

Made available in DSpace on 2014-06-11T19:35:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-02-12Bitstream added on 2014-06-13T20:26:17Z : No. of bitstreams: 1 castrojunior_j_dr_botfm.pdf: 761536 bytes, checksum: 8c6353cd6eec74b90409bf5498e8e3f5 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Durante anestesia geral com intubação traqueal para manutenção das vias aéreas, a umidificação e o aquecimento artificial dos gases inalados são essenciais para a prevenção de alterações na mucosa traqueobrônquica e diminuição do risco de hipotermia não intencional durante a cirurgia. A estação de trabalho de anestesia Primus (Dräger, Lübeck, Alemanha) tem placa de metal aquecida, situada na parte expiratória do circuito, para a prevenção da condensação de água no sistema respiratório. Esta placa aquecida também pode ajudar na manutenção da temperatura do gás no circuito respiratório em valores adequados. O presente estudo teve como objetivo a determinação da temperatura esofágica e da temperatura e umidade dos gases anestésicos no circuito respiratório do aparelho Primus da Dräger usando baixo fluxo de gases frescos (FGF) associado ou não ao uso do permutador de calor e umidade (PCU). Participaram do estudo trinta pacientes adultas com estado físico ASA I e II submetidas a cirurgias ginecológicas eletivas. As pacientes foram distribuídas aleatoriamente em dois grupos sob ventilação com baixo FGF de 1 L.min-1 com ou sem PCU durante anestesia geral com sistema circular respiratório com absorvedor de CO2. Todas as pacientes receberam aquecimento ativo da superfície cutânea por meio de manta térmica colocada sobre os membros inferiores. A temperatura e umidades relativa e absoluta dos Introdução e Literatura 6 gases e a temperatura esofágica foram medidas aos 15 minutos (tempo controle) após instalação do sistema de ventilação nas pacientes e, então, a cada 30 minutos até 120 minutos após o tempo controle. A temperatura e a umidade relativa e absoluta dos gases inalados no grupo com baixo FGF ao PCU apresentaram valores mais elevados comparados aos do grupo com baixo FGF sem PCU (p < 0,05). Não houve redução na temperatura... / In general anesthesia with endotracheal intubation, maintenance of airway humidity and temperature is important to prevent damage to the tracheobronchial mucosa and to risk the drop in body temperature during surgery. The anesthesia Primus’s work station (Dräger, Lübeck, Germany) has a built-in hot plate coupled to heat expired gases to prevent water condensation in the breathing system, but this heating plate also may help maintaining gas temperature in the respiratory system at adequate levels. In the present study, we measured the inspired gas temperature and humidity of the anesthetic circuit in the Dräger Primus machine using low fresh gas flow with or without a heat and moisture exchanger (HME). Thirty adult ASA I and II women patients scheduled to gynaecologic surgeries were randomly assigned into two groups to received low fresh gas flow of 1 L.min-1 with or without HME in the circle anesthesia system. All patients received active skin-surface warming with a specific blanket from a warming device. Relative humidity, absolute humidity, and temperature of inspired gases and esophageal temperature were measured at 15 min and then every 30 min up to 120 min after the installation of the respiratory system. There was a significantly higher relative humidity, absolute humidity and temperatures of the inspired gases in the HME group compared to without HME group (p < 0.05). The esophageal temperature did not decrease in Introdução e Literatura 8 the group HME (p > 0.05), but decreased significantly intraoperatively in without HME group (p < 0.05). Low-flow with the breathing system of the Dräger Primus anesthesia workstation have inherent humidifying properties sufficient to reduce the risk of respiratory tract dehydration only after 90 minutes of anaesthesia. The addition of HME improves the inspiratory absolute humidity, relative humidity and temperature of the anesthetic... (Complete abstract click electronic access below)

