THERMAL TRANSFERS IN WET HYPERBARIC ENVIRONMENT

Transcription

1 Annals of the Academy of Romanian Scientists Series on Engineering Sciences ISSN olume 6, Number 1/ HERMAL RANSFERS IN E HYPERBARIC ENIRONMEN amara SANCIU 1, Anca CONSANIN 2, Cecilia ADUMIRESI 3 Rezumat Pierderile de căldură ale organismului uman sunt mai mari în mediul subacvatic decât în atmosferă datorită coeficientului de transfer termic al aei mai ridicat emeratura corului la scafandrii aflaţi în imersiune a fost studiată ţinându -se cont şi de resiunea la care sunt euşi subiecţii A fost stabilită ecuaţia teoretică a transferului total de căldură, la amândouă nivelele, cutanat şi resirator, ţinând cont de conducţie, convecţie, şi de încălzirea şi umidificarea gazului resirator emeratura corului scafandrilor a fost măsurată într-o serie de scufundări, la diferite adâncimi, realizate în simulatorul umed al Centrului de Scafandri Constanţa Rezultatele eerimentale au fost în concordanţă cu temeratura calculată duă modelul matematic stabilit Abstract he heat losses of human body are greater in underwater environment than in dry, normal atmoshere, due to the great heat caacity of water Body temerature of divers in immersion was studied taking into account the ressure the divers are subjected to he theoretic equation that describes the total heat transfer- at both levels: skin and resiratory system- was established, considering conduction, convection and resiratory gas heating and humidification he body temerature of the divers was measured in a series of dives at different deths of immersion, conducted in the wet simulator of the Diving Center, in Constanta he eerimental results were in good accordance with the temerature redicted by the mathematical model Keywords: conduction, convection, thermal balance 1 Introduction he diverse actual underwater activity requires man to send more time in wet hyerbaric environment Hostile factors like high ressure, low temerature, and weak visibility require aroriate rotection equiment for the diver hermal comfort is one of the most imortant requirements for a diver to accomlish his underwater task and return safely to the surface he comfort is maintained temerature margin C Under 32 C for signs of hyothermia, vasoconstriction, tachycardia and tremor [3] 1 Senior Researcher Eng, Research Laboratory, Diving Center, Constanta, Romania tamarastanciu@navyro 2 Assoc Prof, PhD Eng, Faculty of Civil Engineering, University Ovidius, Constanta, Romania, aconstantina@univ-ovidiusro 3 Lecturer Doctor, Faculty of Medicine, University Ovidius, Constanta, Romania, cadumitresi@yahoocom

2 56 amara Stanciu, Anca Constantin, Cecilia Adumitresi hermal balance of the human body has been studied and deicted by rigorous teams of hysiologists and engineers, but the ublished theoretical and eerimental data refer mainly to normal ressure condition or to eeriments develoed in dry hyerbaric environment he first form of the biothermal equilibrium equation was develoed by Pennes who investigated heat transfer between tissue and blood, and measured temeratures distribution in human body His model describes the effects of metabolism and blood erfusion on the energy balance within tissue [4] c k q q m 1 t where -tissue density; c tissue secific heat; -tissue temerature; k-thermal conductivity; q erfusion heat flu; q m metabolic roduction rate [/m 3 ] metabolic heat flu Equation 1 reflects the thermal balance of the body in normobaric atmoshere Scientists like Klingel, Cheng and Holmes, Nakayama and Kuwahara [5], mainly on the theory of orous media A simle model for bioheat transfer was roosed by arlochan and Ramesh [7] Divers oerating in ressurized dry and wet rooms, as the hyerbaric diving deth ensemble of Diving Center from Constanta, see Figure 1 Fig 1 Hyerbaric Comle: 1 dry hyerbaric chamber, 2 sas, 3 wet hyerbaric chamber Retrosective recent studies of the heat losses at the hyerbaric resiration, rovides a hysiological database for raising the minimum hysiological insired gas temerature he curve roosed to maintain the temerature of the insired gas, is a maimum loss of 20 /m 2, into a hot water warmed suit his level of thermal loss by resiratory system, is destinated to fall the rectal temerature with 025 C/h

3 hermal ransfers in et Hyerbaric Environment 57 hermal comfort of the diver, a free contaminants resiratory level and maintaining the level of artial oygen ressure in the normal range, is one of the most imortant requirements for a diver to accomlish his underwater task and return safely to the surface For the natural ventilation, at norm baric ressure, the thermal comfort for the body is defined by ASHRAE Standard 55 conf 031 aeret 178[ K] 2 A more elaborated model was conceived by Majchrzycka Her theoretical researches on bioheat transfer in hyerbaric, but dry environment were sustained by rigorous eerimental recordings of human body temerature She took into account the metabolic heat roduction, and losses by evaoration from skin, by resiration, by convection and even radiation from the outer surface of the clothing [2] he studies effectued in wet hyerbaric environment of the Hyerbaric Comle from Diving Center Constanţa, come to add new data regarding the evolution of human body temerature in the diving, deending on the ressure as the main arameter e focused on human thermal sub sea comfort, therefore the water temerature was of 20 C and the duration of a dive was of 30 min 2 Heat transfer mathematical model he differential equation that governs the transient heat transfer was derived taking into account both grous of heat losses: through skin by conduction and convection and through the breathing system by convection and humidification of the resiratory gas miture [1] e were interested only in the human body temerature variation in time, related to the sea water temerature and ressure So we considered the mathematical model offered by the following heat balance equation: mc b d dt m - body mass [kg], c b - body core secific heat, body temerature core, level heat flu lost 21 Metabolic thermal flu 3 m c - skin level heat flu lost, c r - metabolic heat flu, [K] m r - resiratory system o kee a better control on the heat roduction, the divers stood still during the dives hus, they roduced only the basal metabolic heat he basal metabolic flu was determined knowing that the heat roduced by a healthy man in 24 hours is given by the Harris-Benedict relationshi:

