MANUFACTURING PROCESS FOK COSMETIC CREAM 653 Since the cream is particularly work-sensitive, it was not desirable to exceed 200 rpm. As a result, Type B was dropped from considera- tion. Type C heat exchanger could not be run at 20'0 rpm but the re- sults at 54 rpm indicate that if this unit operated at 200 rpm, it could approach a U of 200-225. However, the manufacturer of Type C did not specifically manufacture exchangers for sanitary service and had little experience with the cooling of cosmetic creams. After considera- tion of the foregoing Type A was selected. __ The average overall heat transfer coefficient Uw (Btu/ft2-øF-hr) * was determined according to the following sample calculation: Water in, Product out, Trout • Water out, • • Product in, A T,• = Tv•. -- Tw A To = Tv .... -- Twi• ATe = Tpi n -- Tvou,, • Tw = Tw .... -- Q = UA•T•.• where Q •- the heat transferred U = the overall heat transfer coefficient A = the transfer area zxT•,• z the log-mean temperature difference between the water and the cream Q is obtained from the energy balance in the water stream. For example, using the in[ormation contained in pass 1 of Type A exchanger we get. (2 = MC•,aTw (2) where M -- the mass flow of water Cv -- the heat capacity of the water therefore, Q = 528 lb/hr (1 Btu/lb-øF) 24.8øF Q = 13094 Btu/hr (3) * Since overall heat transfer coefficient is traditionally expressed in Btu/hr-ft•-øF, these units are retained in this section.

654 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The log-mean temperature difference during this pass is calculated as follows: ATa -- ATb A Tlm -- ln(/X Td/X Tb) = --21.3/--0.26 = 81.9 (4) then Q = UAAT•,,, (1, 5) U = Q/A/XT•m (6) thus U -- 13094/(0.7) (81.9) --- 228 Btu/hr-ft"øF. The cream cooled through the Type A heat exchanger was of ac- ceptable quality and after 4 days' refrigeration exhibited the character- istic consistency and structure desired. Some of the detailed data col- lected on Type A exchanger are found in Table IX. The data for the remaining exchangers are not shown as they were eliminated from con- sideration. CONCLUSION In this study, it was found that the consistency and structural char- acteristics of the cosmetic cream under study were due to the ammonium Table IX Data Collected on Type A a Heat Exchanger Flow Flow Rate Rate Pass Pvln T•,out Trout T•,in Prod. Water No. rpm (øC) (øC) (øC) (øC) (lb/hr) (lb/hr) 3T•,• q• Uw 1 88 65.3 25.7 63.3 11.9 2580 528 2 88 63.3 30.5 61.7 11.8 2580 528 3 88 61.7 24.3 60.5 11.8 2580 528 3' 200 61.7 25.4 54.4 11.8 2580 528 4 200 58.9 24.6 53.9 11.7 2580 528 5 200 56.7 24.0 53.3 12.0 2580 528 6 200 55 23.3 53.9 12.3 2580 525 7 200 51.7 22.1 47.8 12.2 2352 523 8 200 45.0 18.9 42.2 12.4 2352 528 9 200 41.7 14.4 39.4 12.3 2352 528 81 73 76 70 67 8 66 2 64 1 58 3 50.3 48.9 9 13,094 228 3 17,846 348 9 11,928 221 9 12,488 261 12,302 259 11,457 247 10,401 232 9,398 230 6,126 173 2,006 58.6 Ave 225 Transfer area (A) = 0.7 ft 2 and U = Q/AATg,•