Performance Definitions for Three-Fluid Heat and Moisture Exchangers

This paper presents performance definitions for calculating the overall effectiveness of three-fluid heat and moisture exchangers. The three-fluid heat and moisture exchanger considered in this paper is a combination of a liquid-to-liquid heat exchanger for heat transfer between a desiccant solution and a refrigerant and an energy exchanger for heat and moisture transfer between desiccant solution and air streams. The performance definitions presented in this paper are used to calculate the overall sensible and latent effectivenesses of a three-fluid heat and moisture exchanger, which has been tested under air cooling and dehumidifying operating conditions in a previous work (Abdel-Salam et al., 2016, “Design and Testing of a Novel 3-Fluid Liquid-to-Air Membrane Energy Exchanger (3-Fluid LAMEE),” Int. J. Heat Mass Transfer, 92, pp. 312–329). The effectiveness of this three-fluid heat and moisture exchanger is compared when calculated using the traditional energy exchanger effectiveness equations and the overall performance definitions. Results show that the overall performance definitions provide effectiveness values that are less sensitive to changes in the inlet refrigerant temperature and therefore are more generally applicable for energy exchanger design than the traditional effectiveness equations used in the literature.

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Heat and moisture exchanger used in a cardiothoracic surgery intensive care unit: Airway resistance and changing interval

Turkish Journal of Thoracic and Cardiovascular Surgery ◽

10.5606/tgkdc.dergisi.2020.20088 ◽

2020 ◽

Vol 28 (4) ◽

pp. 593-600

Author(s):

Huan Liu

Keyword(s):

Intensive Care Unit ◽

Intensive Care ◽

Airway Resistance ◽

Cardiothoracic Surgery ◽

Lung Model ◽

Heat And Moisture Exchanger ◽

Moisture Exchanger ◽

Heat And Moisture Exchangers ◽

Heat And Moisture

Background: This study aims to investigate the efficacy and safety of heat and moisture exchanger on airway resistance in a cardiothoracic surgery intensive care unit. Methods: A total of 31 patients (18 males, 13 females; mean age 51.5 years; range, 39 to 61 years) who were treated with long-term mechanical ventilation due to low cardiac output syndrome after cardiopulmonary bypass and cardiac surgery were retrospectively analyzed between December 2014 and December 2018. In addition, an in vitro lung model and different doses of hydroxyethyl starch in the heat and moisture exchangers to mimic the airway secretions were used and the proper interval to change heat and moisture exchangers was evaluated. Results: In the in vitro lung model, the mean airway resistance was 19.4±0.2 cmH2O/L/sec in the 5 mL group (p=0.060), 20.3±1.0 cmH2O/L/sec in the 10 mL group (p=0.065), and 30.2±1.7 cmH2O/L/sec in the 15 mL group (p<0.001). The airway resistance of heat and moisture exchangers, and total hospital stay and ventilation duration significantly increased in the seven-day group compared to the one-day and three-day groups. The positive culture of bacteria was also significantly higher in the seven-day group. Conclusion: Our study results suggest that heat and moisture exchangers can be safely used for an efficient and timely removal of airway secretions. Volume of approximately 15 mL of liquid in the airflow can dramatically increase the airway resistance. The three-day interval of changing heat and moisture exchangers is ideal in a cardiothoracic surgery intensive care unit where patients have more airway secretions than patients in the general intensive care unit.

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Shivering and rewarming after cardiac surgery: comparison of ventilator circuits with humidifier and heated wires to heat and moisture exchangers

American Journal of Critical Care ◽

10.4037/ajcc1995.4.4.293 ◽

1995 ◽

Vol 4 (4) ◽

pp. 293-299 ◽

Cited By ~ 8

Author(s):

MT McEvoy ◽

TJ Carey

Keyword(s):

Cardiac Surgery ◽

University Teaching ◽

Heat And Moisture Exchanger ◽

Moisture Exchanger ◽

Heat And Moisture Exchangers ◽

Heated Water ◽

Surgery Patient ◽

Heated Wire ◽

Heat And Moisture ◽

Adult Cardiac Surgery

BACKGROUND: Detrimental physiologic effects of shivering in the cardiac surgery patient have been well documented. Rewarming techniques have been compared, with noted differences in the incidence of shivering. Ventilator circuits have not been examined independently from other rewarming variables. OBJECTIVE: To compare heated wire humidification circuits with heat and moisture exchanger circuits on the incidence of shivering and speed and pattern of rewarming in mechanically ventilated patients. METHODS: A prospective, descriptive, correlational study was done on 140 adult cardiac surgery patients in a university teaching medical center. All subjects underwent cardiac surgical procedures with hypothermic cardiopulmonary bypass. Subjects were randomized to humidified, heated wire circuits (n = 70) or heat and moisture exchanger circuits (n = 70). Heated water blankets were used on all patients. RESULTS: Mean intensive care unit admission temperature was 35.28 degrees C. No statistical differences were found in preoperative, demographic, or operative course data between treatment and control groups. Shivering was more common in the heat and moisture exchanger group than in the heated wire group. In our analysis, the only variable associated with shivering was the type of ventilator circuit. Patients using heated wire systems rewarmed more rapidly and had significantly higher temperatures than did patients using heat and moisture exchangers. CONCLUSION: These data suggest that use of heated wire humidified ventilator circuits with heated water blankets in adult cardiac surgery patients significantly reduces the incidence of shivering and results in a more rapid return to normothermia.

