Lukewarm Bath Prevention MeEn 340 Class Project Devin D. Furse

Objectives Model heat loss of bath water in a standard bathroom Determine primary means of heat loss - convection or evaporation Determine effectiveness of reducing heat loss by covering the water with thin, non- insulating film (plastic wrap)

Heat Transfer Problem and Solution Q lost,water = mC p (T i -T f ) Eq (free convection for a horizontal plate) approximates the covered bath case Compare Q lost in both covered and open cases Treat mass transfer (evaporation) as heat transfer COVERED BATH T∞T∞ OPEN BATH T∞T∞ q conv q evap

Empirical Results For first 10 min, dT/dt in open bath roughly twice that of closed bath Open bath nears saturation, slopes converge (both are now mainly free convection) Save about 50% of heat from escaping by covering the bath

Conclusions Covering the water is an effective way of maintaining hot baths, but not realistic for home use Hot tubs running constantly (in hotels, for example) benefit from covering, both from eliminating evaporation and insulating against convection Evaporation can be reduced by having smaller bathrooms as the air becomes saturated more quickly