UCLA

An anaerobic digester is a part of a wastewater treatment technology and its role is to digest the wastewaters to treat biosolids. Anaerobic digesters typically operates at either 35�C to 37�C or 45�C, and biosolids must be heated from ambient temperature (10-20�C). To heat the sludge in anaerobic digesters steam injection is used which dilute the sludge and the requirement of electricity to heat steam is not economically favorable. Conventional heat exchangers have been used in wastewater treatment plants (WWTP) but there are many difficulties regarding the maintenance, clogging and cleaning, which discourages their use, especially for heat recovery.

Methane gas (CH4) is produced in digesters which is combusted and used for heating the buildings. In the case of large WWTPs, combusted methane is also used for power generation; but it usually combusted to the air. There are largely unused opportunities for heat recovery and it is not practiced due to the low potential heat recovery as well as maintenance problems with heat exchangers.

Heat pipes are an interesting technology and have not been used in WWTPs. In this dissertation heat pipes for wastewater treatment (low temperature heat recovery) and combusted biogas products’ applications are evaluated. Then heat pipe heat exchangers (HPHE) is designed and the simulations of heat pipe heat exchangers (HPHE) for different fluid pairs at Cr<<1 and Cr≈1 is demonstrated and then compared with a conventional heat exchanger (spiral heat exchanger). Then a method to justify when using HPHE is favorable for any design and application is introduced.