348 ENGINEERING EVALUATION 



Q, = U, X A3 X At = 2.49 X 83 X 40 

 Q3 = 8,300 Btu/hr. 



TOTAL HEAT LOSS 



Q total = Q sides & ends + Qfop + Qp + Qd + Qs 



= 17,300 + 16,500 + 1,140 + 11,100 + 8,300 

 = 54,340 Btu/hr. 



Appendix C 

 SPECIFIC -HEAT RELATIONS 



Constant-pressure specific heat (Cp) is defined as that quantity of heat required to cause 

 an increase of one degree in the temperature of a unit quantity of material under constant 

 pressure conditions [Btu/lb-°F]. For air at standard conditions, Cp is equal to 0.241 Btu/ 

 lb-°F. 



The Sealab II environment consisted of 85 percent helium, 11 percent nitrogen, and 4 per- 

 cent oxygen. The specific heat of this mixture of gases can be determined using the relation 



^ Cp^wi + Cp^wg + ... + Cp^w„ 



= 1.25(0.85) + 0.247(0.11) + 0.217(0.04) 



= 1.1 Btu/lb-°F. 



The operating pressure of Sealab n required seven times the amount of gas needed to fill 

 it to standard atmospheric pressure. To remove a given quantity of heat from a unit volume of 

 the gas mixture under Sealab n operating conditions would require 32 times the energy required 

 to remove the same amount of heat from a unit volume of air at standard atmospheric pressure, 

 i.e. 



Heat Capacity (SEALAB environment) 

 Heat Capacity (Air at sea level) 



Cp (Specific heat of mix) Xp (Density of mix) = 1.1 x .141 



Cp (Specific heat of air) X p (Density of air) = .241 X .074 



= 8.6. 