4 58 amara Stanciu, Anca Constantin, Cecilia Adumitresi were L 6755 a [kcal] 4 m m - basal metabolic heat [kcal]; L- height [cm]; a-age [years] 22 Conduction and convection thermal flu at skin level he heat balance equation 3 was established assuming the human body consists of a core, acting like a homogenous source of metabolic heat, covered by thin insulation layers: subcutaneous fat, dermis and eidermis Part of the metabolic heat rate is transferred by conduction and convection to the environmental sea water; we drafted in Figure 2 the ensemble human body-skin-water film-suitwater It may be written: c A 5 R 2 [K] water temerature, R [K m /] - thermal resistance of the outer layers of human body, t - time [s] Fig 2 Heat transfer by ensemble human body-skin-water film-suit-water he thermal resistance was theoretically determined for each diver, according to his secific hysiologic features, at normal ressure For each deth value, the resistance was corrected considering an isothermal comression for the air in the neorene cells It was taken into account only free convection at the neorene suit-sea water surface, as the divers stood still during the dives 23 hermal flu at resiratory system level 6 r s latent heat flu that brings the inhaled dry air to 100% humidity ehaled air

5 hermal ransfers in et Hyerbaric Environment 59 sensible heat flu that increases the inhaled air temerature from 20 C to the body temerature, Both comonents deend on ressure deth of immersion, as it may be noticed from their formulas given below: l 7 ere l secific vaorization latent heat [J/kg], - air density 2 [kg/m ] ; - absolute humidity of resiratory air [kg/kg]; - resiratory volume flow rate 2 [m /s] c s 8 c air secific heat at constant ressure, [J/kg K] 24 hermal balance equation he equation 3 becomes: c l A R m dt d b mc 9 and the solution is: m mc c R m c R l e c R l b ere, ] / [ 3470 kgk J c b, the secific heat of the human body core, ] [ 0 K - the initial body temerature 3 Eerimental rocedures he eerimental study of human body temerature variation in hyerbaric conditions was develoed in two stages: the first focused on the heat lost through the resiratory system and the second on the total heat loss, during immersion he theoretic values of thermal resistance, for each diver, were eerimentally validated in a first dive down to 15 m Resistance R has the most imortant variation on this range of immersion deth, as the hydrostatic ressure increases significantly

6 60 amara Stanciu, Anca Constantin, Cecilia Adumitresi All the dives were conducted in the simulator of the Diving Center from Constanta hey used air as resiratory miture In the first stage were conducted a series of SCUBA diving, with breathing air, in the wet simulator he breathing air was dry and at the same temerature as water Each one of the three divers wore, by turn, a wet neorene suit of 5mm and resectively 7 mm thickness Body temerature was measured by a thermometer laced inside the ear and skin temerature by a thermometer laced on the arm ater temerature was ket at 20 C he duration of each dive was of 30min and temeratures were measured at every 2 min he first set of measurements was carried out at normal ressure, 0 m deth he second set of measurements was carried out at 15 m deth hese data were used to correct the theoretically determined thermal resistance R he third set of measurements was develoed at 30 m deth of immersion Attended by two grous of three divers to testing e eemlified the divers grou 1, 2 and 3 hermal comfort is differently erceived by individuals It deends on their own hysiological features and own thermoregulatory system heir hysiologic features are given in able 1 able 1 Divers hysiologic features Diver Ages Mass Height Body area A/m ratio Metabolic heat flu [year] [kg] [m] [m 2 ] [m 2 /kg] [] It may be noticed that the divers 1 and 3 slender, having very similar characteristics, while diver 2 is more corulent It is known that individuals with more fat content can survive longer in cold water as the fat is a natural insulator to the body [6] Resistance R has the most imortant variation on this range of immersion deth, as the hydrostatic ressure increases significantly he second stage aimed to determine the breathing features variation with the deth of immersion here were measured and recorded: the resiratory volume flow rate, breathing frequency, duration of one breath, and the air temerature before and after ehalation All these data were collected during a series of simulated dives, in dry environment, at the following deths: 9 m; 21 m; 30 m; 51 m; 60 m Breathing flow rate E of each diver was determined by the use of lung function recorder tye SP-10, with an accuracy of 2 %