Orientador: Jose Reinaldo Cerqueira Braz / Banca: Regina Helena Garcia Martins / Banca: Flora Margarida Barra Bisinotto / Banca: Luiz Vicente Garcia / Banca: Artur Udelsmann / Resumo: Durante anestesia geral com intubação traqueal para manutenção das vias aéreas, a umidificação e o aquecimento artificial dos gases inalados são essenciais para a prevenção de alterações na mucosa traqueobrônquica e diminuição do risco de hipotermia não intencional durante a cirurgia. A estação de trabalho de anestesia Primus (Dräger, Lübeck, Alemanha) tem placa de metal aquecida, situada na parte expiratória do circuito, para a prevenção da condensação de água no sistema respiratório. Esta placa aquecida também pode ajudar na manutenção da temperatura do gás no circuito respiratório em valores adequados. O presente estudo teve como objetivo a determinação da temperatura esofágica e da temperatura e umidade dos gases anestésicos no circuito respiratório do aparelho Primus da Dräger usando baixo fluxo de gases frescos (FGF) associado ou não ao uso do permutador de calor e umidade (PCU). Participaram do estudo trinta pacientes adultas com estado físico ASA I e II submetidas a cirurgias ginecológicas eletivas. As pacientes foram distribuídas aleatoriamente em dois grupos sob ventilação com baixo FGF de 1 L.min-1 com ou sem PCU durante anestesia geral com sistema circular respiratório com absorvedor de CO2. Todas as pacientes receberam aquecimento ativo da superfície cutânea por meio de manta térmica colocada sobre os membros inferiores. A temperatura e umidades relativa e absoluta dos Introdução e Literatura 6 gases e a temperatura esofágica foram medidas aos 15 minutos (tempo controle) após instalação do sistema de ventilação nas pacientes e, então, a cada 30 minutos até 120 minutos após o tempo controle. A temperatura e a umidade relativa e absoluta dos gases inalados no grupo com baixo FGF ao PCU apresentaram valores mais elevados comparados aos do grupo com baixo FGF sem PCU (p < 0,05). Não houve redução na temperatura... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In general anesthesia with endotracheal intubation, maintenance of airway humidity and temperature is important to prevent damage to the tracheobronchial mucosa and to risk the drop in body temperature during surgery. The anesthesia Primus's work station (Dräger, Lübeck, Germany) has a built-in hot plate coupled to heat expired gases to prevent water condensation in the breathing system, but this heating plate also may help maintaining gas temperature in the respiratory system at adequate levels. In the present study, we measured the inspired gas temperature and humidity of the anesthetic circuit in the Dräger Primus machine using low fresh gas flow with or without a heat and moisture exchanger (HME). Thirty adult ASA I and II women patients scheduled to gynaecologic surgeries were randomly assigned into two groups to received low fresh gas flow of 1 L.min-1 with or without HME in the circle anesthesia system. All patients received active skin-surface warming with a specific blanket from a warming device. Relative humidity, absolute humidity, and temperature of inspired gases and esophageal temperature were measured at 15 min and then every 30 min up to 120 min after the installation of the respiratory system. There was a significantly higher relative humidity, absolute humidity and temperatures of the inspired gases in the HME group compared to without HME group (p < 0.05). The esophageal temperature did not decrease in Introdução e Literatura 8 the group HME (p > 0.05), but decreased significantly intraoperatively in without HME group (p < 0.05). Low-flow with the breathing system of the Dräger Primus anesthesia workstation have inherent humidifying properties sufficient to reduce the risk of respiratory tract dehydration only after 90 minutes of anaesthesia. The addition of HME improves the inspiratory absolute humidity, relative humidity and temperature of the anesthetic... (Complete abstract click electronic access below) / Doutor

Introduction: Several problems arise when HMEs are used while giving aerosolized medication including increased airway resistance (Raw) or the need to open the ventilator circuit. Recently, heat and moisture exchangers designed to allow aerosol delivery (HME-AD) have been developed to solve this problem, but no tests have been performed to confirm their effectiveness. The purpose of this study is to evaluate the effect of HME-ADs on aerosol deposition and Raw. Methods: An in-vitro lung model consisting of an 8.0 mm ID endotracheal tube (ETT) connected to a standard ventilator circuit and ventilator was connected to a rubber test lung via cascade humidifier set to deliver 37˚C and 100% relative humidity. The ventilator settings were as follows: Vt 450 ml, RR 20/min, PIF 50 L/min, PEEP 5 cm H2O, and I:E ratio 1:2. HME-ADs used in this study include Circuvent HME/HCH bypass (Smiths-Medical, Keene, NH), Gibeck Humid-Flo HME (Hudson RCI, Arlington Heights, IL), and Airlife BHME (Carefusion, San Diego, CA). As a control, albuterol sulfate (2.5 mg/3mL) was delivered with a vibrating mesh nebulizer (Aeroneb Solo, Aerogen Inc) placed at the wye without any HME-AD in the circuit. Then, the aerosol and HME configurations of each HME-AD were tested by measuring pre-post Raw and aerosol deposition at the end of each run. Each condition was repeated in triplicate (n=3). Aerosol deposition between the aerosol and HME configurations of each HME-AD was compared with a series of student t-tests. Then, differences both in aerosol deposition and in airway resistance among the HME-ADs were analyzed using one-way analysis of variance (ANOVA). Significance was determined as p<0.05. Results: Raw increased after each albuterol treatment with every HME-AD. In the aerosol configuration, the Circuvent and Humid-Flo delivered significantly less aerosol compared to the control (p=.004 and p=.002, respectively), while there was no significant difference on aerosol delivery between the Airlife and the control (p=.084). The Airlife gave the highest aerosol deposition which was not significantly different than control (p=.084). When aerosol delivery between the HME and aerosol configurations in each HME-AD was compared, aerosol deposition with the Humid-Flo was not significantly different (p=.078) but both the Airlife and the Circuvent showed a statistically significant reduction in aerosol deposition with the HME configuration (p=.002 and p=.005). Conclusions: Aerosol delivery and Raw with each HME-AD differ in simulated mechanically ventilated patients. Further studies are needed to determine the effectiveness of these devices over time and with different aerosol generating devices.

Introduktion: Befuktning vid mekanisk ventilation är nödvändigt för att inte skador skall uppstå i luftvägarna. Luften kan befuktas aktivt eller passivt och då tekniken ständigt utvecklas kan tidigare riktlinjer för vilken metod som är bäst behöva revideras. Syfte: Studiens syfte var att undersöka evidensen för användning av aktiv befuktning hos intuberade eller trakeostomerade patienter. Metod: I enlighet med Whittemore &amp; Knafls metod utfördes en integrerad litteraturstudie. Litteratursökning gjordes i databaserna PubMed, CINAHL och Cochrane. Även en manuell sökning i referenslistor utfördes och ledde till att totalt 14 artiklar valdes ut, varav 13 var kvantitativa och 1 kvalitativ. Resultat: Analysen av de 14 artiklarna resulterade i fyra huvudkategorier med efterföljande underrubriker: Aktiv befuktnings påverkan på nosokomiala infektioner: Infektionsincidens och Infektionstyp; Aktiv befuktnings påverkan på luftvägsproblem: Ocklusionsproblemoch Sekretviskositet/sekretmängd; Aktiv befuktnings påverkan på mekanisk ventilation: Vårdtid med mekanisk ventilation och Påverkan på andningsarbete;Upplevelse av aktiv befuktning: Upplevd påverkan på hälsa och Negativ påverkanpå vårdmiljön. Konklusion: Denna studie var att aktiv befuktning har en viktigfunktion att fylla hos vissa patienter, men borde inte användas slentrianmässigt.Sjuksköterskan har en viktig roll i att hitta de patienter som är mest hjälpta av det. / Introduction: Humidification during mechanical ventilation is necessary to avoid damage in the airways. The air can be humidified actively or passively and since thetechnique is constant developing the guidelines for which of the alternative that’sthe best may need to be revised. Aim: The aim of the study was to examine the evidence of using active humidification in intubated patients or in patients withtracheostomy. Method: An integrated literature review according to Whittemore &amp;Knafl was carried through. The literature search was done in the databases PubMed, CINAHL and Cochrane. A manual search in reference lists was also made and resulted in a total of 14 articles whereof 13 were quantitative and one was qualitative. Result: The analysis of the 14 articles led to four main categories with the following subcategories: Active humidifications influence on nosocomial infections: Infectionincidence and Infection type; Active humidifications influence on airway problems: Occlusion problems and Mucus viscosity/mucus volume; Active humidifications influence on mechanical ventilation: Time on mechanical ventilation and Influenceon respiratory work; Experience of active humidification: Experienced influence on health and Negative impact on hospital environment. Conclusion: The conclusion of this study was that active humidification is the better choice among certain patientgroups but should not be used routinely. The nurse plays an important role in finding the patients who can benefit the most of it.