Thermodynamics HW Solutions 370

Thermodynamics HW Solutions 370 - Chapter 4 Transient Heat...

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Chapter 4 Transient Heat Conduction 4-101 Turkeys are to be frozen by submerging them into brine at -29°C. The time it will take to reduce the temperature of turkey breast at a depth of 3.8 cm to -18°C and the amount of heat transfer per turkey are to be determined. Assumptions 1 Steady operating conditions exist. 2 The thermal properties of turkeys are constant. Brine -29 ° C Turkey T i = 1 ° C Properties It is given that the specific heats of turkey are 2.98 and 1.65 kJ/kg.°C above and below the freezing point of - 2.8°C, respectively, and the latent heat of fusion of turkey is 214 kJ/kg. Analysis The time required to freeze the turkeys from 1 ° C to - 18ºC with brine at -29ºC can be determined directly from Fig. 4-45 to be t 180 min. 3 hours ( a ) Assuming the entire water content of turkey is frozen, the amount of heat that needs to be removed from the turkey as it is cooled from 1 ° C to -18 ° C is Cooling to -2.8ºC: kJ 79.3 C] (-2.8) - C)[1 kJ/kg kg)(2.98 7 ( ) ( fresh fresh cooling, = ° ° = Δ = T C m Q Freezing at -2.8ºC: kJ 1498 kJ/kg) kg)(214 7 ( latent freezing = = = h m Q Cooling -18ºC: kJ 175.6 C 18)] ( 2.8
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