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An Evaluation of Six Disposable Heat and Moisture Exchangers

Anaesthesia and Intensive Care ◽

10.1177/0310057x8701500312 ◽

1987 ◽

Vol 15 (3) ◽

pp. 317-322 ◽

Cited By ~ 24

Author(s):

M. J. Turtle ◽

A. H. Ilsley ◽

A. J. Rutten ◽

W. B. Runciman

Keyword(s):

Steady State ◽

Gas Flow ◽

Care Setting ◽

Intensive Care Setting ◽

Heat And Moisture Exchanger ◽

Moisture Exchanger ◽

Heat And Moisture Exchangers ◽

The Times ◽

Heat And Moisture ◽

Better Than

Six disposable heat and moisture exchangers were tested on patients undergoing anaesthesia requiring mechanical ventilation. Inspiratory humidity and temperature were monitored to find the steady-state values reached with each device together with the times taken for these to be achieved. The exchangers were tested in a non-rebreathing T-piece circuit and in a conventional circle system with a fresh gas flow of 6 l/min: the Siemens 150 provided 28 and 32 mg of water/litre of inspired gas (at about 30°C) in 10 and 5 min respectively, but is rather heavy and bulky. The Portex Humidvent provided 25 and 30 mg/l, and although taking longer to reach steady state (27 and 15 min respectively) is small, light and cheap. The Siemens 151 provided 25 and 27 mg/l in 18 and 10 min respectively, but is heavier than the Portex exchanger. The performances of these three devices were not significantly different from each other in either study (P < 0.05). For the T-piece system the Pall and Engstrom exchangers were the next most efficient. The Pall device provided 18 and 23 mg/l (in 18 and 8 min respectively) and the Engstrom provided 20 and 23 mg/l (in 19 and 10 min respectively). In the circle system, there were no significant differences between the peformances of the Portex, Siemens 151, Pall and Engstrom exchangers. The Pall is also a very effective bacterial filter and has been found to be satisfactory in the intensive care setting. The Terumo appeared to perform no better than a circle system with catheter mount (13 mg/l at 27°C). It would seem that more complex humidification equipment is not necessary during anaesthesia if an efficient heat and moisture exchanger is used.

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Changing Heat and Moisture Exchangers Every 48 Hours Does Not Increase the Incidence of Nosocomial Pneumonia

Infection Control and Hospital Epidemiology ◽

10.1086/501631 ◽

1999 ◽

Vol 20 (05) ◽

pp. 347-349 ◽

Cited By ~ 17

Author(s):

Françoise Daumal ◽

Eric Colpart ◽

Benoît Manoury ◽

Mercedès Mariani ◽

Marc Daumal

Keyword(s):

Mechanical Ventilation ◽

Prospective Study ◽

Nosocomial Pneumonia ◽

Demographic Characteristics ◽

Surgical Patients ◽

Incidence Density ◽

Heat And Moisture Exchanger ◽

Moisture Exchanger ◽

Heat And Moisture Exchangers ◽

Heat And Moisture

Abstract This prospective study was conducted to evaluate the risk of nosocomial pneumonia when changing heat and moisture exchangers every 48 hours in 1996 instead of every 24 hours in 1995 for patients needing continuous mechanical ventilation. Medical and surgical patients in the two periods did not differ in terms of demographic characteristics and markers of acute or underlying illnesses. The incidence density of nosocomial pneumonia was not different in the two groups. Extended heat and moisture exchanger use reduces circuit manipulation and cost.

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Numerical Simulation of Flow, Heat and Moisture Transfer in Heat and Moisture Exchanger (HME) Devices

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.553.121 ◽

2014 ◽

Vol 553 ◽

pp. 121-129

Author(s):

Seyed Pezhman Payami ◽

Masud Behnia ◽

Barry Dixon ◽

John Santamaria ◽

Mehrdad Behnia

Keyword(s):

Flow Rate ◽

Gas Flow ◽

Moisture Transfer ◽

Breathing Circuit ◽

Absolute Humidity ◽

Cfd Model ◽

Heat And Moisture Exchanger ◽

Moisture Exchanger ◽

Flow Heat ◽

Heat And Moisture

Heat and Moisture Exchanger (HME) is a simple solution to the problems of warming and humidification of inspired gases during ventilator treatment. The device acts as an “artificial” nose or passive humidifier, added to the breathing circuit to retain and exchange heat and moisture between inspiration and expiration. The HME traps expiratory heat and moisture from patient’s exhaled breath in a porous medium and returns a portion of them through the subsequent inspiratory cycle. The aim of our paper is to develop a computational fluid dynamics (CFD) model of an HME device commonly used in anaesthesia and intensive care. The CFD results allow a better understanding of flow behaviour leading to the design of more efficient devices. The CFD model solves the gas flow, heat and mass transfer equations in a DAR Hygrobac S (Mallinckrodt DAR, Mirandola, Italy). The temperature, absolute humidity and pressure fields are obtained during expiratory phase to evaluate heat and moisture conserving efficiencies and air flow resistance. The effect of flow rate as one of the major parameters in ventilator setting on temperature, humidity and pressure drop is determined. Inside the HME device, areas of recirculation are observed. As the flow rate increases the output temperature and absolute humidity go up causing a reduction in heat and moisture conserving capacities. Comparison of the CFD results with previously obtained experimental data shows a satisfactory agreement.

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