某列管换热器,用100℃水蒸气将物料由20℃加热至80 ℃,传热系数K=100 W/(m2 .℃).经半年运转后,由于污垢的影响,在相同条件下物料出口温度仅为70℃.现欲使物料出口温度仍维持在80℃,问加热蒸气温度应取何值?原????qc(80-20)=KAΔ t 1 (1)Δ t =(80-20)/ln(80/20)=43.28℃ 半年后????qc(70-20)=K AΔ t 2???? (2)Δ t= 80-30????/ln(80/30)=50.98℃ ????2????/????1????得????????70-20????/????80-20=????K Δ t 1/????KΔ t2????(K /100)×50.98/43.28K =70.75 w.m .K 保持原生产能力,即 KAΔ t K AΔ t (2’)Δ t =KΔ t /K =100×43.28/70.75????=61.17℃ (3’)Δ t =(T-20)-(T-80)/ln(T-20)/(T-80)???????

某列管换热器,用100℃水蒸气将物料由20℃加热至80 ℃,传热系数K=100 W/(m2 .℃).经半年运转后,由于污
垢的影响,在相同条件下物料出口温度仅为70℃.现欲使物料出口温度仍维持在80℃,问加热蒸气温度应取何值?
原????qc(80-20)=KAΔ t 1 (1)
Δ t =(80-20)/ln(80/20)=43.28℃
半年后????qc(70-20)=K AΔ t 2???? (2)
Δ t= 80-30????/ln(80/30)=50.98℃
????2????/????1????得????
????70-20????/????80-20=????K Δ t 1/????KΔ t2
????(K /100)×50.98/43.28
K =70.75 w.m .K
保持原生产能力,即 KAΔ t K AΔ t (2’)
Δ t =KΔ t /K =100×43.28/70.75
????=61.17℃ (3’)
Δ t =(T-20)-(T-80)/ln(T-20)/(T-80)????
????=61.17
∴ 60/61.17????ln(T-20)????/????(T-80)????
∴2.667=T-20????/????T-80????
T=115.8℃