Comparison of thermal efficiency of laser mirrors and their cooling systems

Аuthors

Leonov E. V.^*, Shanin Y. I.^**

NII NPO "LUCH", Podolsk, Russia

*e-mail: leonovev@sialuch.ru
**e-mail: ShaninYuI@sialuch.ru

Abstract

A review and brief analysis of various approaches to assessing the thermal efficiency of heat exchange devices and heat exchangers and assessing the impact of heat exchange intensification on it are provided. The intensity of heat transfer increases with an increase in the flow velocity of the working medium around the heat exchange surface. In a turbulent flow regime, the heat transfer coefficient increases proportionally to the velocity V0,7–V0,8. In this case, the hydraulic resistance of a complex topological surface increases proportionally to the square of the velocity (V2), and the energy consumption to overcome the hydraulic resistance (to pump the coolant) increases proportionally to the cube of the velocity (V3). Most of the methods for assessing the efficiency of heat exchangers actually come down to one – the energy coefficient (the ratio of the thermal performance of the heat exchanger to the power for pumping the coolant), proposed by Academician M.V. Kirpichev. It is stated that: a) the choice of determining quantities is very important for constructing a successful method for comparing heat exchange surfaces, b) the optimal heat exchanger can be determined only for each specific case of application in accordance with the requirements imposed on it. Based on the analysis of the presented materials, conclusions were made that allow increasing heat transfer without a significant increase in hydraulic resistance and improving the efficiency of heat exchange surfaces. It is established that the efficiency of the laser mirror heat exchanger is determined by the reduced heat transfer coefficient and the degree of "thermal insulation" of the mirror base. Using a channel cooling system as an example, the effect of changing the design parameter (channel height) and fin material on the efficiency of mirror cooling is illustrated under the condition of either a constant Reynolds number or a limited pressure drop due to friction in the cooling channel. It is revealed that for flow-through and transfer cooling systems of mirrors there are optimal dimensions of the cooling layer that provide the necessary and sufficient thermal efficiency. A method for comparing the efficiency of a CS and a mirror is proposed. 

Keywords:

laser mirror, cooling system (CS), hydraulic resistance, heat transfer, thermal efficiency, pumping power, thermal displacement

References

1. Dreitser GA, Kuzminov VA, Neverov AS. The simplest methods for assessing the efficiency of heat transfer intensification in channels. Izvestiya vysshykh uchebnykh zavedeniy. Energetika. 1973;(12):77–84. (In Russ.).
2. Kalinin EK, Dreitzer GA, Yarkho SA. Intensification of heat transfer in channels. Moscow: Mashinostroyeniye; 1981. 205 p. (In Russ.).
3. Antufiev VM. Efficiency of various forms of convective heating surfaces. Moscow-Leningrad: Energiya; 1966. 184 p. (In Russ.).
4. Kirpikov VA, Leifman II. Graphical method for assessing the efficiency of convective heating surfaces. Thermal Engineering. 1975;(2):34–36. (In Russ.).
5. Gukhman AA. Intensification of convective heat exchange and the problem of comparative evaluation of heat exchange surfaces. Thermal Engineering. 1977;(4):5–8. (In Russ.).
6. Kovalenko LM. Comparison of thermal energy efficiency of convective heat exchange surfaces of various shapes used in chemical production equipment. Khimicheskoye i neftyanoye mashinostroyeniye. 1979;(3):14–17. (In Russ.).
7. Kalinin EK, Dreitzer GA, Kopp IZ et al. Effective heat transfer surfaces. Moscow: Energoatomizdat; 1998. 480 p. (In Russ.).
8. Kirpichev MV. On the most advantageous shape of the heating surface. Izvestiya ENIN AN SSSR. 1944;12:5–9. (In Russ.).
9. Gortyshov YuF (ed.) Thermal hydraulic efficiency of promising methods of heat transfer intensification in heat exchange equipment channels. Heat transfer intensification: monograph. Kazan: Tsentr innovatsionnykh tekhnologiy; 2009. 531 p. (In Russ.).
10. Yudin VF. Heat transfer of transversely finned tubes. Leningrad: Mashinostroyeniye; 1982. 189 p. (In Russ.).
11. Shanin YuI, Shanin OI. Comparison of the efficiency of cooling of laser mirrors. In: Teplomassoobmen-MMF-96. Teplomassoobmen v dvukhfaznykh sistemakh. Minsk: ANK «ITMO A.V. Lykova» ABN; 1996;4(2):174–177. (In Russ.).
12. Bergls A. Heat Transfer Intensification. Teploobmen: Dostizheniya. Problemy. Perspektivy. Izbrannyye trudy 6-y mezhdunarodnoy konferentsii po teploobmenu. Moscow: Mir; 1981. pp. 145–192. (In Russ.).
13. Kharitonov VV. Thermal physics of laser mirrors. Moscow: MIFI; 1993. 152 p. (In Russ.).
14. Fedoseev VN, Shanin OI, Shanin YuI et al. Heat transfer in rectangular channels with heat-conducting walls under one-sided heating. High Temperature. 1989;27(6): 1132–1138. (In Russ.).