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Table 5.5 Comparison of condensation between experimental results and model outputs vs. tube heating under CPAP pressure setting at 12cmH2O, heating element setting at 55°C and normal room temperature Pressure Setting 12 cmH2O Ambient Conditions T 21.9°C RH 64.0% Heating Element Setting 55°C Tube Heating 140 0 W 15 W 30 W Condensation (Exp.) Condensation (Model) Yes Yes Starts from Lump 5 Starts from Lump 19 No No No No From the experimental observation and model outputs, the higher humidifier heating element temperature setting generates more condensation. On the other hand, higher CPAP pressure setting, ambient temperature and tube heating decrease the condensation. Overall, the condensation in HADT is determined by its wall temperature and the airflow humidity. The influences by factors are listed below: Table 5.6 Factors influencing HADT condensation Factor Trends condensation Ambient temperature Increase Less ambient humidity Increase More CPAP pressure setting Increase Less Humidifier heating Increase More Tube heating Increase Less Generally the model slightly under-predicts condensation in the HADT. This may be because: 1. There is a small in-room air movement which is not included in the model. The in-room air movement can increase thermal convection on the outer surface of the HADT thus decreases HADT wall temperature and increases condensation. 2. The model also generally gives a slightly lower evaporation rate which will also reduce the condensation in the HADT.
3. The corrugated grooves on the HADT inner surface may create partly-dead space (eddies). Such dead space reduces heat exchange between the internal airflow and the HADT wall and makes this part of the wall has a lower temperature (Figure 5.32). This may be the reason why sometimes condensation can only be seen in the grooves (Figure 5.33). Figure 5.32 Temperature in grooves of the corrugated HADT may be lower Figure 5.33 Condensate in grooves On the other hand, it was observed in experiments that condensation started from lump 2 or lump 3 at several settings but the model predicts condensation starting from lump 1. This may be because the CPAP case was warm and a certain quantity of heat might conduct to the HADT. Since the model simplifies that there is no axial heat conduction 141
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The Effects of CPAP Tube Reverse Fl
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Acknowledgement First of all, I wou
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When deep breathing induced reverse
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2.4.1 Reverse flow calculation ....
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5.3.1 Thermal dynamic model under s
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XI.3 Steady state mask thermal bala
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List of Figures Figure 1.1 Obstruct
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Figure 5.10 Comparison between expe
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Figure 6.13 Fluctuation of airflow
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Table 5.3 Comparison of condensatio
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Nomenclature Symbol Meaning of the
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CMFeO CMFet C O C t Concentration o
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m C 23 m Ca m cv m Cw m store m i m
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Nu Cp Nu dir Nu Ti Nu To Nuwsn Nuws
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QMor QMwst QTastn QTicn QTin Q
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R Mic R Moc R Ticn R Toc R Torn Mas
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V Capacity of the container m 3 V C
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1.1 Background Chapter 1 Introducti
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The MRD is worn in user’s mouth w
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Figure 1.4 CPAP machine Figure 1.5
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1.3 Literature survey A literature
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CPAP fluid dynamic performance with
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Chapter 2 Mathematical Modelling of
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2.3 Fluid dynamic analysis This sec
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If there are minor pressure drops,
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Figure 2.6 Pressure sensor - Honeyw
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The pressure readings were taken af
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Figure 2.12 Experimental set up for
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2.3.4 Chamber air space mass balanc
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From the above analysis, the pressu
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Figure 2.18 Full face mask and the
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Inserting Eq. (2.26) and Eq. (2.27)
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Where n( ) t is the airflow proper
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However in reality, mixing turns ou
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Chapter 3 Mathematical Modelling of
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An Environment Control Chamber (Vö
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Figure 3.4 Thermal enthalpy gain of
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Figure 3.6 Heating element beneath
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Figure 3.8 Chamber water heat balan
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Table 3.1 Thermal resistance from h
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3.3.1.2 Heat balance at the outer s
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3.3.2 Heat flow from chamber water
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through ADU which is a function of
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It is assumed that the direct impac
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Sc a a (3.47) Dwa Analogous to th
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and keep them in gaseous status. On
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through the walls and natural conve
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Where d Ca is the specific humidity
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TTa ( n1) is also considered as inl
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R Torn 2 2 ATlor ( TTWn T )( TTWn
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condensation severity but cannot ca
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condensation has occurred at all or
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The inlet is the air from HADT duri
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3.9 Average temperature of inhaled
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Table 4.1 Inputs to the fluid dynam