7 hermal ransfers in et Hyerbaric Environment 61 he human thermal comfort is maintained as long as the body temerature is between 37 C and 35 C As the temerature decreases down to 32 C mild signs of hyothermia may occur: hyertension, vasoconstriction, tachycardia, tachynea, and shivering [3] 4 Results he results with resect to body temerature variation during the immersion are grahically resented below, allowing one to comare the theoretical and the eerimental data Figures 3-5 he theoretical curve is the grahical reresentation of relationshi 10 1 good correlation of the theoretic and eerimental data may be observed in grahics, where temerature decrease is resented for the three divers, in immersion at 30 m deth herefore we considered that the mathematical model is valid and we used it to estimate the temerature variation for longer duration of the dive Fig 3 Body temerature variation for the diver 1, at 30 m deth heoretic and eerimental curves, R Fig 4 Body temerature variation for the diver 3, at 30 m deth, wearing a 7 mm neorene wet suit heoretic and eerimental curves, R

8 62 amara Stanciu, Anca Constantin, Cecilia Adumitresi Fig 5 Body temerature variation for the diver 2, at 30 m deth, wearing a 5 mm neorene wet suit heoretic and eerimental curves, R Fig 6 Lost thermal flu variation [/m 2 ] by diver 1, in time, at 15 m and 30 m deth Equation 3 was used to determinate the thermal flu lost by a diver, at two levels 15 m and 30 m, Figure 6 Earlier diving body temerature dros quickly, but after about 10 minutes slower heat flow is lost Heat flu lost to 30 m at the same moment of time, is slightly lower than body temerature is 15 m, therefore the body temerature is higher than 30 m deth, than at 15 m, due to ressurization simulator he theoretical study led to the assessment of diver s temerature evolution over diving time and of his lost heat flu For the same diver, at the same deth of immersion, the increase with 2 mm of the insulation neorene wet suit resulted in about 50 /m 2 decrease of the lost heat secific flu In Fig 7 there is reresented the body temerature of diver 3 for 5 mm and resectively 7 mm thickness of the diving suit

9 hermal ransfers in et Hyerbaric Environment 63 Conclusions Fig 7 Body temerature variation for the diver 3, at 30 m deth, for two different thickness of the neorene wet suit: 5 mm and 7 mm 1 he study of thermal transfers in wet hyerbaric environment rovided an easy-to-use mathematical model for body temerature decrease, for a diver at rest during immersion he roosed thermal balance equation is a simlified model of very comle henomena It takes into account only art of the involved variables: sea water temerature and hydrostatic ressure corresonding to the deth of immersion, the main hysiologic features of healthy individuals, their breathing characteristics, and resiratory air roerties 2 he roosed mathematical model is valid, as it was roved during a series of wet diving down to 60 m, conducted in a hyerbaric facility he theoretic and eerimental study ointed out a few data useful to choose the most aroriate diving suit, according to the level of effort the diver is going to deliver in the subsea working site In the first 15 hours of immersion, body temerature decreases faster at small deths of immersion he increase with 2mm of the insulation neorene wet suit resulted in about 50 /m 2 less heat loss emerature differential across the neorene suit varies from1 5 0 C, at surface, to C, at 30 m deth A difference of 1 0 C in body temerature was recorded for the same diver with 2 mm thickness difference of the neorene suit, after 15 min at 30 m deth 3 he diagrams resented above show the most unfavorable situation, the most enhanced temerature decrease, as the study was develoed for divers at rest In ractice the metabolic heat roduction is higher and the thermal comfort lasts longer 4 he net ste in our study is to validate the model for artificial breathing mitures

10 64 amara Stanciu, Anca Constantin, Cecilia Adumitresi R E F E R E N C E S [1] AncaConstantin, amara Stanciu, Eerimental determination of the thermal flu density variation lost in time by a diver Annals of the Oradea University, Fascicle of Management and echnological Engineering, Oradea, Romania, 2010 olume IX XIX, [2] Majchrzycka A, Model of hermal Comfort in the Hyerbaric Facility Polish Maritime Research 168, Poland, 2011, ol 18; [3] McCullough L &Arora S, Diagnosis andreatment of HyothermiaAmerican FamilyPhysician, 70 12, 2004, [4] McIntosh RL & Anderson A, Comrehensive issue Proerties Database Provided for the hermal Assessment of a Human at Rest Biohysical Review and Letters, 53, 2010, [5] Nakayama A &Kuwahara F, A general bioheat transfer model based on the theory of orous media International Journal of Heat and Mass ransfer issue 51, 2008, [6] Nuckton J, ClamanD M, Goldreich, DF endt C& NucktonJ G, Hyothermia andafterdro following Oen ater Swimming: healcatraz/san Francisco Swim Study heamerican Journal of Emergency Medicine, 18, 2000, [7] arlochan F&Ramesh S, Phys Heat ransfer Model for Predicting Survival ime in Cold ater Immersion, Biomedical Engineering Alications,Basis & Communications, 2005, vol 17, [8] halmann E D, Phys Cold water eosure Guidelines for assive thermal Garments NMRC ork Unit N M00901B-1004, 1990 [9] Paris, 1980