Rational synthetic combination genetic devices boosting high temperature ethanol fermentation

The growth and production of yeast in the industrial fermentation are seriously restrained by heat stress and exacerbated by heat induced oxidative stress.In this study,a novel synthetic biology approach was developed to globally boost the viability and production ability of S.cerevisiae at high temperature through rationally designing and combing heat shock protein(HSP)and superoxide dismutase(SOD)genetic devices to ultimately synergistically alleviate both heat stress and oxidative stress.HSP and SOD from extremophiles were constructed to be different genetic devices and they were preliminary screened by heat resistant experiments and anti-oxidative experiments,respectively.Then in order to customize and further improve thermotolerance of S.cerevisiae,the HSP genetic device and SOD genetic device were rationally combined.The results show the simply assemble of the same function genetic devices to solve heat stress or oxidative stress could not enhance the thermotolerance considerably.Only S.cerevisiae with the combination genetic device(FBA1p-sod-MB4-FBA1p-shsp-HB8)solving both stress showed 250%better thermotolerance than the control and displayed further 55%enhanced cell density compared with the strains with single FBA1p-sod-MB4 or FBA1p-shsp-HB8 at 42
C.Then the most excellent combination genetic device was introduced into lab S.cerevisiae and industrial S.cerevisiae for ethanol fermentation.The ethanol yields of the two strains were increased by 20.6%and 26.3%compared with the control under high temperature,respectively.These results indicate synergistically defensing both heat stress and oxidative stress is absolutely necessary to enhance the thermotolerance and production of S.cerevisiae.

Energy and exergy analyses and optimizations for two-stage TEC driven by two-stage TEG with Thomson effect

Based on the non-equilibrium thermodynamics and energy and exergy analyses,a thermodynamic model of two-stage thermoelectric(TE)cooler(TTEC)driven by two-stage TE generator(TTEG)(TTEG-TTEC)combined TE device is established with involving Thomson effect by fitting method of variable physical parameters of TE materials.Taking total number of TE elements as constraint,influences of number distributions of TE elements on three device performance indictors,that is,cooling load,maximum COP and maximum exergetic efficiency,are analyzed.Three number distributions of TE elements are optimized with three maximum performance indictors as the objectives,respectively.Influences of hot-junction temperature of TTEG and coldjunction temperature of TTEC on optimization results are analyzed,and difference between optimization results corresponding to three performance indicators are studied.Optimal performance intervals and optimal variable intervals are provided.Influences of Thomson effect on three general performance indicators,three optimal performance indicators and optimal variables are comparatively discussed.Thomson effect reduces three general performance indicators and three optimal performance indicators of device.When hot-and cold-junction temperatures of TTEG and TTEC are 450,305,325 and 295 K,respectively,Thomson effect reduced maximum cooling load,maximum COP and maximum exergetic efficiency from 9.528 W,9.043×10^(-2)and2.552%to 6.651 W,6.286×10^(-2)and 1.752%,respectively.

Performance optimization of a class of combined thermoelectric heating devices

A detailed model of thermally-driven combined thermoelectric(TE) heating device is established. The device consists of twostage TE heat pump(TTEH) and two-stage TE generator(TTEG) with four external heat exchangers(HEXs). Both internal losses and external heat transfer irreversibilities are considered in the model. The heating capacity and the coefficient of performance(COP) of the device are improved through numerical optimization,which is of great significance to the application of the device. The distribution of the total TE element number among four TE devices and the distribution of the total external heat conductance among the four external HEXs are optimized. The results show that both the reservoir temperatures of TTEG and TTEH have significant influences on the performance and the corresponding optimum parameters of the device. The COP can reach 0.14 after optimization when the temperature difference of heat source is 150 K and the temperature difference of heating is 10 K.

Influences of external heat transfer and Thomson effect on the performance of TEG-TEC combined thermoelectric device

A thermodynamic model of a thermoelectric generator(TEG)-driven thermoelectric cooler(TEC) device considering Thomson effect and external heat transfer(HT) is established based on the combination of non-equilibrium and finite time thermodynamic theories. The expressions of cooling capacity and coefficient of performance(COP) are obtained. Performances are compared with and without considering Thomson effect using numerical optimization method. The influences of Thomson effect on the optimal performances, optimum allocations of thermoelectric(TE) element number and HT surface area are discussed. The results indicate that Thomson effect decreases the maximum cooling capacity and COP. More TE elements should be allocated to TEG, and more HT area should be allocated to the heat exchanger(HEX) of TEG, the hot-side HEX of TEG and the cold-side HEX of TEC in the design of the device considering Thomson effect. The results obtained can be used to help design TEG-TEC devices.