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Figure 4.2 Simulink TM model for fl
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Table 4.4 Outputs from the overall
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Gain block after input 1 is to conv
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Figure 4.7 Varying Transport Delay
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4.2.5 Mask mixing calculation subsy
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4.3 Computational model of thermal
Page 123 and 124: Figure 4.11 Block diagram of CPAP t
Page 125 and 126: Figure 4.13 Simulink TM model for t
Page 127 and 128: The outputs are listed in Table 4.1
Page 131 and 132: Figure 4.16 Dynamic chamber-air the
Page 133 and 134: Figure 4.17 HADT lump thermal balan
Page 135 and 136: Figure 4.18 Steady state HADT lump
Page 137 and 138: Figure 4.19 HADT lump air dynamic f
Page 141 and 142: Figure 4.21Steady state mask full t
Page 143 and 144: 4 Temperature of airflow from HADT
Page 145 and 146: Average evaporation rate subsystem
Page 147 and 148: HADT and connects those upstream se
Page 149 and 150: The experiment was also carried out
Page 151 and 152: air flowing through the elbow, a ce
Page 153 and 154: expansion from the elbow to the mas
Page 155 and 156: Figure 5.12 Environmental control r
Page 157 and 158: Table 5.1 shows the combinations of
Page 159 and 160: Figure 5.17 Comparison of model out
Page 161 and 162: The comparison of experimental resu
Page 167 and 168: 5.3.1.4 Airflow temperature at the
Page 169 and 170: flow rate had been even further inc
Page 171 and 172: Figure 5.31 Comparison of condensat
Page 173: Table 5.3 Comparison of condensatio
Page 177 and 178: 5.3.2.1 Validation of evaporation r
Page 179 and 180: The experiment observation showed t
Page 181 and 182: Figure 6.1 Reverse flow under diffe
Page 183 and 184: It can also be seen in Figure 6.2 t
Page 185 and 186: within the same period. However, wh
Page 187 and 188: Figure 6.6 Comparison of evaporatio
Page 189 and 190: Figure 6.8 Airflow velocity in HADT
Page 191 and 192: Figure 6.11 Airflow velocity in HAD
Page 193 and 194: In Figure 6.14 the blue curve repre
Page 195 and 196: 6.3.3.1.2 Comparison when heating e
Page 197 and 198: This vaporization potentiality (coi
Page 199 and 200: Figure 6.20 In-tube condensation of
Page 201 and 202: When using different sized masks, t
Page 203 and 204: Figure 6.23 Average specific humidi
Page 205 and 206: The average specific humidity in an
Page 207 and 208: Table 6.5 Comparison of average spe
Page 209 and 210: 6. The deep breathing and reverse f
Page 211 and 212: Appendices Appendix I Regression of
Page 213 and 214: Appendix I. Regression of the press
Page 215 and 216: Figure I. 1 Tested results and the
Page 217 and 218: Appendix II. Regression of the pres
Page 219 and 220: Table III. 2 Airflow temperature an
Page 221 and 222: Appendix IV. The corrugated HADT ou
Page 223 and 224: The total area of the complicated c
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Figure V. 1 Regression of saturated
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This ratio can be regressed against
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Appendix VII. Details of the CPAP f
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VII.4 The mask pressure subsystem F
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Inputs to this water-centred subsys
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Input port number Input Unit 1 Heat
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input 4 is the portion of impact ar
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VIII.2.3 Water surface mass transfe
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This subsystem also contains two su
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VIII.2.5 Chamber wall 1 heat transf
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Figure VIII. 13 Wall 1 outer surfac
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Wall 2 and 3 inner surface temperat
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Figure VIII. 17 Chamber wall 2 and
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Inputs to this subsystem are listed
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Appendix IX. Details of steady stat
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Figure IX. 3 The HADT lump wall out
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Appendix X. Details of HADT lump ai
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2 Absolute value of airflow velocit
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Figure X. 5 HADT lump inlet absolut
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Figure XI. 2 Steady state mask mixi
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Figure XI. 4 Steady state mask wall
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Input port number Input Unit 1 Aver
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Appendix XII. Details of mask air d
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4 Length of the triangular plate in
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8 Length of the triangular plate in
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Appendix XIII. Details of the auxil
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XIII.3 Breath load average subsyste
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Figure XIII. 7 Average evaporation
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XIV.1.2 Under normal ambient temper
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XIV.2.3 Under high ambient temperat
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XIV.4 Airflow temperature at the en
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XIV.5.2 Under normal ambient temper
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XIV.6.3 Under high ambient temperat
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Appendix XVI. Regression of kinetic
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Figure XVII. 2 Condensation/evapora
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Figure XVIII. 2 Condensation/evapor
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at point C. Right after that, here
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Appendix XIX. Coefficient and param
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Average water thermal conductivity
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Appendix XXI. Fluid dynamic and the
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The lung simulator drives the air.
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Appendix XXII. Model user instructi
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The input blocks and their values a
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Dynamically fluctuating air tempera
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References [1] Good sleep advice. W
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[28] Schettino GPP, Chatmongkolchar
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[60] Marek R, Straub J. Analysis of
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